Ascidian spicules of Quaternary sediments from the lower slope of the Campos Basin (Brazil)

摘要

Piston core GL-77 was collected in the lower slope of the northern Campos Basin, Brazil, and consists essentially of muds that have been deposited in turbiditic currents over the last 130 ka, at least, which corresponds to the Upper Pleistocene-Holocene interval. The identified ascidian spicules belong to the Didemnidae Family and are represented by species Micrascidites vulgaris, Bonetia brevis, Rigaudia andtiradiata and Monniotia fasciculata. These species have irregular abundance and distribution, with Micrascidites vulgaris being the most common. Their occurrence is interpreted as resulting from transport to the depositional site in response to climate fluctuations (glacial and interglacial periods). The transport of ascidian spicules from a shallow-water sea is supported by the presence of terrestrial organic matter, mainly phytoclasts, sporomorphs and microphytoplankton, which were transported to the slope by the river systems. The results found in this study show that the relative frequency distribution pattern of didemnid spicules is a useful tool for monitoring sediment transport in the slope.