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1
Mel’nikov, N. V. "The Vendian–Cambrian Cyclometric Stratigraphic Scale for the Southern and Central Siberian Platform". Russian Geology and Geophysics 62, n. 08 (1 agosto 2021): 904–13. http://dx.doi.org/10.2113/rgg20214339.
Testo completoAbstract (sommario):
Abstract —The general Vendian stratigraphic scale of Siberia, with the uncertain age of the Vendian base ranging from 600 to 630– 640 Ma in most of recent publications, remains worse constrained than the Cambrian scale, in which the boundaries of epochs and stages have been well defined. However, the imperfect classical stratigraphic division has been compensated by data on the cyclicity of the Vendian–Cambrian sedimentary section. The Vendian stratigraphy of the Siberian Platform and the related deposition history with cycles of sedimentation and gaps, as well as the hierarchy of sedimentation processes, can be inferred from the succession of alternating clastic, carbonate, and salt units. The cyclicity of geologic processes and their recurrence are attributed to periodic oscillatory motions of the crust. The ranks of these motions correlate with the cyclicity of sedimentary strata, including regocyclites, nexocyclites, and halcyclites separated by gaps. Each Vendian long-period oscillatory motion begins with a regocyclite and ends with a regional-scale gap. The Cambrian section includes one pre-Mayan regional gap at the end of the early Cambrian long-period cycle. Cambrian regocyclites are composed of carbonate subformations and formations in the lower part and alternating salt and carbonate beds in the upper part.
2
Idrissi, Assia, Mohamed Saadi, Yassir Astati, Ali Bouayachi e Kawtar Benyas. "Mapping of Genetic Sequences of the Cambrian Series in the Jbel Saghro Massif, Eastern Anti-Atlas, Morocco: Implications for Eustatic and Tectonic Controls". Iraqi Geological Journal 55, n. 1D (30 aprile 2022): 1–20. http://dx.doi.org/10.46717/igj.55.1d.1ms-2022-04-17.
Testo completoAbstract (sommario):
In this paper, a sedimentological and sequence stratigraphy analysis was performed on Lower and Middle Cambrian deposits of Jbel Saghro, Eastern Anti-Atlas. The field data analysis and the application of sequence stratigraphy concepts were used to classify sedimentary processes and depositional environment, and to define the Lower to Middle Cambrian basin’s detailed geometry. The Cambrian sedimentation of northeastern Saghro indicates a deltaic environment, which is composed of two depositional sequences. These sequences are made of a transgressive system-tract with retrograding sediments and a highstand system tract with prograding sediments. In response to sea-level change, these system-tracts were formed by several genetic units, and limited by various stratigraphic surfaces. The genetic unit stacking-patterns combined with the study of synsedimentary tectonics enabled to follow the sedimentary record’s Spatio-temporal evolution and its three-dimensional geometry. The study area deposits display significant dissimilarities in thickness. The western part shows a Lower Cambrian hiatus and an important reduction of the thickness in the Middle Cambrian deposits. However, the marine trend (progradation/retrogradation) remains similar in the study area. This suggests the same eustatic origin of all genetic sequences and variations in their preservation rate. This configuration is the result of differential subsidence that affected the Anti-Atlas during the Cambrian.
3
Sennikov, N. V., O. T. Obut, N. G. Izokh, A. V. Timokhin, Yu F. Filippov, T. P. Kipriyanova, E. V. Lykova et al. "THE REGIONAL STRATIGRAPHIC CHART FOR THE ORDOVICIAN OF THE WEST SIBERIAN LOWLAND". Geology and mineral resources of Siberia, n. 3 (2023): 3–39. http://dx.doi.org/10.20403/2078-0575-2023-3-3-39.
Testo completoAbstract (sommario):
A new version of the Regional stratigraphic chart for the Ordovician of the West Siberian Lowland and the explanatory note, compiled in accordance with the Russian Stratigraphic Code, introduce changes, additional and specified data in comparison with the previous (first edition) chart. Since 1998, the stages of the Ordovician chart were changed completely. New stages – Tremadocian, Floian, Dapingian, Darriwilian, Sandbian, Katian and Hirnantian were adopted by Interdepartmental Stratigraphic Committee of Russia. The independent Regional Stratigraphic Scheme for the Devonian of the West Siberian Lowland and the Regional Stratigraphic Scheme for the Cambrian of the Pre-Yenisei Part of West Siberian Lowland were adopted. The proposed scheme for the Ordovician of West Siberian Lowland fills the lower part of the Ordovician-Silurian interval for the West Siberia. New paleontological, stratigraphical, lithological, seismo-stratigraphical data for the Ordovician of the West Siberian Lowland were obtained and generalized. For the first time independent Regional stratigraphic chart for the Ordovician of the West Siberian Lowland was compiled.
