A muddy megaturbidite in the deep central South China Sea deposited ~350yrsBP

Abstract

In the central South China Sea basin below 4200 m water depth in an area of about 90,000 km 2 a mud turbidite was observed that is a few centimeters to several tens of centimeters thick and hence, represents a fairly large volume of 15 to 20 km 3 classifying the deposit as megaturbidite. The host sediment accumulated below CCD and the mud turbidite itself does not contain any carbonate. Nonetheless, emplacement time could be dated by the AMS C-14 method at ~ 350 yrs BP while burrowing organisms that colonized the mud turbidite shortly after deposition stored shells of planktic foraminifera in their burrows. The origin of the mud mass is unknown, but it can be inferred from the grain size at the base of the turbidite that decreases from SE to W and NW. Furthermore, towards its SE tip, the turbidite occurs in a somewhat shallower water depth. These observations and topographical considerations imply the NW margin of Borneo as a possible source area wherein mass movements are known to occur frequently. The mud turbidite is throughout fine-grained and rich in organic matter (~ 0.8% C org ). The thickness of the cover sediment reflects local variations of sedimentation rate within the central South China Sea basin. • A ~ 15–20 km 3 muddy turbidite occurs in the central South China Sea below 4200 m. • Below CCD, colonizing animals stored shells in burrows allowing C-14 age dating. • At the time of deposition a high energy event has been recorded for the South China Sea. • Cover sediment reflects sedimentation pattern in an otherwise hardly datable deposits.