Mosher, D.C., Erbacher, J., and Malone, M.J. (Eds.) Proceedings of the Ocean Drilling Program, Scientific Results Volume 207
CAMPANIAN THROUGH EOCENE MAGNETOSTRATIGRAPHY OF SITES 1257–1261, ODP LEG 207, DEMERARA RISE (WESTERN EQUATORIAL ATLANTIC)1 Yusuke Suganuma2 and James G. Ogg3
ABSTRACT Ocean Drilling Program (ODP) Sites 1257–1261 recovered thick sections of Upper Cretaceous–Eocene oceanic sediments on Demerara Rise off the east coast of Surinam and French Guiana, South America. Paleomagnetic and rock magnetic measurements of ~800 minicores established a high-resolution composite magnetostratigraphy spanning most of the Maastrichtian–Eocene. Magnetic behavior during demagnetization varied among lithologies, but thermal demagnetization steps >200°C were generally successful in removing present-day normal polarity overprints and a downward overprint induced during the ODP coring process. Characteristic remanent magnetizations and associated polarity interpretations were generally assigned to directions observed at 200°–400°C, and the associated polarity interpretations were partially based on whether the characteristic direction was aligned or apparently opposite to the low-temperature “north-directed” overprint. Biostratigraphy and polarity patterns constrained assignment of polarity chrons. The composite sections have a complete polarity record of Chrons C18n (middle Eocene)–C34n (Late Cretaceous).
1Suganuma,
Y., and Ogg, J.G., 2006. Campanian through Eocene magnetostratigraphy of Sites 1257– 1261, ODP Leg 207, Demerara Rise (western equatorial Atlantic). In Mosher, D.C., Erbacher, J., and Malone, M.J. (Eds.), Proc. ODP, Sci. Results, 207, 1–48 [Online]. Available from World Wide Web: . 2 Paleogeodynamics Research Group, Geological Survey of Japan, AIST, 1-1-1 Central 7, Higashi, Tsukuba, Ibaraki, 305-8567, Japan.
[email protected] 3 Department of Earth and Atmospheric Sciences, Civil Engineering Building, Purdue University, 550 Stadium Mall Drive, West Lafayette IN 47907-2051, USA. Initial receipt: 26 May 2004 Acceptance: 23 May 2005 Web publication: 14 March 2006 Ms 207SR-102
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LOCATION, GENERAL STRATIGRAPHY AND PALEOMAGNETIC GOALS
Magnetostratigraphy with constraints from biostratigraphy provides a chronostratigraphic framework in deep-sea sediments for paleoceanographic studies, including stable isotope trends and developing a highresolution cyclostratigraphy tuned to orbital cycles. The primary goal of our paleomagnetic study was to establish a high-resolution magnetostratigraphy spanning the Late Cretaceous–Eocene at all Leg 207 sites with particular emphasis on continuous splices of cyclic sediments. Note: for clarity in discussing calibrated chronostratigraphy vs. relative stratigraphic positions, we capitalize the official international subdivisions of epochs (e.g., Middle Eocene subepoch spans the Bartonian and Lutetian stages; Early Eocene subepoch is the Ypresian stage, etc.) The term “Lower” Eocene indicates the associated rock record that corresponds to the Early Eocene. Terms in lower case (“upper Eocene,” “lower Lower Eocene,” etc.). indicate only a relative position within the recovered strata of that international epoch or subepoch.
METHODS Sampling Shipboard magnetometer measurements were generally compromised by weak magnetizations, slurry intervals separating coherent blocks, and the inability to perform progressive thermal demagnetization. Therefore, we relied on extensive shore-based paleomagnetic and rock magnetic measurements of discrete samples.
12° N
80°W
60°
40°
20° N
11° 0°
40 00
10°
1257 1258 1259 1260
9°
1261
3000
00
1. Albian clay to sandstone overlain by Cenomanian–Santonian organic-rich “black shale;” 2. Campanian–Paleocene chalk with subtle oscillations in color and physical properties; 3. Eocene–lower Oligocene chalk to calcareous ooze with cyclic characteristics. Most sites have a major hiatus within the middle Eocene; and 4. Post-Oligocene deposition of primarily nannofossil ooze.
F1. Bathymetric map, p. 20.
20
Demerara Rise is a projection of the continental margin off the northeast coast of Surinam and French Guiana, South America, in depths deeper than 700 m. Ocean Drilling Program (ODP) Leg 207 employed coring in multiple holes at each site to obtain continuous records of the expanded sections of Albian–Oligocene strata (Erbacher, Mosher, Malone, et al., 2004) (Fig. F1). Sites 1257–1261 recovered nearly 5000 m of sediment along a depth transect at 1900–3100 meters below seafloor (mbsf). In addition to high-resolution records of the Late Cretaceous Ocean Anoxic Events, Paleocene/Eocene Thermal Maximum, and Eocene/Oligocene boundary, several stratigraphic intervals were characterized by cyclic sedimentation that appear to be responses to Milankovitch orbital cycles. These cyclic intervals were the focus of our detailed magnetostratigraphic studies. The generalized stratigraphy across the Demerara Rise consists of four main units:
8°
10 00
7° 57°W
56°
55°
54°
53°
52°
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261 Approximately 800 paleomagnetic minicores were collected from the Leg 207 sites. Cylindrical samples (12 cm3) were cut using a watercooled nonmagnetic drill bit attached to the standard drill press and trimmed with a diamond saw. The trimmed ends of such minicores were retained for analysis of carriers of magnetization. Shipboard sampling was generally at 3-m intervals from Hole B at each site. Guided by this initial magnetostratigraphic framework, additional postcruise sampling of selected priority intervals at ~1-m spacing was performed at the ODP Bremen core repository. This second set of detailed studies was designed to delimit the interpreted polarity reversals and to enhance the reliability of magnetostratigraphy from zones that had displayed relatively poor magnetic behavior.
Magnetic Measurement Procedures Magnetic measurements for the main magnetostratigraphy program were carried out in the mu-metal-shielded facility at the Laboratory for Paleo- and Rock Magnetism at the Niederlippach complex of the Institut Für Allgemeine und Angewnandte Geophysik, Ludwig-MaximiliansUniversität, Munich, Germany. The natural remanent magnetization (NRM) of each sample was measured using a cryogenic 2G Enterprises direct-current superconducting quantum interference device (DCSQUID) magnetometer. The effective background noise of this threeaxis cryogenic magnetometer for a minicore is ~1 × 10–6 A/m (1 × 10–3 emu/cm3), which implies that reliable polarity information can be obtained from samples with remanent magnetizations as low as 4 × 10–6 A/m. To further increase the signal-to-noise ratio, we performed duplicate measurements whenever a sample had a remanent magnetization 300°C to detect formation of new magnetic minerals or other anomalous changes in magnetic characteristics. For visualizing the demagnetization behavior, computing characteristic directions, and assigning polarity ratings, we used the PALEOMAG software package, which has a combined graphical and analytical package designed for interpreting magnetostratigraphy and paleomagnetic statistics for large suites of samples (Zhang and Ogg, 2003; and as documented freeware available from Purdue University at www.eas.purdue.edu/paleomag/). We conducted a separate study to investigate the nature of the remanence and the minerals responsible for stable remanence. A few representative specimens were selected based on differences of lithology and behavior of demagnetization characteristics through magnetic measurements for a set of rock magnetic experiments. These rock magnetic experiments were performed at the paleomagnetic laboratory of the Department of Environmental Sciences, Ibaraki University, Japan. The experiments included (1) progressive isothermal remanent magnetization (IRM) and (2) subsequent stepwise thermal demagnetization of acquired IRM.
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Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
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MAGNETIC CHARACTERISTICS AND POLARITY ASSIGNMENTS Generalized Rock Magnetic Behavior Examples of typical magnetic behavior during combined AF and thermal demagnetization of the minicores are diagrammed in Figure F2. Nearly all samples displayed an NRM with positive inclination that is generally significantly steeper than the 20° inclination expected for the present latitude of the Leg 207 sites. A similar downward magnetic overprint is a common feature observed by ODP paleomagnetic studies and is considered to be induced during the downhole coring process (summarized in Acton et al., 2002). Upon reduction of this downward overprint using 5-mT AF demagnetization, most minicores displayed a relatively shallow inclination, low-temperature magnetic component that was gradually removed by progressive thermal demagnetization to ~200°C. As this low-temperature component was removed, the remanent magnetic directions generally either shifted slightly or else displayed a pronounced “hooklike” swing. As will be elaborated below, these two contrasting behaviors were utilized to assign magnetic polarity. During higher heating steps, the magnetic directions tended to be stable with a gradual loss of intensity—a trend toward the origin on vector plots—which permitted the isolation of a single component of magnetization. Characteristic magnetization directions and associated variances were computed for each minicore by applying the least-squares threedimensional line-fit procedure of Kirschvink (1980). The characteristic direction was visually assigned to the set of vectors that appeared to display removal of a single component in equal-area and vector plots during progressive demagnetization. The intensity of characteristic magnetization was computed as the mean intensity of those vectors used in the least-squares fit.
Curious Artifacts in Moist, Gray Minicores— Possible Goethite Formation? In rare cases, some “fresh” minicores of relatively unoxidized gray facies that were still damp with the original pore water displayed a fascinating and temporary magnetodiagenetic artifact upon heating through an initial thermal demagnetization step of 150° or 200°C (see example in Fig. F2B). After this first heating step, the measured magnetic vector from these moisture-bearing cores (only the gray ones) was often offset from the main trend from initial NRM to the 5-mT AF step and through the higher heating steps. Even though the color of these minicores was generally lighter or bleached after the initial heating, there were no detectable changes in magnetic susceptibility. This behavior was never observed in minicores of the same lithologies that had experienced drying prior to the initial heating step; therefore we suspect that this curious artifact is a low-temperature alteration phenomenon. One possibility is that hydration of some of the reactive iron minerals (maybe iron sulfides?) occurred in these gray sediments to form a goethite-type mineral or similar low-susceptibility compound that acquired a spurious in-laboratory magnetic field upon the initial heating below 150°C but then later dehydrated or had exceeded its Curie point upon heating >200°C.
F2. AF and thermal demagnetization samples, p. 21. A
B
N
N W Up
W Up E S
W
5 mT
N 400°C
E
S
300°C 200°C 5 mT
N 300°C
S
200°C
S Jo = 3.4E-N2 (kA/m)
1.0
Div. = 5.0E-N4 (kA/m)
5 mT
100°
E Dn
400°C
N
C W Up
1.0
Div. = 1.0E-N2 (kA/m)
Jo = 4.4E-N3 (kA/m) 5 mT
0°C E Dn
E
150°C
W Up E
W
400°C 300°C
S
350°C
250°C
300°C 350°C
200°C 5 mT 150°C
1.0
W
N
N
Jo = 2.1E-N3 (kA/m)
Jo = 3.8E-5 (kA/m)
150°C
1.0
5 mT
5 mT
5 mT
0°C Div. = 2.0E-N4 (kA/m)
300°C
N
S
E Dn
100°
D S
S
W
0°C
0°C 100°
400°C
Div. = 5.0E-N6
E Dn
100°
400°C
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
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Diagenetic alternation of iron minerals upon sample storage was also observed in some Leg 207 cores sampled at the ODP repository at Bremen. In just 2 months, many intervals in these refrigerated sediments had already changed surface color from the original greenish gray to grayish tan. Neither the tannish altered minicores from the dark gray zones nor the dried (but still retaining the original gray color) minicores displayed the “anomalous 150°C directions.” However, when this phenomenon was explained to some other paleomagnetists, they expressed skepticism about a goethite mineral being involved; therefore, we simply indicate this oddity of low-temperature thermal demagnetization of still-moist, fresh, gray sediments.
IRM and Magnetic Mineralogy Studies
Interpretation of Polarity Using Relative Declinations of Removed Vectors Rotary drilling generally produces relative rotation between different sediment blocks within the core liner. In higher latitudes, one would rely on the stratigraphic clustering of positive or negative inclinations of the characteristic directions to assign normal polarity or reversed polarity zones, depending whether the site was known to be north or south of the paleoequator. The Leg 207 sites are presently between 9° and 10°N latitude. Generalized global plate reconstructions generally indicate that South America has experienced a small amount of northward drift with negligible plate rotation since the Early Cretaceous (Chris Scotese, pers. comm. 2002); therefore, the pre-Oligocene paleolatitudes of the Leg 207 sites were projected to be within a few degrees of the paleoequator, and these reconstructions and independent compilations of South American paleomagnetic data were sometimes contradictory whether the Leg 207 sites would be north or south of that paleoequator. The near-equatorial
F3. IRM acquisition, p. 23. A
B
Normalized magnetization
1.0
Eocene 207-1259B-15R-1, 86 cm 207-1259B-19R-2, 15 cm 207-1258B-3R-5, 53 cm 207-1258B-5R-2, 54 cm 207-1258B-7R-3, 79 cm 207-1258B-8R-3, 33 cm 207-1258B-13R-2, 38 cm 207-1258B-15R-7, 59 cm
0.8
0.6
0.4
0.2
0 1.0
Normalized magnetization
Progressive direct magnetic fields up to 1.0 T were applied to typical light gray, dark gray, and reddish chalk to clayey chalk specimens from Hole 1258B (11 samples) and Hole 1259B (2 samples) in order to determine their IRM acquisition patterns (Fig. F3A). IRM values increase quickly and with relatively weak fields. Most specimens acquire more than 90% of their maximum IRM by 0.3 T and then display a slow increase to 1.0 T. The steep IRM acquisition curve below 0.3 T suggests the presence of a low-coercivity magnetic mineral in the sediments. A few specimens display a more continuous increase up to 1.0 T, which might be caused by a relatively higher concentration of a higher-coercivity mineral. Subsequent stepwise thermal demagnetization of acquired IRM for all specimens displays a maximum unblocking temperature of ~600°C (Fig. F3B), which indicates that a dominant magnetic mineral is magnetite. A low-blocking-temperature component is also present, as suggested by the inflection point of the IRM demagnetization curves at 200°–350°C for several samples, which may indicate the presence of iron sulfides. The rock magnetic experiments suggest that magnetite is an important carrier of magnetization in most sediments. We interpret that the characteristic magnetization (and polarity) carried by magnetite is indicative of the original primary magnetization acquired when the sediments were deposited.
