The focus of this field and lab integrated study is on the Cyrenaican Miocene 13C-isotope changes... more The focus of this field and lab integrated study is on the Cyrenaican Miocene 13C-isotope changes in the sequence stratigraphic, and diagenetic context. The field work included 29 measured stratigraphic sections along 135 km, 14 spectral gamma-ray profiles. 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. The TST of the younger 2nd order sequence is separated by a sharp disconformity surface from the 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 thick), 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 thick 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. The chemostratigraphic data shows that 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 Middle Miocene is characterized by a prominent positive increase in the δ13C, Monterey event, which coincides with influx of siliciclastic facies that have high gamma ray zone, and evaporite deposits. In addition, this δ13C enrichment event is roughly coinciding with major changes in facies lithologies, textures, and diagenetic patterns. The pre-Monterey event facies are dominated by silicified dedolomitized red algal and bioclastic packstones, where the syn-and-post-Monterey event facies are dominated by silicified and recrystallized oolitic grainstone, microbial-bioclastic-oolitic grainstone. The global Monterey event is preserved in the δ13C record of the Cyrenaican Miocene carbonate platform in the Central Mediterranean, and associated with major sedimentological, stratigraphic, and diagenetic changes.
Microbialites distribution in the Cyrenaican Miocene carbonate-evaporite platform is a part of ou... more Microbialites distribution in the Cyrenaican Miocene carbonate-evaporite platform is a part of our regional study in NE Libya. The study included 29 detailed measured stratigraphic sections, petrographic studies of 503 thin sections. The sequence stratigraphic framework is based on integrated correlation of outcrop sections, oxygen and carbon stable isotope profiles, and gamma-ray logs. The Ar-Rajmah Group Miocene carbonate rocks record two 2nd order supersequences of 97 m maximum thickness. The restricted peritidal microbialite facies does exist in the HST and TST of these two supersequences. The microbialite facies comprises cryptalgal laminites, stromatolites, and thrombolites, and reached a maximum thickness of 12 m. The microbialite beds thickness range is from a few centimetres up to 3 m with very sharp top surface that usually marked by mudcracks. Some dwarfed bivalves and gastropods, and composite ooids “grapestones” occur within the internal structure of the microbial facies. The microbial facies increase in thickness, size and frequency towards the southern part; they change from reefal patches of 20 cm to 50 cm in diameter in the Al-Jabal Al-Khdar Uplift north into elongated mounds of more than 1.5 m in diameter in the Soluq Trough south. These microbial facies are commonly intercalated with oolitic grainstone, evaporites, and pelletal wackestone/packstone facies. The cryptalgal laminites dominate the Al-Jabal Al-Khdar Uplift north, whereas the stromatolites dominate the central part and usually intercalated with oolitic grainstone facies, and the thrombolites dominate the Soluq Trough south. The amount and size of the polycrystalline quartz sand grains increases upwards and towards the south. Micritization, recrystallization, and dissolution are the dominant diagenetic features in the microbialite facies. Replacement with gypsum and then silica is common, and there is only minor dolomitization. Dissolution seams are always associated with fracture porosity. Fenestral and vuggy porosity are common in the microbial facies.
A sequence stratigraphic, chemostratigraphic and diagenetic study of the Miocene rocks in the Cyr... more A sequence stratigraphic, chemostratigraphic and diagenetic study of the Miocene rocks in the Cyrenaica, northeast Libya, extends from the northwestern part of Al-Jabal Al-Khdar southwards to the Soluq Trough, between 31°-33° N Latitude and 19°30'-21°E Longitude. The sequence stratigraphic study involves determining detailed regional facies relationships from field and lab observations. The field work included measuring 25 stratigraphic sections bed-by-bed, 14 Spectral gamma-ray profiles constructed using a hand-held gamma-ray scintillometer at 0.5 m intervals, and annotating panoramic digital photomosaics. Special attention was given to identifying stratigraphic time surfaces. 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 will be based on the sedimentological analysis, correlation of stratigraphic time surfaces and vertical stratigraphic sections, o...
The Ar-Rajmah Group Miocene carbonate rocks record two 2nd order supersequences (97 m maximum thi... more The Ar-Rajmah Group Miocene carbonate rocks record two 2nd order supersequences (97 m maximum thickness); contain six 3rd order sequences, and at least 10 higher frequency parasequences. The older 2 nd order sequence is not complete and only the shallowing upward unit (HST) preserved, where the younger 2nd order sequence is complete and both the deepening upward unit (TST), and the shallowing upward unit (HST) are preserved. 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), 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). The HST of the older 2nd order sequence includes two 3rd order sequences, S1 and S2....
