辽西早白垩世义县组大康堡层纹泥的古环境意义
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摘要
辽西地区义县组湖泊沉积层中产出著名的"热河生物群"化石,对于此时期古环境的研究一直是诸多学者关注的焦点.本文对大康堡层湖相纹泥展开研究,重建此时期古环境.通过野外及室内对纹泥组成、类型、厚度等方面的观测,对此时期古气候有了新的认识.纹泥厚度特征变化表明沉积期降水量和沉积速率逐渐减小,统计洪水沉积间纹层数量可指示沉积期洪水事件的频率和规模.结合近现代纹泥形成和保存条件,可知该地区沉积期湖泊水体较深,湖水分层,存在一个缺氧环境,具有较小的表面积/深度比,湖盆形态适合,未受到风的侵扰.
Lake sediments of Yixian formation in the western part of Liaoning Province output the famouse "Jehol Biota"fossils,it is a hot issue for the study of the palaeoenvironment at this period.This paper focuses on the varves in Dakangpu Layer and reconstruct the lacustrine palaeoenvironment.Newunderstanding of the palaeoclimate in this period is obtained through carefully observing the composition,type,thickness of varve in the field and laboratory. The change of varve thickness indicates the decrease in the precipitation and deposition rates in Dakangpu stage. The thickness of the varve between the flood deposits can be used to interpret the frequency and scale of the flood events.Combined with the deposition and preserved environmental conditions of modern varves,during the deposition period of Dakangpu Layer,there is a specific depositional environment and a deep,stratified,oxygen-restricted,lowsurface area/depth ratio lake.
Lake sediments of Yixian formation in the western part of Liaoning Province output the famouse "Jehol Biota"fossils,it is a hot issue for the study of the palaeoenvironment at this period.This paper focuses on the varves in Dakangpu Layer and reconstruct the lacustrine palaeoenvironment.Newunderstanding of the palaeoclimate in this period is obtained through carefully observing the composition,type,thickness of varve in the field and laboratory. The change of varve thickness indicates the decrease in the precipitation and deposition rates in Dakangpu stage. The thickness of the varve between the flood deposits can be used to interpret the frequency and scale of the flood events.Combined with the deposition and preserved environmental conditions of modern varves,during the deposition period of Dakangpu Layer,there is a specific depositional environment and a deep,stratified,oxygen-restricted,lowsurface area/depth ratio lake.
引文
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[2]Martin P C,Matthes K,Brauer A,et al.Regional atmospheric circulation shifts induced by a grand solar minimum[J].Nature Geoscience,2012,5:397-401.
[3]Cui Y,Gong E P,Wang T H,et al.Palynomorph assemblages and paleoclimate records from the Zhuanchengzi bed of the Yixian formation,western Liaoning Province,China[J].Science China:Earth Sciences,2015,58(9):1538-1552.
[4]Ding Q H,Tian N,Wang Y D,et al.Fossil coniferous wood from the Early Cretaceous Jehol Biota in werstern Liaoning,NE China:new material and palaeoclimate implications[J].Cretaceous Research,2016,61:57-70.
[5]陈登辉,巩恩普,梁俊红,等.辽西上白垩统义县组湖相碳酸盐岩碳氧稳定同位素组成及其沉积环境[J].地质学报,2011,85(6):987-992.(Chen Deng-hui,Gong En-pu,Liang Jun-hong,et al.The carbon and oxygen stable isotopic compositions and sedimentary environment of the lacustrine carbonate from the upper cretaceous Yixian formation,Western Liaoning,NE China[J].Acta Geologica Sinica,2011,85(6):987-992.)
[6]Zolitschka B,Francus P,Ojala A E K,et al.Varves in lake sediments—a review[J].Quaternary Science Reviews,2015,117:1-14.
[7]Pierre F,Raymond S B,Ted L,et al.Limnological and sedimentary processes at Sawtooth Lake,Canadian High Arctic,and their influence on varve formation[J].Journal of Paleoliminology,2008,40(3):963-985.
[8]Stockhecke M,Anselmetti F S,Meydan A F,et al.The annual particle cycle in Lake Van(Turkey)[J].Palaeogeography,Palaeoclimatology,Palaeoecology,2012,333/334:148-159.
[9]Stockhecke M,Sturm M,Brunner I,et al.Sedimentary evolution and environmental history of Lake Van(Turkey)over the past600000 years[J].Sedimentology,2014,61(6):1830-1861.
[10]Jean Y G,Abdullah D,Bertrand F,et al.Geochemical behaviour of silia and magnesium during the evaporation of waters in Chad[J].Chemical Geology,1997,19(1/2/3/4):215-228.
[11]Zhou A F,Chen F H,Qing M R,et al.The discovery of annually laminated sediments(varves)from shallow Sugan Lake in inland arid China and their paleoclimatic significance[J].Science in China Series D:Earth Sciences,2007,50(8):1218-1224.
[12]Francus P,Suchodoletz H V,Dietze M,et al.Varved sediments of Lake Yoa(Ounianga Kebir,Chad)reveal progressive drying of the Sahara during the last 6100 years[J].Sedimentology,2013,60(4):911-934.
[13]李万春,李世杰,濮培民.高分辨率古环境指示器——湖泊纹泥研究综述[J].地球科学进展,1999,14(2):172-176.(Li Wan-chun,Li Shi-jie,Pu Pei-min.Review on the highresolution varved lake sediments as a proxy of palaeoenvironment[J].Advance in Earth Science,1999,14(2):172-176.)
[14]Schillereff D N,Chiverrell R C,Macdonald N,et al.Flood stratigraphies in lake sediments:a review[J].Earth-Science Reviews,2014,135:17-37.