Advances in Environmental Biology · Advances in Environmental Biology, 8(7) May 2014, Pages:...

Advances in Environmental Biology, 8(7) May 2014, Pages: 2407-2418

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Advances in Environmental Biology ISSN-1995-0756 EISSN-1998-1066

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Corresponding Author: Seyed Hadi Sajadi, Department of Geology, North Tehran Branch, Islamic Azad University,

Tehran, Iran.

Tel: +989176239352 E-mail: [email protected]

Facies Distribution, Paleoecology and Sedimentary Environment of the

Oligocene-Miocene (Asmari Formation) deposits, in Qeshm Island, SE Persian

Gulf 1Seyed Hadi Sajadi,

2Darioush Baghbani,

3Jahanbakhsh Daneshian

1Department of Geology, North Tehran Branch, Islamic Azad University, Tehran, Iran 2Department of Geology, Damavand University, Tehran, Iran 3Department of Geology, Earth Sciences Faculty, Kharazmi University, Tehran, Iran

A R T I C L E I N F O A B S T R A C T

Article history:

Received 25 March 2014

Received in revised form 20 April 2014

Accepted 15 May 2014

Available online 17 June 2014

Key words:

Asmari Formation, microfacies, palaeoecology, benthic foraminifera,

Oligocene-Miocene, Qeshm Island.

This research is focused on facies distribution, palaeoecology and palaeoenvironment of

the Asmari Formation at the Qeshm Island, Southeast Persian Gulf. The Asmari

Formation is composed of limestone, marly limestone and marl. The subsurface data is indicated the thickness of the Asmari succession is about 148 meters and two

assemblage zones have been recognized by distribution of these large foraminifera in

the study area that indicate late Oligocene (Chattian)–early Miocene (Aquitanian) age. Because of gradual facies changes and absence of turbidite deposits indicate that the

Asmari Formation was deposited in a carbonate ramp environment. Based on

depositional textures, petrographical studies and fauna of 60 thin sections, seven microfacies have been identified and characterizing upward gradual shallowing trend of

an open marine which based on the paleoecology, lithology and environmental

interpretations, three distinct depositional settings can be recognized: lagoon, barrier, and open marine. MF1 was characterized by the occurrence of hyaline benthic and

planktonic foraminifera representing distal middle ramp and below the storm wave base

of other ramp. MF2 with large and small hyaline benthic foraminifera represent a deeper fair water wave base of a middle ramp setting. MF 3–6 were characterized by

the occurrence of large and small porcelaneous benthic foraminifera representing a

shallow-water setting of an inner ramp influenced by wave and tide processes. Palaeolatitudinal reconstructions based on skeletal grains suggest that carbonate

sedimentation of the Asmari Formation took place in tropical waters within photic zone.

© 2014 AENSI Publisher All rights reserved.

To Cite This Article: Seyed Hadi Sajadi, Darioush Baghbani, Jahanbakhsh Daneshian, Facies Distribution, Paleoecology and Sedimentary

Environment of the Oligocene-Miocene (Asmari Formation) deposits, in Qeshm Island, SE Persian Gulf . Adv. Environ. Biol., 8(7), 2407-

2418, 2014

INTRODUCTION

This paper deals with the Asmari Formation (one of the best known carbonate reservoirs in the world) [68],

an Oligocene-Miocene carbonate succession in the southeastern Zagros basin, southern Iran (Fig. 1). At the type

section in Tang-e Gel-e Tursh (Valley of Sour Earth) on the southwestern flank of the Kuh-e Asmari anticline,

the Asmari Formation consists of 314 m of mainly limestones, dolomitic limestones, and argillaceous

limestones [44,45]. In the Qeshm Island, the Asmari shallow-marine limestone is located in the subsurface and

was deposited over the Pabdeh Formation gradational. The contact with the overlying Gachsaran Formation

(i.e., evaporates rocks) is conformable and gradual (Fig. 3). This formation is present in most of the Zagros

basin and lithologically, consists of limestone, dolomitic limestone, dolomite and marly limestone. Some

anhydrite (Kalhur Member) and lithic and limy sandstones (Ahwaz Member) also occur within the Asmari

Formation [44,45]. The previous studies have focused on biostratigraphy and lithostratigraphy of the Asmari

Formation and was originally defined in primary works by [18,54,64,63]. Later, [40,70,39] introduced the

microfaunal characteristics and assemblage zones for the Asmari Formation. More recent studies of the Asmari