Paleocene ~ Late Cretaceous 207-1258B-23R-2, 49 cm 207-1258B-28R-1, 31 cm 207-1258B-31R-3, 1 cm 207-1258B-36R-2, 59 cm 207-1258B-43R-2, 83 cm
0.8
0.6
0.4
0.2
0
0
200
400
600
Field (mT)
800
1000
0
100
200
300
400
Temperature (°C)
500
600
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261 paleolatitudes and uncertain northern vs. southern hemisphere positions through time implied that it would be inappropriate to assign polarity zones based solely on inclination patterns. Therefore, we utilized the relative directions of low-temperature overprints (secondary magnetization) vs. the directions of higher-temperature characteristic magnetizations of the sediments to assist in interpreting the polarity of each minicore. The assumptions and procedure are detailed in Shipboard Scientific Party (2004a). This procedure is similar to that used by other paleomagnetists working with Deep Sea Drilling Project (DSDP) and ODP cores (e.g., Shibuya et al., 1991), who have demonstrated that relative orientation of overprints removed during progressive demagnetization can be used for identification of paleomagnetic polarity. The critical assumptions are that (1) an overprint vector of present-day north-directed polarity is superimposed on the original polarity vector, (2) there have not been major (>45°) tectonic rotations of the sites after sediment deposition, and (3) the relative declinations of the overprint vector and the underlying primary polarity vector can be deduced during progressive demagnetization. Ideally during progressive demagnetization, the north-directed vector of secondary magnetization (present-day magnetization) is removed, then the component of characteristic magnetization is resolved. If this characteristic magnetization also has normal polarity, then there would be only a minor change in magnetic declinations. However, if this characteristic magnetization is reversed polarity, then there would be a 180° rotation of declination. We called these two patterns “N-type” and the “hook-type,” respectively. For some intervals, the hook-type demagnetization plots enabled identification of the low-temperature secondary vector and the characteristic vector (e.g., Figs. F2E, F2F, F2G). By assigning the direction of this low-temperature component to be north (0° declination), we reoriented the characteristic vectors of the hook-type samples, which is a method also used by Shibuya et al. (1991). The clustering of these reoriented hook-type vectors toward “south” (180° declination) (Fig. F4) gives us renewed confidence in this procedure. However, isolation and resolution of secondary component vectors was generally not possible because either the last stages of their removal overlapped with onset of decreases in the intensity of the characteristic component or the few low-temperature demagnetization steps were inadequate to enable isolation or other behaviors during demagnetization (e.g., Figs. F2H, F2I, F2J). Of course, it is probable that there are a few erroneous assignments of polarity with this interpretation method. For example, a sample having only a reversed polarity characteristic direction without a significant secondary overprint might display a consistent linear decay upon demagnetization and be mistakenly assigned as N-type. Therefore, we do not trust the polarity interpretation of any single sample, but only the broader patterns. Approximately 80% of the minicore demagnetization behavior could be assigned as N-type or hook-type (sharp or curved), and these types were generally in stratigraphic clusters which we interpret as polarity zones. A test of this method of polarity interpretation is possible in certain intervals that have biostratigraphic constraints on the possible primary polarity. For example, at all sites, the Paleocene/Eocene boundary occurred within an interval that was characterized by curved or sharp hook-type demagnetization paths. This is consistent with the placement of the Paleocene/Eocene boundary within the reversed polarity Chron C24r. Similarly, the Albian sediments displayed only N-type de-
6
F4. Magnetic behavior comparisons, p. 24. N
W
E
S
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261 magnetization paths, which is consistent with their deposition within normal polarity Superchron C34n. About 20% of the samples yielded uncertain polarities for a variety of reasons, including very weak magnetizations near the background noise level of the cryogenic magnetometer upon early stages of demagnetization, persistent steep downward-directed overprints, unstable magnetic directions, or ambiguous intermediate behavior between Ntype and hook-type demagnetization paths. Each characteristic direction was assigned a polarity and a qualitative reliability rating based upon its demagnetization behavior: (1) welldefined N or R directions computed from least-squares fits of at least three vectors; (2) normal polarity (NP) or reversed polarity (RP) directions computed from only two vectors or a suite of vectors displaying high dispersion but displaying clear polarity; (3) NPP or RPP samples that did not achieve adequate cleaning during demagnetization but their general N-type or hook-type behavior indicated the polarity; and (4) samples with uncertain N?? or R?? or indeterminate (INT) polarity that are not used to define polarity zones. To reduce the bias of a single observer, each of us made independent assignments of polarity and the selection and rating of characteristic magnetization vectors. In cases where the two paleomagnetists had different opinions, the samples were assigned a lower reliability rating.
Paleolatitudes When both polarity and characteristic inclination are known for a discrete sample, its magnetic paleolatitude can be computed. The paleolatitude analyses and implications for South American plate reconstructions will be detailed in a separate publication, but the main results are summarized here. The suites of discrete minicores revealed that the Leg 207 sites were at approximately 15°N latitude during the Albian (α95 = 5°, k = 25), then progressively drifted southward to ~4°N during the Campanian– Maastrichtian (3.6°N, α95 = 2.6°, k = 14) and Paleocene (4.4°N, α95 = 2.5°, k = 19) and 1°S of the paleoequator during the early Eocene (1.5°S, α95 = 0.7°, k = 51) and middle Eocene (1.0°S, α95 = 0.7°, k = 82) (Suganuma and Ogg, unpubl. data). After the middle Eocene, there was a cumulative northward drift of ~10° to the present location of the sites. The general trends and projected paleolatitudes do not agree with published generalized global reconstructions (e.g., compilations by Alan Smith [in Gradstein et al., 2004] and Chris Scotese [2001, and www.scotese.com]). However, these paleolatitudes are consistent with some aspects of Apparent Polar Wander Path curves compiled for South America from local paleomagnetic studies combined with projections of selected North American and African paleomagnetic poles (e.g., Beck, 1998, 1999; Randall, 1998). A portion of this apparent disagreement between paleolatitudes computed from regional paleomagnetic data and those implied by global reconstructions may be an offset of the hotspot reference frame (used in global reconstructions) from the dipole reference frame (deduced from paleomagnetic analyses) and/or a “farsighted” effect noticed in statistics of apparent poles from paleomagnetic data (A. Smith, pers. comm., 2003).
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Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
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MAGNETOSTRATIGRAPHY The standard geomagnetic timescale for the Late Cretaceous– Cenozoic is the “C-sequence” of marine magnetic anomalies and their calibration in other ODP-DSDP sites to foraminifer and nannofossil datums (e.g., Cande and Kent, 1992, 1995; Berggren et al., 1995). Characteristic portions of this pattern, when coupled with biostratigraphic constraints, generally enabled unambiguous correlations to the polarity zones recorded at Sites 1257, 1258, 1259, 1260, and 1261. For example, the relatively long reversed-polarity Chron C24r that spans the Paleocene/Eocene boundary could be confidently assigned to the reversed-polarity zone spanning this boundary at all sites. In sedimentary intervals deposited by fluctuating deposition rates or spanning rare interruptions by major hiatuses, the available biostratigraphic control was essential for proposing polarity chron assignments to the distorted pattern of polarity zones. Of course, it is inevitable that a few intervals among the array of sites had unreliable polarity interpretations or lacked biostratigraphic constraints which precluded unambiguous chron assignments. We have flagged uncertain chron assignments, but later revisions in biostratigraphy and/or methods of polarity determination may alter a few of the other assignments. The following site-by-site summary of the Campanian–Eocene magnetostratigraphy is updated from our paleomagnetic sections in the site chapters within the Leg 207 Initial Reports volume (Erbacher, Mosher, Malone, et al., 2004). Paleomagnetism of the underlying Albian– Santonian at each site is merged into a concluding synthesis discussion.
Site 1257
Late Paleocene–Early Eocene The thick upper Paleocene yielded two major pairs of normal– reversed polarity zones, and their placement within foraminifer Zone P4 indicates an assignment to Chrons C26n-C25r-C25n-C24r. The base of this Paleocene section is a massive slump deposit, and its magnetization appears to have been acquired during redeposition in a normal polarity field, which was probably Chron C26n. A compact, hiatus-delimited slice of Lower Eocene yielded primarily normal polarity, which may be Chron C24n. The apparent normal po-
100
100
1R 2R 3R
9X
4R
Foraminifer nannofossil chalk (high biogenic silica)
5R 6R
11X
1R
7R
12X 100
100
13X
8R
14X
9R
15X
10R
3R 4R
11R
14R
19X
15R 16R 17R 18R 19R
21X
200
22X 200
150 13R
18X
20X
23X 24X 25X
to upper
NP20 RP18 P16 P14
P11
P6
20R 21R 200 22R 23R 24R 25R 26R 27R
C15n? Hiatus C17n? C18n
RP17?
NP17 RP16
P13 P12 NP16
RP15
C20n?
Rare
NP12 RP 8-7
150
Hiatus
NP9
? C24r?
Nondiagnostic
NP8
C25n P4 NP7
C25r C26n Hiatus
7R
IIIB
8R
Foraminifer nannofossil chalk (w/ zeolites)
9R 10R 11R
IV
12R
Laminated black shale
200 13R
Hiatus
C24n?
NP9/10
6R
12R 17X 150
NP22
P5
IIIA Foraminifer nannofossil chalk (w/ zeolites)
Characteristic magnetization
Inclination Intensity (A/m) Polarity chron 1E-3 assignments -60° 0° 60° 1E-6
lower P18 NP21 RP20
5R
16X
150
2R
N
Nonearly diagMaastrich. KS30 CC23 nostic
C31r
-24 A. tylodus
late Campanian
KS29
CC22 -23
e. Camp.
17-18
Santonian
CC16 -17
C32n C32r top of C33n
A. pseudoconulus
CC14 Coniacian
CC13 Turonian
14R
CC12
Barren
50
8X
early Eocene
7X
10X
Int
RP20
IIB
6X 50
Polarity rating R
P19 NP23
Barren
5H
50
Rads.
Miocene
Plank. foram Calc. nanno.
Age
I IIA Foraminifer nannofossil ooze
4H
Depth (mbsf)
When Campanian–Maastrichtian magnetostratigraphies from the three independent holes of Site 1257 are merged using the composite depth offsets, a consistent and simple polarity pattern emerges. The upper Campanian interval is constrained by foraminifer biostratigraphy to be uppermost Chron C33n–C32n (Fig. F5A). The early Maastrichtian age of the reversed polarity zone in the upper half of the succession implies an assignment to Chron C31r.
Recovery
Depth (mcd) Core
3H
Magnetostratigraphy Polarity interpretations
Biostratigraphy Lithology
early Oligocene
2H
middle Eocene
Depth (mcd)
Recovery
Core
(Major offsets to mcd in yellow) Hole Hole Hole 1257A 1257B 1257C
0
late Paleocene
A
Recovery Depth (mcd)
Campanian–Maastrichtian
F5. Magnetostratigraphy and characteristic directions, p. 25. Core
Paleomagnetic analysis of minicores from combined Holes 1257A, 1257B, and 1257C revealed upper Chron C33n–C31r within a thick upper Campanian–lower Maastrichtian section, Chron C26n–C24r in an expanded upper Paleocene section, and portions of Chron C20r–C17n within a relatively condensed Middle Eocene interval (Shipboard Scientific Party, 2004b) (Fig. F5A).
10-11 Cenoman.
15R
within C34n
16R
26X
250
27X 250 28X 29X
280
V Clayey carbonate siltstone
m. to l. Albian
NC8
30X 280 31X TD= 284.7
Hole 1257A Hole 1257B Hole 1257C
Hole 1257A Hole 1257B Hole 1257C
Hole 1257A Hole 1257B Hole 1257C
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261 larity of the uppermost Paleocene below the basal Eocene hiatus has no equivalent chron in the standard reference set (e.g., Cande and Kent, 1992), therefore may be an early Eocene remagnetization associated with the nondeposition interval or other artifact.
Middle and Late Eocene A hiatus spanning a minimum of foraminifer Zones P7–P10 separates lower Eocene strata from the Middle Eocene unit. The relatively compact Middle Eocene greenish white foraminifer nannofossil chalk yields a relatively well defined suite of polarity zones. However, assignments of these zones to polarity chrons is inhibited by the low biostratigraphic resolution and apparent inconsistencies between currently available zonal identifications from the foraminifer and calcareous nannofossil assemblages and by gaps in core recovery. The limited stratigraphic control suggests that the basal polarity zones of this Middle Eocene segment might correspond to Chrons C20r–C20n and that the upper portion records Chrons C18r-C18n-C17r and the base of Chron C17n. A thin Upper Eocene unit (foraminifer Zone P16) of normal polarity is bounded by disconformities between the underlying Middle Eocene (Zone P14) and overlying lower Oligocene (Zone P18) units. The only normal polarity chron within foraminifer Zone P16 is Chron C15n.
Site 1258 Paleomagnetic analysis of combined Holes 1258A, 1258B, and 1258C reveal Chrons C26r–C20r of the late Paleocene through the early Middle Eocene (Shipboard Scientific Party, 2004c) (Fig. F5B). Polarity chron assignments within the Campanian–Maastrichtian sediments are more ambiguous due to weak magnetizations but seem consistent with Chrons C33r–C29r of age. The high-resolution magnetostratigraphy of the relatively expanded Lower Eocene–lowermost Middle Eocene provides an important reference section for future cycle and isotope stratigraphy studies.
Campanian–Maastrichtian The calcareous nannofossil clay to chalk of Campanian–middle Maastrichtian is characterized by very weak magnetic intensity. Many minicores were demagnetized to near the noise level of the cryogenic magnetometer upon heating >200°C, thereby introducing significant uncertainty in polarity interpretations. Clustering of normal and reversed polarity samples in both holes allowed identification of the main polarity zones (Fig. F5B), but assignment of polarity chrons is inhibited by the lack of detailed biostratigraphic constraints. The general pattern and age are consistent with the uppermost Chron C34n–C30n, but these tentative interpretations may be modified after further paleontological studies. The uppermost Maastrichtian contains reddish brown chalk layers that display high magnetic intensities with NRMs dominated by normal overprints. Thermal demagnetization yielded reversed polarity in both Holes 1258A and 1258B, which is constrained by nannofossil Zone CC26 to be Chron C29r (Fig. F5B).
9
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
Paleocene The greenish white foraminifer nannofossil chalk of the Paleocene is generally characterized by relatively weak intensity. The composite polarity zone pattern and foraminifer zonation of the merged holes is consistent with Chrons C26r-C26n-C25r-C25n-C24r (Fig. F5B), although the lowermost portion currently has a significant discrepancy between the foraminifer and the nannofossil age assignments.
