Linking the oxygen isotope record of late Neogene

Marine Geology 185 (2002) 95^120 www.elsevier.com/locate/margeo

Linking the oxygen isotope record of late Neogene eustasy to sequence stratigraphic patterns along the Bahamas margin: results from a paleoceanographic study of ODP Leg 166, Site 1006 sediments Silvia Spezzaferri a; , Judith A. McKenzie b , Alexandra Isern c a

c

Institute of Paleontology, University of Vienna, Althanstr. 14, 1090 Vienna, Austria b Geological Institute, ETH-Zentrum, Sonneggstr. 5, 8092 Zu«rich, Switzerland National Academy of Sciences Ocean Studies Board (HA-470), 2101 Constitution Ave. NW, Washington, DC 20418, USA Received 2 August 2001

Abstract During ODP Leg 166, the recovery of cores from a transect of drill sites across the Bahamas margin from marginal to deep basin environments was an essential requirement for the study of the response of the sedimentary systems to sea-level changes. A detailed biostratigraphy based on planktonic foraminifera was performed on ODP Hole 1006A for an accurate stratigraphic control. The investigated late middle Mioceneêarly Pliocene sequence spans the interval from about 12.5 Ma (Biozone N12) to approximately 4.5 Ma (Biozone N19). Several bioevents calibrated with the time scale of Berggren et al. (1995a,b) were identified. The ODP Site 1006 benthic oxygen isotope stratigraphy can be correlated to the corresponding deep-water benthic oxygen isotope curve from ODP Site 846 in the Eastern Equatorial Pacific (Shackleton et al., 1995. Proc. ODP Sci. Res. 138, 337^356), which was orbitally tuned for the entire Pliocene into the latest Miocene at 6.0 Ma. The approximate stratigraphic match of the isotopic signals from both records between 4.5 and 6.0 Ma implies that the paleoceanographic signal from the Bahamas is not simply a record of regional variations but, indeed, represents glacio-eustatic fluctuations. The ODP Site 1006 oxygen and carbon isotope record, based on benthic and planktonic foraminifera, was used to define paleoceanographic changes on the margin, which could be tied to lithostratigraphic events on the Bahamas carbonate platform using seismic sequence stratigraphy. The oxygen isotope values show a general cooling trend from the middle to late Miocene, which was interrupted by a significant trend towards warmer sea-surface temperatures (SST) and associated sea-level rise with decreased ice volume during the latest Miocene. This trend reached a maximum coincident with the Miocene/ Pliocene boundary. An abrupt cooling in the early Pliocene then followed the warming which continued into the earliest Pliocene. The late Miocene paleoceanographic evolution along the Bahamas margin can be observed in the ODP Site 1006 N13 C values, which support other evidence for the beginning of the closure of the Panama gateway at 8 Ma followed by a reduced intermediate water supply of water from the Pacific into the Caribbean at about 5 Ma. A general correlation of lower sedimentation rates with the major seismic sequence boundaries (SSBs) was observed. Additionally, the SSBs are associated with transitions towards more positive oxygen isotope excursions. This observed correspondence implies that the presence of a SSB, representing a density impedance contrast in the sedimentary

* Corresponding author. Fax: +43-1-47229535.

E-mail address: [email protected] (S. Spezzaferri).

0025-3227 / 02 / $ ^ see front matter ? 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 5 - 3 2 2 7 ( 0 1 ) 0 0 2 9 2 - 4

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S. Spezzaferri et al. / Marine Geology 185 (2002) 95^120

sequence, may reflect changes in the character of the deposited sediment during highstands versus those during lowstands. However, not all of the recorded oxygen isotope excursions correspond to SSBs. The absence of a SSB in association with an oxygen isotope excursion indicates that not all oxygen isotope sea-level events impact the carbonate margin to the same extent, or maybe even represent equivalent sea-level fluctuations. Thus, it can be tentatively concluded that SSBs produced on carbonate margins do record sea-level fluctuations but not every sealevel fluctuation is represented by a SSB in the sequence stratigraphic record. ? 2002 Elsevier Science B.V. All rights reserved. Keywords: Bahamas carbonate platform; stable isotope stratigraphy; seismic sequence stratigraphy; paleoceanography; eustasy

1. Introduction Sea-level £uctuations are known to have occurred throughout the Earth’s history, but their global synchroneity, amplitude and rate are still largely unquanti¢ed. Deep-sea pelagic sediments can provide a proxy for glacio-eustasy through variations in the oxygen isotopic composition of planktonic and benthic foraminifera, whereas continental margin sediments record glacio-eustatic history by means of unconformities and stratigraphic patterns in their sedimentary architecture. The sedimentary record recovered from a carbonate margin potentially encodes both the timing and amplitude of sea-level changes, together with indications of paleo-depth (Eberli et al., 1997a). Thus, correlating the global oxygen isotope record with the seismic lithostratigraphic record on a carbonate margin can potentially yield information to better understand sea-level £uctuations. This can be accomplished by developing an isotopic record in a basinward sequence deposited on a carbonate margin whose sedimentary architecture has been de¢ned seismically. The Bahamas archipelago is a carbonate province consisting of several platforms situated on the southern end of the eastern continental margin of the USA. The Great Bahama Bank (GBB) is a pure carbonate environment in a subtropical, low-latitude setting and, as such, is an ideal place to evaluate the sedimentary record and timing of global sea-level changes. A transect of sites was drilled on the western margin of the GBB during ODP Leg 166, Bahamas Transect. Drilling recovered a thick sequence of Neogene drift deposits with relatively few hiatuses which extends the sedimentary record from the platform top (Unda and Clino Holes) across the Bahamian margin

into deeper water (Figs. 1 and 2) (Eberli et al., 1997a,b). A primary objective of this drilling campaign was to link eustasy to sequence stratigraphic patterns in a carbonate platform setting using the regional oxygen isotopic stratigraphy developed from foraminifera deposited at a more basinal site on the margin, ODP Site 1006. This intermediate water isotope record was to be (1) correlated with the global glacio-eustatic isotope curve using biostratigraphic events and astrochronology and (2) traced directly to the depositional facies on the margin using the seismically imaged sequence stratigraphic pattern along the drilled transect. An ultimate goal of the drilling program was to retrieve a low-latitude oxygen isotopic signal of the ‘Icehouse World’ in the Neogene and compare it with the corresponding lithostratigraphic record to evaluate whether there is a causal link between eustasy and sequence stratigraphic pattern. The ODP Leg 166 drilling campaign was part of a larger program to study the impact of sea-level £uctuations on continental margins and was the carbonate complement to the drilling conducted on the New Jersey margin into siliciclastic sequences (Miller et al., 1996, 1998). The goal of our speci¢c study was to evaluate, using oxygen isotope stratigraphy at the more basinal ODP Site 1006 on the Bahamas Transect, if there is a causal link between eustatic sea-level £uctuations and sequence stratigraphic pattern on the Bahamas margin. This work proposes to investigate if sea-level changes interpreted from oxygen isotope variations recorded in marginal sequences can be correlated with the stratigraphic response of carbonate sediments to sea-level changes, as deduced from the facies variations in the recovered depositional sequences along the Bahamas Transect.

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Fig. 1. Map of the Bahamas showing the locations of the ODP Leg 166 drill sites including ODP Hole 1006A, which comprise the margin transect, and the boreholes, Unda and Clino, on the platform.

2. Bahamas Transect ^ ODP Site 1006 ODP Site 1006 is located in 658 m of water in the northern portion of the Santaren Channel, approximately 30 km from the western platform edge of the Great Bahama Bank (Fig. 1). Being at the basinward end of the Bahamas Transect, it was the designated paleoceanographic site, selected to yield the prerequisite material for the low-latitude, intermediate water, oxygen isotopic study. ODP Hole 1006A was drilled to 717.3 m below sea £oor (mbsf) into a Neogene drift depos-

it with high sedimentation rates and relatively few hiatuses, an ideal sequence for paleoceanographic investigations (Eberli et al., 1997a). The sediment drifts inter¢nger with the carbonate bank deposits prograding into the Straits of Florida. An extended (500-m-thick), nearly continuous late middle Miocene to early Pliocene sequence of mixed periplatform and pelagic sediments was recovered. The sediments comprise light gray to light greenish gray nannofossil chalk containing abundant, well-preserved microfossils ideal for isotopic analysis. This study focuses on the lower 400 m of the

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Fig. 2. Sedimentation rates at ODP Site 1006 adapted from Kroon et al. (2000). Uppercase letters indicate sequence boundaries, whereas lowercase letters indicate seismic sequences (Anselmetti et al., 2000). Open circles denote the position of planktonic foraminiferal events that have not been well calibrated and are, therefore, not used in the age^depth plot. Open squares denote uncertainty in the depth of the planktonic foraminiferal events. Black squares denote selected planktonic foraminiferal events.

sequence, which comprises middle Miocene to earliest Pliocene sediments contained in lithostratigraphic Units II^V (Eberli et al., 1997a; Betzler et al., 1999, 2000b). The lower part of lithostratigraphic Unit II contains lower Pliocene nannofossil oozes and chalk. Lithostratigraphic Unit III comprises upper Miocene to lowermost Pliocene light gray and light greenish gray chalk. Within this latter unit, a series of ¢ning upward intervals was observed. Firmgrounds characterized by sharp burrowed contact prevail in the upper part of the unit. Lithostratigraphic Unit IV consists of upper middle to upper Miocene light gray and greenish gray nannofossil chalk. The upper part of Unit IV contains a series of thick intervals with sharp basal contacts. The lower part is punctuated by a series of ¢rmgrounds (Eberli et al., 1997a). Lithostratigraphic Unit V is composed of middle Miocene chalk and light gray nannofossil chalks with foraminifera alternating with intervals of nannofossil chalk. The degree of lithi¢cation increases downhole with chalks intercalating limestones in the lowermost portion of the hole. In summary, the pattern of the repeated facies successions at ODP Site 1006A indicates the interplay of current activity and sea-level £uctuations in the sedimentation process (Eberli et al., 1997a; Betzler et al., 1999; Anselmetti et al., 2000; Kroon et al., 2000; Eberli et al., 2002). For example, the presence of clay at the bottom of the high-frequency cycles re£ects erosion and siliciclastic episodes indicative of lowstands (Betzler et al., 1999; Williams and Pirmez, 1999; Karpo¡ et al., 2002; Reuning et al., 2002). These are followed by renewed neritic production and the deposition of nannofossil ooze with platform-derived bioclasts with transgressions. Finally, under highstand conditions, pelagic production with deposition of nannofossil and foraminiferal oozes dominates at this more basinward site on the margin.