4
Myrow, P. M., N. C. Hughes e N. R. McKenzie. "Reconstructing the Himalayan margin prior to collision with Asia: Proterozoic and lower Paleozoic geology and its implications for Cenozoic tectonics". Geological Society, London, Special Publications 483, n. 1 (21 novembre 2018): 39–64. http://dx.doi.org/10.1144/sp483.10.
Testo completoAbstract (sommario):
AbstractReconstructing the stratigraphic architecture of deposits prior to Cenozoic Himalayan uplift is critical for unravelling the structural, metamorphic, depositional and erosional history of the orogen. The nature and distribution of Proterozoic and lower Paleozoic strata have helped elucidate the relationship between lithotectonic zones, as well as the geometries of major bounding faults. Stratigraphic and geochronological work has revealed a uniform and widespread pattern of Paleoproterozoic strata >1.6 Ga that are unconformably overlain by <1.1 Ga rocks. The overlying Neoproterozoic strata record marine sedimentation, including a Cryogenian diamictite, a well-developed carbonate platform succession and condensed fossiliferous Precambrian–Cambrian boundary strata. Palaeontological study of Cambrian units permits correlation from the Indian craton through three Himalayan lithotectonic zones to a precision of within a few million years. Detailed sedimentological and stratigraphic analysis shows the differentiation of a proximal realm of relatively condensed, nearshore, evaporite-rich units to the south and a distal realm of thick, deltaic deposits to the north. Thus, Neoproterozoic and Cambrian strata blanketed the northern Indian craton with an extensive, northward-deepening, succession. Today, these rocks are absent from parts of the inner Lesser Himalaya, and the uplift and erosion of these proximal facies explains a marked change in global seawater isotopic chemistry at 16 Ma.
5
Anderson, Donna, e Mark Longman. "Subsurface Reinterpretation of Ordovician and Devonian Strata in Southwest Wyoming with Implications for Upwarping Across the Transcontinental Arch". Mountain Geologist 55, n. 3 (luglio 2018): 91–118. http://dx.doi.org/10.31582/rmag.mg.55.3.91.
Testo completoAbstract (sommario):
A new interpretation of the subsurface geometries of the Ordovician Bighorn Dolomite and overlying Devonian strata across southwestern Wyoming arises from revising the stratigraphy in a core from the Mountain Fuel Supply UPRR #11–19–104–4 well drilled on the crest of the Rock Springs Uplift in 1962. One of only a few wells to penetrate all or part of the Lower Paleozoic succession in the subsurface of southwestern Wyoming, the well was almost continuously cored through the Devonian–Cambrian succession. From a reinterpretation of the stratigraphy in the core, 22 ft of Bighorn Dolomite is recognized based on the characteristic Thalassinoides bioturbation fabric in skeletal dolowackestone typical of Late Ordovician subtidal carbonate facies ranging from Nevada to Greenland along the western margin of the Great American Carbonate Bank. This lithology is in complete contrast with the alternating dolomitic flat-pebble conglomerate and dolomudstone of the underlying Cambrian Gallatin Limestone and the cyclical units of brecciated anhydritic dolomudstone and quartzose sandstone of the overlying Devonian Lower Member of the Jefferson Formation. Stratigraphic re-interpretation yields insights regarding Ordovician–Devonian stratal geometries across southwestern Wyoming. More widespread than previously portrayed, the Bighorn Dolomite pinches out on the eastern flank of the Rock Springs Uplift. Similar to past interpretations, Devonian strata pinch out east of the Rock Springs Uplift at Table Rock Field. A true-geometry multi-datumed stratigraphic cross section yields insights not obtainable by mapping. Regionally, top truncation of stratigraphic units below the base-Madison Limestone unconformity normally progresses stratigraphically deeper eastward. However, in southwestern Wyoming, the Devonian Lower Member of the Jefferson Formation overlaps the older Bighorn Dolomite by marked onlap across the Rock Springs Uplift and then pinches out by top truncation/onlap near Table Rock Field, forming an “abnormal” overlap relationship along the northern margin of the Transcontinental Arch. The underlying Bighorn Dolomite shows little to no onlap onto the underlying Cambrian section, but is markedly top truncated below the Lower Member of the Jefferson Formation. Comparing proportions of onlap versus top truncation for the two formations constrains the timing of two successive upwarping episodes along the northern margin of the Transcontinental Arch across southwestern Wyoming. The first is arguably Middle Devonian, and the second spans the Devonian–Mississippian boundary. Two subtle and different angular unconformities created by these two episodes imply a persistent fold or tilt axis that sequentially was reactivated along the northern margin of the Transcontinental Arch in southwestern Wyoming.
