17. Synopsis of Cretaceous Planktonic Foraminifera from the Indian Ocean
- J.R. Heirtzler,
- H.M. Bolli,
- T.A. Davies,
- J.B. Saunders and
- J.G. Sclater
Published Online: 23 MAR 2013
Copyright © 1977 by the American Geophysical Union.
Indian Ocean Geology and Biostratigraphy
How to Cite
Herb, R. and Scheibnerova, V. (1977) Synopsis of Cretaceous Planktonic Foraminifera from the Indian Ocean, in Indian Ocean Geology and Biostratigraphy (eds J.R. Heirtzler, H.M. Bolli, T.A. Davies, J.B. Saunders and J.G. Sclater), American Geophysical Union, Washington, D. C.. doi: 10.1029/SP009p0399
- Published Online: 23 MAR 2013
- Published Print: 1 JAN 1977
Print ISBN: 9780875902081
Online ISBN: 9781118664919
The oldest planktonic foraminifera in cores from the Indian Ocean are of Barremian or questionable Early Aptian age and occur at DSDP site 249 on the Mozambique Ridge. Typical Aptian planktonic foraminifera, however, have not been found in the Indian Ocean. Albian assemblages, recovered at five sites in the eastern Indian Ocean, contain a few species with the genus Hedbergella being predominant, and Ticinella, Praeglobotruncana and Rotalipora being very rare. Cenomanian planktonic foraminifera have so far been recovered only from the Naturaliste Plateau and the Kerguelen Plateau. Assemblages of this age contain a few species with slightly more species being present in samples from the Kerguelen Plateau than in the former area. The species diversity of the Indian Ocean assemblages increased during later periods of the Late Cretaceous, but important tropical index forms are still missing; notably in the Coniacian to Santonian interval of the Naturaliste Plateau. Globigerine-shaped and heterohelicid taxa dominate over double-keeled Globotruncana. These features are typical for the non-tropical, cool Austral biogeoprovince of the Cretaceous. Terminal Cretaceous sediments were penetrated on the northern Ninetyeast Ridge and on the Mozambique Ridge. Despite their content in good index species, they are still of a similar Austral or transitional aspect, however with greater Tethyan affinities than earlier in the Cretaceous, especially in the Late Maastrichtian of the Ninetyeast Ridge, where a tropical assemblage occurs for the first time as effect of the rapid northward shift of the Indian plate.
Based on the distributional patterns of benthonic and planktonic foraminifera an evaluation of depositional water depth for different periods of the Cretaceous in the Eastern Indian Ocean is attempted. Deep open basin facies can be assumed for the Albian of the Eastern Indian Ocean at some DSDP-sites (256, 257 and upper part of 260), while others (sites 258, lower part of 260, and 263) show shallow water assemblages. An increase of water depth and deposition below the CaCO3 compensation depth prevailed in the basins of the eastern Indian Ocean during the Late Cretaceous, whereas on the Naturaliste Plateau and on the Broken Ridge shallow open marine conditions are indicated by planktonic and benthonic foraminifera during earlier parts of the Late Cretaceous, similar to what can be observed in the Perth basin of Western Australia.
The biostratigraphic significance of the Austral planktonic assemblages is discussed. The low species diversity, combined with the lack of many index species known from tropical areas, is a major difficulty for precise age determinations in many cases, particularly with respect to the Albian-Cenomanian boundary and a subdivision of the Albian and Cenomanian. In the Late Cretaceous the lack or rare occurrence of index forms, such as Globotruncana concavata or species of the G. fornicata-group makes precise age determinations equally difficult.