Tidal inlet sequence, Sundance Formation (Upper Jurassic), north‐central Wyoming

Abstract

The sandstones and coquinas of the upper 20 m of the Sundance Formation are interpreted as a tidal inlet, back‐barrier shoal and sandy tidal‐flat sequence deposited at the close of marine Jurassic sedimentation in north‐central Wyoming. The barrier strandline maintained a generally E‐W trend as it prograded to the north. The lateral migration of inter‐barrier tidal inlets along the regressive shoreline of the late Sundance sea caused the coquinas and sandstones of the uppermost Sundance Formation to be deposited as tabular, laterally‐extensive units. Tidal bundles, sigmoidal reactivation surfaces, herringbone cross‐lamination and abundant mud drapes within the sandstones are evidence of considerable tidal influence during the deposition of the uppermost Sundance Formation. Earlier models, which attach an offshore environment of deposition to the sequence, do not explain the tabular geometries of the sandstone and coquina units and their conformable stratigraphic relationship with the overlying non‐marine sediments of the Morrison Formation.

Tidal influence in Cretaceous fluvial strata from Utah, USA: a key to sequence stratigraphic interpretation

“…Scale bar= 15 cm. Uhlir et al, 1988). Tidal bundle sequences are characterized by several internal mudstone drapes and reactivation surfaces that may have been produced by migration of the tidal bedform in response to a few tidal cycles near spring tide conditions.…”

Stacked fluvial and tide‐dominated estuarine deposits in high‐frequency (fourth‐order) sequences of the Eocene Central Basin, Spitsbergen

“…The sigmoidal beds with increasing to decreasing foreset angle and cross‐strata thickness are interpreted as representing as acceleration changing to full vortex flow conditions, followed by deceleration within a single ebb tide (sigmoidal beds in Shanley et al ., 1992; see also Boersma & Terwindt, 1981b; Allen & Homewood, 1984; Kreisa & Moiola, 1986; Uhlir et al ., 1988). The reactivation surfaces bounding the sigmoidal beds have also here been interpreted as resulting from reversals of flow directions (Boersma, 1969; Boersma & Terwindt, 1981a,b; Allen & Homewood, 1984; Shanley et al ., 1992).…”

Integrated approach of lithofacies and granulometric analysis of the sediments of the Proterozoic Upper Kaimur Group of Vindhyan Supergroup, Son Valley, India: Palaeo‐environmental implications

“…The tidal bundles are formed as a result of fluctuation in current strength, direction, and water depth (Basilici, Deluca, & Oliveria, ; Boersma & Terwindt, ). The thickness variation in bundles is believed to result from neap–spring variations in maximum tidal current velocity and a number of other factors, which cause sediment transport rates in the dominant current direction (and therefore bedform migration rates) to vary (Uhlir, Akers, & Vondra, ). During a neap cycle, tidal bundles are arranged in thin bundles because the tidal range and current speed is at a minimum at that time (Mazumder & Arima, ), and during a spring cycle, thick bundles of a tidal rhythms are present.…”