6
Elicki, Olaf, e Gerd Geyer. "The Cambrian trilobites of Jordan – taxonomy, systematic and stratigraphic significance". Acta Geologica Polonica 63, n. 1 (1 marzo 2013): 1–56. http://dx.doi.org/10.2478/agp-2013-0001.
Testo completoAbstract (sommario):
Abstract Elicki, O. and Geyer, G. 2013. The Cambrian trilobites of Jordan - taxonomy, systematic and stratigraphic significance. Acta Geologica Polonica, 63(1), 1-56. Warszawa. Marine carbonates and siliciclastic rocks of the Burj Formation in Jordan include paucispecific trilobite associations of the (traditional) Lower-Middle Cambrian boundary interval. Comprehensive new material of these trilobites allows a review of their taxonomy and systematic positions as well as a refined morphological description and a reconsideration of previous interpretations of their stratigraphic position and thus the correlation of the fossiliferous beds. In addition to the classic species Kingaspis campbelli (King, 1923) and Redlichops blanckenhorni Richter and Richter, 1941, Timnaella? orientalis (Picard, 1942) and Hesa problematica Richter and Richter, 1941, the discussed trilobites include Issalia gen. nov. with Issalia scutalis gen. nov., sp. nov., Tayanaspis gen. nov. with Tayanaspis bulbosus gen. nov., sp. nov., Uhaymiria gen. nov. with Uhaymiria glabra gen. nov., sp. nov., Cambrunicornia ? jafnaensis sp. nov., Myopsolenites palmeri (Parnes, 1971), M. hyperion sp. nov., and Enixus cf. antiquus (Chernysheva, 1956). Myopsolenites boutiouiti Geyer and Landing, 2004 is now regarded as a junior synonym of Myopsolenites altus (Linan and Gozalo, 1986). A detailed discussion of the correlation with a focus on global aspects provides clues for the utility of potential index fossils for the global Cambrian Series 3 and Stage 5.
7
Jie-Dong, Yang, Sun Wei-Guo, Wang Zong-Zhe e Wang Yin-Xi. "Sm—Nd isotopic age of Precambrian—Cambrian boundary in China". Geological Magazine 133, n. 1 (gennaio 1996): 53–61. http://dx.doi.org/10.1017/s001675680000724x.
Testo completoAbstract (sommario):
AbstractBy the new method of Sm—Nd isotopic dating on phosphatic small skeletal fossils and collo-phanite minerals, the Zhongyicun Member of the earliest Cambrian Meishucun Stage at Meishucun in Yunnan, southern China, has been dated at 562.8 ± 7.9 Ma and 562.1 ± 5.7 Ma. Another Sm—Nd age, 570.3 ± 17.1 Ma, has been obtained with samples from the Zhongyicun Member in Yunnan and its stratigraphic equivalents in Sichuan and Xinjiang. These data tend to suggest that the best age estimate of the Precambrian—Cambrian boundary is very likely within the range of 560–570 Ma. As biophosphates and sedimentary phosphates are widely distributed in sequences of the Precambrian—Cambrian transition, the Sm-Nd isotopic method is recommended as an effective approach for precise dating of the initial Cambrian boundary.
8
Kontorovich, A. E., A. I. Varlamov, A. S. Efimov, V. A. Kontorovich, I. V. Korovnikov, V. A. Krinin, S. V. Saraev, N. V. Sennikov e Yu F. Filippov. "Stratigraphic Scheme of Cambrian Deposits, South of the Cis-Yenisei Area of West Siberia". Russian Geology and Geophysics 62, n. 03 (1 marzo 2021): 357–76. http://dx.doi.org/10.2113/rgg20204317.
