Microfacies and sedimentary environment of the Early-Middle Miocene deposits (Mishan Formation) in...

Advances in Environmental Biology, 8(10) June 2014, Pages: 1031-1039

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

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Corresponding Author: Roya Fanati Rashidi, Department of Geology, science and research Branch, Islamic Azad

University, Tehran, Iran.

E-mail: [email protected]

Microfacies and sedimentary environment of the Early-Middle Miocene deposits

(Mishan Formation) in South of Iran

1Roya Fanati Rashidi,

2Seyed Hamid Vaziri,

3Keyvan Khaksar,

4Hossein Gholamalian

1Department of Geology, science and research Branch, Islamic Azad University, Tehran, Iran.

2Department of Geology, Faculty of Basic Sciences, North Tehran Branch, Islamic Azad University, Tehran, Iran.

3Islamic Azad University, Qom, Iran. 4Department of Geology, Faculty of Sciences, Hormozgan University, Bandar Abbas, Iran.

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

Article history: Received 21 April 2014

Received in revised form 23

May 2014 Accepted 13 June 2014

Available online 10 July 20144

Keywords:

Mishan Formation, Microfacies,

Depositional environment, Iran

In order to interpret the microfacies and depositional environment of the Mishan

Formation, two stratigraphic sections were studied in the Khorgu and Khamir anticlines

at the north and west of the Bandar Abbas southern Iran. The Khamir section in the

Khamir anticline includes: medium-bedded to massive limestone, medium-bedded dolomitic limestone, medium-bedded marly limestone, chalk and green marl. The

Mishan Formation in the Khorgu anticline includes: medium to thick-bedded limestone,

medium-bedded marly limestone, calcareous marl, grey marl and green marl. Two different facies types (i.e., clastic and carbonate facies) have been recognized in this

study. Also, detailed petrographic analysis of the carbonate facies led us to the

recognition of 12 microfacies types grouped into three major depositional environments (inner, middle and outer shelf) in Khamir section and two depositional environments in

Khorgu section (middle shelf and outer shelf). The inner shelf facies is characterized by

mudstone, wackstone, packstone and grainstone,dominated with miliolid, Dendritina, bryozoa and small perforate foraminifera dominated microfaunas. The middle shelf

facies is represented by wackstone to packestone with diverse assemblage of large

perforate benthic foraminifers, Ditrupa and the rare planktonic foraminifers. Outer shelf facies is dominated by planktonic and perforate foraminifers and Ditrupa.

© 2014 AENSI Publisher All rights reserved.

To Cite This Article: Names Roya Fanati Rashidi, Seyed Hamid Vaziri, Keyvan Khaksar, Hossein Gholamalian., Microfacies and

sedimentary environment of the Early-Middle Miocene deposits (Mishan Formation) in South of Iran. Adv. Environ. Biol., 8(10), 1031-

1039, 2014

INTRODUCTION

The Mishan Formations was introduced by James and Wynd [6] and the type section was measured in the

Gachsaran oilfield. Generally, it overlies the Gachsaran Fm. and underlies the Aghajari Formation. It consists of

carbonate deposits (i.e., thick-bedded to massive, feature forming, hard and fossiliferous limestones) called the

Guri Member and green marl with intercalations of thin to medium bedded limestones. The studied areas are

located in the Khorgu (56 29' 05.5" longitude and 27 35' 36" latitude) and Khamir anticlines (55 41' 53"

longitude and 27 07' 23" latitude). The rocks were classified in the field using a hand lens and their depositional

fabric were described [5]. Indeed, more than 120 thin sections were provided from limestone and marl particles

for micropaleontology and microfacies studies. Khorgu and Khamir sections are located at the southeastern end

of the Zagros Folded Zone consisting of a simple anticline-syncline system [7]. Khorgu section is 430 m in

thickness with uncertain lower boundary and conformable and gradual upper boundary between the Mishan and

Aghajari formations. The Khamir section is 1104 m in thickness with conformable and sharp lower boundary

between the Guri Member and the Gachsaran Fm. and also with sharp upper boundary (between the Mishan and

the Aghajari Formations). The age of the Mishan Fm. in the studied sections based on the occurrence of

Triloculina tricarinata, Asterigerina rotula, Amphistegina lessoni, Neorotalia viennotti, Ammonia beccari,

Ammonia stachi, Elphidium sp.14, Elphidium sp.1, Miogypsina sp., Operculina complanata, Orbulina universa,

Globigerinoides sp., Globigerina sp., Globorotalia sp. Globigerina bulloides, Globigerinoides trilobus and

Globigerinoides sicanusis Early to Middle Miocene (Aqutanian to Langhian).

Geological Setting:

Late Cenozoic and Recent tectonic and sedimentary features in the Zagros basin have been resulted by the

final collision between of the African/Arabian and central Iran plates, which was started during the Mesozoic

1032 Roya Fanati Rashidi et al, 2014


[2]. The Zagros region is an active growth area of the mountains belt and can be divided into five structural

zones: 1) magmatic arc of Urumieh-Dokhtar, 2) metamorphic of Sanandaj-Sirjan, 3) high Zagros 4) Zagros

simply folded belt and 5) foreland of Persian Gulf (Alavi, 2004). The studied areas of this research are located in

the Southeastern part of the Zagros simply folded belt (Fig. 1).

