A new method for the U–Th dating of a carbonate chimney deposited during the last glaciation in the northern Okinawa Trough, East China Sea
Journal
Quaternary Geochronology
Journal Volume
66
Date Issued
2021
Author(s)
Wang L et al.
Abstract
Authigenic carbonates from cold seep systems, such as chimney and crust carbonate deposits, are important archives of biogeochemical processes associated with the migration and seepage of methane-rich fluids and seepages on the seafloor. Here we use a new U–Th dating method to precisely determine the ages of the authigenic carbonates of a chimney in the Okinawa Trough (OT), East China Sea. The method uses a series of heavy liquids (HL, a mixture of tribromomethane and alcohol with a density of 2.71–2.80 g/cm3) to separate subsamples of carbonate contaminated by detrital material. The contents of relevant elements (Al, Rb, Zr, Nb, and rare earth elements) of the subsamples reveal that the separation of the mineral phase was successful. Five samples from along the radius of a well-structured chimney (PES-1) from station D2-5 in the OT were analyzed and yielded U–Th ages of 28.8 ± 0.4 ka, 26.1 ± 0.5 ka, 24.4 ± 0.7 ka, 22.5 ± 0.6 ka and 20.1 ± 0.6 ka, from the exterior to the interior of the chimney section, and AMS 14C dating of the same samples produced the similar results. The agreement between the 230Th/U and AMS 14C ages suggests that the application of heavy liquid methods in U–Th dating can be very successful, and it reduces the influence of detrital contamination. Therefore, the approach has a great potential space for studying the evolutionary history of authigenic carbonates in cold seep systems. Moreover, the new 230Th/U ages show that the carbonate chimney was formed during the Last Glacial Maximum (LGM), which corresponding to the large sea-level fall in the East China Sea. Together with information on biogeochemical processes, the results will provide valuable geochronological information for the future study of active fluid venting on continental margins. ? 2021
Subjects
AMS 14C dates
Carbonate chimney
MC-ICPMS 230Th/U dates
Methane seep
Okinawa Trough
biogeochemistry
carbonate sediment
hydrocarbon seep
last glaciation
methane
radiocarbon dating
thorium
uranium series dating
East China Sea
Pacific Ocean
Type
journal article