جستجوی مقالات مرتبط با کلیدواژه « آلبین » در نشریات گروه « زمین شناسی »

Pteriomorpha, Heterodonta, Paleoheterodonta and Anomalodesmata bivalves from the Kazhdumi Formation of the Geno and Gerash sections in the southeast of  Zagros Mountains are studied here. In order to this research, bivalve speies are identified and described as follow: Arctica angulata, Birostrina concentrica, Ceratostreon flabellatum, Crassatella manzourensis, Flaventia belviderensis, Granocardium productum, Gyrostrea delettrei, Illymatogyra africana, Mytiloides concentricus, Neithea dutrugei, Neithea sp. 1, Neithea sp. 2, Paraesa faba, Pinna cfcretacea, Pholadomya fabrina, Pholadomya vignesi, Protocardia hillana, Pterotrigonia scabra, Rhynchostreon suborbiculatum, Tenea delettrei, Venericardia deserti. Many of these species excluding Ceratostreon flabellatum, Illymatogyra africana, Neithea dutrugei and Pterotrigonia scabraare reported for the first time from Iran. Kazhdumi Formation disconformably overlies the top of the Dariyan Formation and underlies the Gurpi Formation.

In this investigation, the foraminifera and oligosteginids of Sarvak Formation (Late Albian-Middle Turonian) at the Khumi Anticline section (East of Izeh Zone) has been studied. It consists of limestone of 213m thick which overlies the Kazhdumi Formation conformably and underlies the Gurpi Formation unconformably at Khumi Anticline. The biostratigraphy of Sarvak Formation in this section indicates 80 genera and 39 species (19 genera and 49 species of plankton foraminifers, 17 genera and 22 species of benthic foraminifers and 8 genera and 4 species of oligosteginids). Based on received paleontological data 8 biozones and 2 subzones in study area were established: Pseudothalmanninella subticinensis Partial range Zone (Late Albian), Pseudothalmanninella ticinensis Interval Zone (Late Albian), Thalmanninella appenninica Interval Zone (Latest Albian), Rotalipora globotruncanoides Interval Zone (Early Cenomanian), Thalmanninella reicheli Total range Zone (Early to Middle Cenomanian), Rotalipora cushmani Total range Zone (Middle to Late Cenomanian), Whiteinella archaeocretacea Partial range Zone (Latest Cenomanian to Early Turonian), Whiteinella archaeocretacea Interval subzone (Latest Cenomanian), Dicarinella hagni Interval subzone (Early Turonian), Helvetoglobotruncana helvetica Interval range Zone (Early Turonian- Middle Turonian). Based on these biozones the age of Sarvak Formation in Marin section is Albian-Middle Turonian.

The Kopet-Dagh Basin is located in the northeast of Iran, extended over Iran, Turkmenistan, and Afghanistan with a west-northwest to east-southeast trend. The Iranian part of the basin is located between 61°14ˊ and 54°00ˊE and 38°16ˊ and 36°00ˊ N. Cretaceous successions are thick and well exposed in the northeast of Iran. The Cretaceous Ammonites are studied by Seyed-Emami (1980), Seyed-Emami & Aryai (1981), Seyed-Emami et al. (1984), Immel et al. (1997), Raisossadat (2004, 2006), Mosavinia et al. (2007, 2014), and Mosavinia & Wilmsen (2011). Calcareous nannoplankton biostratigraphy of Aitamir formation is studied by Susani (2005) and Hadavi & Musazadeh (2005).

The studied section, the Amirabad section, is located at a distance of 65 km to the northeast of Mashhad city, on the Mashhad-Kalat road (coordinates: N36°34ˊ59˝ and E60°09ˊ24˝; altitude: 720 m). Aitamir Formation is measured 668 m in this section and comprised siltstones, fossiliferous (bivalve and ammonite) sandstones, glauconitic sandstones, dark gray to greenish-gray silty shales, and dark gray shales. It conformably overlies the Sanganeh Formation and is overlain by the Abderaz Formation. A total of 139 samples were collected from the section at intervals 3-5 m to study the calcareous nannofossils. In addition, 40 m part of the topmost of the underlying Sanganeh Formation as well as the lowermost of the overlying Abderaz Formation were also measured and sampled. For nannofossil biostratigraphic investigations, all samples were processed using the gravity settling technique (Bown & Young, 1998). The prepared slides were observed under a Nikon Optiphot II Pol light microscope with a magnification ×1000. Bibliographic references for the calcareous nannofossils are given in Perch-Nielsen (1985), Varol (1992), and Burnett (1998). Ammonite samples were collected across the section and named and photographed at the paleontology laboratory of the Payam-e-Noor University of Mashhad. 

