10 research outputs found
Palynostratigraphy of Middle Cambrian to lowermost Ordovician stratal sequences in the High Zagros Mountains, southern Iran: Regional stratigraphic implications, and palaeobiogeographic significance
No full textA palynological investigation of Cambro-Ordovician stratal sequences in the High Zagros Mountains of southern Iran permits the definition of a series of successive acritarch assemblage zones of chronostratigraphic significance, much improving the current knowledge of the Lower Palaeozoic stratigraphy of this important area for oil exploration. The five acritarch assemblage zones can be readily correlated with previously established palynostratigraphic schemes constrained by co-occurrence of independent age evidence, confirming the utility of organic-walled microfossils for the detailed biostratigraphic characterization of sedimentary units. The proposed biozonation will facilitate accurate dating of the southern Iranian Cambrian sequences during future drilling of deep test oil wells. Acritarch assemblage zone I (Middle Cambrian), occurs at the base of Member C of the Mila Formation; assemblages zone II (late Middle to earliest Late Cambrian) extends through the middle and upper part of the same lithostratigraphic unit; zone III (early Late Cambrian in age) characterizes the lower part of the Ilebeyk Formation; zone IV (middle Late Cambrian up to Cambrian/Ordovician transitional levels) occurs in the middle and upper part of the Ilebeyk Formation; finally, acritarch assemblage zone V ranges through the basal part of the Zardkuh Formation and proves an early Tremadocian age for the latter unit. The Mid-Late Cambrian acritarch associations show a marked Avalonian palaeobiogeographical affinity, also sharing a high proportion of taxa with typical Baltican and North Africa-Gondwanan assemblages; on the other hand, they are clearly different from known Laurentian (North America) fossil microphytoplankton suites. These results are in general agreement with current palaeogeographical models which place Avalonia, Baltica, and the North African part of Gondwana, all at relatively high southern palaeolatitudes, in contrast with the sub-equatorial position of Laurentia. However, the presence of many typical "Avalonian" taxa in the Iranian Mid-Late Cambrian assemblages would suggest a closer position of Iran to Avalonia than currently envisaged. The observed breakdown of acritarch biogeographic differentiation in earliest Ordovician times possibly represents a major disruption of oceanic current patterns and a lessened palace latitudinal thermal gradient. (c) 2008 Elsevier B.V. All rights reserved
Latest Ordovician-early Silurian chitinozoans from the eastern Alborz Mountain Range, Kopet-Dagh region, northeastern Iran: biostratigraphy and palaeobiogeography
No full textChitinozoans were extracted from latest Ordovician to early Silurian strata in the Alborz Mountain Range, northeastern Iran; 24 species were identified and six local biozones established. Five new chitinozoan species are described: Ancyrochitina bqjnourdensis, AnciTochitinafatemae, Ancyrochitina longifilosa, Angochitina iranica, and Angoehitina multipodspina. Correlation with existing formal biozonations suggests that the uppermost part of the Ghelli Formation is of mid-Ashgill age and that Member I of the Niur Formation ranges from early Rhuddanian to late Telychian. The recovered chitinozoan fauna is dominated by species which are endemic to the study area. A significant proportion of taxa is shared with typical Baltican assemblages, suggesting palaeobiogeographical affinities between Iran and the Baltica palaeocontinent. Taxa shared with typical North Gondwanan assemblages are only a minor component of the Iranian chitinozoan fauna. The present results confirm previous observations that current appreciation of chitinozoan provincialism may be affected by sample-and (palaeo)geographic coverage biases, particularly for the Silurian. Similarly, the application of existing biostratigraphic schemes for the dating of the Iranian Silurian sediments proved problematical, confirrriing the need of incorporating more data from little known areas (such as Iran) in global databases. (c) 2006 Published by Elsevier B.V
Palynology and isotope geochronology of the Upper Ordovician-Silurian successions (Ghelli and Soltan Maidan Formations) in the Khoshyeilagh area, eastern Alborz Range, northern Iran; stratigraphic and palaeogeographic implications