Testo completoAbstract (sommario):
Abstract ––In this paper we present a stratigraphic scheme for the subdivision and correlation of the Cambrian deposits in the south of the cis-Yenisei area of West Siberia, which was adopted as a current scheme by the decision of the Interdepartmental Stratigraphic Committee in 2018. This scheme is based on the data from stratigraphic test wells (Lemok-1, Averinskaya-150, Tyiskaya-1, Vostok-1, Vostok-3, Vostok-4, etс.). In the study area, two structure-facies zones were identified: Kas (Lemok-1, Averinskaya-150, Tyiskaya-1, Vostok-4, and Eloguiskaya-1 wells), where sedimentary complexes accumulated in a salt subbasin, and Ket’ (Vostok-1 and Vostok-3 wells) with the deposition in an open sea basin. The boundary between these structure-facies zones is drawn along the inferred N–S-trending barrier reef zone. The rubrication in this paper is compiled in accordance with the requirements of the Stratigraphic Code of Russia for explanatory notes for regional stratigraphic schemes. Local stratigraphic subdivisions (formations, strata) are described and compared with the adjacent Turukhansk–Irkutsk–Olekma facies region of the Siberian Platform.
9
Lindsay, J. F., M. D. Brasier, D. Dorjnamjaa, R. Goldring, P. D. Kruse e R. A. Wood. "Facies and sequence controls on the appearance of the Cambrian biota in southwestern Mongolia: implications for the Precambrian–Cambrian boundary". Geological Magazine 133, n. 4 (luglio 1996): 417–28. http://dx.doi.org/10.1017/s0016756800007585.
Testo completoAbstract (sommario):
AbstractNeoproterozoic–Cambrian rocks of the Zavkhan Basin (Govi-Altay, western Mongolia) comprise large-scale alternations of siliciclastic- and carbonate-dominated units (cf. ‘Grand Cycles’). Analysis of such depositional sequences near the base of the Cambrian confirms that the distribution of trace fossils, small shelly fossils and calcimicrobial structures was strongly controlled by ecology and taphonomy, corresponding to specific points in a sea-level cycle. Evolution of the Cambrian biota is thus viewed through aseries of narrow time windows, once only for each depositional cycle. Correlation of the Precambrian–Cambrian boundary level on the basis of the first appearance of thePhycodes pedumassemblage is also fraught with difficulty, since stratigraphic resolution may be limited to a single sea-level cycle(c. 1–5 Ma). It is suggested that, in many cases, basin analysis will need to be undertaken before this boundary can be drawn.
10
Korobova, Natalia I., Evgeniya E. Karnyushina, Nadezhda S. Shevchuk, Sergei V. Frolov, Elena A. Bakay e Grigorii G. Akhmanov. "Geology aspects, sedimentation environments and oil-and-gas bearing capacity of Vendian and Cambrian deposits of Lena-Tunguska basin". Georesursy 24, n. 2 (16 maggio 2022): 60–74. http://dx.doi.org/10.18599/grs.2022.2.9.
Testo completoAbstract (sommario):
At present time several dozen hydrocarbon fields are known in the Vendian-Cambrian complex of the Lena-Tunguska basin, which clearly does not exhaust its potential. The significant stratigraphic interval of the complex, its thickness (up to 3000 m), favorable properties laid down in sedimentogenesis, namely the presence of source, reservoir and seal deposits, allow us to hope for the discovery of new oil and gas deposits. Sedimentological studies of the Vendian-Cambrian complex, carried out using a network of key lithological sections and outcrops, made it possible to create a series of schematic maps of sedimentation environments on a scale of 1:5000000 for six time intervals (Nepa, Tira, Danilovo, Tommotian-Early Atdabanian, Botomian-Amgaian and Late Cambrian). The evolution of sedimentation of the Vendian-Cambrian complex is considered, as well as an assessment of its oil and gas properties, which are primarily associated with various sedimentation environments.
11
GEYER, G. "The Fish River Subgroup in Namibia: stratigraphy, depositional environments and the Proterozoic–Cambrian boundary problem revisited". Geological Magazine 142, n. 5 (settembre 2005): 465–98. http://dx.doi.org/10.1017/s0016756805000956.
