Impact into unconsolidated, water‐rich sediments at the Marquez Dome, Texas
Impact into unconsolidated, water‐rich sediments at the Marquez Dome, Texas
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对德克萨斯州马克斯圆顶松散、富含水的沉积物的影响
DOI：
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
A. Reid
中科院分区：
文献类型：
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作者：
P. Buchanan;C. Koeberl;A. Reid
摘要-Marquez圆顶，莱昂县，得克萨斯州代表了一个直径13公里的古新世/始新世的影响结构，在很大程度上松散的沉积物中形成的近海岸环境。本研究是对中央隆起边缘和周围环形盆地分别钻孔取芯样品的分析。在该结构的环形盆地中钻探的钻孔穿透了一系列夹层砂、粉砂和页岩，这是周围区域地层的典型特征。相比之下，在中央隆起边缘钻的钻孔穿透了化学成分和质地相对均匀的物质，可能代表了来自撞击前地层较深层次的砂、粉砂、粘土和少量碳酸盐的混合物。未发现含有假玄武质角砾岩的矿脉，并且在这种环境中也不存在，因为低强度目标材料不利于摩擦熔融。类似地，这些目标材料的低强度和未固结性质不利于形成其他类型的典型冲击角砾岩（例如，熔融岩石或苏云金岩）。这种岩性的缺失要么是由于目标沉积物的富水特性导致这些物质的爆炸性喷射，要么更可能是由于这些物质被比以前所建议的更深的撞击后侵蚀所去除。平面变形特征（PDF）没有发现在石英颗粒从任何这些样品。石英颗粒与PDF的稀缺性，这只在罕见的影响角砾岩从中央隆起的报告，和大量的垂直位移表明中央隆起的这个结构也可能是一个结果的目标材料的强度低。
Abstract— The Marquez Dome, Leon County, Texas represents a 13 km diameter Paleocene/Eocene impact structure formed in largely unconsolidated sediments in a near‐shore environment. The present study is an analysis of samples from cores taken from boreholes drilled separately on the edge of the central uplift and in the surrounding annular basin. The borehole drilled in the annular basin of the structure penetrated a sequence of interbedded sands, silts, and shales that is typical of the stratigraphy of the surrounding area. In contrast, the borehole drilled on the edge of the central uplift penetrated material that is relatively homogeneous in chemical composition and texture and may represent a mixture of sand, silt, clay, and minor carbonate derived from deeper levels in the preimpact stratigraphy. Veins containing pseudotachylitic breccias are not found and are not expected in this environment because low‐strength target materials are not conducive to frictional melting. Similarly, the low strength and unconsolidated nature of these target materials are not conducive to the formation of other types of typical impact breccias (e.g., melt rocks or suevites). The absence of such lithologies results either from explosive ejection of these materials caused by the water‐rich character of the target sediments or, more probably, from removal of these materials by deeper postimpact erosion than has been suggested previously. Planar deformation features (PDFs) were not found in quartz grains from any of these samples. The scarcity of quartz grains with PDFs, which have only been reported in rare impact breccias from the central uplift, and the large amount of vertical displacement indicated for the central uplift of this structure may also be a consequence of the low strength of target materials.