campanian through eocene magnetostratigraphy of

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

Y. SUGANUMA AND J.G. OGG CAMPANIAN–EOCENE MAGNETOSTRATIGRAPHY, SITES 1257–1261

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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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4

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


5

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


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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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



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


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


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


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


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


Relative truncation by a fault?

?

Paleocene

31r

32n

Polarity Rating Int N

NP14

P9

P8

P3b

Danian

early

31n

N R


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


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)


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?


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


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


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.










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°


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


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


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


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

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


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


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


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


N

NP22

5R

16X

150

2R

Int


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


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





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


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


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


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


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


Recovery

Core

I

Age



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



27

Figure F5 (continued). C. Holes 1259A and 1259B (Eocene–Cretaceous).

C

Magnetostratigraphy

100

Biostratigraphy

Lithology

Age


Recovery

Core

Recovery

Core

Foraminifer nannofossil chalk

13R 14R

Polarity rating R

Int

N


P18

Inclination -60°

0°

Intensity (A/m)

60° 1E-6

1E-3

NP21

NP20 late P16 Eocene NP19

C15n?

Hiatus

15R

150



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


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


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 ?





28

Figure F5 (continued). D. Holes 1260A and 1260B (middle Eocene–Campanian and Albian). Magnetostratigraphy Biostratigraphy Lithology

Age

Polarity rating R

Int


N

I Nanno/for clay

3R

IIA

4R


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



Rads.

Recovery

Core

Recovery

Core

Hole Hole 1260A 1260B


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


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




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


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


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


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




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


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


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


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


30

KS12

NC9 NC9b

Turonian

Albian

KS13

C25r C26n C26r

C22n

P14

C15n?

350

KS14 Biticinella breggiensis

RP8 to RP5


CC10a UC3 NC10b UC2 UC1

Rotalipora globotruncanoides

400

NP8

NP5

CC18 UC14

KS17

R. appenninica

Early Cretaceous


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


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


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


P13

N

150

M13b NN10

P14

Turonian

P14

middle Eocene

18r

NP17

Depth (mcd)

18n

Maast./ Campanian

Bartonian

17n 17r

40

Int


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


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


NP17 RP16

M1a

P21a

12r 13n

Site 1259


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)



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


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


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


Depth (mcd)

19X-1, 136

166.86

20X-1, 26



Error


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


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.


Table AT1 (continued).

32


33

Table AT2. Late Eocene–Albian paleomagnetic analysis, Hole 1257B. (This table is available in an oversized format.)


Depth (mcd)

207–1257C– 7R–5, 130

148.76

9R–1, 80

9R–3, 84

9R–5, 41



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


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


Comments

Hook–type swing in declination RP C31r

161.91 N–type relatively strong NP C32n

164.95 N–type NP


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)



Error


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.



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


38


39


Depth (mcd)

207-1260A17R-1,86

143.25

17R-3, 43

18R-1, 42

18R-3, 61

18R-5, 15

18R-7, 63



Error


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


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


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


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!


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


19R-1, 61

19R-3, 95

20R-1, 30

20R-3, 130

20R5, 62

Depth (mcd)



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


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


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


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


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


Comments

162.01 Hook-type R

(near 180; horiz)

165.34 Hook-type R C20r (near 180; horiz)

171.29 Hook-type R



175.29 N-type N

C21n

177.61 N-type N

41


21R-1, 28

23R-1, 58

23R-3, 43

24R-1, 6

24R-3, 35

Depth (mcd)



Error

TT 350 TT 400

70.9 69.8

–9.6 –8.7

2.21E–02 2.03E–02

0.04 0.02


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


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


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


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


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


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)



209.35 Hook-type R

C21r

212.44 Swing in decl Hook-type R

42


Depth (mcd)

24R-5, 31

215.29

25R-1, 12



Error


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


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


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


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



224.74 N-type N

227.71 Nice hook-type R

C23r

43


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


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.



44


45


46


Depth (mcd)

207-1261B2R-1, 25

534.85

2R-3, 72

2R-3, 117

3R-1, 79

3R-3, 58



Error


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


Comments

Hook-type NP

538.32 Nice hook-type RPP Flip in declination

538.77 Maybe hook-type Very weak! RPP Dead

541.87


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


3R-5, 58

4R-1, 59

4R-3, 62

Depth (mcd)



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


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


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


Comments

547.74 Hook-type; but weak RPP

550.83 Steep, but looks like hook-type behavior RPP



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