3. Materials and methods For this study, high-resolution sampling of the sediments from Hole 1006A was done at closely spaced intervals of approximately 50 cm through-

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out the middle Miocene to early Pliocene pelagic sequence. The sedimentation rate was signi¢cantly high enough throughout the studied sequence to achieve a good time resolution without more detailed sampling. Samples of about 10 cm3 volume were soaked in distilled water, washed under running water through a 40 Wm mesh sieve and studied with a binocular microscope. Distributions of planktonic foraminifera, sponge spicules, radiolarians, Bachmayerella tenuis and Calcdinocysts spp., together with reworked specimens, were plotted in a range chart. The complete range chart, compiled from over 300 samples, is reported in Kroon et al. (2000). Samples were then dry-sieved through the 250^355 Wm mesh and specimens for isotopic analyses were picked. Three to 10 specimens of benthic foraminifera and 10^15 specimens of Globigerinoides sacculifer were picked from each sample for stable isotope analysis. As the benthic foraminifera were scarce in the studied samples, samples of three species (Planulina wuellestor¢, Cibicidoides ungerianus and Parrelloides robertsonianus) were combined and evaluated for their isotopic composition. As these three species were present in all of the benthic samples, the mixed analysis is considered to be a continuous isotope record throughout the sequence. All samples for oxygen and carbon isotopic analysis were reacted in orthophosphoric acid at 90‡C on a VG Isogas autocarbonate preparation system. Isotopic ratios of the CO2 gas were then measured on-line by a triple collector VG Isogas precision isotope ratio mass spectrometer (PRISM). The isotope data are corrected following the procedure of Craig (1957) modi¢ed for a triple collector. Isotope compositions are expressed in the N notation as permil deviations from the international PDB (Pee Dee Belemnite) carbonate standard. Analytical precision based on routine analysis of the internal reference standard (Carrara marble) is O 0.10x for N18 O and O 0.05x for N13 C. The isotope data, together with the sample depth below sea £oor (mbsf), are presented in Table 1. Table 2 contains the ages of the sequence stratigraphic boundaries (SSB) recognized in seismic pro¢les which image the Bahamas margin along

99

the transect line. The depths of the sequence boundaries were calculated using velocities from the integrated sonic log and the vertical seismic pro¢le (Eberli et al., 1997a; Anselmetti et al., 2000). The ages that we assign to the sequence stratigraphic boundaries were calculated using an age^depth plot as de¢ned by our extended biostratigraphic analysis of the sequence. Our ages di¡er from those used in Eberli et al. (2002) (Table 2) because we used our re¢ned planktonic foraminifera analysis to de¢ne the age^depth plot (see below). Additionally, we did not include the nannofossil ages in our age^depth plot because they may represent arti¢cially old datum since the ¢ner fraction of the sediment is readily reworked in the margin setting where ODP Site 1006 is located (Kroon et al., 2000).

4. Results and analyses 4.1. Biostratigraphy The ODP Hole 1006A biostratigraphy is extensively discussed in Kroon et al. (2000). For this study, however, a more detailed analysis of the foraminiferal biostratigraphy was undertaken. As this re¢ned analysis resulted in the discovery of additional datum levels and has implications for calculated sedimentation rates and, hence, for the age of speci¢c SSBs, we have opted to fully discuss the biostratigraphy used for this study. The planktonic and benthic foraminifera of the middle Mioceneêarly Pliocene assemblages evaluated from ODP Hole 1006A are very well preserved and abundant throughout this interval. Reworking and contamination of older and younger specimens and/or shallow water benthic species are very rare or absent. Reworking generally consists of rare specimens of shallow water benthic foraminifera and older planktonic foraminifera species, such as Eocene turborotaliids or the Oligocene species Paragloborotalia pseudokugleri. The integrity of the foraminiferal data is in stark contrast to anomalies in the nannofossil data because of the strong reworking of ¢ne-grained material on the Bahamian margin (Kroon et al., 2000).

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Table 1 Stable carbon and oxygen isotope ratios (x, PDB) of planktonic and benthic foraminifera from ODP Hole 1006A Samples

36X-1, 36X-2, 36X-3, 36X-4, 36X-5, 36X-6, 37X-1, 37X-2, 37X-3, 37X-4, 37X-5, 37X-6, 38X-1, 38X-1, 38X-2, 38X-2, 38X-3, 38X-3, 38X-4, 38X-4, 38X-4, 38X-5, 39X-1, 39X-1, 39X-1, 39X-2, 39X-2, 39X-2, 39X-3, 39X-3, 39X-3, 39X-4, 39X-4, 39X-4, 39X-5, 39X-5, 39X-5, 40X-1, 40X-1, 40X-1, 40X-2, 40X-2, 40X-2, 40X-3, 40X-3, 40X-4, 40X-4, 40X-5, 40X-5, 40X-5, 40X-6, 40X-6,

81^86 81^86 81^86 81^86 81^86 81^86 85^90 85^90 85^90 85^90 85^90 85^90 85^90 135^137 35^37 85^90 85^90 135^137 35^37 85^90 135^137 85^90 35^37 85^90 138^140 35^37 85^90 138^140 35^37 85^90 138^140 35^37 85^90 138^140 35^37 85^90 138^140 35^37 85^90 135^137 35^37 85^90 135^137 85^90 135^137 35^37 85^90 35^37 85^90 135^137 35^37 85^90

Depth

Cibicidoides spp. 13

G. sacculifer

(mbsf)

N C

N O

N13 C

N18 O

322.310 323.810 325.310 326.810 328.310 329.810 331.450 332.950 334.450 335.950 337.450 338.450 340.650 341.150 341.650 342.150 343.650 344.150 344.650 345.150 345.650 346.650 349.250 349.750 350.280 350.750 351.250 351.780 352.250 352.750 353.250 353.750 354.250 354.780 355.255 355.750 356.280 358.450 358.950 359.450 359.950 360.450 360.950 361.950 362.450 362.950 363.450 364.450 364.950 365.450 365.950 366.450

0.973 0.905 0.969 0.652 0.752 0.889 0.834 0.463 0.619 0.685 0.997 0.709 1.043 0.880 0.575 0.639 0.772 0.323 0.501 1.098 0.869 0.870 0.670 1.048 30.254 30.110 0.897 0.740 0.914 1.075 0.047 0.296 0.835 0.186 0.187 0.673 0.272 0.562 0.795 0.876 30.215 0.558 0.728 0.647 0.613 0.717 0.835 0.119 0.843 0.635 0.916 0.814

1.683 2.180 1.868 2.313 1.915 1.799 1.684 1.606 1.721 1.843 1.667 1.834 1.825 1.748 1.837 1.872 1.730 2.103 1.864 1.771 1.724 1.672 1.765 1.843 1.849 0.876 1.951 1.919 1.694 1.770 1.252 1.935 1.695 1.721 1.887 1.902 2.070 1.915 1.698 1.808 0.092 1.883 1.780 1.750 1.944 1.881 1.882 2.090 1.828 1.740 1.820 1.911

1.780 1.875 2.079 1.410 1.416 1.897 1.746 1.874 1.877 1.841 1.961 1.676 2.292 2.135 1.651 1.669 1.921 1.380 1.700 2.255 2.171 2.159 1.618 1.910 2.211 1.680 2.333 1.998 2.187 2.330 1.949 1.488 1.841 1.776 1.818 1.961 1.846 1.728 2.467 1.803 1.515 1.637 1.733 1.949 1.770 2.248 2.095 1.490 2.102 0.961 1.673 2.008

30.949 30.245 31.018 30.330 30.642 30.800 30.586 31.188 31.149 30.984 31.017 30.600 31.032 31.109 30.993 31.116 31.019 31.202 31.269 31.147 31.670 31.530 31.294 31.203 31.024 31.549 31.155 31.401 31.201 31.005 31.469 31.269 31.205 31.285 31.135 31.066 30.987 31.463 31.201 30.993 31.119 30.744 31.286 31.245 31.101 31.164 31.202 31.355 31.015 31.140 31.032 31.185

