The problem of how sand and mud was distributed downslope, within linked alluvial-brackish water-marine shoreline systems of an extensive clastic wedge is addressed here. The Iles Clastic wedge accumulated over a time period of a few million years (my), and its component high-frequency regressive-transgressive sequences have a duration of a few 100 thousand years (ky). The sediment partitioning study provides insight into where the thickest sandstones and mudstones were located, and generates a model that can be applied to improving the management of hydrocarbons or water resources. A 300 km 2-D study transect across the Iles Clastic Wedge in SW Wyoming and N Colorado included subsurface well log information and outcrop stratigraphic columns. This information was used to correlate high-frequency sequences across several hundred kilometers, characterize depositional processes from proximal to distal reaches, develop a sediment partitioning model, and understand the role of the likely drivers in the development of the wedge and its internal sequences. The main results of this study are: (1) The Iles Clastic Wedge spans 3 my (500 m thick) and is composed internally of 11 sequences of 200-400 ky, each of which have significant regressive-transgressive transits of up to 90 km. Sediment partitioning analysis shows that within the regressive limb of the large wedge, the component regressive compartments tend to thicken basinwards, whereas transgressive compartments thicken landwards. This geometry is driven by preferential erosion in proximal areas during regression, bypassing much sediment to the marine shorelines, and transgressive backfilling into proximal areas previously eroded more deeply. (2) The greatest concentration of sands tends to be located in the proximal fluvial and estuarine facies of the transgressive compartments and within the medial shoreline/deltaic facies of the regressive compartments. (3) As the high-frequency sequences developed, the effectiveness of basinward sand partitioning reaches a maximum value near the peak regression level of the wedge, reflecting stronger erosion and sediment bypass during this times. (4) The development of the Iles Clastic Wedge was influenced by both tectonic and eustatic drivers, with important tectonic control in the upstream reaches. On a 4th-order timescale, the Iles Wedge internal sequences were likely influenced mainly by eustasy. / text

Subsidence is one of the main factors controlling the stratigraphy and overall stratal architecture in tectonically active basins. This was particularly important in the Western US Cordilleran foreland and Laramide basins when some other controls were minor, e.g. reduced eustatic fluctuations in the late Cretaceous greenhouse period. The first part of the dissertation examines the upper Campanian Williams Fork Clastic Wedge (WFCW) in southern Wyoming and northern Colorado, through an outcrop and subsurface database. The WFCW built out from the Sevier orogenic belt like earlier clastic wedges, but its large-scale geometry changed as basement involved Laramide structures partitioned it. At the center of the WFCW there is an extensive fluvial sandstone sheet, the Canyon Creek Member of the Ericson Formation. From its proximal to distal reaches (~200 km) there is a first order trend of stratigraphic thickening and net-to-gross reduction, and a change from braided to meandering depositional style. These trends are caused by isostatic rebound of the foreland basin during periods of relative quiescence in the Sevier orogenic belt and by the eastward migration of dynamic subsidence. However, this long spatial trend was markedly modified by differential subsidence across Laramide-style structures. The Campanian age initiation of the Laramide structures appears to be earlier than the Maastrichtian to Paleogene age commonly attributed to the initiation of this orogeny. The second part of this research focuses on the transgressive limb of the WFCW, particularly on two sandstone bodies isolated in marine mudstones in the uppermost Almond Formation. The sandstone bodies previously interpreted as lowstand shoreline deposits are re-interpreted as transgressive shelf ridges generated by tidal currents and storm waves. There are limited examples of ancient tidal shelf ridges published and no facies model was described. Using Almond Fm. outcrops and examples from the literature, the diagnostic characteristics of storm and tidal shelf ridges are presented. The third part of the dissertation investigates the effects of differential subsidence on the large scale stratigraphic infill of a foreland basin through a geometric model and a series of flume experiments. The mathematical model and flume experiments show that despite constant allogenic forcing, three distinct autogenic responses in stratal architecture, associated with the imposed tectonic and sediment supply conditions are possible. The first response was “autoretreat”, where shoreline migration switched from initial progradation to retrogradation. The second response was progradation followed by constant aggradation. The third response was maintained progradation with a markedly accelerating rate, a new autogenic behavior termed “shoreline autoacceleration”. / text

<p dir="ltr">The Intermontane terranes represent one of the largest composite accreted terranes that built the northern Cordillera. To better understand the interactions between the continental margin of Laurentia and the Intermontane terranes, this study analyzes twelve detrital zircon samples (n=3232) from a Neoproterozoic (?) to Cretaceous metasedimentary stratigraphic section exposed in central Alaska. Distinct detrital zircon populations have been identified and are interpreted to represent four stages in the geologic development of this part of western North America. Stage 1 extends from the Neoproterozoic (?) to the Early Paleozoic, and is characterized by Proterozoic and Archean detrital zircon populations that correlate with Laurentian sources of sediment. We interpret Stage 1 to represent deposition along the northwestern continental margin of Laurentia. Stage 2 extends from the Silurian (?) to the Devonian and is characterized by a dominant Devonian and Silurian detrital zircon population. We interpret Stage 2 to have been deposited in a backarc basin coeval with active volcanism as the Yukon-Tanana terrane was rifted away from the Laurentian continental margin as the Slide Mountain Ocean opened. Stage 3 extends from the Mississippian to the Jurassic and records a shift back to sediment sources with abundant Proterozoic and Archean zircon. We interpret this stage to represent deposition of Laurentian detritus along the eastern margin of the Slide Mountain Ocean basin. Stage 4 is represented by the Lower Cretaceous strata of the Manley basin that contain one major Late Triassic to Early Jurassic detrital zircon population. We interpret this population to be sourced from the syn-collisional and post-collisional Late Triassic to Early Jurassic plutons and related sedimentary basins of the Intermontane terranes that were exhumed and eroded during the closure of the Slide Mountain Ocean and the subsequent collision with the Laurentian continental margin. We interpret the Manley basin as a syn- to post-collisional extensional basin associated with regional detachment faults that formed because of crustal thickening in the collisional zone. From a regional perspective, an extensive clastic wedge prograded northward away from the zone of crustal thickening and can be identified in a series of Mesozoic sedimentary basins that are discontinuously exposed over 1500 km in southern Alaska. Results of our study better delineate the tectonic processes that set the framework for the construction of the Late Mesozoic and Cenozoic Cordilleran orogen.</p>