Facies of Asmari Formation in the studied sections:
1. Tidal zone facies:
Mf1: Evaporites (Figure 4)
Mf2: Cryptalgal/Bioturbated/Dolomitized/Fenestrate or Pure Limemudstone (Figure 4)
2. restricted Lagoon Facies
Mf3: Bioclastic, Miliolidae, Moluska Wackstone-Packstone (Figure 5)
Mf4: Bioturbated, Pelloidal, Mudstone -Wackestone (Figure 5)
Mf5: Bioclastic, Ostracod, Rotalia Wackstone-Packstone (Figure 5)
3. Carbonate shoal facies:
Mf6 : Bioclastic Benthic Foraminifera, Peyssoneliacean Algae Rudstone- Grainstone (Figure 6 )
Mf7 : Bioclastic, ooid Grainstone-Packstone (Figure 6)
Mf8 : Echinoid Oyster, Benthic Foraminifera, Red Algae Packstone-Grainstone (Figure 6)
4. Open marine ( below normal wave base):
Mf10: Bioclastic, Benthic Foraminifera, Coraline Red Algae Rudeston -Packstone (Figure 7)
Mf11: Bioclastic, Echinoid, Porcelaneous Benthic Foraminifera, Peyssoneliacean Algae Boundstone (Figure 7)
Mf12: Peyssoneliacean Algae Boundstone (Figure 7)
Mf13: Bioclastic, Echinoid, Wackestone (Figure 7)
Mf14: Bioclastic, Echinoid, Bryozoer, larger Benthic Foraminifera Wackstone (Figure 7)
5. Open marine (below storm wave base):
Mf15 : Hemipelagic, Bioclastic Packstone-Grainstone or Tempestite (Figure 8)
Mf16 : Bioclastic, Planktonic Foraminifera Wackstone-Packston (Figure 8)
Mf17 : Bioclastic,Planktonic Foraminifera, Arenaceous Wackstone (Figure 8)
Sedimentary environment of Asmari Formation in the studied section:
The absence of significant reef facies and the absence of shallow bioclasts in deep areas, which is common in edged shelves, indicate the deposition of carbonate sequences of the Asmari Formation in a carbonate ramp (Tucker and Wright 1990; Flugel 2004). On the other hand, the presence of thick and energetic facies of Ooid grainstones (Mf7), which is an indicator of the ramp environment, is evidence of the deposition of this Formation in a carbonate ramp environment. The absence of Slumps, Breccia and turbidites in the facies of the deep sections of these sequences, which represent distally steepened ramp (Flügel 2013), indicates that the type of ramp in this basin was a homoclinal ramp. The distribution of facies across the ramp and their changes over time show the necessity of the describing of the Asmari ramp model by dynamic models (Flügel 2013). Based on studies and especially stratigraphic analyses of sequences, major changes are seen in the distribution of Asmari Formation facies over time. The facies of Asmari Formation sequences have significant differences from each other.
The facies model of the first sequence of this Formation is highly similar toconventional Tertiary models (Buxton and Pedley 1989; Pedley 1998; Pomar 2001) and equivalents of the Asmari basin. Also, the distribution model of facies and their nature is very similar to other sections of this formation in Khuzestan and Fars basins (Seyrafian and Hamedani 1998, 2003; Seyrafian and Mojikhalifeh 2005; Seyrafian 2000, Vaziri-Moghaddam et al., 2006; Amirshahkarami et al., 2007a, b; Mosadegh et al., 2009). However, the sequence characteristics of the upper part of the Asmari Formation are fundamentally different from the mentioned models. This is the unique presence of a group of red algae with an Aragonite wall called Peyssoneliacean algae in this part of the Asmari Formation. This algal facies has never been reported in world geological records to this extent.
In this section, the most important Asmari facies, which are the main and most extensive facies, is the facies that is formed of this allochem. Also, one of the distinguishing features of Asmari Formation sequences in the studied field is the presence of extensive evaporative facies in it. Based on sedimentological and stratigraphic studies of sequences, these facies have been deposited in periods of low sea level and in the sedimentary basin, which indicates the restriction of the Asmari basin in the region in terms of hydrography, and as a result of its isolation, it becomes a shallow evaporative basin during periods of sea level decline (Emery and Myers, 1996; Warren 2006). These basins have a limited connection with water and open seas, and in periods of low sea level, their connection with open water is cut off, and the whole basin becomes an evaporative basin due to increased evaporation. Therefore, the sedimentation environment of the Asmari Formation in the mentioned region is a privileged case in the world. To simplify the sedimentary model of the Asmari Formation, its facies changes are described in the form of a conceptual model that expresses the sequences of the Formation.
