ALBERT

Description: :  Recent analysis of modern aggradational continental sedimentary basins reveals that sedimentation patterns are dominated by distributive fluvial systems (DFSs). The Salt Wash Member of the Late Jurassic Morrison Formation has previously been described as a fan-shaped fluvial system. This study characterizes facies variations across the Salt Wash DFS to quantitatively test predicted trends in conceptual DFS models. Notable proximal-to-distal trends include a change in total thickness of the fluvial succession from 174 m to 40 m, and an average grain size from coarse sand to silt, while the percentage of sand decreased from 70% in the proximal region to 8% in the distal region. The proportion of amalgamated channel-belt deposits decreased from 67% to 0%, while floodplain facies and lacustrine deposits increase (38% to 94% and 0.1% to 7% respectively). A downstream decrease in average channel-belt thickness (15 m to 3.8 m, from thickest to thinnest) and average story thickness (7.7 m to 2.3 m, from thickest to thinnest) is also recorded. Significant downstream changes in deposit architecture were also noted, with proximal regions dominated by stacked channel-belt deposits with a high degree of amalgamation. Distal deposits are dominated by floodplain muds and sheet sandstones and sparse ribbon channels, with little to no amalgamation of channel deposits. This study provides quantified information for an ancient DFSs with the aim of providing a dataset that can be used for objective comparison between different DFSs, as well as providing numerical data to aid resource exploration and modelling efforts.

Description: A bstract :  Regression relationships are derived relating the areal extent of large distributive fluvial systems (DFSs) (〉 30 km in length) formed in endorheic basins to contributing drainage area. The resulting correlation coefficients vary between 79% and 98%. Derived correlation values are strikingly similar when stratified by climate, large-scale tectonic regime, and basin context. Regression-equation exponent values range from 0.41 to 0.75, indicating a strong positive relationship between drainage area and DFS area, while coefficients account for the influence of external parameters on the derived relationships. Analysis of the dataset using planform morphology and drainage-basin slope as additional variables reveals that regressions for braided bifurcating DFS produce a highly significant relationship. The relationship suggests that drainage-basin relief influences sediment supply to the sedimentary basin in terms of volume or caliber, which in turn affects the depositional gradient of the DFS surface and resultant channel planform. An evaluation of the predictive capability of the regression equations reveals that the relationships derived from braided bifurcating DFSs perform best, with 80% of the predicted values falling within ± 25% of the measured DFS area value, with a third of the predicted values within ± 10% of the measured DFS area value. Application of the regression relationships derived here to rock-record examples of fluvial deposits interpreted as large DFSs show that DFS area can be used as a proxy to predict the surface area of fluvially transported sediment deposited in a sedimentary basin from the contributing drainage-basin area. The regression relationships for modern drainage areas and corresponding DFS areas from a range of tectonic and climatic settings suggest a measurable link between source and sink in the sedimentary rock record. The results provide a potential tool for more accurate reconstruction and prediction of preserved fluvial deposits and basin-fill architecture within basin-scale climatic and tectonic contexts.

Description: A bstract :  Large Igneous Provinces (LIPs) have been implicated in some of the largest environmental perturbations to have affected the Earth through geological time. Yet the impact of LIP development on drainage and ecosystem development in the immediate vicinity of these provinces are still poorly constrained to date. Based on a detailed, integrative facies scheme we characterize the interaction between volcanism and fluvial, lacustrine, and wetland environments in the Miocene Columbia River Flood Basalt Province (CRBP) LIP exposed in central Washington State, USA. The facies scheme proposed here comprises a detailed description and interpretation of siliciclastic, bioclastic (diatomite), volcaniclastic, and paleosol facies and subfacies intercalated with lavas of the Columbia River Basalt Group (CRBG). Facies and facies associations of individual interbeds are further correlated to reconstruct changes in sedimentary settings and topography of lava fields during deposition. Field observations and facies analysis help to explain the effects of flood-basalt volcanism on drainage-system development. We propose a generic model of lava–drainage interplay and distribution of sedimentary settings in flood-basalt provinces, which will contribute to our understanding of sedimentological, environmental, and volcanic processes in the CRBP. Hydrocarbon exploration in volcanic terrains requires detailed information on the distribution and development of sedimentary settings. This model will help to better predict the character and distribution of sedimentary bodies and potential hydrocarbon reservoirs in volcanic terrains.

Description: A bstract :  Knowing the position of an apex of a distributive depositional system can provide important spatial constraints on paleogeographic reconstructions, and thus can greatly help facies predictions, at both a system and a basin scale. To date, predicting the position of an apex of a sedimentary system is often limited to generalized statements based on facies mapping and qualitative analyses of paleocurrent readings. This paper presents a user-friendly quantitative methodology based on the von Mises distribution and uses the method of maximum likelihood to obtain an estimated apex and associated confidence regions for a dataset. The methodology presented has been applied to two modern distributive fluvial systems (DFSs), the Taquari DFS, situated in southwestern Brazil, and the Gilbert DFS, situated in northwestern Queensland, Australia. The position of each apex is known for the two systems, thus allowing the accuracy of the methodology to be tested. A range of datasets, within which the amount and spatial distribution of localities were selected independently, was analyzed. The predicted apices came within encouraging proximity of the true apices, ranging in distance from 2.7 km to 40.3 km (1.6 to 23.4% of the total DFS length) away, with accuracy generally increasing with increasing dataset size and proximity to the apex. Data collected from the Late Jurassic Salt Wash DFS were also analyzed using the code. Results have helped to give better geographical constraints on the system and apex location as well as on the southern margin of the Morrison depositional basin. Although tested on modern and outcrop-based datasets from DFS, the methodology can be applied to any dataset, subsurface or surface, in which dispersion occurs from a point source, thus unlocking the potential for better paleogeographic constraint on a broad range of sedimentary environments such as deltas and submarine fans.