Nannofossil bioevents have been utilized to biostratigraphically classify the exposed sedimentary succession based on the CC biozonation scheme of Sissingh (1977, modified by Perch-Nielsen, 1985) and the NC biozonation scheme of Roth (1978, modified by Bralower et al., 1995). The biozones CC8 to CC10 and NC9 to NC13 were determined, and accordingly, the Aitamir Formation is attributed to Albian to late Cenomanian time interval. The lithology of sandstones and siltstones at the lower part of the Aitamir Formation influenced the preservation of nannofossil taxa. In this part, the Ammonite biozones have covered the gap of nannofossil biozones. The upper part of Leymeriella tardefurcata, Hoplites dentatus, Euhoplites loricatus, Euhoplites lautus Mortoniceras (M.) inflatum, Stoliczkaia dispar, Mantelliceras mantelli, Mantelliceras dixoni, Cunningtoniceras inerme and Acanthoceras rhotomagense biozones were determined at the Aitamir Formation except for the upper 20 meters, which contains no ammonite sample. Based on Ammonite biozones, the age of Late Early Albian to Middle Cenomanian is attributed to the Aitamir Formation.

Ammonite biostratigraphy could be used in age determination and correlation of rock units in different sedimentary basins. Qumenjan section with 125 meters thickness is mainly formed by grey sandy limestone with grey and thick-bedded limestone intercalations. The study area is located in the eastern margin of the Lut Block. For a stratigraphical study of Lower–Upper Cretaceous deposits in southwestern of Qayen area, a stratigraphic section was selected and measured. Eight ammonites, including Anisoceras, Calycoceras, Hypoturrilites, Hysteroceras, Mantelliceras, Puzosia, and Scaphites genera and thirteen representative species were identified. Based on the identified assemblage fossils and comparison with international biozones, Hysteroceras orbignyi subzone for Late Albian age, Mantelliceras mantelli biozone for the lower part of Early Cenomanian age, Mantelliceras dixoni biozone for the upper part of Early Cenomanian age, and Turrilites costatus biozone for Middle Cenomanian age is suggested. According to identified genera and species a Late Albian–Middle Cenomanian age is assigned for ammonite bearing of the section. The first occurrence of Mantelliceras mantelli is taken as the base of Cenomanian. Compression of the identified ammonites with other basins shows that the east Iran basin was a part of Tethys Realm during late Albian–middle Cenomanian.

Kazhdumi Formation strata in Anguran section (NW Bandar Abbas) are investigated and eight echinoid species belonging to eight genera have been identified. These species are: Tetragramma malbosii, Orthopsis ruppelli, Phyllobrissus aff. angustatus, Epiaster dartoni, Hemiaster sp., Pliotoxaster comanchei, Iraniaster douvillei, Coenholectypus planatus. Iraniaster douvillei that has already been reported from the Coniacian – Santonian beds of Lorestan Zone (West of Iran); is present in the Albian – Cenomanian strata of Anguran section. So; we can propose the new range of Middle Albian – Santonian for this species. Kazdumi Formation in the studied area has the age of Middle Albian to Early Cenomenian on the basis of foraminifers those accompany with echinoids. This formation conformably overlies the Dariyan Formation and disconfomably underlies the Gurpi Formation.

In this research Cretaceous deposits of Kerch section in the southwestern Qayen that is located in the eastern margin of the Lut Block, were studied from point of systematics and biostratigraphy. This section with 260 meters thickness, mainly formed by gray to cream color marl and shale, marly limestone and limestone that is laid on a light-colored limestone bed at the base. Seventeen genera and twenty two species from benthic and planktonic foraminifera have recognized and four biozones including Microhedbergella rischi Interval Zone, Ticinella praeticinensis Interval Zone, Ticinella raynaudi Interval Zone, Lenticulina subangulata -Lenticulina macrodisca assemblage zone have determined. Based on identified foraminifera an Albian to Early Cenomanian age have been suggested for Kerch section.

