201 / 2019-06-17 17:04:24

Sedimentary Characteristics of alluvial fan outcrop: Late Cretaceous, Wangshi Group in Zhebu Village, Jiaolai Basin, Shandong, Eastern China

alluvial fan,sedimentary characteristics,Cretaceous,Jiaolai basin,outcrop

Abstract：The characteristics of alluvial fan is extremely complicated and the particle diameter, scale and spatial superimposed morphology of the sediment vary greatly in both lateral and vertical directions. It is of great theoretical and practical significance to strengthen the study of alluvial fan. The field outcrop has an intuitive advantage for the study of sedimentary systems. The outcrop section of Zhebu Village, located in the north of Jiaolai Basin, is more than 550 meters in lengths and develops alluvial fan deposits of the Xingezhuang formation at the top of the Late Cretaceous Wangshi Group. The geometry of sandy conglomerate body in different locations is clarified through the study of lithofacies, lithofacies associations and spatial superimposed morphology of sandy conglomerate body.
Total of 11 lithofacies types are established in the outcrop of Zhebu Village, which are classified into conglomerate facies, sandstone facies and mudstone facies according to lithology. The conglomerate facies is the main lithofacies type in the study area, and 7 types of conglomerate facies are classified according to the propping ways and sedimentary structure. The non-sedimentary structure and unsorted conglomerate are classified into disorganized clast-support conglomerates (Gcd), disorganized sand-support conglomerates (Gsd) and disorganized mud-support conglomerates (Gmd). The conglomerate facies with sedimentary structures are classified into imbricated conglomerates (Gi), trough cross-bedding conglomerates (Gt), planar cross-bedding conglomerates (Gp), graded bedding conglomerates (Gg). The sandstone facies are classified into massive sandstone (Sm), parallel-bedding sandstone (Sp), trough cross-bedding sandstone (St). The mudstone facies develops pebbly mudstone facies (Mp).
3-D digital outcrop geological model of Zhebu is built based on the unmanned aerial vehicle (UAV) oblique photography and the full-section continuous comparison and characterization of the outcrop of Zhebu are conducted by combining the field photos and measurements. The Late Cretaceous alluvial fan of the Zhebu, Jiaolai Basin, developed(from north to south) lower fan, mid fan and upper fan deposits, with the color gradually changing from grayish yellow to red purple, which is indicated to be a prograding sequence. The upper fan develops debris flow intermixed mud-sand-rock showing poor to moderate sorting that the thin to middle layer sandy conglomerate bodies are isolated in. The mid fan, which is composed of sandy conglomerate and sandstone, mainly develops braided channels with scour-and-fill structure. The lower fan sediments are dominated by sandstone and gravel mudstone with less gravel. With characterizing the morphological and overlapping relationship of sandy conglomerate, combining with the analysis of glunite genetic structure, the five types of geometry of sandy conglomerate body are summarized, which include (A) amalgamated geometry, (B) Semi-amalgamated geometry, (C)Offset stacked geometry, (D) Isolated geometry, (E)Floodplain geometry.