DIFFERENTIAL EVOLUTION OF JURASSIC-CRETACEOUS SEDIMENTARY SYSTEMS IN THE SOUTHWESTERN JUNGGAR BASIN,XINJIANG,NW CHINA
The southwestern part of Junggar Basin,Xinjiang,NW China,the study area of this study,represents a prototypical multi-cycle superimposed basin.However,the characteristics of sedimentary system and its relationship with regional paleoclimatic and paleotectonic changes remain poorly understood due to intense tectonic movements in multi-phased superimposition and varying degrees of uplift and denudation in piedmont areas.Therefore,this comprehensive study was conducted integrating drilling,logging,core analysis,field outcrop observations,and laboratory data to determine precisely the types and characteristics of Jurassic-Cretaceous sedimentary systems in the study area.In addition,considering the paleoclimatic and paleotectonic evolutionary history,the differential evolutionary process of Jurassic-Cretaceous sedimentary systems and its intrinsic cause were reconstructed.Results indicate that the alluvial fan-fan delta,braided river-braided river delta,and shore-shallow to deep lake sedimentary systems were developed in the Jurassic-Cretaceous period in the study area.The paleoclimate in the Early Jurassic to early Middle Jurassic was humid;in the late Middle Jurassic to Late Jurassic,the climate was from dry-wet alternation to extremely dry at last;and it became humid again in the Early Cretaceous.The paleotectonic pattern is characterized by a cyclic evolution from depression to compression-shear depression,and returned to depression at last.Moreover,the Yanshanian multi-phase movements induced an overall continuous uplift of surrounding mountains in late Middle Jurassic to Early Cretaceous.In specific,there developed a depressed lacustrine basin under humid climate in the Early Jurassic to early Middle Jurassic,featuring braided river delta and shore-shallow lake sedimentary systems with periodic fluctuation in lake level and significant variations in depth and area.Later,a compression-shear lacustrine basin occurred under alternating dry-wet conditions and eventually an extremely arid climate in late Middle Jurassic to Late Jurassic,characterized by an alluvial fan to fan delta,braided river to braided river delta,and shore-shallow lake sedimentary system,with rapid fluctuations in water level,and the significant shrinkage in area resulted in shallow lakes.Finally,in the Early Cretaceous,a united depressed lacustrine basin was born characterizing a fan delta and braided river delta sedimentary system;flat topography resulted in rapid lake transgression and substantial increases in water depth and area.This study provided a scientific basis for evaluation and prediction of source rocks and reservoirs in the Jurassic-Cretaceous oil and gas exploration in the southwestern part of Junggar Basin.
North XinjiangJurassicCretaceoussedimentary system evolutionpalaeoclimatepalaeotectonic pattern
万方数据
维普
