Lithostratigraphy and Microfacies Analysis of Upper Triassic Deposits in the Southern parts of Lut Block, Central Iran Microcontinent

doi:10.21203/rs.3.rs-5297272/v1

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Lithostratigraphy and Microfacies Analysis of Upper Triassic Deposits in the Southern parts of Lut Block, Central Iran Microcontinent

https://doi.org/10.21203/rs.3.rs-5297272/v1

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In order to conformity of the sedimentary environment and biological faunal assemblage of Late Triassic deposits in the Central Iran subcontinent, stratigraphical section in the Lut block was selected. Shahdad section in the mentioned block with a thickness of 340 meters is mostly composed of shale, sandstone and limestone. According to the identified index microfossils, 10 interval biozones (Triasina hantkeni, Trochammina almtalensis, Ophtalmidium exiguum, Agathammina oustroalpina, Duostomina alta, Planiinvoluta regularis, Ammodiscus parapriscus, Pilamminella falsofriedli, Glomospirella minima, Tetrataxis inflata, Interval Zone) were recognized in the Upper Triassic deposits. Based on the identified biozones, the geological age of the studied sequences, considered as Late Norian- Earlist Lias which is equivalent to the Howz-e- Khan and Qhadir members of the Nayband Formation in central Iran. Distribution of scattered coral reefs and absence of turbidite sediments indicate a relatively gentle and uniform homoclinal shallow carbonate platform. Also diversity of foraminifera in this basin show the normal conditions of the initial environment in terms of water circulation, salinity and oxygen levels. In general, the facies of the sedimentary basin of the Upper Triassic deposits in the region are formed from the lagoon or near the coast to the shallow area of the coastline with high to medium energy and to the open sea area in the range of marginal reefs.

subcontinental Blocks of Central Iran

Nayband Formation

Central Iran

Lut block

sedimentary environment

microfacies

Late Triassic deposits

Kerman

Iran

Central Iranian Microcontinent (CEIM) (Takin, 1972) includes Lut, Tabas and Yazd blocks (Davodzadeh and Schmidt, 1982). The platform of Iran, which covers the entire area of middle, northern and southern Iran, according to the geological evidence, it was a part of the Cimmerian continent (Sengur, 1990) and middle and northern Iran were separated from the northern edge of the Gondwana supercontinent and pushed northward during the Permian and Triassic periods due to the action of rifting, simultaneously with the subsidence and gradual closing of the Paleotethys oceanic basin and the collision of the Iranian plate with the southern edge of the Eurasian supercontinent or the Turan Plate at the beginning of the Late Triassic (Shtoklin, 1974), the orogeny event of the early Simmerian and the formation of the Simmerid Mountains were established (Fig. 1).

At the front of the rising mountains of Simmerid and along with the simultaneous dynamic tectonics of sedimentation, a thick series of siliceous-clastic rocks related to alluvial plains, marshes, coastal and sea environments has been deposited, which is called Shemshak Group (Aghanbati, 1998; Seyid Emami. et al., 2001). The Shemshak Group is actually a large structural-sedimentary cycle that is limited by the Early Cimmerian (Norian) and Middle Cimmerian (Middle Bajocian) events. The homogeneity and adaptation of rock strata facies of Shemshak group (Norian to Lower Bajocian) in central and northern Iran shows that the Iranian plate has acted as a continuous and integrated area during this cycle.

The Upper Triassic deposits of the Nayband Formation are distributed over a large area from different provinces such as Yazd, Khorasan, Isfahan, Arak and Kerman (Fig. 1), (Seyed-Emami, 2003; Aghanabati, 2004).

In fact, the breaking of the Iranian plate into several structural and sedimentary units such as Lut, Tabas, Posht Badam, Yazd blocks, has been done in relation to the Middle Cimmerian event at the end of the early Bajocian (Seied Emami and Alavi Naini, 1990). Among the three Simrid events, it has had the greatest impact on the tectonics of central and northern Iran. As a result, after the middle Cimmerian event in the early Bajocian, which caused the Iranian plate to break into several structural pieces or blocks, tectonic unrest has intensified in it. Therefore, during the following periods, in the Middle and Late Jurassic, numerous tectonic movements, in the form of block movements along with frequent global fluctuations of sea water, played a decisive role in the sedimentation pattern of the region and it has created various stratigraphic facies, whose time regulation and Correspondence of stratigraphy with each other in the past has led to many inadequacies and ambiguities in the geological in perception and interpretation of the region (Shtoklin et al., 1965).

