摘要:
研究发现,在江陵凹陷中南部梅槐桥向斜带内沙市组发育两套膏盐岩层。通过对钻井、岩心、地震资料的分析,明确了膏盐岩的岩性、电性及地震响应特征:岩性变化主要为由湖盆中心至边缘膏盐类矿物的含量越来越低而陆源碎屑物质含量越来越高;电性特征表现为低伽马、低密度、高电阻、中子趋于0、扩径明显;在地震剖面上表现为强振幅、低频率的反射特征。结合研究区古气候和古构造背景,对沙市组两套膏盐岩的沉积特征进行分析,结果表明,两套膏盐岩在凹陷内的分布差异巨大且沉积中心具有向南迁移的趋势,物源、古地貌和湖平面变化三种因素的综合作用是造成这种差异的主要原因。最后总结出研究区沙市组所沉积的膏盐岩是一种“非匀称补给”的成盐模式,主要形成于湖盆基准面下降晚期浅水蒸发沉积环境中。
Abstract:
Located in southern central Jianghan Basin, the Shashi Formation of Jiangling Depression is composed of two sets of gypsum-salt rocks. Based on an analysis of drilling, seismic and core data, the authors sum up lithology, electrical properties and seismic response characteristics of the gypsum-salt rock. Main lithologic changes find expression in the reduction of saline minerals and the increase of terrigenous detritus content from bottom to top;electrical character is characterized by low gamma, low density, high resistivity, zero neutron and expanding caliper;there exist high amplitude, low-frequency reflection characteristics on seismic section. In combination with the paleoclimate and ancient tectonic background of the study area, the authors made an analysis of sedimentary characteristics of gypsum-salt rocks in Shashi Formation and reached the conclusion that the distribution of gypsum-salt rocks in the depression is mainly affected such comprehensive factors as material sources, ancient landscapes and lake level changes. Based on the above study, the authors hold that the salt rock deposition model of Shashi Formation is a“non-symmetrical supply”salt-formation model, mainly formed in a shallow water evaporation sedimentary environment in the late falling period of the lake basin datum level.
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