Evidence for Isolated Platform Development in the Cenomanian on the Passive Margin of Neotethys, Southwest Iran (original) (raw)
Related papers
2012
The Cretaceous Sarvak Formation (and its equivalents on the Arabian platform) is one of the most important carbonate reservoirs to have developed under the warm equable climate. This formation in the Abteymour Oilfield contains a hydrocarbon reservoir in a carbonate ramp formed under a humid tropical oceanic climate during the middle Cretaceous in the far southwest margin of Zagros Basin, in the transition zone of the Mesopotamian Basin and Dezful Embayment. Detailed petrography assisted by image analysis resulted in the recognition of 12 microfacies grouped in six facies associations indicating a homoclinal ramp-type platform. The importance of climatic control over the facies types and patterns and diagenetic history is elaborated in this study. Interactions of sea-level fluctuations, local tectonic activity and climate are reflected by the substantial dissolution and development of reservoir quality in different horizons of this mud-dominated carbonate unit. The history of reservoir formation and its evolution during post-depositional events are revealed by a high-resolution study of primary and secondary textural features and their relationships. Accordingly, the relative timing of these processes and their paragenetic sequences indicate a complex reservoir history. From the Late Albian to the Mid Turonian three phases of emergence originated from eustatic changes and movements of basement blocks (palaeohigh formation), which led to extensive leaching and karstification. The Mid Cenomanian eustatic sea-level fall led to the first disconformity. A second emergent period and disconformity was the result of Late Cenomanian–Early Turonian movement of basement blocks. An Early–Middle Turonian sea-level rise or local subsidence of the palaeohigh led to inundation of this area and deposition of the upper division of the Sarvak Formation. This buried the middle Sarvak Formation to shallow depths and caused some cementation and mechanical compaction. A widespread Mid Turonian fall in sea level and basin-wide exposure lasting several million years led to the formation of an important regional disconformity in the upper Sarvak unit, represented by major diagenetic dissolution and an over-mature karst profile. Concurrently, deep circulation of meteoric waters led to another phase of non-fabric selective leaching beneath the C–T disconformity (telogenetic diagenesis) in the middle Sarvak Formation. These two stages of diagenesis (eo- and telogenetic) resulted in considerable improvement of the reservoir in the middle Sarvak succession. Generally, these diagenetic features show a good correlation with depositional facies and sequence stratigraphic positions (systems tracts). As shown in this study, they are predictable in the sequence stratigraphic framework of the formation. Three third-order sequences in the Mid Cenomanian–Mid Turonian interval are recognized. These are clearly correlated over the Abteymour Oilfield and other areas in the Zagros Basin and Arabian Platform (Oman) and provide a suitable framework for reservoir correlations and further modelling.
Marine and Petroleum Geology, 2015
This study covers a 300 km long, NE/SW oriented transect including five outcrop sections, and provides new biostratigraphic data and a sequence stratigraphic interpretation of the Albian, Cenomanian and Turonian sediments (Kazhdumi and Sarvak Formations) present in Coastal Fars (SW Iran). Two different carbonate depositional systems are distinguished, one for the Albian and one for the Cenomanian/ Turonian. During the Albian eustatic control was the dominant factor influencing sedimentation, while during the Cenomanian and Turonian large and small scale tectonics were dominant. This resulted in significant thickness variations and local diagenetic overprint of the sequence boundaries.
Facies, 2010
The Callovian-Lower Kimmeridgian Kamar-e-Mehdi Formation of the Tabas Block (east-central Iran) is an up to 1,350-m-thick, Wne-grained, marly-calcareous unit containing a basal Echellon Limestone Member (up to 180 m thick) and a terminal Nar Limestone Member (up to 100 m thick). The formation was deposited in a relatively deep shelf-lagoon that was part of the large-scale carbonate system of the Esfandiar Subgroup, extending N-S for about 500 km along the strike with a width of up to 100 km. The lagoonal Kamar-e-Mehdi Formation shows sedimentation rates of 150 m/myr, twice as high as those of the shelf-edge carbonate barrier (Esfandiar Platform). The repetitive lithologies and uniform depositional environment suggest equilibrium conditions between sedimentation and subsidence, related to constant slow rotation of the Tabas faultblock around a horizontal axis, the platform sitting on the crest, and the lagoon occupying the dip-slope. Lagoonal sedimentation was dominated by suspended carbonate mud and peloids from the eastern Esfandiar Platform whereas the subordinate siliciclastic material was derived from the west (Yazd Block). The diverse macrobenthos (mainly bivalves) suggests fully marine conditions for the major part of the Kamar-e-Mehdi Formation. However, towards the upper part, biotic impoverishment and the deposition of skeletal-poor, evaporitic sediments indicate increasing restriction. The overlying Magu Gypsum Formation marks the end of an arid basin-Wll cycle and possibly forms an eVective seal for hydrocarbon reservoirs in that area. The Esfandiar Subgroup was a Neotethys-facing carbonate margin, forming part of a belt of carbonate systems tracking the margins of the Iran Plate during Callovian to Late Jurassic times.
