Advances in Environmental Biology

Advances in Environmental Biology, 8(7) May 2014, Pages: 2407-2418
AENSI Journals
Advances in Environmental Biology
ISSN-1995-0756
EISSN-1998-1066
Journal home page: http://www.aensiweb.com/aeb.html
Facies Distribution, Paleoecology and Sedimentary Environment of the
Oligocene-Miocene (Asmari Formation) deposits, in Qeshm Island, SE Persian
Gulf
1
Seyed Hadi Sajadi, 2Darioush Baghbani, 3Jahanbakhsh Daneshian
1
Department of Geology, North Tehran Branch, Islamic Azad University, Tehran, Iran
Department of Geology, Damavand University, Tehran, Iran
3
Department of Geology, Earth Sciences Faculty, Kharazmi University, Tehran, Iran
2
ARTICLE INFO
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.
ABSTRACT
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), 24072418, 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
Corresponding Author: Seyed Hadi Sajadi, Department of Geology, North Tehran Branch, Islamic Azad University,
Tehran, Iran.
Tel: +989176239352 E-mail: [email protected]
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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
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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].
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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 wellpreserved 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.
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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
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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
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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. Miliolidsdominate 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,
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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
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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 finegrained 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 ChattianAquitanian 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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