Petrographical and geochemical evidences for paragenetic sequence interpretation of diagenesis in mixed siliciclastic–carbonate sediments: Mozduran Formation (Upper Jurassic), south of Agh-Darband, NE Iran

Abstract

The Upper Jurassic Mozduran Formation with a thickness of 420 m at the type locality is the most important gas-bearing reservoir in NE Iran. It is mainly composed of limestone, dolostone with shale and gypsum interbeds that grade into coarser siliciclastics in the easternmost part of the basin. Eight stratigraphic sections were studied in detail in south of the Agh-Darband area. These analyses suggest that four carbonate facies associations and three siliciclastic lithofacies were deposited in shallow marine to shoreline environments, respectively. Cementation, compaction, dissolution, micritization, neomorphism, hematitization, dolomitization and fracturing are diagenetic processes that affected these sediments. Stable isotope variations of d 18 O and d 13 C in carbonate rocks show two different trends. High depletion of d 18 O and low variation of d 13 C probably reflect increasing temperatures during burial diagenesis, while the higher depletion in carbon isotope values with low variations in oxygen isotopes are related to fresh water flushing during meteoric diagenesis. Negative values of carbon isotopes may have also resulted from organic matter alteration during penetration of meteoric water. Fe and Mn enrichment with depletion of d 18 O also supports the contention that alteration associated with higher depletion in carbon isotope values with low variations in oxygen isotopes took place during meteoric diagenesis. The presence of bright luminescence indicates redox conditions during precipitation of calcite cement.

Facies mosaic and diagenetic patterns of the early Devonian (Late Pragian–Early Emsian) microbialite‐dominated carbonate sequences, Qasr Member, Jauf Formation, Saudi Arabia

“…The diagenetic processes that occurred during this stage include cementation (blocky, drusy and poikilotopic cements), compaction (physical and chemical), dissolution and dolomitization to form subhedral and anhedral dolomites. Dolomites experience an evolving route with regard to size and shape as they pass through different diagenetic stages during burial and experience changes in pore‐fluid chemistry, temperature and pressure (Warren, ; Mahboubi et al ., ). Euhedral dolomites are most developed in the region that is likely to have experienced high temperature.…”

Facies analyses and depositional setting of the Lower Cretaceous Shurijeh–Shatlyk formations in the Kopeh Dagh–Amu Darya Basin (Iran and Turkmenistan)

“…The back reef (carbonate shelf) was separated on the northern and western parts from deep marine facies towards the south and south‐east (to the north of Afghanistan) by the barrier reefs (Ulmishek, ). In the Kopeh Dagh and Dauletabad ranges, thick, shallow back‐reef carbonate rocks were deposited during Oxfordian to Tithonian time (Kavoosi, ; Kavoosi, Lasemi, Sherkati, & Mossavi‐Harami, ; Lasemi, ; Mahboubi, Moussavi‐Harami, Carpenter, Aghaei, & Collins, ). At the same time, the carbonate facies changes to siliciclastic coastal and delta facies towards the basin margins and palaeo‐highs, such as the Aghdarband area (Zand‐Moghadam, Moussavi‐Harami, Mahboubi, & Aghaei, ).…”

“…At the same time, the carbonate facies changes to siliciclastic coastal and delta facies towards the basin margins and palaeo‐highs, such as the Aghdarband area (Zand‐Moghadam, Moussavi‐Harami, Mahboubi, & Aghaei, ). Carbonate facies deposition continued until the Tithonian and probably to the Early Cretaceous in the Kopeh Dagh Foldbelt (Kavoosi, Lasemi, Sherkati, & Mossavi‐Harami, ; Mahboubi, Moussavi‐Harami, Carpenter, Aghaei, & Collins, ; Zand‐Moghadam, Moussavi‐Harami, Mahboubi, & Aghaei, ). While in the Murgab Depression, the Callovian to Oxfordian shallow carbonate facies was overlaid by the thick salt–anhydrite of the Gaurdak Formation (Ulmishek, ).…”

“…The back reef (carbonate shelf) was separated on the northern and western parts from deep marine facies towards the south and south-east (to the north of Afghanistan) by the barrier reefs (Ulmishek, 2004). In the Kopeh Dagh and Dauletabad ranges, thick, shallow back-reef carbonate rocks were deposited during Oxfordian to Tithonian time (Kavoosi, 2014;Kavoosi, Lasemi, Sherkati, & Mossavi-Harami, 2009;Lasemi, 1995;Mahboubi, Moussavi-Harami, Carpenter, Aghaei, & Collins, 2010 The age of the boundary between marine and continental deposits is not recognized, precisely, but the generally accepted age is Tithonian-Berriasian based on ostracods, foraminifers, and algae from carbonates of the lagoonal and shallow marine deposits (Jamali, 2011;Kim, Salimova, Abduasimova, & Meshchankina, 2007;Mortazavi, 2013).…”

Microfacies and diagenetic overprints in the limestones of Middle Jurassic Fort Member (Jaisalmer Formation), Western Rajasthan, India: Implications for the depositional environment, cyclicity, and reservoir quality

“…Marine diagenetic environments are recognized by first generation of micritization, non‐ferron‐isopachous fibrous cements (El Ghar et al, 2015; Khalifa, 2005; Mahboubi, Moussavi‐Harami, Carpenter, Aghaei, & Collins, 2010; Taghavi, Mørk, & Emadi, 2006; Vincent et al, 2007). Micritization is the most striking diagenetic feature that is identified in the Fort Member limestones, likely to be formed in marine environment.…”