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101

Table 1 (Continued). Samples

41X-1, 85^90 41X-1, 135^137 41X-2, 85^90 41X-2, 135^137 41X-3, 85^90 41X-3, 85^90 41X-3, 135^137 41X-4, 35^37 41X-4, 85^90 41X-4, 135^137 41X-5, 35^37 41X-5, 85^90 41X-5, 135^137 41X-6, 35^37 41X-6, 85^90 42X-1, 35^37 42X-1, 85^90 42X-1, 135^137 42X-2, 35^37 42X-2, 85^90 42X-2, 135^137 42X-3, 35^37 42X-CC, 43X-1, 35^37 44X-1, 35^37 44X-1, 85^90 44X-1, 135^137 44X-2, 35^37 44X-2, 85^90 44X-2, 130^132 44X-3, 35^37 44X-3, 85^90, 44X-3, 135^137 44X-4, 35^37 44X-4, 85^90 44X-4, 135^137 44X-5, 35^37 44X-5, 135^137 44X-6, 35^37 44X-6, 85^90 44X-6, 137^137 44X-7, 35^37 45X-1, 35^37 45X-1, 85^90 45X-1, 135^137 45X-4, 35^37 45X-4, 85^90 45X-4, 135^137 45X-5, 35^37 45X-5, 85^90 45X-5, 135^137 45X-6, 35^37 45X-6, 85^90

Depth


G. sacculifer

(mbsf)

N C

N O

N13 C

N18 O

368.150 368.650 369.650 370.150 371.150 371.150 371.650 372.150 372.650 373.150 373.650 374.150 374.650 375.150 375.650 376.750 377.250 377.750 378.250 378.750 379.250 379.750 380.130 385.970 395.050 395.550 396.050 396.550 397.050 397.500 398.050 398.550 399.050 399.050 400.050 400.050 401.050 402.050 402.550 403.050 403.550 404.050 404.350 404.850 405.350 405.850 406.350 406.850 407.350 407.850 408.350 408.850 409.350

0.819 0.614 0.576 0.132 0.808 ^ 0.498 0.313 0.804 0.535 0.334 0.508 0.279 0.743 0.560 0.523 0.599 0.062 0.654 0.682 0.350 0.700 0.045 0.870 1.092 1.075 1.164 0.982 0.910 0.918 1.009 1.194 0.797 0.814 1.014 1.108 1.057 ^ 1.066 1.082 1.099 1.008 1.135 1.094 1.084 1.254 1.073 0.747 1.212 ^ 0.971 1.138 1.139

1.790 1.882 2.064 1.269 1.841 ^ 1.893 1.970 1.867 1.808 1.668 1.879 1.837 1.745 1.832 1.718 1.760 2.034 1.821 1.791 1.748 1.703 1.613 1.698 1.954 1.802 1.802 1.601 1.620 1.970 1.651 1.466 1.473 1.830 1.672 1.816 1.767 ^ 1.875 1.558 1.898 1.826 1.831 1.669 1.542 1.222 1.746 1.665 1.667 ^ 1.372 1.670 1.731

2.073 1.885 1.665 2.242 2.059 1.005 1.628 1.553 1.729 1.729 1.685 1.664 1.640 2.159 1.923 1.798 2.176 1.744 1.577 1.766 1.777 2.026 1.656 2.155 2.463 2.278 2.507 2.359 2.433 2.172 2.210 2.578 1.906 2.084 2.613 2.541 2.098 2.222 2.316 2.443 2.315 2.202 2.376 2.435 2.351 2.127 ^ 2.576 2.449 2.774 2.544 2.184 2.384

30.710 30.920 31.144 31.587 31.137 32.858 31.372 31.556 31.260 31.291 31.110 30.984 31.408 31.130 31.433 31.486 31.510 31.161 31.584 31.161 31.511 31.255 31.656 31.414 31.040 31.174 31.020 31.436 31.264 31.217 31.221 31.470 31.342 31.110 31.104 31.302 31.043 31.250 31.099 31.311 30.758 31.073 30.997 30.931 31.521 31.495 ^ 31.018 31.296 31.732 31.636 31.555 31.356

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102



46X-1, 46X-1, 46X-1, 46X-2, 46X-2, 46X-2, 46X-3, 46X-1, 46X-1, 46X-2, 46X-2, 46X-2, 46X-3, 46X-3, 46X-3, 46X-4, 46X-4, 46X-4, 46X-5, 46X-5, 46X-5, 46X-6, 46X-6, 47X-1, 47X-1, 47X-1, 47X-2, 47X-2, 47X-2, 47X-3, 47X-3, 47X-3, 47X-4, 47X-4, 47X-5, 47X-5, 47X-6, 47X-6, 47X-6, 48X-1, 48X-1, 48X-1, 48X-2, 48X-2, 48X-2, 48X-3, 48X-3, 48X-3, 48X-4, 48X-4, 48X-4, 48X-5, 48X-5,

35^37 85^90 135^137 35^37 85^90 135^137 35^37 85^90 135^137 35^37 85^90 135^137 35^37 85^90 132^134 35^37 85^90 135^137 35^37 85^90 135^137 35^37 85^90 35^37 85^90 135^137 35^37 85^90 132^134 35^37 85^87 135^137 85^90 135^137 35^37 85^90 35^37 85^90 135^137 35^37 85^90 135^137 35^37 85^90 135^137 35^37 85^90 135^137 35^37 85^90 135^137 35^37 85^90

Depth


G. sacculifer

(mbsf)

N C

N O

N13 C

N18 O

409.850 410.350 410.850 411.350 411.850 412.350 413.750 414.250 414.750 415.250 415.750 416.250 416.750 417.250 417.720 418.250 418.750 419.250 419.750 420.250 420.750 421.250 421.750 423.150 423.650 424.150 424.650 425.150 425.620 426.150 426.650 427.150 427.650 428.150 428.650 429.150 429.650 430.150 430.650 432.350 432.850 433.350 433.850 434.350 434.850 435.350 435.850 436.350 436.850 437.350 437.850 438.350 438.850

1.190 1.287 1.240 1.000 1.008 1.191 1.328 0.999 0.989 1.221 1.063 1.340 1.272 1.290 1.308 1.204 1.247 1.427 1.210 1.468 1.372 1.204 0.948 1.462 1.474 1.392 1.311 1.515 1.546 1.477 1.405 1.384 1.523 1.675 1.423 1.465 1.590 1.488 1.446 1.566 1.532 ^ 1.560 1.569 1.315 1.115 1.235 1.598 1.446 1.482 1.439 1.499 1.545

1.577 1.583 1.059 1.471 1.665 1.451 1.900 1.552 1.611 1.421 1.392 1.652 1.592 1.589 1.696 1.731 1.544 1.592 1.271 1.816 1.780 1.806 1.798 1.607 1.694 1.758 1.688 1.848 1.476 1.327 1.335 1.570 2.008 1.082 1.448 1.767 1.931 1.894 1.692 1.880 1.691 ^ 1.923 1.587 1.659 1.981 2.110 1.502 1.726 1.787 1.889 1.803 1.923

2.643 2.285 2.474 2.442 2.287 2.372 2.349 2.207 2.155 2.489 2.202 2.424 2.076 2.316 2.667 2.711 2.712 2.856 2.759 2.623 2.559 2.326 2.108 2.956 2.488 2.867 2.532 2.938 2.965 2.350 3.064 ^ 2.696 2.915 2.788 2.706 2.862 2.524 2.568 2.764 2.720 2.802 2.887 2.600 2.577 2.451 2.474 2.775 2.819 2.624 2.275 2.741 2.642

31.505 31.308 31.548 31.291 31.212 31.165 30.997 31.128 31.252 31.502 32.227 31.330 31.272 30.975 30.946 31.316 31.180 31.064 31.090 31.020 30.988 31.105 30.973 31.256 31.212 30.983 30.923 30.969 30.971 31.541 30.778 ^ 30.740 30.786 30.746 31.072 30.720 31.023 30.685 30.859 30.955 31.495 30.750 30.320 31.038 30.481 30.554 31.301 31.223 30.990 30.717 30.785 30.790

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18


103


48X-5, 135^137 49X-1, 35^37 49X-1, 85^90 49X-1, 135^137 49X-2, 35^37 49X-2, 85^90 49X-2, 135^137 49X-3, 35^37 49X-3, 85^90 49X-3, 135^137 49X-4, 35^37 49X-4, 85^90 49X-5, 35^37 49X-5, 85^90 49X-5, 135^137 49X-6, 35^37 49X-6, 85^90 50X-1, 35^37 50X-1, 85^90 50X-1, 138^140 50X-2, 35^37 50X-2, 85^90 50X2, 132^134 50X-3, 35^37 50X-3, 85^90 50X-3, 135^137 50X-4, 35^37 50X-4, 85^90 50X-4, 140^142 50X-5, 35^37 50X-5, 85^90 50X-6, 38^40 50X-6, 85^90 51X-1, 85^90 51X-2, 85^90 51X-3, 85^90 51X-4, 85^90 51X-5, 85^90 51X-6, 85^90 52X-1, 85^90 52X-3, 85^90 52X-4, 85^90 52X-5, 85^90 52X-6, 85^90 53X-1, 85^90 53X-2, 85^90 53X-3, 85^90 53X-4, 85^90 53X-5, 85^90 53X-6, 85^90 54X-1, 35^37 54X-1, 85^90 54X-2, 85^90

Depth


G. sacculifer

(mbsf)

N C

N O

N13 C

N18 O

439.350 441.350 441.850 442.350 442.850 443.350 443.850 444.350 444.850 445.350 445.850 446.350 446.850 447.850 448.350 448.850 449.350 450.450 450.950 451.450 451.950 452.450 452.920 453.450 453.950 454.450 454.950 455.450 455.970 456.450 456.950 458.080 458.580 460.150 461.650 463.150 464.650 466.150 467.650 469.550 472.550 474.550 475.550 477.050 478.950 480.450 481.950 483.450 484.950 486.450 487.550 488.050 489.550

1.216 1.228 1.040 1.027 1.048 1.259 1.107 1.135 1.255 1.181 1.224 1.207 30.132 1.130 1.385 1.183 1.019 1.215 1.280 1.180 1.271 1.407 2.190 0.974 1.499 1.199 1.271 1.208 1.442 1.387 1.414 1.392 1.496 1.310 1.253 1.060 1.107 1.443 1.426 ^ 1.287 30.159 1.333 1.066 0.870 1.315 1.393 1.466 1.477 1.477 1.126 1.287 1.450