Formation have been conducted on facies and sedimentary environment [66,5,6,6252,4,58,61,65] This paper

reports in the subsurface sedimentological study of Asmari Formation, whose results could correlate and

compare to a better understanding of the outcrops Asmari Formation in adjacent areas. The objectives of this

study are (1) a description of the facies and their distribution on the Oligocene-Miocene carbonate platform and

(2) interpretation of the paleoenvironment features based on the assemblages of benthic hyaline and imperforate

2408 Seyed Hadi Sajadi et al, 2014


foraminifera. In this article one stratigraphic subsurface section was chosen and subjected to detailed

microfacies analysis based mainly on the distribution of Oligo-Miocene foraminiferal assemblages.

Fig. 1: Cenozoic stratigraphic correlation chart of the Iranian sector of the Zagros Basin, adopted from (James

and Wynd 1965).

Fig 2: (A) General map of Iran showing the Zagros province (B) Structural of Zagros Basin [2] (C) Location

map of the studied section modified after [31](Geological Division 2004).

Geological Setting:

The Zagros Basin is the second largest basin in the Middle East and defined by a 7–14 km thick succession

of cover sediments deposited over a region along the north–northeast edge of the Arabian plate. This basin was

part of the stable Gowndwana supercontinent in the Paleozoic era and a passive margin in the Mesozoic era and

it became a site of convergent orogeny in the Cenozoic era [7]. The Zagros Fold-and-Thrust Belt of Iran is a

result of the Alpine orogenic events[55,57] in the Alpine–Himalayan mountain range. It extends in a NW–SE

direction from eastern Turkey to the strait of Hormoz in southern Iran. The tectonic activity of this area was



entirely due to converging of the Arabian and Eurasian continents. After the closure of the Neo-Tethys basin,

during late Oligocene-early Miocene times the Zagros basin was gradually narrowed and the Asmari Formation

was deposited with lithology, including lithic sandstone (Ahwaz Member) and evaporites (Kalhur Member)

[3,68]. The maximum thickness of the Asmari Formation is found in the northeastern corner of the Dezful

Embayment. On the basis of lateral facies variations, the Iranian Zagros fold-thrust belt is divided into different

tectonostratigraphic domains that are from SE to NW: the Fars Province or eastern Zagros, the Khuzestan

province or Central Zagros and finally the Lurestan Province or Western Zagros [44.45] (Fig. 2B). Also, from

southwest to northeast of the Zagros basin are the Zagros folded belt, folded and thrusted belt and High Zagros

and crush zone [26,59,60, 25]. Hormozgan province is located in southern Iran and is part of Zagros Folded belt.

This region is accompanied by NW-SE, W-E and N-S trending simple anticlines and synclines with very great

thickness of Fars Group deposits (Gachsaran, Mishan, Aghajari and Bakhtiari formations) and presence of 118

salt plugs. So, for these specific features, [44,45] called this area as the “Bandar Abbas Hinterland” (Fig. 2).

Methods and Study Area:

This study involves one stratigraphic subsurface section from the Asmari Formation. The study area is

located at Qeshm Island, southern Iran (Fig. 2C). The lithologies and the microfacies types were classified and

described according to [23]. Some samples from the underlying Pabdeh and overlying Gachsaran formations

were also analyzed for boundaries distinction. A total of 60 thin sections of the cores and cuttings are analyzed

under the microscope for biostratigraphy and facies. Petrographic studies were carried out for facies analysis

and paleoenvironmental reconstruction of the Asmari Formation. Facies were determined for each

paleoenvironment according to carbonate grain types, textures and interpretation of functional morphology of

small and larger foraminifers. Biostratigraphy are determined based on the well-known benthic foraminifera

biozones of [1].

