Mass-transport complexes (MTCs) are one of the most sedimentologically and seismically distinctive depositional elements in deep-water depositional systems. Seismic reflection data provide spectacular images of their structure, size, and distribution, although a lack of borehole data means there is limited direct calibration between MTC lithology and petrophysical expression or knowledge of how they may act as hydrocarbon reservoir seals. In this study, we evaluated the lithological and petrophysical properties and seismic characteristics of three deeply buried (>2300 m below the seabed) Pleistocene MTCs in the northern Gulf of Mexico. We show that (1) MTC lithology is highly variable, comprising a mudstone-rich debrite matrix containing large (4.5-km3), deformed, sandstone-rich blocks; (2) MTCs are generally acoustically faster and are more resistive than lithologically similar (i.e., mudstone-dominated) slope deposits occurring at a similar burial depth; (3) MTC velocity and resistivity increase with depth, likely reflecting an overall downward increase in the degree of compaction; and (4) the lowermost 15–30 m of the MTCs, which represent the basal shear zones, are characterized by relatively high P-wave velocity and resistivity values, likely caused by shear-induced overcompaction. We conclude that detailed analysis of petrophysical data, in particular velocity and resistivity logs, may allow recognition of MTCs in the absence of high-quality seismic reflection data, including explicit identification of the basal shear zone. Furthermore, the relatively thick basal shear zone, rather than the overlying and substantially thicker MTC itself, may form the primary permeability barrier and thus seal for underlying hydrocarbon accumulations.

中文翻译：

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墨西哥湾北部大规模运输复合体的岩性、岩石物理和密封特性

传质复合体 (MTC) 是深水沉积系统中最具沉积学和地震学特征的沉积元素之一。地震反射数据提供了它们的结构、大小和分布的壮观图像，尽管缺乏钻孔数据意味着 MTC 岩性和岩石物理表达之间的直接校准有限，或者它们如何作为油气储层密封的知识有限。在这项研究中，我们评估了墨西哥湾北部三个深埋（海床以下 >2300 m）更新世 MTC 的岩性和岩石物理性质以及地震特征。我们表明 (1) MTC 岩性变化很大，包括富含泥岩的碎屑岩基质，其中包含大 (4.5-km3)、变形、富含砂岩的块体；(2) MTC 通常在声学上更快，并且比在类似埋藏深度发生的岩性相似（即以泥岩为主）的斜坡沉积物更具抵抗力；(3) MTC速度和电阻率随深度增加，可能反映压实程度整体向下增加；(4) 代表基底剪切带的 MTC 的最低 15-30 m 具有相对较高的 P 波速度和电阻率值，这可能是由剪切引起的过度压实引起的。我们得出结论，对岩石物理数据，特别是速度和电阻率测井数据的详细分析，可以在缺乏高质量地震反射数据的情况下识别 MTC，包括明确识别基底剪切带。此外，相对较厚的基底剪切带，