Testo completoAbstract (sommario):
The Fish River Subgroup of the Nama Group, southern Namibia, is restudied in terms of lithostratigraphy and depositional environment. The study is based on partly fine-scaled sections, particularly of the Nababis and Gross Aub Formation. The results are generally in accordance with earlier studies. However, braided river deposits appear to be less widely distributed in the studied area, and a considerable part of the formations of the middle and upper subgroup apparently were deposited under shallowest marine conditions including upper shore-face. Evidence comes partly from sedimentary features and facies distribution, and partly from trace fossils, particularly Skolithos and the characteristic Trichophycus pedum. Environmental conditions represented by layers with T. pedum suggest that the producer favoured shallow marine habitats and transgressive regimes. The successions represent two deepening-upward sequences, both starting as fluvial (braided river) systems and ending as shallow marine tidally dominated environments. The first sequence includes the traditional Stockdale, Breckhorn and lower Nababis formations (Zamnarib Member). The second sequence includes the upper Nababis (Haribes Member) and Gross Aub formations. As a result, the Nababis and Gross Aub formations require emendation: a new formation including the Haribes and Rosenhof and possibly also the Deurstamp members. In addition, four distinct sequence stratigraphic units are deter-minable for the Fish River Subgroup in the southern part of the basin. The Proterozoic–Cambrian transition in southern Namibia is most probably located as low as the middle Schwarzrand Subgroup. The environmentally controlled occurrence of Trichophycus pedum undermines the local stratigraphic significance of this trace fossil which is eponymous with the lowest Cambrian and Phanerozoic trace fossil assemblage on a global scale. However, occurrences of such trace fossils have to be regarded as positive evidence for Phanerozoic age regardless of co-occurring body fossils. Other suggestions strongly dispute the concept of the formal Proterozoic–Cambrian and Precambrian–Phanerozoic boundary. Carbon isotope excursions and radiometric datings for the Nama Group do not help to calibrate precisely the temporal extent of the Fish River Subgroup. Fossil content, sequence stratigraphy and inferred depositional developments suggest that this subgroup represents only a short period of late orogenic molasse sedimentation during the early sub-trilobitic Early Cambrian.
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Ambrose, G. J., P. D. Kruse e P. E. Putnam. "GEOLOGY AND HYDROCARBON POTENTIAL OF THE SOUTHERN GEORGINA BASIN, AUSTRALIA". APPEA Journal 41, n. 1 (2001): 139. http://dx.doi.org/10.1071/aj00007.
Testo completoAbstract (sommario):
The Georgina Basin is an intracratonic basin on the central-northern Australian craton. Its southern portion includes a highly prospective Middle Cambrian petroleum system which remains largely unexplored. A plethora of stratigraphic names plagued previous exploration but the lithostratigraphy has now been rationalised using previously unpublished electric-log correlations and seismic and core data.Neoproterozoic and Lower Palaeozoic sedimentary rocks of the southern portion of the basin cover an area of 100,000 km2 and thicken into two main depocentres, the Toko and Dulcie Synclines. In and between these depocentres, a Middle Cambrian carbonate succession comprising Thorntonia Limestone and Arthur Creek Formation provides a prospective reservoir-source/seal couplet extending over 80,000 km2. The lower Arthur Creek Formation includes world class microbial source rocks recording total organic carbon (TOC) values of up to 16% and hydrocarbon yields up to 50 kg/tonne. This blanket source/seal unconformably overlies sheetlike, platform dolostone of the Thorntonia Limestone which provides the prime target reservoir. Intra- Arthur Creek high-permeability grainstone shoals are important secondary targets.In the Toko Syncline, Middle Cambrian source rocks entered the oil window during the Ordovician, corresponding to major sediment loading at this time. The gas window was reached prior to structuring associated with the Middle Devonian-Early Carboniferous Alice Springs Orogeny, and source rocks today lie in the dry gas window. In contrast, high-temperature basement granites have resulted in overmaturity of the Arthur Creek Formation in the Dulcie Syncline area. On platform areas adjacent to both these depocentres source rocks reached peak oil generation shortly after the Alice Springs Orogeny; numerous structural leads have been identified in these areas. In addition, an important stratigraphic play occurs in the Late Cambrian Arrinthrunga Formation (Hagen Member) on the southwestern margin of the basin. Key elements of the play are the pinchout of porous oil-stained, vuggy dolostone onto basement where top seal is provided by massive anhydrite while underlying Arthur Creek Formation shale provides a potential source.