Result:

Biostratigraphy: Biostratigraphic criteria of the Asmari Formation were established by [70] and reviewed by [1] in

unpublished reports only. Biozonation and age determinations in the study area are based on benthic

foraminifera biozonation of (Adams and Bourgeois 1967). From base to top, two foraminiferal assemblages

were recognized and were discussed in ascending stratigraphic order as follows:

Assemblage I. This assemblage corresponds to the Eulepidina-Nephrolepidina-Nummulites Assemblage

Zone (3) of [1]. The assemblage is considered to be Chattian in age. The most diagnostic species include

Miliolids gen. et sp. Indet., Peneroplis evolutus, Archaias sp., Peneroplis sp., Operculina spp., Peneroplis

thomasi, Austrollina asmariensis, Reussella sp., Dendritina rangi, Elphidium sp. 1, Spiroculina sp.,

Quinqueloculina sp., Asterigerina sp., Nummulites spp., Neorotalia viennoti, Cibicidae gen. et sp. Indet,

Archaias kirkukensis, Hetererilina sp., Glomospira sp., Textularia sp., Meandropsina anahensis, Ammonia sp.,

Discorbis sp., Pyrgo sp. 1, Valvulinid sp. 1, Spirolina cf. clyndracea, Lepidocyclina (Nephrolepidina spp.),

Nummulites intermedius/fichteli, Heterostegina sp., Schlombergerina sp., Triloculina trigonula, Eulepidina

dilatata, Rotalia sp., Bolivina sp., Paragloborotalia mayeri, Globigerina spp.

Assemblage II. This assemblage corresponds to the Miogypsinoides-Archaias - Valvulinid sp. 1 Assmblage

Zone (2) of [1]. The assemblage is considered to be Aquitanian in age and The most important foraminifera in

this assemblage are Miliolids gen. et sp. Indet., Peneroplis evolutus, Archaias sp., Peneroplis sp., Operculina

spp., Peneroplis thomasi, Austrollina asmariensis, Reussella sp., Dendritina rangi, Elphidium sp. 1, Spiroculina

sp., Quinqueloculina sp., Archaias kirkukensis.

Microfacies Analysis:

Facies analysis of the Asmari Formation in the study areas resulted in the definition of seven facies types

which characterize platform development. Each of the microfacies exhibits typical skeletal and non-skeletal

components and textures. These facies are related to the three depositional settings (lagoon, barrier, and open

marine) of inner, middle and outer portions of a carbonate platform (Fig. 5). Since Asmari Formation in the

study area overlies the Pabdeh and underlies the Gachsaran formations conformably, some samples from Pabdeh

and Gachsaran formations have been studied too. The general environmental interpretations of the microfacies

are discussed in the following paragraphs.

MF.1. Marl facies (Fig. 6/A-D):

There are intercalations of marl across the section but mainly this facies occurs in the lower parts of the

succession. They are gray to green and contain benthic (miliolids, Nummulites, Neorotalia, Elphidium,

Operculina, Amphistegina and textularids) and planktonic (Paragloborotalia mayeri and Globigerina spp.)

foraminifera. The planktonic foraminifera occurrence of the base of succession, where is the boundary between

Pabdeh and Asmari formations [51].



Interpretation:

The feature of benthic fauna and stratigraphic relationships with the other microfacies suggest that marl

facies were deposited in an open lagoon, calm, deep and normal-salinity water but the co-occurrence of

planktonic and some benthic (Nummulitidae) foraminifera in the base of the Asmari marl and marly limestone,

suggest that this facies was deposited in calm, low energy hydrodynamic and deep normal salinity water which

indicates deposition below the storm wave base [69,19,22,28]

MF.2. Bioclast lepidocyclinidae, nummulitidae, Neorotalia, wackstone-packstone (Fig. 6/E-G):

This microfacies is composed of grain–supported texture with abundant larger benthic foraminifera. The

foraminiferal assemblage is represented by numerous larger benthic perforate foraminifera such as

lepidocyclinidae and nummulitidae (Nummulites and Operculina). Other components such as Astrigerina and

red algae are rare. Due to changes in the type of fauna in some samples, the name of this facies changes to

bioclast, lepidocyclinidae, nummulitidae, Neorotalia wackstone-packstone. biostratigraphy distribution and

Paleoenvironmental model of the Asmari Formation in this interval is most prominent in the lower parts of the

Asmari Formation Iran [5].

Interpretation:

It consists of grey marly limestone beds. The combination of micritic matrix and abundance of typical

open-marine fauna including large Nummulitidae, Lepidocyclinidae and Neorotalia suggest low–medium

energy, open-marine environment. Other bioclasts such as red algae and shell fragments are rare. This

microfacies show an environment between the storm wave base and fair-weather wave base [69,28]. The

presence of large nummulites and lepidocyclinids represents that this microfacies took place in relatively deep

water and was formed in the lower photic/oligophotic zone in the distal middle ramp [35,36,43,53,33,32,

30,50,56,11,48,9,10,57].