One detailed field measured section A1 of 74 m thick selected out of 29 measured sections along 1... more One detailed field measured section A1 of 74 m thick selected out of 29 measured sections along 130 km distance to represent the Miocene Ar-Rajmah Group carbonate sequence in Cyrenaica, northeast Libya. It was sampled every 0.5 m for XRF trace and common elements analysis, whole rock stable isotope (δ 18 O, δ 13 C) chemostratigraphy, and thin sections petrographic analysis. The Ar-Rajmah Group carbon isotope data indicates this unit preserves a record of almost the entire Miocene. The Cyrenaican Miocene carbonate succession is made up of two shallowing upward 2 nd-order supersequences (SS1-SS2) that comprise six main 3 rd-order sequences (S1-S6). The XRF measured Ca wt% curve indicates three intervals of pronounced CaCO 3 dissolution occurred: (1) within the Early Miocene coinciding with the flooding surface of 3 rd-order sequence 1, (2) above the Early-Middle Miocene boundary, within the TST of the 2 nd-order supersequence 2, and within the transgressive system tract of 3 rd-order ...
The investigated Late Miocene carbonate succession of Wadi Yunis Member of Al Khums Formation is ... more The investigated Late Miocene carbonate succession of Wadi Yunis Member of Al Khums Formation is exposed in central Sirt Basin along a narrow belt running parallel to the present-day coastline between the villages of Al Aqaylah and Ben Jawwad. It rests uncomfortably on the Middle Miocene section of Marada Formation. The study area is located on the northern extension of the NW-SE trending Zaltan - Jahama structural platform. It is bound by Ajdabiya trough to the east and Marada trough to the west respectively. Thirty eight high-resolution sedimentological sections along 167 km, which were measured and laboratory analysis of samples, indicate that Wadi Yunis Member is divided into two successive shallowing-up sequences consisting of six vertically stacked depositional facies. These are; 1. Oolitic grainstone facies; 2. Oo-skeletal grainstone - packstone facies; 3. Algal pelle-skeletal facies, 4. Bioclastic wackestone facies; 5. Algal stromatolite facies and 6. Coarsely crystalline selenite gypsum facies. These are interpreted as an association of high-energy; wave dominated oolitic shoals–channel complex and low-energy lagoonal facies, constituting a carbonate ramp system. The oolitic shoal palaeocurrents measurements suggest a southwest (206°) vector mean transport direction, a result of a north-easterly dominated Mediterranean wind. Constructed facies ratios, isopach and palaeogeographic maps of the study area demonstrate that the oolitic shoals carbonate factory was located to the northwest, whereas the shelf lagoon was influenced by siliciclastic input from the southeast. At times, during eustatic low-stands the shelf lagoon was subjected to restricted circulation and evaporites precipitation. Due to environmental compartmentalization and rapid lateral facies changes, a multi-datum technique is used in this study. This carbonate ramp body with its elongated narrow morphology along the NW-SE strike and the SW unimodal palaeocurrent mode of 206° azimuth is the end product of wave dominated sedimentological processes and inherited structures that control to an extent the palaeocurrents flow directions and facies distribution. However, at some stage in time the basin suffered of restriction and complete isolation. The primary gypsum ratio map shows a bulls-eye pattern with evaporites in the basin centre surrounded completely with carbonates, typical of completely enclosed basins. Detailed laboratory work for petrographic analysis and diagenesis of the limestone facies has been conducted on 53 representative sample thin sections. The dolomitization and gypsification ratio maps indicated that the diagenetic patterns are facies controlled in the study area. The dolomitization process is intensive and largely restricted to the permeable high energy deposits that dominated by lime sand-sizes, while the gypsification process is largely restricted to the impermeable low energy deposits that dominated by lime mud-sizes.
The focus of this field and lab integrated study is on the Cyrenaican Miocene 13C-isotope changes... more The focus of this field and lab integrated study is on the Cyrenaican Miocene 13C-isotope changes in the sequence stratigraphic, and diagenetic context. The field work included 29 measured stratigraphic sections along 135 km, 14 spectral gamma-ray profiles. 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. The TST of the younger 2nd order sequence is separated by a sharp disconformity surface from the 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 thick), 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 thick 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. The chemostratigraphic data shows that 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 Middle Miocene is characterized by a prominent positive increase in the δ13C, Monterey event, which coincides with influx of siliciclastic facies that have high gamma ray zone, and evaporite deposits. In addition, this δ13C enrichment event is roughly coinciding with major changes in facies lithologies, textures, and diagenetic patterns. The pre-Monterey event facies are dominated by silicified dedolomitized red algal and bioclastic packstones, where the syn-and-post-Monterey event facies are dominated by silicified and recrystallized oolitic grainstone, microbial-bioclastic-oolitic grainstone. The global Monterey event is preserved in the δ13C record of the Cyrenaican Miocene carbonate platform in the Central Mediterranean, and associated with major sedimentological, stratigraphic, and diagenetic changes.