13
AHN, SOO YEUN, e MAOYAN ZHU. "Lowermost Cambrian acritarchs from the Yanjiahe Formation, South China: implication for defining the base of the Cambrian in the Yangtze Platform". Geological Magazine 154, n. 6 (13 febbraio 2017): 1217–31. http://dx.doi.org/10.1017/s0016756816001369.
Testo completoAbstract (sommario):
AbstractTheAsteridium–Heliosphaeridium–Comasphaeridium(AHC) acritarch assemblage is composed of common organic-walled microfossils in the basal Cambrian chert–phosphorite units in South China, indicating that the AHC assemblage can be a useful biostratigraphic tool for the Ediacaran–Cambrian boundary successions in the Yangtze Platform. To test the validity of the AHC acritarch assemblage as a biostratigraphic tool, the stratigraphic range of the AHC acritarch assemblage was confirmed, and its spatial and temporal relationships to other bio- and chemostratigraphic tools were analysed in the Yanjiahe Formation, Yangtze Gorges area, South China. The result shows that the AHC assemblage temporally correlates to theAnabarites trisulcatus–Protohertzina anabaricaAssemblage Zone, and spatially correlates to the large negative carbon isotope anomaly of the lowermost Cambrian (BACE) in the Yanjiahe Formation. This implies that the radiation of phytoplankton occurred slightly before the radiation of the small shelly fossils, and the AHC acritarch assemblage can be another important chronological reference to the lowermost Cambrian successions in South China, and potentially to global correlations.
14
Felitsyn, Sergey B., e Eugeny S. Bogomolov. "Nd isotope composition of the Ediacaran and earliest Cambrian phosphorite nodules and Fe sulphide from the East European Platform". Geological Magazine 157, n. 12 (19 agosto 2020): 2081–88. http://dx.doi.org/10.1017/s0016756820000497.
Testo completoAbstract (sommario):
AbstractAn enhanced concentration of phosphorus has been found at the stratigraphic level of the disappearance of Ediacaran taxa in two areas, the Cis-Dniester region and the Moscow syneclise, on the East European Platform (EEP). The isotope composition of neodymium was determined in Fe sulphide and phosphorite in the same beds. Measured εNd(t) values in diagenetic phosphate nodules are similar to those in iron sulphide from the same layer. During the Ediacaran − Early Cambrian, accumulation of radiogenic Nd in the epeiric basins on the EEP increased progressively from −17.9 and −19.4 in pyrite from the sequence bottom to −7.9 and −8.5 in the Early Cambrian pyrite of the central part of the EEP. The Ediacaran phosphate nodules show εNd(t) ranging from −12.9 to −15.0, while that in the Early Cambrian nodules is typically c. −9.0. These data indicate the secular change in Nd isotope composition of the water reservoir on the EEP from Ediacaran to Cambrian.
15
GEHLING, JAMES G., SÖREN JENSEN, MARY L. DROSER, PAUL M. MYROW e GUY M. NARBONNE. "Burrowing below the basal Cambrian GSSP, Fortune Head, Newfoundland". Geological Magazine 138, n. 2 (marzo 2001): 213–18. http://dx.doi.org/10.1017/s001675680100509x.
Testo completoAbstract (sommario):
The range of Treptichnus pedum, the index trace fossil for the Treptichnus pedum Zone, extends some 4 m below the Global Standard Stratotype-section and Point for the base of the Cambrian Period at Fortune Head on the Burin Peninsula in southeastern Newfoundland. The identification of zigzag traces of Treptichnus isp., even further below the GSSP than T. pedum in the Fortune Head section, and in other terminal Proterozoic successions around the globe, supports the concept of a gradational onset of three-dimensional burrowing across the Proterozoic–Cambrian boundary. Although T. pedum remains a reasonable indicator for the base of the Cambrian Period, greater precision in the stratotype section can be achieved by a detailed re-evaluation of the stratigraphic ranges and the morphological variation of ichnotaxa included in the T. pedum Zone.
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Ripperdan, R. L., M. Magaritz e J. L. Kirschvink. "Carbon isotope and magnetic polarity evidence for non-depositional events within the Cambrian-Ordovician Boundary section near Dayangcha, Jilin Province, China". Geological Magazine 130, n. 4 (luglio 1993): 443–52. http://dx.doi.org/10.1017/s0016756800020525.
