Influence of Climate on Deep-Water Clastic Sedimentation: Application of a Modern Model, Peru–Chile Trough, to an Ancient System, Ouachita Trough
N. Terence Edgar, C. Blaine Cecil, 2003. "Influence of Climate on Deep-Water Clastic Sedimentation: Application of a Modern Model, Peru–Chile Trough, to an Ancient System, Ouachita Trough", Climate Controls on Stratigraphy, C. Blaine Cecil, N. Terence Edgar
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Traditionally, an abrupt and massive influx of siliciclastic sediments into an area of deposition has been attributed to tectonic uplift without consideration of the influence of climate or climatic change on rates of weathering, erosion, transportation, and deposition. With few exceptions, fluvial sediment transport is minimal in both extremely arid climates and in perhumid (everwet) climates. Maximum sediment transport occurs in climates characterized by strongly seasonal rainfall, where the effect of vegetation on erosion is minimal.
The Peru–Chile trench and Andes Mountain system (P–CT/AMS) of the eastern Pacific Ocean clearly illustrates the effects of climate on rates of weathering, erosion, transport, and deep-sea sedimentation. Terrigenous sediment is virtually absent in the arid belt north of lat. 30° S in the P–CT, but in the belt of seasonal rainfall south of lat. 30° S terrigenous sediment is abundant. Spatial variations in the amount and seasonality of annual precipitation are now generally accepted as the cause for this difference. The spatial variation in sediment supply to the P–CT appears to be an excellent modern analogue for the temporal variation in sediment supply to certain ancient systems, such as the Ouachita Trough in the southern United States.
By comparison, during the Ordovician through the early Mississippian, sediment was deposited at very slow rates as the Ouachita Trough moved northward through the southern hemisphere dry belt (lat. 10° S to lat. 30° S). The deposystem approached the tropical humid zone during the Mississippian, coincident with increased coarse clastic sedimentation. By the Middle Pennsylvanian (Atokan), the provenance area and the deposystem moved well into the tropical humid zone, and as much as 8,500 m of mineralogically mature (but texturally immature) quartz sand was introduced and deposited. This increase in clastic sediment deposition traditionally has been attributed solely to tectonic activity. However, we contend that the principal control on the introduction of abundant terrigenous sediment was the movement of the deposystem from an arid or semiarid climate into a seasonally wetter climatic regime. The physical and mineralogical maturity of the quartz sand is the result of tropical weathering in provenance areas.
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The role of climate as a primary control on stratigraphy is the cornerstone of this volume. The emphasis on climate is in distinct contrast to most previous studies, in which stratigraphic variability has been related to changes in sea level and in tectonic activity. Furthermore, the findings, derived from several years of detailed study of modern and ancient key geologic sections around the world, indicate that traditional depositional models generally do not fully explain the origin of fossil fuels. Although the results of the studies presented in this volume are intended to contribute to the disciplines of sedimentary geology and stratigraphy, the contributors recognize that their results may also contribute to a better understanding of global climate change. The theoretical background of climate control on sediment supply and stratigraphy is presented in the volume. With this background in place, detailed documentation and analysis of climate control on the lithologic variation of a single Middle Pennsylvanian.