川西南上震旦统灯影组沉积期的暴露标志及其意义

对川西南乃至整个扬子区上震旦统灯影组的研究已有约70年的历史。以往的研究成果大致可归结为:(1)根据地层的岩石及生物特征将灯影组划分为:一段(下贫藻段)、二段(富藻层和上贫藻层)、三段、顶段(麦地坪段),其中一、二、三段的年代为晚震旦世,顶段为早寒武世;(2)从沉积学研究的角度出发,认为灯影组为潮坪环境的碳酸盐台地沉积;(3)通过生物地层学的研究,确定了大量的藻类、微古植物、小壳生物门类及其属种,以及与生物生存活动有关的生物遗迹化石。以往的研究成果无疑对我们分析、认识灯影组

THE EXPOSURE INDICATORS FORMED DURING THE DEPOSITION OF THE UPPER SINIAN DENGYING FORMATION IN SOUTHWESTERN SICHUAN AND THEIR SIGNIFICANCE

This paper deals with large amount of the subaerial exposure indicators recognized in the Upper Sinian Dengying Formation in southwestern Sichuan, including vadose pisolites, ruiniform houizons, tepee structures and palaeokarst sediments. The dolostones comprising these subaerial exposure indicators in the Dengying Formation have long been considered as oncolitic dolostone, snowflate dolostone, comb-crust algal dolostone and husklike algal dolostone. They are also interpreted as having formed in the tidal flat environments and as being of biological origin under the influence of sea water. The discovery of the subaerial exposure indicators leads us to the following new explanations.
(1)There must be some important depositional omissions in the Dengying Formation and subaerial exposure environments during the Sinian.
(2)The botryoidal dolostones may be interpreted to be of palaeokarst origin.
(3)Some so-called algal fossils or algae-related fossils such as oncolite, clotted stone and deformed stone are now recognized as a kind of secondary rock structures.
(4)According to the theory of sequence stratigraphy, two sequences and associated depositional systems tracts can be distinguished for the Upper Sinian strata: the one is from the Guanyinya Formation to the lower part of the second member of the Dengying Formation, the other is from the top of the former sequence to the top of the Maidiping Formation.