Core characteristics and preliminary stratigraphic classification of the New-5 Hole in Beijing Plain

Beijing Plain is composed of a suite of considerably thick alluvia and diluvia,and the establishment of the standard stratigraphic sequences of the whole plain is difficult because of the remarkable changes of lithology and lithofacies.With the rapid development of dating technology,the establishment of long dated sequences of sediments has become possible.Through observing the core of unconsolidated strata,this paper divided the core into 8 characteristic lithologic sections on the basis of the characteristics of sediment color,sedimentary environment,cycle and structure.Also,the result of paleomagnetism dating shows that 0-96.59 m of core is the Brunhes Normal Polarity Zone,96.59-246.79 m is the Matuyama Reversed Polarity Zone,and 246.79-413.64 m is the Gauss Normal Polarity Zone.By mean of pollen analysis and a comparison with the evolution history of Cenozoic climate in North China,the authors hold that the depth of 246.5 m can be regarded as Q/N boundary,the depth of 534.5 m is N/E boundary,and the depth of 803.4 m is E/K boundary.Based on the principle of magnetic and climatic stratigraphy with the aid of rock stratigraphy,the authors studied the new No.5 borehole and divided Cenozoic stratigraphic sequence into the late,middle and early Pleistocene,with Q/N boundary located at the depth of 248.4 m,N/E at the depth of 511.9 m,and E/K at the depth of 804.1 m.