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-  2015 

鄂尔多斯湖盆西南部晚三叠世深水坡折特征 及其对砂体的控制

Keywords: 坡折带,重力流,鄂尔多斯盆地,延长组
slopebreakbelt
,gravityflows,OrdosBasin,YanchangFormation

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Abstract:

该文对鄂尔多斯盆地晚三叠世发育的坳陷型湖盆坡折带进行研究,通过岩石类型及相组合分析法、地震反射特征识 别法在湖盆西南缘、东北缘识别出了深水坡折,分别是西南坡折和东北坡折。通过地层厚度变化率计算坡降对坡折点进行 定位,确定长7-长6沉积期坡折带的展布特征。西南坡折规模大,东北坡折规模小。坡折带具有明显的控砂作用,主要体 现在对砂体成因类型、砂体厚度变化以及砂体展布形态三方面。深水坡折之上发育三角洲前缘成因砂体,坡折之下以重力 流为主,多发育湖底扇、滑塌体体等重力流砂体,同时由于坡度的不同,西南坡折与东北坡折也发育不同类型重力流砂 体。同一物源形成的砂体厚度由坡折带上方至坡脚形成“厚-薄-厚”的变化趋势。坡折带上方砂体呈条带状及席状展布, 坡折带下方根据坡度陡缓以及距坡脚的距离不同而砂体形态有所不同。
DuringtheLateTriassic,theslopebreakbeltofdepressionlakebasinwasdevelopedintheOrdosBasin.Basedontherock types,faciesassociations,andseismicreflectioncharacters,thedeep-waterslopebreakbeltswererecognizedinthesouthwesternand northeasternpartofthelakebasin,whichwerenamedasthesouthwestslopebreakbeltandthenortheastslopebreakbeltaccordingly. Theterrainslopewascalculatedwiththerateofformationthicknesschange,andthustheslopebreakpointswereorientatedtoidentify thedistributionofslopebreakbeltsduringtheChang7-Chang6period.Thesouthwesternslopebreakbeltisoflargescale,whilethe northeasternoneissmaller.Theslopebreakbeltsobviouslyhavecontrolsonsandbodies,mainlyreflectedinthreeaspects:origin types,thicknessvariations,anddistributionalmorphology.Uponthedeep-waterslopebreaks,sandbodiesofdeltafrontweredeveloped. However,underthedeep-waterslopebreaks,sandbodieswereformedmostlybygravityflows,suchassublacustrinefanandslump olistolith.Meanwhile,differenttypesofgravityflowssandbodiesdevelopedinsteepslopebeltandgentleslopebelt.Thethicknessofsandbodiesfromthesameprovenancedecreasedfirstlyandthenincreasedfromtheupperslopebreakbelttotheslopetoe.Uponthe slopebreakbelt,sandbodiesoccurinstripsorasasheet.Undertheslopebreakbelt,theirpatternsvariedaccordingtotheterrainslope andthedistancetotheslopetoe.

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