Weighing controls on shoreline and shelf-margin growth : insights from Wilcox Group, Gulf of Mexico and from numerical models
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This research investigates the relative importance of sediment supply, accommodation, and a series of morphological parameters in controlling shoreline migration, the fundamental process and building block during the accretion of entire shelf-margin sedimentary prism. A better understanding of these controls provides insights on different source-to-sink systems and on the evaluating hydrocarbon potential of frontier basins. These studies were carried out in Wilcox Group, Gulf of Mexico (Chapters 2 and 3) and include two numerical modeling studies (Chapters 4 and 5). The greenhouse Wilcox shoreline shows repeated long-distance shoreline regression and retreat, in fact about 37 times during building of Wilcox Group, a stratigraphic scenario a bit different from previous hypotheses that the shoreline movement in low-amplitude, low-frequency greenhouse conditions should be limited. We therefore, suggest that the Wilcox shoreline was controlled by both greenhouse eustasy and variable sediment supply, the latter likely caused by Paleogene hyperthermals. Furthermore, integrated analysis on the paleohydrology of feeder channels, shelf-edge trajectory, and published eustatic curve indicates that a decreasing sediment supply and increasing accommodation controlled the transition of Lower Wilcox shelf margin from being progradation-dominated to aggradation-dominated. BQART model, a widely accepted method of reconstructing sediment load, and Monte Carlo simulation are used for reconstructing the Paleogene Wilcox sediment supply. By comparing with the downstream sediment record, this method shows reliable accuracy and precision. The downstream sediment records are mostly within P10-P90 reconstructed sediment load. This study also shows various tectonic, climatic, and geologic factors controlling the sediment supply. A geometric model of shoreline regression is integrated with sensitivity analysis to understand the relative importance of controls on the formation of highstand shelf-edge deltas. The result indicates the formation of highstand shelf-edge deltas is controlled by multiple accommodation and morphological parameters. Among them, the shelf width is the most important control, whereas subsidence and eustasy are much less important than previous literature implied. This dissertation emphasizes that there are multiple factors that control the shoreline and shelf-margin growth. It is important for future researches to develop and assess multiple hypotheses for evaluating combinations of controls including sediment supply, relative sea level, and morphological parameters.