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

In this research biostratigraphy of the Eocene deposits of the Eastern margin of Lut Block based on calcareous nannofossils in Alanj stratigraphic section was investigated to determine the biozones and finally exact age of these deposits based on them.The Eocene deposits in this stratigraphic section are about 633 m thickness, and lithological composition mainly contain shale and marl with intercalations of sandstone and sandstone unites. According to taxonomical studies, 45 nannofossil species belong to 20 genera in Alanj stratigraphic section were identified and photographed. Based on the identified species, in north Alanj stratigraphic section biozones were divided as follows:Discoaster binodosus Zone (NP11), Tribrachiathus Orthostylus Zone (NP12), Dicoaster lodoensis Zone (NP13), Discoaster sublodoensis Zone (NP14), Nannotetrina fulgens Zone (NP15), Discoaster taniinodifer Zone (NP16), Discoaster saipanensis Zone (NP17), Chiasmolithus oamaroensis Zone (NP18), Isthmolithus recurvus ZONE (NP19) According to the identified biozons, the age of this sequence, Ypresian (early Eocene) to Periabonian (Late Eocene) is suggested for the studied thickness

The calcareous nannofossils are important in determining the relative age of the Mesozoic and Cenozoic layers.To study Cretaceous-Paleogene boundary, the section in East Ramhormoz were studied based on calcareous nanofossils. In this interval, were studied sediment thickness of 40 meters of shale and limestone and in this study, for the first time were identified 39 species of nannofossils. As a result this study were identified bio zones include Reinhardtites Levis Zone (UC18/CC24) and Arkhangelskiella cymbiformis (CC25/UC19) with Late Cretaceous ageand Heliolithus kleinpelli Zone (NP6) with Selandian/Thanetian age. Based on the zones obtained, the transition period examined is Maastrichtian-Selandian/Thanetian (Middle/Late Paleocene) and was determined the boundary between the Cretaceous to Paleogene of discontinuity type.

The studied section is located in east Iran, Lut block (a part of flysch basin east of Iran) and west of Afzalabad (north Birjand city). The mentioned flyschoids are more than 4200 m thick. The studied section consists of two units including 200 m shale and sandstone of Paleocene age (abbreviated as Pef in the geological map) and 300 m of shale and sandstone, marl, sandstone and limestone of Eocene (as Ef in the geological map).

290 samples were taken from this sequence. The upper and lower parts of the mentioned sequence were sampled over a smaller distance. In order to avoid weathering, samples were often taken from a depth of 50cm. Most of the samples were from shale and marl. Most samples were prepared using smear slide method and others by gravity method. Nannofossils were studied using Polarizing Light Microscope Olympus (BH2 model) in PPL and XPL lights, and most of them were photographed.

In order to determination calcareous nannofossils of this sequence, (Romein, 1979; Perch-Nielsen, 1985; Bown & Young, 1985) reports were used. According to these studies, 21 genera and 56 species of calcareous nannofossils have been identified in the mentioned sequence. Martini, 1971 biozonation is amongst common biozonations for Paleogene and Neogene. Recently other complementary studies were conducted by Agnini et al., 2014. They have adapted their biozonation to that made by Martini, 1971 using some minor changes. Biozonations introduced in this sequence include:Discoaster binodosus Zone (NP11)
This biozone has been defined based on Martini, 1971 biozonation from the last appearance of Tribrachiatus contortus to the first appearance of Discoaster lodoensis. The age of this biozone is early Eocene (Ypresian). It is worth mentioning that Agnini et al., 2014 have defined their CNE3 biozone, which is started a bit before NP11, at lower edge by the first appearance of Tribrachiatus orthostylus and its upper edge exactly matches that of NP11. In our studied sequence the first appearance of Tribrachiatus orthostylus occurs at the base of the sequence and the first appearance of Discoaster lodoensis was seen 230 m from the sequence base which is the upper boundary of biozone NP11 of Martini, 1971. The age of this biozone is early Eocene (Ypresian).
Tribrachiathus Orthostylus ZONE (NP12)
According to Martini, 1971 biozonation, this biozone continues from the first appearance of Discoaster lodoensis to the last appearance of Tribrachiatus orthostylus. The age of this biozone is early Eocene (Periabonian). In the studied sequence the first appearance of Discoaster lodoensis was seen as the base of NP12 biozone and the upper boundary of this biozone was determined based on the last appearance of Tribrachiatus orthostylus.
Isthmolithus recurvus ZONE (NP19)
Based on NP19 biozone (Martinin, 1971), the lower boundary of this biozone in this sequence was also determined by the first appearance of Istmolithus recurvus and the upper boundary of this biozone was determined by the first appearance of Sphnolithus pseudoradians. The age of this biozone is Late Eocene (Priabonian). The thickness of this biozone is 100 m in Afzalabad sequence.