1.996 1.727 1.832 2.043 1.909 1.601 1.959 1.789 1.809 2.126 1.630 1.681 0.676 1.493 1.709 1.703 1.850 1.800 1.688 1.717 1.661 1.692 1.781 1.728 1.352 1.616 1.756 1.604 1.762 1.686 1.707 1.834 1.753 1.677 1.624 1.653 1.493 1.618 1.709 ^ 1.765 2.409 1.765 1.907 1.669 1.628 1.580 1.796 1.660 1.921 1.637 1.635 1.789

2.476 2.125 2.144 1.835 2.275 2.354 2.272 2.340 2.165 1.735 2.197 2.431 2.074 2.679 2.370 2.383 2.491 2.426 2.481 2.298 2.272 2.362 2.334 2.399 2.282 2.422 2.202 2.690 2.391 2.059 2.389 2.385 2.799 2.452 2.148 2.543 2.004 2.619 2.448 2.269 ^ 1.877 2.395 1.979 1.987 2.503 2.626 2.483 2.543 2.666 2.085 2.362 2.483

30.758 30.505 31.095 30.926 30.791 30.665 30.352 31.032 30.804 31.597 30.969 31.270 31.195 31.343 31.064 30.839 31.302 30.729 30.811 31.269 30.884 31.469 31.017 31.264 30.940 30.610 30.956 31.152 30.681 31.117 30.680 31.043 30.562 30.667 30.610 31.155 30.599 31.009 30.946 31.022 ^ 30.531 31.023 30.471 30.809 30.542 30.985 31.256 31.153 31.020 31.024 30.604 31.304

MARGO 3051 5-6-02

18

104




85^90 85^90 85^90 85^90 133^135 35^37 85^90 135^137 35^37 85^90 135^137 35^37 85^90 135^137 35^37 85^90 135^137 85^90 135^137 35^37 85^90 135^137 10^15 35^37 85^90 138^140 35^37 85^90 135^137 35^37 85^90 135^137 35^37 85^90 135^137 35^37 85^90 135^137 38^40 85^90 135^137 85^90 85^90 84^90 85^90 35^37 85^90 135^137 35^37 85^90 135^137 35^37 85^90

Depth


G. sacculifer

(mbsf)

N C

N O

N13 C

N18 O

491.050 492.550 494.050 495.550 496.030 496.650 497.150 497.650 498.150 498.650 499.150 499.650 500.150 500.650 501.150 501.650 502.150 503.150 503.650 504.150 504.650 505.150 505.400 505.750 506.250 506.780 507.250 507.750 508.250 508.750 509.250 509.750 510.250 510.750 511.250 511.750 512.250 512.750 513.240 513.750 514.250 515.850 518.850 521.850 523.350 525.050 525.550 526.050 526.550 527.050 527.550 528.050 528.550

1.473 1.119 1.127 1.181 1.240 1.243 1.334 1.381 1.070 1.307 1.407 1.446 1.342 1.136 1.118 1.409 1.269 1.470 1.264 1.508 1.640 1.431 1.515 ^ 1.222 1.537 1.460 1.529 1.668 1.511 ^ 1.661 1.467 1.357 1.168 1.243 1.373 1.060 1.257 1.233 1.164 0.752 1.278 1.281 1.276 1.085 1.308 1.306 1.291 1.396 1.280 1.253 1.251

1.891 1.854 1.665 1.686 2.130 1.652 1.665 1.812 1.448 1.852 1.772 1.693 1.616 1.534 1.772 1.640 1.532 1.726 1.538 1.673 1.818 1.844 1.660 ^ 1.714 1.695 1.656 1.727 1.808 1.955 ^ 1.508 1.805 1.586 1.527 1.911 1.874 1.554 1.486 1.833 1.911 1.313 1.734 1.792 1.823 1.385 1.713 1.783 1.658 1.809 1.917 1.681 1.861

2.206 2.485 2.228 2.457 1.986 2.554 2.580 2.484 2.436 2.488 2.749 2.647 2.752 2.212 2.474 2.256 2.705 2.488 2.319 2.266 2.795 2.878 2.998 2.755 2.393 2.324 2.563 2.647 2.825 2.260 2.860 2.328 2.699 2.589 2.519 2.263 2.494 2.179 2.216 2.221 2.376 2.032 2.448 2.328 2.415 2.439 2.450 2.197 2.470 2.423 2.349 2.515 2.331

30.862 30.718 30.840 30.815 30.947 30.999 30.991 30.917 31.377 30.760 30.942 31.076 31.658 31.117 31.098 31.823 31.244 31.405 31.283 31.218 31.339 31.069 30.935 31.345 31.197 30.908 30.962 30.877 30.602 30.160 30.735 30.822 30.960 31.139 30.737 30.909 30.548 30.749 30.637 30.608 30.573 30.745 30.893 30.368 31.178 30.706 30.995 31.087 30.987 30.690 30.630 30.501 30.780

MARGO 3051 5-6-02

18


105



135^137 40^42 85^90 135^137 39^41 130^137 35^37 85^90 85^90 35^37 85^90 85^90 35^37 85^90 85^90 85^90 85^90 85^90 135^137 35^37 85^90 85^90 85^90 85^90 85^90 85^90 135^137 35^37 85^90 135^137 85^90 135^137 35^37 85^90 135^137 35^37 85^90 135^137 35^37 85^90 135^137 35^37 85^90 85^90 85^90 85^90 85^90 85^90 85^90 85^90 85^90 85^90 85^90

Depth


G. sacculifer

(mbsf)

N C

N O

N13 C

N18 O

529.050 529.620 530.050 530.550 531.090 532.050 532.550 533.050 535.150 536.150 536.650 538.150 544.250 544.750 546.250 547.750 549.250 550.750 551.250 553.850 554.350 555.850 557.350 558.850 560.350 561.850 562.350 563.550 564.050 564.550 565.550 566.050 566.550 567.050 567.550 568.050 568.550 569.050 569.550 570.050 570.550 571.050 572.050 573.650 575.150 576.650 578.150 579.650 581.150 583.250 584.750 586.250 587.750

1.034 1.170 1.253 1.255 1.402 1.186 1.174 1.189 1.177 1.225 0.949 1.153 0.967 0.975 ^ 0.735 0.842 0.881 0.922 0.937 1.051 0.908 0.919 0.894 1.101 0.946 0.973 1.058 0.775 0.782 0.935 0.917 0.838 1.093 0.880 0.906 0.567 1.214 1.006 0.907 1.031 0.982 1.156 0.926 1.121 1.276 1.100 1.090 1.111 1.269 0.996 1.225 1.193

1.798 1.975 1.377 1.746 1.046 1.507 1.864 1.802 1.831 1.732 1.904 1.665 1.865 1.680 ^ 1.391 1.780 1.500 1.908 1.701 1.672 1.472 1.445 1.451 1.361 1.195 1.680 1.415 1.571 1.286 1.246 1.497 1.485 1.171 1.526 1.593 1.382 1.342 1.493 1.444 0.999 1.585 1.398 0.736 1.352 1.502 1.375 1.492 1.260 1.871 1.244 1.452 1.253

2.078 2.188 2.309 2.676 2.382 2.138 2.515 2.273 2.299 2.236 1.851 2.295 2.010 2.443 1.738 1.989 2.129 1.999 2.183 2.120 2.250 1.942 2.094 2.127 1.839 1.835 2.262 2.146 1.787 2.094 1.589 ^ 2.215 1.775 2.229 2.187 1.976 1.828 2.179 2.372 1.787 2.293 ^ 2.570 2.108 2.467 2.150 2.160 2.218 2.113 2.058 2.413 2.342

30.596 30.662 30.926 30.777 31.136 31.824 30.399 30.511 30.863 30.264 31.116 31.804 30.565 31.085 30.881 31.157 30.757 30.700 30.898 31.046 31.236 31.343 31.393 31.384 31.072 30.615 31.099 31.207 30.799 31.378 30.626 ^ 31.260 30.397 31.513 31.246 31.408 30.833 31.266 31.448 30.526 31.321 ^ 31.491 31.547 31.077 31.067 31.154 30.861 30.424 31.265 31.526 30.887

MARGO 3051 5-6-02

18

106




85^90 35^37 85^90 135^137 37^39 85^90 85^90 85^90 37^39 131^133 34^36 80^82 135^137 34^36 35^37 85^90 85^90 85^90 135^137 85^90 85^90 135^137 85^90 135^137 27^29 35^37 85^90 135^137 35^37 85^90 135^137 35^37 85^90 135^137 35^37 85^90 135^137 85^90 135^137 35^37 7^9 41^44 74^76 94^95 137^134 102^104 137^140 35^37 83^87 133^134 35^37 83^87 133^136

Depth


G. sacculifer

(mbsf)

N C

N O

N13 C

N18 O

590.750 592.600 593.100 593.600 594.100 595.600 597.100 598.600 599.580 600.560 602.040 602.500 603.000 603.520 611.750 612.250 613.750 615.250 615.750 616.750 618.250 618.750 619.750 620.250 620.670 621.350 621.850 622.350 622.850 623.350 623.850 624.350 624.850 625.350 625.850 626.350 626.850 627.850 628.350 630.950 660.200 661.410 667.740 667.940 668.370 673.220 673.570 688.770 689.250 689.750 690.300 690.750 691.200

