The origin of early-mid Miocene pelagic brown and green claystone from
IODP Site U1503A in the South China Sea: implications to paleoclimate
and paleoceanography
Abstract
The marine pelagic brown claystone was widely recovered in the deep
South China Sea (SCS) by International Ocean Discovery Program (IODP)
Expedition 349, 367, 368 and 368X. The continuous deposition of brown
claystone in Miocene in the SCS may represent a special sedimentary
environment. IODP Site U1503A provides the ideal brown and green
claystone of the early-mid Miocene to study the origin of the red
coloring for sediments and their implications to the paleoclimate and
paleoceanography. In this paper, the reflectance a*, grain size, clay
minerals, major and trace elements, and Sr-Nd isotope analyses in brown
and green claystone from U1503A have been conducted to understand the
sedimentary condition and controlling factors of SCS marine brown
claystone. The results show that the sediments color transition was
caused by the variations of Fe (III) content. The provenance was
relatively stable and sediment was mainly supplied from South China and
Luzon. The source areas underwent strong chemical and physical
weathering since 17 Ma, which is related to Miocene Climatic Optimum
events. The data of redox proxies suggest that both brown and green
claystone were deposited in the oxic condition, while the sedimentary
environment of brown claystone was more oxidizing. We suggest this
difference in the redox condition was mainly controlled by the variation
of the oxygen-rich bottom current in the northern SCS. We attribute this
variation to the larger-scale deep-water circulation change in the
Antarctic and western Pacific due to glacial-deglacial cycle.