Based on what was stated in the description and interpretation of the facies of Asmari Formation, the facies model of the sequences of this Formation along with the part of Pabdeh Formation which samples have been studied is shown in Figure 8. In this model, carbonate ramps can be divided into three sub-sections: outer ramp, middle ramp and inner ramp, based on energy levels. A facies zone expressing restricted carbonate Ooid shoals divided the shallow part of the ramp into two parts and the open sea (facies Mf7). This carbonate shoal is mainly made of thin-cortex Ooids such as non-pore foraminifera. The carbonate Ooid shoal facies are formed in the inner ramp's energetic parts and around the area where normal sea waves hit the seabed.. This zone is located under the lagoon environment in the section facing the beach.. Various facies have been deposited in different parts, all of which have the common feature of their low energy (facies Mf3, Mf4, Mf5). This feature is well observed in these facies' textural and compositional characteristics. These features include mud-dominated texture, Micriticization, Bioturbation, Miliolidae, etc. The last zone of the inner ramp section is the tidal zone (Mf2 facies). The predominant mud-dominated facies of this zone are characterized by features such as lamination structures, algal and microbial textures, stromatolite, evaporative crystals, and fenestral fabric.
The lagoon in this model seems to have been connected to the high seas by canals or periodic storms. The presence of Ooids in some facies near shoal (Mf3 facies) and the presence of bioclasts such as Bryozoans and Echinoderms that require free water circulation for life confirm this hypothesis. One of the most important facies of this model is located in the middle ramp, which contains red algae (Mf10 facies). This facies has become more Rhodolite towards the open sea and in the end parts, it interferes with the facies of large foraminifera. On the other hand, as Pedly (1998) has stated, these facies can extend to the zone of Ooid. Therefore, this is the broadest middle ramp facies. In general, it can be stated that in the upper parts of this facies zone, the main allochems that form the facies together with red algae are Benthic Foraminifera with Porcelaneous wall, the maximum frequency and variety of which is in the Euphotic Zone. Down the ramp and in the Photic Zone of the Euphotic zone or Mesophotic zone to the vicinity of the Oligophotic zone, these allochems give way to other allochems such as Echinoderms and Bryozoans.
In the upper parts of these facies and near the carbonate Ooid shoals, and in the most energetic part of the ramp environment, there is a Ptach Reef, which is located in the heart of the algal zone (Mf9 facies). This zone is in this ramp, and also, as Baxtun and Pedly (1989) and Pedly (Pedly, 1998) stated, it separates the middle ramp from the inner ramp. In other words, Ptach Reefs in the area where normal sea waves hit the bed floor have their maximum expansion. Thus, the broad zone of red coral algae expands so that its main part is in the middle ramp, but probably a small part of it has also spread in the inner ramp. The large floor Foraminifera zone is the deepest middle ramp facies formed in the Photic Zone and is one of the prominent zones of the Cenozoic ramps, and this zone overlaps with the upper-end parts of the algal facies (Mf14 facies).
The outer ramp has been identified by the presence of planktonic organisms as well as storm facies in this part of the Formation (facies Mf15, Mf16). These pelagic facies to deeper they are argillaceous and sandy and are considered deep basin facies in the study (Mf17 facies). Based on studies conducted in the Lorestan region, the ramp that belonged to the Asmari Formation in the upper part of the sequence of Asmari Formation to Miocene age was shallower than its initial part Oligocene age and early Miocene. Due to the lack of detection of storm waves effect area and conventional sediments in it, such as pelagic and storm facies, and detection of only the regular sea waves area, the upper part of the Asmari Formation sequence consists of two parts inner ramp and outer ramp and facies no carbonate shoal was identified.
The inner ramp is located above the base of the normal sea wave effect, and the middle and outer ramp are located above this part, as shown in Figure 9. In the model proposed for the Asmari Formation in Figure 9, The carbonate shoal facies separates the ramp into two parts, the restricted and the open marine. The carbonate shoal zone in the lower part of the Asmari Formation is of the Ooid carbonate shoal type and in the upper part of the carbonate sequence of the Asmari Formation is the bioclastic shoal type which the main allochem is the Aragonite Peyssoneliacean algae (Mf6 facies).
An important and unique event in this period of Asmari Formation deposition history is replacing of the red coral algae zone with the Peyssoneliacean red algae in the middle ramp. The algae sometimes form shells in the lagoon, but it is a sub-allochem and has managed to form a coverstone. The scattering of different facies along the carbonate sequence of the Asmari Formation from the tidal zone environment to the open marine environment in the studied section, along with the changes in the sedimentary environment, is shown in Figure 10.