Sharp‐based, tide‐dominated deltas of the Sego Sandstone, Book Cliffs, Utah, USA

Abstract

The lower part of the Cretaceous Sego Sandstone Member of the Mancos Shale in east‐central Utah contains three 10‐ to 20‐m thick layers of tide‐deposited sandstone arranged in a forward‐ and then backward‐stepping stacking pattern. Each layer of tidal sandstone formed during an episode of shoreline regression and transgression, and offshore wave‐influenced marine deposits separating these layers formed after subsequent shoreline transgression and marine ravinement. Detailed facies architecture studies of these deposits suggest sandstone layers formed on broad tide‐influenced river deltas during a time of fluctuating relative sea‐level. Shale‐dominated offshore marine deposits gradually shoal and become more sandstone‐rich upward to the base of a tidal sandstone layer. The tidal sandstones have sharp erosional bases that formed as falling relative sea‐level allowed tides to scour offshore marine deposits. The tidal sandstones were deposited as ebb migrating tidal bars aggraded on delta fronts. Most delta top deposits were stripped during transgression. Where the distal edge of a deltaic sandstone is exposed, a sharp‐based stack of tidal bar deposits successively fines upward recording a landward shift in deposition after maximum lowstand. Where more proximal parts of a deltaic‐sandstone are exposed, a sharp‐based upward‐coarsening succession of late highstand tidal bar deposits is locally cut by fluvial valleys, or tide‐eroded estuaries, formed during relative sea‐level lowstand or early stages of a subsequent transgression. Estuary fills are highly variable, reflecting local depositional processes and variable rates of sediment supply along the coastline. Lateral juxtaposition of regressive deltaic deposits and incised transgressive estuarine fills produced marked facies changes in sandstone layers along strike. Estuarine fills cut into the forward‐stepped deltaic sandstone tend to be more deeply incised and richer in sandstone than those cut into the backward‐stepped deltaic sandstone. Tidal currents strongly influenced deposition during both forced regression and subsequent transgression of shorelines. This contrasts with sandstones in similar basinal settings elsewhere, which have been interpreted as tidally influenced only in transgressive parts of depositional successions.

Depositional and provenance record of the Paleogene transition from foreland to hinterland basin evolution during Andean orogenesis, northern Middle Magdalena Valley Basin, Colombia

“…Marine influence is deemed significant by the presence of arenaceous foraminifera (Linke and Lutze, 1993) and symmetric ripples suggestive of wave influence. These ripples and the lack of hummocky cross-stratification indicate wave-influenced deposition under relatively weak oscillatory flows (Tye et al, 1999;Willis and Gabel, 2001). Thin (cm-scale) tabular sandstone beds formed as a result of wave reworking and discontinuous storm deposition.…”

Extensive carbonate cementation of fluvial sandstones: An integrated outcrop and petrographic analysis from the Upper Cretaceous, Book Cliffs, Utah

“…2). Due to excellent outcrops, this area has been the focus of several recent sedimentological and stratigraphic studies (e.g., Van Wagoner et al, 1990;Van Wagoner, 1995;O'Byrne and Flint, 1995;Pattison, 1995Pattison, , 2005aPattison, , 2005bHampson et al, 1999Hampson et al, , 2001Hampson, 2000Hampson, , 2010Willis and Gabel, 2001;Hettinger and Kirschbaum, 2002;Howell and Flint, 2003;Pattison et al, 2007), which have significantly improved the understanding of stratigraphic and sedimentological processes in shoreface and coastal plain strata.…”

Deltas and Sea-Level Change

“…Depending on the dominant regime type, mouth-bar to delta-front deposits range from heterolithic hyperpycnites in river-dominated deltas (e.g., Rodriguez et al 2000), hummocky cross-bedded facies in wavedominated systems (e.g., Bhattacharya and Walker 1992), to complex, heterolithic bars in tide-dominated ones (Willis and Gabel 2001), or a combination of these in mixed-energy systems (Bhattacharya and Giosan 2003). It is worth emphasizing that for strong wave or tidal signatures, deltas may not always be easily distinguishable from prograding shorefaces (Bhattacharya and Walker 1992), or estuarine complexes (Porębski 1995(Porębski , 2000, respectively.…”