Depositional sequences, diagenesis and structural control of the Albian to Turonian carbonate platform systems in coastal Fars (SW Iran) (original) (raw)
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Palaeogeography, Palaeoclimatology, Palaeoecology, 2019
A Neo-Tethyan upper Albian-Turonian (hemi-)pelagic carbonate succession (Sarvak Formation), accessible in outcrop in the Zagros, SW Iran, was investigated using sedimentology, microfacies analysis, planktonic foraminifera biostratigraphy, and carbon-isotope stratigraphy. The succession contains six biozones including Thalmaninella (Th.) appenninica, Th. globotruncanoides, Rotalipora cushmani, Whiteinella archaeocretacea, Helvetoglobotruncana Helvetica, and Marginotruncana schneegansi. Some of these biozones show variable stratigraphic positions throughout the Tethyan and Boreal realms that hinder correlation of the studied Iranian section with European reference sections. Therefore, the correlation of the existing biostratigraphic framework was complemented by carbonate carbon-isotope stratigraphy based on bulk carbonate material. Despite the low resolution of the presented carbon-isotope record, pronounced global events including the late Turonian Events, Cenomanian/Turonian Boundary (CTB) Event (OAE 2), and Albian/Cenomanian Boundary (ACB) Event can be distinguished. The δ 13 C excursions provide global synchronous time-lines for correlation. The distinguished biozones were compared among the sections regarding their stratigraphic positions relative to these timelines. The correlation tentatively suggests that the biostratigraphic datum marking the ACB is diachronous with an SE-NW trend. First appearance datum (FAD) of Th. appenninica varies from the upper Albian to the lower Cenomanian. The FAD of Th. globotruncanoides is also variable from the upper Albian to the lower Cenomanian. However, the middle Cenomanian-Turonian biozones including Rotalipora cushmani and Whiteinella archaeocretacea zones are synchronous. Elevated pCO2 contributed to the gradual increase of the SST (sea surface temperature) during the Cenomanian, and the dramatic climax at the earliest Turonian. This trend closely correlates with the change from the diachronous ACB-biozones to synchronous CTB-biozones. Possibly, increasing SSTs provided temperature-tolerance range for the species throughout different latitudes, and assisted their rapid distribution. Moreover, the warming raised the sea level from the
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.
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.
Geological Society, London, Special Publications, 2010
A high resolution sequence stratigraphic model has been constructed for the mid-Cretaceous Sarvak Formation (in the High Zagros region of SW Iran) which was deposited close to the eastern margin of the Arabian Plate. The exceptional outcrop quality, displaying the detailed facies patterns in the transition zone from carbonate platform to intra-shelf basin, offers the rare opportunity to distinguish between the relative control of carbonate sediment supply (S) and accommodation (A) on the depositional geometries of third- and fourth-order depositional sequences.Four third-order sequences have been distinguished in the Sarvak Formation, with a duration varying between 1.5 and 3 Ma, and a thickness of 50–150 m. These are in turn composed of fourth- and fifth-order sequences that form the stratigraphic building blocks of this carbonate system. A significant distinction has been made in the third-order sequences between the early transgression (e-TST) when the system was still flat, and ...
JOURNAL OF AFRICAN EARTH SCIENCES, 2023
This study provides a detailed examination of a condensed Cenomanian-Turonian (C-T) succession of two sections (Dokan Dam and Khalakan) in the Kurdistan Region, Northeastern Iraq, based on biostratigraphy (calcareous nannofossils and planktic foraminifera), carbon and oxygen isotope geochemistry, and facies analysis. The C/T boundary in this region is characterized by a hiatus noticeable due to the absence of the Globigerinelloides benthonensis and Dicarinella hagni subzones and the lack of positive carbon isotope excursion (CIE) peak b during the Oceanic Anoxic Event 2 (OAE2). Positive CIEs in our studied succession include three peaks (a, c, and d) from the four established positive global CIE peaks (a, b, c, and d). Peak a is recognized at the upper part of the Cenomanian Dokan Formation, while peak b is missing within the hiatus across the C/T boundary. Peak c is found within the lowest Turonian above the Gulneri/Dokan formational boundary, and peak d appears at the base of the middle Turonian Kometan Formation. Twelve microfacies and four submicrofacies types are identified and grouped by depositional paleoenvironments into five facies associations, ranging from peritidal to basinal settings. Three incomplete third-order depositional sequences (DSs) and their transgressive-regressive cyclic stacking pattern have been identified in the Cenomanian-Turonian succession studied herein. These DSs are associated with hiatuses, suggesting tectonic control combined with a global sea-level fall. Hiatuses and extreme condensation recorded in the latest Cenomanian-early Turonian successions on many Neo-Tethys platforms resulted from platform exposure, subsequent drowning, and a warming climate.
