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Sedimentation rates from calcareous nannofossil and planktonic foraminifera biostratigraphy in the Andaman Sea, northern Bay of Bengal, and eastern Arabian Sea

Abstract:

In this study we determined calcareous nannofossil and planktonic foraminifera events in sediments recovered during the 2006 Indian National Gas Hydrate Program (NGHP) Expedition-01. Selected bioevents permitted the assignment of orbitally calibrated ages, derivative sedimentation rate estimates, and identification of sedimentary discontinuities. In the Andaman Sea at Hole NGHP-01-17A, a late Miocene to recent record was recovered, but with a significant hiatus during the latest Miocene and Pliocene. Sedimentation rates here vary from 50m/Myr during the Pleistocene to 130m/Myr for the late Miocene. In the northern Bay of Bengal at Hole NGHP-01-19A the base of the cored record also reaches the late Miocene and extends to recent, but the same hiatus, missing the Pliocene, is present at this hole. a. The Early Pleistocene at Hole NGHP-1-19A shows sensible variation in sedimentation rates ranging between 130m/Myr and 10m/Myr during the last 0.5Ma. For the late Miocene the sedimentation rate was ca. 50m/Myr. In the western Bay of Bengal at Hole NGHP-01-10B/D, calcareous nannofossils were sparse and only foraminifera datums are available. The base of the section is latest Early Pliocene to Late Pliocene, and the majority of the record is considered younger than Late Pliocene. Due to the scarcity of calcareous nannofossils and the few foraminifera datums, sedimentation rates were not determined here. However, Hole NGHP-01-16A, in the same region, recorded the highest occurrence of Pseudoemiliania lacunosa, an event that confirms a Pleistocene age, allowing us to estimate a sedimentation rate between 110m/Myr and 450m/Myr. Along the western peninsular Indian margin at Hole NGHP-01-01Aa continuous record from the Holocene to the early Oligocene indicates sedimentation rates of ca. 25m/Myruntil the middle Miocene, and a sensible reduction downward, reaching 4m/Myr in the early Miocene to the early Oligocene. No hiatuses were observed. The large changes in sedimentation rates observed in these cores reflect long timescale changes in the environment likely induced by changes in the strength of the Indian monsoon system.