No full textSurface samples from the Ghelli and Soltan Maidan Formations in the Khoshyeilagh area of the eastern Alborz Range, northern Iran, were analyzed to determine the age and the stratigraphic relationship of these two units. The samples contained rich palynomorph assemblages, dominated by acritarchs (36 species recognized, distributed among 28 genera) and chitinozoans (nine species identified, distributed among seven genera). Cryptospores and scolecodonts as well as a few graptolite remains were also observed, although not studied in detail. Based on the restricted stratigraphic range of chitinozoan and acritarch species, a Late Ordovician (late Katian-Hirnantian) age is assigned to the Ghelli Formation. Palynological samples from the Soltan Maidan Formation yielded acritarch assemblages characterized by species commonly found in Upper Ordovician sediments together with typical middle Silurian forms. Considering reworking of the Upper Ordovician species, the age of the investigated part of the Soltan Maidan Formation is not younger than Gorstian (early Ludlow, early late Silurian). U-Pb zircon ages of 434.4 +/- 6.4 Ma (Telychian, late Llandovery, late early Silurian) obtained for granitic clasts collected at the base of the Soltan Maidan Formation, are consistent with the inferred palynological age and indicate that granite emplacement, cooling, exhumation, erosion, transportation and deposition of its clasts took place in a time interval estimated to be 5 to 10 million year long. Based on the presence of diagnostic chitinozoan taxa, the Ghelli Formation can be assigned to the Armoricochitina nigerica, Ancyrochitina merga, and Spinachitina oulebsiri chitinozoan biozones. Chitinozoan assemblages reflect a clear palaeobiogeographic affinity with the previously defined 'North Gondwana Domain'. The composition of acritarch assemblages also appears to be consistent with newly proposed hypotheses of a Late Ordovician phytoplanktonic biogeographical differentiation between a Laurentian/Baltica realm, and a Gondwanan realm to which the present assemblages belong. The presence of cryptospores together with taxonomically diverse chitinozoan, acritarch, and scolecodont assemblages, suggest a relatively shallow marine, platformal depositional environment for the Ghelli Formation. (C) 2011 Elsevier B.V. All rights reserved
Miospore assemblages from Late Ordovician (Katian-Hirnantian), Ghelli Formation, Alborz Mountain Range North-eastern Iran: Palaeophytogeographic and palaeoclimatic implications
Get PDFWell-preserved miospore assemblages are recorded from the Late Ordovician (Katian-Hirnantian), Ghelli Formation in Pelmis-gorge at the north-eastern Alborz Mountain The palynomorphs were extracted from siliciclastic deposits which are well-dated by using of marine palynomorphs (acritarchs and chitinozoans). The encountered miospore assemblages consist of 14 genera (28 species: 26 cryptospores and 2 trilete spores). Six new cryptospore taxa are described: Rimosotetras punctata, Rimosotetras granulata, Dyadospora asymmetrica, Dyadospora verrucata, Segestrespora iranense and Imperfectotriletes persianense. The present findings contribute to improving knowledge of origin and onset of development of vegetative cover during the Late Ordovician. The recovery of diverse and abundant cryptospores in the Late Ordovician (Katian-Hirnantian) Ghelli Formation are probably related to increasing input of land-derived sediments during the global sea-level fall linked to the Late Ordovician glaciation, and tolerance of the primitive land plants in a wide range of climatic conditions. These miospore taxa were produced by earliest primitive land plants which probably grew close to the shoreline and washed in from the adjacent areas and produced high amount of miospores. The associated marine palynomorphs consist of acritarchs (13 genera and 18 species), chitinozoans (9 genera and 10 species), prasinophycean algae, scolecodonts and graptolite remains which are not discussed in detail herein. The established chitinozoan biozones of this part of Palaeozoic sequences are Armoricochitina nigerica, Ancyrochitina merga, Tanuchitina elongata and Spinachitina oulebsiri, suggesting the Late Ordovician (Katian-Hirnantian). These chitinozoan biozones are well-known only in peri-Gondwanan Domain, indicating that the study area has been part of this palaeo-continent during the Late Ordovician
