Abstract
The Lidam Formation is divided into two units: limestone unit and dolomite unit. These units exhibit clearly tidal flat setting of supratidal, intertidal and subtidal.
The most indicative features of supratidal environment is the regular and irregular laminae (aggregates of pellets) algal mat, anhydrite, replacive dolomite and absence of marine fauna. This particular supratidal environment is present in Masrab high, As-Zahra-Hofra Platform, Beda Platform and Kotla Graben wells P16-59, Z1-59, 3V1-59, F8-59 and F10-59.
The intertidal environment is dominated by algal laminae, anhydrite, quartz and dolomite with echinoderm fragments, ooids and pellets. This environment is present in Ajdaby Trough and Gatter Ridge in wells 5N1-59, E1-57 and 001-11. The subtidal environment is characterized by mudstone and wackestone facies with abundant marine fauna e.g. echinoderm fragments, ostracods and foraminifera.
Locally at D1-32, L1-32, O1-32, C1-NC57, D1-NC57 wells (Azahra-Hofra Platform), and DD2a-59 (Ajdabya Trough), oolitic grainstone with peloids and bioclasts are abundant with indication possibly of shallow shoals reflecting high energy conditions. From the lateral distribution of the Lidam Formation one can conclude that the supratidal and intertidal environments were formed mainly on highs, during the Cenomanian transgression (Vail et al., 1977).
Porosity of intertidal and supratidal environments of the Lidam Formation is mostly secondary, generated by dissolution of materials survived from dolomitization. However, primary porosity either in subtidal or intertidal-supratidal environments had been totally occluded during cementation stage of diagenesis. Dolomitization of matrix, marine cementation and dissolution are the most diagenetic stages which took place in the different environments of the Lidam Formation in the Sirt Basin.