After this event in the Late Bajocian, another structural-sedimentary cycle (Mago Group) begins, which ends with the Late Cimmerian event at the end of the Jurassic and the beginning of the Early Cretaceous. During this cycle, especially in the microcontinent of Central Iran, due to a combination of tractional, traversal and rotational movements and general block movements in connection with numerous tectonic movements (Seyed Emami et al., 2004), various series of different lithostratigraphy facies related to continental, evaporite, marsh, coastal, shallow to deep marine sedimentation environments have been formed. Determining the correlation of stratigraphy and their compatibility with each other requires very detailed geological and paleontology studies.

The studied area is a small part of Central Iran subcontinent, which is itself a part of Middle Iran in Alpin - Himalayan Orogenic Belt and is limited from the north and northwest by Daroneh fault (Great Desert fault), from the east by Nehbandan fault and from the southwest by Nain-Dehshir- Baft fault. The structural pattern of this subcontinent is of the type of blocks separated by major faults, each of them has a separate features and the dynamics of the subcontinent is not the same.

Extensive structural-sedimentary disparities have caused the Central Iran subcontinent was divided into Lut block, Tabas block, Kalmard block, Posht Bareef block and Yazd block (Aghanbati, 2004) (Figs. 5–8). The Shahdad region is located in the east of the Kerman highlands, in the Lut desert, that the Nayband fault separates the two from each other. The mountain range of the region is mostly northwest-southeast.

The outcraps of the region are mostly Mesozoic units in the highlands and Cenozoic, Pliocene and Quaternary in the desert. The studied section was located in the range of 1: 250,000, 1: 100,000 geological maps of Kerman and 1:25000 Shahdad approximately 80 km south of Shahdad city, with the coordinates N: 57 ̊ 39 ̍ 10 ̎ and E: 30 ̊ 03 ̍ 14 ̎ .

To establish the age and depositional environment studies of the Nayband Formation, the Shahdad stratigraphic section was measured and sampled systematically, emphasizing lithology and facies changes and the characterization of sedimentary structures. 48 rocky samples were collected from the studied section. Thin sections were prepared, and detailed studies were based on thin sections.

Lithostratigraphy

Field studies on the Upper Triassic deposits in the studied area indicate that the most of the studied area have an NW-SE trending fold and fracture. Lithological studies of the deposits of this section were based on field studies and of microscopic studies of rocks and their microfacies results.

The lithostratigraphic characteristics of the studied section with 340 m thickness mainly composed of medium to thin layer olive green silty shales with gray sandstones interlayers and abundant corals, sponges, bivalves and foraminiferal microfossils in the age range of Upper Triassic to Lower Jurassic (Fig. 2–7). The upper surface of the section is also covered by layereds lower Jurassic/Lias or sandstone and shales of Ab Haji Formation with quartzitic sandstone base.

The outcrop of the Nayband Formation in this section with a thickness of about 340 m, is mainly composed of progressive carbonate rocks among shales and shallow regressive sandstones dominated by deltaic-river environment. This outcrop is observed and repeated in frequent synclines and anticlines with northwest-southeast direction, which in the center and its folds axis due to continued pressure, fracture and finally parallel faults in the same northwest-southeast direction has been created. In this section, which starts almost from the center of the first anticline, there is a cream to brown medium layer limestone and dark gray dolomite belonging to the Jamal Formation (Permian), covered by red color gypsum sandstone and dolomitic sandstone and limestone interbedded of Sorkh shale Formation (lower Triassic).

The mentioned sequence covered by dolomite and layer thick dolomitic limestone with a karst structure belonging to the Shotori Formation (Middle Triassic). Also there is an erosional discontinuity in uppermost contact of Shotori Formation with Nayband Formation (Howze Khan to Qadir members / Upper Late Triassic). In the center of the first syncline, the red color quartz arnite sandstones of Ab-e-Haji Formation (lower Jurassic) covered Triassic deposits which description of them are as follow Fig. 2–7 :

The lithofacies and paleo-environments were identified based on occurrence of skeletal and non-skeletal grains, size, roundness, sorting, orientation of the grains, and type of matrix. Lithofacies were determined based on Dunham (1962). The skeletal grains are comprised of benthic foraminifers, echinoderms, bivalves, microgastropods, and coral remains, and the green algae are recognizable as organic constituents. Specifically, the non-skeletal grains are composed of intraclasts and extraclasts. The stratigraphic distribution of both skeletal and non-skeletal grains (bioclast, intraclast, and extraclast) is presented in Fig. 3. The presence of Dasycladacean algae at the studied area indicates an intertidal environment (Khosrow Tehrani, 2011).

