滇东田坝黔西土城晚二叠世煤系上段沉积相及含煤性

晚二叠世煤系上段相当于长兴阶,是浅水三角洲复合体破坏阶段沉积。本区可分为上三角洲平原、上下三角洲过渡带、下三角洲平原三大相区及发育在三角洲体系外侧的坝湾体系。西部以河流作用为主,东部具河流和潮汐作用双重特征。形成于上下三角洲过渡带的煤层最具工业价值,其次是上三角洲平原,其它沉积类型的煤层一般不具工业价值。

FACIES AND COAL-BEARING CHARACTERS OF THE UPPERMEMBER OF THE LATE PERMIAN COAL MEASURES IN TIANBA(EASTERN YUNNAN ) AND TUCHENG( WESTERN GUIZHOU )

The studied area is situated in Tianba mining area ( Yangchang Syncline in Eastern Yunnan) and Tuchen mining area (Panxian Syncline in Western Guiz- ou ). The Late Permian coal measures, which is divided into three members ( tipper, middle and lower), is a shallow water delta complex in this area. The upper member of the coal measures, which is 80-120 metre thick, and compares to the Changxingian, is the main coal-bearing section representing the deposits of destructive period of the delta complex. A great quantities of facies analysis data shows that the sedimentary environments of this area belongs to a shallow water delta of invasion type behind a barried bar. Tianba area is covered by river sediments, in which the sand bodies are banded in shape along N-S or S-E directions. In Tuchen area, sedimentation is characterized by both river and tidal actions under the influence of alongshore current. The wave action is very weak. Sand bodies are lobe, bird's feet and mat in shapes mostly along S-E direction. The river inflows into the studied area from northwest and bifuractessin Tianba mining area, where the environment begins to change into upper delta plain from alluvial plain. There are always 1-2 distributary channels flowing by the Tianba Coal Mine, and after entering the Tuchen mining area, the environments begin to change into the upper-lower delta transitional zone till the lagoon-ba trier system. There are 4 rather stably developed distributary channels passing by each area ( Datianba, Tuchen Coal Mine, Songhe and Xiasuzuo ). These flu-viation-dominated sand bodies and the barrier bod ies constitute the sedimentary rramework of Changxingian in studied area. According to the vertical sequences of the facies and their spacial dispositions fhe studied area can be divided into three major facies belts: 1. Upper delta plain facies belt: It is located in the western mining area (Tianba) and dominated by distributary channel facies, flood plain facies and lake facies. Lake-delta deposits can be seen in the roof of coal seams K2+1, K0 No animal fossils are found, but plant fossils and siderite nodules are common, also there are some erect tree stem and plenty worm boring in this area. 2. Upper-lower delta transitional zone facies belt: its location is from Tuchen mine field 1-2 to Datianba. Predelta consists of the lagoon ( freshed lagoon ) facies, Delta-front consists of the mouth bar facies and distributary-tidal channel facies. Delta plain consists of the distributary channel, flood plain and ind tcrdistributary bay deposits. The prodelta is small in thickness, and intercalated with 3-5 marine-brackish water animal fossils layers in this belt. 3,Lower delta plain facies belt:It is located from the Songhe mine field to the east Datianba. Delta complex is similar to the upper-lower delta transitional zone belt in structure, but the prodelta deposits is relatively thick and intercalated with 5-10 marine-brackish water animal remains layers. On the outside of the delta system, marine animal remains are common and lagoon facies, tidal flat facies and barrier facies are developed. They belong to a barier-lagoon system deposits which are distributed from Hetaozhai to the east of the studied area, as well as the upper strata of lower delta plain facies belt Coal-bearing characters have a close relationship with palcogeographic environments in this area.In the upper delta plain facies belt, coal seams are mainly formed in the flood plain. Because of the plenty supplement of terigenous elastics,the depositional area under the state of depositional over-compensation and as well as the frequent crevassing and changing the way of rivers, coal seams are often scoured, so most coal seams vary largely in thickness and bifurcate, pinch-out frequently with high ash and low s ;lphur. During the coal-forming period of coal seams K2+1, K6-K7 and K9, crustal subsidence is relatively large so that relatively long stable environments are kept, rather thick and stable coal seams are formed. In the upper-lower de