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

Hashemabad deposit is located in southeastern part of Esfahan province (Naein), in Central-Iran Zone and within Cretaceous-volcanic rocks. This system is a part of Naein-Ardestan basin which consists of Cretaceous sub-seafloor lava, volcano-sedimentary rocks, and ultrabasic-rocks which formed in extensional environment. This complex located in a tectonic zone (strike-slip fault) adjacent to Urumieh-Dokhtar magmatic arc. Main altered and metamorphosed rocks in this area include Middle-Upper Cretaceous basaltic-lava, andesite, basaltic-andesite, rhyolite and rhyolitic-tuff and younger subvolcanic masses which emplaced in relation to strike-slip faults. Andesite and basaltic andesite which well distributed in whole area are the main host of copper mineralization. Propylitic, argillic, sericitization, silicification, carbonatization and sulfidation are main alterations which well distributed along fault and fractures. However, the intensity of silicification and carbonatization increases in proximity of the mineralized zone. Ore mineralization generally is concomitant with bedding of host basaltic andesite lava in form of disseminated and lens shape and has observed with stratabound geometry along local and cross-cutting faults. Ore minerals have vein-veinlet, open space-filling, disseminated and replacement textures. Ore minerals include chalcocite, bornite, chalcopyrite and pyrite along with secondary minerals such as covellite, chalcocite, malachite, hematite, goethite and azurite. Geochemical studies proposed high potential and enrichment of copper (less Ag&Mo) in this area. The presence of relatively good amounts of gold in tuff units containing jasper as well as in the place of argillic-alteration is one of the unique features of this area. Considering the above evidences, this deposit could be considered as Manto type copper deposit.

The current research was conducted with the aim of investigating environmental changes based on calcareous nannofossils. For this purpose, a section of the Kazhdumi Formation was sampled southwest of Yasouj. As a result of the study of 60 smear slides, 42 species belonging to 21 genera of calcareous nannofossils were identified from marine deposits. According to the recorded nannofossils, the age of Albian for Kazhdumi Formation in the studied section was determined. In addition, this study led to the establishment and differentiation of the following bio-zones: Prediscosphaera columnata Zone and Eiffelithus turriseiffelii Zone. Also, the evaluation of facies in the present study shows rapid sea-level changes. On the other hand, it seems that the activity of the Kazerun fault has caused changes in the sedimentary conditions and the creation of different facies during the Albian stage. Therefore, fossil data together with lithostratigraphic studies indicate sedimentary changes from a shallow carbonate system to deep marine sediments.

The Cretaceous deposits of Golbaf region are part of the Rhine-Guk-Khana Khatun zone in the stratigraphic-structural belt of Rafsanjan (Dimitrijevic and Djokovic, 1973). In this belt, Cretaceous deposits are divided into shallow to deep facies, and the most complete Cretaceous deposits can be found in the Rhine-Guk-Khan Khatun area (Dimitrijevic, 1973). The studied sedimentary sequence is exposed in the south of Golbaf and southeast of Kerman and its thickness is 147 meters. The age of these sediments is Upper Cretaceous (Coniacian-Santonian). These sediments contain clastic deposits that are gradually and with the same slope on the Lower Cretaceous and Neogene, and the upper boundary of this section is in the form of marl limestone related to MaisTrichtian facies. This section has a lithological sequence of columnar silt, silty sandstone, and shale, which contain fossils and species that have been identified in the debris layers of this section. These fossils are mostly creeping-nutritional or nutritional traces. These fossils are found in shallow to turbidity marine environments, which are well preserved and varied, and their most abundance can be seen in the middle part of this section. In this article, an attempt was made to systematically identify the existing fossils and discuss and examine their behavioral patterns.

This study includes two stages of field and laboratory operations. In the field operation, after identifying the intended cut and determining the boundaries as well as the beginning and end of the desired cut, the thickness of each layer was measured and examined.  The required information was noted down, and if sampling was done, fossils were taken from the sediments. In the laboratory, after photographing each sample, the characteristics of each fossil, such as shape, size, dimensions and type of preservation in relation to the level of layering, decorations and various components, were identified (Miller, 2007; Seilacher, 2007). Then the trace fossils were classified based on the behavioral status first presented by (Seilacher, 1964) and discussed by (Bromley, 1996) and finally the fossil systematics was written completely.