Biostratigraphy of Acritarchs and Chitinozoans in Ordovician Strata from the Fazel Abad Area, Southeastern Caspian Sea, Alborz Mountains, Northern Iran: Stratigraphic Implications
Get PDFSixty-four surface samples from the Lower Palaeozoic rock units (mainly Lalun,Abastu and Abarsaj formations) near Kholin-Darreh village in the Fazel Abad area,southeastern the Caspian Sea, Northern Iran, were analyzed to determine their agerelationships. The samples of Lalun Formation were barren, but those of Abastu andAbarsaj formations contained well-preserved and abundant palynomorph entities, whichare dominated by acritarchs (23 species belonging to 15 genera) and chitinozoans (29species distributing among 15 genera) with remains of scolecodonts, graptolite and afew cryptospores, although not determined in detail. Based on the restricted stratigraphicrange of acritarch species, an Early Ordovician (Tremadocian) age was assigned to theAbastu Formation; while based upon index chitinozoan and acritarch taxa, a LateOrdovician (Katian to Hirnantian) age was assigned to the Abarsaj Formation. Likewise,based on the presence of diagnostic chitinozoan taxa, the Abarsaj Formation can beassigned to the Armoricochitina nigerica, Ancyrochitina merga, Tanuchitina elongataand Spinachitina oulebsiri chitinozoan Biozones. These chitinozoan assemblages reflecta clear palaeobiogeographic affinity with the so-called "North Gondwana Domain".Two major hiata are present within the studied Lower Palaeozoic succession in the FazelAbad area. The first hiatus appeared between the Lalun Formation (Early Cambrian) andthe Abastu Formation (Tremadocian) and includes the Middle-Upper Cambrian MilaFormation. The second hiatus occurs between the Abastu Formation (Tremadocian) andthe Abarsaj Formation (Katian-Hirnantian) and spans the interval of the Floian-Sandbian, which corresponds to uplift related to the initial stage of rifting of the Palaeo-Tethys Ocean
Palynostratigraphy, Palaeogeography and Source Rock Evaluation of the Nayband Formation at the Parvadeh area, Central Iran, Iran
Get PDFThe Nayband Formation was measured and sampled in Parvadeh area, southern Tabas city. In this area, this formation has a thickness of 1410 m, dividing into four members, namely Gelkan, Bidestan, Howz-e-sheikh and Howz-e-khan. A total 573 samples were treated for Palynological analysis, and only 120 samples were productive. A total of 57 miospore taxa and 11 plant macrofossil were encountered. Based on stratigraphic distribution of macrofossil and miospore taxa ten assemblage zones were established throughout the Nayband Formation. The encountered miospore taxa and plant macrofossil suggest Upper Triassic (Norian-Rhaetian) for the Nayband Formation.Rock-Eval data shows the presence of organic matter-rich shales with Type III kerogen. The Nayband Formation in the studied section has experienced high temperature which is confirmed by vitrinite reflectance measurements of 0.9-1.2 %VRr. At this thermal maturity stage, organic-rich shales in the formation have generated liquid hydrocarbons as evidenced by the occurrence of solid bitumen in the respective samples
Chronostratigrahy of Acritarchs and Chitinozoans from upper Ordovician Strata from the Robat-e Gharabil Area, NE Alborz Mountains, Northern Khorassan Province: Stratigraphic and Paleogeographic Implications
Get PDFThe Palaeozoic rock units mainly, Ghelli, Niur, Padeha, Khoshyeilagh and Mobark formations are well-exposed in the north of Robat-e Gharabil village. 116 out of 157 surface samples were analyzed to determine aged relationships of Ghelli Formation. The samples of Ghelli Formation are dominated by acritarchs (42 species belonging to 23 genera) and chitinozoans (26 species distributing among 15 genera). Two new acritarch species are introduced, consisting of Goniosphaeridium iranense n.sp., and Goniosphaeridium persianense n. sp. Based on the restricted stratigraphic range of chitinozoan species, Late Ordovician (Ashgill) age is assigned to the Ghelli Formation. On the other hand, the presence of diagnostic chitinozoan taxa in the Ghelli Formation consisting of Armoricochitina nigerica, Ancyrochitina merga, and Spinachitina oulebsiri chitinozoan biozones, suggest a clear palaeobiogeographic affinity between NE Alborz Mountain and North Gondwana Domain. The presence of some chitinozoan and acritarch taxa from the Baltic and Laurentia in Gondwanan chitinozoan biozones of the Robat-e Gharabil area suggests the existence of counter-clockwise marine currents that resulted in bringing planktonic organisms (acritarchs and chitinozoans) from lower latitudes (Baltica) to higher latitudes (Northern Gondwanan Domain) settings
