Browsing by Subject "Clinoform"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item High frequency sequence stratigraphic controls on stratal architecture of an upper Pennsylvanian "regressive limestone" (Bethany Falls limestone), Midcontinent, USA(2010-12) Butler, Graham J.; Holterhoff, Peter; Barrick, James E.; Asquith, George B.The Early Missourian (Upper Pennsylvanian) Bethany Falls Limestone (BFL) is the highstand–falling stage carbonate member of the Swope high frequency sequence as developed on the northern platform of the Mid-continent Basin. It is underlain by the condensed Hushpuckney Shale (maximum flooding surface) and is overlain by the Galesburg Shale (lowstand of the Dennis sequence). The Swope sequence is a significant hydrocarbon reservoir in the subsurface of western Kansas with outcrops of excellent reservoir analog lithofacies exposed in eastern Kansas and adjacent states. Although the BFL is often considered a uniform shallowing–upward carbonate system, we hypothesize that traceable flooding and erosion surfaces can be recognized within the BFL and that these surfaces define basinward–stepping carbonate clinothems. Recognizing this internal architecture is critical for understanding the potential controls on the deposition and diagenesis of oolite facies developed across the region within the BFL. Flooding surfaces within the BFL are recognized by mudrock (clay-rich shale) partings throughout the carbonate succession. Distinctive conodont biofacies collected from these mudrocks aid in correlation and provide some confidence in mapping these surfaces across the region, although not without some ambiguity. Correlations indicate that basinward stepping clinothem packages can be recognized within the BFL. Conodont abundances and species occurrences also aid in the determination of the depositional environments of the flooding surfaces. Proximal occurrences of the mudrock partings contain a lower abundance, lower diversity fauna compared to more distal locations along a clinoform profile. Unexpected faunas with the presence of “deepwater” genera and high overall abundances in the lower BFL are noted at some locations. These occurrences appear to coincide with structural highs and may represent transitional facies with the underlying condensed horizon. Distinctive lithofacies offsets and internal exposure surfaces indicate the presence of high frequency sequence boundaries within the BFL. These offsets are mappable and, like the flooding surfaces, define clinothem packages. The distribution of carbonate lithologies within these stratal packages is consistent with basinward progradation of facies throughout clinothem deposition. Using this combined knowledge it is possible to identify high frequency sequence boundaries (HFSB) within this forced regressive package.Item Slope to basin-floor evolution of channels to lobes, Jurassic Los Molles Formation, Neuquén Basin, Argentina(2013-12) Vann, Nataleigh Kristine; Steel, R. J.; Olariu, CornelAbstract Slope to Basin-floor Evolution of Channels to Lobes, Jurassic Los Molles Formation, Neuquén Basin, Argentina Nataleigh Kristine Vann, MS Geo Sci The University of Texas at Austin, 2013 Supervisor: Ronald J. Steel and Cornel Olariu The relatively steep and short-headed Neuquén Basin margin provides an excellent laboratory for demonstrating down slope changes in sediment gravity flow bed thickness, grain size and facies, as well as channel to lobe transitions. Approximately 400m high clinoformal, shelf-slope-basin-floor deposits of Jurassic Los Molles Formation outcrops are evaluated for reservoir scale definition of facies and architectures in the La Jardinera field area, Neuquén Basin. Slope deposits represent the accretionary front of the prograding shelf margin that were fed by a coarse grained shelf (Lajas Formation). Mapping of a high-resolution satellite images draped on digital elevation model resolved a sub-meter stratigraphic framework. Thirty-three measured sections from outcrops exposed along a 5km transect characterize the evolution of sand body architectures from the shelf edge to the basin floor. The Neuquén Basin margin is typified by four main depositional environments that transition from shelf edge incisions filled with conglomerates, to confined channels in upper- to middle-slope reaches, to weakly confined channels on the lower slope to sheet-like lobes and distributary channel complexes that drape onto both the lower slope and basin floor. Along the slope to basin floor profile the depositional architecture changes by overall decrease in grain size, amalgamation of beds and degree of erosion. Confined slope channels are up to 25m deep, isolated within muddy slope deposits and have complex multistory fills marked by basal and internal erosive contacts lined with mud-clast and/or pebble conglomerates. Channel axes contain amalgamated, medium to coarse sandstones that thin and fine towards channel margins over 100m. Down dip, lower slope channels are up to 400m wide and less than 10m thick. A marked reduction in mud clasts and conglomeratic material at basal erosional surfaces in weakly confined channels represent a downslope decrease in flow energy. However, distinct meter scale erosion surfaces continue to be recognizable where thin ripple laminated sands are truncated on channel margins by amalgamated structureless sands. Erosional surfaces are absent in laterally extensive (>5km), sheet-like lobes of basin-floor fans that are generally finer grained than lower or upper slope channel fills. There are lenticular debrites and thin micro-conglomerates associated with basin-floor fans.Item Stratigraphic implications of the spatial and temporal variability in sediment transport in rivers, deltas and shelf margins(2010-05) Petter, Andrew Lucas, 1980-; Steel, R. J.; Mohrig, David; Fisher, William; Wood, Lesli; Olariu, CornelSediment delivery to a basin exerts a first-order control over sedimentation, and therefore study of sedimentary rocks can reveal information about the nature of sediment delivery in the past. This dissertation examines several aspects of this problem using experimental, outcrop, and subsurface data. Flume experiments were undertaken to test the combined effects of autogenic alluvial aggradation and forced regression on the development of fluviodeltaic stratigraphy. Alluvial aggradation occurred in response to steady relative sea-level fall, and eventually consumed the entire sediment budget as the river lengthened in response to forced regression. The Campanian Lower Castlegate Sandstone (Utah) was studied as a potential ancient analog resulting from similar autogenic behaviors as observed in the experiments. Extensive measurement of grain-size distributions and paleo-flow depths from outcrop were utilized to explore downstream changes in paleo-hydraulics of the ancient fluvial systems in the Lower Castlegate in response to extensive alluvial aggradation and consequent loss of sediment from transport. An interesting finding was the stratigraphic signature of backwater hydraulic conditions in the distal reaches of the Lower Castlegate paleo-rivers. Finally, a simple and novel inversion scheme was developed for estimating paleo-sediment flux from ancient shelf-margin successions. An advantage of the methodology is that it allows for both spatial and temporal reconstruction of paleo-sediment flux patterns. The inversion scheme was applied to shelf-margin successions in the Washakie-Sand Wash Basin of Wyoming, the New Jersey Atlantic margin, the North Slope of Alaska, and the Zambezi margin of East Africa using published subsurface datasets. The Neogene passive margins within the studied datasets were found to consistently deposit around one-third of their total sediment budget on the shelf-margin topset, and bypass two-thirds of their budget beyond the shelf edge. The implications of this finding on the flux of terrestrial-derived particulate organic carbon (POC) from rivers to the ocean were explored, and a long-term average flux of POC to deepwater storage was estimated. The sediment-flux inversion scheme was also applied to derive input parameters for stratigraphic modeling of the Ebro margin. The modeling results indicate that the autostratigraphic behavior of the margin may have been previously underestimated.