Planktic Foraminiferal Biochronostratigraphy Of LW13-1-1 In Zhujiangkou Basin Northern South China Sea

This paper studies the biostratigraphic division of drilling LW13-1-1,located in Zhujiangkou Basin,northern South China Sea.LW13-1-1 is 1920m depth,199 samples are from debris,sampling interval is 8-16m.We identified from top to bottom,and focused on the LADs of planktonic foraminifera,while the FADs only have some reference value.The foraminifera fossils in LW13-1-1 are very abundant,some samples contain over 14000 fossils,they usually have high abundance,good preservation,and white tests.The planktonic foraminifera accounts for 63%-94%percent of all the foraminifera,including 16 genera 67 species,they are:Catapsydrax dissimilis、Globoquadrina binaiensis、Globigerina ciperoensis、Paragloborotalia kugleri、Globigerinoides primordius、Paragloborotalia opima,etc.Almost all of the biostratigraphers use the planktonic foraminiferal zonal scheme developed by Blow(1979)and Bolli&Saunders(1986).to classify strata in Zhujiangkou Basin,which is based mainly on FADs,Since the debris data,this zonal scheme led inaccuracy even mistakes of division.This research divided LW13-1-1 into:Miocene M3,M2,M1 three zones;Oligocene O7-O6,O5-O4,O3,O2 four zones.We identified Catapsydrax dissimilis in sample 1,that means the latest zone in LW13-1-1 is M3;Then we marked the tops of the M2 and M1 by the LAD of Globoquadrina binaiensis and LAD of Paragloborotalia kugleri.The top of the O7-O6 is marked by LAD of Globigerina euapertura;LAD of Paragloborotalia opima marked the top of the O5-O4,the bottom of O5-O4 zone about 10m above the LAD of Subbotina angiporoides;The top of O2 is marked by LAD of Turborotalia ampliapertura,and O3 is the "gap" zone between O2 and O4.Our result of stratigraphic division is made based on the zonal scheme developed by Wade et al.,(2011);Gradstein et al.,(2012);Luciani&Giusberti,(2014).The boundary of M1 and O7 at 2830m depth is also the boundary of Miocene and Oligocene,we marked it by LAD of Globigerina euapertura.