Lower and Middle Eocene The greenish white foraminifer nannofossil chalk that dominates the Eocene succession yields a relatively well defined suite of polarity zones (Fig. F5B). A reddish brown chalk that spans the Lower Eocene (Ypresian)–Middle Eocene (Lutetian) at ~40–100 meters composite depth (mcd) has strong magnetic intensity with a relatively steep downward-directed magnetic inclination. Thermal demagnetization >150°C of this reddish brown chalk was very effective in removing this downward overprint, and univectorial characteristic directions are from 250° through 400° or 450°C. Polarity chron assignments are based on average paleontological ages. The reversed polarity zone at the Paleocene/ Eocene boundary must be Chron C24r; therefore, the overlying normal polarity zone is Chron C24n. The assignment of Chron C23n to the normal polarity zone at ~100 mcd is dictated by its position in the upper portion of foraminifer Zone P7. This implies that the narrow reversed polarity zone underlying Chron C23n in both holes must be a relatively condensed record of Chron C23r. The uppermost zone of reversed polarity within nannofossil Zone NP15 is constrained to be Chron C21r, and the underlying polarity pattern and biostratigraphic constraints are consistent with Chrons C22n and upper C22r. However, there is an inconsistency in the interpreted polarity patterns between Holes 1258A and 1258B after adjusting to a composite meter depth scale in the interval between lower Chron C23n (~100 mcd) and Chron C22n (~50 mcd) (Fig. F5B). First, the top of polarity Chron C23n is offset between the two holes. Fault displacements that caused apparent relative removal of ~20 m of stratigraphic section between holes (shown by yellow squares in Fig. F5B) were assigned from shipboard comparisons of sedimentary features, biostratigraphic datums vs. depth, and other inconsistencies in the composite stratigraphy of the Paleocene–Early Eocene. An offset in the shipboard assignment of the foraminifer Zone P8/P7 boundary near the top of this distorted Chron C23n suggests the possibility of another unrecognized fault in Hole 1258A, which may have truncated uppermost Chron C23n in Hole 1258B and/or truncated the overlying Chron C22r in Hole 1258A. More worrisome is the interval of apparent normal polarity at ~80 mcd at each site, which, being between our assignments of Chron C22n and C23n, would seem to be in the middle of reversed polarity Chron C22r. There are at least two possible explanations for this “anomalous” normal polarity zone: (1) a stratigraphic interval within the reddish brown chalk characterized by a pervasive normal polarity overprint that was not effectively removed by our thermal demagnetization procedure, or (2) a duplication of a portion of the polarity pattern by another fault that could not be resolved from biostratigraphic constraints. Other than this annoying inconsistency within upper Chron C23n and lower Chron C22r, the Eocene polarity pattern is well resolved.
10
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
Site 1259 Paleomagnetic analysis of minicores from combined Holes 1259A and 1259B resolved numerous magnetic polarity zones within the Campanian–Eocene section (Shipboard Scientific Party, 2004d) (Fig. F5C). Chrons C31r–C29r are assigned to the Maastrichtian succession, and a complete record of Chrons C23n–C18r is resolved in the strata spanning late Early Eocene–Middle Eocene. This is one of the rare sites with a continuous magnetostratigraphy spanning the boundary interval between Early Eocene and Middle Eocene—a time span that is typically represented as a hiatus in most marine sections.
Campanian–Maastrichtian The greenish gray chalk of upper Campanian–Maastrichtian is characterized by light–dark cycles. This interval was extensively sampled for postcruise paleomagnetic analyses for applying cyclostratigraphy to constrain the duration of the polarity chrons. The merged Maastrichtian polarity pattern from Holes 1259A and 1259B is consistent with Chrons C31r–C31n and C30n–C29r.
Paleocene A ~25-m interval of negligible recovery within the upper Paleocene gray chalk and the extreme condensation of the lower Paleocene reddish brown chalk precludes reliable assignments of chrons to the observed polarity zones. If one assumes that the recovery gap had a similar sedimentation rate as the Lower Eocene, then it represents nonrecovery of Chron C25n and the underlying polarity pattern of the lower Upper Paleocene must be Chrons C26r-C26n-C25r.
Eocene The uppermost Paleocene and lower Lower Eocene is weakly magnetized white chalk of predominantly reversed polarity, which is consistent with the expected Chron C24r at the Eocene/Paleocene boundary (Fig. F5C). Within Chron C24r, a thin normal polarity band is recorded in Core 207-1259A-37R—this and similar intra-C24r features at other sites are examined in the summary discussion. An apparent hiatus in sedimentation during the middle Lower Eocene spans the time interval of foraminifer Zone P7, nannofossil Zone NP11 and portions of adjacent microfossil zones, and the associated Chrons C24n and C23r. The upper Lower Eocene strata (foraminifer Zones P8–P9) display distinctive cycles of reddish brown–gray or dark–light green. Similarly to the coeval cyclic unit at Site 1258, hematite seems to be both the source of the reddish coloration and the carrier of a normal polarity overprint. Progressive thermal demagnetization was effective in resolving polarity zones, which are constrained by the biostratigraphy to be Chrons C23n-C22r-C22n. The greenish white chalk facies of the lower Middle Eocene (foraminifer Zones P10 and P11) and upper Middle Eocene (foraminifer Zones P12–P14) have, respectively, very weak and moderate magnetic intensities (Fig. F5C). The pattern of well-defined polarity zones is constrained by biostratigraphy to be the complete succession of Chrons C21r–C18r and, possibly Chron C17r above a gap in recovery.
11
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261 A narrow 10-m-thick zone of Late Eocene greenish gray chalk has relatively strong magnetization, and biostratigraphy (foraminifer Zone P16) constrains the dominance of normal polarity to be Chron C15n.
Site 1260 Closely spaced paleomagnetic sampling of combined Holes 1260A and 1260B produced a detailed record of Middle Eocene Chrons C21r– C18r (Shipboard Scientific Party, 2004e) (Fig. F5D). Lower-resolution sampling was adequate to identify Chrons C26n–C23n of the Late Paleocene and Early Eocene.
Campanian–Maastrichtian Compared to other sites, the magnetostratigraphy of the Campanian–Maastrichtian was less successful. This white to greenish white chalk at Site 1260 displayed very weak magnetizations that generally approach the background noise level of the Munich cryogenic magnetometer upon heating >200°C. Very few minicores yielded reliable characteristic directions; and, especially in the Campanian, polarity assignments were also difficult (Fig. F5D). In addition, the biostratigraphic constraints are too broad to make assignments of polarity chrons to strata older than Chron C31n. In contrast, the thermal demagnetization of the relatively strongly magnetized reddish brown chalk of the uppermost Maastrichtian effectively resolved reversed polarity Chron C29r.
Paleocene Paleocene clayey nannofossil chalk is also characterized by weak magnetization, but it is significantly better than the underlying Campanian–Maastrichtian. No chron assignments were attempted in the relatively condensed lower Paleocene where biostratigraphic ages are inconsistent between foraminifer and nannofossil assignments. The upper Paleogene polarity pattern resolved by minicore analyses is constrained by biostratigraphy to represent Chron C26n through the lower portion of Chron C24r.
Lower and Middle Eocene The clayey chalk of the earliest Eocene and reddish brown chalk of middle Early Eocene yielded a pattern of polarity zones that matches upper Chron C24r–lower C23n. The lower Middle Eocene is also reddish brown chalk. Its polarity pattern fits uppermost Chron C22n–lower C21n (Fig. F5D). A hiatus spanning foraminifer Zone P9 and nannofossil Zone NP13 in the uppermost part of Core 207-1260A-1R apparently caused the juxtaposition of two normal polarity zones—uppermost Chron C22n directly overlies lower Chron C23n. The upper Middle Eocene (~40–185 mbsf) mainly consists of greenish white foraminifer nannofossil chalk. The combined magnetostratigraphy of the two holes yielded a detailed polarity pattern identical to Chrons C21n–C18r, which is consistent with the paleontological ages.
12
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
13
Site 1261 Compared to other sites, Site 1261 is relatively condensed and the main successions of polarity chrons are bound by hiatuses (Shipboard Scientific Party, 2004f) (Fig. F5E). Chrons C31r–C29r (Maastrichtian), Chrons C27n–C24r (Paleocene–Early Eocene), and Chrons C21r–C19r (Middle Eocene) were resolved.
Campanian–Maastrichtian As in Site 1260, the weakly magnetized Maastrichtian–Campanian greenish gray clayey chalk with light–dark cycles was commonly near the noise level of the Munich cryogenic magnetometer upon heating >200°C. Even though many of the individual-sample polarity interpretations are uncertain, when the data from the two holes are merged using composite depths, the generalized polarity zones and biostratigraphic constraints suggest Chrons C31r, C30n/C31n, and C29r (Fig. F5E).
Paleocene Medium–light gray clayey chalk of the Paleocene has slightly stronger magnetizations than Late Cretaceous sediments. The upper Paleocene section contains the record of Chrons C27n–lower Chron C24r (Fig. F5E).
Eocene Light greenish gray to medium gray chalk of Early–Middle Eocene age is very weakly magnetized, but the polarity of most samples was evident. The lowermost Eocene section at Site 1261 is entirely within Chron C24r, but is truncated by a hiatus that probably spanned Chrons C23r and C24n of middle Early Eocene. A second hiatus at the Early (Ypresian)/Middle (Lutetian) Eocene stage boundary spanned Chrons C22n and C22r. A sediment piece recovered from between these two hiatuses has normal polarity, and its biostratigraphic age suggests an assignment to Chron C23n. Within the Middle Eocene, we resolved the complete succession of Chrons C20r-C20n-C19r and possibly portions of the underlying Chrons C21n and C21r. Above a sampling gap, the uppermost meters of the Middle Eocene yielded a dominance of normal polarity, and its age within with foraminifer Zones P13 and P14 indicates an assignment to Chron C18n.
NW
NE
SE
NW
Site 1260
Campanian
Late Cretaceous
33n
Turonian Cenomanian
95
99.1 100
KS26 Globotruncana ventricosa
CC22
CC21 CC20 UC15 CC19
KS24 Dicarinella asymetrica
KS23 Dicarinella concavata
KS20
W. archaeocretacea
C25n P4
NP5
CC17 UC13 CC16 UC12 CC15 UC11
P1
CC14 UC10 CC13 UC9
300
CC11 UC7
KS19 Rotalipora cushmani R. reicheli
UC6 UC5 UC4
NC10b UC2 UC1
NC10a
Rotalipora globotruncanoides
R. appenninica
NC9 NC9b NC9a NC8c
CC25
KS 30b CC24
C29r
C31r
C32r including C32r.1n? C33n? C33r?
20-18
NC8 NC8 a-b
Hedbergella planispira
Cenom. 450
C34n? CC 10a to NC 10b
450
C30n-C30r -C31n
C32n CC23 to CC22
400
Turonian
Ticinella primula
KS 30a
350
R. ticinensis
KS14 Biticinella breggiensis
C25r C26n C26r
NP2
KS31 CC26 to 25c
CC10a UC3
KS16
KS12
112.2
400
NP8
250
CC18 UC14
CC10b
KS17
KS13
CC26 -25
KS30a CC25 KS30b -23 KS29
early Olig.
C19r C20n
Polarity Chron Assignments
Age
lower
P3b P3
no data
NP3 -2
KS24 CC14
KS29 CC25 not CC23 zoned
KS23 CC13
C25n probably not recovered
P6
C22r C23n
400
early Eocene 100
Hiatus?
NP10
C24r
P2
NP8 NP7
KS 30a CC25
KS 29/28
NP16
C25r? C26n? C26r?
rare
-12
Int
N
Polarity Chron Assignments Hiatus
C15n? C17n?
C18n C20n?
Hiatus
C24n? Hiatus
NP9 nondiagnostic
NP8
P4 NP7
? C24r? C25n C25r Hiatus
non-
early diagMaastrich. KS30 CC23 nostic -24
e. Camp.
17-18
A. pseudoconulus
C31r C32n C32r top of C33n
CC16 -17 CC14
200
Coniacian CC13 Turonian
CC12 10-11
Cenoman.
within C34n
C29r C30n-C31n C31r
CC23
KS24
Polarity Rating R
RP15
NP12 RP 8-7
NP9/10
A. tylodus
NP3 CC26
KS 30b Campan.
P6
late KS29 CC22 Campanian -23
Santonian P4
P11
C26n
possible brief normal-polarity zone in C24r?
C25n not resolved
KS31
RP17?
NP17 RP16
P13 P12
NP9
P3b early Paleoc.
Micro Zone F N R P16 P14
P5
150
450 CC10
NP12
P5
CC11
KS19
P8
350
C32n?
CC12
KS21 -20
50
C22n
P9 NP13
C24r C25r C26n C26r C27n/C27r? C29r C30n-C31n C31r
C21n C21r NP14
middle Eocene
NP15 P10
300
late Paleocene
P5
Site 1257 Composite of Hole A and B
250
barren
C20r
Hiatus
P4
Hiatus
C20n
C20r
C21n? C21r? Hiatus? C23n?
NP 13
C15n?
C17r?
NP16
P11
Santon. 500 Coniacian KS23 CC13
Hiatus
C34n
N
C18r C19n C19r
P12
upper
KS31 CC26
?
middle Eocene
Depth (mbsf)
early Eocene 650
CC10 KS19 KS17
KS13
Int
NP21
P14 NP17
200
KS22
Hiatus
KS23 CC13 to CC12 KS22 to KS20 CC11
C34n
500
RP NP 15 11-14
P7
Sant. Con.
600
C32n
?
P18
NP20 late Eocene P16 NP19
150
C18n? C18r-C19n probably not recovered
early Eocene
middle Eocene
P11
P2
550
? ? C29r C30n-C31n
CC23
Paleocene
early Eocene
Reversed polarity of Core 22R of Hole B suggests depth-shift error
C25n
C25n C25r C26n
NP8
KS31
350
NP9
KS15
110
NP9
P5
C24r
lower
NP7
NP3
200
KS22 M. sigal CC12 UC8 KS21 Helvetoglobotrun. helvetica
RP 12-15
NP9
P4
Polarity Rating R
barren
UC18
UC16
NP 16
P11/ P9
C22n 500
NP9
P3P1
possible brief normal-polarity zones in C24r?
UC19
Gansserina gansseri
P12
NP 14/15
Hiatus
upper
RP8 to RP5 P5
300
C24r
UC20 CC25 CC24
10-11 P6
(implied by biostrat)
condensed C23r?
NP10
nondiagnostic
450
Top of C22n
C23n C23r C24n
Polarity Chron Assignments
P13
RP 14-15
late Paleocene
R. fructicosaC. contusa
150
NP4
93.5
C23n C24n
NP11
P6
NP2 NP1
89.0
105
NP12 P7
NP4
KS30
KS25
85.8
250
NP 17
Maastrich./ Campanian
early Eocene
100
NP6
CC26
C21n C21r
NP12 P7
Turonian
Abathomphalus mayaroensis
Globotruncanita elevata
83.5 Santonian
Coniacian
34n
P8
late Cenomanian
NP8
?
