Facies nearshore

Phytoplankton should be regarded as the main supplier of organic carbon in ancient marine sediments. However, it should be kept in mind that the distribution of observed in the facies profile does not coincide spatially with the distribution of phytoplankton and production of oxygen, as most dead plankton decomposes in the surface layer, as a result of which the accumulation of organic matter would be considerably greater in the nearshore zone than in the deep sea. 

The sediments of the marine transgression are represented by the wave- and tidal-dominated sandstones and interbay mudstones of the Upper Marine Molasse. Within the Upper Marine Molasse, four major facies belts can be recognized (i) the proximal fan delta facies, (ii) the coastal facies, (iii) nearshore facies and (iv) the offshore facies (Homewood, 1981). The cumulative thickness of the unit may be as much as 1.3 km (Matter et ai, 1980). 

The Middle Jurassic and younger section on the stable Saharan Platform is dominated by relatively thin lagoonal dolomites, evaporates, and shales. Cretaceous sediments consist of alternating evaporates, limestones, dolomites, and thin layers of sandstone. Aptian-Albian nearshore carbonate facies are oU-bearing in Tunisia. Tertiary sedimentation is particularly present in Tunisia and farther over a wide scale of thickness (up to 7000 m). These sediments occvn from the Paleocene to the Pliocene in the east, and... 

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