The Kopet-Dagh sedimentary basin is located in north-east Iran, southern Turkmenistan and Afghanistan and is composed of Mesozoic and Cenozoic sedimentary successions. Fifteen formations have been introduced in the Kopet-Dagh Basin. The Cretaceous formations include Shurijeh, Zard, Tirgan, Sarcheshmeh, Sanganeh, Aitamir, Abderaz, Abtalkh, Neyzar and Kalat (Afshar-Harb 1994).
Aitamir Formation is one of the main rock units in the Kopet-Dagh basin. This paper presents the biostratigraphic data obtained based on nannofossils from the upper part of the Aitamir Formation. In order to study calcareous nannofossils a stratigraphic section was chosen in northwest Kopet-Dagh. The measured section is located about 35 km west of Maraveh Tappeh city and near Cherli village at 37 50' N latitude and 55 31' E longitude.
Based on foraminifera assemblage, Kalantari (1969) suggested Cenomanian age for the Aitamir Formation. Thereafter, Seyed-Emami (1980), Seyed-Emami and Aryai (1981), Seyed-Emami et al. (1984), Immel et al. (1997), Mosavinia et al. (2007) and Mosavinia and Wilmsen (2011), based on ammonites, reported a late Albian-middle Cenomanian age for this formation. Moreover, Moradi Salimi (2012), and Raisossadat et al. (2013) in the center and west of Kopet-Dagh, Sharifi et al. (2012) and Garmabi and Mosavinia (2012) in the east of Kopet-Dagh discussed the ammonite contents and paleobiogeography of ammonites in the Aitamir Formation. The calcareous nanoplanktons of the formation have been studied by Susani (2005), Mousazadeh (2005), Moheghy et al. (2014) and Mousavi et al. (2016a, b).
In the measured section, the formation conformably overlies the Sanganeh Formation and underlies the Abderaz Formation. The lower sandstone member is 711 m, consists of glauconitic coarse to fine grained sandstones with some intercalation of silty sandstones while the upper shale member is 359 m, composed of green to greenish grey, grey shales and marlstone that changes to limestone beds of Abderaz Formation at the top. A total of 100 samples were collected from the section with a thickness of 1070 m. The preservation and abundance of calcareous nannofossils in the lower sandstone member of the Aitamir Formation is very rare and poor but in the upper shale member it is good and the most abundant nannofossils belong to this member.
Thirty-five (35) samples were collected from the shale member and used for calcareous nannofossil studies. For detailed calcareous nannofossil examination, simple smear slides were prepared using standard procedures. Smear slides were made from the fresh surface of raw sediment samples. Prepared slides were studied by using a polarized microscope and photographed by a digital camera. Corel draw and Photoshop softwares were used for drawing charts and figures.
Discussion and The standard Upper Cretaceous calcareous nannofossil biozonation Sissingh (1977) (the CC zones), which was modified by Perch-Nielsen (1985) and UC biozonation of Burnett (1998) were used. This scheme largely resulted from the examination of potential stage-boundary sections. Both biozonations were applied to the data on the range-charts.
The biostratigraphic studies of the shale member of the Aitamir Formation resulted to the identification of 23 genera and 32 species of calcareous nannofossils are as follows;
Amphizygus megalosa, Broinsonia enormis, Calcicalathina alta, Corollithion kennedy, Cyclagelosphaera margerelii, Eiffellithus turriseiffelii, Eprolithus floralis, Gartnerago segmentatum, Haqius circumradiatus, Icrorhabdulus belgicus, Lithraphidites carniolensis, Manivitella pemmatoidea, Marthasterites furcatus, Microrhabdulus decorates, Prediscophaera intercisa, Prediscosphaera columnata, Quadrum gartneri, Radiolithus planus, Retecapsa angustiforata, Retecapsa crenulata, Rhagodiscus angustus, Rhagodiscus splendens, Stoverius achylosus, Tranolithus orionatus, Tranolithus phacelosus, Watznaueria barnesiae, Watznaueria biporta, Watznaueria fossacincta, Zeugrhabdotus fibuliformis, Zeughrabdotus diplogrammus, Zeugrhabdotus embergeri, Zeugrhabdotus xenotus.
The following biozones are suggested based on Sissingh (1977) and Burnett (1998). According to the first occurrence and last occurrence of index species and fossil assemblages, three biozones of Sissingh (1977) Eiffellithus turriseiffelii Zone (CC9), Microrhabdulus decorates Zone (CC10) and Quadrum gartneri Zone (CC11) equivalent to biozones UC0-UC7 of Burnett (1998) are suggested. The identified nannofossils zones, could confirm a Late Albian to Early Turonian age for the shale member at the Cherli section in the north western Kopet-Dagh. The determined age is nearly equal with the age obtained by foraminifera (Motamedalshariati et al. 2012). The age of the uppermost part of the Aitamir and the lowest part of Abderaz formations is the Early Turonian. Therefore, it appears that the contact between the Aitamir and Abderaz formations conform and sedimentation was continuous. In the boundary, lithology transitionally changes from shale in the uppermost part of the Aitamir Formation to limestone in the lowest part of the Abderaz Formation. However, more studies are required on this boundary in the western part of the basin.