Facies, 2013
Integrated facies and diagenetic analyses within a sequence stratigraphic framework were carried out on mid-Cretaceous Sarvak carbonate reservoirs in five giant and supergiant oilfields in the central and southern parts of the Dezful Embayment, SW Iran. Results of facies analysis indicate a homoclinal ramp-type carbonate platform for this formation with the frequencies of different facies associations in six wells reflecting their approximate position in the sedimentary model. Diagenetic studies indicate periods of subaerial exposure with different intensities and durations in the upper Sarvak carbonates producing karstified profiles, dissolution-collapse breccias, and thick bauxitic-lateritic horizons. Sequence stratigraphic interpretations show that the tectonic evolution of the NE margin of the Arabian Plate (Zagros Basin) during Cenomanian-Turonian times shaped the facies characteristics, diagenetic features, and strongly influenced reservoir formation. Reactivation of basement-block faults and halokinetic movements (related to the Hormoz salt series) in the middle Cretaceous, resulted in the development of several paleohighs and troughs in the Dezful Embayment hydrocarbon province. Movements on these structures generated two and locally three disconformities in the upper parts of Sarvak Formation in this region. The paleohighs played an important role in reservoir evolution within the Sarvak Formation in three giant-supergiant oilfields (including Gachsaran, Rage -Safid, and Abteymour oilfields) but where these structures are absent reservoir quality is low.
Book Publisher International, 2020
In this study, two stratigraphic sections of Sarvak Formation were selected which are nominated Bavan and Kherameh sections. Over 379.5 meters of the Sarvak Formation and 260 thin sections have been studied. Index microfacies and foraminifers have been identified. Index microfacies include Boundstone, Wackestone and Packstone. The frequency of bioclast has been determined as larger that of the other microfacies elements. Based on the type and abundance of skeletal and nonskeletal grains and type of matrix, 14 sublithofacies have distinguished in 3 depositional environments which are include 1) Lagoon 2) Reef 3) Open marine. The mentioned determined microfacies were deposited in a Carbonate Platform of Homoclinal Ramp. Based on micropalentological data, the age of the Sarvak Formation is assigned to Cenomanian.
Carbonates and Evaporites, 2021
The Sarvak Formation is a thick carbonate sequence of Cenomanian age that has been deposited in a foreland basin across the Zagros Basin. Sarvak Formation is the main petroleum reservoir rock in the Zagros Basin. To study the foraminiferal paleoecology in the Sarvak Formation, the section was selected in the east of Shiraz (Khane Kat section) and 66 samples with a total thickness of 140 m were prepared. Then, these thin sections were studied precisely based on the lithostratigraphy, microfacies, geochemical stratigraphy (chemical XRF analysis), and paleoecology. Besides, the biozones were identified and geochemical changes of elements in each biozone were investigated. Totally, three biozones were identified in which the hyaline tests were abundant in biozone-1 and porcelaneous tests were accumulated in biozones-2 and-3. Based on the study of the foraminifera dispersion pattern, the age of the Sarvak Formation in Khane Kat section was determined as Cenomanian. The results indicated that the various environmental factors affected the test type, test size and the quantitative expansion of the test in the sedimentary basin. Geochemical, microfacies and paleoecology data indicated that the most appropriate and inappropriate condition of life was belonged to wackestone and mudstone facies, respectively. Increase in the ratio of benthic to pelagic (B/P ratios) throughout the section and the enhancement of microfossils with agglutinated tests represented the shallowness of the sedimentary basin and retrogradation of the sedimentary basin from the open marine to the Subtidal and intertidal.
The Paleocene–Eocene Taleh Zang Formation of the Zagros Basin is a sequence of shallow-water carbonates. We have studied carbonate platform, sedimentary environments and its changes based on the facies analysis with particular emphasis on the biogenic assemblages of the Late Paleocene Sarkan and Early Eocene Maleh kuh sections. In the Late Paleocene, nine microfacies types were distinguished, dominated by algal taxa and corals at the lower part and larger foraminifera at the upper part. The Lower Eocene section is characterised by 10 microfacies types, which are dominated by diverse larger foraminifera such as alveolinids, orbitolitids and nummulitids. The Taleh Zang Formation at the Sarkan and Maleh kuh sections represents sedimentation on a carbonate ramp. The deepening trends show a gradual increase in perforate foraminifera, the deepest environment is marked by the maximum occurrence of perforate foraminifers (Nummulites), while the shallowing trends are composed mainly of imperforate foraminifera and also characterised by lack of fossils in tidal flat facies. Based on the facies changes and platform evolution, three stages are assumed in platform development: I; algal and coralgal colonies (coralgal platform), II; coralgal reefs giving way to larger foraminifera, III; dominance of diverse and newly developing larger foraminifera lineages in oligotrophic conditions.
Sedimentary Geology, 2019
This study focuses on the facies associations and depositional sequences of a Cenomanian/Turonian (C/T) outcrop, spanning the upper part of the Sarvak Formation in the Izeh zone, Zagros basin, Iran. The significant variations in sedimentary facies of the studied succession suggest an evolution from a late Cenomanian open-shelf to an early Turonian ramp system. This change is believed to be response of transition in the tectonic regime of Arabian plate from a passive to an active margin during the late Cretaceous. Two partial and one complete thirdorder depositional sequences and also several fourth-order sequences and small-scale cycles were recognized in the studied section. The global correlation of the third-order sequences suggests that they were eustaticallydriven. However, local tectonic activities overprint the eustatic signature from the latest Cenomanian. The association of transgressions with cooling and regressions with warming during the fourth-order sequences support the aquifer-eustasy model as a controlling factor for the sea-level fluctuations under C/T supergreenhouse conditions.