Optically Stimulated Luminescence Chronology For HJ003 Coreof Jianghan Basin

The Jianghan Plain,suited in Central China,is a typical floodplain of the middle Yangtze and Hanjiang River composed of many interchannel depressions,the first unloading basin after the Yangtze River goes out of the Three Gorges.Quarternary sediments of plain areas are results of alternate fluvial and lacustrine environment,therefore,the sediments are good geologic body in the research on climate and environment records.A lot of researches has been carried out here and they mainly focused on the stratigraphy classification,rivers and lakes evolution,new tectonic movements and climate cycle.However,a common drawback of those researches is the lack of reliable and complete chronology data.So it is important to establish a high resolution chronostratigraphic frame.With the development of optical stimulated luminescence(OSL)methods in dating of Quaternary sediments,OSL dating has been successfully applied in the Quaternary sediments,such as glaciers,rivers,lakes,loess,deserts,etc.The HJ003 borehole in Tianmen from the north Jianghan Plain was chosen for the case study,14 samples were collected from it.According to the results of the OSL age and the changing of deposition rate,we get the following conclusions:1.The OSL age of HJ003 hole at depth 8.90 m is 5.23±0.34 ka and 9.50 m is 25.02±1.68 ka,the sedimentary facies change from yellow clay to greenish gray clay abruptly.We have preliminarily consider that Holocene sediments have been recorded in the HJ003 hole since 5.23±0.34 ka,and the minimum thickness is 8.90 m.2.There was an obvious change in the deposition rate since the 80 ka,the sedimentary model of the Jianghan Plain responds well to the process of the Quaternary climate cycle and the sea level fluctuation.During the period of 71.64±4.77 ka to 82.50 ±7.67 ka,the deposition rate is the maximum since 80 ka,which corresponds to the transition phase between MIS 4 and MIS 5a.The climate is warm and humid,with slightly higher temperature and precipitation,and its sea level is slightly higher than that of today.During this period,the sedimentation is stable,and the depositional environment is dominated by shallow lacustrine deposits,with continuous and rapid deposition rate.From 25.02±1.68 to 71.64 ±4.77 ka,the deposition rate is 0.066m/ka,which related to global sea-level changes.In the LGM,the global sea level fell and the ancient coastline extended to the sea.The sea level of the East China Sea was about 120 m lower than that of the present.The ancient Yangtze River datum declined and formed the ancient river trough in the LGM.At this time,the Jianghan Plain was difficult to deposit.The study shows that many research hole appear sedimentary discontinuity,which is a typical erosion stage.However,HJ003 does not show the feature,which may be enslaved to the location of boreholes,and the deposition rate suggests that it may still be affected by the LGM sea level plummeting,but only slightly.The HJ003 hole is strongly influenced by human factors,so it does not record the data since Holocene.Combined with previous studies,it has been shown that the increase of rainfall in the post glacial,and the sea level rises rapidly.The Jianghan Plain responds to the change of sea level,and there is a rich sediment and faster deposition rate.