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Biochronostratigraphy of the western equatorial Atlantic for the last 1.93 Ma

Abstract:

Planktonic foraminifera are an important biochronostratigraphic tool and one of the main proxies used in paleoceanographic studies. Here we present the integration of quantitative analyses of planktonic foraminifera biostratigraphy, planktonic and benthic foraminifera oxygen isotopic data, and planktonic foraminifera radiocarbon ages in a biochronostratigraphic framework for the last 1.93 Ma of the western equatorial Atlantic. The ages of the biostratigraphic events derived from our records are consistent with previous works except for the highest occurrences of Globigerinoidesella fistulosa (~1.82 Ma; MIS 66), Globigerinoides obliquus (~1.48 Ma; MIS 49), Globorotalia tosaensis (~1.05 Ma; MIS 31), and G. viola (~0.34 Ma; MIS 10). The largest difference in age (~1.13 Ma) was found for the highest occurrence of G. viola. In addition, we describe for the first time in the equatorial and western South Atlantic the oldest Pleistocene Globorotalia menardii disappearance (D) and reappearance (R) events D5 (~1.79 Ma; MIS 64), R5 (~1.68 Ma; MIS 60), D4 (~1.05 Ma; MIS 30) and R4 (~0.96 Ma; MIS 26). Our records present a consistent difference in the ages of G. menardii D and R events compared to the North and South Atlantic. While the onset of D events occurs initially at high latitudes and later in the equatorial region, the timing of R events exhibit the opposite trend. The oscillations in abundance of the complexes Pulleniatina and Globorotalia crassaformis together with the species Globorotalia truncatulinoides and Globoconella inflata allowed the subdivision of the last 1.93 Ma into 20 subzones, substantially improving the biochronostratigraphic resolution for the western equatorial Atlantic.