1.001 1.081 1.049 1.064 ^ 1.032 0.951 0.954 1.130 1.103 0.903 1.018 1.058 0.901 1.100 0.829 0.817 0.939 0.577 0.882 0.884 1.165 ^ 0.832 0.843 0.536 0.956 1.115 1.040 1.059 1.205 1.286 1.140 1.131 1.077 1.046 0.999 1.137 1.468 1.342 0.833 1.586 31.076 0.995 0.381 0.583 0.749 0.546 0.683 0.556 0.629 0.829 0.749

1.274 1.594 1.523 1.446 ^ 1.315 1.086 1.396 1.794 1.493 1.508 1.326 1.693 1.440 0.816 1.432 1.249 1.200 1.379 1.393 1.318 1.268 ^ 1.331 1.433 1.586 1.272 1.390 1.376 1.279 1.154 0.910 1.427 1.533 1.415 1.393 1.481 1.585 1.159 1.616 1.529 0.898 0.716 1.328 0.444 1.384 1.408 1.516 1.133 1.253 1.248 1.386 1.177

1.815 2.619 1.784 2.193 2.166 2.206 1.650 2.055 2.316 2.259 1.949 1.912 1.633 1.694 1.682 2.253 2.412 2.284 2.008 2.121 2.232 2.273 2.331 2.301 2.353 2.270 2.410 2.679 2.446 2.892 2.649 2.396 2.809 2.671 2.721 2.864 2.712 2.919 2.551 2.911 2.593 2.732 2.849 2.578 2.672 2.291 2.426 2.651 2.730 2.678 2.301 2.917 2.700

30.750 31.486 30.818 30.612 30.686 30.908 30.626 31.012 30.742 30.710 30.549 30.473 0.010 30.142 30.493 31.468 31.393 31.357 31.121 31.455 31.458 30.917 31.297 31.334 31.384 31.513 31.334 31.624 31.118 31.453 30.919 30.763 31.391 31.241 31.164 31.322 31.323 31.214 30.352 30.806 31.329 30.475 31.527 31.438 30.791 31.570 31.549 31.487 32.270 31.600 31.482 31.960 31.628

MARGO 3051 5-6-02

18


107


Depth

75X-3, 35^37 75X-3, 83^87 75X-3, 131^132 76X-1, 34^36 76X-1, 83^85 76X-CC, 34^36 77X-1, 5^7 77X-2, 37^39 77X-2, 60^62 77X-2, 90^92 77X-2, 134^136 77X-3, 63^65


G. sacculifer

(mbsf)

N C

N O

N13 C

N18 O

691.700 692.230 692.710 698.440 698.930 699.440 707.750 709.570 709.800 710.100 710.540 711.330

0.797 0.884 1.056 0.932 1.073 1.606 0.765 0.914 1.070 0.969 0.657 1.268

1.308 0.928 1.199 1.392 1.406 0.768 1.431 1.097 1.181 1.026 0.853 1.243

2.557 2.694 2.354 2.864 2.953 2.572 2.495 2.687 2.714 2.720 2.567 2.960

31.493 31.440 31.469 31.617 31.548 30.689 31.511 31.808 31.681 32.011 31.950 31.692

ODP Hole 1006A planktonic foraminiferal fauna is very rich in tropical warm-water species. Thus, the low-latitude standard zonation of Blow (1969, 1979), with slight modi¢cation by Kennet and Srinivasan (1983) and Curry et al. (1995), was applied for the biostratigraphic interpretation, following the criteria outlined in Eberli et al. (1997a). Age estimates for the datum levels are from Berggren et al. (1995a,b), except for the ¢rst occurrence of Globigerinoides conglobatus at 6.2 Ma (Chaisson and Pearson, 1997). The major bioevents used for the identi¢cation of the zonal boundaries and zones, together with the planktonic foraminiferal datum, samples and depth, are summarized in Table 3. Below is the summary

18

of the Biozones as identi¢ed for ODP Hole 1006A. Zone N12 (from Sample 77X-2, 90^92 cm, to 72X-2, 72^74 cm, thickness approximately 48.4 m). De¢nition: interval from the ¢rst occurrence (FO) of Fohsella fohsi to the last occurrence (LO) of the Fohsella group. Zone N13 (from Sample 69X-1, 75^76 cm, to 68X-2, 85^90 cm, thickness approximately 9.5 m). De¢nition: interval from the LO of the Fohsella group to the FO of Zeaglobigerina nepenthes. Zone N14 (from Sample 68X-1, 85^90 cm, to 64X-3, 85^90 cm, thickness approximately 35.5 m). De¢nition: interval from the FO of Zeaglobigerina nepenthes to the LO of P. mayeri.

Table 2 Depth and ages of seismic sequence boundaries (SSBs) at ODP Hole 1006A Anselmetti et al. (2000), Eberli et al. (1997a,b)

Present paper

SSB

Age of boundary

Composite age (Ma)

Maximum age o¡set

TWTT (ms)

Depth (mbsf)

Age of SSB (Ma)

F G H I K L

Mioc./Plioc.

5.4 8.7 9.4 10.7 12.2 12.7

0.6 0.1 0.4 0.7 0.2 0.2

410 530 550 585 660 675

380 505 530 570 660 675

V5.48 V8.24 V8.4 V10.2 V12.1 12.5^13

Mid. late Mioc.

Partially modi¢ed after Eberli et al. (1997a,b) and Anselmetti et al. (2000). Depth of SBB is given in ms of two-way travel time (TWTT) and in meters below sea £oor (mbsf). Depth of SBB was obtained through time to depth conversion,. The composite age is the averaged biostratigraphic ages of the SBBs across the entire transect. Ages used in Eberli et al. (1997a,b) and Anselmetti et al. (2000) are based on shipboard nannofossil data. Ages used in the present paper are extrapolated from the age model based on post-cruise foraminiferal data. All datum ages are from Berggren et al. (1995a,b).

MARGO 3051 5-6-02

108


Table 3 Depth and age of bioevents identi¢ed in ODP Hole 1006A Bioevents

Samples

Depth (mbsf)

Age (Ma)

FO LO FO FO FO LO LO FO FO FO FO FO FO LO FO FO FO FO FO FO FO FO LO FO FO FO FO FO FO FO

37X-1, 38X-3, 40X-1, 40X-5, 43X-1, 44X-1, 44X-1, 48X-2, 50X-6, 51X-1, 54X-3, 54X-6, 55X-3, 55X-4, 55X-6, 56X-1, 56X-3, 56X-3, 56X-6, 57X-2, 60X-3, 60X-4, 64X-3, 65X-5, 67X-5, 68X-1, 69X-1, 72X-2, 73X-3, 75X-3,

331.45 343.65 358.95 364.95 385.95 395.05 395.05 434.85 458.45 460.15 491.05 495.55 500.15 501.65 504.65 506.25 509.25 509.25 514.25 517.35 547.75 549.25 586.25 598.95 618.25 621.85 631.35 661.72 673.57 691.70

4.50 4.60 ^ ^ 5.60 5.80 6.00 6.20 6.40 7.12 7.80 8.10 8.10 ^ 7.80 ^ 8.30 8.30 ^ ^ 8.50 ^ 11.40 ^ ^ 11.80 ^ 12.10 12.50 ^

G. crassaformis G. cibaoensis G. aemiliana N. pseudopima G. tumida Gq. dehiscens G. laenguaensis G. conglobatus G. margaritae G. conomiozea G. cibaoensis C. nitida G. juanai P. christiani G. suterae G. mediterranea G. plesiotumida G. extremus G. sphericomiozea G. merotumida N. humerosa P. christiani P. siakensis/P. mayeri gr. N. acostaensis G. menardii Z. nepenthes G. praemenardii G. fohsi robusta G. fohsi lobata R. archaeomenardii

85^90 85^90 85^90 85^90 85^90 85^90 85^90 135^137 85^90 85^90 85^90 85^90 85^90 85^90 85^90 85^90 85^90 85^90 135^137 85^90 85^90 85^90 85^90 85^90 85^90 85^90 85^90 72^74 137^140 35^37

Ages are from Berggren et al. (1995a,b). Numbers in bold indicate unreliable events. See Kroon et al. (2000) for detailed explanation.

Zones N15^N16 (from Sample 64X-2, 85^90 cm, to 56X-4, 85^90 cm, thickness approximately 74 m). At ODP Hole 1006A, Zones N15 and N16 must be considered as a single interval because the two zones, as traditionally described, were not identi¢ed. See Kroon et al. (2000) for details. Zone N17 (from Sample 56X-3, 85^90 cm, to 44X-1, 35^37 cm, thickness approximately 113 m). De¢nition: interval from the FO Globorotalia plesiotumida to the FO of Globorotalia tumida. Zones N18^19 (from Sample 43X-1, 35.37 cm, to 36X-1, 81^86 cm, thickness, approximately 63.6 m). At ODP Hole 1006A, Zones N18 and N19 must be considered as a single interval because the species Sphaeroidinella dehiscens, used

to mark the lower boundary of Zone N19, was not identi¢ed. 4.2. Miocene/Pliocene transition The Miocene/Pliocene transition deserves some comments. This boundary is currently accepted as de¢ned at the base of the Trubi Formation at Capo Rossello in Sicily (Cita and Gartner, 1973; Cita, 1975). Traditionally, the beginning of the Pliocene (the base of the Zanclean stage) is equated with the recovery of the Mediterranean Sea to full marine conditions after the ‘Messinian Salinity Crisis’, a period when the basin became completely isolated (Ryan and Hsu« ; 1973; Hsu«

