Dynamics and facies model of a macrotidal sand‐bar complex, Cobequid Bay—Salmon River Estuary (Bay of Fundy)

Abstract

The 40‐km‐long, Cobequid Bay—Salmon River estuary has a maximum tidal range of 16·3 m and experiences limited wave action. Sediment, which is derived primarily from areas seaward of the estuary, is accumulating faster than the high‐tide elevation is rising, and the system is progradational. The deposits consist of an axial belt of sands, which is flanked by mudflats and salt marshes in the inner half of the estuary where a funnel‐shaped geometry is developed, and by erosional or non‐depositional foreshores in the outer half where the system is confined by the valley walls. The axial sands are divisible into three facies zones: zone 1—elongate, tidal sand bars at the seaward end; zone 2—sand flats with a braided channel pattern; zone 3—the inner, single‐channel, tidal—fluvial transition. Tidal current speeds reach a maximum in zone 2, but grain sizes decrease headward (from medium and coarse sand in zone 1, to fine and very fine sand in zones 2 and 3) because the headward termination of the major flood channels prevents the coarse, traction population from entering the inner part of the estuary. Longitudinal progradation will produce a 20‐m‐thick, upward‐fining succession, the lower 1/2–2/3 of which will consist of cross‐bedded, medium to coarse sand deposited on the zone 1 sand bars. The ebb‐dominated portion of this unit will be finer grained than the flood‐dominated part, and will contain trough crossbedding produced by 3‐D megaripples; the flood‐dominated areas, by contrast, will consist mainly of compound cross‐bedding created by sandwaves with superimposed megaripples. Headward migration of swatchways (oblique channels that link the ebb‐ and flood‐dominated areas) will create packages of ebb cross‐bedding that is orientated at a high angle to the long axis of the estuary and that contains headwardinclined, lateral‐accretion surfaces. The overlying fine and very fine sands of zones 2 and 3 will be composed mainly of upper‐flow‐regime parallel lamination. The succession will be capped by a 4‐m‐thick unit of mixed flat, mudflat and salt marsh sediments. A review of other macrotidal estuaries with tidal ranges greater than 10 m suggests that the major elements of the model have general applicability.

Sedimentary record of subaerial volcanic activity in the basal Ordovician shoal-marine deposits: the Třenice Formation of the Prague Basin, Bohemian Massif, Czech Republic

“…It is common, tides produce water currents in settings of marine embyments (e.g. Knight 1980, Dalrymple et al 1990). Finally, storms are not speculated to have forme the currents because to pure occurrence of typical storm sedimentary structures (e.g.…”

Formation and Evolution of Wetland and Landform in the Yangtze River Estuary Over the Past 50 Years Based on Digitized Sea Maps and Multi-Temporal Satellite Images

“…Water discharge greater than 60,000 m 3 /s, increase the water surface gradient and the sediment carrying capacity in the estuary (Yang et al, 1999). Estuarine sedimentation and landform features have been observed and studied in various settings around the world, including the Thames Estuary, Cobequid Bay, and the Bay of Fundy (Dalrymple and Rhodes, 1995;Knight, 1980;Dalrymple et al, 1990), as well as Chesapeake Bay (Ludwick, 1974) and Moreton Bay (Harris et al, 1992). These studies found that tidal bars in all these estuarine settings are important sedimentary features.…”

Márgenes costeros híbridos de la Cuenca Neuquina (Formación Allen, Cretácico Superior, Argentina).

“…In particular marsh deposits are characterized by the recognition of siltypelitic sediments rich in organic matter with lesser amounts of sandstone, and levels of calcareous levels and abundant root molds in compact layers (Lander et al, 1990). This is due to the fact that marshes are confined to areas above the average elevation of water (Dalrymple et al, 1990) and poor drainage on these elevated areas within the flats favors the preservation of organic material. Because they are reducing environments, wetlands are conducive to the development of soils with gley horizons, which is why mottling is common and abundant (Aslan and Autin, 1998).…”

“…The presence of parallel lamination in this association demonstrates the migration of low-amplitude waves on flat surfaces by currents that reached speeds of 2 m/sec and depths less than 2-3 m or the combination of storm events and tidal action (Dalrymple et al, 1990;Fielding, 2006). The varied bedforms and the stability field of these structures is a function of changes in the speed and size of grain for a constant water depth and temperature (Fielding, 2006).…”

“…The close relationship with ShT lithofacies make it possible to consider this as the most probable cause under conditions of high flow rate (ShT). The origin of this association is interpreted as a sand tidal flat in a subtidal environment (Dalrymple et al, 1990). (Figs.…”