Testo completoAbstract (sommario):
AbstractCarbon isotope and magnetic polarity stratigraphic results from the Cambrian-Ordovician Boundary section at Xiaoyangqiao, near Dayangcha, Jilin Province, China, in comparison to a contemporaneous section at Black Mountain, Australia, indicate strata equivalent to major portions of the Australian sequence are either absent or are restricted to highly condensed intervals. These intervals are correlative with regressive sea level events identified in Australia and western North America, suggesting regional or eustatic sea level changes strongly influenced deposition of the Xiaoyangqiao sequence. These results also suggest the Xiaoyangqiao section is unfavourable as the site of the Cambrian-Ordovician Boundary Global Stratotype Section and Point.
17
Hughes, Nigel C. "Biostratigraphical dating conundrums in the Cambrian and earlier stratigraphy of the Indian subcontinent". Journal of Palaeosciences 66, n. (1-2) (31 dicembre 2017): 1–15. http://dx.doi.org/10.54991/jop.2017.275.
Testo completoAbstract (sommario):
Dating rocks by using fossils remains one of the most important stratigraphic tools both for Phanerozoic sedimentary rocks and, increasingly, for older rocks too. Inevitably situations arise in which different types of data offer seemingly contradictory indications of age, of which several examples from Cambrian and earlier rocks of Indian subcontinent are discussed herein. These examples highlight the main kinds of biostratigraphical conundrums and their resolution, their role in moving stratigraphic geology forward, and also surprising ways in which they are misused. The growth of geological knowledge regionally and globally, along with the introduction of additional techniques for dating rock strata, means that the temporal range of the alternative explanations related to particular conundrums has tended to decline with time, although a controversy with alternatives over 1.0 Ga apart is currently active concerning Vindhyan geology. Although important in their own right, the solutions to this and other conundrums must integrate with other types of geological data if age determination is to be satisfactorily concluded and the wider geological and evolutionary implications of biostratigraphical dating are to be realised.
18
Gubin, I. A., A. E. Kontorovich, I. V. Korovnikov e T. M. Parfenova. "The Structure of Cambrian Deposits of the Vilyui Hemisyneclise, Based on an Integrated Analysis of Drilling and Seismic Data". Russian Geology and Geophysics 62, n. 08 (1 agosto 2021): 914–28. http://dx.doi.org/10.2113/rgg20214353.
Testo completoAbstract (sommario):
Abstract —We present a model of the stratigraphic and lateral distribution of Cambrian deposits in the Vilyui hemisyneclise, based on an analysis of drilling data and interpretation of seismic data. The study shows a series of formations and sequences penetrated by wells (Syugdzher saddle, Khorgochum monocline, Ygyatta depression, Tyukyan–Chybyda monocline, Arbai–Sinyaya megaswell, etc.). In the areas where the Cambrian was not penetrated by wells, the distribution of Cambrian deposit was inferred based on the available seismic data. The distribution of the Kuonamka Horizon formed by Cambrian organic-rich rocks is characterized in detail. These are the Kumakh and Sinyaya–Kutorgina sequences and the Inikan and Kuonamka formations. It has been found that the Kuonamka Horizon was deposited during two stages, Botomian and Toyonian–early Mayan. The horizon is overlain by younger deposits of the Mayan Stage, with characteristic cross-bedding structures. Schemes of facies zoning of the Cambrian for Botomian, Toyonian–early Mayan, and middle Mayan times were constructed based on the most recent geological and geophysical understanding of the Vilyui hemisyneclise.
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Gubin, Igor A., e Vladimir A. Kontorovich. "Seismogeological structure model of the Anabar-Olenek region". Georesursy 23, n. 1 (30 marzo 2021): 70–77. http://dx.doi.org/10.18599/grs.2021.1.7.
