Microstratigraphy and interpretation of the karst sedimentary fillings associated to the Aptian-Albian unconformity in Jebel Semmama (central Tunisia)

摘要

In this paper, the aim was proposing a new microstratigraphy and interpretation of the karst sedimentary fillings associated to the Aptian-Albian unconformity in Jebel Semmama, central Tunisia. In all the previous studies, this unconformity was interpreted as the result of a major sea-level fall followed by a continuous emersion of the Aptian platform that lasted broadly the Lower and Middle Albian. In the present work, the field examination of the exposure surface in Jebel Semmama area in central Tunisia shows several centimetric epikarsts filled with different marine and non-marine deposits. According to the sedimentologic and microstratigraphic analyses, the karstic fillings may be linked with several sea-level oscillation cycles. Accordingly, the presence of such fillings suggests that the Aptian platform was not continually emerged during the lower and middle Albian as already assumed in previous works. Rather, it was episodically inundated by marine incursions. At least eighteen different sedimentary fillings have been recognized and sampled from the epikarsts. As these fillings are never totally regrouped in the same epikarst, the reconstruction of their microstratigraphy was based on (i) identification of their facies (ii) comparison and correlation of the different fillings between epikarsts (iii) analysis of the stratigraphic relation between the different fillings. A composite microstratigraphic column was established, it shows a regular alternation of shallow marine and non-marine deposits which are arranged into nine karstic sedimentary cycles. The latter may understandably be the result of nine relative sea-level oscillation cycles that broadly happened during the Lower and Middle Albian. For lack of biostratigraphic markers, the previous karstic cycles remain neither dated nor correlated with any eustatic chart. Moreover, the previous cycles have been controlled by significant local salt tectonics. (C) 2015 Elsevier Ltd. All rights reserved.