Lysocline and CCD Fluctuations Record in Pelotas Basin During the Late Quaternary

Abstract

Planktonic foraminifera are good indicators of age and paleoclimatic variations, being widely used in relative dating, sedimentary basin analysis and stratigraphic correlations. In the lower slope of the Pelotas Basin there is a difficulty to develop paleoclimatic models due to the low quality of the fossil remains, which can be easily dissolved or remobilized, but the low preservation, when well quantified, can become a paleoceanographic proxy, since the non-preservation occurs due to measurable environmental changes. The goal of this study is to identify variations of the planktonic foraminifera fauna and the preservation of CaCO3 recorded in two cores in the Pelotas Basin and to relate them to the paleoceanographic changes occurred in the region. The cores were collected by the oceanographic expedition Geomar VII, on the lower slope of the Pelotas Basin. The samples were prepared with the standard methods for paleomicrontological analysis. The basic paleoclimatic zoning was elaborated based on the presence or absence of carbonate and the occurrence of species of the Globorotalia menardii plexus, whose disappearances and reappearances are related to climatic oscillations of glacial and interglacial intervals. Since there is no significant textural change in the facies, the two cores were subdivided into five intervals, based on the presence or absence of foraminifera (pelagic volume) and the presence or absence of the G menardii plexus. The intervals with good carbonate preservation were attributed to the Marine Isotopic Stages (MIS) 5 and 1. Carbonate-free intervals were attributed to an upward displacement of the lysocline and the Carbonate Compensation Depth (CCD). At the end of the Pleistocene, a downward migration of the lysocline and CCD was registered as a function of the transition from the MIS 2 to the MIS 1 or by the Pleistocene/Holocene boundary. Finally, the boundary of the Y and Z biozones was identified between 0.4 and 0.3 m in one core of the lower slope of the Pelotas Basin

Keywords

• planktonic foraminifera
• carbonate dissolution
• glacial
• interglacial
• Pleistocene
• Holocene