广西合山马滩地区晚二叠世沉积环境的研究

该区晚二叠世分合山和大隆两个组。文章从岩石特征,沉积构造、古生物化石群组和遗迹化石方面论述了其沉积环境特征。合山组在桂中地区为含煤岩系,煤层顶底板是灰岩和硅质岩。古生物化石较单一,以裸松藻科为主,有少量有孔虫、(竹蜓)、介形虫和腕足类海百合的碎屑。遗迹化石以居住潜穴Skolithos为主。研究证明,合山组属低能潮坪环境。大隆组在该区出露不足10m,以凝灰岩、硅质岩和硅质泥岩为主。浊流沉积特征明显以鲍马层序中A.C.E段最为发育。并在硅质泥岩中,发现半深水遗迹化石Chondrites,Planolites和Rind Burrow等,说明大隆组属深水或半深水沉积环境。合山与大隆两组的接触界线不清,尚待研究。

THE DEPOSITIONAL ENVIRONMENT OF THE LATE PERMIAN IN THE MATAN AREA, HESHAN COUNTY, GUANGXI PROVINCE

The characteristics of depositional environment of Heshan and Dalong Formations, Late Permian in the Matan area, Heshan county, are studied in this paper based on petrological, fos-sil-petrological and trace fossil data.The Heshan Formation is made up basically ef limestones interlayered with four beds of coal. It’s sedimentological characteristics are as follows:1. Horizontalbbedding typifying low-energy and quiet envirnoment, and wavy bedding formed under tide action.2. Micro-paleobiota with abundant Gymnocodium living in the lower part of intertidal subtidal zone. There are some ostracades and forminifera living in the confined lows with low energy and abnormal salinity of intertidal zone. There is no evidence about the biota living in normal shallow sea.3. The biota of normal shallow sea are located brequently on the bedding surface or concentrated as bioclastic interlayers They are products brought into tidal flats by ride current or storm.4. Various trace fossils were found in many layers. Among them skolithos, small planli-tes and phycodes(P)used to live in intersubtidal shallow water. 5. On some bedding surfaces there exists bird-eye and dry cracking-like structure formed in deposits of showt term exposition.6. All the rocks studied can be classified as micritelimestone.On the basis of the above characteristics it is thought that the Heshan Formation was formed in tidal flat with intertidal and subtidal shallow water environment. It was connected with the open sea during transgression, spring tide or violent storm.Dalong Formation is a set of strata consisting of pyroclastic rocks. Turbidite consisted of pyroclastics are developed quite well:1. There are distinct Bouma Sequences. The divisions A. C. and E were especially well developed. Organisms such as Ammonite, siliceous radiolaria and siliceous spicule occur in division E of the Bouma Sequence.2. There also exist trace fossils of deep qwater environment such as Chondrites, big pla-nolites and Rind Burrow.