A detailed biostratigraphic and statistical analysis of faunal assemblage of Ocean Drilling Program (ODP) sites from the middle latitude showed great variability and instability in the paleoclimatic conditions in the Indian Ocean during the Late Cretaceous (late Santonian to Maastrichtian).

Faunal composition, species diversity and equitability, species dissolution susceptibility, ratios of climatic index species and paleoclimatic curves were used to deduce paleoclimatic conditions as well as the construction of climatic curves. The paleoclimatic curves constructed showed particularly striking and similar trends for most of the sites studied.

Three paleoclimatic intervals namely, Interval 1 (late Santonian to early Campanian), Interval 2 (late Campanian to middle Maastrichtian), and Interval 3 (late Maastrichtian) can be identified in the paleoclimatic curves. Interval 1 (late Santonian to early Campanian) suggests a relatively warm paleoclimate as evidenced by an abundance of Tethyan and warm indices, high species diversity and equitability, and high positive values in the paleoclimatic curves; Interval 2 (late Campanian to middle Maastrichtian) indicates warm and cool fluctuations as depicted by the mixture of Tethyan and Austral species within the Transitional realm, varying abundances of warm and cool water species, fluctuations in the species diversity, equitability and climatic curve values. Within this interval, a pronounced negative peak is noted during the latest Campanian. This represents the coolest interval of the late Santonian to Maastrichtian as reflected by the preponderance of cool indices, low species diversity and equitability, and a high negative values in the paleoclimatic curve, and Interval 3 (late Maastrichtian) which marked another warm interval due to a shift in the dominance of the cool indices to warm indices, high species diversity and equitability and high positive values in the paleoclimatic curve. Such results imply that paleoclimatic conditions in the Indian Ocean during the late Santonian to maastrichtian are very unstable. This instability could be attributed to an interplay of several geologic and tectonic events (i.e. breakup of the southern Gondwanaland continents; seafloor spreading and subsidence between Antarctica, Australia, and New Zealand; northward drift of South America from the Antarctic Peninsula; global rise in the sea level during the middle Campanian; and opening, reemergence and closure of gateways) which occurred in the Southern Hemisphere before, during, and after the identified paleoclimatic intervals.

To summarize, the paleoclimatic conditions through the late Santonian to early Campanian from the sites under study fluctuated from warm-Tethyan (Holes 761B and 762C) during the late Santonian; warm-Transitional (Holes 758A, 761B and 762C) during early Campanian; Transitional with varying Tethyan and Austral influences (Holes 758A, 761B and 762C) during the late Campanian to middle Maastrichtian; and Tethys with Transitional influence (Holes 758A and 761B) and Transitional with pronounced Tethyan influence (Hole 762C) during the late Maastrichtian.

Key words: Late Cretaceous (late Santonian to Maastrichtian), paleoclimate, planktonic foraminifera, mid-latitude, Indian Ocean, Tethyan, Transitional, Austral.