نشریه دیرینه شناسی
پیاپی 1 (بهار و تابستان 1392)

Tirgan Formation with Lower Cretaceous age (Barremian-Aptian) in the Kopet-Dagh basin consists of carbonate and siliciclastic rocks (calcareous shale and sandstone) which conformably lay between siliciclastic rocks of Shurijeh Formation below، and marly Sarcheshmeh Formation at the top. In this study، Tirgan Formation in two stratigraphic sections of Abgarm (77 m in thickness) and Sirzar (46 m in thickness) in northeast Mashhad were measured and sampled. Facies variations and lithological characteristics in the carbonate sequences led to the recognition of 19 facies (17 carbonate and 2 silisiclastic lithofacies). Facies analysis indicates that they were deposited in four facies belts including open marine، shoal، lagoon and tidal flat in a shallow carbonate ramp. Three third-order sedimentary sequences in these sections were identified based on field observations، facies analysis and sequence stratigraphy. The transgressive parasequences (TST) including a predominance deep water facies and high stand tract (HST) contains shallow facies parasequens. Sequences are bounded by type 2 sequence boundaries. Interpreted sea level curve is comparable with the worldwide sea level curve. However، some differences are probably due to regional events.

Coccolithophores are important primary producers in the modern world ocean and were almost certainly important in the Mesozoic oceans، prior to the evolution and rise of diatoms in the phytoplankton. Calcareous nannofossils are abundant، planktonic، rapidly evolving and largely cosmopolitan، so they are a good tool for biostratigraphy and paleoecology studies especially in the Cretaceous system. According to these specifications and due to the lack of precise paleontological study، the nannofossils of the last layers related to eastern Alborz Cretaceous deposits have been investigated in Cheshmeh Gholghol section. Using polarize microscope، 23 genera and 51 species were identified in this section. Based on identify nannofossils، the age of this section is Late Santonian- Late Maasrichtian corresponding to CC16- CC26 (Sissingh، 1977). On the bases of paleoecological interpretation، the last layers related to eastern Alborz Cretaceous deposits were deposited in shallow marine environment in relatively low latitude، warm climate condition and basin shalloer toward Fajan Formation.

In order to study biostratigraphy of the Surgah Formation in Zagros sedimentary basin، two subsurface sections of this formation in Maleh Kuh and Sarkan oil fields at Pol-e-Dokhtar area، Lorestan Province، have been selected. The thickness of Surgah Formation at Maleh kuh and Sarkan، was 82 and 46 meters respectively and is composed of shale with intercalation of limestone and calcareous shale. The lower and upper boundaries of Surgah Formation at mentioned wells with Sarvak and Ilam formations are conformably. According to study of planktonic foraminifera، 37 species belong to 10 genera in Maleh Kuh well and 32 species belong to 10 genera in Sarkan well، were recognized. On the bases of these fossils، 3 biozones have been distinguished as below: 1-Dicarinella primitiva (caron1978) Interval Range Zone2- Dicarinella concavata (Sigal1995) Interval Range Zone3- Dicarinella asymetrica (Postuma1971) Total Range ZoneFinally، based on the study of planktonic foraminifera، the age of late Middle Turonian- Late Santonian has been proposed for two subsurface sections of Surgah Formation.

For the study of Upper Triassic calcareous algae، four sections from the Bidestan and Howz-e Khan members of the Nayband Formation، exposed in the southeast area of the Nayband Mountain were measured and sampled. To obtain the variation of algae، additional scattered samples were collected from this region. Algal carbonate layer، rich of dasycladales was recovered in the Howz-e Khan member. After the laboratory and microscopic investigations، four genera and four species of calcareous algae، including Griphoporella curvata (Gümbel)، Chinianella carpatica (Bystrický)، Diplopora interiecta Fenninger and Acicularia antique Pia. have been recognized.

In order to determine the Dalichai Formation Paleoecology (Middle Jurassic)، with measured thicknesses of 255 m at Bar section، NW Neyshabour، 28 samples systematically were collected. Based on 112 Palynological slides studies، 29 species of spore and pollen، which belong to 21 genera، have been identified. In addition to spores and pollens، dinoflagellate and fungus bodies form the palynomorphs assemblages in these strata. The spore and pollen grains parental flora، in the study section، are related to Filicopsida، Lycopsida، Cycadopsida، Coniferopsida، Ginkgoopsida. Through the miospores genera of Dictyophyllidites، Klukisporites، Cyathidites، Gleicheniidites (belonging to Pterophyta) are more abundant. According to Klukisporites genera abundance، Middle Jurassic age is suggested for Dalichai Formation، at Bar section. Also، the identified dinoflagellate، type proximate which includes، Ctenidodinium ornatum، Dichadogonyaulax sellwoodii، Gonyaulacysta centriconata، Gonyaulacysta jurassica، Nannoceratopsis pellucidae، Pareodinia ceratophora، Rhynchodiniopsis cladophor، defines the warm and semi-warm climatic condition. Additionally، the presence of fungus body is also a confirmation of a warm and moist climatic condition. Finally، Dalichai Formation probably precipitated at a moist and warm climate.

Middle-Late Eocene deep marine deposits (483 m.) of the Islam-Ghaleh section، south Mashhad، rich in ichnofossils in shale and sandstone layers. These flysch type sediments are composed of sandstone، shale and marl in gray to green in color and are divided into five subunits. The lower boundary of these successions is gradual with red conglomerate and sandstone and their upper boundary is gradual with gypsum and red gypsiferous marls of probably Eocene age. The most important identified ichnofossils in these successions are Bergaueria isp.، Gyrophillites isp.، Halopoa annulata، Halopoa storeana، Helmintopsis tenuis، Ophiomorpha isp.، Paleodictyon (Glendodictyon) goetzingeri، Paleodictyon (Glenododictyon) strozzi and Thalassinoides isp. that are abundant in middle and upper parts of the section. Increasing of bioturbations and ichnofossils accumulation in these relatively deep water sequences can be related to concentration of sparse marine nutrition and formation of oxic conditions in the deep environments that could be related to sea floor currents. So، presence of abundant and index ichnofossils can be used as an important indicator for identification and confirmation of turbidite systems in the Middle – Late Eocene sequences of the studied area and their correlation with similar successions in other parts of Iran and the world.

Studied sedimentary succession، situated in Kerman region between Seh Konj and Kuh-e-Shishto، is divided into three lower، middle and upper units of Flysch deposits and one conglomerate unit. This succession consists of sandstone، alternation of sandstone and shale، green marls with sandy marl intercalations and conglomerate. In vicinity of Chaahar Tagari village، middle and upper parts of mentioned flysches are cropped out. In order to investigation the biogenic structures of upper unit (Paleocene-Eocene)، a stratigraphic section was selected and measured. Six ichnogenera and six ichnospecies are identified as follows; Ophiomorpha annulata، Ophiomorpha rudis، Ophiomorpha isp.، Planolites beverleyensis، Punctorhaphe parallela، Thalassinoides suevicu، Palaeophycus tubularis، Helminthopsis isp. Ichnotaxa variation is low (twelve ichnotaxa) but their abundance is relatively high. A sublittoral sedimentary environment with high oxygen، normal salinity and medium to low energy is suggested for studied unit. It seems that the depth of basin decreases gradually from middle unit toward the upper unit. Intensity of biotorbation in ichnofossil bearing beds is different and four different ichnofabrics were identified.