The Aitamir Formation (Albian-Cenomanian) composed of siliciclastic rocks and several carbonate horizons. In order to study depositional environment and sequence stratigraghy, two stratigraghic sections studied in east Koppeht Dagh basin near the Baghak and Shurijeh villages. Field and petrograghic studies led to siliciclastic and carbonate facies that deposited in lagoon, barrier, shoreface and open marine environments. Sequence stratigraghy analysis led to identification of three depositional sequences in both sections. Comparision of interpreted sea level curves at studied area with Albian-Cenomanian global curve shows similarities and differences that can be relatedto tectonic setting and sedimentation rate.

Considering importance of ammonite fauna in biostratigraphy and sedimentary basins and due to the lack of studies on the ammonite fauna in the Kazhdumi Formation, the Nar stratigraphic section was ed and studied in the coastal Fars, northeast of Kangan (East Bushehr). The formation with a thickness of 87 meters in the studied section contains alternation of cream to brown limestone and brownish red marl. The lower boundary with the carbonate of the underlying Dariyan Formation is unconformable and in the upper boundary is gradually covered by the Madoud Member of Sarvak Formation. In the present study, 110 ammonites have been collected which are belong to three genera and seven species. These include Knemiceras sp., Knemiceras persicum, Knemiceras dubertreti, Knemiceras syriacum, Knemiceras comperessum, Tegoceras camatteanum and Lyelliceras lyelli. Based on these one subzone was differentiated indicating a late Early to Middle Albian age for the formation.

Kazhdumi Formation has been noticed as a hydrocarbon mother rock. On the other hand, it contains very diverse fauna such as corals, bivalves, gastropods, ammonites and echinoids, but there are a few investigations on these groups. Some researchers as Bulot (2010), Kennedy et al. (2009); Asadi et al. (2015) studied ammonites of Kazhdumi Formation. Dehghani et al. (2012) introduced some bivalves and echinoids from northern Shiraz. Kamyabi-Shadan et al. (2014) implicated the stratigraphic position of genus Macraster.

Studied section is located in the eastern flank of Kuh-e-Gurgen, 21 km NW Noor-Abad, West of Fars Province. Kazhdumi Formation with 194.7 m of shale and a few limestone beds is studied here. A rich echinoid fauna (126 speciements) of regular and irregular echinoids is collected from 11 beds (N1 to N9 and N9a to N10) of the Kuh-e-Gurgen section. Echinoid species are identified based on their general characteristics and diameter ratios as well as fine structures and sculptures. Eighteen thin sections have been provided for age determination.  

Eight species belonging to five genera are identified as: Anorthopygus orbicularis, Cidaris (Dorocidaris) taouzensis, Coenholectypus planatus, Macraster douvillei, Macraster longesulcatus, Macraster obtritus, Pedinopsis aff. sinaica and Toxaster granosus. One species, Dorocidaris taouzensis has been reported from Iran for the first time. Presence of the mentioned species shows the age of Cenomanian for the top of Kazhdumi Formation in the Kuh-e-Gurgen section.

Aitamir Formation is one of the formations in sedimentary basins of Koppeh-Dagh in the north east of Iran. This formation has been made of a sandstone part in the lower and a shale part in the upper. Both the part are Glauconitic and often seen in Olive-green color. This research is on a section of a Aitamir formation based on Palynomorphs which has been conducted on the route from Mashhad to Kalat-e-Naderi, isn the edge of Zavin village with the thickness of 506 meters and the coordinates 36°43̒45.42" north latitude, and 59°57̒5.56"east longitude. 40 samples of this section have been gathered and 120 Palynological slides have been prepared. The study of these slides has resulted in the identification of 28 genera and 47 species of Dinoflagellates. Regarding the identified Dinoflagellates, the age of Aitamir formation in the mentioned Albian-Cenomanian section was determined. The study of the factors involved in preservation of organic materials shows the low to moderate levels of oxygen conditions, with low deposition and an inner to the outer Neritic environment for an Aitamir formation in the mentioned section. Based on the studies that have been done, three Palynofacies were identified for the Aitamir formation in Zavin section.

