平顶山煤田山西组沉积体系与聚煤模式

DEPOSITIONAL SYSTEMS AND COAL ACCUMULATION OF SHANXI FORMATION IN PINGDINGSHAN COALFIELD, HENAN PROVINCE, CENTRAL CHINA

讨论了河南平顶山煤田山西组的沉积体系和聚煤模式。文中提出山西组下段形成于碎屑障壁海岸环境,山西组上段为三角洲沉积体系的进积部分。已组煤形成于障壁海岸沉积体系的上部,其发育过程明显受到基底沉积环境的控制。已组煤的聚煤作用特征是沉积基底地形高差、压实沉降率与泥炭堆积速率之间的平衡关系随海平面变化而变化。己组煤发育的气候条件可能属热带背景。

The Shanxi Formation of early Permian is approximately 100 meters thick in Pingding-shan Coalfield, western Henan Province. It is composed of sandstones, siltstones, mud-stones , and thick, widespread coals which are believed to be deposited in barrier-lagoon environments and delta environments. The analysis of the deposition is mainly based on depo-sitional sequences, sedimentary structures, palaeocurrent direction, geometry of depositional units and coal bodies, and coal quality.In the lower Shanxi Formation, the barrier-lagoon systems are developed, principal components recognized in it are tidal channel, tidal flat, lagoon, inlet-barrier sequence, and swamp. The upper Shanxi Formation is a progradation sequence of delta systems. Bay, mouth bar, subaqueous distributary channel, and interdistributary deposits are recognized. It is concluded that the basin filled by the barrier-lagoon systems and the delta systems is a brackish, medium-low wave energy, and low-medium tidal range bay.The thick, widespread coals developed in the Shanxi Formation consists of a major coal bed plus associated splits. A clear relationship exists between the geometries of the coal beds and the depositional units underlain the coals. On the inlet-barrier sequences, the coal bed is extremely thick (5 - 7m) and elongates parallel with the trend of the sandstone bodies. Landward, the coal bed splits into two beds both on the lagoon and tidal flat deposits by a thin transgressive depositional unit. In the areas where lagoonal deposits underlie the coals, the lower split is commonly thicker(4 - 5m) than the upper(1 -2m). Inverse situation (the upper is 3-4m, the lower is 1-2m) occurs in the areas where tidal flat deposits underlie the coals. A discontinuous and pinchout belt of the coals occurs on the inlet tidal channel deposits.It is suggested that the thick and widespread coals are developed on the platform of abandoned barrier-lagoon systems, except the discontinuous and pinchout belt where there is an active tidal channel coexisting with the coals.