A lost Tethyan evaporitic basin: Evidence from a Cretaceous hemipelagic meta‐selenite – red chert association in the Eastern Mediterranean realm
Franziska SchefflerAdrian ImmenhauserAmaury PourteauMarcello NatalicchioOsman CandanRoland Oberhänsli
3
Citation
120
Reference
10
Related Paper
Citation Trend
Abstract:
Abstract Ancient evaporite deposits are geological archives of depositional environments characterized by a long‐term negative precipitation balance and bear evidence for global ocean element mass balance calculations. Here, Cretaceous selenite pseudomorphs from western Anatolia (‘Rosetta Marble’) — characterized by their exceptional morphological preservation — and their ‘marine’ geochemical signatures are described and interpreted in a process‐oriented context. These rocks recorded Late Cretaceous high‐pressure/low‐temperature, subduction‐related metamorphism with peak conditions of 1·0 to 1·2 GP a and 300 to 400°C. Metre‐scale, rock‐forming radiating rods, now present as fibrous calcite marble, clearly point to selenitic gypsum as the precursor mineral. Stratigraphic successions are recorded along a reconstructed proximal to distal transect. The cyclical alternation of selenite beds and radiolarian ribbon‐bedded cherts in the distal portions are interpreted as a two type of seawater system. During arid intervals, shallow marine brines cascaded downward into basinal settings and induced precipitation. During more humid times, upwelling‐induced radiolarian blooms caused the deposition of radiolarite facies. Interestingly, there is no comparable depositional setting known from the Cenozoic world. Meta‐selenite geochemical data ( δ 13 C, δ 18 O and 87 Sr/ 86 Sr) plot within the range of reconstructed middle Cretaceous seawater signatures. Possible sources for the 13 C‐enriched (mean 2·2‰) values include methanogenesis, gas hydrates and cold seep fluid exhalation. Spatially resolved component‐specific analysis of a rock slab displays isotopic variances between meta‐selenite crystals (mean δ 13 C 2·2‰) and host matrix (mean δ 13 C 1·3‰). The Cretaceous evaporite‐pseudomorphs of Anatolia represent a basin wide event coeval with the Aptian evaporites of the Proto‐Atlantic and the pseudomorphs share many attributes, including lateral distribution of 600 km and stratigraphic thickness of 1·5 to 2·0 km, with the evaporites formed during the younger Messinian salinity crisis. The Rosetta Marble of Anatolia may represent the best‐preserved selenite pseudomorphs worldwide and have a clear potential to act as a template for the study of meta‐selenite in deep time.Keywords:
Dolomitization
Petroleum reservoir
Cite
Citations (61)
ABSTRACT The lower Eocene Rus Formation in Qatar reflects carbonate deposition in a semirestricted to fully restricted marine setting on a shallow ramp. Petrographic, mineralogical, and geochemical evidence from three research cores show early diagenesis has extensively altered nearly every petrological attribute of these rocks despite not having been deeply buried. In southern Qatar, the lower Rus (Traina Mbr.) consists of fabric-retentive dolomite intervals that preserve mudstone, wackestone, and packstone textures that are interbedded with depositional gypsum beds. In northern Qatar, the same member is dominated by fabric-destructive planar-e dolomite, and evaporites are absent. In both northern and southern Qatar, the upper Rus (Al Khor Mbr.) is composed of fabric-retentive dolomite intervals as well as limestone intervals rich with Microcodium textures that display evidence of dedolomitization. Geochemical analysis reveals that the limestones have an average δ18Ocal of –10.73‰ VPDB and δ13Ccal of –7.84‰ VPDB, whereas average dolomite δ18Odol is significantly higher (–1.06‰ VPDB) but δ13Cdol values (–3.04‰ VPDB; range –10 to 0‰) overlap with δ13Ccal values. Additionally, δ13Cdol trends toward normal marine values with depth away from the calcite–dolomite contact in all three cores. Petrographic observations demonstrate that dolomite crystals are commonly included in calcite and partially to completely replaced by calcite in these intervals and suggests that dolomite formed before calcite in the Microcodium-bearing intervals. Furthermore, the dolomites are commonly cemented by gypsum in the Traina Mbr. in southern Qatar, suggesting that dolomitization may have also occurred before, or concurrent with, bedded gypsum formation and indicates that dolomitization occurred early. Early dolomites were subsequently replaced by Microcodium-bearing limestones at and immediately below paleo-exposure surfaces, and at greater depths recrystallized in mixed marine–meteoric fluids, producing a negative δ13Cdol signature that trends toward more positive values away from the limestone–dolomite contact. Lastly, the dolomites underwent another phase of recrystallization in either marine-dominated fluids or possibly a well-mixed aquifer setting, resulting in a near-0‰ δ18Odol signature but retaining the negative δ13C signature. These findings thus have implications for reconstructing the diagenetic history of carbonate rocks, as they suggest that early diagenesis of carbonates can be extremely complex, resulting in multiple stages of mineral replacement and isotopic exchange in meteoric and shallow marine fluids before significant burial. Furthermore, this study shows that dolomitization of a limestone does not necessarily prevent additional early diagenesis and multiple recrystallization events. Lastly, it emphasizes the importance of incorporating petrographic observations with geochemical data when interpreting the diagenetic history of carbonate rocks.