In Afzalabad flyschoid (north Birjand), 21 genera and 56 species of calcareous nannofossils were identified. Based on the identified species, NP11 and NP12 biozons (Martini, 1971) were identified for lower part of this sequence which nearly matches CNE3 and CNE4 biozons from Agnini et al., 2014 biozonation. In the upper part of the studied sequence NP19 biozone (Martini, 1971) was determined. Agnini et al., 2014 biozonation measures were not seen in this section. According to the identified biozons, the age of studied sequence, Ypresian (early Eocene) to Periabonian (Late Eocene) is suggested for the studied thickness. Considering the presence of NP11 biozone in the upper part of Pef and the lower part of Ef, the pass of mentioned units is continuous and gradual.
Keywords: Nannostratigraphy; Flyschoid; Afzalabad; Birjand.
References
Agnini, C., Fornaciari, E., Raffi, I., Catanzariti, R., Palike, H., Backman, J., & Rio, D., 2014. Biozonation and biochronology of Paleogene calcareous nannofossils from low and middle latitudes. Newsletters on Stratigraphy, 47 (2): 131-181.
Martini, E., 1971. Standard Tertiary and Quaternary Calcareous Nannoplankton Zonation. In: Farinacci, A., (ed.), Proceeding of 2nd International Conference of Planktonic Microfossils, Roma, 2: 739-785.
Perch-Nielsen, K., 1985. Cenozoic calcareous nannofossils. In: Bolli, H.M., Saunders, J.H., & Perch-Nielsen, K., (eds.), Plankton Stratigraphy, Cambridge University Press, 427-554.
Romein, A.J.T., 1979. Lineagesin early Paleogene Calcareous Nannoplankton Utchret Microplaentol. Utrecht micropaleontological bulletins, 22: 1-230.

The Kopet-Dagh basin extended in the north and north east of Iran and consists of marine strata from Middle Jurassic to Paleogene time. Abtalkh Formation is one of the thickest lithostratigraphic units of Cretaceous in the Kopet-Dagh basin and is composed of light gray، green to bluish marl and silty marl. The Abtalkh Formation conformably overlies the marls and chalky limestones of the Abderaz Formation and is conformably overlain by the Nayzar Formation (sandstone، silty marl and limestone). In this study، the Padeha stratigraphical section in the eastern Kopet-Dagh basin was selected and studied in high resolution for its calcareous nannofossil biochronology. Padeha section contains very abundant، rich and moderately preserved calcareous nannofossil assemblages of Tethyan realm. A total of 268 samples in Padeha stratigraphical section were collected from the Abderaz، Abtalkh and Nayzar formations. The thickness of measured Abtalkh Formation in Padeha section was 974. 5 (m). One hundred and fourteen nannoplanktonic species belonging to forty nine genera and seventeen families were identified and the biostratigraphic study allowed the recognition of the calcareous nannofossil biozones of Sissingh (1977)، emended by Perch-Nielsen (1985) and Burnett (1998). From bottom to top، identified biozones in the Padeha section including a part of CC19، CC20، CC21، CC22، probably a part of CC23a and a part of UC14dTP، UC15bTP، UC15cTP، UC15dTP and probably a part of UC16. The results of this study indicate that the age of Abtalkh Formation in the Padeha section spans from late Early Campanian to Latest Campanian.

