Sediment cores representative of contrasting environments in salt flats of the Moknine continental sabkha (Eastern Tunisia): Sedimentology, bulk features of organic matter, alkane sources and alteration

The Moknine continental sabkha exhibits particularly contrasting situations in terms of inundation, silting up, evaporite deposition, vegetation and detrital material input. Following extensive preliminary studies, eight representative cores were selected. Marked differences in sedimentology were observed between the cores; they are accounted for by the present (and past) position of the core in the sabkha, the depth of the zone and the extent of detrital material input from oueds. Examination of 58 sections from the cores showed conspicuous differences in organic matter abundance and aliphaticity (not related to the nature of the facies) and also in the abundance of the total lipid extracts and aliphatic hydrocarbons. Alkane distributions in the 58 sections and their variations reflect the complex and variable interrelationships in the contrasting environments of the sabkha, between the (i) nature of the different types of sources (bacteria, cyanobacteria, microalgae and higher plants), (ii) composition of these different sources and (iii) extent of bacterial degradation of the alkanes from primary sources.