(Table 5) Distribution of benthic foraminifers in the late Cretaceous of DSDP Hole 71-511

The book is devoted to stratigraphy of Cretaceous deposits from high latitudes of the southern hemisphere (subantarctic part of the ocean), as well as to geological and climatic Cretaceous history of the area. Correlation with Cretaceous sediments from warm water regions is carried out. Description and photos of characteristic species of planktonic and benthic foraminifera and calcispherulides are given.

Geochemistry of Cretaceous sediments from Argo and Gascoyne Abyssal Plains

The accumulation of organic matter, ferrous and pyrite iron, and the ratios of organic carbon/total sulfur and organic carbon/total phosphorus in the Lower Cretaceous sediments from the Argo and Gascoyne abyssal plains have been used as indicators of both the source and reactivity of organic matter in the sediments and the depositional environment. Total sulfur, used as an indicator of pyrite sulfur, is more abundant in sediments from the Gascoyne Abyssal Plain than in those from the Argo Abyssal Plain. Sulfur positively correlates with TOC at both sites (although poorly at the Argo Abyssal Plain site, R = 0.48), with an extension of the line of best-fit through the origin, indicating that pyrite (TOC <2 wt%) is diagenetic and deposited from normal marine conditions. The average ratio of C/S for samples of TOC <2 wt% is 5.4 at Argo Abyssal Plain (compared to the modern normal marine value of 2.8) indicating deposition of organic matter probably of mixed terrestrial and oxidized marine sources that is unreactive to the sulfate-reducing bacteria. One sample from the Aptian sediments is rich in TOC (5.1 wt%) and has a C/S ratio of 0.5. The average C/S ratio in Gascoyne Abyssal Plain sediments is 0.8 (R = 0.97), which indicates the formation of abundant pyrite in addition to burial and preservation of relatively fresh organic matter that is reactive to the sulfate-reducing bacteria. Organic carbon to phosphorus ratios (C/P) in the sediments indicate preferential remobilization of organic carbon over phosphorus with increasing water depth. Estimates of the degree of pyritization (DOP) increase with increasing TOC at both sites, indicating iron is not limiting and pyrite is formed diagenetically. The one sample with a TOC content of 5.1 wt%, from the Argo Abyssal Plain near the Barremian-Aptian boundary, is composed mostly of framboidal pyrite, finely laminated and not bioturbated, and hence may have been deposited during a brief period of anoxia in the overlying waters.

Miocene to Pleistocene diatom biostratigraphy with a focus on Thalassiosira in sediments of ODP Leg 186 sites

Late Neogene biostratigraphy of diatoms has been investigated from two sites occupied during Ocean Drilling Program (ODP) Leg 186 off the coast of northeast Japan. A unique aspect of ODP Leg 186 was the installation of two permanent borehole geophysical observatories at the deep-sea terrace along the Japan Trench. The Neogene subsidence history of the forearc was documented from both Sites 1150 and 1151, and Quaternary to middle Miocene (16 Ma) sediments represent a nearly continuous stratigraphic sequence including numerous ash records, especially during the past 9 m.y. Diatoms are found in most samples in variable abundance and in a moderately well preserved state throughout the sequence. The assemblages are characterized consistently by age-diagnostic species of Denticulopsis and Neodenticula found in regions of high surface water productivity typical of middle to high latitudes. The Neogene North Pacific diatom zonation divides the Miocene to Quaternary sequences fundamentally well, except that the latest Miocene through early Pliocene Thalassiosira oestrupii Subzone is not applicable. Miocene and late Pliocene through Pleistocene diatom datum levels that have been proven to be of great stratigraphic utility in the North Pacific Ocean appear to be nearly isochronous within the level of resolution constrained by core catcher sample spacing. The taxonomy and stratigraphy of previously described species determined to be useful across the Miocene/Pliocene boundary have been investigated on the basis of the evolutionary changes within the Thalassiosira trifulta group. The biostratigraphically important forms belonging to the genus Thalassiosira have been illustrated with scanning electron micrographs.

