Evolution of Lower Pennsylvanian Estuarine Facies within Two Adjacent Paleovalleys, Illinois Basin, Indiana
Erik P. Kvale, Mark L. Barnhill, 1994. "Evolution of Lower Pennsylvanian Estuarine Facies within Two Adjacent Paleovalleys, Illinois Basin, Indiana", Incised-Valley Systems: Origin and Sedimentary Sequences, Robert W. Dalrymple, Ron Boyd, Brian A. Zaitlin
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The lower Pennsylvanian strata in Indiana, Illinois, and western Kentucky rests unconformably on Mississippian to Devonian deposits within the midcontinent Illinois Basin. These deposits fill a complex drainage network of sub-Pennsylvanian paleovalleys with as much as 140 m of shale, sandstone, coal, and mudstone. Paleovalley widths are variable ranging from a kilometer to several kilometers wide and trend roughly northeast to southwest. Timing of valley incision is difficult to constrain and may have been diachronous. Filling of the southern reaches of the drainage system commenced during earliest Pennsylvanian while incision may have continued in the more northern (upland) reaches in Indiana.
The paleovalleys progressively filled from south to north during an overall transgressive sea-level rise. During sea-level rise, these valleys became the sites for estuarine deposition. Two relatively small paleovalleys (1 to 1.5 km wide) have been studied in detail in south-central Indiana. Lithofacies can be mapped down the valleys for several kilometers by using subsurface and outcrop data. Within these valleys, conglomerate and conglomeratic sand-dominated inner (upper) estuarine, mud-dominated estuarine central basin, and sand-dominated outer (lower) estuarine deposits can be identified. Central basin sediments overlie fluvial deposits. Direct evidence of tidal influence within the central basin deposits can be recognized by the presence of intertidal rhythmites that exhibit well developed neap-spring cycles. Outer estuarine deposits overlie the central basin deposits and accumulated during the final stages of valley-filling.
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Incised-Valley Systems: Origin and Sedimentary Sequences
Incised-Valley Systems: Origin and Sedimentary Sequences - Incised valleys were not widely recognized prior to the 1980?s. Most early workers forced the isolated, incised-valley deposits along an uncomformity into a single continuous unit, ignored them by including them within larger stratigraphic units, or interpreted them as deltaic distributaries or non-incised fluvial channels. In the last decade, intense interest in the influence that changes in accommodation space have on stratigraphic organization has focused attention on incised-valley systems, because they are one of the most visible records of major decreases in accommodation. In practical terms, they are also a significant key to the identification of sequence-bounding uncomformities. As a result, many successions have been re-examined and incised-valley fills are being found in rapidly growing numbers. This volume is an outgrowth of this widespread interest in incised-valley sedimentation. Many of the papers were initially presented at the Special Session on ?Recognition and Facies of Incised Valley Fills? held at the AAPG-SEPM Annual Meeting (Calgary) in June, 1992.