(Table T1) Biostratigraphy and distribution of Quaternary and Miocene calcareous nannofossils in ODP Site 188-1165

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During Ocean Drilling Program (ODP) Leg 188, piston and rotary cores were recovered at three southern Indian Ocean sites on the continental margin in Prydz Bay, Antarctica, in order to obtain a detailed sedimentary record reflecting Cenozoic Antarctic glacial history and paleoenvironments. Coring at continental rise Site 1165 revealed a relatively continuous, ~1000-m, lower Miocene to upper Pliocene section overlain by a thin Quaternary cover. No nannofossils were noted at shelf Site 1166, where a discontinuous, ~343-m section of Quaternary- to Late Cretaceous-age predominantly glacial marine diamictons was recovered. At slope Site 1167, ~447 m of clayey silty sands was recovered, where nannofossils are rare and sporadic but indicate Pleistocene age for at least the upper ~227 m there. This report focuses on data collected from Site 1165, where Neogene-Quaternary calcareous nannofossils are moderately to well preserved and sporadically present, but abundant in several intervals. Assemblages are characterized by low diversity with one or two dominant taxa. Mid- and low-latitude age-diagnostic marker species are absent. Nannofossil Zone CN15 and Subzones CN14b and CN13b-CN14a were identified in Pleistocene sediments based on the presence of Emiliania huxleyi, Pseudoemiliania lacunosa, and large Gephyrocapsa caribbeanica. Pliocene sediments are barren of nannofossils. Only general age and zonal assignments are possible for the relatively complete Miocene section (as dated by siliceous microfossils). The presence of Minylitha convallis in one sample permits the identification of upper Miocene Zones CN7-CN9. Cyclicargolithus floridanus is used to delineate presence of middle Miocene Zone CN5 and older. Assemblages in samples from the base of the section at Site 1165 are indicative of an early Miocene age (CN1-CN3). Overall, nannofossil assemblages are characterized by dominant Reticulofenestra spp., which are typical of high latitudes. Reticulofenestra perplexa and Reticulofenestra producta form nearly monospecific assemblages in a few intervals. M. convallis has not previously been reported in upper Miocene sediments from the Antarctic margin and likely indicate a brief warming event. Sporadic nannofossil abundance increases at deepwater (~3500 m) Site 1165 may be due to the following processes or combination of processes: (1) high nannofloral productivity in surface waters around Prydz Bay, possibly associated with warmer intervals; (2) periodic downward fluctuations in the calcium carbonate compensation depth, permitting less dissolution (possibly the result of the first condition); or (3) rapid transport and burial downslope.

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