Trace fossils are biological constructions in sedimentary environments that are formed by organisms in soft to hard sediments. Trace fossils are biological constructions in sedimentary environments that are formed by organisms in soft to hard sediments. Trace fossils are biological constructions in sedimentary environments that are formed by organisms in soft to hard sediments. Turbidites are generally found as flysch deposits and are considered as deep basin rock facies. These sediments, in expanded patterns, Boma include a series of diverse clastic-mudstone facies (Pickering et al, 1989). On the other hand, trace fossils have complex geometrical shapes that are usually observed with marine and deep pelagic sediments. Since the trace fossils in Golbaf region are widespread and abundant, therefore, in order to achieve turbidite sedimentary environments, based on the data of Archeology It is necessary to combine the archeology data with sedimentological data and structural elements. The rock facies of the studied sequence include The facies are siltstone, silty sandstone, and Chile. In these beds, the amount of sedimentation is low to high. According to the archeological data, diversity and abundance of fossils in the studied sedimentary sequence, on the surface of silty sandstone and siltstone layers, it can be concluded that most of the fossils are in the form of molds on their lower surface, in other words, the activity of animals has an effect on They are concentrated on the upper surface and have been molded by silty sandstone and siltstone sediments after deposition. Therefore, most of the fossils were formed in the middle parts after the occurrence of turbulent currents and in a relatively calm environment.

Upper Cretaceous flysch deposits in Golbaf area have a good thickness and ichnofossils in this section have a very high diversity and abundance.Ethnological and sedimentology studies on the sediments of the studied area indicate calm conditions in the bed of the basin. It seems that the availability of environmental conditions such as bed oxygen, amount of organic matter in sediments, time fluctuations, textural composition of sediments, sedimentation rate, abundance of biological communities and their distribution have caused the abundance of effectors.According to the type, frequency and spread of fossils in the studied sequence, it can be concluded that a thickness of the Set bar sequence in the south of Golbaf is in suitable conditions for creating fossils.

The sedimentary basin of Kopeh-Dagh is located in the northeast of Iran. This sedimentary basin has been of interest for a long time because of hydrocarbon materials. Gavelinellids are the most abundant and dominant groups of benthic foraminifera in epicontinenal seas during Cretaceous period which belong to Rotaliinacean foraminifera. They have shown a wide biogeographical distribution and dispersion in many areas of Tethys. Their evolutionary trend during the Cretaceous time was success. The high concentration of marine sedimentary rocks and the absence of igneous activities in the Kope-Dagh sedimentary basinhave caused it to be considered the most suitable basin for the formation and accumulation of hydrocarbons after the Zagros sedimentary basin. This basin has suitable layers of carbonate rocks and porous sandstones to store hydrocarbon materials, also thick layers of shales in this basin can act as suitable source and cap rocks. In this research some genera and species from this family in Sanganeh and Aitamir Formations at five stratigraphic sections including Marave Tappeh, Takal kuh, Sheykh, Gadvecanlou and Kalat from point of biostratigraphical and paleoecological applications have been investigated. In this study, four biozones including Gavelinella flandrini-Gaudryina cf. praedividens assemblage zone, Berthelina intermedia assemblage zone, Berthelina cenomanica Assemblage Zone, Berthelina intermedia-Osangularia schloenbachi Assemblage Zone have been introduced. Based on the reported genera and species of the Gavellinidae family, it can be stated that the studied formations were deposited in the middle and outer part of the continental shelf to the upper part of the continental slope and in aerobic to semi-aerobic environments. The presence of more planktonic foraminifera than benthic foraminifera in the Aitamir Formation, the depth of the basin increases.

In the Kopet Dagh sedimentary Basin in north east of Iran a full record of Mesozoic and Cenozoic strata is present. In the Kopet Dagh Basin, Neyzar and Kalat formations belongs to the upper Cretaceous strata. Neyzar Formation is located on the Ab-Talkh Formation and is overlain by the Kalat Formation and mainly consists of fine to medium grain sandstone in the lower part and limy shale and marl at the upper part of the section (Darvishzadeh, 1370). The main aim of the present study are to investigate on the calcareous nannofossils at the upper part of Neyzar Formation and the lower part of Kalat Formation in order to determine the exact age of the strata in Tange-Neyzar section. For determining the paleoenvironment, the calcareous nannofossils paleoecology has been investigated.

