Sedimentary Characteristics,Developmental Models And Distribution Regularities Of The Triassic Spontaneous Rocks In Lower Yangtze Region Of Anhui Province

The Triassic in the lower Yangtze area of Anhui Province,as one of the important horizons for the development of evaporate,has achieved fruitful results in the gypsum and salt rock exploration field,but the resources of gypsum salt rock are still not clear.The oil and gas exploration under the potassium salt and gypsum salt rock of China's urgently needed minerals associated with salt and salt has not yet achieved important breakthroughs.Geological exploration and prospecting practices have shown that the formation and salinization mechanism of the Early Triassic evaporite rock are the main factors constraining the evaporative rock and the underlying hydrocarbon exploration in the area.Based on the analysis of sedimentary structure,lithology,main trace elements and isotopes of typical boreholes,this paper deeply studies the genetic model and distribution characteristics of this set of gypsum salts,and provides theoretical basis for the study of salt and oil and gas exploration in the study area.Mainly achieved the following understanding:(1)Based on the field profile,typical core structure and rock mineral combination analysis,the rock types of the Middle-Lower Triassic in the study area were divided in detail,and gypsum rocks were systematically classified according to composition,structure,and genesis.It provides support for the analysis of sedimentary environment evolution.(2)By analyzing the major elements,trace elements,Sr isotopes,etc.of the Zhoukongcun Formation section of a typical borehole,he structural and tectonic features of the evaporite and carbonate rocks in this area are combined with the regional geological structure and sedimentary background.The evolutionary characteristics of the Early-Middle Triassic paleo-sedimentary environment in Lower Yangtze region of Anhui Province were discussed.The major developmental basins,the restricted mesophases and the evaporite mesophases of the Middle-Lower Triassic in the study area were clarified.The salinity of the sedimentary waters caused by the rise and fall of the sea level caused oscillations,and the vertical evolution was characterized by significant prosodic deposition.The complete sedimentary sequence of the middle Triassic Zhouchongcun Formation includes the confined sea-lagoon-saline-ultra-saline lagoon-lagoon-clad salt-platform sediment.It reveals that the Early and Middle Triassic of the study area experienced a complete sea-retreating process,and large-scale regression led to the palaeogeography of the lagoon-tidal system developed in the study area,which provided sufficient paleogeography for the deposition of evaporite condition.The formation of evaporite rock in the study area was proposed as a "bull-eyed" paste model.(3)Based on the formation pattern of the gypsum rock and the palaeogeography of the lithofacies,it is believed that there are mainly two salt lakes during the deposition period of the middle Triassic Zhouchongcun Formation in the lower Yangtze region of Anhui Province:Wuwei-Hanshan Depression and Guichi Depression as Prospecting Prospects for Gypsum Salt Deposits in the Research Area.The Wangjiang and Qianshan basins with the most recent seawater withdrawal are located in the west of the Wanxi area where the salt formation conditions are favorable.It is proposed that this area may be a potential exploration area for finding potassium in the lower Yangzi area.