Depositional systems and sequence stratigraphy analysis of the Upper Callovian to Tithonian sediments in the Central and Western Kopet‐Dagh Basin, Northeast Iran

Abstract

Upper Callovian to Tithonian (late Jurassic) sediments represent an important hydrocarbon reservoir in the Kopet-Dagh Basin, NE Iran. These deposits consist mainly of limestone, dolostone, and calcareous mudstone with subordinate siliciclastic interbeds. Detailed field surveys, lithofacies and facies analyses at three outcrop sections were used to investigate the depositional environments and sequence stratigraphy of the Middle to Upper Jurassic interval in the central and western areas of the basin. Vertical and lateral facies changes, sedimentary fabrics and structures, and geometry of carbonate bodies resulted in recognition of various carbonate facies related to tidal flats, back-barrier lagoon, shelf-margin/shelf-margin reef, slope and deep-marine facies belts. These facies were accompanied by interbedded beach and deep marine siliciclastic petrofacies. Field surveys, facies analysis, parasequences stacking patterns, discontinuity surfaces, and geometries coupled with relative depth variation, led to the recognition of six third-order depositional sequences. The depositional history of the study areas can be divided into two main phases. These indicate platform evolution from a rimmed-shelf to a carbonate ramp during the late Callovian-Oxfordian and Kimmeridgian-Tithonian intervals, respectively. Significant lateral and vertical facies and thickness changes, and results obtained from regional correlation of the depositional sequences, can be attributed to the combined effect of antecedent topography and differential subsidence related to local tectonics. Moreover, sea-level changes must be regarded as a major factor during the late Callovian-Tithonian interval. Figure 4. Outcrop photograph indicates reef development on a palaeohigh.Onlapping of pelagic facies of the Chaman-Bid Formation onto an inherited topography was followed by aggradation and finally progradation of carbonate deposits south of Nabia Village (See Fig. 1 for location). With an increase in carbonate production after reef establishment in comparison to relative sea-level rise, aggradation was followed by progradational stacking pattern towards a nearby deep basin. This figure is available in colour online at wileyonlinelibrary.com/journal/gj. Figure 7. (A) High-resolution perspective image (courtesy of Google Earth) of the Kashafrud, the Chaman-Bid and the Mozduran formations. The picture represents onlapping and thinning of the Chaman-Bid Formation on the Middle Jurassic Kashafrud Formation towards the east. Progressive progradation of the Oxfordian carbonates of the Mozduran Formation into deeper marine facies is indicated by oblique clinoform geometry. This geometry signifies limited vertical and enough lateral accommodation space. (B) Ammonites concentrated on the top of an argillaceous limestone of the Chaman-Bid outcrop, indicating a maximum flooding surface (MFS). The length of the pencil is 14.3 cm. (C) Flute mark at the base of a sandstone layer, which was deposited on a submarine fan at the Chaman-Bid section. The arrow points to f...

Microfacies analysis, diagenetic overprints, geochemistry, and reservoir quality of the Jurassic Samanasuk Formation at the Kahi Section, Nizampur Basin, NW Himalayas, Pakistan

“…Based on the above facies distribution, the Jurassic Samanasuk Formation has been interpreted to be deposited in peritidal environment which refers to the supratidal and intertidal zone (Shinn and Robbin 1983), lagoonal environment, carbonate sand shoals on an inner ramp facies belt (Lasemi 1995; Kavoosi et al 2009;Kavoosi 2016). Shoaling upward cycles with occasional lime mudstone at the base followed by bioclastic grainstone with rounded, worn, and coated bioclasts grainstone and some well-formed oolites and/or peloids grainstones are repeatedly present in the Samanasuk Formation as shown in Fig.…”