Fourteen samples from the upper part of Neyzar Formation and 6 samples from the lower part of the Kalat Formation have been studied. Systematic sampling in every mater has been done. For studying calcareous nannofossils regarding biostratigraphy and paleoecology simple smear slides (Perch-Nielsen, 1985) were prepared. For calcareous nannofossil biostratigraphy Sissingh (1977) biozonation emended by Perch-Nielsen (1985) and Burnett (1998) zonation have been applied.

From the base of the section, species such as Reinhardtites Levis, Ceratolithoides aculeus, Uniplanarius sissinghii, Eiffellithus parallelus are present. The first occurrence (FO) of Reinhardtites levis is a marker for the middle part of UC14dTP, the FO of C. aculeus indicates the boundary of UC15aTP and UC15bTP subzones, the FO of U. sissinghii marks the boundary between UC15bTP and UC15cTP, and the FO of E. parallelus shows the boundary between UC15cTP and UC15dTP subzones. From the early parts of the section, E. examine is present that its LO indicates the boundary between UC15 and UC16 biozones and is observed up to the end of the section. According to the mentioned taxa, calcareous nannofossil subzone UC15eTP with early late Campanian age was identified at the studied interval. The presence of taxa with cold water affinity like M. decussata, Prediscosphaera spp., Eiffellithus spp., A. cymbiformis and A. octoradiata and the absence of warm water taxa indicate decrease in temperature and cool greenhouse condition. Micula decussata which marks cool, oligotroph and stressful condition (Pospichal and Wise, 1990; Thibault and Gardin, 2006; Watkins and Self-Trail, 2005) is dominant at the studied interval. Prediscosphaera spp. is also abundant and is a marker of cold (Watkins and Self-Trail, 2005) and oligotroph (Friedrich et al, 2005) surface waters. The highest relative abundance of W. barnesae which is a warm and oligotroph taxa (Thierstein, 1981; Lees, 2002; Sheldon et al, 2010) is recorded at the lower part of the section, Lithraphidites carniolensis with warm and oligotrophic affinity is common is stratified photic zones (Friedrich et al, 2005) that its highest relative abundance is recorded at the lower part of the interval. Eiffellithus spp. with the highest relative abundance of E. turriseiffelii at the lower part of the section is considered as an oligotroph taxa (Friedrich et al, 2005). The highest relative abundance of A. cymbiformis with cold surface water affinity (Thierstein, 1981; Barrera, 1994; Watkins and Self-Trail, 2005) is recorded at the lower part of the section. The highest relative abundance of B. bigelowii is also recorded at the bottom of the section. In the Zagros sedimentary Basin, C. ehrenbergii is considered as cold water taxa, but a decrease in the depth is also important (Razmjooei et al, 2020).

According to the calcareous nannofossil taxa at the upper part of the Neyzar Formation and the lower part of the Kalat Formation, UC15eTP subzone equivalent with the upper part of CC22 biozone of Sissingh emended by Perch-Nielsen has been identified. Because of the week preservation of the calcareous nannofossils, U. trifidus was not recorded. Species such as E. eximius and R. anthophorus that are markers of the uppermost part UC15 and CC22 are recorded up to the top the section. Regarding these data early late Campanian age was determined for the studied interval. The dominance of cold water taxa like M. decussata, Prediscosphaera spp., Eiffellithus spp. and A. cymbiformis and the absence of warm water taxa indicate cool greenhouse condition at this time interval similar to other parts of the world.

The recording of oceanic anoxic event al record and the time of this event in the shallow carbonates of the Dariyan Formation in Zargran mountain (Gadvan) section in the east of Shiraz, was studied based on carbon and oxygen isotopes, microfacies and fossil data. In this section, thickness of the Dariyan Formation is 287 m and 191 samples were taken. Based on field data, the sedimentary sequence of this formation, , begins at the base with thick-layered to massive gray limestones containing orbitolinas and rudists, and in the upper parts it includes medium to thick-layered gray limestones including abundant benthic foraminifera, such as orbitolinas. In the mentioned section, based on the study of the embryonic cells of orbitolinas, a late Barmian-early Aptian age was determined for the lower part of this unit, which is the beginning of the formation of anoxic oceanic deposits. The carbon isotope curves between the C3 and C6 curves in the carbonates at the base of the Daryian Formation show disturbances. These changes and the appearance of the Lithocodium-Bacinella facies in this part of the formation confirm the existence of an oceanic anoxic event. The oceanic anoxic event indicates warming of the environment and greenhouse conditions, which was accompanied by abundant rudists in this section and can be a confirmation for the weather conditions of this event.