Miocene calcareous nannofossil abundance and events in sediments of ODP Leg 189 sites

During Ocean Drilling Program (ODP) Leg 189, five sites were drilled in the Tasmanian Seaway with the objective to constrain the paleoceanographic implications of the separation of Australia from Antarctica and to elucidate the paleoceanographic developments throughout the Neogene (Shipboard Scientific Party, 2001a, doi:10.2973/odp.proc.ir.189.101.2001). Sediments ranged from Cretaceous to Quaternary in age and provided the opportunity to describe the paleoenvironments in the Tasman Seaway prior to, during, and after the separation of Australia and Antarctica. This study will focus on postseparation distribution of calcareous nannofossils through the Miocene. Miocene sediments were recovered at all five Leg 189 sites, and four of these sites were studied in detail to determine the calcareous nannofossil biostratigraphy. Hole 1168A, located on the western Tasmanian margin, contains a fairly continuous Miocene record and could be easily zoned using the Okada and Bukry (1980, doi:10.1016/0377-8398(80)90016-X) zonation. Analysis of sediments from Hole 1169A, located on the western South Tasman Rise, was not included in this study, as the recovered sediments were highly disturbed and unsuitable for further analysis (Shipboard Scientific Party, 2001c, doi:10.2973/odp.proc.ir.189.104.2001). Holes 1170A, 1171A, and 1171C are located on the South Tasman Rise south of the modern Subtropical Front (STF). They revealed incomplete Miocene sequences intersected by an early Miocene and late Miocene hiatus and could only be roughly zoned using the Okada and Bukry zonation. Similarly, Hole 1172A, located on the East Tasman Plateau, contains a Miocene sequence with a hiatus in the early Miocene and in the late Miocene and could only be roughly zoned using the Okada and Bukry (1980, doi:10.1016/0377-8398(80)90016-X) zonation. This study aims to improve calcareous nannofossil biostratigraphic resolution in this sector of the mid to high southern latitudes. This paper will present abundance, preservation, and stratigraphic distribution of calcareous nannofossils through the Miocene and focus mainly on biozonal assignment.

Strontium isotope ratios of fish teeth from ODP sites in the central North Pacific

Strontium isotopic compositions of ichthyoliths (microscopic fish remains) in deep-sea clays recovered from the North Pacific Ocean (ODP holes 885A, 886B, and 886C) are used to provide stratigraphic age control within these otherwise undatable sediments. Age control within the deep-sea clays is crucial for determining changes in sedimentation rates, and for calculating fluxes of chemical and mineral components to the sediments. The Sr isotopic ages are in excellent agreement with independent age datums from above (diatom ooze), below (basalt basement) and within (Cretaceous-Tertiary boundary) the clay deposit. The 87Sr/86Sr ratios of fish teeth from the top of the pelagic clay unit (0.7089891), indicate an Late Miocene age (5.8 Ma), as do radiolarian and diatom biostratigraphic ages in the overlying diatom ooze. The 87Sr/86Sr ratio (0.707887) is consistent with a Cretaceous-Tertiary boundary age, as identified by anomalously high iridium, shocked quartz, and sperules in Hole 886C. The 87Sr/86Sr ratios of pretreated fish teeth from the base of the clay unit are similar to Late Cretaceous seawater (0.707779-0.7075191), consistent with radiometric ages from the underlying basalt of 81 Ma. Calculation of sedimentation rates based on Sr isotopic ages from Hole 886C indicate an average sedimentation rate of 17.7 m/Myr in Unit II (diatom ooze), 0.55 m/Myr in Unit IIIa (pelagic clay), and 0.68 m/Myr in Unit IIIb (distal hydrothermal precipitates). The Sr isotopic ages indicate a period of greatly reduced sedimentation (or possible hiatus) between about 35 and 65 Ma (Eocene-Paleocene), with a linear sedimentation rate of only 0.04 m/Myr The calculated sedimentation rates are generally inversely proportional to cobalt accumulation rates and ichthyolith abundances. However, discrepancies between Sr isotope ages and cobalt accumulation ages of l0-15 Myr are evident, particularly in the middle of the clay unit IIIa (Oligocene-Paleocene).

Miocene dissolution facies and microfacies at Northwest Atlantic Deep Sea Drilling Project Site 93-603

Depth fluctuations of the lysocline and calcite compensation depth (CCD) through time were investigated at Deep Sea Drilling Project Site 603, Leg 93. The CCD fell during the middle Miocene at the onset of the Western Boundary Undercurrent, correlated with seismic Horizon X. Subsequently deposited units show fluctuations of the dissolution curve. Major changes in dissolution facies correspond with lithologic boundaries.

