Middle Miocene warming event and planktonic foraminifera from the Kerguelen Plateau, southern Indian Ocean.

摘要

This study presents a planktonic foraminiferal record of the southern high-latitude ODP Site 744. Two foraminiferal data sets are discussed, a low-resolution data set (24.7–3.5 Ma) and a high-resolution data set (17.0–14.2 Ma). The faunal reconstructions include planktonic foraminiferal census data, faunal diversities, morphologic variations within selected planktonic bio-series, and oxygen and carbon stable isotopic signatures of particular taxa.; The major focus of this study is the mid-Miocene warming period; however, investigations of foraminiferal ecology and their water-depth distribution in particular, as well as paleoceanographic investigation of the entire Miocene Epoch is also conducted.; Among Miocene planktonic foraminifera at Site 744, deep-water taxa include the genera Catapsydrax, Gibborotalia and Turborotalita , while intermediate-water taxa are Globigerina and Tenuitella cf. jamesi. Shallow or intermediate to shallow water taxa include all remaining microperforates and Neogloboquadrina . Among morphologic features, test size is the one factor that best reflects water-depth habitats inferred according to the stable oxygen isotopic analyses. Morphologic diversification appears to be significantly greater among the deep-water dwellers, than in the remaining groups.; General climatic trends throughout the Miocene Epoch at Site 744 mirror global climatic changes. Both the late middle Miocene and the latest Miocene cooling episodes are well expressed by faunal changes and the presence of stratigraphic hiatuses. The mid-Miocene warm period extended between 17.0 and 14.3 Ma, but might extend as far back as 17.7 Ma. Sea surface temperatures were stable between 17.0 and 14.3 Ma at ∼5–6°C. The increase in faunal diversities and acceleration of evolutionary driven morphologic diversification within globorotaliids at ∼15.0 Ma is explained by an increase in seasonality of near-surface marine conditions. The reason for this increase remains uncertain. The presence of warm saline deep waters between 17.0 and 14.3 Ma is highly probable at the location analyzed, which points to this phenomenon as a potential causal factor for the significant warming of the southern Indian Ocean during the mid-Miocene time.