Sequence Stratigraphy, Chemostratigraphy and Diagenesis of the Miocene Carbonate-Evaporite Successions, Al-Jabal Al-Khdar Uplift and Soluq Trough, Cyrenaica, Northeastern Libya

Abstract

The Cyrenaican Miocene carbonate-evaporite platform of NE Libya is the focus of this sequence stratigraphic, chemostratigraphic and diagenetic study. The integrated study involves determining detailed regional facies relationships from field and lab observations. The field work included 25 measured stratigraphic sections, 14 spectral gamma-ray profiles constructed using a hand-held gamma-ray scintillometer at 0.5 m intervals, and annotated panoramic digital photomosaics. The lab work includes petrographic and diagenetic studies of 501 hand samples, thin sections and stable isotope (δ 18O and δ 13C) analyses. The sequence stratigraphic framework is based on the sedimentological analysis, correlation of stratigraphic time surfaces and vertical stratigraphic sections, oxygen and carbon stable isotope profiles, and gamma-ray logs. The Ar-Rajmah Group Miocene carbonate rocks record two 2nd order supersequences (97 m maximum thickness); containing six 3rd order sequences, and at least 10 higher frequency 3rd order sequences. The TST of the younger 2nd order sequence is separated by a sharp disconformity surface from the preserved HST of the older 2nd order sequence, and by maximum flooding zone from the HST of the younger 2nd order sequence. The HST of the older 2nd sequence is the Early Miocene Benghazi Formation (46 m maximum thickness), and dominated by red algal reefs, and bioclastic packstones. The TST and HST of the younger 2nd order sequence occur in the Middle and Late Miocene Wadi Al-Qattarah Formation (26 m and 25m maximum thicknesses respectively), and dominated by continuous oolitic grainstones, microbialites that associated with evaporites and siliciclastics. The 3rd order sequences range in thickness from 5 m to more than 15 m. In the study area, the peritidal facies are dominant in the younger sequences, while the ramp crest-subtidal facies dominant in the older sequences. The chemostratigraphic data suggests the entire Miocene preserved. The Early Miocene is enriched in both δ18O and δ13C, the Middle Miocene is enriched in δ13C but depleted in δ18O, and the Late Miocene is depleted in both δ18O and δ13C. The petrographic analysis shows two distinct lithological, textural and paragenetic patterns. The Langhian and older facies are dominated by silicified dedolomitized red algal and bioclastic packstones, the Serravallian and younger facies are dominated by silicified and recrystallized oolitic grainstone, microbial-bioclastic-oolitic grainstone.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015