RP11 to RP10
P10
NP3
KS29 G. aegyptiaca KS28 Globotruncanella havanensis KS27R. calcarata
400
200
C21r C22n C22r Pervasive overprint of normal polarity?
NP5
P1a
KS31
P11 NP15
C20r
P1c P1b ?
CC23 UC17
90
150
barren
middle
71.3
32r
Polarity Chron Assignments
Relative truncation by a fault?
?
Paleocene
31r
32n
Polarity Rating Int N
NP14
P9
P8
P3b
Danian
early
31n
N R
(implied by biostrat)
NP7
Pa
Maastrichtian
30n
33r
NP9b NP9a
P2
65.0
75
85
NP11 NP10
P6a P5 P4c P4b
P3a
27r 28r
29n 29r
80
P6b
P4a
27n
28n
70
NP12
Maastrichtian
26r
late
Paleocene
26n
P7
NP13
Thanet.
55.0
Int
C21n
?
NP14
50 NP13
P8
Ypresian
early
24r
60
65
P10 NP15
NP14 P9
25n 25r
R
N
Paleocene
NP15
P10
Selandian
55
F
0
middle Eocene
P11
22r 23n 23r 24n
Polarity Rating
Micro Zone
Age
Polarity
Rating Micro Zone F N R R Int N M13b NN10
P13
Mio-Olig
21r 22n
50
0
Campanian
21n
Lutelian
20r
Paleogene Eocene
45
NP16
Zones are Hole A
Age late Mioc.
P14
C20r
barren
P13
P12
350
C19n RP12
rare or poolry preserved throughout
early Oligocene
Depth (mcd)
P14
19n
Maast./ Campanian
Bartonian
18r 19r
Composite of Hole A and B
C19r RP14
C20n
middle Eocene
Hole A and B
NP18
Cenom. - Coniacian
late
Pairbonian
Site 1258
NP20 NP19
NP17
barren
late early
Rupelian
100 NP22 NP21
18n
20n
Site 1261
C18r C19n
NP16 P12
NP23
P16
P15
barren
Chattian
Oligocene
RP15
NP24
P19
Micro Zone F N
100
Hiatus
P13
50
NP25
P20
P18
40
Composite of Hole A and B Age
P21a
33.7
16r
Site 1259
Polarity Chron Assignments
N
NP17 RP16
NN1
P22
P21b
12r
13r 15r 16n
17n 17r
Int
l. Eoc. P16 NP19
Nannos
M1a
23.8
7r
8n 8r 9n
11n 11r 12n
13n
35
R
P21a to NP23 P16
rare to barren
Epoch Forams Mio.
6Cn 6Cr 7n
9r 10n 10r
30
Polarity Rating
Micro Zone F N R 0
E. Albian
6Br
25
e
Age (Ma) Chron
Age
Maastrichtian
Depth (mbsf)
Composite of Hole A and B
Magnetic Polarity Timescale
Albian
Magnetostratigraphic correlations of all five sites are shown in Figure F6. In general, the magnetostratigraphy patterns, when coupled with biostratigraphic constraints, indicate that most sites of Leg 207 contain semicontinuous records of Chrons C18n–C27r of Middle Eocene to Late Paleocene age and Chrons C29r through potentially C33r of Maastrichtian–Campanian.
F6. Correlation of magnetostratigraphy, p. 30.
Early Cretaceous
MAGNETOSTRATIGRAPHIC CORRELATIONS AND THEIR IMPLICATIONS
C32n?
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
Aptian–Santonian Cretaceous strata display progressive expansion toward the deeper sites. Although the pre-Campanian strata were not useful for magnetostratigraphy, owing to their deposition during the long normal polarity Superchron C34n, the paleomagnetism is important for determination of paleolatitudes. Thermal demagnetization of clayey carbonate siltstone of Albian age at Site 1257 displays a relatively weak magnetization of normal polarity with positive inclination. Albian quartz siltstone of Site 1260 is characterized by relatively high intensity (~10–4–10–3 A/m after 15-mT AF demagnetization) and high susceptibility. Progressive AF demagnetization of shipboard cores of Site 1260 siltstone indicated normal polarity with a mean inclination of +30°. Progressive thermal demagnetization of several minicores of this facies also yielded normal polarity with inclinations being uniformly positive. The overlying black shale of the Cenomanian–Santonian at Site 1257 displayed the highest intensity magnetization (10–2–10–1 A/m after 20mT AF demagnetization using shipboard pass-through cryogenic magnetometer) of any facies at Site 1257. In contrast, this black shale unit at Site 1258 has magnetic intensities near the background noise level of the shipboard magnetometer. The positive inclinations that dominate the remanent magnetization of this black shale also indicate a paleolatitude north of the paleoequator. Of course, with any unit of entirely normal polarity, it possible that there is a contribution from a persistent overprint of present-day normal polarity (20° dipole inclination for Leg 207 sites). However, the fact that the mean inclinations of characteristic magnetization of Albian and Cenomanian paleomagnetic minicores are steeper than the present-day field is an indication that the Albian– Cenomanian paleolatitude was slightly northward of the present location of these sites. The Albian samples yield a paleolatitude of 15°N latitude (α95 = 5°, k = 25) (Suganuma and Ogg, unpubl. data).
Campanian–Maastrichtian Magnetostratigraphies of Campanian and Maastrichtian chalk from Sites 1257, 1258, 1259, and 1261 are consistent with assignments and correlations of Chrons C29r–C32n (Site 1260 had inadequate sampling and weak magnetizations that precluded useful polarity zone interpretations). However, until the array of sites have enhanced biostratigraphic studies to delimit microfossil datums, we caution that it is possible that portions of the current biostratigraphy polarity patterns at each site might have alternate assignments to polarity chrons. The expanded succession with duplicate magnetostratigraphic records from two holes at Site 1258 appears to have resolved the complete sequence of magnetic Chrons C29r–C34n. The Cretaceous/Paleogene (K/P) boundary impact event layer at Sites 1258, 1259, and 1260 is within polarity Chron C29r, as is expected from the reference magnetic polarity timescale.
Paleocene At all sites, the Danian stage (Chrons C29r–C27n) is condensed and/ or includes hiatuses. In contrast, the Upper Paleocene (Selandian and Thanetian stages) is present at all sites, and most holes yielded records of Chrons C26r–C24r. The distinctive Chron C26n provides a useful
14
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261 correlation marker among all sites. Magnetostratigraphic correlations and comparison to the reference magnetic polarity timescale suggest that relative sedimentation rates were variable within and among the sites, and minor hiatuses punctuate the record at some locations. For example, the relative widths of polarity zones associated with Chron C26n and overlying Chron C25r indicate relatively rapid deposition at Site 1257, where the early Paleocene is absent above the K/P boundary, whereas the coeval accumulation rates are significantly slower at sites where Paleocene sedimentation was initiated.
Eocene Portions of the Eocene are significantly expanded at some sites. Site 1258 has a very thickened Early Eocene (Chrons C24r–C22n), and Sites 1259 and 1260 have a very thick Middle Eocene (Chrons C21r–C18r). At each site, the chron assignments are constrained by foraminifer and nannofossil biostratigraphy, but many portions also have a distinctive “fingerprint” match to the reference magnetic polarity timescale. A hiatus of variable duration occurs at Sites 1257, 1260, and 1261 between the Lower and Middle Eocene that removes the uppermost Lower Eocene (Chrons C22n and C22r; and an even longer time span at Site 1257). In contrast, the interpreted presence of Chron C22n and overlying Chron C21r at Sites 1258 and 1259 suggests a continuous record across this subepoch boundary. A curious feature within the 2-m.y.-duration Chron C24r of latest Paleocene into Early Eocene are apparent thin normal polarity bands (e.g., at Site 1257 and Site 1258 within lower foraminifer Zone P6). Similar intra-C24r normal polarity subzones were interpreted in ODP Hole 1051A (Ogg and Bardot, 2001). Even though this apparent occurrence at multiple sites suggests that Chron C24r may include one or more short-duration normal polarity events that are not in the standard Csequence model (Cande and Kent, 1992), we are hesitant to propose subchrons within Chron C24r without confirmation in a land-based section with fully oriented paleomagnetic data. One major objective of our study is to provide a high-resolution magnetostratigraphic framework for a detailed cycle-stratigraphy analysis of the subtle facies oscillations and of the duration of polarity chrons and thereby estimation of the spreading rates for the corresponding marine magnetic anomalies. We successfully obtained expanded magnetostratigraphic record of Chrons C24r-C24n-C23r-C23n at Sites 1258 and 1260 and of Chrons C21r-C21n-C20r-C20n-C19r at Sites 1259, 1260, and 1261. This enables multiple sites to be used to verify the cycle-stratigraphy interpretations. Although the Bartonian stage of the upper Middle Eocene (Chrons C18n–C17n) was recovered at four sites, assignment of the polarity zones to chrons was generally uncertain. The recovered strata of the Priabonian stage at Sites 1257 and 1259 on the northeast margin of Demerara Rise record only a brief portion of the Late Eocene Chrons C17n–C15n.
SUMMARY Magnetostratigraphy of the five Leg 207 sites provides an enhanced chronologic control for the Latest Cretaceous–Eocene of Demerara Rise. Thermal demagnetization of ~800 minicores collected from the sites re-
15
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261 moved a downward-directed overprint induced during the drilling process and a low-temperature component that was effectively removed by heating >200°C. The magnetostratigraphy interpretations and biostratigraphic constraints at the five sites enabled identification and commonly a detailed delimiting of Chrons C18n–C27r of the Middle Eocene–Late Paleocene and of Chrons C29r–C31r of the Maastrichtian– Campanian.
ACKNOWLEDGMENTS We thank the ODP staff and crews of the JOIDES Resolution for their help and good company during Leg 207. The weeks of a round-theclock acquisition of magnetic measurements were only possible through the generosity of Professor Valerian Bachtadse and Manuela Weiss, who allowed us to monopolize the paleomagnetic facilities at the Institute of Geophysics at the University of Munich, Germany, and of Makoto Okada at the paleomagnetic laboratory of the Department of Environmental Sciences of the University of Ibaraki, Japan. The energetic group at the ODP Core Repository at Bremen sent us more than 100 additional minicores and then aided us for a 4-day race to drillpress an additional 300 minicores to improve resolution of magnetic reversal boundaries at the midpoint of our analysis marathon. This research utilized samples and/or data provided by the Ocean Drilling Program (ODP). ODP is sponsored by the U.S. National Science Foundation (NSF) and participating countries under management of Joint Oceanographic Institutions (JOI), Inc. The JOI/U.S. Science Advisory Committee (USSAC) provided advance funding to J. Ogg and a special travel grant to accomplish the postcruise collection and analyses of the minicores in Germany.
16
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
REFERENCES Acton, G.D., Okada, M., Clement, B.M., Lund, S.P., and Williams, T., 2002. Paleomagnetic overprints in ocean sediment cores and their relationship to shear deformation caused by piston coring. J. Geophys. Res., 107. doi:10.1029/2001JB000518 Beck, M.E., Jr., 1998. On the mechanism of crustal block rotations in the central Andes. Tectonophysics, 299:75–92. Beck, M.E., Jr., 1999. Jurassic and Cretaceous apparent polar wander relative to South America: some tectonic implications. J. Geophys. Res., 104:5063–5067. Berggren, W.A., Kent, D.V., Swisher, C.C., III, and Aubry, M.-P., 1995. A revised Cenozoic geochronology and chronostratigraphy. In Berggren, W.A., Kent, D.V., Aubry, M.-P., and Hardenbol, J. (Eds.), Geochronology, Time Scales and Global Stratigraphic Correlation. Spec. Publ.—SEPM (Soc. Sediment. Geol.), 54:129–212. Cande, S.C., and Kent, D.V., 1992. A new geomagnetic polarity time scale for the Late Cretaceous and Cenozoic. J. Geophys. Res., 97:13917–13951. Cande, S.C., and Kent, D.V., 1995. Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and Cenozoic. J. Geophys. Res., 100:6093–6095. Erbacher, J., Mosher, D.C., Malone, M.J., et al., 2004. Proc. ODP, Init. Repts., 207 [CD-ROM]. Available from: Ocean Drilling Program, Texas A&M University, College Station TX 77845-9547, USA. [HTML] Gradstein, F.M., Ogg, J.G., and Smith, A. (Eds.), 2004. A Geologic Time Scale 2004: Cambridge (Cambridge Univ. Press). Kirschvink, J.L., 1980. The least-squares line and plane and the analysis of palaeomagnetic data. Geophys. J. R. Astron. Soc., 62:699–718. Ogg, J.G., and Bardot, L., 2001. Aptian through Eocene magnetostratigraphic correlation of the Blake Nose Transect (Leg 171B), Florida continental margin. In Kroon, D., Norris, R.D., and Klaus, A. (Eds.), Proc. ODP, Sci. Results, 171B [Online]. Available from World Wide Web: . [Cited 2004-05-20] Randall, D.E., 1998. A new Jurassic–Recent apparent polar wander path for South America and a review of central Andean tectonic models. Tectonophysics, 299:49– 74. Scotese, C.R., 2001. PALEOMAP project. Available from World Wide Web: . [Cited 2004-05-20] Shibuya, H., Merrill, D.L., Hsu, V., and Leg 124 Shipboard Scientific Party, 1991. Paleogene counterclockwise rotation of the Celebes Sea—orientation of ODP cores utilizing the secondary magnetization. In Silver, E.A., Rangin, C., von Breymann, M.T., et al., Proc. ODP, Sci. Results, 124: College Station, TX (Ocean Drilling Program), 519–523. Shipboard Scientific Party, 2004a. Explanatory notes. In Erbacher, J., Mosher, D.C., Malone, M.J., et al., Proc. ODP, Init. Repts., 207 [Online]. Available from World Wide Web: . [Cited 2004-05-20] Shipboard Scientific Party, 2004b. Site 1257. In Erbacher, J., Mosher, D.C., Malone, M.J., et al., Proc. ODP, Init. Repts., 207 [Online]. Available from World Wide Web: . [Cited 2004-05-20] Shipboard Scientific Party, 2004c. Site 1258. In Erbacher, J., Mosher, D.C., Malone, M.J., et al., Proc. ODP, Init. Repts., 207 [Online]. Available from World Wide Web: . [Cited 2004-05-20] Shipboard Scientific Party, 2004d. Site 1259. In Erbacher, J., Mosher, D.C., Malone, M.J., et al., Proc. ODP, Init. Repts., 207 [Online]. Available from World Wide Web: . [Cited 2004-05-20]
17
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261 Shipboard Scientific Party, 2004e. Site 1260. In Erbacher, J., Mosher, D.C., Malone, M.J., et al., Proc. ODP, Init. Repts., 207 [Online]. Available from World Wide Web: . [Cited 2004-05-20] Shipboard Scientific Party, 2004f. Site 1261. In Erbacher, J., Mosher, D.C., Malone, M.J., et al., Proc. ODP, Init. Repts., 207 [Online]. Available from World Wide Web: . [Cited 2004-05-20] Zhang, C., and Ogg, J.G., 2003. An integrated paleomagnetic analysis program for stratigraphy labs and research projects. Comput. Geosci., 29:613–625.