Cretaceous Heteromorph Ammonites are known as index fossils with widely distribution and narrow range in times which play an important role in Cretaceous biostratigraphy (Seyed-Emami & Aryai, 1981; Seyed-Emami et al., 1984; Immel et al., 1997; Mosavinia et al., 2014). Most of these specimens have short age with order of a sub-stage or a zone. More than ten stratigraphic sections from Kopeh-Dagh sedimentary basin were investigated in order to find the Heteromorph forms in the area, but Heteromorph Ammonites were observed in only three of them. Three stratigraphic sections have been measured and logged in the Koppeh Dagh Mountains north, northeast and east of Mashhad at the following localities: 1- Ghorghoreh, locatedabout 70 km E of Mashhad (coordinates: N 36° 13′ 34″, E 60° 24′ 18″)
2- Taherabad, located about 50 km NE of Mashhad (coordinates: N 36° 37′ 05″, E 60° 04′ 03″)
3- Sheikh, located about 20 km NE of Bojnourd (co-ordinates: N 37° 33′ 51″, E 67° 32′ 46″).
62 Specimen of Heteromorh Ammonites are collected from these sections and described which are systematically arranged in genus, species and subspecies as below:4 specimen of Pseudhelicoceras robertianum (Orbignyi, 1842) from Sheikh Section with the age of Early Late Albian, 3 specimen of Mariella (Mariella) cf. bergeri (Brongniart, 1822) from Taherabad and Ghorghoreh sections occur in Late Albian, 2 specimen of Mariella (Mariella) cf. bicarinata (Kner, 1852) from Ghorghoreh section which occur in Early Cenomanian, 8 specimens of Marialla (Mariella) lewesiensis (Spath, 1926) from Ghorghoreh section show the age of Early Cenomanian, 19 specimens of Mariella (Mariella) cenomanensis (Schluter, 1876) from Ghorghoreh section occur in Early Cenomanian, 11 specimens of Turrilitess cheuchzerianus (Bosc, 1801) from Ghorghoreh and Taherabad sections identifying the age of Late Early to Early Middle Cenomanian, 2 specimens of Turrilites costatus Lamark, (Bosc, 1801) from Taherabad section with the age of Middle Cenomanian, 8 specimens of Hypoturrilites cf. tuberculatus (Bosc, 1801) from Ghorghoreh section occur in Early Cenomanian and 5 specimens of Hypoturrilites wiedmanni (Collignon, 1964) from Ghorghoreh section occur in Early Cenomanian. Well preserved Heteromorph Ammonites have been recorded in this studyarea, consequently 9 taxa are described. The oldest one is Mariella (Mariella) bergeri of Stoliczkaia dispar zone, indicates the Late Albian age of the strata related to 100 ma. The youngest species which has been obtained is Turrilites costatus of Acanthoceras rhotomagense zone and Turrilites costatus subzone of the Middle Cenomanian estimates an age of 95.5 Ma.
The specimens belong to Mantelliceras mantelli zone, are relatively more abundant which are comprised of Mariella (Mariella) cenomanensis, Hypoturrilites cf. tuberculatus, Hypoturrilites wiedmanni, Mariella (Mariella) cf. bicarinata and Marialla (Mariella) lewesiensis. This Zone indicates the base of Early Cenomanian.

Aitamir Formation (Albian-Cenomanian) is one of the stratigraphic units in the Kopet Dagh basin that consists of glauconitic sandstone, siltstone, shale and limestone. Glaucony is present in all lithofacies of this formation and varies based on degree of maturity and color ranging from pale to very dark green. Percentage of glaucony in sandstones and shell beds ranges from 1 to 40, poorly to moderately sorted and sub to well-rounded. Glaucony has two origin including autochthonous and parautochthonous. Autochthonous types have green halo in color, shrinkage and associated with immature glaucony and phosphate, whereas parautochthonous glaucony is moderately sorted, well rounded, iron oxide margins and associated with cross bedding.. Autochthonous types of glaucony are mostly replaced quartz, feldspar, chert, carbonate cement and mica.