Microbialites distribution in the Cyrenaican Miocene carbonate-evaporite platform is a part of ou... more Microbialites distribution in the Cyrenaican Miocene carbonate-evaporite platform is a part of our regional study in NE Libya. The study included 29 detailed measured stratigraphic sections, petrographic studies of 503 thin sections. The sequence stratigraphic framework is based on integrated correlation of outcrop sections, oxygen and carbon stable isotope profiles, and gamma-ray logs. The Ar-Rajmah Group Miocene carbonate rocks record two 2nd order supersequences of 97 m maximum thickness. The restricted peritidal microbialite facies does exist in the HST and TST of these two supersequences. The microbialite facies comprises cryptalgal laminites, stromatolites, and thrombolites, and reached a maximum thickness of 12 m. The microbialite beds thickness range is from a few centimetres up to 3 m with very sharp top surface that usually marked by mudcracks. Some dwarfed bivalves and gastropods, and composite ooids “grapestones” occur within the internal structure of the microbial facies. The microbial facies increase in thickness, size and frequency towards the southern part; they change from reefal patches of 20 cm to 50 cm in diameter in the Al-Jabal Al-Khdar Uplift north into elongated mounds of more than 1.5 m in diameter in the Soluq Trough south. These microbial facies are commonly intercalated with oolitic grainstone, evaporites, and pelletal wackestone/packstone facies. The cryptalgal laminites dominate the Al-Jabal Al-Khdar Uplift north, whereas the stromatolites dominate the central part and usually intercalated with oolitic grainstone facies, and the thrombolites dominate the Soluq Trough south. The amount and size of the polycrystalline quartz sand grains increases upwards and towards the south. Micritization, recrystallization, and dissolution are the dominant diagenetic features in the microbialite facies. Replacement with gypsum and then silica is common, and there is only minor dolomitization. Dissolution seams are always associated with fracture porosity. Fenestral and vuggy porosity are common in the microbial facies.
A sequence stratigraphic, chemostratigraphic and diagenetic study of the Miocene rocks in the Cyr... more A sequence stratigraphic, chemostratigraphic and diagenetic study of the Miocene rocks in the Cyrenaica, northeast Libya, extends from the northwestern part of Al-Jabal Al-Khdar southwards to the Soluq Trough, between 31°-33° N Latitude and 19°30'-21°E Longitude. The sequence stratigraphic study involves determining detailed regional facies relationships from field and lab observations. The field work included measuring 25 stratigraphic sections bed-by-bed, 14 Spectral gamma-ray profiles constructed using a hand-held gamma-ray scintillometer at 0.5 m intervals, and annotating panoramic digital photomosaics. Special attention was given to identifying stratigraphic time surfaces. 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 will be based on the sedimentological analysis, correlation of stratigraphic time surfaces and vertical stratigraphic sections, o...
The Ar-Rajmah Group Miocene carbonate rocks record two 2nd order supersequences (97 m maximum thi... more The Ar-Rajmah Group Miocene carbonate rocks record two 2nd order supersequences (97 m maximum thickness); contain six 3rd order sequences, and at least 10 higher frequency parasequences. The older 2 nd order sequence is not complete and only the shallowing upward unit (HST) preserved, where the younger 2nd order sequence is complete and both the deepening upward unit (TST), and the shallowing upward unit (HST) are preserved. 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), 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). The HST of the older 2nd order sequence includes two 3rd order sequences, S1 and S2....
One detailed field measured section A1 of 74 m thick selected out of 29 measured sections along 1... more One detailed field measured section A1 of 74 m thick selected out of 29 measured sections along 130 km distance to represent the Miocene Ar-Rajmah Group carbonate sequence in Cyrenaica, northeast Libya. It was sampled every 0.5 m for XRF trace and common elements analysis, whole rock stable isotope (δ 18 O, δ 13 C) chemostratigraphy, and thin sections petrographic analysis. The Ar-Rajmah Group carbon isotope data indicates this unit preserves a record of almost the entire Miocene. The Cyrenaican Miocene carbonate succession is made up of two shallowing upward 2 nd-order supersequences (SS1-SS2) that comprise six main 3 rd-order sequences (S1-S6). The XRF measured Ca wt% curve indicates three intervals of pronounced CaCO 3 dissolution occurred: (1) within the Early Miocene coinciding with the flooding surface of 3 rd-order sequence 1, (2) above the Early-Middle Miocene boundary, within the TST of the 2 nd-order supersequence 2, and within the transgressive system tract of 3 rd-order ...
