Abstract

Sequence stratigraphy has followed a natural progression towards increasing stratigraphic resolution and three-dimensionality. The work presented in this dissertation follows in this trend and focuses on the problems of (i) interaction between tectonics and sedimentation, and (ii) stratigraphic architecture of sand and mud-dominated successions. A case study based on outcrop and well-log data of Cemonanian age, from the western margin of Powder River basin, Wyoming, shows evidence for four tectonic pulses for a period of about 2.2 million years. These results are in direct disagreement with previous suppositions suggesting that eustatically-driven cycles are the only mechanism capable of affecting stratigraphy at such frequencies. The fact that these tectonic sequences are coeval to a time period with demonstrated high-frequency eustatic control, comments on the likely complex interaction between the two processes.

One of the four tectonically-driven erosional surfaces, and its relation to the parasequence architecture of an adjacent sand-dominated body, is also examined. It is shown that objective criteria for recognition of tectonically-driven erosion, based on facies criteria and regional mapping, allows differentiation from other erosional mechanisms that can result in similar geometries, such as valley incision. An interesting result is evidence that tectonic forcing directly affects parasequence architecture, leading to an increase in along strike variation.

The problem of stratigraphic architecture of mud-dominated basin fill is also addressed. While modern oceanographic investigations teach us much the complex geometries of shelfal mud-dominated bodies, such features are rarely mapped in the ancient record. To address this issue, a set of conceptual models is proposed, which attempts to show the possible expressions of mud belts in sedimentary basin fill. Three novel ancient mud belt examples strongly suggest that such features are likely abundant in the ancient record. Such findings are highly relevant considering the volumetric significance of mudstones, comprising more than half of the world's sediments.