Middle and Late Cretaceous History of the Indian Ocean
Date of this Version
By the Late Jurassic the Somali and Mozambique basins opened to form a restricted west Indian Ocean and rifting of fragments from Gondwana formed the Argo Basin to the north. The east Indian Ocean opened during the Early Cretaceous when India separated from Australo-Antarctica to form the Wharton Basin where hotspot activity formed the Naturaliste Plateau and Kerguelen Plateau-Broken Ridge (KPBR). By the Albian, east and west Indian Oceans were small arms of the Tethys. Fluvio-deltaic systems developed on continental margins. KPBR was a volcanic archipelago forested by a mild and wet climate-loving climax forest of podocarpaceaen conifers with an understory of tree and seed ferns. Elevated kaolinite at several sites and gibbsite on Kerguelen Plateau further indicate an Albian warming. A mid-Cretaceous marine transgression marked by widespread black shale/radiolarite deposition also brought marine sediment to western Australian basins. The warm climate persisted through the Cenomanian as reefs formed on the southeast margin of India, but began to decline during the Turonian as kaolinite disappeared from southern sites. The Wharton Basin sank to sub-CCD abyssal depths by this time. The western KPBR formed a shallow shelf in a poorly circulated region where thick greensands accumulated over the slowly subsiding Kerguelen Plateau. During the Turonian abundant ash and tuff accumulated at Broken Ridge sites prior to the onset of Ninetyeast Ridge hotspot activity as India drifted northward. A second major Cretaceous transgression occurred in the Santonian and allowed chalk deposition over marginal western Australia. Beginning in the Santonian and persisting into the Paleocene chert-rich nannofossil chalk formed on the elevated plateaus, indicating upwelling. Circulation over KPBR improved and a diverse bryozoan-dominated benthonic fauna and flora developed on KPBR. The mid-Campanian is marked by a nearly ocean-wide disconformity which corresponds to the development of marked provinciality of the calcareous plankton. This divergence of tropical and austral plankton communities continues through the upper Campanian and most of the Maestrichtian and probably resulted from the onset of shallow circum-Antarctic circulation. Subsidence of Ninetyeast Ridge began during the late Campanian, as shallow-water carbonates, some dolomitized by seepage refluxion, became buried by deep-water pelagic carbonates. Another transgression in the late Maestrichtian brought pelagic marls to southwest Australian Perth Basin.