SEDIMENTARY FACIES OF THE TIDAL CREEKS OF KHOR-ALMUFATEH AND KHOR-ALMAMLAHA, KHIRAN AREA, KUWAIT

This paper presents a depositional model for the distribution of sedim entary facies in elongated, narrow tidal creeks debouching into a shal low landlocked sea in an arid region with relatively low eolian sedime nt accumulation. The tidal creeks were part of an active drainage syst em established during the last glacial low-stand of sea-level. Sedimen ts of the creeks are marine, mainly autochtonous carbonates with minor eolian siliciclastics. The carbonates are predominantly preserved as faecal pellets produced by mud-eating invertebrates. The creek deposit s also include abundant skeletal debris. Oolites are formed in areas a gitated by waves. Carbonate muds are partially introduced to the tidal creeks from the open sea by tidal currents. Tidal currents and, to a lesser extent, wind generated currents, are the major agents transport ing sediment in the creeks. Coarser sediments are found in the channel s and finer sediments accumulate in distal parts of the tidal flats an d at the landward end of the major channels. The amount of eolian sedi ments also increases landward. Grain size of sediments and their ''flo oding frequency'' determine the type of the infaunal and epifaunal com munity of organisms living in them. Tidal flat sediments are actively burrowed by crabs and other invertebrates, while the channels contain abundant gastropods and bivalves. The molluscan communities of the cha nnels are more diverse towards the mouth of the creeks, near their con nection to the open sea. Diurnal fluctuations in salinity are only app arent in the tidal flat and at the heads of the tidal channels. Sites of extreme fluctuations at distal parts of the tidal flats and the cre eks are characterised by massive development of algal mats. Similar ca rbonate sediments formed in creeks could be recognised in the fossil r ecord by the predominance of pelletal carbonate facies (pelmicrite) be coming finer landward and surrounded by supratidal, anhydrite-bearing sabkhas. Also the distribution pattern of the biofacies, recognizable through various organic structures (burrows, invertebrate fossil assem blages, stromatolites), can be useful indicators for such geographical settings.