| The paper made study of the Palaeogene Asmari Formation in the Missan Oilfield of Iraq.It was guided by the principle of carbonate sedimentology,cyclic stratigraphy,petrology and mineralogy and karst geology,combined with core,slice,drilling and logging information,research was made into the researched region on the karst characters and gypsum lump by detailed and systems investigation.It was pointed out that sedimentary environment of the study area was restricted platform,semi-restricted platform.Effected by polycyclic sea-level drops,it developed polycyclic superimposed,development layer stable and grain shoal in geomorphic highland controlled by Mesopotamian Basin.On this basis,we were supposed to study development characteristics,main control factors of weathering crust karst in depth.The results showed that the karst of the researched region was controlled by grain shoal facies and it was typically controlled by sedimentary facies.The profile of karst showed that polycyclic superimposed characteristics of high permeability layer and low permeability layer,low permeability layer mainly developed graniphyric corrosion,skew solution karren and partially developed paleo-horizontal karst zone;high permeability not only developed vertical percolating zone but also developed the horizontal karren.Lithologies,palaeogeomorphology and fracture were the control factors of weathering crust karst development of the study area.On the base of core and slice observation,we found karst pore system was packed by gypsum lump,the formation time of gypsum lump was later than other paleokarst filler.Meanwhile we found that paleontology of normal salt in karst pore system.Hereby,we drew at this point was that gypsum lump was formed by Strong brine evaporation in the later period of weathering crust karst.This research achievement provided new reference to gypsum lump study in the future.At the same time,it was of great significance to oil-gas exploration of Asmari Formation in the Missan Oilfield. |
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