18
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
19
APPENDIX Demagnetization data (AF and thermal steps) of all 800 minicores with sample-by-sample summary comments on assignment of polarity and reliability to characteristic directions are shown in Tables AT1, AT2, AT3, AT4, AT5, AT6, AT7, AT8, AT9, AT10, and AT11.
AT1. Paleomagnetic analysis, Hole 1257A, p. 31.
AT2. Paleomagnetic analysis, Hole 1257B, p. 33.
AT3. Paleomagnetic analysis, Hole 1257C, p. 34.
AT4. Paleomagnetic analysis, Hole 1258A, p. 36.
AT5. Paleomagnetic analysis, Hole 1258B, p. 37.
AT6. Paleomagnetic analysis, Hole 1259A, p. 38.
AT7. Paleomagnetic analysis, Hole 1259B, p. 39.
AT8. Paleomagnetic analysis, Hole 1260A, p. 40.
AT9. Paleomagnetic analysis, Hole 1260B, p. 45.
AT10. Paleomagnetic analysis, Hole 1261A, p. 46.
AT11. Paleomagnetic analysis, Hole 1261B, p. 47.
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
20
Figure F1. Bathymetric map of Leg 207 drilling sites on Demerara Rise. 12° N
80°W
60°
40°
20° N
11° 0°
40
00
10°
1257 1258 1259 1260
9°
1261
3000
00
20
8°
10
00
7° 57°W
56°
55°
54°
53°
52°
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
21
Figure F2. Examples of alternating-field demagnetization followed by progressive thermal demagnetization for selected samples. For each sample, the following are shown: an orthogonal vector plot with solid (open) symbols for data projected onto the horizontal (vertical) plane, a normalized plot of the intensity of magnetization vs. demagnetization step, and a stereographic projection. A. Section 207-1258B-8R-3, 33 cm (early Eocene; 72.96 mbsf) = N-type behavior, assigned as N, may represent brief normal zone within Chron C22r. B. Section 207-1258A-22R-3, 9 cm (late Paleocene; 223.62 mbsf) = N-type (150°C step is an artifact— see text), assigned as NP, within Chron C25n. C. Section 207-1260B-13R-1, 14 cm (early Eocene; 238.09 mbsf) = N-type behavior, assigned as N, within Chron C24n. D. Section 207-1261A-25R-1, 51 cm (middle Eocene; 410.81 mbsf) = N-type, assigned as N, within Chron C20n. (Continued on next page.)
A
B
N
N W Up
W Up E S
W
5 mT
N 400°C
E
S
300°C 200°C 5 mT
N 300°C
S
200°C
S Jo = 3.4E-N2 (kA/m)
1.0
5 mT
0°C E Dn
Div. = 5.0E-N4 (kA/m)
5 mT
100°
E Dn
400°C
N
C W Up
1.0
Div. = 1.0E-N2 (kA/m)
Jo = 4.4E-N3 (kA/m)
E
W Up E
W
400°C 300°C
Jo = 2.1E-N3 (kA/m)
E Dn
Jo = 3.8E-5 (kA/m)
150°C
1.0
5 mT
5 mT
5 mT
0°C Div. = 2.0E-N4 (kA/m)
S
350°C
250°C
300°C 1.0
W
N
S
200°C 5 mT 150°C
300°C
N
D
N
350°C
100°
150°C
S S
W
0°C
0°C 100°
400°C
Div. = 5.0E-N6
E Dn
100°
400°C
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
22
Figure F2 (continued). E. Section 207-1259A-26R-1, 13 cm (middle Eocene; 237.04 mbsf) = hook-type, assigned as R, within Chron C20r. F. Section 207-1260A-25R-7, 32 cm (early Eocene; 227.71 mbsf) = hooktype, assigned as R, within Chron C23r. G. Section 207-1261A-23R-3, 37 cm (middle Eocene; 394.47 mbsf) = hook-type, assigned as R, within Chron C19r. H. Section 207-1257B-4R-4, 84 cm (early Eocene; 71.84 mbsf) = quasi-hook-type (declination shifts by 50°), assigned as RP, within Chron C23r. I. Section 2071258A-28R-5, 67 cm (late Maastrichtian; 284.02 mbsf) = hook-type, but no endpoint reached, therefore assigned as RPP, within Chron C29r. J. Section 207-1259A-44R-3, 94 cm (late Paleocene; 415.51 mbsf) = hook-type, assigned as RP, within Chron C25r.
E
F
N
N
W Up
W Up 0°C
S
E
W
S 300°C
N
N E
W
400°C Div. = 2.5E-4 (kA/m)
150°C S
5 mT
S
Div. = 5.0E-6 (kA/m)
300°C
5 mT 400°C
1.0
Jo = 2.1E-3 (kA/m)
1.0
Jo = 2.1E-5 (kA/m)
200°C 0°C
5 mT E Dn
100°
G W Up
W
400°C N Div. = 2.0E-6 (kA/m) 1.0
0°C
E
S
S
N Div. = 1.0E-3 (kA/m)
Jo = 8.2E-6 (kA/m)
Jo = 3.6E-3 (kA/m) 1.0 5 mT
5 mT
E Dn
100°
I 310°C
E Dn
400°C
100°
J
N
W Up
W Up E
E
W S
5 mT
400°C
N
W
N 400°C
150°C S
W
400°C
S
0°C S
W Up
150°C 200°C 240°C
5 mT
400°C
N
5 mT E
100°
H
N
300°C
5 mT
E Dn
400°C
N Div. = 2.5E-3 (kA/m) 1.0
250°C
S
S
200°C Jo = 1.5E-2 (kA/m)
150°C 5 mT Div. = 5.0E-3 (kA/m)
1.0
Jo = 2.0E-2 (kA/m)
5 mT 0°C E Dn
0°C 100°
400°C
E Dn
5 mT 100°
400°C
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
23
Figure F3. Acquisition of IRM and its thermal demagnetization of representative samples. A. Normalized IRM acquisition curves up to 1.0 T. B. Demagnetization of IRM up to 600°C.
A
B
Normalized magnetization
1.0
Eocene 207-1259B-15R-1, 86 cm 207-1259B-19R-2, 15 cm 207-1258B-3R-5, 53 cm 207-1258B-5R-2, 54 cm 207-1258B-7R-3, 79 cm 207-1258B-8R-3, 33 cm 207-1258B-13R-2, 38 cm 207-1258B-15R-7, 59 cm
0.8
0.6
0.4
0.2
0
Normalized magnetization
1.0
Paleocene ~ Late Cretaceous 207-1258B-23R-2, 49 cm 207-1258B-28R-1, 31 cm 207-1258B-31R-3, 1 cm 207-1258B-36R-2, 59 cm 207-1258B-43R-2, 83 cm
0.8
0.6
0.4
0.2
0
0
200
400
600
Field (mT)
800
1000
0
100
200
300
400
Temperature (°C)
500
600
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
24
Figure F4. Comparison for hook-type magnetic behaviors of relative orientation of characteristic remanent magnetization (least-squares fit to higher temperature steps) to the low-temperature component (assigned as “North-oriented,” declination 0°). We assumed that the low-temperature component is dominated by a secondary overprint of present-day field and that hook-type extreme shifts in declination upon demagnetization represented the removal of this normal polarity overprint from a characteristic reversed polarity magnetization. The clustering of higher-temperature directions toward south-directed declinations supports this interpretation. Therefore, even though it was not always possible to adequately resolve the orientation of the low-temperature vector in samples displaying similar hook-type demagnetization paths (e.g., Fig. F2E, p. 22), it is probable that these also are reversed polarity characteristic directions with a superimposed normal polarity secondary vector.
N
W
E
S
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
25
Figure F5. A. Magnetostratigraphy and characteristic directions from Eocene–Cretaceous in Holes 1257A, 1257B, and 1257C based on analysis of discrete samples. The majority of the minicores are from Hole 1257B, with enhanced Maastrichtian–Campanian from Holes 1257A and 1257C. The measured data from the three holes have been merged using the composite depth scale, and these adjustments are shown schematically for each hole (rightmost columns). Polarity ratings are graded according to reliability and number of vectors utilized in the characteristic direction (R = reliable reversed polarity, INT = indeterminate, N = reliable normal polarity; and relative placement of other points indicates degree of precision or uncertainty). Polarity zones are assigned according to clusters of individual polarity interpretations. Normal polarity zones = dark gray, reversed polarity zones = white, and uncertain polarity or gaps in data coverage = cross hatched. Assignments of polarity chrons are based on the polarity zone pattern and the constraints from microfossil biostratigraphy. (Continued on next four pages.)
3H
Age
I IIA Foraminifer nannofossil ooze
Miocene
50
8X
3R
9X
4R
10X
5R 6R
11X
Depth (mbsf)
100
100
Foraminifer nannofossil chalk (high biogenic silica)
1R
7R
12X 100
100
13X
8R
14X
9R
15X
10R
3R 4R
11R
17X
150 13R
18X
14R
19X
15R 16R 17R 18R 19R
20X 21X
200
22X 200
23X 24X 25X
lower P18 NP21 RP20 to upper
P16 P14
20R 21R 200 22R 23R 24R 25R 26R 27R
NP17 RP16
P13 P12 P11
P6
C15n? Hiatus C17n? C18n
RP17?
NP16
RP15
C20n?
Rare
NP12 RP 8-7
150
Hiatus
NP9
? C24r?
Nondiagnostic
NP8
C25n P4 NP7
C25r C26n Hiatus
7R
IIIB
8R
Foraminifer nannofossil chalk (w/ zeolites)
9R 10R 11R
IV
12R
Laminated black shale
200 13R
Hiatus
C24n?
NP9/10
6R
12R 150
IIIA
Inclination Intensity (A/m) Polarity chron 1E-3 assignments -60° 0° 60° 1E-6
RP20
P5
Foraminifer nannofossil chalk (w/ zeolites)
N
NP22
5R
16X
150
2R
Int
Characteristic magnetization
early Maastrich. KS30 CC23
Nondiagnostic
C31r
-24 A. tylodus
late Campanian
KS29
CC22 -23
e. Camp.
17-18
Santonian
CC16 -17
C32n C32r top of C33n
A. pseudoconulus
CC14 Coniacian
CC13 Turonian
14R
CC12
Barren
7X
middle Eocene
50
R
NP20 RP18
early Eocene
50
1R 2R
Polarity rating
P19 NP23
IIB
6X
Rads.
Lithology
Plank. foram Calc. nanno.
Biostratigraphy
4H 5H
Polarity interpretations
Barren
2H
Magnetostratigraphy
early Oligocene
0
Recovery
Recovery
Depth (mcd) Core
Core
Core
Recovery Depth (mcd)
Depth (mcd)
(Major offsets to mcd in yellow) Hole Hole Hole 1257A 1257B 1257C
late Paleocene
A
10-11 Cenoman.
15R
within C34n
16R
26X
250
27X 250 28X 29X
280
V Clayey carbonate siltstone
m. to l. Albian
NC8
30X 280 31X TD= 284.7
Hole 1257A Hole 1257B Hole 1257C
Hole 1257A Hole 1257B Hole 1257C
Hole 1257A Hole 1257B Hole 1257C
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
26
Figure F5 (continued). B. Holes 1258A and 1258B (Eocene–Cretaceous).
50
Drilled
3R
2R
4R
3R
6R
6R
Int
N
R
Int
N
?
11R
IIA
13R
1R
14R
2R
15R
3R
16R
4R
15R
17R
5R
16R
18R
6R
17R
19R
7R
20R
8R
21R
9R
22R
Drilled
150
18R 19R 200
C22r Pervasive overprint of normal polarity? Relative truncation by a fault?
Nannofossil chalk with foraminifers
?
C23n
NP12
(implied by biostrat)
P7
Condensed C23r?
C24n NP11
P6 NP10
C24r
Possible brief normal polarity zones in C24r? NP9
P5
20R
23R 23R
24R
24R
25R
10R 11R
Reversed polarity of Core 22R of Hole B suggests depth-shift error
C25n P4
C25r
26R
250
27R 28R
IIB 12R
P1
Calc. chalk
IIC
31R
31R
32R
300
32R 300
33R
Drilled
Nannofossil chalk w/ forams
Maastrichtian
29R 30R
NP2
KS31 CC26 to 25c
13R
29R 30R
C26n C26r
NP4
26R
28R
NP8
NP5
25R
33R
C29r
KS 30a
C30n-C30r -C31n
CC25
KS 30b CC24
C31r
34R
34R 35R
350
35R 36R 37R
350
40R
40R 41R 42R 400 43R 44R
450
45R 46R 47R 48R 49R
50R
500
Calcareous nannofossil clay
39R
39R
400
38R
400
41R 42R 43R 44R 45R 46R 47R 48R 49R 50R 51R 52R 53R 54R 55R 56R 57R
C32n CC23 to CC22
C32r
including C32r.1n?
C33n? C33r?
14R 20-18
15R 16R 17R 18R 19R 20R 21R 22R 23R 24R 25R 26R 27R 28R 29R 30R 31R 32R 33R 34R
IV Laminated black shale/ limestone (clayey nanno chalk w/organic matter)
V Phosph. calc. clay w/organic matter
C34n? CC 10a to NC 10b
T. primula to B. bregg.
38R
III
Cenom. Turonian
350
37R
Campanian
36R
Albian
Depth (mbsf)
22R
Paleocene
21R
300
1E-3
C21r C22n
P8
10R
100
27R
Intensity (A/m) 60° 1E-6
(implied by biostrat)
9R
14R
250
0°
C21n NP14
13R
250
Inclination -60°
C20r
P10 NP15
P9
Drilled
12R
200
Polarity chron assignments
Mio-Olig
8R
12R
200
Polarity rating R
NP13
11R
150
Ooze
Plank. foram Calc. nanno.