Dolomitization
Recrystallization (geology)
Cite
Citations (16)
Siliciclastic
Transgressive
Stratigraphic unit
Sequence Stratigraphy
Sequence (biology)
Cite
Citations (5)
Sabkha
Dolomitization
Anhydrite
Cite
Citations (32)
Dolomitization
Petrophysics
Aggradation
Dolostone
Sabkha
Hydrocarbon exploration
Siliciclastic
Cite
Citations (11)
Anhydrite
Sabkha
Subaerial
Halite
Cite
Citations (63)
The Jefferson Formation in northwestern Montana consists of a lower member (< 155 m or 508 ft) and the Birdbear Member (< 72 m or 236 ft), which are correlative to the Duperow and Birdbear Formations of the Williston basin. The lower member consists of sucrosic and nonsucrosic dolomites, limestones, and evaporite solution breccias. The Birdbear Member consists of silty nonsucrosic dolomites and limestones, and sucrosic evaporite solution breccias. Paragenesis of diagenetic events based on petrographic cross-cutting relations, cathodoluminescence, microprobe analysis, conodont alteration indices, and field relations indicate that most porosity development and destruction occurred at relatively shallow depth prior to thrusting. Devonian events include early cementation of desiccation structures and intergranular spaces, localized vuggy and moldic porosity development, and dolomitization and formation of intercrystalline porosity. Mississippian to pre-Jurassic events include burial to oil window, kerogen maturation, and loading stylolitization. Later erosion of Mississippian strata and ground-water circulation resulted in brecciation, subvertical fracture development related to collapse, and dedolomitization followed by near-complete calcite cement infilling of available porosity. Paleocene to early Eocene thrusting events include stylolitization, folding of breccias, and nonfilled fracture formation. Post-early Eocene exposure-induced events results in vuggy porosity and precipitation of speletic cements.
Cite
Citations (0)
Subsurface cores were studied petrographically to determine the facies and diagenetic history of the Trenton Limestone on a regional scale in northern Indiana. The Trenton Limestone is a yellowish olive-gray fossiliferous limestone, which is replaced by a light-gray dolostone in northern Indiana. Facies composing the Trenton are: (1) bryozoan-echinoderm packstone, (2) bryozoan-echinoderm grainstone, (3) bryozoan packstone to wackestone, (4) lime mudstone, and (5) dolostone. The bryozoan-echinoderm packstone is the major facies. As many as three muddying-upward (packstone to mudstone) sequences occur. Whether the muddying-upward sequences represent regional or local energy conditions is not known. Coarse-grained (1-4 mm) grainstones are typically 1 ft (30 cm) thick, have abrupt bases, and become muddy upward. They are considered storm deposits. Hardgrounds occur throughout the limestone facies, but they are most numerous toward the base. Thes facies indicate deposition below wave base, interrupted by periods of high energy during storms. Fossiliferous white and gray chert nodules are scattered throughout the unit. Also found in the limestone facies are prevalent stylolites and microstylolites, an indication of chemical compaction. The dolostone facies consists of coarsely crystalline (0.4 mm) idiotopic dolomite. Rhombs have cloudy centers and thin clear rims. Pyrite is associated with the dolomite. Porosity, found only in the dolostone, is discontinuous and characterized as intercrystalline, vuggy, and moldic. Porous zones are commonly oil stained or have been plugged by poikilotopic selenitic gypsum. Minor amounts of celestite are found as cavity fillings. The upper Trenton surface has high concentrations of pyrite and phosphate minerals and is interpreted to have been a submarine corrasion surface. End_of_Article - Last_Page 1919------------
Cite
Citations (4)