To unveil formation mechanism of key sequence boundaries of inland faulting basin and coal accumulation charac- teristics of coal seams in isochrohal stratigraphic framework, sequence stratigraphy, palaeogeographic recovery and other methods were used to research the sequence stratigraphy and coal accumulation in the example of Banding Basn in the west margin of Yangtze Platform, and the authors advanced a coal accumulation model of Faulting basin on the basis of accommo- dation space changes in the background of palaeogeography of sequence framework. The results show that： normal lacustrine regression and forced lacustrine regression are the main driving forces for the formation of sequence boundaries of Faulting ba- sin; basement subsidence is the main source of accommodation space of Faulting basin; and subsidence disequilibrium is the main cause for the difference in generation rate of accommodation space of Faulting basin. Coal accumulation in Faulting basin is obviously controlled by accommodation space changes in sequence framework and basin evolution. As Faulting basin evolves into depression basin, both subsidence rate of basin basement and generation rate of accommodation space decrease vertically, it appears as a progradational reverse-graded sedimentary sequence, coal accumulation in secondary sequence framework intensifies first and then weakens, and coal accumulation at the middle stage of highstand system tract is the best. During steady rifting period, minable coal seams were mostly developed in initial lacustrine flooding surface of fourth-order sequence and at the middle-late period of highstand system tract, and coal accumulation center lay in palaeogeographic unit of delta plain with moderate available accommodation space. During shrinking period, minable coal seams gradually migrated to the maximum lacustrine flooding surface and coal accumulation center lay in palaeographical unit of lacustrine with large available accommodation space.
LU JingSHAO Long-yiYANG Min-fangWANG HaoQING Kang-yangWANG Wei-chao
The sequence stratigraphy of the Jurassic coal measures of northwestern China has been studied based on data from outcrop and borehole sections. Because of the geological background and the diversity of basin types, such as isochronisms of coal seams and recognition of key sequence boundaries, it is rare to summarize and correlate sequence structure and framework. The types and recognition characteristics of the sequence boundaries of the Jurassic coal measures are revealed by comparing climatic characteristics, structural styles and the base level cycle. A total of five third-order sequences and 15 systems tracts have been subdivided and the sequence stratigraphic framework has been reconstructed confirming that the thick coals accumulated in the late stage of transgression system tracts of sequence I （SQ I） and sequence III （SQ III）. This idea is of important academic significance for instructing coal resources exploration, and enhancing geological effects of prospecting engineering. It is also of practical significance for guaranteeing construction of the large-scale coal production base in northwestern China, accelerating the westward development of the coal industry stratagem.
Based on an investigation of the Benxi-Shanxi formations in the southwestern Shandong province,we studied the forming mechanisms of key stratigraphic boundaries in an epicontinental basin and the coal-accumulating characteristics in the paleogeographic background of isochronous stratigraphic frameworks.In total,we sequenced three types of stratigraphic boundaries(i.e.,regional unconformities,the shifting surface of transgressions caused by basin basement subsidence,and fluvial erosional surfaces including exposed surfaces as well as correlative conformities,which are caused by forced regression)and proposed a model for coal-accumulation.The results show that in the high accommodation space of the barrier coast system in the lower Benxi-Taiyuan formations,the base level was higher than sedimentary boundaries,parasequences were bounded by a marine flooding surface and formed during the semi-cycle of base level falling that was influenced by high-frequency fluctuations of base level,and coal seams were thin with multistoried patterns.In this region,the coal accumulating center was located in the transitional zone of the barrier island and tidal-flat.In the low accommodation space of the fluvial delta in the upper Shanxi formation,the base level coincided with sedimentary boundaries,parasequences formed during the semi-cycle of base level rising were bounded by erosional surfaces and a marine flooding surface,and the coal accumulating center was located in the lower deltaic plain and interdistributary lacustrine environment.In this region,the surplus accommodation space was relatively high.
Lu JingShao LongyiYang MinfangWang HaoQing Kangyang