MF.3. Coral boundstone (Fig. 6/H-I):

This facies is characterized by the abundance of scleractinian and massive coral colonies.

Interpretation:

This microfacies is interpreted to be formed by in-situ organisms as an organic reef (Bioherm) in margin of

platform and was located above the fair-weather wave base (FWWB)[69].

MF.4. Miliolids corallinacea bioclastic wackestone (Fig. 6/J-K):

Miliolids, corallinacea red algae and coral are dominating components in this microfacies. Other bioclasts

are rare but include Peneroplis and dendritia fragments. The textures are wackestone.

Interpretation:

The MF4 and MF5 represent low to medium-energy open lagoon shallow subtidal environments, but there

is different from them by their texture and grain composition. Depositional textures, fauna and stratigraphic

position may have taken place in warm, euphotic and shallow water, with low to moderate energy conditions, in

a semi-restricted lagoon. This area is located within inner carbonate platform setting [51]. The presence of well-

preserved coralline algal indicates a relatively quiet-water environment with stable substrate and low

sedimentation rates [47]. The associations of miliolids within this facies support the additional interpretation of

a relatively protected environment, probably the inner part of a platform [29].

MF.5. Miliolids bioclastic wackestone (Fig. 6/L-M):

This facies is characterized by the dominant presence of small benthic foraminifera (miliolids). Other

components such as Peneroplids, Elphidium, Bryozoan and exteraclast are rare. The matrix is fine grained

micrite.

Interpretation:

This facies characterized by low diversity skeletal fauna and was deposited in restricted low energy

lagoonal environments. There is a low biotic diversity of fauna which shows a high-stressed habitat in very

shallow restricted areas, where great fluctuations in salinity and temperature probably occurred [51].

MF.6. Imperforate foraminifera bioclast wackestone-packstone (Fig. 6/N-O):

The main elements of this microfacies are skeletal and non-skeletal components. The skeletal components

include high diversity of imperforate foraminifera in grain-supported textures and several genera of benthic

foraminifera (Austrotrillina, Archaias, Peneroplis, Meandropsina, Elphidium, Dendritina and miliolids). peloid

are rare non-skeletal associations. The other minor biota consists of particles of bryozoans and coral.



Fig. 3: Lithostratigraphy column, microfacies, benthic and planktonic foraminifers’ distribution and biozonation

of the Asmari Formation at Qeshm Island (Well no. 2).

Interpretation:

The occurrence of large number of porcelaneous imperforate foraminiferal tests may point to the

depositional environment being slightly hyper-saline [65]. These deposits include different textures ranging

from wackestone to packstone. Some porcelaneous imperforate foraminiferal (Peneroplis and Archaias) live in

recent tropical and subtropical shallow water environments [13]. Textural characteristics and prolific

porcelaneous foraminifera, suggest that a medium to high energy portion of a restricted lagoon with a nearby

tidal flat sedimentary environment prevailed and shallow marine environments [67]. Such an assemblage

described to be associated with an inner ramp environment [69,27,28,67,13,68].

MF.7. Evaporate (Fig. 6/P):

Anhydrite and gypsum facies have been observed in the upper part of the Asmari Formation which is

represents the beginning of the Gachsaran Formation. The first anhydrite has been deposited above the marly

limestones with a sharp contact.

Interpretation:

Considering the deposition of anhydrite implicates that the depositional environment became isolated from

the open marine at that time, which allowed for the concentration and submarine precipitation of salt. The

thickness of the evaporated deposits indicates that they are submarine deposits formed in an isolated saline

basin. A eustatic sea level drop is one of the most likely causes. This event took place around the early Miocene

(Aquitanian) and in the boundary of the Asmari and Gachsaran formations. But based on [24] this anhydrite is



exposed on top of the Asmari Formation and indicate the Oligocene-Miocene boundary. [24] noted that

strontium dates got from anhydrite formed as an evaporate rather than as a later diagenetic product.