The presence of corals and echinoids and microgastropods at the studied section indicates the lagoon sedimentary environment or the reef depositional system in the uppermost open marine section (Khosrow Tehrani, 2011). Microscopic investigation of the Nayband Formation supported the presence of six major lithofacies, namely: (Fig. 8,9,10)

7.1. From facies belt of the inner ramp (lagoon or behind the reef)

Lithofacies A. Bioclastic Oncoidal / Packstone / Grainstone

The main components of this microscopic facies comprise grains covered with algae or medium to coarse oncoids (about 30–40%) with intraclast cores (30%) with bioclasts or skeletal grains (20%) along with sparite cement (microfacies A). Skeletal grains include fragments of sponges, shells, bivalves, mollusks, crinoids, echinoids, microgastropods, dasycladaceae algae, and benthic foraminifera. Destructive quartz grains (less than approximately

10% in small size, as silt) are sub-elements of this microscopic facies. This microfacies is exposed with a thickness of 1.5 to 2 meters in rock units No. 3 and 12 of Shahdad (sh3, 12).

Considering that the background and matrix of this facies are from sparite to microsparite type and indicate a more energetic to medium energy environment, the presence of lagoon bioclasts such as foraminifera and algae and the low amount of marine bioclasts that found behind the reef confirm that their formation in the lagoon was behind or at the edge of the reef; in other words, the sediments of this sub-environment were deposited in the part of the lagoon edge and near the reef with high energy and in semi-restricted to normal, very shallow marine conditions, such that the sediments in addition to the lagoon environment from the belt A coast have also been provided. As a result, this part of the carbonate platform is a type of carbonate ramp with low subsidence along with small amounts of destructive materials and coastal debris, which has caused the formation and deposition of carbonate sediments in a grainstone to packstone facies, which is comparable with RMF 21 Flugel (2010). It belongs to the inner ramp environment because of the presence of oncoids.

7.2. Inner ramp facies belt (biostructural carbonate reef or bioclast ridge)

Lithofacies B. Sandy Bioclastic Boundstone / Grainstone

The main components of this microscopic facies are 40% bioclasts or different skeletal grains along with microsparitic to asparaitic cement. Among the sub-elements of this microscopic facies, we can mention the destructive quartz grains up to about 25% (microfacies B). Skeletal grains include sponges, worm trace, algae and many crinoids, bryozoa, bivalves, mollusks, microgastropods and corals and with about 5% benthic foraminifera which are found in the Sh8 with a thickness of up to 2 meters and exposed in the rock unit No. 11 of Shahdad.

Because quartz degradation grains and skeletal grains with medium to fairly good sorting and roundness are seen in a grainstone texture with a sparite background without the presence of a micrite matrix (representing a high-energy environment). Moreover, because of the shallow depth, warm to moderate climate, normal water turbulence and salinity, this part of the carbonate platform, which is a type of carbonate ramp with low subsidence along with slight entry of destructive and debris materials, causes the formation and deposition of carbonate sediments in the grainstone facies, along with open sea and lagoon bioclasts, indicates deposition in the high-energy conditions of tidal channels on the edge of the reef. Greenstone in this facies mainly lacks porosity, because all spaces between the particles, inside the particles, and mold porosity are filled by different generations of spar calcite cements. Its formation environment can be compared to 12–14 RMF Flugel (2010) and belongs to the reef environment to shallow reef range.

Lithofacies C. Sandy Bioclastic Grainstone

The main components of this microscopic facies are approximately 20–30% bioclasts or skeletal grains. Destructive quartz grains are the only minor element of this microfacies (microfacies C) at up to about 40%.

Skeletal grains include fragments of bivalves, mollusks, corals, crinoids, echinoids, dacycladaceae algae, shell fragments, and about 5% benthic foraminifera, which are outcropped in samples No. 21 and 22 of Shahdad with thicknesses of up to 2 meters in the rock unit of Shahdad 11.

