GEOCHEMICAL RECORDS OF THE CRETACEOUS LACUSTRINE TRANSGRESSIVE SEQUENCES AND THE MARINE-LAKE CONNECTING EVENTS IN THE SONGLIAO BASIN,NORTHEAST CHINA

Situated in the northeast of China (42-49°N,120-128°E),the Songliao Basin is a Cretaceous nearshore continental basin which has been affected significantly by the adja-cent marine transgression/regression.The authors have recognized in,this paper three main marine transgressive records on the maximum lacustrine transgressive sequences of the basin,which occurred separately during the deposition of the third and fourth members of the Lower Cretaceous Quantou Formation (Albian),the top of the second and third members of the Upper Cretaceous Qingshankou Formation (Turonian),and the first and second members of the Upper Cretaceous Nengjiang Formation (late Santonian-early Campanian).Besides fossil and mineralogical evidences,the marine transgressive geo-chemical records on the continental basin sequences are;(l)the sharp increase of the heav-ier isotopes of ³⁴S,¹⁸O and ¹³C,and the ratios of ⁸⁷Sr/⁸⁶Sr,even up to those of the syn-chronous normal marine sequences,and (2)the sharp increase of the geochemical indexes for salinity (Sr/Ba),alkalinity (Ca+Mg)/(Si+Al),reducibility (Ni+Zn)/Ga and sulfur flux (S-normalized concentration).