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Calcareous nannofossil biostratigraphy and paleoceanography of late Cretaceous Indian Ocean
Abstract
Calcareous nannofossil biostratigraphy and the paleoclimatic/paleoceanographic histories of the late Cretaceous (Maastrichtian-late Campanian) from Ninetyeast Ridge (Sites 217 and 758A) and Mozambique Ridge (Site 249) in Indian Ocean were investigated based on the quantitative studies of calcareous nannofossils and down-core distribution patterns of several environmental variables. The cosmopolitan zonation scheme of Perch-Nielsen (1985) was used in sediment age-dating. Marker species occur continuously and relatively abundantly at three sites. Five zones (CC22 to CC26) were identified at Sites 217 and 758A. Site 249 contains five zones (CC19 to CC23). Diagenetic alteration and bottom current effects are minor or negligible in most of samples from these sites. Site 249 was characterized by relatively minor dissolution, low productivity, and unstable surface water conditions in Zones CC19 and CC20. Zones CC21 and CC22 (late Campanian) was characterized by stable surface water conditions. Bottom water became less corrosive from Zone CC19 to CC22 (early to late Campanian). The late Campanian at Sites 217 and 758A is characterized by lower species diversity and less stable surface water conditions than the Maastrichtian. The Maastrichtian at both sites shows greater species diversity and stable open oceanic conditions. At Site 217, the bottom water becomes less corrosive from Subzone CC22c to Subzone CC23a. At Site 758A, no changes of bottom water occur from Subzone CC22b to the 360 mbsf (upper part of CC23 and CC22c+CC22b). The corrosiveness of bottom water increases from Subzone CC23b to the top of Maastrichtian at both sites. Greater species diversity occurs during warm climatic conditions. The surface water temperature becomes warm from Zone CC19 to the middle of Zone CC22. Then, surface water temperatures cooled from the middle of Zone CC22 to Zone CC23 at Site 249. At Sites 217 and 758A, the early late Campanian was characterized by cool surface water temperatures compared to late late Campanian and Maastrichtian. The surface water temperatures cooled from Subzone CC23b through the Maastrichtian at three sites. This early Maastrichtian cooling event occurred globally by the comparison with several previous workers. Cooling started at (or near) the last appearance datum (LAD) of Aspidolithus parcus constrictus.
Subject Area
Geology|Paleontology|Oceanography
Recommended Citation
Shin, Im Chul, "Calcareous nannofossil biostratigraphy and paleoceanography of late Cretaceous Indian Ocean" (1994). ETD collection for University of Nebraska-Lincoln. AAI9516592.
https://digitalcommons.unl.edu/dissertations/AAI9516592