The absence of a micrite matrix along with open sea and lagoon bioclasts and the abundance of coral, sponge, and microgastropod bioclasts in this microfacies indicate energetic environmental conditions, especially sedimentation in biostructural reef environments formed in bioclast stacks (bio-constructed) and comparable to 14 RMF Flugel (2010), and belong to the open marine environment of the inner ramp. Furthermore, its environment can be considered because of the presence of lithoclasts, energetic tidal channels in front of the reef. The reef was considered towards the open sea, which is exposed in sh21 with a thickness of up to 4 meters in rock unit number 24 of Shahdad. Nevertheless, it seems that the existence of a coral reef bandstone belt or bio constructed patches of sample no. sh 6 with greenstone facies (12 RMF), which is a low expansion and without coral dominant facies, actually existed at the edge of the platform and the environment of the lagoon to some extent. It is separated from the sedimentary environment of the open sea, and as a result, because of its low thickness as well as the density in some places, it is in the form of scattered single coral accumulations or separate and isolated communities (come reefs/ or bio-constructed patches). It can partially represent a reef environment in the shallow open sea, which includes the open marine to the shallower mid-ramp environments.

Therefore, in general, the absence of a significant presence of framework-forming organisms in the euphotic zone (reef-building corals) and the lack of effect of reefs and the type of carbonate sediments produced, as well as the paleoecology of foraminifera in the study area, the sedimentation environment of these deposits, and the presence of four sedimentary environments (i.e. open sea, reef, behind the reef or lagoon, and coastal or tidal), indicate it is a carbonate platform ramp or carbonate ramp.

7.3. The facies belt of the internal ramp (in front of the reef to the open sea)

Lithofacies D. Sandy Bioclastic Packstone

The main components of this facies are often skeletal grains or bioclasts (between 20% and 40% in decreases, and according to the percent abundance of

allocems, towards the open sea, they are separated into three groups: ooid packstone bioclasts, wackestone bioclasts, and fossilized mudstone.

Lithofacies E. Sandy oolitic Biointraclastic Packstone

The main components of this facies are skeletal different samples along with a micrite to microsparite background. Skeletal grains mostly consist of fragments of sponges, shells, bivalves, mollusks, crinoids, echinoids, microgastropods, dasycladaceae algae, and sometimes some bryozoa, sponge nodules and perfect corals individually with a smaller smaller percentage of benthic foraminifera.

Destructive quartz grains (about 10–40% in different samples) form the sub-elements of this microscopic facies (microfacies D) which is outcropped with a thickness of up to 2 meters in sample number 1 of Shahdad / sh 1 in rock unit 11 of Shahdad. This microfacies is comparable to 14 RMF Flugel (2010) and belongs to the open marine environment of the inner ramp. Because of the low roundness, its formation environment is a little far from the bio-structural reef, and the presence of microsparite to micrite matrix indicates medium to low wave energy.

Sandy Lithobioclastic Packstone

The background in this microfacies consists of micrite to microsparite. Allochems account for 60% of this microfacies, which includes 25% bioclasts, mostly rounded and transported fragments of bivalves, mollusks, bryozoa, crinoids, dacycladaceae algae, sponge nodules, and up to 5% benthic foraminifera. Also seen in this microfacies are 20% of medium-sized angular to slightly rounded quartz and 10% of intraclasts, including micrite rock pieces.

The environment of the formation of this microscopic facies with the presence of a micrite background indicates a low to medium energy environment with the dominant presence of open sea bioclasts such as corals, sponges, bivalves, brachiopods, and gastropods. The lack of lagoon bioclasts (benthic foraminifera and algae) with the presence of lithoclasts and the entry of destructive materials and debris from the coastal belt to the basin represents the inner part of the carbonate ramp, especially the open sea, which is comparable to RMF 14 Flugel (2010) and belongs to the open marine environment of the inner ramp.

In fact, the sediments of such facies are mainly in the carbonate ramp platform as the most extreme facies belt, which generally originated from the shallower or lagoonal part and were transported to this environment (open sea) by waves, currents, and storms. By moving away from the coastline, the percent abundance of the constituent components

grains (between 10% and 30% in different samples) along with micrite to microsparite cement. Skeletal grains are different and mostly comprise pieces of coral, sponge, shells, bivalve, mollusk, crinoid, echinoid, microgastropod, dasycladaceae algae, and sometimes a little bryozoa, brachiopod, and sponge and perfect corals individually with a smaller percentage of benthic foraminifera.

Among the sub-elements of this microscopic facies, we can also mentionthe destructive quartz grains (about 10–30% in different samples; lithoclasts [10–30% percentage of igneous rock fragments, micrite, etc.] in the form of extraclasts) sometimes together with a small percentage (less than 5%) of the ooids, indicating that the ooids are single-layered (surficial), and the central core in most of them is an intraclast (microfacies E) which is outcropped with a thickness of up to 2 meters in samples No. 22 and 21 of Shahdad / sh 21, 22 stone unit 11 of Shahdad.