MARGO 3051 5-6-02


and Montadert, 1978; McKenzie et al., 1990; Spezzaferri et al., 1998). Sedimentary expression of this major event is a sharp lithologic change from an evaporative sequence topped by the ‘Lago Mare Facies’ to pelagic sediments rich in planktonic faunas. A sharp lithologic change at the Miocene/Pliocene boundary is not present in the open ocean sediments. In addition, this boundary does not correspond to any major biological event, but is characterized by relatively low degree of biotic turnover (extinction plus origination) within all the microfossil groups and especially in planktonic foraminifera (Kroon et al., 2000). Blow (1969, 1979) placed the Miocene/Pliocene boundary within Zone N18, between the FOs of Globorotalia tumida and Sphaeroidinella dehiscens. The FO of G. tumida is the bioevent most commonly accepted to identify this boundary in open ocean sequences (Premoli Silva et al., 1993; Berggren, 1973; Fleisher, 1974; Vincent, 1975; Berggren et al., 1995a,b). Basically, the absence of any speci¢c marker species makes the correlation of bioevents in the Mediterranean Sea with those from the open ocean di⁄cult. Because the Miocene/Pliocene boundary in Mediterranean sequences and those of the open ocean cannot be directly correlated using only bioevents, McKenzie et al. (1999) proposed to indirectly correlate the Bahamian sequence using the sedimentation rates derived for ODP Hole 1006A. Using the age of the Miocene/Pliocene boundary as determined from the astronomically calibrated time scale as applied in the Mediterranean (5.33 Ma; Hilgen, 1991), the Miocene/ Pliocene boundary was placed at approximately 371 mbsf. The Zones MPL1/MP12 boundary mbsf (5.1 Ma, Hilgen, 1991) was placed at approximately 361 mbsf. A preliminary astronomical calibration of bioevents from ODP Hole 1006A made by Kroon et al. (2000) places the Miocene/Pliocene boundary between 371 and 375 mbsf and, therefore, con¢rms the extrapolation of McKenzie et al. (1999). 4.3. Sedimentation rates The sedimentation rates, as calculated using

109

12 planktonic foraminiferal bioevents (Table 3), vary widely in ODP Hole 1006A between relatively high and low values. The data are plotted on an age vs. depth curve as shown in Fig. 2. Nannofossil data were not plotted because they erroneously record the strong reworking of ¢ne-grained material (Kroon et al., 2000). The calculated sedimentation rates range from 1.32 to 19.35 cm/1000 yr. Progressing downhole from the FO of G. crassaformis (4.5 Ma) to the FO of Globorotalia tumida (5.6 Ma), the sedimentation rate is approximately 4.9 cm/1000 yr and from the FO of G. tumida to the LO of G. dehiscens (5.8 Ma) approximately 4.5 cm/1000 yr. Owing to the low recovery of Core 43X, the exact LO of G. dehiscens may, however, occur within the 9.5 missing meters. A signi¢cant increase in the sedimentation rate to 9.95 cm/1000 yr occurs in the interval from the LO of G. dehiscens and the FO of Globigerinoides conglobatus (6.2 Ma). The sedimentation rate rises to 11.8 cm/1000 yr from the FO of G. conglobatus to the FO of G. margaritae (6.4 Ma). Between the FO of G. margaritae and the FO of C. nitida (8.1 Ma), it drastically decreases to 2.18 cm/1000 yr, but increases again rising to 6.85 cm/1000 yr between the FO of C. nitida and the FO of Globorotalia plesiotumida (8.3 Ma). The next older bioevent is the FO of N. humerosa (8.5 Ma), which de¢nes an interval of 200 000 yr with a very high sedimentation rate of approximately 19.25 cm/1000 yr. The sedimentation rate drastically decreases to 1.32 cm/1000 yr between the FO of N. humerosa and the LO of the P. siakensis/P. mayeri group (11.4 Ma). An increase in the rate of up to 8.9 cm/ 1000 yr is observed between the LO of the P. siakensis/P. mayeri group and the FO of Zeaglobigerina nepenthes (11.8 Ma). A further increase occurs in the interval between the FO of Z. nepenthes and the FO of Fohsella fohsi robusta. This value, however, may not be real because of the very poor recovery in Core 71X. Finally, at the base of ODP Hole 1006A the sedimentation rate decreases to 2.9 cm/1000 yr between the FO of F. fohsi robusta (12.1 Ma) and the FO of F. fohsi lobata (12.5 Ma). Fig. 2 also shows the position of the sequence

MARGO 3051 5-6-02

110


MARGO 3051 5-6-02


111

Fig. 3. Carbon isotope stratigraphy for the middle Miocene to lowermost Pliocene sediments of ODP Hole 1006A. The curves plot both the unsmoothed data from Table 1 and a smoothed seven-point running average of the data. Note the scale change between the unsmoothed and smoothed curves.

stratigraphic boundaries (SSBs), based on their depth in the sequence (Eberli et al., 1997a; Anselmetti et al., 2000). In general, the SSBs tend to correlate with periods of lower sedimentation rates relative to the surrounding higher values. The exception appears to be SSB H, which occurs within a period of exceptionally high sedimentation (19.25 cm/1000 yr). This 200 000-yr period represents the onset of the growing dominance of the drift deposits, which may somehow mask any shorter-term periods of lower sedimentation. Eberli et al. (2002) noted that several of the SSBs at ODP Site 1007, located directly northeast of ODP Site 1006 on the Bahamas Transect, coincide with decreased sedimentation rates. They suggested that this coincidence is an indication of reduced platform production with lowered sea-level. 4.4. Stable isotope stratigraphy The stable carbon and oxygen isotope stratigraphies for ODP Hole 1006A are shown respectively in Figs. 3 and 4, together with the position of the sequence stratigraphic boundaries (SSBs). The ¢gures include both the nonsmoothed and smoothed isotope curves. The latter were smoothed using a seven-point running average, which better illustrates the observed isotopic trends when plotted on an expanded scale. The general trend of the N13 C values for the benthic foraminifera and Globigerinoides sacculifer is similar between about 620 and 360 mbsf, although the respective values are notably di¡erent (Fig. 3). From about 620 mbsf downward and 360 mbsf upward in the studied sequence, the two N13 C curves show opposing trends. Throughout the sequence, N13 C values range from 30.11 to 2.19x for the benthic foraminifera and from 0.96 to 3.06x for G. sacculifer. From 600 up to 420 mbsf, both curves show a general tendency toward more positive values. The N13 C values of

G. sacculifer increase by about 1x (from approximately 1.9 to 2.8x) and the N13 C values of the benthic foraminifera increase by about 0.6x (from 0.9 to 1.5x), as reported in Table 1. A remarkable shift toward lower N13 C values (1.5x in G. sacculifer and 1x in the benthic foraminifera) is observed in both curves from 420 mbsf up to about 360 mbsf. The N18 O values of the benthic foraminifera and Globigerinoides sacculifer are notably di¡erent re£ecting the temperature gradient in the water column (Fig. 4). The overall N18 O values range from 0.77 to 2.31x for benthic foraminifera and from 32.27 to 30.76x for G. sacculifer. Both the benthic and planktonic values vary systematically throughout the sequence by up to 1.5x. Although the magnitude of the N18 O £uctuations is not necessarily the same, the positive and negative excursions observed in the curve of the benthic foraminifera tend to correlate with similar excursions of the N18 O values for G. sacculifer. The N18 O values for benthic foraminifera show a continuous oxygen-18 enrichment from the base to the middle of the studied sequence, with values increasing by nearly 1.0x from 711 to 537 mbsf. Upward in the sequence, the N18 O values £uctuate somewhat but tend to remain around the more enriched value of about 1.8x. Superimposed high-frequency variations can be observed, however, throughout the curve. In the interval 470^ 410 mbsf, the benthic curve shows two cycles of prominent depletion in oxygen-18 with the N18 O values decreasing by approximately 0.5x. The N18 O values of G. sacculifer tend likewise to increase by nearly 1.0x in the same interval across the middle to late Miocene boundary, but afterwards they display several more prominent £uctuations toward more negative values. In particular, the N18 O values of G. sacculifer exhibit a prominent excursion toward overall more negative values by more than 0.5x between 410 and 340 mbsf, an interval which spans the Miocene/Pliocene boundary.

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Fig. 4. Oxygen isotope stratigraphy for the middle Miocene to lowermost Pliocene sediments of ODP Hole 1006A. The curves plot both the unsmoothed data from Table 1 and a smoothed seven-point running average of the data. Note the scale change between the unsmoothed and smoothed curves.

5. Discussion 5.1. Paleoceanographic implications The oxygen isotope record of the benthic foraminifera indicates an overall gradual cooling of Bahamas margin bottom water from 12.5 to 4.5 Ma (Fig. 4). This cooling was probably produced by the onset of the North Atlantic Deep Water (NADW) in the middle^late Miocene consequent to the establishment of full glacial conditions in the North Atlantic (Larsen et al., 1994; Israelson et al., 1994). The N18 O values of Globigerinoides sacculifer indicate that several warming^cooling episodes may have occurred in surface waters during the middle^late Miocene along the Bahamas margin (Fig. 4). In the latest Miocene (Messinian) after approximately 6.2 Ma, the N18 O values of G. sacculifer indicate a particularly distinct warming trend in sea-surface temperatures, which corresponds to signi¢cant decrease in the N18 O values of the benthic foraminifera (Fig. 4). The bottom signal probably indicates a combined temperature/ice volume e¡ect, which would represent a decrease in the global continental ice volume associated with the warming and a consequent sealevel rise. At approximately 6 Ma, the N18 O benthic curve tends towards more positive values, indicating an increase in the global ice volume. McKenzie et al. (1999) suggested that a major sea-level fall occurred in conjunction with the increased ice volume, which they associated with the isolation of the Mediterranean Sea leading to the Messinian Salinity Crisis. Because of the poor recovery of sediments deposited prior to the Miocene/Pliocene boundary at 5.33 Ma, the exact character of the positive trend cannot be determined, but a reversal towards lower N18 O values apparently occurred in association with the boundary leading to a global sea-level rise which £ooded the Bahamas platform and ended the Messinian Salinity Crisis (McKenzie et al., 1999).

