Facies, sedimentary environment and log facies of the Hojedk Formation (Middle Jurassic) in Parvadeh Tabas Coal Mine, South of Tabas

The Middle Jurassic Hojedk Formation in the Parvadeh Coal Mine (90 km south of Tabas) has been studied. The study area is structurally located on the northern Tabas Block in the north of the Parvadeh–Nayband coal-bearing basin, east-central Iran. The Hojedk Formation has a thickness of 40 meters in the studied outcrop section. Five lithostratigraphic units have been identified, which mainly consist of sandstones, shales, conglomerates, siltstones and thin bioclastic sandy limestone. Based on field and petrographic studies, four groups of lithofacies including coarse- (Gcm and Gt), medium- (St, Sp, Sh and Sr) and fine-grained clastic (Fl and Fm) as well as carbonate facies (echinoid brachiopod grainstone-packstone) have been identified in the Hojedk Formation. The architectural elements of channels and point bars of a meandering tidal creek and coastal plain swamp have been identified in the Hojedk Formation and its palaeodepositional conditions can be attributed to the tidal flat of a marginal marine siliciclastic environment. To investigate the characteristics of the Hojedk Formation in the subsurface, the electrical facies were defined in an exploration borehole in the eastern part of Parvadeh Mine. In this borehole, the Hojedk Formation is 48 meters thick, and four electro/log facies have been identified by considering the gamma-ray motif and resistivity logs. These electro facies are compatible with the sub-environments of coastal sand flats, tidal channels and coastal plain swamps.Keywords: Tabas Block, Hojedk Formation, Middle Jurassic, Facies, Log facies IntroductionCentral-East-Iranian-Microcontinent is a part of Iran Plate, which can be structurally divided into Lut, Tabas and Yazd blocks (Takin 1972; Aghanabati 2004). The tectono-sedimentary evolution of east-central Iran during the Late Triassic to the Late Jurassic is governed by the Cimmerian orogenic events (Fürsich et al. 2005; Seyed-Emami et al. 2004, 2020; Wilmsen et al. 2009, 2021). The Hojedk Formation is the last lithostratigraphic unit of the Shemshak Group in east-central Iran, which during the Middle Jurassic in this area was affected by Cimmerian tectonic events resulting in large thickness and facies variations (Wilmsen et al. 2009). Biostratigraphic studies have led to determining the age of this formation (early Bajocian) in eastern central Iran (Seyed-Emami et al. 2020). Macrofloras, palynology and sedimentary environment analysis have been conducted on the Hojedk Formation in