Geology Reference
In-Depth Information
Fig. 17.5
Thickly stacked
(11 m) sets of mainly planar
cross-strata within a
coarsening and thickening-
upward, tide-dominated,
delta-front unit in Seminoe-1
Sandstone, Haystack
Mountains Formation, near
Sinclair, Wyoming. Many of
the dunes were west and
northwest migrating
(landward) (Photo courtesy
S. Ahmed)
Fig. 17.6
Very thin mudstone or organic drapes on tangential cross-stratal foresets are a common tidal signal. There are also thin
ripple-laminated sets within the larger cross-strata. Seminoe Sandstone, Haystack Mountains Formation, south of Rawlins, Wyoming
brought out from the tidal distributaries (Ichaso and
Dalrymple
2009
). Such mudstone layers, in alternation
with medium-grained sandstone beds, create a charac-
teristic grain-size bi-modality within the delta-front
facies succession ( Fig.
17.10
), contrasting greatly with
the more homogeneous grain-size character of storm
wave-dominated delta fronts, that are much more com-
mon in WIS shoreline successions. Another feature of
the prodelta and lower delta front deposits of such tide-
dominated deltas is a somewhat stressed ichnofacies