Recovery
Core
I
Age
Characteristic magnetization
Polarity interpretations
7R
10R
150
Lithology
5R
50
9R
Fault in Hole A 14R-4 (20 m missing)
Biostratigraphy
4R
8R
100
Magnetostratigraphy
middle Eocene
1R
2R
7R
100
Recovery
1R
5R
50
Core
Depth (mcd)
Recovery
Core
0
Depth (mcd)
(Major offsets to mcd in yellow) Hole Hole Hole 1258B 1258C 1258A
early Eocene
B
NC9a to NC8
Hole 1258A
Hole 1258B
Hole 1258A Hole 1258B
Hole 1258A Hole 1258B
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
27
Figure F5 (continued). C. Holes 1259A and 1259B (Eocene–Cretaceous).
C
Magnetostratigraphy
100
Biostratigraphy
Lithology
Age
Plank. foram Calc. nanno.
Recovery
Core
Recovery
Core
Foraminifer nannofossil chalk
13R 14R
Polarity rating R
Int
N
Polarity chron assignments
P18
Inclination -60°
0°
Intensity (A/m)
60° 1E-6
1E-3
NP21
NP20 late P16 Eocene NP19
C15n?
Hiatus
15R
150
Characteristic magnetization
Polarity interpretations
IIA
12R
early Olig.
Recovery
Core
Hole Hole Hole 1259A 1259B 1259C
16R P14
17R
C17r?
NP17
18R 19R P13
C18r
200
21R
IIB
22R
Siliceous foraminifer nannofossil chalk
23R 24R 25R
middle Eocene
20R
C19n C19r
P12 NP16
C20n P11
26R
250
C20r
27R NP15
28R P10
C21n
29R
C21r
30R 31R
4R
2R
Foraminifer nannofossil chalk
3R
36R
5R
4R
37R
6R
5R
38R
7R
6R
39R
8R
7R
40R
9R
IIIA
42R
Clayey nannofossil chalk
44R 45R
10R
46R
11R
47R
450
12R 13R
48R
9R
IIIB
500
15R 16R
51R
17R
52R
18R
53R
19R
54R 55R 56R
20R
57R
Drilled
50R
Foraminifer nannofossil chalk
16R
IV Calcareous claystone with organic matter
23R
550
18R 24R
60R
25R
NP9
C25n not resolved P4
NP8 NP7
C25r? C26n?
P2 Pa
KS31
19R
V Quartz sandstone
C26r? NP3 CC26
C29r
KS 30a CC25
C30n-C31n
KS 30b
C31r
Santon. KS24 Coniacian KS23
17R
59R
Possible brief normal polarity zone in C24r?
Campan.
14R 15R
Hiatus?
NP10
C24r
12R
22R
58R
P6
10R 11R
13R
21R
C23n NP12
P3b early Paleoc.
8R
14R 49R
C22r
P8
P5
41R
43R
early Eocene
35R
NP13
IIC 1R
late Paleocene
3R
Maastrichtian
2R
34R
Cenom. Turonian
400
33R
Drilled
350
C22n
P9
32R
Drilled
Depth (mbsf)
300
NP14
KS 29/28
CC23
C32n?
CC13 -12 KS 20/22 CC11 Cenom. CC10 ?
Hole 1259A Hole 1259B
Hole 1259A Hole 1259B
Hole 1259A Hole 1259B
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
28
Figure F5 (continued). D. Holes 1260A and 1260B (middle Eocene–Campanian and Albian). Magnetostratigraphy Biostratigraphy Lithology
Age
Polarity rating R
Int
Polarity chron assignments
N
I Nanno/for clay
3R
IIA
4R
Foraminifer nannofossil chalk
5R 6R
50
2R
8R
3R
NP19
Hiatus
NP17 RP16
C18r RP15
C19n
12R
8R
13R
9R
14R 15R
IIB Nannofossil radiolarian chalk
10R 11R
16R
150
C19r RP14
P12
17R
middle Eocene
100
NP16
6R 7R
1E-3
0
P13
4R
11R
Intensity (A/m)
60° 1E-6
0
5R 10R
Inclination -60° 0°
P21a to NP23 P16
lt. Eoc. P16 1R
7R
9R
early Oligocene
0
2R
Characteristic magnetization
Polarity interpretations
Rads.
Recovery
Core
Recovery
Core
Hole Hole 1260A 1260B
Plank. foram Calc. nanno.
D
C20n
RP12
C20r
P11 NP15
18R 19R
23R
NP14
27R 28R 29R
12R 13R 14R 15R
Barren
Nannofossil chalk with clay and foraminifers
P8 NP12 P7
P6
upper
NP9
350
33R
20R 21R 22R
36R
23R
37R
24R
38R
41R 42R 43R 44R 45R
500
Clayey nannofossil chalk with foraminifers and calcite
35R
40R
450
19R
34R
39R
400
IIIA
26R
Nannofossil chalk with foraminifers and calcite
NP7
KS31
IIIC
34R
46R
35R
IV
47R
36R
48R
37R
49R
38R
Calcareous claystone with organic matter
50R
39R
51R
40R
52R
41R
53R 54R
42R 43R 44R 45R 46R
C25r C26n
P4
NP3
27R 28R 29R 30R 31R 32R 33R
C25n NP8
P3P1
IIIB 25R
lower
NP9
KS30a
? ? C29r
CC26 -25
C30n-C31n
CC25
KS30b -23
KS29
? Barren
300
P5
18R
Paleocene
32R
C24r
RP8 to RP5
17R
Maast./ Campanian
31R
Cenom. - Coniacian
30R
C24n
10-11
16R
CC23
Hiatus
KS23 CC13 to CC12 KS22 to KS20 CC11
CC10 KS19 KS17
C34n Hiatus V Clayey limestone with quartz
e. Albian
Depth (mbsf)
25R
250
C21r Top of C22n Hiatus C23n C23r
IIC
24R
26R
C21n
RP11 to RP10
P10
early Eocene
200
22R
Rare to barren
21R
Drilled
20R
C34n KS13
Hole 1260A Hole 1260B
Hole 1260A Hole 1260B
Hole 1260A Hole 1260B
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261 Figure F5 (continued). E. Holes 1261A and 1261B (middle Eocene–Campanian).
E
Magnetostratigraphy
Lithology
Age
Rads.
Biostratigraphy Plank. foram Calc. nanno.
Core
Recovery
Core
Recovery
Hole Hole 1261A 1261B
Polarity interpretations Polarity rating R
Int
N
Polarity chron assignments
Characteristic magnetization Inclination Intensity (A/m) -60° 0° 60° 1E-6 1E-3 1.E-03
350
18R 19R 20R
P14
21R
P13
NP 17
P12
28R
middle Eocene
II Calcareous chalk
27R
29R
P11
C21n? C21r?
NP 13
lower
1R 2R
38R
Clayey calcareous chalk
3R 39R 4R
B
40R 5R 41R
P4 P3b P3
P2
No data
NP3 -2
KS31 CC26
Maastrich./ Campanian
IIIA
36R
Paleocene
NP9
34R
Not CC23 zoned
Sant.
KS24 CC14
Con.
KS23 CC13
KS29 CC25
C24r Rare or poolry preserved throughout
early Eocene
Hiatus upper P5
33R
35R
Hiatus?
C23n?
P7
32R
C24n probably not recovered
C25r C26n C26r C27n/C27r? C29r C30n-C31n C31r C32n?
6R
IV
42R 7R 8R 9R 45R 10R 46R 11R 47R 12R 48R 13R 49R 14R
CC12
KS21 -20
CC11
CC10 KS19
50R 15R 51R 669.5 mbsf
16R
V Quartz sandstone
?
Barren
650
KS22
Barren
600
44R
Calcareous claystone with organic matter; and nannofossil chalk with organic matter
Turonian
43R
late Cenomanian
Depth (mbsf)
C20r
NP RP 15 11-14 NP 14/15
P11/ P9
31R
550
C20n
RP 12-15
30R
37R
C19r
NP 16
24R
26R
500
1.E+00
C18r-C19n probably not recovered
Nondiagnostic
23R
25R
450
1.E-01
C18n? RP 14-15
22R
400
1.E-02
IC Nannofossil late M13b NN10 Mioc. clay with exotic blocks
674.1 mbsf
Hole 1261A Hole 1261B
Hole 1261A Hole 1261B
Hole 1261A Hole 1261B
29
NW
NE
SE
NW
Site 1260
31n 31r
71.3
32n
Late Cretaceous
33n
Campanian
75
P1a
R. fructicosaC. contusa
?
P6
NP2 NP1
150
Santonian
Turonian
93.5 Cenomanian
99.1 100
CC25
possible brief normal-polarity zones in C24r?
UC19 CC24
UC18
Gansserina gansseri
KS26 Globotruncana ventricosa
KS24 Dicarinella asymetrica
KS23 Dicarinella concavata
CC22
CC21 CC20 UC15 CC19
KS20
W. archaeocretacea
C25n P4
CC17 UC13 CC16 UC12 CC15 UC11
P1
CC14 UC10 300
CC11 UC7 CC10b
KS19 Rotalipora cushmani R. reicheli
UC6 UC5 UC4
KS16
NC10a
Ticinella primula
P4
NP2
KS31 CC26 to 25c KS 30a CC25
KS 30b CC24
C29r
450
C30n-C30r -C31n
C31r
CC26 -25
KS30a
CC25 KS30b -23 KS29
? ? C29r C30n-C31n
C32n
CC23
Hiatus
KS23 CC13 to CC12 KS22 to KS20 CC11
early Olig.
C19r C20n
C20r
650
P3
no data
NP3 -2
KS31 CC26
Sant.
KS24 CC14
Con.
KS23 CC13
?
Age
NP14
KS29 CC25 not CC23 zoned
NP13
C25n probably not recovered
C22n
NP12
P6
C22r C23n
100
Hiatus?
NP10
C24r
C32n? 400
CC10
Campan.
450
P2 KS31
NP8 NP7
P6
NP16
C25r? C26n? C26r?
CC26
Int
N
Polarity Chron Assignments Hiatus
C15n? C17n?
C18n
RP15 rare
NP12 RP 8-7
C20n?
Hiatus
C24n?
NP9/10
Hiatus
NP9 nondiagnostic
NP8
P4 NP7
early diagMaastrich. KS30 CC23 nostic -24 A. tylodus
? C24r? C25n C25r Hiatus
late KS29 CC22 Campanian -23 e. Camp.
17-18
Santonian
CC16 -17
A. pseudoconulus
C31r C32n C32r top of C33n
CC14
200
Coniacian CC13 Turonian
CC12 10-11
Cenoman.
NP3
KS 30a CC25
within C34n
C29r C30n-C31n C31r
KS 30b KS 29/28
P11
NP9
P3b early Paleoc.
NP17 RP16
P13 P12
Polarity Rating R
non-
C25n not resolved P4
RP17?
C26n
possible brief normal-polarity zone in C24r? P5
Micro Zone F N R P16 P14
P5
150
CC11
KS19
P8
350
CC12
KS21 -20
50
P9
300
C24r C25r C26n C26r C27n/C27r? C29r C30n-C31n C31r
C21n C21r
P10
middle Eocene
NP15
barren
P4 P3b
Composite of Hole A and B
C20n
250
Hiatus P5
Site 1257
NP16
upper
lower
C18r C19n C19r
P12
P11
C20r
KS22
600
?
200
C21n? C21r? Hiatus? C23n?
NP 13
P7
P2
550
C18n? C18r-C19n probably not recovered
Hiatus
C17r?
early Eocene
Depth (mbsf)
C25n
C25n C25r C26n
NP8 NP7
C24r
NP17
CC23
C32n?
KS24
Santon. 500 Coniacian KS23 CC13 -12 CC10 KS19 KS17
C34n Hiatus
500
C34n KS13
NC9a NC8c
C32n CC23 to CC22
C32r including C32r.1n? C33n? C33r?
400 20-18
NC8 NC8 a-b
Hedbergella planispira
Cenom.
112.2 450
C34n? CC 10a to NC 10b
30
KS12
NC9 NC9b
Turonian
Albian
KS13
C25r C26n C26r
C22n
P14
C15n?
350
KS14 Biticinella breggiensis
RP8 to RP5
Polarity Chron Assignments
CC10a UC3 NC10b UC2 UC1
Rotalipora globotruncanoides
400
NP8
NP5
CC18 UC14
KS17
R. appenninica
Early Cretaceous
Reversed polarity of Core 22R of Hole B suggests depth-shift error
250
KS15
110
350
P5
KS22 M. sigal CC12 UC8 KS21 Helvetoglobotrun. helvetica
lower
KS31
NP9
CC13 UC9
P5
NP3
200
UC16
NP 14/15
500
NP9
P3P1
R. ticinensis
105
C24r
UC20
89.0
95
NP10
CC26
NP4
83.5
300
KS30
KS29 G. aegyptiaca KS28 Globotruncanella havanensis KS27R. calcarata
KS25
85.8
34n
C24n
RP NP 15 11-14
NP9 upper
NP9
NP3 P1b
KS31 Abathomphalus mayaroensis
Globotruncanita elevata
Coniacian
90
condensed C23r?
P1c
?
10-11 P6
(implied by biostrat)
NP11
CC23 UC17
32r
C23n
NP12 P7
N
barren
Pa
Maastrichtian
65.0
NP12 P7
NP4
Paleocene
early
28r
early Eocene
NP5
250
Relative truncation by a fault?
?
100
P3b
Danian
28n 29n 29r
Pervasive overprint of normal polarity? P8
RP 12-15
P11
P11/ P9
Top of C22n
Hiatus
Int
late Paleocene
NP6
NP8
C22r
nondiagnostic
450
C21r
C23n C23r C24n
Polarity Rating R
NP21
P13
RP 14-15
NP 16
barren
NP9a
P8
barren
middle late
P5 P4c P4b P4a
P2
30n
85
NP9b
P3a
27r
33r
NP11 NP10
P6a
NP7
27n
80
P6b
P10
C21n
NP 17
P12
200
C21r C22n (implied by biostrat)
Maastrichtian
60
NP12
RP11 to RP10
early Eocene
Ypresian
early
26r
P9
NP13
Selandian
Paleocene
26n
400
NP14
NP13
P7
C20r C21n
?
P8
Thanet.
55.0
25n 25r
70
P10 NP15
NP14
50
P9
24r
Int
C20r
0
NP14
22r
R
N
C19n RP12 P11 NP15
early Eocene
NP15
P10
23n 23r 24n
65
F
150
Paleocene
P11
22n
55
Age
Polarity Chron Assignments
Mio-Olig
21r
50
0
Campanian
21n
Lutelian
20r
Paleogene Eocene
45
NP16
P12
Polarity Rating N R Int N
Paleocene
19n
19r
Polarity Rating
Micro Zone
P13
Maastrich./ Campanian
P13
N
150
M13b NN10
P14
Turonian
P14
middle Eocene
18r
NP17
Depth (mcd)
18n
Maast./ Campanian
Bartonian
17n 17r
40
Int
Polarity Chron Assignments
Maastrichtian
Hole A and B
NP18
Age late Mioc.
