Mechanisms of muddy clinothem progradation on the Southwest Louisiana Chenier Plain inner shelf
Mechanisms of muddy clinothem progradation on the Southwest Louisiana Chenier Plain inner shelf
复制标题
路易斯安那州西南部谢尼尔平原内陆架泥质斜积进积机制
作者：
Kathryn C. Denommee;S. Bentley;Dario Harazim
在现代和古代陆架环境中，泥质占主导地位的层序通常包含复杂的地层几何形状，其中低梯度的地层特征突出。尽管它们无处不在，但在这种环境下负责沉积物扩散和沉积的全部机制尚未得到很好的理解。利用沉积物岩心资料（210PbXS、137Cs、粒度、孔隙度、x射线）和浅层地震观测资料，研究了路易斯安那州西南部阿查法拉亚切尼尔平原泥质内陆架的跨陆架沉积物输运和斜沉积机制。观测结果表明，富有机质沉积物向外顶套的快速转移和斜顶套的翻滚主要发生在波流床剪切应力大的时期（如风暴通过期间），通过流体动力流体-泥浆过程。浅海内的快速沉积、波浪扰动和生物甲烷的发育导致了巨大的内部孔隙水压力的产生，从而使斜层翻滚和森林沉积物固有地处于早期破坏状态。随后向盆地内的沉积物向森林的转移主要与低梯度（<0.02°）的质量破坏事件有关，海床上广泛的陡坡和泥石流就是证据。这代表了研究区域内一个重要的、尚未确定的斜层沉积机制，并可能驱动其他现代和古代泥质陆架斜层体系向盆地内的沉积物搬运。
In both modern and ancient shelf settings, mud-dominated successions commonly contain complex stratigraphic geometries in which low-gradient clinothems feature prominently. Despite their ubiquity, the full range of mechanisms responsible for sediment dispersal and clinothem progradation in such settings is not well understood. Using sediment core data (210PbXS, 137Cs, grain size, porosity, X-radiography) and shallow seismic observations, this study examines the mechanisms of across-shelf sediment transport and clinothem progradation on the muddy Southwest Louisiana Atchafalaya Chenier Plain inner shelf. Observations indicate that rapid transfer of organic matter-rich sediment to the outer topsets and clinothem rollover occurs mainly via hydrodynamic fluid-mud processes during times of high wave-current bed shear stress (e.g., during the passage of storms). Rapid sedimentation, wave perturbation, and the development of biogenic methane within the shallow seabed result in the generation of large internal pore water pressures such that the clinothem rollover and foreset sediments are inherently in a condition of incipient failure. Subsequent basinward sediment transfer to the foresets occurs largely in association with low-gradient (<0.02°) mass-failure events, evidenced by widespread scarping and mudflows on the seabed. These represent an important and as yet unattributed mechanism for clinothem progradation in the study area and are likely to drive basinward sediment transport in other muddy shelf clinothem systems, both modern and ancient.