Comparison of variations in sediment accumulation rates of the upper part of Zakeen Formation through cyclostratigraphic study in 2SK-1 and 2SKD-1 wells in Salman gas field
Get PDFAbstract The Zakeen Formation is one of the possible gas reservoirs in the Zagros sedimentary basin. In this paper, the cyclostratigraphic study of the upper part of the Zakeen Formation was performed by using evolutionary spectral analysis methods. The Multi-Tapper Method (MTM) periodogram is one of the evolutionary spectral analysis methods used in this study to identify and prove the frequency ratios of Milankovitch cycles in the studied sediment sequences. In this study, using the introduced methodology, the frequency ratios of the Milankovitch cycles in the upper part of the Zakeen Formation was identified for the first time, and their existence was confirmed. Besides, the spectral powers of spectral gamma-ray (SGR) and density (RHOB) series, in evolutionary Fast Fourier Transform (FFT) and Wavelet Transform (WT) Scalograms, in 2SK-1 and 2SKD-1 wells of Salman gas field show strong astronomical signals of the Milankovitch cycles (E, e, O, P). After investigating the cyclostratigraphy of the upper part of the Zakeen Formation in the studied wells, by using new methods of evolutionary correlation coefficient and evolutionary significance levels, comparison of sediment accumulation rate variations of the Zakeen Formation was performed in the studied wells. Keywords: Cyclostratigraphy, Sediment accumulation rate, Milankovitch cycles, Zakeen Formation, Salman gas field Introduction The Zakeen Formation is a clastic succession and in its type section at Faraghan Mountains, north Bandar-Abbas, has 285 m thickness. It is composed of sandstones, shales, and with several dolostones horizons (Ghavidel-Syooki 1999). The Zakeen Formation, based on palynological studies by Ghavidel-Syooki (1999 & 2003), is attributed to the early to late Devonian (Lochkuvian to Frasnian). In this study, only the Frasnian sequence of the upper part of the Zakeen Formation in 2SK-1 and 2SKD-1 wells of the Salman gas field was studied. Cyclostratigraphic studies were also focused primarily on proving the existence of Milankovitch cycles in sedimentary sequences, determining timelines, calculating sediment accumulation rates and stratigraphic classifications (Zheng & Luo 2004; Li et al. 2018a; Chen et al. 2019). To compare the sediment accumulation rates of the upper part of the Zakeen Formation in the studied wells, cyclostratigraphy study was first performed to show the existence of the Milankovitch cycles and the way they affect the upper part of the Zakeen Formation. The spectral analysis methods together with density and spectral gamma-ray logs data were used to study the cyclostratigraphy of the studied formation. Milankovitch (Serbian scientist) has calculated the duration of the three main parameters of the Earth's orbit around the sun that affect global climate change, known as eccentricity, obliquity, and precession, and these are referred to Milankovitch cycles (Milankovitch 1941; Fletcher 2013). Cyclostratigraphy of the Devonian system in the different parts of Earth including southern China (Gong et al. 2001; Chen & Tucker 2003; De Vleeschouwer et al. 2017), France, Morocco (Ellwood et al. 2011), Canada (De Vleeschouwer et al. 2012; De Vleeschouwer et al. 2017), Poland (De Vleeschouwer et al. 2013, 2017), Belgium (De Vleeschouwer et al. 2014, 2017), USA (De Vleeschouwer et al. 2017; Pas et al. 2018) and varying frequencies of Milankovitch cycles from the deposits of these areas have been reported. The purpose of this study is to analyze cyclostratigraphy and compare the sediment accumulation rates of the upper part of the Zakeen Formation in 2SK-1 and 2SKD-1 wells of the Salman gas field. Material & Methods In this paper, by using evolutionary spectral analysis techniques (FFT spectrogram and WT scalogram) and MTM periodogram in a series of digital signal processing methods in Acycle v2.0 software (Li et al. 2018a), time series were extracted from SGR and RHOB logs. Afterward, their spectral powers were used in the