返回Google圖書搜尋

Decoding Geologic Signals of the Sedimentary Source-to-sink Pathway with Examples from the Modern and Ancient

出版	Stanford University, 2022
URL	http://books.google.com.hk/books?id=W6eWzwEACAAJ&hl=&source=gbs_api

註釋This dissertation assesses how geologic signals are preserved, or perturbed, in the sedimentary source-to-sink pathway, and to what extent these signals are reliable narrators of Earth's history. We investigate the resilience of geologic signal propagation through an examination of the two fundamental processes of sedimentary geology: erosion and deposition. First, we evaluate how the erosive forms of sedimentary pathways encode information about the mechanistic processes responsible for their creation (Chapters I and II). Second, we examine the depositional records at the terminus of these pathways to determine how well sediment transport histories are preserved in the stratigraphic record (Chapters III and IV). Chapter I presents a quantitative comparison of subaerial and submarine channel networks to determine whether their morphologies are distinct. A global analysis of channel concavity and steepness indices from both terrestrial and submarine catchments demonstrates that these two channel forms are indeed unique from each other. Specifically, statistical comparisons demonstrate that concavities of submarine channels are, on balance, lower than those measured in terrestrial basins, and that submarine tributaries are steeper than their associated mainstem. These differences may reflect distinct drainage formation mechanisms and dynamics of submarine sediment gravity flows as compared to overland flow processes. Chapter II uses a set of numerical experiments based on geomorphic transport laws of channel incision and hillslope diffusion to determine whether an established power-law relationship between channel slope and drainage basin area can be optimally configured across a landscape. We find that even in numerical landscape evolution models where parameters are explicitly defined, a certain level of numerical dispersion persists. We speculate this model variance in slope-area scaling highlights a fundamental instability in the form of channel networks, which is only reconciled by diffusively eroded hillslopes that allow variability in the channel length scaling such that mathematical representation of channel incision can be reconciled with a landscape topology that is continuous in space. Chapter III, through a case study from the Upper Cretaceous La Anita Formation (Southern Patagonia), demonstrates how depositional style can affect detrital zircon provenance signatures, which could be mistakenly interpreted as tectonically significant. We establish the sedimentary context of the La Anita Formation as a shoaling package of continental margin facies and then combine our analysis with systematic detrital zircon sampling from each depositional environment. These data document a systematic shift in provenance trends, which correlates with varying depositional environments. This suggests that competition between transport processes inherent to different depositional environments affects the provenance signature recorded within a single stratigraphic succession. Chapter IV capitalizes on an exposure of thin-bedded turbidites adjacent to a prominent submarine channel meander bend offshore Morro Bay, California to assess how sediment is mobilized across the continental margin, and how allogenic forcings can change sedimentation styles. An analysis of high-resolution multibeam bathymetry, sediment core descriptions, radiocarbon dating, and stable isotope measurements suggests that margin-wide sediment mobilization via sediment gravity flows and slope failures were much more frequent at the Pleistocene-Holocene boundary than under present conditions. This work suggests that sea-level likely plays a significant role in the coarse-grained sediment flux onto the Morro Bay continental slope while also providing a first-hand assessment of the geohazard potential of turbidity currents in this region.