The aim of this research was to interpret environmental conditions of the Pabdeh Formation in Ilam section، North West Zagros basin، based on calcareous nannoplankton. According to identified biozones which is equivalent to NP10-NP25 biozones of Martini (1971)، the age of Pabdeh Formation in studied section is Early Eocene – Late Oligocene. Abundance of Discoaster and Sphenolithus in the lower part of section indicates an oligotrophic condition in sedimentary basin which is related to global warming. Toward the top of section، the Cyclicargolithus floridanus، Sphenolithus moriformis، Coccolithus pelagicus، Reticulofenestrid nannofossils are dominant. On the other hand، the presences of genera Reticulofenestra، Cyclicargolithus، Dictyococcites that are taxa of temperate and cold water، indicate mesotrophic – eutrophic conditions in the upper part of section. Increasing of Discoasters shows warming trend during the Late Oligocene time.

This study presents the nannostratigraphy and nannofossil events in the lower boundary of Kalat Formation in the East and West of the Kopeh- Dagh basin. The Kalat Formation comprises of coarse grained detritus limestone with subordinate sandstone intercalations. In the current study, six sections have been chosen in the East and West of the basin which are as follow: Dobaradar section, Kalat section, Chahchaheh section, Sheikh section, Qaleh Zoo section and Jozak section. In the Dobaradar section 22 species have been determined, in the Kalat section 25 species, in the Chahchaheh section 32 species, in the Sheikh section 28 species, in the Qaleh Zoo section 20 species, and in the Jozak section 18 species have been determined. The boistratigraphy based on calcareous nannofossils allows the identification of nannofossil standard zones CC25- CC26 in the East, and CC21 and CC26 in the West of the Kopeh- Dagh Basin in all of the sections, indicating that the investigated deposits are Late Maastrichtian – late Late Maastrichtian in age in all sections in the East, and early Late Campanian – late Late Maastrichtian in all sections in the West of the Kopeh- Dagh Basin. The nannofossils response to the Maastrichtian climate evolution is investigated in the lower boundary of Kalat Formation. Warm water indicators (Uniplanarius sissinghii, Micula murus and Micula prinsii) suggest warm surface water conditions in the studied thickness. In the lower boundary of the Kalat Formation, based on Lithraphidites spp. and Watznaueria barnesae, lower fertility conditions with low productivity at the end of the Maastrichtian were suggested.

In this paper، the calcareous nannofossils at the contact between Aitamir and Abderaz Formations in Dobaradar and Hammam Qaleh sections in the east and Qalehzoo and Sheykh sections in the west Kopet Dagh basin، for consideration of biostratigraphy and paleaoecology، were studied. On the basis of paleontological studies، 22 genera and 33 species in Dobaradar section، 25 genera and 37 species in Hammam Qaleh section، 9 genera and 13 species in Qalehzoo section and 17 genera and 22 species in Sheykh section، were detected، photographed and counted and the biozonation of studied regions have been determined. On the basis of these biozones، the age of the boundary between Aitamir and Abderaz formations in the Dobaradar and Hammam Qaleh sections is Late Santonian and the age of this boundary in Qalehzoo and Sheykh sections is Early Campanian. The increases in abundance from east to west and paleoecological interpretation show that the depth of the Kopet Dagh basin increased from east to west. Based on reduced diversity and abundance of species in the west، it can be stated that environmental conditions in the east were better for living calcareous nannoplanktons than west Kopet Dagh.

In this study، Gurpi Formation at Mook section has been sampled and studied. Taxonomical studies of calcareous nannofossils lead to identification of 23 genera and 44 species at the Mook section. According to the first occurrence of index species and fossil assemblages، seven calcareous nannofossil biozones (CC21- CC26 of Sissingh، 1997) and biozone NP1 of Martini (1971) equivalent to biozone CP1a of Okada and Bukry (1980) at the Mook section have been recognized. Based on these biozones، age of the Gurpi Formation in SE of Shiraz، is Late Campanian to Early Danian. On the bases of paleoecological interpretation، Gurpi Formation at the Mook section was deposited in low latitude and deep marine environment. But، the depth of the basin decreases toward the top of the Gurpi Formation at this section.