Abstract
Rivers transport sediments in a source to sink system while responding to allogenic controls of the depositional system. Stacked fluvial sandstones of the Middle Pennsylvanian (Desmoinesian Stage, ~310 – 306 Ma) Allegheny Formation (MPAF) exposed at Birch River, West Virginia exhibit change in sedimentary structure and depositional style, reflecting changes in allogenic behavior. Paleohydrologic and numerical analysis were used to quantify geomorphological and paleohydrologic variations reflected by MPAF fluvial deposits with the goal of understanding the controls on resulting fluvial sandstone architecture in these different systems. Channel body geometry, sedimentary structures, and sandstone grain size distribution were used to reconstruct the paleoslope and flow velocity of the MPAF fluvial systems. In order to enhance paleohydrological estimates, machine learning methods including multiple regression and Support Vector Regression (SVR) algorithms were used to improve the dune height, and channel depth estimated from cross-set thickness. Results show that the Channel depths of the lower MPAF beneath the Lower Kittanning coal beds tend to decrease upsection; this decrease may reflect a transition from fluvial systems formed in a humid ever-wet climate to fluvial systems formed in less humid, seasonally wet, semi-arid climate. Paleohydraulic estimations enabled the evaluation of hydraulic changes in the fluvial depositional systems of the Appalachian Basin during the Desmoinesian stage. Paleoslope estimates indicated that the slope was low which indicated that the fluvial gradient response was not driven by the effect of tectonic subsidence or uplift and sea-level change.
Highlights
Fluvial systems are the main terrestrial conduits for transporting the sediment load of a source to sink system
This paper proposes an enhanced methodology with which to estimate the paleohydrology and paleo-geomorphology of fluvial channels, using the fluvial sandstone deposits of the lower part of the Middle Pennsylvanian Allegheny Formation (MPAF) of Central West Virginia as a case example (Figures 1, 2)
This study used numerical modeling to highlight changes in fluvial channel geomorphology and hydrology that coincides with periods of paleoclimate change during the Middle Pennsylvanian
Summary
Fluvial systems are the main terrestrial conduits for transporting the sediment load of a source to sink system. Changes in fluvial hydrology lead to changes in sediment transport and deposition, which alter channel aggradation, channel incision, and channel morphology (Leeder, 1993, 2009; Holbrook and Wanas, 2014). Fluvial channels in seasonal semi-arid climates have different geomorphology and hydrologic processes from fluvial channels of ever-wet humid climates (Fielding et al, 2009; Allen et al, 2014; Plink-Björklund, 2015). Modern fluvial depositional system analogs indicate that fluvial systems in seasonal semi-arid climatic regions typically have a greater channel width to depth ratio than fluvial channels of ever-wet humid climatic region (Fielding et al, 2009; Gibling et al, 2014)
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