Micro Zone F N R R
Polarity Rating
P18
NP20 late Eocene P16 NP19
barren
NP19
350
Zones are Hole A
middle Eocene
Site 1258
NP20
Cenom. - Coniacian
late
P16
RP14
C20n
middle Eocene
100 NP22
P15
C19r
P12
NP23
P19
Pairbonian
16r
Composite of Hole A and B
C19n NP16
P20
Site 1261
C18r
middle Eocene
RP15
NP21
13r
20n
P13
50
NP24
33.7
15r 16n
Hiatus
late Cenomanian
NP25
Micro Zone F N
100
rare or poolry preserved throughout
early Oligocene NN1
P22
P18
35
Composite of Hole A and B
NP17 RP16
M1a
P21a
12r 13n
Site 1259
Polarity Chron Assignments
N
NP19
barren
late
Oligocene
11n 11r 12n
Int
Age
l. Eoc. P16
Nannos
P21b
early
9r 10n 10r
Rupelian
9n
30
Chattian
23.8
7r
8n 8r
R
P21a to NP23 P16
rare to barren
Mio.
6Cn 6Cr 7n
Polarity Rating
Micro Zone F N R 0
E. Albian
6Br
25
Epoch Forams e
Age (Ma) Chron
Age
early Eocene
Magnetic Polarity Timescale
late Paleocene
Depth (mbsf)
Composite of Hole A and B
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
Figure F6. Correlation of magnetostratigraphy of Leg 207 sites on Demerara Rise. Selected magnetostratigraphic correlation horizons (colored lines) are near the stage boundaries of the Paleogene–Maastrichtian. Sites are aligned using polarity Zone C22n at the base of middle Eocene as the horizontal level. Magnetic polarity and biostratigraphic timescale is that used on Leg 207 (Shipboard Scientific Party, 2004). (This figure is available in an oversized format.)
Core, section, interval (cm)
Depth (mcd)
207-1257A18X-1, 118
157.280
18X-3, 110
18X-5, 133
18X-7, 24
Demagnetization Declination (mT/°C) (°)
Inclination ChRM intensity (°) (mA/m)
Error
NRM 0 AF 50 TT 150 TT 200 TT 240 TT 270 TT 300 TT 330 TT 360 TT 400
165.3 164.0 188.8 175.7 143.9 149.4 163.9 180.4 160.7 187.4
68.5 76.8 72.9 74.3 74.5 73.4 75.5 76.9 74.6 70.5
7.69E–02 3.37E–02 2.56E–02 1.87E–02 1.60E–02 1.48E–02 1.14E–02 1.19E–02 1.17E–02 1.33E–02
0.09 0.07 0.04 0.07 0.05 0.09 0.18 0.09 0.08 0.07
NRM 0 AF 50 TT 150 TT 150 TT 200 TT 200 TT 240 TT 240 TT 300 TT 300
149.8 186.0 184.3 173.4 218.2 222.6 217.4 208.6 216.9 204.9
83.9 82.4 67.3 63.3 65.1 61.5 60.3 59.6 59.6 66.1
3.42E–02 1.06E–02 6.74E–03 6.88E–03 4.38E–03 4.11E–03 4.25E–03 4.38E–03 3.65E–03 3.48E–03
0.13 0.22 0.17 0.26 0.27 0.29 0.19 0.18 0.16 0.17
NRM 0 AF 50 TT 150 TT 150 TT 200 TT 200 TT 240 TT 240 TT 270 TT 270 TT 300 TT 300 TT 330 TT 330 TT 360 TT 400 TT 400
177.2 210.7 132.7 130.8 110.0 109.0 125.0 118.9 126.2 123.7 136.8 146.6 139.5 135.5 139.5 108.8 108.6
78.1 80.5 77.8 73.0 61.1 62.7 50.4 48.8 42.5 43.3 59.1 62.2 55.9 52.2 42.6 52.5 54.0
5.75E–02 1.42E–02 1.35E–02 1.01E–02 9.72E–03 1.00E–02 6.25E–03 7.04E–03 6.28E–03 6.04E–03 4.59E–03 4.67E–03 4.11E–03 3.74E–03 3.19E–03 4.86E–03 4.51E–03
0.01 0.05 0.29 0.06 0.17 0.07 0.21 0.16 0.35 0.40 0.43 0.30 0.38 0.40 0.53 0.25 0.36
NRM 0 AF 50 TT 150
117.3 107.9 121.2
52.6 29.6 19.1
4.82E–02 2.50E–02 2.21E–02
0.06 0.13 0.07
TT 200 TT 240 TT 300
129.4 128.8 130.5
22.2 22.5 26.7
1.57E–02 1.43E–02 1.23E–02
0.07 0.05 0.04
Polarity assignments
Comments
INT or N-type Linear, no indication of R N?
160.200 Steep down, INT
Weak after 150°C Stable DII, no decay N?
163.39
Steep down, INT NPP
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
Table AT1. Early Maastrichtian to mid-Campanian paleomagnetic analysis, Hole 1257A. (See table notes. Continued on next page.)
Seems linear => N?? Weak, high errors
165.3 Relatively strong, and low-angle Looks N-type N (Suganuma had NP, but Jim decided to lean towards his comments)
31
Core, section, interval (cm)
Depth (mcd)
19X-1, 136
166.86
20X-1, 26
Demagnetization Declination (mT/°C) (°)
Inclination ChRM intensity (°) (mA/m)
Error
NRM 0 AF 50 TT 150 TT 200 TT 240 TT 270 TT 300 TT 330 TT 360 TT 400
151.2 137.6 166.0 174.2 153.2 167.3 181.2 200.9 184.8 199.3
–29.1 –56.6 –63 –65.9 –63.5 –64.1 –63.2 –61.9 –70.6 –65.7
2.92E–02 2.94E–02 2.45E–02 1.96E–02 1.59E–02 1.74E–02 1.59E–02 1.28E–02 9.81E–03 9.28E–03
0.08 0.04 0.04 0.08 0.04 0.12 0.09 0.09 0.13 0.11
NRM 0 AF 50 TT 150 TT 200 TT 240 TT 300
345.1 346.9 343.0 341.6 340.8 334.7
53.5 37.7 38.1 37.1 38.6 35.2
1.62E–01 8.17E–02 6.08E–02 5.55E–02 5.39E–02 4.46E–02
0.10 0.11 0.07 0.10 0.05 0.06
Polarity assignments
Comments
Begins NEGATIVE General behavior looks “N” Weird INT
175.46 Nice N, essentially stable Decl NRM to 240°C N
Notes: NRM = natural remanent magnetization, AF = alternating-field demagnetization, TT = thermal demagnetization. Characteristic direction polarity ratings: N or R = well-defined directions computed from at least three vectors, NP or RP = less precise directions computed from only two vectors or a suite of vectors displaying high dispersion, NPP or RPP = samples that did not achieve adequate cleaning during demagnetization but their polarity was obvious, N?? or R?? = uncertain, INT = indeterminate.
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
Table AT1 (continued).
32
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
33
Table AT2. Late Eocene–Albian paleomagnetic analysis, Hole 1257B. (This table is available in an oversized format.)
Core, section, interval (cm)
Depth (mcd)
207–1257C– 7R–5, 130
148.76
9R–1, 80
9R–3, 84
9R–5, 41
Demagnetization Declination (mT/°C) (°)
Inclination ChRM intensity (°) (mA/m)
Error
NRM 0 AF 50 AF 50 TT 150 TT 150 TT 200 TT 200 TT 250 TT 250 TT 300 TT 300 TT 350 TT 350
330.9 331.0 328.0 226.3 223.2 118.3 128.7 142.6 137.5 137.9 138.1 198.8 212.4
50.7 19.9 16.6 51.6 50.5 52.1 48.1 19.8 24.8 29.9 36.3 4.6 –0.4
1.52E–02 6.23E–03 6.24E–03 1.28E–02 1.18E–02 3.34E–03 3.20E–03 5.04E–03 5.45E–03 3.69E–03 3.90E–03 3.61E–03 3.85E–03
0.08 0.09 0.07 0.07 0.04 0.17 0.11 0.09 0.21 0.19 0.22 0.09 0.07
NRM 0 AF 50 TT 150 TT 200 TT 240 TT 270 TT 300 TT 330 TT 360 TT 400
63.3 57.3 55.2 51.4 51.4 51.1 49.0 53.4 46.4 44.8
27.0 24.6 20.9 21.0 18.0 20.1 22.7 12.9 8.2 17.0
2.02E–01 1.55E–01 1.32E–01 1.08E–01 1.01E–01 1.01E–01 7.44E–02 6.29E–02 4.56E–02 4.86E–02
0.04 0.06 0.04 0.06 0.05 0.04 0.05 0.05 0.05 0.04
NRM 0 NRM 0 AF 50 AF 50 TT 150 TT 150 TT 200 TT 200 TT 240 TT 240 TT 300 TT 300
61.9 61.9 45.6 45.6 39.3 39.3 36.3 36.3 36.6 36.6 33.4 33.4
41.9 41.9 34.1 34.1 28.2 28.2 35.8 35.8 39.5 39.5 33.4 33.4
5.35E–02 5.35E–02 3.35E–02 3.35E–02 2.56E–02 2.56E–02 1.54E–02 1.54E–02 1.59E–02 1.59E–02 1.41E–02 1.41E–02
0.05 0.05 0.04 0.04 0.11 0.11 0.21 0.21 0.06 0.06 0.06 0.06
NRM 0 AF 50 TT 150 TT 200 TT 240 TT 300
245.0 244.2 235.6 237.9 242.7 234.2
31.7 7.5 6.4 2.5 –3.8 –3.4
4.25E–02 4.78E–02 6.13E–02 5.94E–02 5.70E–02 4.68E–02
0.14 0.04 0.12 0.07 0.09 0.04
Polarity assignments
Comments
Hook–type swing in declination RP C31r
161.91 N–type relatively strong NP C32n
164.95 N–type NP
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
Table AT3. Maastrichtian–Campanian paleomagnetic analysis, Hole 1257C. (See table notes. Continued on next page.)
167.46 Hook–type RP C32r
34
Core, section, interval (cm) 9R–6,59
Depth (mcd)
Demagnetization Declination (mT/°C) (°)
Inclination ChRM intensity (°) (mA/m)
Error
Polarity assignments
Comments
168.64 NRM 0 AF 50 TT 150 TT 200 TT 240 TT 270 TT 300 TT 300 TT 330 TT 360 TT 400
270.5 309.4 323.7 335.8 339.0 338.1 333.2 331.7 328.1 334.3 335.8
78.8 69.9 61.5 37.8 36.1 36.0 14.9 14.1 0.5 0.0 8.3
1.65E–01 8.75E–02 6.93E–02 4.63E–02 4.06E–02 3.76E–02 2.98E–02 3.00E–02 2.25E–02 2.33E–02 2.25E–02
0.02 0.01 0.08 0.05 0.05 0.04 0.08 0.07 0.09 0.08 0.06
Begins steep down Sort–of–hook RP
Notes: NRM = natural remanent magnetization, AF = alternating–field demagnetization, TT = thermal demagnetization. Characteristic direction polarity ratings: NP or RP = less precise directions computed from only two vectors or a suite of vectors displaying high dispersion.
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
Table AT3 (continued).
35
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261 Table AT4. Paleomagnetic analysis, Hole 1258A. (This table is available in an oversized format.)
36
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261 Table AT5. Paleomagnetic analysis, Hole 1258B. (This table is available in an oversized format.)
37
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261 Table AT6. Paleomagnetic analysis, Hole 1259A. (This table is available in an oversized format.)
38
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261 Table AT7. Paleomagnetic analysis, Hole 1259B. (This table is available in an oversized format.)
39
Core, section, interval (cm)
Depth (mcd)
207-1260A17R-1,86
143.25
17R-3, 43
18R-1, 42
18R-3, 61
18R-5, 15
18R-7, 63
Demagnetization Declination (mT/°C) (°)
Inclination ChRM intensity (°) (mA/m)
Error
Polarity assignments
Comments
Hook-type NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
62.1 68.9 68.7 71.1 70.0 69.7 66.7 73.1
30.7 11.1 10.8 2.9 7.2 2.4 0.6 1.2
2.20E–02 2.46E–02 2.48E–02 2.63E–02 2.51E–02 2.20E–02 1.73E–02 1.75E–02
0.06 0.09 0.02 0.04 0.03 0.06 0.26 0.07
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
11.1 23.8 24.6 25.8 27.8 27.7 24.6 26.6
39.7 19.3 14.2 5.3 4.2 5.8 12.7 5.7
1.87E–02 1.89E–02 2.05E–02 2.22E–02 2.05E–02 1.89E–02 1.60E–02 1.35E–02
0.07 0.05 0.07 0.02 0.02 0.04 0.20 0.09
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
303.1 292.2 268.5 283.9 284.3 281.5 284.5 283.3
20.3 12.5 5.5 0.8 2.8 –0.7 7.7 2.4
1.60E–02 1.82E–02 1.79E–02 2.02E–02 1.75E–02 1.65E–02 1.32E–02 1.20E–02
0.02 0.07 0.05 0.06 0.07 0.10 0.05 0.04
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
210.5 205.1 194.0 205.1 210.6 209.9 203.0 200.1
51.8 23.5 20.2 7.6 1.5 3.2 3.1 10.2
8.39E–03 1.08E–02 1.56E–02 1.40E–02 1.21E–02 1.02E–02 8.45E–03 6.51E–03
0.13 0.05 0.10 0.06 0.05 0.08 0.10 0.05
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
321.9 319.9 321.1 319.9 320.9 319.8 319.8 318.6
6.1 4.8 2.5 –3.2 –0.9 –1.9 0.8 –4.4
4.06E–02 4.24E–02 4.26E–02 4.39E–02 3.91E–02 3.58E–02 2.93E–02 2.57E–02
0.04 0.02 0.03 0.04 0.01 0.03 0.03 0.04
NRM 0 AF 50
318.3 318.5
31.2 22.2
2.65E–02 2.69E–02
0.04 0.06
R
C20r
145.82 Hook-type R
152.11 Hook-type R
155.30 Nice hook!
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
Table AT8. Paleomagnetic analysis, Hole 1260A. (See table notes. Continued on next four pages.)
