The Early Cretaceous Sedimentary Characteristics And Analysis Of The Provenances In Jixi Basin

Jixi Basin is one of the important coal-bearing Basin ,locating the southeast of Hei Long Jiang Province. Exploring proving ,some oil-gas exploring cores and coalfield exploring cores have been seen different degree oil-gas showing in Jixi Basin. But because of the data and the precision of the study ,many scholars have divarications about it that the point of the Early Cretaceous in Jixi basin and these Cretaceous basins in eastern Hei Long jiang Province, there into the biggest dispute is that if it was uniform basin in the early Cretaceous .This paper discusses the sedimentary facies types ,analyse the rule of sedimentary facies areas and evolvement history ,and base on the composition of conglomerate, light mineral of sandstone, composing of lithology and the heavy mineral assemblage analyse the source of sediments , resuming the place of mother rock in sedimentary basin integrating the direction of the paleocurrent ,and then analyse the tectonic settings of the provenance through the Dickinson chart and Geochemical characteristics of detrital rocks ,the last purpose is that provide the evidence for the formation mechanisms and retoration of prototype basins in Sanjiang areas ,at the same time provide academic precondition condition for exploring oil.Jixi basin was locating fault---depression basin in the early Cretaceous. It made of Didao Formation ,Chengzihe Formation ,Muleng Formation and Dongshan Formation. The Sediment include allogenic rocks, endogenetic rocks and lava. Though stating sandstone thin-section's clastic constituents of outcrop sandstones and core sandstones ,collecting sandstones'clastic constituents datum from Jican1 core,Ji3 core, it's judged to the rock type be detritus feldspar sandstone and feldspathic detritus sandstone of outcrop sandstones and core sandstones in studied layer. The sedimentary structure main-ly made by the physical formation types. The sedimentary facies in the area is mainly composed of continental facies, and including m-arine layers in Chengzihe Formation and Muleng Formation. Though the integrative analysis of the Jican1 core, field sections, well log, seismic and palaeontologic datum indicates that, the sedimenta-ry assemblages in this area are mostly made up of the continental facies, and others are marine-continental transitional and marine facies. The continental facies can father be divided into alluvial fan facies, river, (fan)delta, lacustrine. Through the study of thestratum in upright direction, concluded that the tectonic evoluting in the early Cretaceous : Fault (Didao Formation)--- depression( the early Chengzihe Formation and Muleng Formation)---comprssive ov-erturn (the later of Muleng Formation)---fault (Dongshan Formatio-n).The sedimentary features and spread rules of the Early Cretaceous indicate: during the sedimentary periods of Didao Formation, whi-ch mainly develop alluvial fan-(fan)delta-lacustrine sedimentary sy-stems. during the sedimentary periods of Chengzihe Formation and Mu-ling Formation , the basin turn more bigger obviously , which develop fluvial-(fan)delta-shallow lake-semi-lake sedimentary systems, provenance came from westward ,and there exist marine events. It's direction is southward. The north and south of the basin absent edge facies ,which show that the Jixi basin , the north Boli basin and northeast Hulin basin maybe a uniform basin.We know the lithologies of the source of sediments were main granite, middle to low grade metamorphite, intermediate-basic volcanic rock; and part of sedimentary rock .through analyzing the component of conglometate, the minerals of sandstone,the component of rock fragment, assembly characters of heavy minerals. Combination of lithology and palaeocurrents indicates that the palaeocurrents were dispersed in the Didao Formation, characterized by nearby provenance and multiple supply sources. The palaeocurrents were primarily come form the western, eastern or southeastern basins in Chengzihe Formation. We can infer that the early Cretaceous source of sediments primaryly came from Zhangguangcai Mountains .We could conclude that the whole tectonic setting of the source of sediments is determined as the active continental margine through geochemistry analysis of Dickinson diagrams, constant element, microelements, and lathanons.