cyclostratigraphic analysis of the upper part of the Zakeen Formation. Milankovitch cycles recorded in the upper part of Zakeen Formation were identified using a set of evolutionary spectral analysis methods for the desired logs including MTM and subsequently analyzed in the FFT Spectrogram (Kodama and Hinnov 2015). The influence of such cycles on sedimentation of the upper part of the Zakeen Formation and their abundance in this formation at different depths from the two studied wells were studied. The WT scalogram is then used to compare statistically significant zones between time series (Grinsted et al. 2004). The frequency ratio method (Mayer & Appel 1999) was used to establish the link between the cycles identified in the sedimentary signals and the theoretical astronomical parameters. After identifying the Milankovitch cycles in MTM periodograms, they were then extracted from the SGR logs by filtering the cycles of 405 kyr (E), 100 kyr (e), 34.4 kyr (O) and 21.3 kyr (P). Subsequently, confidence levels with median, 90, 95, 99% levels were plotted for each MTM periodogram and almost all cycles were sampled from the median confidence level and some above 90%. Through performing MTM periodograms, Milankovitch cycles were detected. Also, by using FFT spectrograms (reviewed by Hinnov), their influence on deposition of the upper part of Zakeen Formation and their abundance were labeled. Through the extraction of WT scalograms, high statistical significance zones were compared (correlation against E, e, O, and P cycle filters) to find the main lithological changes, probabilistically. Finally, cyclostratigraphic results in two studied wells were investigated. Moreover, sediment accumulation rates of the upper part of the Zakeen Formation in two studied wells (2SK-1 and 2SKD-1) were estimated. Through applying evolutionary correlation coefficients and evolutionary significance levels of spectral analysis methods for the SGR logs in both wells, estimates of sediment accumulation rates of the upper part of Zakeen Formation was precisely carried out. Discussion of Results & Conclusions Through plotted MTM periodograms for each well logs, the cycles ratio were identified in well 2SK-1 based on SGR MTM periodogram as 18.03, 5.63, 3.6, 2.39, 2.08, 1.58, 1.2, while with refer to RHOB MTM periodogram they are 20.8, 7.11, 4.0, 2.33, 2.0, 1.48, 1.33. This is close to the ratio of 20:5:2:1 cycles (from left to right we have the component ratio of the cycles E, e, O, and P). In contrast, in the MTM periodogram plotted for the SGR log, the ratios are 18.24, 6.08, 3.78, 2.87, 2.38, 1.55, while in MTM periodogram plotted for the RHOB log, ratios of 19.38, 6.45, 4.43, 3.6, 2.62, 2.16, 1.83, 1.49 were obtained. All ratios in two wells, being approximately equal to 20:5:2:1 and thus the relative ratios, each based on their value, are interpreted as one of the Milankovitch cycles (E or e or O or P). In this study, by evolutionary spectral analysis methods including MTM periodograms, FFT spectrograms, and WT scalograms, cyclostratigraphy study of the upper part of the Zakeen Formation were performed in 2SK-1 and 2SKD-1 wells of Salman gas field. Evaluation of sediment accumulation rates of the upper part of Zakeen Formation in these two wells was performed with evolutionary correlation coefficients and evolutionary significance levels. This allows them to be observed in the stratigraphic domain alongside the well log data. Based on FFT spectrograms in 2SK-1 well, three cycles including E, e and O have more effect on the sedimentation rate of the upper part of the Zakeen Formation. In 2SKD-1 well such an effect is due to four cycles comprising of E, e, O and P. Subsequent analyses by the evolutionary correlation coefficient spectrogram plotted for the SGR log in 2SK-1 well revealed that only the E cycle affected the deposition of the upper part of the Zakeen Formation. The evolutionary correlation coefficient plotted for SGR log in 2SKD-1 well also confirmed the effect of E and O cycles on the deposition of Zakeen Formation. Other cycles with low impact on cyclic sedimentation of the upper part of the Zakeen Formation have been involved in these two wells. Sediment accumulation rates of the upper part of Zakeen Formation were estimated by time columns from cyclostratigraphy and thickness of the upper part of the Zakeen Formation for both wells by approximately 0.8 cm per thousand