Regional stratigraphic architecture and reservoir types of the Oligo-Miocene deposits in the Dezful Embayment (Asmari and Pabdeh Formations) SW Iran

Abstract

A regional sequence stratigraphic model is proposed for the Oligo-Miocene Asmari and Pabdeh Formations in the Dezful Embayment of SW Iran. The model is based on both new detailed sedimentological observations in outcrops, core and well logs, and an improved high-resolution chronostratigraphic framework constrained by Sr isotope stratigraphy and biostratigraphy. A better understanding of the stratigraphic architecture distinguishes four, geographically separated types of Asmari reservoirs.Three Oligocene sequences (of Rupelian, early Chattian and late Chattian age) and three Miocene sequences (of early Aquitanian, late Aquitanian and early Burdigalian age) have been distinguished, representing a period of 15.4 Ma. The stratigraphic architecture of these sequences is primarily controlled by glacio-eustatic sea-level fluctuations, which determined the distribution of carbonates, sandstones and anhydrites in this sedimentary system. Tectonic control became important in the Burdigalian with a regional tilt down towards the NE. The lithological heterogeneity, the complex geometries, and both early and late diagenetic alterations are the basis for a classification of four main stratigraphic reference types for the Asmari Reservoirs: Type 1, sandstone dominated; Type 2, mixed carbonate-siliciclastic; Type 3, mixed carbonate-anhydrite; and Type 4, carbonate dominated. The sequence stratigraphic model predicts how and when these types change laterally from one to another.

Biostratigraphy and paleoecology of the Oligo-Miocene Asmari Formation in the Izeh zone (Zagros Basin, SW Iran)

“…These two reports were used by many authors (e.g., Seyrafian, 2000;Vaziri-Moghaddam et al, 2006;Amirshahkarami et al, 2007a, b). Recently, Ehrenberg et al (2007), Laursen et al (2009) and Van Buchem et al (2010) conducted strontium isotope dating to improve the biostratigraphic ages for the Asmari Formation across most parts of the Zagros basin (Izeh zone and Dezful Embayment) ( Table 2). This biozonation is used by many recent authors (e.g., Allahkarampour Dill et al, 2010;Van Buchem et al, 2010;Sooltanian et al, 2011;Rahmani et al, 2012).…”

“…Recently, Ehrenberg et al (2007), Laursen et al (2009) and Van Buchem et al (2010) conducted strontium isotope dating to improve the biostratigraphic ages for the Asmari Formation across most parts of the Zagros basin (Izeh zone and Dezful Embayment) ( Table 2). This biozonation is used by many recent authors (e.g., Allahkarampour Dill et al, 2010;Van Buchem et al, 2010;Sooltanian et al, 2011;Rahmani et al, 2012). The biozonation scheme of Laursen et al (2009) and Van Buchem et al (2010) have some basic differences compared to the old scheme (Adams and Bourgeois, 1967).…”

“…This biozonation is used by many recent authors (e.g., Allahkarampour Dill et al, 2010;Van Buchem et al, 2010;Sooltanian et al, 2011;Rahmani et al, 2012). The biozonation scheme of Laursen et al (2009) and Van Buchem et al (2010) have some basic differences compared to the old scheme (Adams and Bourgeois, 1967). In the old scheme, the noticeable thickness of the Asmari limestone, containing Archaias, has been considered Aquitanian.…”

“…Also in the biozonation of Laursen et al (2009) andVan Buchem et al (2010), the Oligocene sediments are divided to Rupelian and Chattian. The area of the new biostratigraphic studies which used the biozonation of Laursen et al (2009) and Van Buchem et al (2010) is very small in comparison to the total area of the Asmari basin (more than 150 km × 700 km). There are a lot of areas with unpublished sections for which the new biozonation should be considered.…”

“…The data obtained from biostratigraphic studies in this area will be used for the future regional study. The abundance of large benthic foraminifera in the limestones of the Asmari Formation offers an excellent opportunity to study paleoenvironmental controls on larger benthic foraminiferal assemblages in The objectives of this study are (1) to reconstruct a coherent biostratigraphic framework for the carbonate deposits of the Asmari Formation in the studied area based on available biozonation schemes (Cahuzac and Poignant, 1997;Laursen et al, 2009;Van Buchem et al, 2010) (Tables 1 and 2), and (2) to present the paleoenvironmental factors which affect the distribution of biogenic components of the Asmari Formation.…”