Sedimentary environment and provenance of sandstones from the Qadir member in the Nayband Formation, Tabas block, east-central Iran

Abstract

Qadir Member of Nayband Formation, located in East of Central Iran, has developed to a great extent. Investigation of the lithofacies and sedimentary environment, resulted in identification of the deltaic and marine deposits. Based on field evidence and facies features, Qadir Member consists of two lithofacies, including carbonate and siliciclastic facies. The siliciclastic facies were identified as having four sandstone facies including Sr, Sh, Sp, St, three fine-grained lithofacies, including FI, Fm, Fl (Sr) / Sr (FI) and one coal facies. Also, regarding the field, laboratory studies, and identification of lithofacies, the coastal plain, deltaic (including deltaic plain, proximal delta front, distal delta front, and prodelta) and open marine environments were identified for Qadir Member which is is under the impact of tidal currents. The chemical weathering index (71%) indicated semi-arid to semi-humid conditions and plotting the geochemical data showed the provenance of re-cycling and active continental margin and because of Chemical Index of Alteration, the weathering rate was found to be rather medium to high. The geochemical diagrams also showed a probable source of the intermediate igneous and sedimentary rocks. The active continental margin conditions for this deposit could suggest the Neotethys subduction under Iran’s plate and volcanic activity at the end of Triassic, which coincided with the early Cimmerian orogeny in Alborz and Central East Iranian Microcontinent.

Depositional and thermal history of a continental, coal-bearing Middle Jurassic succession from Iran: Hojedk Formation, northern Tabas Block

“…This essentially early Bajocian unit also reflects a short-term subsidence pulse and was deposited in c. 1.5 Ma on the way to the Mid-Cimmerian tectonic event (Salehi et al 2018), which is reflected by a conspicuous unconformity surface associated with regional block-faulting and folding as well as widespread erosion in different parts of Iran (Wilmsen et al 2003(Wilmsen et al , 2009bFürsich et al 2009a), followed by widespread post-Mid-Cimmerian exhumation in Central Iran (Gyomlai et al 2022). However, despite its obvious tectono-stratigraphic significance, the Hojedk Formation has received little attention with respect to detailed facies analyses and palaeogeographic reconstructions, in marked contrast to the underlying siliciclastic successions of the Upper Triassic and Lower Jurassic part of the Shemshak Group of east-central Iran (Nayband and Ab-e-Haji formations) that have been studied in considerable detail (Fürsich et al 2005a;Salehi et al 2014Salehi et al , 2018Zamanian et al 2021). On the other hand, there are numerous studies on the macrofloras and palynology of the Hojedk Formation from several locations on the Tabas Block (e.g.…”

“…2014, 2018; Zamanian et al . 2021). On the other hand, there are numerous studies on the macrofloras and palynology of the Hojedk Formation from several locations on the Tabas Block (e.g.…”