Epeirogenic movement

Abstract: The stratigraphy and correlation of Triassic to Plio-Pleistocene sediments within the Iranian Oil Consortium Agreement Area are discussed. Rock-stratigraphic units are named and defined. These are correlated with the Iraq, Kuwait, and Saudi Arabian stratigraphic successions. The Agreement Area, situated northeast of the Arabian shelf and including part of the Zagros orogenic area, has been the site of more or less continuous sedimentation from Triassic to Plio-Pleistocene time. Regional disconformities occur at the top of the Aptian, the Cenomanian-Turonian, the Cretaceous, and the Eocene. A major angular unconformity produced by Mio-Pliocene folding occurs at the top of the Fars Group. Carbonate and shale deposition controlled by epeirogenic movements dominated until Late Cretaceous time when movements within the Zagros area began to influence sedimentation. Upper Cretaceous, Paleocene, Eocene, and Oligocene deposits are characterized by sharp facies and thickness changes as a result of orogenic movements in the Zagros area. Following deposition of the O igocene-lower Miocene Asmari Formation the Agreement Area was part of a trough trending northwest-southeast. After initial evaporitic and marine phases, this trough was filled by clastics derived from the rising Zagros Mountains on the northeast. Conglomerates of the Bakhtyari, deposited unconformably upon the Fars Group, mark the end of this basinal filling.

Abstract: A mechanism is proposed to explain epeirogenic motions of craton interiors in terms of the response of the lithosphere to subduction. The effects of changes in sea level are distinguished from subsidence of the basement by analyzing the tilt of chronostratigraphic sequences in which the bounding horizons were deposited at approximately the same elevation with respect to sea level. As an example, the Late Cretaceous subsidence and Tertiary uplift of the western interior of North America is examined, and a maximum tilt amplitude of 3 km, with a horizontal deflection scale of approximately 1400 km, is inferred. The link between platform sedimentation and subduction is tested by using numerical models of mantle convection which mimic the subduction and by examining the horizontal scale of the deflections to the overlying lithosphere. It is found that this scale is relatively insensitive to the temperature contrast between the slab and the surrounding mantle, the flexural rigidity of the lithosphere, and even the physical process assumed to govern the subduction. The most important factor affecting the scale is the dip of the subduction zone, and shallower subduction angles (less than 45°) can produce horizontal deflections of the order of 1000 km or more. In contrast, the vertical scale of the deflection is sensitive to all the above parameters. Using these results, two subduction models are introduced which predict both the time and length scales of the North American tilt, and it is conjectured that the process may be responsible for other regions of platform subsidence where subducted lithosphere may have passed beneath the continent at a shallow angle.

Abstract: The Cenozoic fill of the Gulf of Mexico basin contains a continuous record of sediment supply from the North American continental interior for the past 65 million years. Regional mapping of unit thickness and paleogeography for 18 depositional episodes defines patterns of shifting entry points of continental fluvial systems and quantifies the total volume of sediment supplied during each episode. Eight fluvio-deltaic axes are present: the Rio Bravo, Rio Grande, Guadalupe, Colorado, Houston-Brazos, Red, Mississippi, and Tennessee axes. Sediment volume was calculated from digitized hand-contoured unit thickness maps using a geographic information system (GIS) algorithm to sum volumes within polygons bounding interpreted North American river contribution. General age-dependent compaction factors were used to convert calculated volume to total grain volume. Values for rate of supply range from >150 km to <10 km3/Ma. Paleogeographic maps for eleven Cenozoic time intervals display the evolving matrix of elevated source areas, intracontinental sediment repositories, known and inferred drainage elements, and depositional fluvial/deltaic depocenters along the northern Gulf of Mexico basin margin. Patterns of sediment supply in time and space record the complex interplay of intracontinental tectonism, climate change, and drainage basin evolution. Five tectono-climatic eras are differentiated: Paleocene late Laramide era; early to middle Eocene terminal Laramide era; middle Cenozoic (Late Eocene–Early Miocene) dry, volcanogenic era; middle Neogene (Middle–Late Miocene) arid, extensional era; and late Neogene (Plio–Pleistocene) monsoonal, epeirogenic uplift era. Through most of the Cenozoic, three to four independent continental-scale drainage basins have supplied sediment to the Gulf of Mexico.