The Permian–Triassic boundary section at Baghuk Mountain, Central Iran: carbonate microfacies and depositional environment

Sections at Baghuk Mountain, 45 km NNW of Abadeh (Central Iran), have excellent exposures of fossiliferous marine Late Permian to Early Triassic sedimentary successions. Detailed bed-by-bed sampling enables the analysis of microfacies changes of three successive rock units across the Permian–Triassic boundary. The Late Permian Hambast Formation is mainly the result of biogenic carbonate production. Its carbonate microfacies is dominated by biogen-rich and bioturbated nodular limestones, indicating a well-oxygenated aphotic to dysphotic environment. The biogen-dominated carbonate factory in the Permian ceased simultaneously with the main mass extinction pulse, which is marked by a sharp contact between the Hambast-Formation and the overlaying Baghuk Member (= ‘Boundary Clay’). The clay and silt deposits of the Baghuk Member with some carbonate beds show only a few signs of bioturbation or relics of benthic communities. The Early Triassic Claraia Beds are characterised by a partly microbially induced carbonate production, which is indicated by frequent microbialite structures. The depositional environment does not provide evidence of large amplitude changes of sea level or subaerial exposure during the Permian–Triassic boundary interval. The deposition of the Baghuk Mountain sediments took place in a deep shelf environment, most of the time below the storm wave base.

MICROFACIES ANALYSIS OF CRETACEOUS SEDIMENTS OF DUKUL FORMATION, YOLA SUB-BASIN, NORTHERN BENUE TROUGH, NIGERIA: PALEO-ENVIRONMENTAL IMPLICATIONS

Carbonate microfacies analysis was conducted on the exposed sediments of Dukul Formation from Yola Sub-basin of the Northern Benue Trough with an objective to reconstruct the paleodepositional environment. The study revealed four (4) major microfacies; oyster wackestone, ostracod oyster wackestone-packestone, bioclastic wackestone and bioclastic packestone microfacies. The microfacies assemblages indicate and affirm that the Dukul Formation sediments were deposited in shallow marine (mid-inner ramp) environment under suboxic to relatively anoxic conditions due to sea-level drop. This is further supported owing to the occurence of corals, brachiopods, bivalves and ostracods immediately below the mean fair-weather wave base (FWWB)

Sea-level fluctuations in the late Middle Permian estimated from palaeosols of the Sichuan Basin, SW China

Two upper Middle Permian palaeosols, consisting of coal and pyrite intercalated with a 20 cm thick limestone, were found near Mount Emei in the SW Sichuan Basin, China. The macro- and micromorphology and physico-chemical properties, in conjunction with the mineralogical composition of the palaeosol horizons were investigated. This type of palaeosol is common within the Permian intertidal facies of the Upper Yangtze Craton. The section reflects fluctuations within the range of 0–25 m in relative sea-level, with the depositional environment changing from shallow-marine to littoral, followed by tidal-flat to littoral, and finally to continental volcanic rocks, based on a combination of palaeopedological and carbonate microfacies analyses. Such short-term relative sea-level fluctuations in late Middle Permian times in the SW Sichuan Basin of South China are consistent with the long-term falling trend on a global scale in late Middle Permian times, and may be related to regionally variable subsidence and global cooling. The combination of coastal palaeosol and carbonate microfacies analyses is proposed as an additional tool for estimating the amplitude of sea-level changes.

The palaeoshoreline of Early Miocene formations (Euphrates and Jeribe) at the periphery of the Zagros Foreland Basin, Sulaimani Governorate, Kurdistan Region, NE Iraq

A sedimentological investigation of the Early Miocene deposits at the periphery of the Zagros Foreland Basin, Kurdistan Region, around Qishlagh-Sargrma and Darbandikhan, reveals the presence of the Euphrates and Jeribe Formations in this area. A carbonate-dominated unit, comprising four regressive carbonate cycles, at the base of the Fatha Formation, has been investigated to characterize the depositional environments and stratigraphic context of these Early Miocene deposits. Outcrop and thin-section analyses of the carbonate succession reveal a gently inclined, carbonate-dominated ramp based on the depositional lithofacies and microfacies. Eight carbonate microfacies were identified and interpreted to have been deposited in a shallow marine environment. The Euphrates Formation passes up from deposits of restricted lagoon to shoal depositional environments, while the Jeribe Formation was deposited in a hypersaline lagoon to a restricted lagoon. The Early Miocene index fossil Borelis melo melo was identified in the deposits of the Euphrates Formation. Stratigraphic correlation of the studied sections allows the development of a revised palaeogeography for the Early Miocene deposits in the Kurdistan Region.

Famennian carbonate microfacies from the Preslavtsi-2 well (Moesian Platform, north-eastern Bulgaria)

The most representative subsurface section of the Famennian carbonate succession from the Moesian Platform in Bulgaria occurs in the R-2 Preslavtsi well. Nine microfacies types (MFTs 1–9) have been distinguished and described in the intraclastic and peloidal limestone unit and the organogenic limestone unit. They are grouped in four microfacies associations: 1) protected shallow subtidal (lagoon) (MFT 1, bioclastic-peloidal packstone/grainstone; and MFT 2, oncoidal wackestone); 2) wave-dominated shallow subtidal (MFT 3, intraclastic-peloidal grainstone and rudstone; MFT 4, oncoidal rudstone; MFT 5, peloidal-bioclastic packstone and grainstone); 3) reef (MFT 6, solenoporacean-calcimicrobial-stromatoporoid boundstone; MFT 7, crinoid-stromatoporoid floatstone); and 4) open-marine (MFT 8, bioclastic wackestone/packstone with intraclasts and peloids; and MFT 9, bioclastic wackestone and packstone). The carbonate deposits are interpreted as formed in various shallow- to open-marine environments at or above the fair-weather wave base (MFTs 1–7) and below it (MFTs 8 and 9). Most of the described microfacies are comparable with Wilson’s (1975) Standard Microfacies Types.