The investigated Late Miocene carbonate succession of Wadi Yunis Member of Al Khums Formation is ... more The investigated Late Miocene carbonate succession of Wadi Yunis Member of Al Khums Formation is exposed in central Sirt Basin along a narrow belt running parallel to the present-day coastline between the villages of Al Aqaylah and Ben Jawwad. It rests uncomfortably on the Middle Miocene section of Marada Formation. The study area is located on the northern extension of the NW-SE trending Zaltan - Jahama structural platform. It is bound by Ajdabiya trough to the east and Marada trough to the west respectively. Thirty eight high-resolution sedimentological sections along 167 km, which were measured and laboratory analysis of samples, indicate that Wadi Yunis Member is divided into two successive shallowing-up sequences consisting of six vertically stacked depositional facies. These are; 1. Oolitic grainstone facies; 2. Oo-skeletal grainstone - packstone facies; 3. Algal pelle-skeletal facies, 4. Bioclastic wackestone facies; 5. Algal stromatolite facies and 6. Coarsely crystalline selenite gypsum facies. These are interpreted as an association of high-energy; wave dominated oolitic shoals–channel complex and low-energy lagoonal facies, constituting a carbonate ramp system. The oolitic shoal palaeocurrents measurements suggest a southwest (206°) vector mean transport direction, a result of a north-easterly dominated Mediterranean wind. Constructed facies ratios, isopach and palaeogeographic maps of the study area demonstrate that the oolitic shoals carbonate factory was located to the northwest, whereas the shelf lagoon was influenced by siliciclastic input from the southeast. At times, during eustatic low-stands the shelf lagoon was subjected to restricted circulation and evaporites precipitation. Due to environmental compartmentalization and rapid lateral facies changes, a multi-datum technique is used in this study. This carbonate ramp body with its elongated narrow morphology along the NW-SE strike and the SW unimodal palaeocurrent mode of 206° azimuth is the end product of wave dominated sedimentological processes and inherited structures that control to an extent the palaeocurrents flow directions and facies distribution. However, at some stage in time the basin suffered of restriction and complete isolation. The primary gypsum ratio map shows a bulls-eye pattern with evaporites in the basin centre surrounded completely with carbonates, typical of completely enclosed basins. Detailed laboratory work for petrographic analysis and diagenesis of the limestone facies has been conducted on 53 representative sample thin sections. The dolomitization and gypsification ratio maps indicated that the diagenetic patterns are facies controlled in the study area. The dolomitization process is intensive and largely restricted to the permeable high energy deposits that dominated by lime sand-sizes, while the gypsification process is largely restricted to the impermeable low energy deposits that dominated by lime mud-sizes.
The focus of this field and lab integrated study is on the Cyrenaican Miocene 13C-isotope changes... more The focus of this field and lab integrated study is on the Cyrenaican Miocene 13C-isotope changes in the sequence stratigraphic, and diagenetic context. The field work included 29 measured stratigraphic sections along 135 km, 14 spectral gamma-ray profiles. 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. The TST of the younger 2nd order sequence is separated by a sharp disconformity surface from the 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 thick), 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 thick 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.
The chemostratigraphic data shows that 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 Middle Miocene is characterized by a prominent positive increase in the δ13C, Monterey event, which coincides with influx of siliciclastic facies that have high gamma ray zone, and evaporite deposits. In addition, this δ13C enrichment event is roughly coinciding with major changes in facies lithologies, textures, and diagenetic patterns. The pre-Monterey event facies are dominated by silicified dedolomitized red algal and bioclastic packstones, where the syn-and-post-Monterey event facies are dominated by silicified and recrystallized oolitic grainstone, microbial-bioclastic-oolitic grainstone. The global Monterey event is preserved in the δ13C record of the Cyrenaican Miocene carbonate platform in the Central Mediterranean, and associated with major sedimentological, stratigraphic, and diagenetic changes.
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The Ar-Rajmah Group Miocene carbonate rocks record two 2nd order supersequences (97 m maximum thickness); containing six 3rd order sequences. The TST of the younger 2nd order sequence is separated by a sharp disconformity surface from the 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 thick), 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 thick 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.
The chemostratigraphic data shows that 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 Middle Miocene is characterized by a prominent positive increase in the δ13C, Monterey event, which coincides with influx of siliciclastic facies that have high gamma ray zone, and evaporite deposits. In addition, this δ13C enrichment event is roughly coinciding with major changes in facies lithologies, textures, and diagenetic patterns. The pre-Monterey event facies are dominated by silicified dedolomitized red algal and bioclastic packstones, where the syn-and-post-Monterey event facies are dominated by silicified and recrystallized oolitic grainstone, microbial-bioclastic-oolitic grainstone. The global Monterey event is preserved in the δ13C record of the Cyrenaican Miocene carbonate platform in the Central Mediterranean, and associated with major sedimentological, stratigraphic, and diagenetic changes.