Lagoonal deposits

Archaic fossils can only be found in geological formations which have not suffered any dramatic changes or deformations since their formation. The area of Western Australia near Marble Bar and North Pole is part of the geological formation known as the Pilbara Shield (Buick et al 1995). The hot, desolate North Pole region is about 40 km from the small town of Marble Bar. The sediments containing the fossils are in a former volcanic lagoon, which was formed in a complicated process (Groves et al., 1981). This area of western Australia was explored and described in detail years ago because of the many ore deposits it contains. In Swaziland, in the... 

The 210Pb tracer data have shown 1) the year of the detonation which affected this station, and 2) that material is being eroded in one area and transported for deposition at another area by the currents in the lagoon and 3) that this has occurred at a constant rate between 1954 and 1972. 

In the event of a decline in sea level, the supratidal zone will move seaward, causing evaporites to deposit on top of old lagoonal sediments. When sea level rises back, it drowns these evaporites. These low-amplitude fluctuations in sea level build up laminated sediments in which layers of biogenic oozes and organic-rich muds alternate with evaporites. 

Fig. 15.4 The position of Fe oxides in a sequence of Fe minerals deposited in a lagoon environment (Reprinted with permission of Economic Ceology.v. 78 8, p. 1670, Fig. 9,Torrez-Ruiz, J., 1983).

Walter, M. R., Golubic, S-, and Preiss, W. V. Recent stromatolites from hydromagnesite and aragonite depositing lakes near the Coorong Lagoon, South Australia. J. Sed. Petrol. 43, 1021-1030 (1.973). 

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... 

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... 

In the south of Moldova, the Karangatian epoch corresponds [8] to the lagoonal sediments of the second terrace of the Prut and Danube rivers they contain one or two layers with shells of Caspian didacnas separated by a layer of lacustrine deposits. 

Thus a recent formation of pyrites has been observed at Karlsbad, in the well-known springs, which have a temperature of about 55° C. The waters are faintly alkaline and contain dissolved sulphates and a trace of hydrogen sulphide.3 Similarly the Tuscan lagoons are gradually depositing pyrites, whilst the hot vapours of the Icelandic fumaroles are slowly converting the ferrous silicate of the rocks into pyrites.4... 

The chemistry of the carbonic acid system in seawater has been one of the more intensely studied areas of carbonate geochemistry. This is because a very precise and detailed knowledge of this system is necessary to understand carbon dioxide cycling and the deposition of carbonate sediments in the marine environment. A major concept applicable to problems dealing with the behavior of carbonic acid and carbonate minerals in seawater is the idea of a constant ionic medium. This concept is based on the observation that the salt in seawater has almost constant composition, i.e., the ratios of the major ions are the same from place to place in the ocean (Marcet s principle). Possible exceptions can include seawater in evaporative lagoons, pores of marine sediments, and near river mouths. Consequently, the major ion composition of seawater can generally be determined from its salinity. It has been possible, therefore, to develop equations in which the influence of seawater composition on carbonate equilibria is described simply in terms of salinity. 

---