Fig. 1: (A) General map of Iran showing the Zagros province (B) Structural of Zagros Basin (Aghanabati A.

2004) (C) Location map of the studied area

Microfacies Analysis:

There are two different facies types in the Mishan Fm.; clastic and carbonate facies. Facies analysis of the

carbonate part has resulted in the definition of 12 microfacies types.

Clastic Facies

Clastic facies consists of marls, but most outcrops are erroded or covered by alluvium deposits in some

areas. These marls contain large amounts of quartz in size of sand and silt particles. The particles of clastic

material transported from land to the sea which are exogenetic. The carbonate cycles are separated by the marls.

This microfacies is highly diverse in larger benthic foraminifera with perforate wall such as Neorotalia

viennotti, Ammonia beccari, A. stachi and pelagic foraminifera such as Globigerinoides sp., Globigerina sp.,

Globigerina bulloides, Globigerinoides trilobus and Globigerinoides sicanus. Based on lithological and

paleontological evidence, it can be confirmed that the clastic facies in, comparision to the carbonate facies are

formed in the deeper basin.

Carbonate Facies:

MF1. Ditrupa- planktonic foraminifera-quartz wackestone (Fig. 2.a):

This type is distinguished from MF11 by the presence of Globorotalia sp. and the lack of benthic

foraminifera. The presence of planktonic foraminifera, abundant micrits and stratigraphic position indicate that

the deposition has been taken place in a low energy deep water environment (outer shelf environment) [3]. It

occurs at the lower part of the Khorgu section.

MF2. Bentic/planktonic foraminifera wackestone (Fig. 2.b):

This type is characterized by an association of pelagic foraminifera (i.e., Globigerina, Globigerinoides and

Globorotalia), small benthic foraminifera (i.e., Ammonia beccarii andNeorotalia viennoti), Ditrupa, ostracoda

and small quartz grains. Quartz grains probably have been transported by wind from land to the sea. This



microfacies has been observed in from of limestone, marly limestone and calcareous marl in the many parts of

the Khorgu section. This facies indicates the outer shelf environment, too.

MF3. Quartz mudstone (Fig. 2.c):

This facies consists of a high percentage of carbonate mud, quartz grains and the rare faunal elements (i.e.,

Globogerina, Globorotalia and Ammonia). This microfacies have been observed in from of light grey limestone,

white marly limestone and dark grey calcareous marl in the Khorgu section. The plankton faunal elements and

stratigraphic position show that the deposition has been occurred in a deep and low energy the outershelf

environment.

MF4. Operculina wackestone to packestone (Fig. 2.d,e):

The main components are bioclasts and large perforate foraminifera. Bioclasts include bivalve, red algae,

echinoderm and bryozoa fragments. The foraminifera are characterized by a relatively diverse assemblage of

Operculina, Amphistegina, Asterigerina and Miogypsinoides. Also, the Lack of planktonic foraminifera is the

other character of this facies. This facies dominates in the Khamir section and has been observed in from of

limestone and marly limestone. The presence of red algae and larger foraminifera such as Amphistegina

indicates that sedimentation in the end of middle shelf environment [10,8,4].

MF5. Ditrupa packestone (Fig. 2.f):

In this type of microfacies, bioclast fragments (i.e., abundant Ditrupa sp., Neorotalia, Ammonia and

Bigenerina and echinoderms) are dominant biotic components. Also, there are rarely planktonic foraminifers

including non-keeled Globigerinids. This facies in from of cream-brown limestones in the middle parts of the

Khorgu section. Ditrupa has an infaunal-epifaunal life-style in fine sediments, from mud to clean sand.

However, it is preferentially found between 20 and 30 m depth [12]. Accompanied planktonic foraminifers show

a deeper environment. This microfacies represents deposition in middle shelf.

MF6. Rotaliids-bryozoan wackestone to packestone (Fig. 3.a):

This microfacies is characterized by the abundant occurrence of small rotaliids (i.e., Neorotalia and

Ammonia), bryozoa (i.e., Tubucellaria, Memberanipora and Onychocella) and abundant micrite matrix. It

occurs in the cream-brown, thin to medium-bedded limestones in the upper parts of the Khorgu and Khamir

sections. Rotaliids are abundant in the high energy shallow water (inner shelf) and bryozoans are found between

60 and 120 m from the base. This microfacies represents deposition in the end of inner shelf.

MF7. Bioclast wackestone (Fig. 3.b):

The main bioclastic components are bivalve and gastropods fragments. Foraminifers such as small Rotaliids

are very rare. This facies has been observed in the limestones of the lower and upper parts of the Khamir

section. The presence of abundant micrite, fragments of molluska and lack of foraminifera indicate that

sedimentation has been taken place at the turbulent environment in the inner shelf.