years. Subsequently, through the analysis of evolutionary correlation coefficients plotted for SGR logs, it was determined that sediment accumulation rates of the upper part of the Zakeen Formation in 2SK-1 wells show ascending, constant and descending trends. In contrast, in the 2SKD-1 well, sediment accumulation rates have been almost constant. In general, the sediment accumulation rates of the upper part of Zakeen Formation in 2SK-1 well are estimated more compared to 2SKD-1 well. Also, large variations in sediment accumulation rates of the upper part of the Zakeen Formation were observed in the 2SK-1 well compared to the 2SKD-1 well, indicating the occurrence of hidden effective processes for these changes
Ordovician conodonts of the Katkoyeh formation in the Kuh-e-Bonorg section, Kalmard Horst (west of Tabas)
Get PDFAbstract In this research, Ordovician conodonts obtained from the sedimentary succession of the informal Katkoyeh formation is studied in a stratigraphic section at the south of Kuh-e-Bonorg, eastern flank of Kalmard Anticline in the west of Tabas (Central Iran). The formation which is partly equivalent to the succession of the Shirgesht Formation in Tabas Block is unconformably overlaid the Kalmard Formation (attributed to the Neoproterozoic) and disconformably overlain by the Carboniferous Gachal formation. The Katkoyeh formation with 214.8 meter thickness is divided into three lithostratigraphic members including the Lower Sandstone (mostly quartzarenite to litharenite), Middle Shale (red to green shales interbedded with some dolomitic and calcareous sandstones, in laminated wavy stromatolite structure at the base) and Upper Carbonate (limestones, dolostones and marls). The section was sampled bed by bed for conodont studies so that 80 samples have been selected, however only seven of them were productive. Within the selected samples, six genera and 14 species of coniform and ramiform conodont elements are determined, a few of them are reporting for the first time from Iran. The obtained conodonts demonstrate the faunal assemblages equal to the proteus, elegans-evae and diprion Zones which confirm the age of Early Ordovician (late Tremadocian–Floian) for the studied section. The whole conodont material display a faunal affinity with the Baltoscandic and Argentina paleobiogeographic provinces. Keywords: Conodont, Floian, Katkoyeh formation, Ordovician, Tremadocian. Introduction In spite of the moderately -exposed outcrops of the Ordovician successions throughout the country, most of the stratigraphical studies in Iran are focused on Alborz Range (e.g.; Gansser and Huber 1962, Muller 1973, Ghavidel-Syooki 2006, Ghobadi Pour et al. 2007, 2011; Jahangir et al. 2016) and the appropriate data from the other regions are restricted to a few published reports (e.g.; Ruttner et al. 1968, Aghanabati 1977, Hamedi 1995, Ghaderi et al. 2008). Especially our knowledge is very little about the conodont contents of the Ordovician rocks in Iran. The Ordovician sedimentary succession in the north of Tabas in central Iran have been introduced as the Shirgesht Formation by Ruttner et al. (1968). The rock sequences of this formation composed of brown, cream, and green to red limestones, shales and partly sandstones with hardly more than 800 m in thickness (Ghobadi Pour et al. 2006). Lithostratigraphically, the Ordovician sedimentary interval in adjacent Kalmard Block (Aghanabati 2010) is different, includes more siliciclastic rocks somewhat carbonate beds in upper part. These succession has been considered as the Katkoyeh formation by Hamedi and Wright (1992). The less known Katkoyeh formation as an informal stratigraphic rock unit in central Iran has been regarded to Arenigian to Ashgillian in the type area in Kerman region, but the age of the formation in the Kalmard type region is dissimilar in different studies. In the current research we have looked for the succession Katkoyeh formation in a section at the south of Kuh-e-Bonorg, eastern flank of the Kalmard anticline, from the age dating view, based on the conodont contents. Material & Methods In the Kuh-e-Bonorg section, 80 rock samples were collected bed by bed for conodont content while only seven of them were productive. For this purpose, sandy limestones, dolomitic limestones and pure limestones with about 3–5 kg were dissolved by 10% formic acid and 20% acetic acid following the standard procedure for conodont