SEDIMENTARY CHARACTERISTICS OF HOLOCENE COQUINITE FROM THE HAISHAN ISLAND OF EASTERN GUANGDONG PROVINCE AND ITS PETROLOGICAL IMPLICATIONS

There is an extensive area of Holocene carbonate rocks developed in the marine-deposition plain in the south of Haishan Island, eastern Guangdong Province. The carbonate rocks spread from the slope of inland hill to the sea, with a length of 3 km in E-W direction and 0.8 km in N-S direction, and the total area is almost 2.0 km².According to our field surveys as well as sedimentary environment and petrology analyses, the carbonate rock in the Haishan Island is defined as coquinite, rather than beachrock or chenier. The coquinite is well-compacted, well-indurated, firmly cemented, and chiefly composed of fossil debris that was mechanically sorted and has experienced transport and abrasion before deposition.Most of the fossil fragments are larger than 2.0 mm in size. Three ¹⁴C samples were taken from bottom to top on a standard cross section, and their ¹⁴C ages are 3 080±90, 1 920±75 and 1 330±60 aBP respectively. The ¹⁴C data and sedimentary features indicate that the coquinite in Haishan Island was formed in mid-late Holocene (about 4~1.5 ka) in a littoral to shallow-marine environment, corresponding to the mid-Holocene high stand. The coquinite distributed around the foot of the hill indicated the location of paleo-intertidal zone. The paleo-shoreline was confirmed by the distributions of coquinite in the paleo-intertidal zone and the paleo-sea notch.