Facies, sedimentary environment and log facies of the Hojedk Formation (Middle Jurassic) in Parvadeh Tabas Coal Mine, South of Tabas[رخسارهها،محیطرسوبیورخسارههایالکتریکیسازندهجدک(ژوراسیکمیانی)درمعدزغالسنگپرودۀطبس،جنوبطبس]

Abstract

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. © 2024 University of Isfahan.