3-D Architecture and Sequence Stratigraphic Evolution of a Forced Regressive Top-Truncated Mixed-Influenced Delta, Cretaceous Wall Creek Sandstone, Wyoming, U.S.A.

Abstract

Ground-penetrating radar (GPR) is used to delineate the 3-D facies architectural elements and examine the evolution of a top-truncated, forced-regressive, mixed-influenced delta front in the Cretaceous Wall Creek Member of the Frontier Formation, Wyoming. The GPR data provide a bridge between outcrop facies architecture and recently published high-resolution 2-D seismic studies of Quaternary delta systems. The GPR data were integrated with outcrops, photomosaics, cores, and GPS data. Two orthogonal grids of 2-D GPR profiles provide information on the 3-D facies architecture and stratigraphy of the deltaic deposits. Three main GPR architectural elements are identified within the delta front: (1) mouth bars are characterized by seaward-dipping reflections (foreset beds) in dip view, and mounded bidirectionally downlapping reflections in strike view; (2) shallow delta-slope channels show truncation and onlap and also show low-angle landward (northwest) dipping reflections. The mouth bars are locally interrupted by (3) sub-horizontal radar reflections that are interpreted as tidally modulated bars. Within the mouth-bar radar facies, both top-preserved (proximal) and top-truncated (distal) examples are observed. Top-preserved proximal bars show evidence of mounded bar crests and landward accretion, as is observed in the upstream end of mouth bars on the modern Atchafalaya Delta in the Gulf of Mexico. Distal bar deposits primarily comprise the top-truncated, seaward-dipping foresets.The GPR interpretation shows two laterally overlapping delta lobes, interpreted to represent autocyclic delta switching. The older lower lobe forms a fan-shaped delta lobe composed of top-truncated coalesced mouth bars. The second phase of bars is largely top-preserved, building over the older bars. The presence of thicker bedsets and upstream accretion suggests that the younger lobe was quickly abandoned, as seen in the overlying transgressive ravinement. Although marine erosion during transgression was less effective on these later-stage bar deposits, ravinement increased landward. A comparison of the architectural elements at a more regional scale in two separate Wall Creek delta lobes (Murphy Creek and Raptor Ridge, , 30 km apart) indicates that the bar complexes were deposited on the delta fronts as accretionary forced-regressive deposits during a relative sea-level fall; the older river-dominated deltaic deposits at the Murphy Creek site prograded southeastward (, 124u), whereas the younger and more tidally influenced Raptor Ridge bar deposits expanded southward (, 171u) before final abandonment and regional transgression. The most distal lowstand lobe sediments within the offlapping parasequence at Raptor Ridge are more completely preserved and also show the greatest tidal influence, compared to the more severely toptruncated Murphy Creek, which is in an otherwise more landward location. This challenges the notion that tidal facies are predominantly associated with transgressive or highstand systems tracts. Greater preservation of de...

Architecture of a forced regressive systems tract in the Turonian Ferron “Notom Delta”, southern Utah, U.S.A.

“…Reynolds, 1999;Enge and Howell, 2010;Olariu et al, 2010). Data from this study and others (Reynolds, 1999;Mellere and Steel, 2000;Tesson et al, 2000;Garrison and Van den Bergh, 2004;Lee et al, 2007) show that many of the forced regressive deposits have limited dip width and thickness, typically less than 5 km and 20 m respectively (Fig. 10), despite that sharp-based forced regressive deposits up to 100 km wide have been documented (e.g.…”

“…In recent years, there has been considerable increase in studies of forced regressive deposits due to their importance as hydrocarbon reservoirs (Posamentier et al, 1992;Plint and Nummedal, 2000;Posamentier and Morris, 2000; other papers in Hunt and Gawthorpe, 2000;Lee et al, 2007). Large-scale stratigraphic architecture of forced regressive deposits has been addressed in many previous studies (e.g., Posamentier et al, 1992;Posamentier and Allen, 1999;Posamentier, and Morris, 2000).…”

“…Very few of these studies, however, attempt to document bed-scale facies architecture to identify changes in sedimentology and reservoir architecture from one stage of relative sea-level fall to another. Lee et al (2007), using integrated outcrop and GPR data, recognized a change from river-dominated to strongly tide-influenced deltaic deposition in the forced regressive deposits in the Cretaceous Wall Creek Sandstone, Wyoming. Mellere and Steel (2010) identified down-dip changes in offlapping deltas that change from tide-influenced to fluvial-and waveinfluenced in the Cretaceous outcrops in Wyoming.…”

Variability In Sedimentological and Ichnological Signatures Across A River-Dominated Delta Deposit: Peay Sandstone Member (Cenomanian) of the Northern Bighorn Basin, Wyoming, U.S.A

“…Many of these bodies are top-truncated and elongate in planform, and have been interpreted as deltaic progradational cycles formed in response to lowering of relative sea level at various times during the Cenomanian and Turonian stages of the Cretaceous (Bhattacharya and Willis 2001;Sadeque et al 2007;Hutsky et al 2012). In the Powder River Basin of northeast Wyoming, such sandstone bodies have been interpreted as a series of overlapping wave-, tide-, and river-dominated delta lobes separated by prodelta mudstones (Lee et al 2007;Sadeque et al 2007;Gani et al 2007). …”

Facies control on sandstone composition (and influence of statistical methods on interpretations) in the John Henry Member, Straight Cliffs Formation, Southern Utah, USA

“…This facies represents the remains of a mouth bar (Orton and Reading, 1993;Bhattacharya and Giosan, 2003;Fielding et al, 2005;Lee et al, 2007). It is interpreted as a channel because it contains low velocity current-generated sedimentary structures and erosional surfaces.…”