extraction (e.g., Jeppsson & Anehus, 1995). Residue washed on appropriate clean 18 and 230 mesh sieve-stack (0.85 to 0.063 mm). The extracted conodont collections stored in the Ferdowsi University of Mashhad, Iran under the collection name with the FUM#MC prefix. Discussion of Results & Conclusions The Katkoyeh formation in the south of Kuh-e-Bonorg section is unconformably overlaid the Neoproterozoic rocks attributed to the Kalmard Formation and disconformably overlain by the Carboniferous Gachal formation. The Katkoyeh formation of 214.8 meter thickness in the studied area is divided into three members such as the Lower Sandstone (mostly quartzarenite to litharenite), Middle Shale (red to green shale interbedded with some dolomitic and calcareous sandstone, in laminated wavy stromatolite structure at the base) and Upper Carbonate (limestones, dolostones and marls). Among the seven fossiliferous beds, we obtained the index conodonts of Lower Ordovician which belong to six genera and 14 species of coniform and ramiform elements. The assemblage is correlative with the same collections from the Baltoscandic and Argentina paleobiogeographic provinces (e.g.; Mannik and Virra 2012; Voldman et al. 2017). The distribution of taxa in the stratigraphic succession is variable, in abundance of elements as well as in the number of taxa. The oldest conodonts in the section, Drepanodus arcuatus and Drepanoistodus costatus, come from the dolostones and dolomitic limestones of uppermost Tremadocian-early Floian proteus Zone (equivalent to Acodus apex Zone in NW Argentina Province) the sample MC208B. The next fossiliferous bed, MC232, comprises Acodus triangularis, Acodus cf. deltatus, Drepanoistodus cf. nowlani, Drepanoistodus cf. bassiovalis, Drepanoistodus bassiovalis and Gothodus costalatus which confirm Floian elegans - evae Zones (equivalent to Gothodus vetus–Gothodus andinus Zones in NW Argentina Province). The last productive beds, MC263–MC265, contain Trapezognathus diprion as the index taxon for upper evae Zone (equivalent to Trapezognathus diprion Zone in NW Argentina Province). This species confirm the age of late Floian for the uppermost part of the Katkoyeh formation in the Kuh-e-Bonorg section
The palynology and stratigraphy of the Cambrian Nolichucky Shale and associated formations at Thorn Hill, Tennessee, USA
Get PDFA detailed palynological and stratigraphic study was undertaken on the Cambrian Nolichucky Shale, Maynardville Limestone and Copper Ridge Dolomite (Conasauga Group), as exposed at Thorn Hill, northeastern Tennessee, USA. The majority of palynological samples show low abundance and diversity. Fifty two acritarch taxa (fifteen assigned to species; twenty six left in open nomenclature; eleven new forms), two problematica and four invertebrate components are described. Based upon trilobite biostratigraphy and stable carbon isotope chemostratigraphy, the stratigraphic position of the Cambrian Series 3/Furongian (Marjuman/Steptoean; Aphelaspis Zone/Crepicephalus Zone) boundary is broadly indentified within the uppermost section of the Nolichucky Shale. The first record of SPICE identified using organic residues is also reported, the onset of which is coincident with the Aphelaspis Zone/Crepicephalus Zone boundary). Recovered acritarchs have little immediate, comparative, stratigraphic value but some forms (Acritarch sp. 1 and Acritarch sp. 2) may have future potential use as biostratigraphic markers for shallow marine upper Cambrian Series 3 units. Palynofacies data and sedimentology indicate that the acritarch abundance peak in the Nolichucky Shale may represent maximum water depth within a transgressive/regressive cycle. Based on TEM analysis of vesicle wall ultrastructure, Peteinosphaeridium? sp. 1, Peteinosphaeridium? sp. 2, and Acritarch sp. 2 are interpreted as belonging to the Class Chlorophyceae. The vesicle wall ultrastructure of Acritarch sp. 1 is trilaminar, consisting of a central alveolar layer bounded by two, thin, electron dense layers and is comparable to that of diapause egg cases of extant branchiopods. Based upon wall ultrastructure, vesicle size and surface ornament, recalcitrant wall biochemistry and evidence of co-occurrence of branchiopod-type crustaceans, Acritarch sp. 1 is interpreted as being the egg case of a Cambrian branchiopod-type crustacean, and as such represents the earliest evidence for diapause-type dormancy in the fossil record
