Nonmarine time-stratigraphy in a rift setting: An example from the Mid-Permian lower Quanzijie low-order cycle, Bogda Mountains, NW China  

作　　者：Jonathan Obrist-Farner Wan Yang 

机构地区：[1]Geology and Geophysics Program, Missouri University of Science and Technology,Rolla, Missouri 65409, USA [2]Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences

出　　处：《Journal of Palaeogeography》2015年第1期27-51,共25页古地理学报（英文版）

基　　金：supported by four student research grants from Geological Society of America, Ed Picou/GCSSEPM, American Association of Petroleum Geologists;the Al Spreng Graduate Research Grant from the Geology and Geophysics Program of Missouri University of Science and Technology to Jonathan Obrist-Farner;a research grant from University of Missouri Research Board and a research grant (No.2011ZX05008 004 053) from Institute of Geol-ogy and Geophysics of Chinese Academy of Sciences to Wan Yang

摘　　要：Sedimentological and stratigraphic studies of seven stratigraphic sections of Permian Hongyanchi （HYC） and Quanzijie （QZJ） low-order cycles （LCs） in the Tarlong-Taodonggou half graben and Dalongkou area in Bogda Mountains, NW China, demonstrate effective approaches and methodology in cyclo- and time-stratigraphic analyses of complex fluviallacustrine deposits in an intracontinental rift setting. A new synchronous stratigraphic unit, the lower QZJ LC is defined. The lower and upper boundaries of this cycle include a regionally correlative disconformity, erosional unconformity, and conformity, across which significant and abrupt changes in palaeoenvironments and tectonic and climatic conditions occurred. The lower boundary is an erosional unconformity and disconformity with a high-relief topography that juxtaposes lacustrine deposits of the underlying HYC LC with the overlying meandering stream deposits of the lower QZJ LC, and was caused by a regional tectonic uplift. The up- per boundary is a disconformity and local erosional unconformity and conformity, juxtaposing stacked paleosols developed on fluvial sediments with overlying fluvial and loessial deposits of the upper QZJ LC. The paleosols indicate landscape stability and a prolonged period of subaerial exposure and minimal deposition and suggest that climatic conditions were semiarid with strong precipitation seasonality in the Tarlong-Taodonggou half graben and subhumid in the Dalongkou area. The fluvial-loessial deposits indicate a renewed tectonic uplift and a change in the atmospheric circulation pattern. The newly-defined lower QZJ LC facilitates accurate palaeogeographic reconstruction in the study area during a period of major tectonic and climatic changes. The interpreted tectonic and climatic conditions provide a critical data point in the mid-latitude east coast of NE Pangea during the Mid-Permian icehouse-hothouse transition. The results demonstrate that a process-response approach is effective in time- stratigraphic analysis of complexSedimentological and stratigraphic studies of seven stratigraphic sections of Permian Hongyanchi （HYC） and Quanzijie （QZJ） low-order cycles （LCs） in the Tarlong-Taodonggou half graben and Dalongkou area in Bogda Mountains, NW China, demonstrate effective approaches and methodology in cyclo- and time-stratigraphic analyses of complex fluviallacustrine deposits in an intracontinental rift setting. A new synchronous stratigraphic unit, the lower QZJ LC is defined. The lower and upper boundaries of this cycle include a regionally correlative disconformity, erosional unconformity, and conformity, across which significant and abrupt changes in palaeoenvironments and tectonic and climatic conditions occurred. The lower boundary is an erosional unconformity and disconformity with a high-relief topography that juxtaposes lacustrine deposits of the underlying HYC LC with the overlying meandering stream deposits of the lower QZJ LC, and was caused by a regional tectonic uplift. The up- per boundary is a disconformity and local erosional unconformity and conformity, juxtaposing stacked paleosols developed on fluvial sediments with overlying fluvial and loessial deposits of the upper QZJ LC. The paleosols indicate landscape stability and a prolonged period of subaerial exposure and minimal deposition and suggest that climatic conditions were semiarid with strong precipitation seasonality in the Tarlong-Taodonggou half graben and subhumid in the Dalongkou area. The fluvial-loessial deposits indicate a renewed tectonic uplift and a change in the atmospheric circulation pattern. The newly-defined lower QZJ LC facilitates accurate palaeogeographic reconstruction in the study area during a period of major tectonic and climatic changes. The interpreted tectonic and climatic conditions provide a critical data point in the mid-latitude east coast of NE Pangea during the Mid-Permian icehouse-hothouse transition. The results demonstrate that a process-response approach is effective in time- stratigraphic analysis of complex

关 键 词：FLUVIAL loess CYCLOSTRATIGRAPHY PERMIAN China 

分 类 号：P534.46[天文地球—古生物学与地层学]