Fig. 4: Foraminifera and non-foraminifera distribution of the Oligocene deposits, adopted from joint project of

French and Iran oil company (IFP-INOP 2006)

Discussion:

Sedimentary development of the Oligocene-Miocene Fars sub-basin:

During the Paleogene Pabdeh (basinal marls and argillaceous limestones) Formation were deposited in the

middle and on both sides of the Zagros basinal axis [44] (Fig. 1). The shallow-marine limestones of the Asmari

Formation were deposited above the Pabdeh Formation in the section of this study (Fig. 1), During the Rupelian

and early Chattian, outer ramp facies (Pabdeh Formation) was predominant at the Qeshm section (well no. 3)

(Fig. 3). This is visible in the lower part of the Asmari Formation. So, the Chattian sediments of the Asmari

Formation in this section overlie gradationally the Pabdeh Formation. Restricted shallow subtidal environments



are observed during Chattian times and indicated by an assemblage of abundant imperforate benthic

foraminifera.

Fig. 5: Depositional model for the carbonate platform of the Asmari Formation at the southeast of Zagros basin,

Qeshm Island. Interpretation adopted from [37].

Paleoecology:

Large benthic foraminifera (such as Nummulitidae) produced great amount of carbonates during the Early

and Middle Paleogene. In the Oligocene, euphotic conditions prevailed and carbonate production related to

these foraminifers (especially Nummulites) declined [49]. Larger perforate forms are represented by

Amphistegina, nummulitids and lepidocyclinids. Perforate foraminifera that live in shallow waters are

characterized by hyaline walls and so protect themselves from ultra violet light by producing very thick,

lamellate test walls to prevent photo inhibition of symbiotic algae within the test in bright sunlight. These large

forms are the most important indicators for constructing paleo-environmental models in the warm, shallow

marine environments [30]. The presence of these large and flat forms (lepidocyclinidae and nummulitidae) in

the lower part of Asmari Formation, in comparison with analogues in the modern platform allowed interpreting

these sediments as having been deposited in the lower photic zone [35,36,43,53,33,32]. In contrast, coralline red

algae communities become dominant, as most phototrophic carbonate producers thrive in shallow marine

environments [49], especially through Early Miocene to Tortonian [14]. Coralline red algae and large benthic

foraminifera (Nummulites, Operculina, Lepidocyclina, Archaias, Peneroplis and Dendritina) are the most

significant and dominant biota in the Asmari Formation at the study area. Other components such as corals,

bryozoan and echinoderms are present within the matrix. The distribution of larger foraminifera and coralline

red algae are largely depended on the salinity, depth, light, temperature and climate, nutrients, effect of

hydrodynamic energy and flows substrate on the biostrate and dispersion of taxa [46,61]. Small benthonic

foraminifera are common locally and include porcelaneous (miliolids) and perforated (rotaliids) forms. Rotaliids

are dominated by Neorotalia viennoti specimens. Larger foraminifera are represented by the porcelaneous

imperforate tests such as Archaias and Peneroplis may point to the depositional environment being within the

photic zone in tropical carbonate platforms and slightly hypersaline [69,27,28,67]. Flatter tests and thinner test

walls with increasing water depth reflect decreased light levels at greater depths or perhaps poor water

transparency in shallow waters [11]. These test shapes reflect adaptation to low hydrodynamic energy. Some

biogenic components such as miliolids indicate stress conditions within restricted environments. Miliolids-

dominate benthic foraminifer assemblages reflect decreased circulation and probably reduced oxygen contents

or euryhaline conditions. Miliolids are found in a variety of very shallow, hyposaline to hypersaline

environments, or are even common in the sand shoal environments of normal salinities [15,16] and are generally

taken as evidence of restricted lagoon [51].

Depositional Environment:

Three depositional environments are identified in the Oligocene-Miocene succession in the Qeshm Island,



on the basis of the distribution of the foraminifera, non-foraminifera and vertical facies relationships (Fig. 4).

These include lagoon, barrier, and open marine (Fig. 5).

Fig. 5: Microfacies types of the Asmari Formation. (A-D) MF. 1, Marl facies. (E-G) MF. 2, Bioclast

lepidocyclinidae, nummulitidae, Neorotalia, wackstone-packstone. (H-I) MF. 3 Coral boundstone.

(J-K) MF. 4, Miliolids corallinacea bioclastic wackestone. (L-M) MF. 5, Miliolids bioclastic

wackestone. (N-O) MF. 6, Imperforate foraminifera bioclast wackestone-packstone.

(P) MF7, Evaporate.