The recorded warming episodes are probably related to astronomical cycles, which also control the carbonate production on the surrounding platforms (Kroon et al., 2000). During the late Miocene, intervals with more positive N13 C values (Fig. 3) may indicate an associated increase in productivity. The presence of sponge spicules (between 450.5 and 544.7 mbsf) and in some levels sponge spicules and radiolarians (between 399.5 and 415.2 mbsf) may indicate that, from 8.5 to 5.8 Ma, sediments were deposited in the Bahamas basin under upwelling conditions. Shackleton and Hall (1997) developed a hypothesis, previously expressed by Woodruf and Savin (1991), which demonstrated a clear association between N13 C values and long orbital eccentricity cycles (400 kyr) in the late Miocene. They produced a detailed N13 C curve, which shows orbital-related N13 C £uctuations. They state that the power in the N13 C record could have originated from climatically controlled changes in organic carbon storage in marginal seas, in terrestrial biomass, or in sediments under an upwelling system. Similarly, Vincent and Berger (1985) have suggested that the anomalous positive N13 C values that are observed in the middle Miocene sediments could have arisen from episodes of rapid accumulation of organic carbon due to intense upwelling along the Californian margin. Shackleton and Hall (1997) suggest that this or an analogous process could have been controlled by orbital-driven climatic variability and that the long residence time of carbon in the ocean could have given rise to the long period response. In particular, they identify a gradual shift of about 1x toward less positive values between 6.2 and 5.8 Ma. This carbon isotope shift was ¢rst recognized by Keigwin (1979) in deep-sea sediments of the Indo-Paci¢c region, but it now appears to be global and can be reasonably correlated in timing and amplitude with the similar shift observed in the N13 C record from the sediments of ODP Site

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1006 at about 440 mbsf (Fig. 3). According to their observation, this shift of the N13 C values may be related to decreasing global upwelling intensity. Therefore, we likewise interpret the N13 C shift toward less positive values occurring at ODP Site 1006 between about 6.2 and 5.8 Ma as a gradual decrease in the upwelling intensity along the Bahamas margin. As additional support of this interpretation, the siliceous components of ODP Hole 1006 sediments, radiolarian and sponge spicules, disappear at approximately 5.8 Ma and upward, indicating a decrease in the upwelling intensity. A signi¢cant upward decrease in the aragonite content of the sediments was also observed for this time interval (Eberli et al., 1997a). This change in the bulk carbonate mineralogy re£ects a decrease in the aragonite-rich neritic £ux to the margin, possibly related to decreased productivity on the carbonate platform resulting from a sea-level lowstand as indicated by a shift towards more positive N18 O values. An inverse association between decreasing aragonite contents and more positive N18 O values was succinctly demonstrated for the glacial intervals of the Pleistocene section of ODP Hole 1006A (Rendle et al., 2000). Additionally, late Miocene changes in the paleocirculation pattern on the Bahamas margin may have resulted from the restriction of an e⁄cient connection between the Paci¢c and Caribbean through the Panama gateway beginning at 8 Ma. A high-resolution Nd isotope time series developed in ferromanganese crusts from the Blake Plateau provides additional evidence for circulation changes (Reynolds et al., 1999). They detected a remarkable shift in ONd between 8 and 5 Ma, which they relate to a decreased supply of Paci¢c water £owing eastward through the Panama gateway into the Caribbean. They also proposed a circulation model, which implies the restriction of intermediate Paci¢c water into the Caribbean by around 5 Ma. The ¢nal closure of the Isthmus of Panama at approximately 4.6 Ma would have led to a complete reorganization of ocean circulation in the Bahamas region (Haug and Tiedemann, 1998). Kroon et al. (2000) also proposed the closure of the Panama gateway as the main cause of the increased sedimentation rate

after the Miocene/Pliocene boundary (5.33 Ma), which was a result of the reorganization of the paleocirculation system. 5.2. Eustatic sea-level £uctuations Interglacial^glacial changes in the volume of continental ice-sheets result in the respective rises or falls of global sea-level, which are recorded by sedimentary patterns on continental margins. With the contraction or expansion of the ice caps, water is either returned or removed from the world’s oceans a¡ecting the oxygen isotopic composition of sea-water. Thus, there should be a causal link between the proxy record of N18 O in sea-water and the sedimentary record of sea-level £uctuations on the continental margins. Indeed, the composite isotope record does show several eustatic episodes that are consistent with the geological record of ice-sheets evolution (Abreu and Anderson, 1998). In particular, negative excursions of the N18 O values should correspond to high sea-level stands and positive excursion to low sea-level stands. Correlation of the glacio-eustatic oxygen isotopic record with the sequence stratigraphic pattern of sea-level change can potentially document a causal link between glacioeustasy and stratal pattern (Miller et al., 1991). In fact, oxygen isotope stratigraphy o¡ers an independent geochemical test of the in£uence of sealevel derived from onlap records and sequence boundary interpretation (Williams, 1988) and is, therefore, a proxy for eustasy during the Cenozoic (Abreu and Anderson, 1998). The sedimentary sequence at ODP Hole 1006A is remarkably continuous, expanded and well dated, making this site an excellent location to compare isotopic and sedimentary records. It may even become a classic site for late Cenozoic paleoceanography in the low-latitude Atlantic (Eberli et al., 1997a). McKenzie et al. (1999) have already demonstrated that variations in the late Mioceneêarliest Pliocene oxygen isotope record from benthic foraminifera at ODP Hole 1006A are linked to an ice volume e¡ect rather than a local temperature e¡ect. They compared the benthic foraminifera oxygen isotope record of ODP Hole 1006A to a corresponding deep-

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Fig. 5. Correlation of benthic oxygen isotope curve (smoothed curve using a three-point running average) from ODP Site 1006 with the corresponding deep-water benthic oxygen isotope curve from ODP Site 846 in the Eastern Equatorial Paci¢c (Shackleton et al., 1995).

water benthic oxygen isotope curve from ODP Site 846 in the Eastern Equatorial Paci¢c, which was drilled in a water depth of 3307 m (Shackleton et al., 1995; Fig. 5). The latter isotope curve represents the late Mioceneêarliest Pliocene interglacial^glacial cycles with a minimum temperature e¡ect and shows ¢rst-order interglacial^glacial cycles of the duration of approximately 0.5 Myr with several higher-frequency cycles throughout. Several of these major isotopic excursions can be identi¢ed in the benthic oxygen isotope curve generated for ODP Hole 1006A and are

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similar in their timing and magnitude to the corresponding cycles of ODP Site 846 (Fig. 5). Based on this interpretation of the isotope data, McKenzie et al. (1999) proposed that the oxygen isotope signal compiled from benthic foraminifera on the Bahamas Transect does, indeed, re£ect global eustasy. In the present research, we extend our investigation to the middle Miocene sedimentary sequence recovered at ODP Hole 1006A and focus on the sediments spanning the middle Miocene (approximately 12.5 Ma) to the early Pliocene (approximately 4.5 Ma). The ODP Leg 166 scienti¢c party described the presence of pervasive cyclicity in the entire middle Miocene^lower Pliocene section (Eberli et al., 1997a). Further shorebased spectral analysis of the sedimentation rate time series shows short- and long-term cycles of eccentricity (120 and 400 kyr, respectively) throughout the section (Kroon et al., 2000). The analysis demonstrates that the cyclicity is related to sea-level changes that result in £uctuations in carbonate production on the Great Bahama Bank. Anselmetti et al. (2000) relate 17 seismic sequences they identi¢ed along the Bahamas margin from the Neogene to Quaternary to third-order sea-level changes with an average duration of 1^1.5 Ma. Combining the previous results of McKenzie et al. (1999) with those of Eberli et al. (1997a), Anselmetti et al. (2000) and Kroon et al. (2000), we propose that the entire middle Mioceneêarly Pliocene oxygen isotope record compiled from benthic foraminifera re£ects global eustasy. Abreu and Anderson (1998) examined the geological evidence for Cenozoic ice-sheet evolution. They compiled a smoothed composite oxygen isotope record (Fig. 6) using several sites in the Atlantic, Paci¢c, Indian and Southern Oceans spanning the interval from the lower Paleocene to the Quaternary (e.g. Shackleton and Kennet, 1975; Miller et al., 1987; Prentice and Mathews, 1988). A comparison of the smoothed composite oxygen isotope record and the oxygen isotope record of benthic foraminifera and Globigerinoides sacculifer from ODP Site 1006 shows that the numbers of £uctuations are similar although the characters of the curves are not (Fig. 6). Addi-

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Fig. 6. Smoothed composite oxygen isotope record of Abreu and Anderson (1998) plotted vs. the benthic and planktonic foraminifera N18 O values from ODP Site 1006. The terms of Abreu and Anderson (1998) are used to indicate the positive isotope excursions (PZi = Pliocene, Zanclean; MMi = Miocene, Messinian; MTi = Miocene, Tortonian; MSi = Miocene, Serravallian; and Mli = Miocene, Langhian). The correlation is based on the position of the single excursion in the temporal framework (age) represented by the dashed line. Plain lines mark the separation of the various stages.

