Environmental Engineering Reference
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FIGURE 4
Early Cambrian St. Piran Formation, Gog Group, southern Rocky Mountains, Canada.
(A) Vertical succession of two intertidal parasequences composed of mixed-flat and mud-flat
deposits. (B) Mud flat bedding-plane view (top) containing wrinkle marks (W), associated with
the grazing trace fossils
Helminthoidichnites
isp. (
He
) and
Helminthopsis tenuis
(
Hp
).
2.3 Mixed Flats
Mixed flats occur across the transition between sand flats (
<
5% mud content)
and mud flats proper (
95%mud content), and are characterized by alternating
bedload sedimentation and fallout from suspension (
Figs. 2 and 4
A;
Flemming,
2012
). Deposits typically consist of thinly interbedded wave- and current-ripple
cross-laminated, very fine-grained sandstone and massive or parallel-laminated
mudstone. Heterolithic tidal bedding is typical, being mostly represented by
sand/mud rhythmites and flaser or wavy bedding (
Fig. 5
A). Flat-topped ripples
and washout structures may also be present.
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