Abstract:

Continental basins of the Late Cretaceous in southeast China are characterized by red coarse terrestrial clastic rocks. Fabric analysis of gravels was carried out at 19 outcrops of the Upper Cretaceous Hekou Formation of Fuzhou-Chongren basin in western Gan-Hang tectonic belt, and the composition, particle size, shape and preferred orientations of gravels were also studied in detail. As a whole, the gravel deposits are featured by complex composition, poor sorting, subangular to subrounded particles and low degree of weathering. Combined with lithologic features of bedrocks, the source, genesis and formation conditions of gravels at different areas are analyzed and discussed. The research result shows that the gravels of the Late Cretaceous Hekou Formation were the products of alluvial fan and braided river facies in a semiarid to arid climate condition with multi-source and rapid accumulation. The composition assemblages of gravels from different areas of the basin are obviously different, reflecting complex provenance condition around the basin. Based on the  characteristics of bedrock strata and the rose diagrams of the maximum flat planes (ab-planes) of gravels, the sediment source was inferred to come mainly from northeastern, northern, northwestern and southeastern parts of the basin during the sedimentation period of Hekou Formation.

Key words: fabric analysis of gravel, provenance, continental red bed, Upper Cretaceous, Gan-Hang tectonic belt, Fuzhou-Chongren basin