tionally, the £uctuations are weaker in the N18 O record of G. sacculifer, probably because the eustatic signal is weaker in the surface waters. Abreu and Anderson (1998) concluded that a reasonable correlation exists between sequence boundaries and oxygen isotope positive events for almost the entire Cenozoic. Our oxygen isotope records of benthic foraminifera and Globigerinoides sacculifer from ODP Site 1006 reveal, however, that the relation between the position of sequence stratigraphic boundaries and the N18 O excursions is not entirely straightforward. Fig. 4 shows the oxygen isotopic record and the position of the sequence boundaries at ODP Site 1006. If we consider a 20-m uncertainty in the range of occurrence of the SSBs, it is evident that both positive and negative N18 O excursions may coincide with SSB intervals, but, in general, £uctuations in the oxygen isotope record are coincident with the broad range covered by all of the SSBs. On the other hand, there

are de¢nitely more signi¢cant £uctuations in the oxygen isotope record than there are SSBs. For example, the distinctive late Miocene positive isotope excursion at 6.2 Ma is not represented by the presence of a SSB (Fig. 4). Considering these observations, it is still possible to make a rough generalization that the SSBs appear to occur at positions in the isotope curve where the overall trend in the N18 O values tends to be changing from a more negative to a positive direction. Such a transition could represent a change from higher to lower sea-level. This observation, together with the fact that the SSBs tend to correlate with periods of lower sedimentation rates (Fig. 2), could imply that a transition to a lowered sea-level would lead to reduced platform production and, thus, the £ux of neritic material to the margin. The study of Anselmetti et al. (2000) revealed that the record of sea-level changes in the drift deposit in the basin adjacent the Great Bahama

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Bank is mostly interpreted from the sediment thickness and composition. The sedimentary load carried by the Florida currents was derived largely from the adjacent platforms, and was greatly reduced during sea-level lowstands. In fact, shallow water carbonate factories are generally not very productive during sea-level lowstands. As mentioned above, Fig. 2 indicates that the SSBs tend to correlate with periods of lower sedimentation rates relative to the surrounding higher values. These sedimentation rates (1.32^6.85 cm/1000 yr) fall within a plus or minus range around the average pelagic sedimentation rate of about 3 cm/1000 yr (i.e. during sea-level lowstands when the carbonate platform contribution is minimized). Erosion is probably not a factor in reducing the sedimentation rate because there is an integrity in the biostratigraphic data. The higher sedimentation rates (8.9^19.25 cm/ 1000 yr) re£ect the relative increase in the deposition of ¢ne-grained platform-derived material during periods of intensi¢cation of carbonate production on the platform (i.e. during sea-level highstands, Eberli et al., 1997a; Kroon et al., 2000). In summary, we propose that, at ODP Site 1006, SSB F, G, H, I and K correspond to oxygen isotope transitions towards more positive values and are associated with lower sedimentation rates. During lowstands, platform exposure leads to reduced sedimentation rates and mostly pelagic deposition. With the subsequent rise in sea-level, the platform is £ooded and renewed carbonate production leads to the shedding of neritic components to the margins increasing sedimentation rates. It is this contrast between these two sediment types, pelagic and mixed pelagic/neritic or periplatform sediments, and their di¡erent diagenetic potentials that produces the seismic re£ections along the depositional surfaces (Eberli et al., 2002).

6. Conclusions Oxygen isotope stratigraphy developed from deep-sea pelagic sections provides a widely recognized proxy for glacial/interglacial cycles, whereas seismic sequence stratigraphy imaged on conti-

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nental margins is considered to be a record of eustatic sea-level £uctuations. These two records have a common determining factor, i.e. the varying of continental ice volume due to climate change. Our isotope study of carbonate sediments deposited on the distal margin of the Bahamas platform attempts to test the validity of the sequence stratigraphic approach to evaluate eustatic sea-level and determine how it links to the open ocean oxygen isotope record of ice volume £uctuations. We demonstrate that oxygen isotope stratigraphy produced using basinal sediments deposited on a distal carbonate margin can provide a record of glacial/interglacial cyclicity. Further, this marginal isotope record directly links the deep-sea pelagic record of ice volume change, using biostratigraphic events and astrochronolgy, to the seismic sequence geometric pattern of sea-level £uctuations by tracing the isotope excursions along the SSBs. Considering a 20-m uncertainty in the depth range of the individual SSBs, the imaged Neogene boundaries on the Bahamas margin occur approximately synchronous with measured positive oxygen isotope excursions, that is they occur at the same approximate depth in the section. Additionally, they are generally associated with relatively lower sedimentation rates, re£ecting a decreased neritic input with sea-level lowstands (Droxler and Schlager, 1985; Reijmer et al., 1988). These results indicate that the SSBs probably developed during sea-level lowstands or during the transition from high to lowstands. Thus, the seismic re£ectors producing the SSBs may represent a distinct changeover from mixed pelagic/neritic or periplatform sediment to a predominantly pelagic sediment deposition during eustatic sea-level lowstands as the carbonate platform decreases production with the falling eustatic sea-level. The di¡erent diagenetic potentials of these two sediment types may lead to di¡erent seismic contrasts producing the seismic re£ectors. On the other hand, not all of the excursions in the oxygen isotope record are coincident with SSBs, indicating that eustatic sea-level £uctuations may have variable impact on the carbonate platform environment. Betzler et al. (2000a) also noted that there is only a moderate match between their interpreted

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sea-level lowstands on the Great Bahama Bank and the ages of postulated global sea-level lowstands (Haq et al., 1988; Hardenbol et al., 1998). These observations may not be an unexpected conclusion as noted by Eberli (2000) in his ODP Leg 166 synthesis paper. Comparing the SSBs on Great Bahama Bank with the events in the eustatic sea-level curve, only approximately two-thirds of the ages of SSBs coincide with proposed global sea-level falls. Considering the in£uence of local tectonics and sediment supply on the position and resolution of sea-level falls, Eberli (2000) considers this a remarkably high correlation. There may be a stronger correlation of the eustatic sea-level curve of Haq et al. (1988) with the oxygen isotope sea-level curve generated for ODP Hole 1006A. For example, the notable oxygen isotope sea-level fall recorded in our isotope stratigraphy prior to 6.2 Ma (Fig. 4) coincides with a sea-level event in the eustatic sea-level curve of Haq et al. (1988), but it is not marked by the presence of prominent seismic re£ector in the Bahama seismic pro¢le. Fundamentally, the results of this study corroborate the existence of a causal link between sealevel and sequence stratigraphic pattern. Glacioeustatic variations interpreted from the benthic oxygen isotope proxy can be correlated with the stratigraphic response of the carbonates to sealevel changes, as deduced from the depositional facies of the recovered sedimentary sequence along the transect. Additionally, this study provided important information about the paleoceanographic evolution of the Bahamas during the middle and late Miocene. The sediments from ODP Hole 1006A record a distinct cooling, possibly representing the onset of the NADW consequent to the establishment of full glacial conditions in the North Atlantic. This trend was interrupted by a warming in the surface waters and a decrease in global ice volume in the latest Miocene (Messinian), which culminated at the Miocene/Pliocene boundary and was followed by an early Pliocene cooling. Carbon isotopes of foraminifera shells also record evidence for the gradual closure of the Panama gateway, with the consequent changes in paleocirculation on the Bahamas margin. Finally, this study demon-

strates that transect drilling on carbonate margins is an innovative way to monitor ocean history.

Acknowledgements We acknowledge ODP for inviting two of us (J.A.M. and A.I.) to participate as shipboard scientists on ODP Leg 166 and for providing us with the large number of samples required for this study. We thank K.G. Miller, J.F. Sarg, J.J.G. Reijmer and an anonymous reviewer, who carefully reviewed and provided many suggestions which greatly improved the manuscript. Miriam Andres and Stefano Bernasconi are warmly acknowledged for their assistance with the stable isotope measurements. The ESF Consortium for Ocean Drilling (ECOD) and ETH-Zu«rich provided financial support to S.S.

References Abreu, V.S., Anderson, J.B., 1998. Glacial eustasy during the Cenozoic: Sequence stratigraphic implications. AAPG Bull. 82, 1385^1400. Anselmetti, F., Eberli, G.P., Zan Dong, D., 2000. From the Great Bahama Bank into the Strait of Florida: A margin architecture controlled by sea-level £uctuations and ocean currents. GSA Bull. 112, 829^844. Berggren, W.A., 1973. The Pliocene time scale: calibration of planktonic foraminifera and calcareous nannoplankton zones. Nature 243, 391^397. Berggren, W.A., Hilgen, F.J., Langereis, C.G., Kent, D.V., Obradovich, J.D., Ra⁄, I., Raymo, M.E., Shackleton, N.J., 1995a. Late Neogene chronology new perspectives in high-resolution stratigraphy. GSA Bull. 107, 1272^1287. Berggren, W.A., Kent, D.V., Swisher, C.C., Aubry, M.P., 1995b. A revised geochronology and chronostratigraphy. In: Geochronology Time Scales and Global Stratigraphic Correlation. Tulsa, SEPM Spec. Publ. 54, pp. 129^212. Betzler, C., Kroon, D., Reijmer, J.J.G., 2000a. Synchroneity of major late Neogene sea-level £uctuations and paleoceanographic controlled changes as recorded by two carbonate platforms. Paleoceanography 15, 722^730. Betzler, C., Pfei¡er, M., Saxena, S., 2000b. Carbonate shedding and sedimentary cyclicities of a distally steepened carbonate ramp (Miocene, Great Bahama Bank). Int. J. Earth Sci. 89, 140^143. Betzler, C., Reijmer, J.J.G., Bernet, K., Eberli, G.P., Anselmetti, F.S., 1999. Sedimentary patterns and geometries of the Bahamian outer carbonate ramp (Miocene-Lower Pliocene, Great Bahama Bank). Sedimentology 46, 1127^1144.

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