Sequence stratigraphy and ichnology of Early Cretaceous reservoirs, Gadvan Formation in southwestern Iran

• Published in: Marine and petroleum geology Vol. 81; pp. 294 - 319
• Main Authors: Bayet-Goll, Aram, Samani, Pouran Nazarian, Neto de Carvalho, Carlos, Monaco, Paolo, Khodaie, Navab, Pour, Mehran Morad, Kazemeini, Homayoan, Zareiyan, Mohammad Hossein
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.03.2017
• Subjects: Abadan plain; Gadvan formation; Genetically-related ichnocoenoses; Iran; Sedimentary environments; Third-order sequences; Genetically-related ichnocoenoses; Sedimentary environments; Iran; Abadan plain; Third-order sequences; Gadvan formation
• ISSN: 0264-8172; 1873-4073
• DOI: 10.1016/j.marpetgeo.2016.11.008

The siliciclastic Gadvan Formation from Abadan Plain, southwestern Iran, is highly bioturbated and allows relationships between changes in ichnocoenoses within a depositional system to be documented and placed in a high-resolution sequence stratigraphic framework. Relying on the sedimentary and ichnological characteristics, the siliciclastic succession is divided into two facies associations: a wave-dominated offshore-shoreface complex and a tide-river influenced delta. The first includes facies that have been deposited in shelf-offshore, upper offshore, lower shoreface and upper/middle shoreface environments, the latter includes facies that have been deposited in prodelta and delta front. Integrated ichnologic and sedimentologic studies of the Gadvan Formation, allow distinction between prodelta and delta front and open marine deposits. With the identification of maximum flooding and ravinement surfaces as bounding surfaces of the stratal units, detailed analysis on systematic changes in the stacking pattern (cycle thickness, cycle type, and facies proportion) are made. Eight ichnocoenoses could be differentiated in the studied sections. The positions of the ichnocoenoses within genetically related stratal units (genetically related ichnocoenoses), indicate three large-scale cycles (DS1 to DS3, from oldest to youngest). The cyclical nature of the Gadvan Formation is attributed to low-amplitude eustasy in greenhouse conditions formed under interaction of eustatic high-frequency cycles and longer term tectonically driven sea-level variations during the long-term transgressive sea-level trend of the early Cretaceous. Stratigraphic architectural style of sequences DS1 to DS3 (which includes scarce evidence of lowstand deposits, partial or total truncation of the HST, and predominance of thick transgressive deposits), is remarkably similar to long-term transgressive sea-level trend of the Early Cretaceous across the Arabian Plate. This study suggests a more relatively seaward position of the siliciclastic successions of the Gadvan Formation of Abadan Plain than the Mesopotamian Basin (upper Zubair Formation equivalent in western Iraq and Kuwait), which would be concordant with the prevailing view of an easterly prograding coastline across the Arabian Plate. This study reveals important sedimentological and ichnological features and permits the development of predictive models for the paleoenvironmental and sequence stratigraphical significance of trace fossil assemblages that can be readily compared or translated to analogous depositional systems worldwide. The ichnological analysis is based on cores and can be especially applied to evaluate the applicability of current ichnological models to the study of Cretaceous reservoirs of western Iraq, Kuwait and western Saudi Arabia. •Sequence stratigraphy and ichnology analyses of Early Cretaceous reservoirs of the Gadvan Formation have been conducted.•Eight ichnocoenoses were recognized in the facies associations of the Gadvan Formation.•Paleoichnocoenoses provided a basis for the interpretation of sedimentary processes and depositional systems.•The hierarchy analysis of cycles is useful for the identification of three 3rd-order depositional sequences.•Results are useful for evaluate the applicability of current ichnological models to the study of Middle East reservoirs.