Eight sites and 16 holes (1207A and 1207B, 1208A, 1209A through 1209C, 1210A and 1210B, 1211A through 1211C, 1212A and 1212B, 1213A and 1213B, and 1214A) cored on Shatsky Rise recovered a virtually complete composite section ranging from upper Pleistocene to uppermost Tithonian representing 143 m.y. of geological history. A number of short intervals of lower and middle Miocene stratigraphy were not identified shipboard but are part of a fascinating regional sedimentation history which, grossly simplified, saw rapid deposition in the PliocenePleistocene, reduced sedimentation rates in the late Miocene, condensation and hiatuses through the middle Miocene to Oligocene, complete but relatively slow deposition in the Paleogene (almost entirely on the Southern High), and rapid deposition for much of Maastrichtian to latest Tithonian time. Chert-rich sediments dominate from the mid-Campanian to lowest recovered sediments (Figs. F21, F36, F42).
With the exception of Site 1214, all sites include complete and rapidly deposited PliocenePleistocene sections (814 m/m.y. sedimentation rates [SRs] and >1.0 g/cm2/k.y. mass accumulation rates [MARs]) in which the noncarbonate fraction forms a significant proportion (Fig. F43). A particularly expanded drift-deposit succession (200 m and 42.4 m/m.y. SR) was recovered at Site 1208, and this section should prove to be invaluable for timescale studies allowing the integration of calcareous and siliceous biostratigraphies, cyclostratigraphy, and paleomagnetic polarity and intensity records. The PliocenePleistocene at Site 1207 was particularly rich in siliceous microfossils most likely due to cool, productive waters, which were also responsible for the paucity of tropical-subtropical species of planktonic foraminifers at this location on the Northern High. The influx of warmer water planktonic foraminifers and reduction of biosiliceous plankton to the south at Site 1209 shows the paleobiogeographic and paleoceanographic importance of the Shatsky Rise drill sites near the path of the Kuroshio Current.
The lowermost Pliocene and uppermost Miocene sections show reduced sedimentation and mass accumulation rates (<1.0 g/cm2/k.y. MAR) and overlie intervals of condensed section and unconformities that include parts of the upper, middle, and lower Miocene, the Miocene/Oligocene boundary interval as well as the upper Oligocene at most sites (Figs. F21, F43). The amount of missing section is variably expressed across Shatsky Rise and, for example, at Sites 1209 and 1211, much of the Oligocene is present. Northern and Central High Sites 1207 and 1208 and Sites 1213 and 1214 on the Southern High are also missing all or most of the Paleogene and uppermost Cretaceous. However, Southern High Sites 1209, 1210, and 1211 recovered apparently complete lower Oligocene to Paleocene sections that were deposited relatively slowly (0.27.6 m/m.y. SR and <1.0 g/cm2/k.y. MAR) and dominated by carbonate. These sections include complete and lithologically well-expressed LPTM and Eocene/Oligocene boundary intervals and provided excellent records of biotic response to these periods of rapid environmental change. Preliminary shipboard analysis of calcareous nannofossils through the LPTM interval reveals striking changes in assemblages, in particular the decline and extinction of Fasciculithus within the event and the subsequent increase in Zygrhablithus bijugatus.
Four Southern High Sites (12091212) include complete and relatively expanded K/T boundary sections characterized by a lithological switch from white Maastrichtian ooze to a thin, pale orange basal Paleocene ooze (~812 cm) with pyrite specks overlain by a distinctive pure white ooze. The boundary is bioturbated but otherwise undisturbed. The paleontological succession across the boundary interval is well preserved and apparently complete with the recognition of nannofossil Zones CC26 and lowermost CP1 and foraminifer Zones uppermost KS31, P0 (within burrows) and P. Clay spherules were observed at all sites. The calcareous plankton record above the boundary is exceptionally good, and in particular, there is only limited Cretaceous nannofossil reworking and foraminiferal mixing. Both calcareous nannofossils and planktonic foraminifers reveal the classic succession of abrupt extinction, followed by assemblages dominated by "disaster" taxa and rare "survivor" taxa, succeeded by assemblages that record the gradual introduction of new Danian "recovery" taxa. These sections represent some of the best preserved and least disrupted deep sea records of this major extinction event and the following recovery and diversification of calcareous plankton.
At the same four sites (Sites 12091212), we also recovered thick, carbonate-dominated, rapidly deposited sections of pure white Maastrichtian to Campanian ooze (6.531.6 m/m.y. SR and 1.0 g/cm2/k.y. MAR). Calcareous plankton preservation was generally good throughout, and the sections will allow the integration of calcareous plankton biostratigraphies and the study of the response of these groups to the mid-Maastrichtian and other events that include environmental changes.
Below the upper Campanian, the occurrence and stratigraphy of the Cretaceous section is variable (Fig. F21). Good lower Campanian sections were recovered below major unconformities on the Northern and Central Highs but below this interval recovery was poor and dominated by chert. Paleontological material was often limited to scraping chalk and limestone from chert pieces. However, a relatively complete Campanian to Barremian section was cored at Site 1207 with remarkably uniform and high sedimentation rates (8.7 m/m.y. SR) and moderate recovery through the Aptian and Barremian. An outstanding record of OAE1a is well constrained by the plankton biostratigraphy.
Site 1213 yielded another thick Cretaceous section including a rapidly deposited Cenomanian to Albian succession and an Aptian section that includes OAE1a. Below this was an expanded section of Hauterivian to basal Berriasian/uppermost Tithonian. This Neocomian section yielded only few planktonic foraminifers but includes the FO in the Pacific of the tiny Hauterivian plankton foraminiferal ancestors (hedbergellids and globigerinelloidids) of the diverse Aptian assemblages. The section is rich in calcareous nannofossils and radiolarians, and the Berriasian in particular represents one of the best records of this time interval in the deep sea.
The consistent occurrence of pervasive chert lithologies from the Campanian to Tithonian across the range of sites drilled on Shatsky Rise is strongly suggestive of a long-term location beneath high-productivity surface waters related to a near paleoequator position during much of the Cretaceous. Preliminary paleontological observations support this hypothesis (e.g., very low diversity mid-Cretaceous planktonic foraminifer assemblages, indicative of high-productivity regimes, contrast strongly with peak diversities in the CampanianMaastrichtian as Shatsky Rise drifted out of the equatorial zone). There are also intriguing and conspicuous absences within the lower Cretaceous nannofossil assemblages, particularly the almost total lack of Nannoconus and Micrantholithus nannoliths, which are such important, often rock-forming components in coeval Tethyan and Atlantic sites. Again, the location beneath highly productive surface waters may prove to have been the controlling factor.
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