Distribution characteristics and genesis analysis of geological relics in Zhaoyang district,Zhaotong City,Yunnan Province
Geological relics are one of the important components of geoscience culture,so studies on their distribution characteristics and genesis are helpful to the effective investigation and evaluation of the landscape resources in geological relics.Zhaotong City is located on the southeastern margin of the Tibetan Plateau in the northeastern Yunnan Province of Southwest China.It belongs to the Yangtze plate of South China,which is located at the southwest edge of the Yangtze block—a secondary tectonic unit within the plate.The formation and distribution of landscapes of geological relics in Zhaoyang district are closely related to the formation and evolution of the Zhaotong intermountain basin.On the basis of detailed field investigations of geological relics,this study comprehensively classifies and analyzes the genesis of various geological relics in Zhaoyang district of Zhaotong City in northeastern Yunnan Province.The strata in the Zhaoyang area are fully exposed,ranging from the Cambrian Meishucun Formation(Zhongyicun member of Dengying Formation)to the Quaternary system(Neogene).The Cambrian and Ordovician systems are mainly exposed in Yanshan township and Dazhaizi township by the Jinsha river,and are mainly buried deep underground in other areas.The Meishucun Formation at the bottom of the Cambrian is a phosphate-bearing rock series,with the upper Qiongzhusi Formation and Canglangpu Formation being a combination of terrigenous sandstone and mudstone.The Longwangmiao Formation to the Erdaoshui Formation and the Ordovician Formation at the top of the lower Cambrian are mostly composed of carbonate rocks.Meishucun Formation at the bottom of the Cambrian is composed of the phosphorus-bearing rock series.The upper Qiongzhusi Formation and Canglangpu Formation are the combination of terrigenous sand and mudstone.The top of the lower Cambrian Longwangmiao Formation to the Erdaoshui Formation and the Ordovician are mostly composed of carbonate rocks.The combination of terrigenous sand and mudstone,accompanied by muddy limestone,is developed in Hong'anpo Formation of the Silurian system to the upper part of middle Devonian.Thick carbonate deposits are developed in Qujing Formation at the top of middle Devonian to the Maokou Formation of the lower Permian.From the Xuanwei Formation at the top of Permian to the Cretaceous,there are only sporadic outcrops—mainly terrigenous sand and mudstone—in Zhaoyang district.The Paleogene mainly consists of sand,mudstone and thick lignite.The bottom of the Neogene is mainly composed of conglomerate with a small amount of limestone and sandstone;the clay soil is interbedded with gravel in the middle part;the grey clay soil is interbedded with siltstone at the bottom.The Quaternary system is filled with swampy sediments of clays,silts,etc.and abundant biological fossils,such as ostracods,stonewort,ichthyodont and viviparus.The results show that the geological relics of Zhaoyang district can be divided into western region and eastern region.The western region is a basalt platform like Dashanbao,including volcanic landform,plateau lakes and wetland.The eastern region takes carbonate rock karst landform of Zhaotong mountain basin as the center by paleontological fossil landscape.The abundant lithology,like carbonate rock,shale,sandstone,basalt and so on,contributes to karst development and karst geomorphology difference.The tectonic landforms formed by different degrees of fault-fold are the main factors of the differentiation of geological relics.Under background of stratigraphic lithology and tectonic geomorphology,hydrologic conditions provide external dynamic factors for abundant geological landscapes.Our research is of great scientific value of geological relics resources in Zhaotong,and also provides a basis for studies on mammal fossils in Late Neogene.It is concluded as follows,(1)Geological relics of Zhaoyang district in Zhaotong City include canyon landform,volcanic landform,karst landform,plateau lake,wetland and fossil landscape,etc.,with great value of tourism.(2)Abundant stratigraphic lithology is the basis for the development of different geological relics.Two sets of outcrops of carbonate rocks widely shaped the modern geological landscape with karst landform and water landform in the study area.Vertically,the strata of Zhaoyang district are characterized by an interphase pattern of three sets of water-resisting rock series and two sets of water-bearing rock series,being the geological foundation of geological relics.From the bottom to the top of strata are distributed the water-resisting rock series mainly composed of mudstone from the Cambrian Qiongzhusi Formation to the Canglangpu Formation,the water-bearing rock series composed of carbonate rock and diamictite from the Cambrian Longwangmiao Formation to the Ordovician Daqing Formation,the water-resisting rock series mainly composed of sand and mudstone with marine-terrestrial transitional facies from the Silurian Longmaxi Formation to the Devonian Hongyapo Formation,the water-bearing rock series composed of carbonate rock from the Devonian Qujing Formation to the Permian Maokou Formation,and the water-resisting rock series composed of the Permian Emei basalt.(3)The tectonic process forms a structural pattern of east-west differences in Zhaoyang district,controlling the distribution pattern of geological relics in this district.The reasons are as follows:the Indosinian Movement caused the overall uplift of the northeastern Yunnan into land;the Yanshan movement formed open and gentle folds in the west and relatively tight folds and large-scale faults in the east,resulting in east-west differences;the Xishan movement formed the Zhaotong intermountain basin,caused strong downward erosion of rivers,and controlled the direction of groundwater runoff,becoming a direct controlling factor for the formation of geological relics in Zhaoyang district.
万方数据
维普