Age and strontium isotope composition for Cretaceous in DSDP Hole 74-525

Firm stratigraphic correlations are needed to evaluate the global significance of unconformity bounded units (sequences). We correlate the well-developed uppermost Campanian and Maestrichtian sequences of the New Jersey Coastal Plain to the geomagnetic polarity time scale (GPTS) by integrating Sr-isotopic stratigraphy and biostratigraphy. To do this, we developed a Maestrichtian (ca. 73-65 Ma) Sr-isotopic reference section at Deep Sea Drilling Project Hole 525A in the southeastern Atlantic Ocean. Maestrichtian strata can then be dated by measuring their 87Sr/86Sr composition, calibrating to the GPTS of S. C. Cande and D. V. Kent (1993, personal commun.), and using the equation Age (Ma) = 37326.894-52639.89 (87Sr/86Sr). Sr-stratigraphic resolution for the Maestrichtian is estimated as +-1.2 to +-2 m.y. At least two unconformity-bounded units comprise the uppermost Campanian to Maestrichtian strata in New Jersey. The lower one, the Marshalltown sequence, is assigned to calcareous nannofossil Zones CC20/21 (~NC19) and CC22b (~NC20). It ranges in age from ~74.1 to 69.9 Ma based on Sr-isotope age estimates. The overlying Navesink sequence is assigned to calcareous nannoplankton Zones CC25-26 (~NC21-23); it ranges in age from 69.3 to 65 Ma based on Sr-isotope age estimates. The upper part of this sequence, the Tinton Formation, has no calcareous planktonic control; Sr-isotopes provide an age estimate of 66 +- 1.2 Ma (latest Maestrichtian). Sequence boundaries at the base and the top of the Marshalltown sequence match boundaries elsewhere in the Atlantic Coastal Plain (Owens and Gohn, 1985) and the inferred global sea-level record of Haq et al. (1987); they support eustatic changes as the mechanism controlling depositional history of this sequence. However, the latest Maestrichtian record in New Jersey does not agree with Haq et al. (1987); we attribute this to correlation and time-scale differences near the Cretaceous/Paleogene boundary. High sedimentation rates in the latest Maestrichtian of New Jersey (Shrewsbury Member of the Red Bank Formation and the Tinton Formation) suggest tectonic uplift and/or rapid progradation during deposition of the highstand systems tract.

Sr stratigraphy and biostratigraphy for samples from DSDP Hole 32-305 and ODP Hole 123-766A

The strontium isotope ratios (87Sr/86Sr) of marine barite microcrystals separated from Cretaceous sedimentary deposits from Ocean Drilling Program and Deep Sea Drilling Project sites from the Pacific and Indian Oceans have been compared to the composite Sr isotope curve of McArthur et al. The barite in these cores accurately recorded the seawater 87Sr/86Sr ratio, thereby reaffirming the composite Cretaceous strontium curve. Moreover, marine barite is a more reliable recorder of 87Sr/86Sr than is carbonate in sedimentary deposits with high clay content, thereby providing an opportunity for Sr isotope stratigraphy and dating in carbonate-poor or diagenetically altered sections. We have used the barite-derived Sr isotope record to refine the biostratigraphic age models of the sites investigated.

Planktonic foraminifera stratigraphy of ODP Holes 198-1209C and 198-1211C

During Leg 198, the Cretaceous/Paleocene (K/P) boundary was recovered in a remarkable set of cores in nine separate holes at Sites 1209, 1210, 1211, and 1212 on the Southern High of Shatsky Rise. The boundary succession includes an uppermost Maastrichtian white to very pale orange, slightly indurated nannofossil ooze overlain by lowermost Paleocene grayish orange foraminiferal ooze. The boundary between the uppermost Maastrichtian and the lowermost Paleocene is clearly bioturbated. The contact surface is irregular, and pale orange burrows extend 10 cm into the white Maastrichtian ooze. Preliminary investigations conducted on board revealed that the deepest sections of these burrows yielded highly abundant, minute planktonic foraminiferal assemblages dominated by Guembelitria with rare Hedbergella holmdelensis and Hedbergella monmouthensis, possibly attributable to the lowermost Paleocene Zone P0. The substantial thickness of the uppermost Maastrichtian Micula prinsii (CC26) nannofossil Zone and the lowermost Danian Parvularugoglobigerina eugubina (Palpha) foraminiferal Zone suggested that the K/P boundary was rather expanded compared to the majority of deep-sea sites (see Bralower, Premoli Silva, Malone, et al., 2002, doi:10.2973/odp.proc.ir.198.2002). This data report concerns the planktonic foraminiferal biostratigraphy across the K/P boundary in Hole 1209C, the shallowest site (2387 m water depth), and in Hole 1211C, the deepest site (2907 m water depth), where the foraminiferal record across the boundary appeared to be best preserved.

