Location, intervals and thickness of Cretaceous sections in Indian Ocean DSDP and ODP sites (Table 2)

The Indian Ocean covers approximately 73.5 * 10**6 km**3 from 25°N to 67°S and from 20° to 120°E. Several legs of the Deep Sea Drilling Project (DSDP) and the Ocean Drilling Program (ODP) have operated in its waters, many penetrating the Cretaceous. Most of the scientific drill sites are DSDP related and thus pre-dated modern biostratigraphic conventions. Foraminifers and calcareous nannoplankton were by far the dominant fossil groups studied in the earlier work, supplemented occasionally by studies of other fossil groups, The results of the Ocean Drilling Project phase are yet too young to be fully integrated but have been based on a broader range of techniques and fossil groups. During most of the Cretaceous, the proto-Indian Ocean basin lay in middle to high latitudes. Thus, it is unrealistic to expect successful routine application of low-latitude zonations. No planktonic foraminifer zonal scheme has been developed for the Indian Ocean basin for several reasons. There are no sections with complete or even significant partial sections to allow development of such a zonation. Carbonate compensation depth (CCD) effects have been marked in most sections, and significant intervals are devoid of planktonic foraminifers. The Indian Ocean now covers a great latitudinal range from tropics to polar regions and, at first glance, no scheme can be expected to be applicable over that entire range. In the Cretaceous the area was much smaller, though expanding progressively, and the paleolatitude range was quite small. Calcareous nannoplankton have proved valuable in dating Indian Ocean Cretaceous sediments and have, perhaps in contrast with the foraminifers, been consistently a more reliable means of applying zonal schemes developed elsewhere. For the Albian-Aptian, zonations based on well-known benthic foraminifer lineages (Scheibnerova, 1974) have been useful when nothing else was available or effective. Palynology has been used little, but where used, has proved excellent. It has the added value of providing valuable information on nearby terrestrial vegetation as the fossils were resistant to dissolution. Normally, when different fossil groups have been applied to a section, the results have been compatible or compatible to an acceptable degree. There are a few instances where incompatibility is noteworthy, and Site 263 is a classic example, as even two calcareous nannoplankton studies show irreconcilable differences here. All groups gave different results, but one benthic foraminifer analysis agreed with one calcareous nannoplankton study.

(Table 1) Sedimentation rates in the Reykjanes rift near 58° for time intervals 0-11 ka, 11-18 ka, and 18-21 ka

Sedimentation rates in the Reykjanes rift near 58°N have been measured on the base of radiocarbon datings of bottom sediments collected during Cruise 4 of R/V Akademik Mstislav Keldysh.