One of the most extensive Cretaceous strata is the marine strata of the Gurpi Formation in Zagros, which was studied based on paleontology studies. The Gurpi Formation type section is located in Tang-e Pabdeh, North of Masjed Soleyman city (James & Wynd, 1965). One of the most important achievements obtained from the Gurpi Formation is the evaluation of stage boundary and biostratigraphy of it. In this section, the Gurpi Formation consists of 143 m thick which mainly consists of marl and marly limestone.

In this study, 73 samples from the Gurpi Formation interval have been studied. Samples were prepared following the standard smear slide method (Bown & Young 1998). All the slides were examined under the polarized light microscope at ×1000 magnification. The nomenclature of calcareous nannofossil follows the taxonomic schemes of Perch-Nielsen (1985) and Burnett (1998).

To study biostratigraphy based on calcareous nannofossils, the Gurpi Formation succession in the southwest of the Aghar anticline, SW Shiraz, was selected. In this section, the Gurpi Formation with 143 m thickness mainly consists of marly limestones and marl. For introducing index species, calcareous nannofossil assemblages, and bio-zones, slides have been studied at the Gurpi Formation, which led to the determination of 40 species and 21 genera of calcareous nannofossils. In this study, ten biozones were recognized in the Gurpi Formation. Bio-zones including Lucianorhabdus cayeuxii Zone (CC16), Calculites obscurus Zone (CC17), Aspidolithus parcus Zone (CC18), Calculites ovalis Zone (CC19), Ceratolithoides aculeus Zone (CC20), Quadrum sissinghii Zone (CC21), Quadrum trifidum Zone (CC22), Tranolithus phacelosus Zone (CC23), Reinhardtites levis Zone (CC24) and Arkhangelsiella cymbiformis Zone (CC25) with Late Santonian - middle Maastrichtian in age. According to the first and last occurrence of index species the following bio-zones are identified

The Shurijeh Formation (Upper Jurassic-Early Cretaceous) is composed of siliciclastic facies in the eastern KopetDagh basin. Moreover, the identified paleosol in this formation is calcisol type. The identified calcisols of the Ghorghoreh section have particular micro and macro morphology shapes. Since the beta microfabric is dominant in these paleosol, therefore microorganisms activity plays an important role in the formation of calcretes. The paleosols in this section have been affected by processes such as boring, micritization, cementation, and pyritization. The CO2 paleopressure has been calculated to be about 2237.1 to 2981.08, which is about 7.99 to 10.65 times more than todaychr('39')s values and seems to be similar to the modeled values for that period. In addition to biogenic activities, the water table fluctuations in the phreatic zone led to the formation of calcretic paleosols in the studied section.

The Shurijeh Formation is a Late Jurassic–Early Cretaceous (Late Kimmeridgian–Hauterivian) siliciclastic rock unit of the Kopet-Dagh Basin, up to 392 m thick. In the Estarkhi section, it rests disconformably on the Mozduran Formation (Oxfordian), and is disconformably overlain by carbonate rocks of the Tirgan Formation (Barremian–Aptian). The sandstones are predominantly subarkose, sublitharenite, feldspathic litharenite, and litharenite with minor quartzarenite, rich in quartz and feldspars, sedimentary and igneous rock fragments (plutonic), and rarely metamorphic fragments. Based on petrological and geochemical studies, minor diagenetic events in the early diagenetic stage include cementation by calcite and iron oxide. Deep burial diagenetic events were dominated by compaction, cementation (silica, dolomite, chlorite), fracturing, dissolution, pressure solution, and albitization. Minor late diagenetic events include dissolution and cementation (calcite, iron oxide). Based on diagenetic events, a temperature of >80°C during burial diagenesis is suggested for Shurijeh Formation. The existing porosity is secondary, resulting largely from the dissolution of feldspar and carbonate cement, with some fracture porosity. The porosity and permeability of 11 core plugs average 7.78% and 4.84 md, and the point count of 38 thin sections shows an average porosity of 10.05%. The good porosity and permeability of the middle part of the section predict an acceptable reservoir potential for this formation in the study area.

