East Matagorda Peninsula in southwestern Texas is characterized geologically by active, regional-scale and near-surface growth faulting. Decimeter scale (up to 0.42 m) vertical displacement was recorded at the study site over a period of four years, not believed to be associated with growth faulting. This research tested the hypotheses that fault slip rates were correlated with sediment accumulation rates, and that the observed vertical displacement was produced by shrink-and-swell clays in near surface sediments. To quantify sediment accumulation rates, a suite of radionuclides (7Be, 137Cs, and 210Pb) were used. To understand the effects of shrink-and-swell clays, analyses including particle size distribution, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) were completed. Additionally, the free swell index test (FSI) was used to record the swelling potential of the sediment. Strong correlation (R2 = 0.99) indicates coupling between mean fault slip rates and mean sediment accumulation rates. Near surface sediment clay size fraction percentages ranged from 0.96 - 6.26% containing more than 90% smectite. Based on FSI results, maximum volume change in the top six cm was determined to be 208%. The presence and behavior of shrink-and-swell clay minerals in the region is an important contributor to the vertical displacement observed.

The depositional styles of sediment gravity currents depend, in part, on the relationship of flow magnitude to the scale of topographically controlled containment and range from unconfined lobes to fully contained deposits. Determining the degree of containment is important for understanding depositional processes, land to ocean sediment transfer and subsurface reservoir characterization/prediction. Depositional models of the fully contained (commonly referred to as 'ponded') end member have been developed (e.g. fill-and-spill model). However, fully contained deposits represent only a portion of deepwater deposits and little work has been done identifying and examining the degree of containment of the more complex, partially contained deposits in outcrop. Here, I document the sedimentological facies and stratigraphic architecture of the Zorrillo Unit, a partially contained system exposed at Cerro Solitario within the Upper Cretaceous Tres Pasos Formation of the Magallanes Basin. The evolution of partial containment at this outcrop is expressed as: 1) bypass in the proximal zone and flow stripping in the distal zone, 2) backstepping and blanketing of the outcrop, followed by 3) renewed bypass. The partially contained system at Cerro Solitario deviates from the widely used fill-and-spill model due to subtle relief. This record of infilling provides insight into the overall evolution of the depositional system. Within the Magallanes Basin, the partially contained and linked depocenters along the Chingue Clinoform represent the dying breaths of the Cerro Toro axial conglomerate channel system as the canyon-fed point source collapsed and choked off the sediment routing system out to the distal basin. / Master of Science / Subaqueous sediment gravity flows are responsible for moving large quantities of sediment from off the continent to the oceanic abyssal plain and the resulting deposits serve as some of the largest hydrocarbon reservoirs in the world. These deposits vary in a number of ways depending on numerous variables, including containment. Containment is related to how the sediment gravity flows interact with the seafloor topography. Models have been created describing at one end of the spectrum sediment gravity flows that have been fully contained (i.e., the fill-and-spill model) where the flows are trapped and not able to escape the confining topography. The other end of the spectrum is where flows do not experience any containment (unconfined lobes). There is a lack of work done addressing the middle ground of partial containment of sediment gravity flows and their resulting deposits. The Zorrillo Unit crops out at Cerro Solitario within the Late Cretaceous Magallanes Basin in southern Chile and offers a perfect location to study partially contained deposits. The architecture (the structure of the rocks) and facies (the character of the rocks) were identified. By characterizing and understanding the processes that created the partially contained outcrop, this outcrop can now be used as an analog for other similar depositional systems. Oil and gas companies use these outcrop analogs to aid in reservoir prediction for comparable deposition systems in the subsurface. Regionally, the context of the Zorrillo Unit within the Magallanes Basin is ambiguous and by characterizing it, details are added to this part of the basin’s history.