Browsing by Subject "Incised valley"
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Item Contribution of additional sediment to a basin by valley incision and controls on valley preservation in stratigraphy(2015-05) Pace, Allison Jonell; Fisher, W. L. (William Lawrence), 1932-; Mohrig, DavidIn stratigraphy, there have been many studies looking at the geomorphological features generated during sea level variations and the resulting preserved erosional composite unconformities that evolve over time and thus do not correlate to a valley that existed at one given time (Strong & Paola, 2008). Data from the XES 02 experiment that isolated sea level variations from sedimentation and subsidence rates offered a way to look at the exclusive influence of sea level fluctuations on sediment transportation and stratigraphic preservation of valleys (Kim et al., 2006a). This study estimated the amounts of sediment deposited in an experimental basin through time in order to determine (1) the role of valley incision as a basinal sediment source, , and (2) how much of a valley formed during maximum sea level fall is preserved within the basin stratigraphy. Significant valley incision was found during times of rapid sea level fall. Valley incision increased erosion rates up to 5 times those recorded during sea level highs, resulting in a doubling of the basinward sedimentation rates. Stratigraphic preservation of valleys was low, but in those locations where a valley fragment was observed, most of the original valley wall remained. More instances of valley preservation occurred when rapid sea level falls occurred during times of slow, overall sea level rise. Maximum reworking and basinward transport of sediment occurred during rapid sea level falls in an overall falling sea level regime, while preservation of the valleys was greatest during times when rapid falls occurred in an overall rising sea level regime.Item Evidence for changes in coastline-controlled base level from fluvial stratigraphy at Aeolis Dorsa, Mars(2014-12) Cardenas, Benjamin Thomas; Mohrig, David; Kocurek, GaryThere is evidence that a subset of fluvial deposits at Aeolis Dorsa, a basin on Mars, preserve incised valleys carved and filled during changes in base level, which was likely controlled by water surface elevation of a large lake or sea. Three low-albedo, channelized corridors, each several tens of kilometers long, contain relict point bars and scooped boundaries at their bases, indicating that the base and lateral extent of each corridor was defined by a migrating, net-erosional river. Above the basal deposits are stacks several tens of meters thick of “inverted sinuous ridges”, which are channel-filling deposits that have been exhumed and topographically inverted. Indicators of avulsions, channel re-occupations, an overall flattening of basal topography, and confinement of inverted sinuous ridges to the dark corridors are evidence of the gradual filling of a valley cut by the basal migrating river. Valley incision and fill are common responses to sea level change on Earth. Aeolis Dorsa is currently open to the northern lowlands of Mars, where an ocean has been hypothesized to have once existed, although a large lake could have also controlled base level. Cross-cutting valleys require at least two episodes of base level fall and rise. The magnitudes of the base level changes are estimated at about 80 meters, based on the thickness of the valley-filling stratigraphy. Meander asymmetry is consistent with a southeastern flow direction, and is supported by a set of branching fluvial deposits 40 km to the southeast which, qualitatively, appear to be deltaic in origin.Item Regional character of the lower Tuscaloosa formation depositional systems and trends in reservoir quality(2012-12) Woolf, Kurtus Steven; Wood, Lesli J.For decades the Upper Cretaceous Lower Tuscaloosa Formation of the U.S. Gulf Coast has been considered an onshore hydrocarbon play with no equivalent offshore deposits. A better understanding of the Lower Tuscaloosa sequence stratigraphic and paleogeographic framework, source-to-sink depositional environments, magnitude of fluvial systems, regional trends in reservoir quality, and structural influences on its deposition along with newly acquired data from offshore wells has changed this decades-long paradigm of the Lower Tuscaloosa as simply an onshore play. The mid-Cenomanian unconformity, underlying the Lower Tuscaloosa, formed an extensive regional network of incised valleys. This incision and accompanying low accommodation allowed for sediment bypass and deposition of over 330 m thick gravity-driven sand-rich deposits over 400 km from their equivalent shelf edge. Subsequently a transgressive systems tract comprised of four fluvial sequences in the Lower Tuscaloosa Massive sand and an overlying estuarine sequence (Stringer sand) filled the incised valleys. Both wave- and tide-dominated deltaic facies of the Lower Tuscaloosa are located at the mouths of incised valleys proximal to the shelf edge. Deltaic and estuarine depositional environments were interpreted from impoverished trace fossil suites of the Cruziana Ichnofacies and detailed sedimentological observations. The location and trend of valleys are controlled by basement structures. Lower Tuscaloosa rivers were 3.8m – 7.8m deep and 145m – 721m wide comparable to the Siwalik Group outcrop and the modern Missouri River. These systems were capable of transporting large amounts of sediment indicating the Lower Tuscaloosa was capable of transporting large amounts of sediments to the shelf edge for resedimentation into the deep offshore. Anomalously high porosity (>25%) and permeability (>1200md) in the Lower Tuscaloosa at stratigraphic depths below 20,000 ft. are influenced by chlorite coating the detrital grains. Chlorite coatings block quartz nucleation sites inhibiting quartz cementation. Chlorite coats in the Lower Tuscaloosa are controlled by the presence and abundance of volcanic rock fragments supplying the ions needed for the formation of chlorite. Chlorite decrease to the east in sediments derived from the Appalachian Mountains. An increase in chlorite in westward samples correlates with an increase of volcanic rock fragments derived from the Ouachita Mountains.