In this study, the upper part of the Garau Formation with a thickness of 24 m in the section of Sheikh Saleh anticline located in the northwest of Kermanshah was investigated from the calcareous nannofossils. In this section, the Garau Formation is mainly composed of medium bedded argillaceous limestone. In order to introduce the index species and biozones, 17 slides from the Garau Formation were studied, which resulted in the identification of three biozones. As a result of this study, 20 species and 15 genera of calcareous nannofossils were identified. Based on the obtained biozones, the age of the upper part of the Garau Formation in the studied section is suggested the late early Cenomanian to the late late Cenomanian. This age is corresponding to the upper part of Eiffellithus turriseiffelii Zone (CC9), Microrhabdulus decorates Zone (CC10), lower part of Quadrum gartneri Zone (CC11) from the Sissingh (1977) zonation and UC1, UC2, UC3, and lower part of UC7 from the Burnett (1998) zonation.

n this study, calcareous nannofossils are investigated in the upper part of the Gurpi Formation and lower part of the Pabdeh Formation at the Par-e Nobar section located in the northwest of Shiraz. The thickness of the studied section is about 41 m. The upper part of the Gurpi Formation is mainly composed of shales and pelagic limestones while the lower part of the Pabdeh Formation consists of shale facies. As a result, 32 species and 22 genera of calcareous nannofossils were detected. According to the first and last occurrence of index species and fossil assemblages, two bio-zones including Nephrolithus frequens Zone (CC26/ UC20dTP) and Markalius inversus Zone (NP1) are recognized in the upper part of the Gurpi Formation, respectively. Fasciculithus tympaniformis Zone (NP5) and Heliolithus kleinpellii Zone (NP6) are reported for the first time from the lower part of the Pabdeh Formation, respectively. Based on the identified calcareous nannofossils zones, the age of the upper part of the Gurpi Formation is the latest Maastrichtian–early Danian, and the lower part of the Pabdeh Formation is the middle Paleocene/Selandian. Therefore, according to the nannofossil data, the boundary between the two formations is unconformable.

In the Talesh area (western Alborz), a thick sedimentary- volcanic association formed in a littoral- deltaic environment during the Late Cretaceous. The extrusives comprise volcanoclastics (tuffs), lava flows (pillow and massive) and basic dykes. The lava flows are dominated by basalts. Basalts are petrographically diverse including clinopyroxene- and plagioclase- phyric suites. Clinopyroxene is chemically in the ranges of augite to diopside and plagioclase is labradorite to bytownite. Here, using clinopyroxene chemistry, we performed thermobarometry and hygrometry calculations. Thermometric results of different samples are in the ranges of 1000 to 1200 °C. Moreover, barometric calculations show pressure ranges of <2.5 and 2.5 to 6 kbar correlating with crystallization depth of upper to middle continental crust (<10 to 22 km). Regarding parental melt chemistry and the magmatic series, the clinopyroxene and whole rock chemistry suggest two alkaline and subalkaline series. Hygrometric calculations provide H2O contents of 2.7- 2.97 and 2.97- 3.53 wt.% for alkaline and subalkaline basalts, respectively. Tectonically, the alkaline basalts could be related to extensional tectonic regime, asthenosphere upwelling or mantle plume/hot spots, while the subalkaline basalts resulted from subduction- related magmatism probably related to northward subduction of an oceanic basin beneath western Alborz or a Neo-Tethyan branch below southern margin of the  Eurasia.

One of the most extensive Cretaceous and Paleogene deposits in Zagros are the marine sediments of the Gurpi Formation, they were first identified in the Zagros based on stratigraphy and paleontology. One of the most important researches that can be done given this formation in Zagros, is determining the exact boundaries, by calcareous nannofossil assemblages. At the Anar anticline section, the Gurpi Formation with 163 m thickness was selected which mainly consists of shale, silty shale and plagic limestone.

The Gurpi Formation with a thickness of 190 m at the Kouh-e sefid anticline is investigated with regard to the calcareous nannofossils. In this section, Gurpi Formation is mainly consists of shale, marls and argillaceous limestones. As a result of this study, 21 genera and 41 species of calcareous nannofossil have been recognized. Based on distribution of index species calcareous nannofossils bio zones of have been recognized, including CC16-CC25 biozones, that corresponding to UC12-UC20aTP. According to the identified biozones, the age of the Gurpi Formation in this section is middle/late Santonian to early late Maastrichtian. The study in the Kouh-e sefid anticline, show that the sedimentation of Gurpi Formation has been started at the middle/late Santonian and to continue to the early late Maastrichtian.