Two stratigraphic sections of Tang-e-Chenarbashi (712 meters) and Tang-e-Bavolak (870 meters) in the Kabir kuh anticline were selected for investigating planktonic foraminiferal biostratigraphy of the Sarvak Formation. These sections encompass of pelagic facies and containing rich microfauna of Middle Albian to Cenomanian. The results of this study show the age of Middle Albian for lower strata of the Sarvak Formation. First appearance of Biticinella breggiensis correspond with the onset of Upper Albian strata, and is a cosmopolitan marker for Middle and Late Albian boundary. Also, based on investigated biozones including Ticinella roberti Zone, Ticinella primula Zone, Biticinella breggiensis Zone, Rotalipora ticinensis Zone, Paracostellagerina libyca zone, Microhedbergella rischi zone, Rotalipora cushmani Zone,Whiteinella archaeocretacea Zone, several paraconformities have been recognized in the examined sections.

The Aitamir Formation (Albian- Cenomanian) in the Kopet- Dagh Basin consists of fine to medium grained sandstone، siltstone، shale and limestone. Its lower contact with the Sanganeh Formation is gradual and its upper contact with The Abderaz Formation is unconformable. Field and petrographic studies of the Aitamir Formation in Artenj and Ghorghoreh sections، located in Bazangan area- east of Kopet- Dagh Basin، led to identification of 3 facies association consisting of sandstone، mudrocks and limestone. Based on this study، they were deposited in marine، shoreface، barrier and Lagoon environments. Five depositional sequences in Artenj section and four depositional sequences in Ghorghoreh section were identified based on field observations، facies and sequence stratigraphic analysis. In studied sections، the sequence boundary of the first depositional sequence is in the Sanganeh Formation and upper boundary of the last sequence with the Abderaz Formation is type 1 but the rests are type 2 (SB2). The transgressive parasequences (TST) including a predominance of deep facies and regressive parasequences (HST) contains shallow facies parasequens. Interpretive sea level curve of studied sections are relatively comparable with the world wide curve. However، some differences could be occurred due to regional events.

The Aitamir Formation follows conformably but with a sharp boundary the dark shales of Sanganeh Formation (Aptian-early Albian) and is followed discontinuously by the whitish marls and chalky limestones of the Abderaz Formation (Turonian-Coniacian). 7 species, 13 genera and 2 subgenera of ammonites are reported in this paper. The following genera and species, found in the Iranian Kopeh Dagh region, are reported for the first time: Anahoplites cf. praecox Spath, 1925, Anahoplites mantelli Spath, 1925, Epihoplites aff. trifidus (Spath, 1923) and Hysteroceras orbignyi (Spath, 1922). The described specimen of Dinosauria comes from theupperpartof the Aitamir Formation in Zawin Section. The fragment of the Dino was found on the topmost sandstone layer of the section, together with a number of mortonoceratid ammonites, indicating a late Albian (Mortoniceras inflatum Zone) age. So far, it is the first record of marine Dinosauria from the Certaceous of Iran.

One of the stratigraphic units of the Kopet-Dagh Basin is Aitamir Formation. This formation has been studied at four locations including Sheikh and Sorkhezoo in the Sheikh Syncline and Gadganloo and Paskooh in the Bibahreh syncline. The Aitamir Formation consists of fine glauconitic sandstone، siltstone، shale and carbonate rocks. This formation in studied area contains shell beds or shell concentrations. Three types of shell concentrations can be distinguished according to differences in stratigraphic، sedimentologic، palaeoecological، and taphonomic features. These three types of shell concentrations are found in distinct positions within the depositional sequence. Ammonite-dominated concentration (S3) in the early TST has a distinct basal erosional surface (ravinement surface)، and the shells are completely disarticulated، fragmented and abraded with a chaotic orientation، suggesting reworking of previous deposited sediments، and redeposition in a semi-restricted lagoon environment. Shell concentration at the end of the TST is a hiatus type or condensed back lap shell bed. It is characterized by (S1 S2 G1G3 G4P2P4 and P5) high percentage of whole shell، low abrasion and fragmentation، poorly sorted and diversity of fauna. This concentration was accumulated during periods of high rates of production of biogenic hard parts and low sedimentation rates، in an offshore environment. Shell concentrations at the top of the HST (top lap shell bed) (G2، P3) are multiple-event type. Taphonomic features of this concentration are very similar to the early TST concentrations. One distinct difference in characteristic of these two types is lateral extension، so that TST concentration is commonly seen as a bed، whereas the late HST concentration is a lenticular، patchy or pavement form.