Chemostratigraphy of Cenomanian-Turonian Carbonates of the Sarvak Formation, Southern Iran
Journal of Petroleum Geology, 2012
Stable-isotope and trace-element analyses from five surface and subsurface sections of the mid-Cretaceous Sarvak Formation in southern and offshore Iran confirm the presence of the regional-scale Turonian unconformity and of a more local Cenomanian-Turonian unconformity. The geochemical results indicate the presence of previously unrecognized and/or undifferentiated subaerial exposure surfaces. Sarvak Formation carbonates at or near palaeo-exposure surfaces show varying degrees of diagenetic modification, and more extensive alteration is associated with longer periods of exposure. The subaerial exposure and associated diagenetic processes greatly influenced reservoir quality and amplified karstification and evolution of porosity in the Upper Sarvak Formation. The palaeo-exposure surfaces are identified by their negative δ 13 C values (as low as-6.4‰) and negative δ 18 O values (as low as-9.4‰), together with low Sr concentrations and relatively high 87 Sr/ 86 Sr ratios. These geochemical characteristics are interpreted to be the result of the interaction of the Sarvak Formation carbonates with meteoric waters charged with atmospheric CO 2. The meteoric waters also caused karstification and soil formation which in some places extends a few metres below the exposure surfaces. Depleted carbon values were not recorded in areas where palaeosols are not well developed or where the uppermost layers of the Sarvak Formation have been removed by erosion.
2010
The objective of this work is to study the Mesozoic turbiditic sediments from the southern Tethys margin in Iran. These sediments are exposed as nappes in the Pichakun Mountains (i.e. the Zagros Mountains in the Neyriz area), which inverted during latest Cretaceous time. Radiolarians are used to both define and date four main lithostratigraphic formations: (1) the Bar Er Formation (undated, probably Late Triassic to Early Jurassic); (2) the Darreh Juve Formation (Aalenian–early Bajocian to middle Callovian–early Oxfordian); (3) the Imamzadeh Formation (middle Callovian–early Oxfordian to Aptian); (4) the Neghareh Khaneh Formation (late Aptian to Turonian–Coniacian). Most of the sediments are deep-sea gravity-flow lobe deposits. Channel deposits occurred during the Bajocian (i.e. the Darreh Juve Fm) and deeply incised channels (canyons?) occurred during the Albian (i.e. the Neghareh Khaneh Fm). Twenty-seven facies, grouped into eight facies associations, are defined. Based on a seque...
Depositional sequences diagenesis and st
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. Regional correlations were established constrained by ammonite data, as well as sedimentological and sequence stratigraphic considerations. In the Albian interval, including the Kazhdumi Formation and redated Mauddud Member, three 3rd order sequences have been distinguished. The depositional system consists of muddy carbonate ramps, rich in orbitolinid benthic foraminifers, which laterally interfinger with green marls. Albian deposits are present throughout the area and vary in thickness from 100 to 160 m. Subaerial exposure has only been observed on top of the Albian-3 sequence (Top Mauddud Member). In the upper part of the succession, which is of Cenomanian/Turonian age, the depositional system changed to rudist-rimmed carbonate platforms surrounding local organic-rich, intra-shelf basins. The thickness in this interval varies greatly, from 0 to 300 m, which was controlled by both large scale (Qatar-Fars high) and local scale (salt domes) tectonic processes. In this tectonically active setting, three Cenomanian and one Turonian 3rd order sequences have been distinguished. Several sequence boundaries show evidences for long-lasted subaerial exposures (up to 13 Ma), with the local preservation of soil sequences and continental deposits. The expression of these exposures varies laterally considerably, and macroscopic evidences are sometimes lacking. Petrographic and C & O stable isotope investigations supplement classic sedimentology to reveal the record of these exposures.
Minerals
In the Cenomanian, the southern passive margin of the Neotethys Ocean was dominated by a giant carbonate factory. This succession is known as Sarvak Formation, a significant reservoir in Iran. This study focuses on a detailed analysis of facies variations and paleoenvironmental reconstruction, including the interpretation of the platform types, during this time interval. Based on field observations and petrographical studies, 12 facies have been recognized and ascribed to six facies belts on a carbonate ramp. Sub-environments include the outer ramp and basin (distal open marine), talus and channel (mid-ramp) and lagoon and shoal (inner-ramp). The frequency of the facies and isochore maps indicate the paleoenvironmental conditions and their spatial variations in the study area. Based on all data and analyses, the suggested conceptual model for the Sarvak Formation in the Lurestan Zone is an isolated platform surrounded by two ramps. The upwind and downwind parts of these ramps were l...