四川重庆凉风垭长兴期有孔虫动物群及微相

A STUDY OF THE CHANGXINGIAN FORAMINIFERA AND MICROFACIES IN LIANGFENGYA, CHONGQING, SICHUAN PROVINCE

Foraminifera, the most abundant and diverse group of the Changxing Forma-tion ( about 77m ) in Liangfengya, Chongqing,are represented by 8 genera, 35 spe-cies of fusulinids and 34 genera, 131 species of non-fusulinids, which have been determined under the present study. Many genera abundant in Wujiapingian Stage decreased considerably during the Changxingian Stage, while many genera uncommon in the Wujiapingian Stage became quite abundant in some beds of Changxingian Stage.In Changxingian there occurred also some new complicated forms.At the top of the Changxingian, however, these important forms disappeared and only a few survived into the Triassic.On the whole, the history of the foraminifera of Changxing Fm. is a comp-lete cycle of a special group developing from the beginning to prosperity and final extinction, which can be divided clearly into four phases, Another aspect exa-mined is the lithology of the Changxing Fm. which indicates that most strata were formed in normal shallow water and only a few beds ( mainly at the top ) resulted from a somewhat unusual condition. Variations in microfacies are shown by the amount of mud content increasing upward in the limestones and the quality of pre-servation of the specimens in the strata decreases successively.