These three environments are represented by seven microfacies types (MF1: distal middle ramp and below

the storm wave base of other ramp, MF2: deeper fair water wave base of a middle ramp setting and MF 3–6:

shallow-water setting of an inner ramp influenced by wave and tide processes). Carbonate ramp environments



are characterized by: (1) the inner ramp, between the upper shore face and fair weather wave base, (2) the

middle ramp, between fair weather wave base and storm-wave base, and (3) the outer ramp, below normal

storm-wave base down to the basin plain [17]. Inner ramp deposits represent marginal marine deposits

indicative of open lagoon and protected lagoon. In the restricted lagoon environment, faunal diversity is low and

normal marine fauna are lacking, except for imperforate benthic foraminifera such as miliolids and Dendritina

which indicate quite conditions. A large number of porcellaneous imperforates points to somewhat hypersaline

waters [30,51]. The presence of imperforate foraminifera that include Archaias, Peneroplis, Dendritina,

Meandropsina, Austrotrillina, and miliolids indicates a low-energy, upper photic, shallow lagoonal depositional

environment. The large porcelaneous foraminifera types such as Archaias, Peneroplis and Dendritina are

present in MF 6. The occurrence of Archaias and Peneroplis is typical of recent tropical and subtropical

shallow-water environments [42,34] and are characteristics of the upper part of the upper photic zone (inner

ramp). Furthermore, these large porcelaneous foraminiferas are also common fossils in the Mesozoic and

Cenozoic neritic sediments [14]. And also, inner ramp deposits represent a wider spectrum of marginal marine

deposits, indicative of a high-energy reef (MF 3). The middle ramp setting is represented by the medium to fine-

grained foraminiferal–bioclastic wacke-packstone dominated by assemblages of larger foraminifera with

perforate walls such as Amphistegina, Operculina and Nummulites (Fig. 6). The faunal association suggests that

the depositional environment was situated in the mesophotic to oligophotic zone [37,50]. Open lagoon shallow

subtidal environments are characterized by microfacies types that include mixed open marine bioclasts (such as

red algae, echinoids and corals) and protected environment bioclasts (such as miliolids). The diversity

association of skeletal components represents a shallow subtidal environment, with optimal conditions as

regards salinity and water circulation. The change in larger foraminiferal fauna from porcelaneous imperforated

to hyaline perforated forms point to a decrease in water transparency [9]. The microfacies 1 and 2 are subjected

to an open marine environment of a proximal outer ramp and middle ramp, respectively. More common

components of the microfacies 1 is biota association, such as large benthic foraminifera (lepidocyclinidae,

Nummulites and Operculina), small benthic foraminifera (Neorotalia), corallinacea red algae which is

dominated in lower photic zone. Moreover, the red algae association with these larger foraminifera places the

middle ramp in an oligophotic to mesophotic zone [50,37,12,13,14].

Conclusions:

The Oligocene–Miocene Asmari Formation is a thick sequence of shallow water carbonate and is

widespread in the Zagros basin. The subsurface section of the Asmari Formation in southeast of the Zagros and

Qeshm Island allow the recognition of different depositional environments, on the basis of sedimentological

analysis, distribution of foraminifera and microfacies studies. Occurrence of large foraminifera (Nummulites,

Operculina, Lepidocyclina, Archaias, Peneroplis), coralline red algae, coral debris and fragments of

echinoderms, mollusks and bryozoan represent high nutrient stability in an oligo to mezothrophic and tropical

condition existed during deposition of the Asmari Formation. Based on the occurrence of these fossils, two

assemblage zones (Eulepidina-Nephrolepidina-Nummulites Assemblage Zone and Miogypsinoides-Archaias -

Valvulinid sp. 1 Assmblage Zone) have been recognized and the Asmari carbonate at the study area is Chattian-

Aquitanian in age. Based on the occurrence of skeletal (large benthic foraminifera and coralline red algae) and

non-skeletal components, the following environmental and paleoecological implications are defined for the

Asmari depositional environment at the Qeshm Island, southern Bandar Abbas Hinterland. Based on

components and texture, seven microfacies types have been recognized and they are grouped into three

depositional environments that correspond to the inner, middle and outer ramp. The microfacies 1 and 2 are

subjected to an open marine environment of a proximal outer ramp and middle ramp, respectively. The

microfacies 3 to 6 are belong to inner ramp/platform environment. These assemblages of the Asmari Formation

suggest that carbonate sedimentation took place in tropical waters and oligotrophic to slightly mesotrophic

conditions.

ACKNOWLEDGMENTS

The studies were supported by National Iranian Oil Company (NIOC). The authors wish to thanks the

Exploration Directorate (NIOC) for financial support and permission to publish this research.

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