Facies architecture and geometry of landward‐stepping shoreface tongues: the Upper Cretaceous Cliff House Sandstone (Mancos Canyon, south‐west Colorado)

Abstract

The Campanian Cliff House Formation represents a series of individually progradational shoreface tongues preserved in an overall landward‐stepping system. In the Mancos Canyon area, the formation consists of four, 50‐ to 55‐m‐thick and 10‐ to 20‐km‐wide sandstone tongues, which pinch out landwards into lower coastal plain and lagoonal deposits of the Upper Menefee Formation and seawards into offshore shales of the Lewis Shale Formation. Photogrammetric mapping of lithofacies along the steep and well‐exposed canyon walls was combined with sedimentary facies analysis and mapping of the detailed facies architecture. Two major facies associations have been identified, one comprising the mostly muddy and organic‐rich facies of lagoonal and lower coastal plain origin and one comprising the sandstone‐dominated facies of shoreface origin. Key stratigraphic surfaces were identified by combining the mapped geometry of the lithofacies units with the interpretation of depositional processes. The stratigraphic surfaces (master ravinement surface, shoreface/coastal plain contact, transgressive surface, maximum flooding surface and the sequence boundary) allow each major sandstone tongue to be divided into a simple sequence, consisting of a basal transgressive system tract (TST) overlain by a highstand system tract (HST). Within each sandstone tongue, a higher frequency cyclicity is evident. The high‐frequency cycles show a complex stacking pattern development and are commonly truncated in the downdip direction by surfaces of regressive marine erosion. The complexities of the Cliff House sandstone tongues are believed to reflect changes in the rate of sea‐level rise combined with the responses of the depositional system to these changes. Synsedimentary compaction, causing a thickness increase in the sandstone tongues above intervals of previously uncompacted lagoonal/coastal plain sediments, also played a role. This study of the facies architecture, geometry and sequence stratigraphy of the Cliff House Formation highlights the fact that there may be some problems in applying conventional sequence stratigraphical methods to landward‐stepping systems in general. These difficulties stem from the fact that no single stratigraphic surface can easily be identified and followed from the non‐marine to the fully marine realm (i.e. from the landward to the basinward pinch‐out of the sandstone tongues). In addition, the effects of synsedimentary compaction and changes in the shoreface dynamics are not easily recognized in limited data sets such as from the subsurface.

Cenomanian rocks in the Sinai Peninsula, Northeast Egypt: Facies analysis and sequence stratigraphy

“…The paucity of carbonate fossils in this lithofacies implies unfavorable ecological conditions for organisms (such as low oxygenation and high organic acid). Such conditions prevail in the depositional setting close to a supratidal environment where coastal marshes generate organic acids responsible for dissolving calcareous shells (Olsen et al, 1999). This dolomitic quartzarenite is closely similar to that described by Khalifa (1996) at the supra-and upper intertidal zone of mixed clastic-carbonate cycles.…”

Preserved Stratigraphic Architecture and Evolution of A Net-Transgressive Mixed Wave- and Tide-Influenced Coastal System: The Cliff House Sandstone, Northwestern New Mexico, U.S.A.

“…Analysis of net-transgressive systems has demonstrated that significant sandbody thicknesses can be preserved (Olsen et al 1999;Allen and Johnson 2011) given the right conditions of shoreline migration during regressive-transgressive cycles. Of further importance is the preferential preservation of facies types which form the greater part of the rock record in these systems.…”

“…These characteristics arise from incomplete preservation and pronounced reworking of shoreline systems during their overall retreat (e.g., Curray 1964), however, thick net-transgressive shallow-marine successions containing abundant stacked sandbodies have been documented (Olsen et al 1999;Allen and Johnson 2011). Conceptual models indicate that preservation of nettransgressive shallow-marine strata requires overall retreat of the shoreline punctuated by periods of limited shoreline regression (e.g., Swift 1968;Swift et al 1991;Cattaneo and Steel 2000).…”

“…The Cliff House Sandstone crops out around the perimeter of, and is extensively penetrated by, wells in the center of the San Juan Basin in northwestern New Mexico and southwestern Colorado, where it comprises a mixed wave-and tide-dominated succession of stacked seaward-to landward-stepping units that record an overall transgression (Palmer and Scott 1984;Molenaar 1983;Donselaar 1989;Olsen et al 1999). Our mapping of facies architecture in a series of adjacent, depositional-dip-oriented canyons in Chaco Cultural Natural Historical Park has enabled quantitative three-dimensional reconstruction of key stratigraphic surfaces and sandbody distributions from near the local up-dip to down-dip pinch-outs of the transgressive sandstone complex.…”

Re-interpreting Great Lakes shorelines as components of wave-influenced deltas: An example from the Portage River delta (Lake Erie)

“…Rare outsized clasts and shell debris can be incorporated into the cross-bed sets. These deposits are interpreted as breaker bar deposits in a highenergy coastline setting (Olsen et al, 1999;Nouidar and Chellai, 2002).…”