Neogene planktonic foraminifera of DSDP Leg 41 holes

During Leg 41 Neogene sediments were recovered from five sites off northwest Africa. On the Sierra Leone Rise (Site 366), Neogene sediments consist of nanno oozes, nanno chalk, and calcareous clays 230 meters thick, resting conformably on the late Oligocene sediments. The common succession of zones occurs with two hiatuses. The lower gap corresponds to an interval around the lower/middle Miocene boundary (the Praeorbulina glomerosa and Orbulina suturalis-Globorotalia peri-pheroronda zones are absent) and the upper gap coincides with an interval around the middle/upper Miocene boundary (the Sphaeroidinellopsis sub-dehiscens-GIobigerina druryi, Globigerina nepenthes-Globorotalia siakensis and Globorotalia conlinuosa zones are missing). In the Cape Verde Basin (Site 367) deep-water Neogene turbidites (about 200-250 m thick) contain poor fauna of redeposited and sorted Cretaceous, Eocene, Oligocene, and Neogene species. On the Cape Verde Rise (Site 368) the Neogene section starts with slightly calcareous and non-calcareous clays with poor planktonic foraminifers of the lower Miocene. Later on this area was uplifted and clayey sediments have been replaced upsection in order by more shallow-water clayey nanno and nanno-foraminifer oozes and marls and pure calcareous oozes. In the middle Miocene, planktonic foraminifers are still not diverse, but since the level of the Globigerina nepenthes-Globorotalia siakensis Zone, almost all Neogene zones have been traced. The minimum thickness of the Neogene sediments is about 230 meters. On the continental slope off Spanish Sahara (Site 369) monotonous calcareous pelagic sediments of Neogene age (164 m thick) overlie the late Oligocene comformably, or with a small time gap. A set of zones beginning from the Globigerinoides primordis-Globorotaiia kugleri Zone up to the Globorotalia fohsi fohsi Zone has been revealed with a gap corresponding to the Globigerinita stainforthi and the Globigerinatella insueta-Globigerinoides irilobus zones. Above that follow sediments with heterogeneous microfauna which result from redeposition or mixing of sediments during drilling. The section ends with sediments of the late Miocene and lower Pliocene with abundant planktonic foraminifers. The latter are unconformably overlain by the Quaternary ooze. In the Morocco basin (Site 370) deep-water marls and calcareous clays of the lower Miocene contain poor assemblages of planktonic foraminifers. The middle and upper Miocene are represented by turbidites (alternation of nanno oozes, clays, siltstones, and sands) with heterogeneous microfauna. Total thickness of Neogene is up to 200 meters. In general the Neogene foraminifer microfauna of the area studied includes the majority of species which developed within the tropical-subtropical belt. The entire succession of the Miocene and Pliocene foraminifer zones occurs. The only exclusion is the Sphaeroidinellopsis subdehiscens-Globigerina druryi Zone of the middle Miocene. The distribution of species is shown on three tables. Comments are given for 47 species and subspecies of foraminifers (stratigraphic ranges, peculiarities of morphology, and ultrastructure of the shell wall).

Middle Miocene stable carbon and oxygen isotope record of ODP Holes 130-805B and 130-806B

Bulk carbon isotope records are an effective chemostratigraphic tool for the middle Miocene because of the large and systematic variation in first-order d13C signals. Bulk d13C measurements support the presence of a hiatus at 305 mbsf in Hole 805B (latest middle Miocene), provisionally located while on board ship using biostratigraphic and magnetostratigraphic events. Records at Holes 805B and 806B show the middle Miocene Monterey carbon isotope excursion although the record at Hole 806B is apparently more stratigraphically continuous. Detailed analysis of multispecies foraminiferal carbon isotope records during the middle Miocene ("Monterey excursion") segment at Hole 806B support the assertion that this carbon isotope excursion comprises mainly between-reservoir effects. The benthic d18O data increase after 15.3 Ma, which we suggest corresponds to the mid-Miocene cooling step/ice volume increase of other authors. Planktonic foraminiferal d18O evidence exists for steepening of the thermocline at 17.4 Ma. A second-order d13C excursion superimposed at 13.8 Ma on the first-order Monterey excursion is associated with a second-order negative d18O excursion.

Whole-rock oxygen and carbon isorope record across the Cretaceous/Tertiary boundary in ODP Hole 130-807C

Whole-rock d18O analyses of the Paleogene and Upper Cretaceous succession at Ocean Drilling Program Hole 807C suggest the presence of hiatuses between 876.95 and 894.47 mbsf and between 1138.82 and 1140.94 mbsf. The d13C data show a pronounced positive excursion between 1130 and 1180 mbsf that corresponds to the positive d13C values characteristic of the Paleocene. Despite the stratigraphic breaks in the section, the d18O data show a systematic increase between 1360 mbsf and the hiatus between 876.95 and 894.47 mbsf, which is consistent with previous suggestions of long-term climatic cooling through the Paleogene. The Cretaceous/Tertiary transition is apparently complete in this section and is of remarkable thickness. The expanded nature of this portion of the succession is probably the result of secondary depositional processes. High-resolution sampling across this boundary may reveal detailed structure of the d13C decline associated with the extinctions that mark the termination of the Cretaceous.