The existence of a few single-layered and thin radial ooids in this facies indicates the location of its depositional environment in the vicinity of the reef, which is usually associated with lithoclasts of different types and amounts. The study of this carbonate facies, which has a micrite to slightly microsparic background, shows that these deposits were left in a quiet environment with low to medium energy. The fauna in the sediments of this section, which consists of groups of corals, sponges, and brachiopods, algae, gastropods and benthic foraminifers, are indicative of shallow marine environments and light-influenced areas, and their distribution depends on changes in water salinity and type of substrate.

The formation environment of this microscopic facies has been determined to be in front of the reef or near the reef towards the open sea, which is comparable to RMF 14 Flugel (2010) and belongs to the open marine environment of the inner ramp.

7.4. Middle ramp facies belt

Lithofacies F. Silty Bioclastic Wackestone / Mudstone

The main components of this microscopic facies are skeletal grains (between 5% and 20% in different samples) along with micrite background. One of the characteristics of this facies is the presence of a mixture of open sea benthic and pelagic fossils, which in the studied samples of benthic fossils included fragments of sponges, echinoids,

dacycladaceae algae (especially Diplopora), and some crushed benthic foraminifera along with the predominant presence of pelagic bivalves. The destructive quartz grains are also seen in small amounts (5–10%) and scattered in the micrite field (microfacies F) which is exposed in most Shahdad samples numbers 13–16, 23–25 with different thicknesses.

The sedimentary environment of this facies is based on the micrite context and the presence of pelagic bivalves and the low abundance and small size of its allocems with grains less than 1 mm in diameter, in the deeper area of the open sea and in accordance with the standard facies RMF 5 Flogel, 2010, and it belongs to the shallower environments above the mid-ramp, after which the facies of the deeper part can be seen as dark shale, which sometimes becomes shallower due to the influence of river or deltaic surface currents, alternating with more Grivaki sandstone. Sometimes it is deepened with a thin layer of limestone, and sometimes it is marly. Therefore, when the conditions for calcium carbonate sedimentation are dominant, the sediments are fine-grained limestone (micrite), and in the absence of the mentioned conditions, sedimentation of the type. The fine-grained sediments were from Chale.

One of the most important components of this facies is the abundance of carbonate mud along with small bioclasts such as benthic foraminifera and pelagic bivalves, which indicates sedimentation in a low-energy environment as well as the lack of biological disturbances, which indicates a lack of oxygen production.

According to the theory of Boudagher-Fadel (2008) in the Tethys region, during the Carnian Episode, the weather was abnormally hot and dry, and as a result, sea water salinity increased, causing the disintegration and failure of the reef systems. At the end of the Carnian-Norian interval, most of the reefs became extinct, which was reflected by the disappearance of many species of foraminifera in the west of Tethys.

After that, the early Norian reef systems were replaced by the expansion of larger reef systems in the late Triassic period, which coincided with the global increase in sea level. At this time, new groups of Involutinoidea foraminifers were expanded. Late Triassic benthic foraminiferal assemblages include Ammodiscoidea, Involutinoidea, Duostominoidea and Nodosarioidea, which were found in shallow marine facies and were often limited and ecologically very unstable. In general, they are examples of low-energy or lagoon-like bays that exist in carbonate ramps in shallow areas where water salinity is sometimes higher than normal.

Based on the information obtained from the investigation of rock facies and their formation environments and considering the lack of widespread and massive growth of reefs, the absence of dominant coral facies and expansion as marginal reefs or scattered coral reef, the low slope of the basin, and the absence of turbidite sediments or a deposit, a shallow ramp-type carbonate platform can be suggested for these deposits. Based on the classification of ramps by Read (Read, 1985), this ramp is relatively gentle and uniform based on facies and sub-environments determined from the homoclinal carbonate ramp type, which stretches from the coastline to the basin. In addition, the diversity of foraminifera shows that the initial environment was in normal conditions in terms of water circulation, salinity, and oxygen levels (with the increase of sea water level due to subsidence of the basin floor).

Therefore, according to the quantity and type of skeletal and non-skeletal components of the facies, the formation conditions of each of the facies, the energy of the environment, and the abundance of forming allocems in different parts of the sequence, it is possible to separate four sub-environments on this carbonate environment.

