Sequence stratigraphy of Cambrian in Western Hills,Beijing

For the purpose of obtaining more comprehensive geological knowledge and providing contrast to other areas,the authors studied the Cambrian strata exposed in the Western Hill area in the aspects of sequence stratigraphy and sedimentology.In the Western Hills,Cambrian strata are composed of many carbonate rock types comprising various kinds of limestone and dolomite.In accordance with the principles of sequence stratigraphy and the working methods,combined with sequence characteristics of interfaces between the Cambrian strata,the authors defined sixteen major third-order depositional sequences:SQ1-SQ3 for typeⅠand much more(SQ4-SQ16) for typeⅡ.The Cambrian sedimentary strata in this area are typical sediments of stable platform.As Cambrian strata were deposited in the littoral area characterized by gentle topography and stable tectonic subsidence,deep valleys and other deep-cut phenomena are not very obvious,and deposits of lowstand system tracts(LST)or shelf marginal system tracts(SMST)are not found in all sequences.