Ecostratigraphic Datums and Sequence Stratigraphy: Application to the Marine Quaternary

Abstract

The marine Quaternary is characterized by few evolutionary appearances and extinctions of planktonic foraminifera. Because climatic fluctuations are a fundamental characteristic of Pleistocene, however, better stratigraphic resolution of the marine Quaternary can be gained by the establishment of biozones based on climatically controlled foraminiferal assemblages. Utilizing relative abundances of the warm-water Globorotalia menardii complex and temperature-water G. inflata, supplemented by left- and right-coiling varieties of G. truncatulinoides, the authors have subdivided the prezone-W Pleistocene of the tropical Atlantic (Core V16-205), Caribbean Sea (DSDP Core 502B), and northeast Gulf of Mexico (ODP Core 625B, Eureka Core E67-135) into 17 subzones, each with an average duration of {approximately}100,000 yrs. The subzones appear to reflect water mass shifts and disjunct species distributions resulting from expansion and contraction of northern hemisphere ice sheets. Hence, subzonal boundaries should also reflect change in eustatic sea level and sequence boundaries. Indeed, graphic correlation of the subzones, along with biostratigraphic markers and paleomagnetic and oxygen isotope datums, reveals changes in sediment accumulation rate (especially on the continental slope) and missing section, as well as intervals of deformation (core breaks) that affect the occurrence of subzonal boundaries and biostratigraphic markers.