These environments are, in order from deep to shallow areas

open marine environments to shallow sea in front of the marginal reefs or scattered coral reef, marginal reefs or bio-structural bioclast ridges, lagoon or behind the marginal reefs, and coastal.

8.1. The facies of the deeper areas of the open marine (facies F): were deposited in low-energy environments, which is characterized by the presence of micrite. The presence of skeletal grains in small amounts, including the simultaneous presence of fossil fragments from the open marine, such as sponges, crinoids, echinoids, dacycladaceae algae, and some crushed benthic foraminifera, together with pelagic fossils such as pelagic bivalves, indicate the conditions of sedimentation in the deep parts of the open marine.

8.2. Shallow facies of the open marine up to the front of the marginal reefs or scattered coral reef: were deposited in environments with high to medium energy. The type of texture and the size of the skeletal grains indicate that these (facies E, B) were deposited in the shallower parts of the open marine up to the front of the marginal reefs. The fossils in this microfacies, with the predominant presence of open marine bioclasts such as sponges, shells, bivalves, corals, brachiopods, bryozoa, mollusks, crinoids, and echinoids, and the lack of lagoon bioclasts such as Dasycladaceae algae and a little benthic foraminifera, represent the sea conditions as open marine and

shallow. The presence of a little ooid in this facies indicates that it is in the environment in front of the marginal reefs, which is associated with various bioclasts. This facies with a sparitic to microsparic and micritic indicates deposition in a high-energy environment from the front of the marginal reefs to the middle of the open marine and under the influence of light, which forms a shallow sea.

8.3. Environment front of the marginal reefs to the marginal reefs or scattered coral reef: The amount of lime mud is reduced and spar calcite cement is increased. The presence of a marginal reefs belt of coral bondstone with a low and scattered spread (scattered coral reef), with grainstone facies and high energy, which was located at the edge of the platform, separates to some extent the wetland or lagoon environment from the sedimentary environment of the open marine. As a result, with paying attention to its low thickness can indicate the environment of the border of a marginal reefs or scattered coral reef. This category of corals comprises those that are scattered on the shallow sea floor and do not form a reef but exist individually or in separate communities (facies C).

8.4. Environment lagoon or wetland of behind the marginal reefs until the tide region: The presence of scattered coral accumulations, green algae, and dacycladaceae as well as fossil fragments that had com from the open marine sedimentary environment, such as bryozoa and echinoderms, indicate good water circulation and salinity close to normal in the lagoon; therefore, in this region, only limited fauna that are compatible with these conditions have become abundant. This environment is characterized by facies A and mainly includes benthic foraminifers characteristic of the lagoon. The bioclastic and non-skeletal assemblage (oncoid and ploid) found in the studied area corresponds with the photozoan assemblage (James, 1997). The biological components of this collection depend on light and indicate warm and shallow sea environments. The collection of photozoans is mainly limited to the latitudes of 30 degrees north and south and seems to be the main controlling factor.

8.5. Environment tidal to coastal: It is characterized by sandstone facies that were obtained in areas near the coast or under the influence of storm currents that are common in carbonate ramps. Thus, due to the abundance of sand grains, the textural maturity of these sandstones. As a result, their energy level is high. Quartz sandstone or arenite quartz found in this area contains more than 95% quartz grains. This abundance of quartz grains in this category of sandstones can be explained by the erosion and removal of other grains such as feldspars due to weathering, erosion, and washing.

Therefore, in general, the sedimentary facies of the Upper Triassic deposits of the region are equivalent to zone Y (the area near the coast with high to medium energy) to zone Z (the shallow area of the coastline) (Irwin model, 1965), and facies belt No. 5 (fz 5) (facies of marginal reefs) (Wilson, 1975).

Author Contribution

massih afghah reviewed the manuscript

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No competing interests reported.

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Lithostratigraphy and Microfacies Analysis of Upper Triassic Deposits in the Southern parts of Lut Block, Central Iran Microcontinent

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Abstract

Figures

1. Introduction

2. Geological settings

3. Material and Methods

4. Discussion

5. Stratigraphic units of Shahdad section

7. Facies Analysis

7.1. From facies belt of the inner ramp (lagoon or behind the reef)

7.2. Inner ramp facies belt (biostructural carbonate reef or bioclast ridge)

7.4. Middle ramp facies belt

8. Conclusion and Interpreation of the sedimentary environment

Declarations

Author Contribution

References

Additional Declarations

Status:

Version 1