MF8. Bioclast-dendritina grainstone (Fig. 3.c):

Identifiable components of this facies include abundant Dendritina, Elphidium, Ammonia, bryozoa,

interclast and quartz grains. Imperforated crusts of Dendritina have been hematitize. This facies has been

observed as cream to brown limestones in the base of the Khamir section. The features of these facies indicate

the moderate to high energy shallow water conditions such as inner shelf lagoonal environment.



Fig. 2: (a) MF1. Ditrupa- planktonic foraminifera-quartz wackestone, (b) MF2. Bentic/planktonic foraminifera

wackestone, (c) MF3. Quartz mudstone, (d,e) MF4. Operculina wackestone to packestone, (f) MF5.

Ditrupa packestone.

MF9. Bioclast grainstone (Fig. 3.d,e):

This type is characterized by abundant bryozoans and fragments of bivalves. Other bioclasts are rare and

include gastropods, algae and small benthic foraminifera such as Ammonia. The texture is grainstone. It has

been observed as brown on suggest that deposition occurred in a shallow and high energy environmentin the

innershelf environlimestone in the upper part of the Khamir section. The texture of facies, faunal elements and

stratigraphic position suggest that deposition occurred in a shallow and high energy environment in the inner

shelf.

MF10. Mudstone (Fig. 3.f and4.a):

This facies consists of fine–grained microcrystalline limestone. There are lacks of sedimentary structures.

Very rare bioclasts (i.e., Elphidium and Neorotalia) are also present. This microfacies occurs at the lower parts



of the Khamir section. This facies was deposited in a lagoon. Evidence for this interpretation includes the lack

of fauna both in diversity and abundance, and a stratigraphic position below the lagoonalfacies [14].

Fig. 3: (a); MF6. Rotaliids-bryozoan wackestone to packestone, (b) MF7. Bioclast wackestone, (c) MF8.

Bioclast-dendritina grainstone, (d,e) MF9. Bioclast grainstone, (f) MF10. Mudstone.

MF11. Miliolid packestone (Fig. 4.b): The most abundant benthic foraminifera in this type are milolids such as Quinquloculina, Pyrgo,

Schlumbergerina and Triloculina The other fossil components of this microfacies are mainly Dendritina,

Ammonia, Discorbis and fragments of echinoderms. This microfacies has been observed as grey limestones in

the lower part of the Khamir section. The fossil diversity, biological perturbations and abundant micritic matrix

indicate of low energy and a shelf lagoon deposition environment.



MF12. Dolomudstone(Fig. 4.c):

The abundanc of micrite matrix, lack of fossils, presence of evaporate deposits and fenestral porosity

indicates the facies the formed in the tidalflat environment [13]. This microfacies has only been observed at the

base Mishan Formation in the Khamir section in from of limestones and dolomitic limestones.

Fig. 4: (a) MF10. Mudstone, (b) MF11. Miliolid packestone, (c) MF12. Dolomudstone

Sedimentary Model:

On the basis of the distribution of the foraminifera and vertical facies relationships, three major depositional

environments have been identified in the Early to Middle Miocene succession of the Khamir section. These

include inner, shelf and outer shelf environments. There are three environments in the Khamir section in

carbonate facies which are represented by 11 microfacies (Mf 2 to Mf12) (Fig.5). Serious facies changes are

specially observed at the base of Khamir section. This can be related to the salt dome activites that has been very

influential in Miocene marine basin of southern Iran.

Two major depositional environments have been identified in the Khorgu section, too. These include

middle and outer shelf which are represented by 6 microfacies (Mf 6 to Mf12) (Fig.6). There are gradual

transitions in the lithofacies and biofacies of this section.

Inner shelf deposits represent a wider spectrum of marginal marine deposits Faunal diversity is low and

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

perforate rotaliids which indicate quite sheltered conditions [11]. The middle shelf environment is characterized

by abundant hyaline, lamellar, perforate larger foraminifera and smaller perforate taxa (rotaliids). Larger

perforate forms are represented by Amphistegina, Operculina, Asterigerina, Miogypsina and Miogypsinoides.

The most common smaller foraminiferal fauna are constituted by Neorotalia and Ammonia. The outer shelf

environment is characterized by hematitized, well-bedded and laterally continuous deposits those are marked by

abundante planktonic foraminiferal contents [9].



Fig. 5: Vertical facies distribution of Khorgu section



Fig. 6: Vertical facies distribution of Khamir section

Conclusions:

There are two different facies types in the Mishan Formations clastic and carbonate facies. Based on

biogenic and abiogenic components and texture, there are 12 microfacies in the carbonate facies, those are

grouped into three depositional environments corresponding to the inner, middle and outer shelf. It can be

interpreted as a carbonate platform that is developed in an open shelf situation. In the inner shelf, the most

abundant lithofacies are the wackestone-packstone with rotaliids foraminifera and bryozoan. The middle shelf is

represented by wackstone-packestone with larger foraminifera with perforate wall. The outer ramp is dominated



by wackestone characterized by planktonic foraminifera and rotaliids. The depth changes in the Khorgu section

are gradual and the extreme fluctuations in the Khamir section are probably related to the syn-depositional

activities of the salt domes.

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