Tidal flat deposits

A typical barrier-island system can be divided into three depositional environments (barrier beach, lagoonal/bay, and tidal channel -delta complex) each of which contains a number of smaller subenvironments (2). This work focused on a typical bay-fill sequence in which bay sediments are overlain by tidal flat deposits... 

Iron monosulfides show an antithetic relationship with pyritic sulfur (Table I). The highest amounts of acid volatile sulfides (which remained small compared to S in pyrite) occur directly beneath the marsh sediments within the upper portions of the tidal flat deposits. The high value for iron monosulfides in the upper part of the tidal creek sediments may be related to high rates of sulfate reduction at these depths. 

These clays occur in limestones, dolomites, evaporites, shales, siltstones, and hydrothermal deposits. All the sedimentary material appears to have a diagenetic origin. Although the physical environments vary, the chemical environments should be similar. Saline or even super-saline conditions are implied by the presence of evaporite minerals associated with some of the deposits. In the other deposits it is possible that temporary evaporitic conditions (e.g., tidal flats) existed long enough for brucite to precipitate between the layers of expanded-layer minerals. It appears plausible that the parent material was a montmorillonite-like mineral (probably detrital in most cases). 

Eutrophication Processes in Coastal Systems Origin and Succession of Plankton Blooms and Effects on Secondary Production in Gulf Coast Estuaries, Robert J. Livingston Handbook of Marine Mineral Deposits, David S. Cronan Handbook for Restoring Tidal Wetlands, Joy B. Zedler Intertidal Deposits River Mouths, Tidal Flats, and Coastal Lagoons, Doeke Eisma... 

Carbonate sediments can be subdivided into skeletal and nonskeletal components. Nonskeletal carbonate grains have been divided into five major types mud, pellets, ooids, lithoclasts, and relict. Carbonate muds are common deposits in low-energy environments, such as tidal flats and subtidal areas. Pellets are formed by the ingestion of sediment by marine organisms and excretion... 

Figure 11.10 Photographs of outcrops of other cemented beach deposits. (A) Pleistocene coastal deposit on the coast of Cat Cay, western margin of Great Bahama Bank. Note inclined bedding and root structures. (B) Elevated Holocene reef terraces on the southwestern coast of Barbados, West Indies. (C) Indurated dolomite crust on tidal flats. Near western coast of Andros Island, Bahamas.

The variety of environments (which includes beaches, tidal and sub-tidal flats, lagoons, reefs, shelves, slopes and deep basins) gave rise to many types of deposit, whose characteristics are related to the particular environment in which they were formed [2.1-2.4]. 

The Lower Series was deposited on a flooded erosion surface over a Paleozoic substrate, a marine surface on which were developed vast lagoons, volcanic flows, tidal flats and barriers. Truely marine conditions prevailed only over the northern part of the region. The sandstones of the Lower Series are not as uniformly continuous as those of the Tj and T. They are generally lenticular or sometimes form wedges interrupted by the volcanic rocks. A great potential for the accumulation of hydrocarbons in lithostratigraphic traps may develop under these conditions like in the sandstones in the upper part of the Lower Series in TKT-i, BKZ-i and BKZ-2. 

Unit C encompasses the basal sediments of a marine transgression. As the sea level continued rising the eroded material coming from the tidal flats, the intertidal zones, the lagoons and the volcanic expanses of the Lower Series was deposited on the coastal sea floors under a shallow water cover. Most of these materials were derived from the reworking of the Cambro-Ordovician sediments and transported along the coast by coastal currents. 

Triassic sediments are deposited only in the eastern and northern parts of the Sahara, in the Triassic Province. Triassic sandstones are mainly a combination of deltaic to prodeltaic facies represented by upper deltaic fluvial system deposits, lower distributary channel rivers, mouth bars, beach sands and tidal flat and prodeltaic shales. Typical marine Triassic shales are restricted in extent in the study area. Triassic Lower, Middle and Upper sandstones are stratigraphically separated by shale intervals, but occasionally also by carbonates or volcanic interbeds. They are often medium grained, and range from friable to cemented with clay mineral, carbonate, anhydrite and siliceous cement. Porosity ranges from 12 to 22%. With respect to mineralogical composition and maturity, Triassic sandstones are mature sublitharenite (Lower Triassic), sublitharenite to submature subarkose (Middle Triassic) and submature subarkose (Upper Triassic). 

Sedimentary evidence for tsunamis is found along the shorelines of marine and lacustrine environments. The shorelines of the Earth vary from place to place and can be simplified into two characteristic environments flat sandy coasts or marshes and cliffed rocky coasts (Fig. 3a, b). The formation of a coast with sediments at the seashore depends on several parameters including the position of the sea level, the tidal influence, and the presence of river inlets (e.g., sculpted into bays, cuspate forelands with mudflats, marshes, sandy beaches, or dunes). The geomorphology of a coast plays a major role in preserving tsunamigenic deposits. 

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