R
(near 180; horiz)
157.84 Hook-type Increases intensity to TT50 R
161.32 Hook-type
40
R
Core, section, interval (cm)
19R-1, 61
19R-3, 95
20R-1, 30
20R-3, 130
20R5, 62
Depth (mcd)
Demagnetization Declination (mT/°C) (°)
Inclination ChRM intensity (°) (mA/m)
Error
TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
320.3 338.3 338.3 337.6 337.6 337.1
25.2 4.8 4.6 4.6 4.0 –0.9
2.45E–02 2.91E–02 2.53E–02 2.23E–02 1.90E–02 1.64E–02
0.06 0.02 0.03 0.04 0.05 0.02
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
243.0 224.8 221.8 215.2 219.7 217.9 217.1 216.3
23.7 10.0 6.6 2.6 3.6 1.7 4.7 1.9
1.07E–02 1.46E–02 1.64E–02 1.62E–02 1.56E–02 1.36E–02 1.05E–02 1.03E–02
0.06 0.06 0.08 0.07 0.09 0.07 0.05 0.03
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
188.8 171.0 177.9 175.6 175.4 178.9 173.7 171.9
57.0 22.4 16.3 7.8 8.6 3.1 2.2 1.5
1.19E–02 1.45E–02 1.63E–02 1.78E–02 1.57E–02 1.47E–02 1.30E–02 1.16E–02
0.06 0.05 0.03 0.04 0.03 0.05 0.04 0.02
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
111.4 120.9 124.4 124.6 122.4 126.3 121.7 125.4
4.7 0.3 –6.2 –1.5 –0.1 –6.3 –6.2 –2.9
1.93E–02 2.47E–02 2.63E–02 2.46E–02 2.21E–02 2.05E–02 1.66E–02 1.51E–02
0.04 0.03 0.03 0.03 0.04 0.05 0.04 0.02
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
64.0 70.1 72.1 73.1 74.4 75.8 76.5 75.5
5.7 1.3 3.8 –2.8 –7.5 –3.1 –10.8 –7.4
4.12E–02 3.01E–02 2.78E–02 2.25E–02 2.27E–02 2.20E–02 2.03E–02 1.79E–02
0.06 0.07 0.05 0.09 0.05 0.09 0.03 0.08
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300
61.6 66.2 68.2 69.9 69.7 69.1
7.0 –0.2 –0.7 –3.2 –4.4 –7.2
4.96E–02 4.08E–02 3.64E–02 2.96E–02 2.86E–02 2.61E–02
0.07 0.08 0.07 0.08 0.06 0.03
Polarity assignments
Comments
162.01 Hook-type R
(near 180; horiz)
165.34 Hook-type R C20r (near 180; horiz)
171.29 Hook-type R
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
Table AT8 (continued).
175.29 N-type N
C21n
177.61 N-type N
41
Core, section, interval (cm)
21R-1, 28
23R-1, 58
23R-3, 43
24R-1, 6
24R-3, 35
Depth (mcd)
Demagnetization Declination (mT/°C) (°)
Inclination ChRM intensity (°) (mA/m)
Error
TT 350 TT 400
70.9 69.8
–9.6 –8.7
2.21E–02 2.03E–02
0.04 0.02
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
195.0 195.8 197.0 193.5 194.1 196.2 192.4 189.6
2.4 1.9 –3.8 –6.6 –7.1 –6.1 –9.7 –6.9
3.51E–02 3.12E–02 3.02E–02 2.45E–02 2.31E–02 2.15E–02 2.02E–02 1.93E–02
0.04 0.04 0.05 0.07 0.02 0.04 0.04 0.03
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
358.3 305.9 294.7 292.8 292.5 290.1 290.0 289.8
37.7 23.6 18.2 15.6 12.3 13.9 14.7 14.7
8.60E–01 6.69E–01 5.53E–01 5.64E–01 5.14E–01 4.52E–01 4.10E–01 3.68E–01
0.03 0.06 0.06 0.01 0.05 0.03 0.06 0.01
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
211.3 207.6 206.5 205.7 204.8 204.0 204.2 205.3
17.1 0.8 1.2 0.8 –0.1 2.2 1.8 1.5
1.10E+00 1.15E+00 9.54E–01 8.22E–01 7.22E–01 6.32E–01 5.97E–01 5.39E–01
0.05 0.06 0.03 0.04 0.05 0.02 0.02 0.03
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
167.1 168.9 169.5 169.9 169.6 168.5 170.1 170.2
35.1 17.9 13.9 7.8 6.6 6.0 5.1 6.3
1.93E–01 2.01E–01 2.02E–01 2.05E–01 1.97E–01 1.80E–01 1.58E–01 1.45E–01
0.05 0.04 0.03 0.02 0.02 0.02 0.03 0.02
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
344.6 15.6 42.0 46.6 52.3 54.2 54.7 56.7
22.0 21.5 18.2 17.8 13.0 16.0 11.7 13.5
2.37E+00 1.19E+00 9.51E–01 9.61E–01 9.30E–01 7.68E–01 6.88E–01 6.16E–01
0.01 0.04 0.03 0.07 0.01 0.08 0.07 0.10
Polarity assignments
Comments
180.98 N-type N (near 180; horiz)
200.17 Some decl swing; more hook-like than N-type NPP
probably still C21n
203.02 NPP Somewhat hook-type but lot of “N” appearance (near 180; horiz)
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
Table AT8 (continued).
209.35 Hook-type R
C21r
212.44 Swing in decl Hook-type R
42
Core, section, interval (cm)
Depth (mcd)
24R-5, 31
215.29
25R-1, 12
Demagnetization Declination (mT/°C) (°)
Inclination ChRM intensity (°) (mA/m)
Error
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
84.5 99.3 106.9 106.5 107.1 110.2 110.0 111.4
14.7 5.1 5.2 5.7 5.8 0.9 –1.8 2.9
2.09E+00 1.58E+00 1.19E+00 1.03E+00 8.88E–01 7.44E–01 6.75E–01 6.19E–01
0.06 0.08 0.06 0.06 0.09 0.02 0.02 0.05
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
13.9 29.9 36.8 37.2 37.5 38.6 38.7 38.7
22.2 11.9 7.6 7.6 5.1 4.8 4.5 5.1
1.96E+00 1.50E+00 1.19E+00 1.10E+00 9.68E–01 7.75E–01 6.70E–01 5.95E–01
0.03 0.08 0.03 0.06 0.06 0.01 0.04 0.05
Polarity assignments
Comments
Midway between N-type and hook-type R??
219.01 N-type N top of C22n?
Biostrat gap of P9 = C22n and C22r = between 24R-CC and 25R-1, 50 cm; but uncertain about the above sample. 25R-3, 91
25R-5, 5
25R-7, 32
222.80 NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
343.0 337.2 335.6 335.8 335.3 334.5 334.5 334.8
17.3 8.4 7.1 8.1 6.2 5.3 5.8 6.8
5.63E+00 4.89E+00 4.04E+00 3.62E+00 3.09E+00 2.46E+00 2.13E+00 1.92E+00
0.03 0.05 0.03 0.03 0.04 0.01 0.02 0.01
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300 TT 350 TT 400
53.3 62.6 76.5 77.4 79.3 82.1 82.1 82.8
39.7 41.3 35.9 25.1 13.0 10.6 9.4 6.9
3.19E+00 1.18E+00 7.50E–01 6.14E–01 6.42E–01 5.89E–01 4.96E–01 4.84E–01
0.06 0.04 0.04 0.05 0.03 0.02 0.05 0.06
NRM 0 AF 50 TT 150 TT 150 TT 200 TT 250
355.3 215.2 193.0 192.9 195.5 195.5
47.0 69.8 33.9 33.9 27.9 25.3
2.10E+00 7.55E–01 6.95E–01 6.94E–01 6.93E–01 6.39E–01
0.06 0.07 0.03 0.07 0.05 0.06
N-type N
lower C23n
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
Table AT8 (continued).
224.74 N-type N
227.71 Nice hook-type R
C23r
43
Core, section, interval (cm)
Depth (mcd)
Demagnetization Declination (mT/°C) (°) TT 300 TT 350 TT 400
196.0 195.4 194.7
Inclination ChRM intensity (°) (mA/m) 22.9 25.0 24.7
5.52E–01 4.67E–01 4.26E–01
Error 0.05 0.06 0.04
Polarity assignments
Comments
(near 180; horiz)
Notes: NRM = natural remanent magnetization, AF = alternating-field demagnetization, TT = thermal demagnetization. Characteristic direction polarity ratings: N or R = well-defined directions computed from at least three vectors, NPP = samples that did not achieve adequate cleaning during demagnetization but their polarity was obvious, R?? = uncertain.
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
Table AT8 (continued).
44
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261 Table AT9. Paleomagnetic analysis, Hole 1260B. (This table is available in an oversized format.)
45
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261 Table AT10. Paleomagnetic analysis, Hole 1261A. (This table is available in an oversized format.)
46
Core, section, interval (cm)
Depth (mcd)
207-1261B2R-1, 25
534.85
2R-3, 72
2R-3, 117
3R-1, 79
3R-3, 58
Demagnetization Declination (mT/°C) (°)
Inclination ChRM intensity (°) (mA/m)
Error
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 250 TT 300 TT 300
258.5 249.6 236.2 238.9 250.5 244.9 239.1 234.5
62.4 39.6 32.8 39.3 41.4 41.6 51.4 46.8
3.63E–02 2.58E–02 1.50E–02 7.97E–03 4.66E–03 4.98E–03 3.13E–03 3.29E–03
0.11 0.06 0.08 0.13 0.32 0.26 0.38 0.36
NRM 0 AF 50 TT 150 TT 200 TT 250 TT 300
348.9 344.5 317.4 191.0 186.4 180.6
51.1 49.6 74.4 53.7 19.8 1.9
5.32E–02 3.01E–02 1.37E–02 8.60E–03 7.89E–03 7.08E–03
0.04 0.05 0.1 0.12 0.14 0.16
NRM 0 AF 50 TT 150 TT 200 TT 200 TT 250 TT 250 TT 300 TT 300 TT 350 TT 350
87.7 92.5 99.9 62.6 58.2 307.8 317.0 306.0 282.1 225.4 231.5
55.9 36.1 36.2 78.9 82.0 53.4 61.1 32.8 50.4 –34 –37.9
3.67E–02 2.37E–02 9.96E–03 3.34E–03 3.26E–03 2.45E–03 2.37E–03 1.36E–03 4.62E–03 2.22E–03 2.39E–03
0.07 0.05 0.09 0.21 0.15 0.3 0.32 0.89 0.56 0.34 0.15
NRM 0 AF 50 TT 150 TT 150 TT 200 TT 200 TT 240 TT 240 TT 270 TT 270 TT 300 TT 300 TT 330 TT 330 TT 360 TT 360
40.3 42.7 53.1 51.2 34.2 334.9 52.3 39.3 46.5 52.6 47.7 56.4 2.3 19.6 322.8 18.8
57.9 44.3 46.8 48.7 65.6 51.3 60.2 62.0 48.9 41.6 16.5 23.8 58.8 59.7 11.7 –61.3
2.65E–02 1.61E–02 8.17E–03 8.33E–03 3.38E–03 2.25E–03 3.11E–03 3.12E–03 1.72E–03 1.52E–03 1.64E–03 1.81E–03 2.46E–03 1.98E–03 1.19E–03 1.95E–03
0.01 0.03 0.07 0.04 0.18 0.47 0.37 0.42 0.5 0.57 0.75 0.54 0.35 0.35 1.46 1.47
NRM 0 AF 50
245.4 252.6
68.4 49.9
1.26E–02 1.05E–02
0.21 0.11
Polarity assignments
Comments
Hook-type NP
538.32 Nice hook-type RPP Flip in declination
538.77 Maybe hook-type Very weak! RPP Dead
541.87
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
Table AT11. Paleomagnetic analysis, Hole 1261B. (See table notes. Continued on next page.)
Uncertain N? (NRM-200 only)
Dead
544.66 NP
47
Seems mainly linear; no significant hook
Core, section, interval (cm)
3R-5, 58
4R-1, 59
4R-3, 62
Depth (mcd)
Demagnetization Declination (mT/°C) (°)
Inclination ChRM intensity (°) (mA/m)
Error
TT 150 TT 200 TT 200 TT 250 TT 250
235.0 229.1 228.7 229.1 247.2
44.4 49.6 52.8 45.2 49.7
6.89E–03 4.45E–03 4.58E–03 2.15E–03 2.35E–03
0.1 0.12 0.15 0.32 0.28
NRM 0 AF 50 TT 150 TT 150 TT 200 TT 200 TT 250 TT 250
287.0 259.9 246.9 265.1 27.8 29.1 45.4 40.0
69.8 57.4 69.3 68.5 67.7 75.7 54.2 47.5
1.44E–02 7.38E–03 4.25E–03 4.12E–03 3.15E–03 3.35E–03 2.26E–03 2.54E–03
0.12 0.07 0.18 0.16 0.33 0.22 0.38 0.38
NRM 0 AF 50 TT 150 TT 200 TT 200 TT 240 TT 240 TT 270 TT 270 TT 300 TT 300 TT 330 TT 330 TT 360 TT 360
214.3 201.9 225.9 301.9 294.2 321.8 334.1 306.4 299.5 336.9 338.7 18.1 16.8 19.5 24.5
58.5 55.8 67.7 64.4 57.6 63.1 68.2 41.0 40.8 19.7 20.3 30.5 33.8 1.1 13.1
3.71E–02 1.85E–02 1.18E–02 5.09E–03 4.98E–03 6.19E–03 5.60E–03 3.81E–03 4.12E–03 2.97E–03 3.26E–03 3.43E–03 3.62E–03 2.85E–03 2.99E–03
0.14 0.1 0.13 0.22 0.26 0.3 0.25 0.55 0.5 0.66 0.56 0.52 0.47 1.32 0.91
NRM 0 AF 50 TT 150 TT 150 TT 200 TT 200 TT 250 TT 250 TT 300 TT 300
172.5 240.7 243.4 243.3 280.1 280.1 292.6 288.5 279.8 280.5
67.5 76.6 34.7 35.4 30.0 27.2 20.6 18.0 17.7 22.8
1.39E–02 1.51E–02 7.95E–03 8.28E–03 5.74E–03 6.16E–03 4.78E–03 4.45E–03 3.81E–03 4.35E–03
0.04 0.07 0.12 0.15 0.19 0.22 0.23 0.2 0.07 0.13
Polarity assignments
Comments
547.74 Hook-type; but weak RPP
550.83 Steep, but looks like hook-type behavior RPP
Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261
Table AT11 (continued).
553.86 Looks hook-type RP
Notes: NRM = natural remanent magnetization, AF = alternating-field demagnetization, TT = thermal demagnetization. Characteristic direction polarity ratings: N = well-defined directions computed from at least three vectors, NP or RP = less precise directions computed from only two vectors or a suite of vectors displaying high dispersion, RPP = samples that did not achieve adequate cleaning during demagnetization but their polarity was obvious.
48