Testo completoAbstract (sommario):
The velocity characteristics of the Upper Proterozoic-Phanerozoic sedimentary cover of the Anabar-Olenek region were studied, in particular, the bimodal character of the distribution interval P-wave velocities was established. Taking into account modern ideas about the chronostratigraphy of sediments encountered by the Charchykskaya-1, Burskaya-3410 and Khastakhskaya-930 deep boreholes, stratification of reflecting horizons was carried out and time sections from previous years were reinterpreted. From the perspective of seismic stratigraphic and seismic facies analysis, the Cambrian, Vendian, and Riphean intervals of the section were examined in detail. In the course of the analysis, adjustments to the stratigraphic breakdown of the Burskaya-3410 and Charchykskaya-1 boreholes are proposed. The study shows that the Lapar Formation, which underwent Prepermian erosion, increase in the thickness multiple in an eastward direction. The distribution areas of the Tuessal Formation, the Lower and Middle Cambrian clinoform complex, as well as the areas of the Upper Riphean Formations reaching the Prevendian erosion surface are contoured. An Intrariphean tectonic disagreement between the Kulady Formation and older deposits was established.
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Żylińska, Anna. "The oldest Cambrian trilobites from the Holy Cross Mountains, Poland: taxonomic, stratigraphic and biogeographic reappraisal". Acta Geologica Polonica 63, n. 1 (1 marzo 2013): 57–87. http://dx.doi.org/10.2478/agp-2013-0002.
Testo completoAbstract (sommario):
Abstract Żylińska, A. 2013. The oldest Cambrian trilobites from the Holy Cross Mountains, Poland: taxonomic, stratigraphic and biogeographic reappraisal. Acta Geologica Polonica, 63 (1), 57-87. Warszawa. Authorship issues are clarified, new photographic documentation is provided and emended systematic descriptions are presented for the oldest Cambrian trilobite taxa from the Holy Cross Mountains (Poland). Biostratigraphic analysis of the fauna allows correlation with the traditional Holmia kjerulfi-group Zone of Scandinavia, the Callavia Zone of Britain and Newfoundland, the lower and middle part of the Sectigena Zone of Morocco and the Marianian Stage of Spain. The trilobites display a strong biogeographic signal linked with West Gondwana and Avalonia and a suggestion is made that the TESZ margin of Baltica with the Małopolska Massif was liable to currents from those areas that distributed planktonic trilobite larvae.
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Álvaro, J. Javier, e Marie-Madeleine Blanc-Valleron. "Stratigraphic and structural framework of the Neoproterozoic Paracuellos Group, Iberian Chains, NE Spain". Bulletin de la Société Géologique de France 173, n. 3 (1 maggio 2002): 219–27. http://dx.doi.org/10.2113/173.3.219.
Testo completoAbstract (sommario):
Abstract The Neoproterozoic Paracuellos Group of the Iberian Chains constitutes the core of two disconnected faulted blocks, named the Paracuellos and Codos antiforms. Precise lithostratigraphic correlations between both areas are not possible due to the structural complexity and because marker beds do not persist laterally. This paper presents a crustal cross-section of the Neoproterozoic axial core (the Paracuellos antiform) based on surface geology, boreholes and seismic reflection profiles. Seismic reflection data reveal that the basement was directly involved by a major Hercynian structure, named here the Paracuellos fault, which splits longitudinally the Paracuellos axial core. In seismic profiles this fault occurs as a northeasterly-dipping reflector (60–70° steep), evidencing a bivergent geometry of the lateral crustal elements. The sedimentary evolution of the Neoproterozoic Iberian platform ranges from transgressive, non-cyclic, offshore to hemipelagic, black and green shales (Sestrica Formation) to progradational trends recording shoaling during episodes of rapid sediment influx (Saviñán Formation), presumably in response to a low standing sea-level. The siliciclastic succession is punctuated in the inner platform by deposition of phosphatic limestones (Codos Bed), representing a major shoaling event and demarcating a sharp regional change of sedimentation separating two similar siliciclastic tendencies. A diagenetically induced bedded chert (Frasno Bed) occurs in the outer platform, and is interpreted as being the product of at least two silicification episodes. Both the Codos and Frasno Beds are overlain by the Aluenda Formation, which exhibits nearshore to offshore features. An important sedimentary discontinuity appears across the Neoproterozoic-Cambrian transition. The Cambrian(?) Bámbola Formation is paraconformable with the Paracuellos Group displaying a gradual transition in inner platform areas, whereas an erosive unconformity occurs in outer areas. The horizon of the Neoproterozoic-Cambrian boundary is not identified in the Iberian Chains, where neither Cadomian deformation nor discordances are recognisable.
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Phillips, Bruce J., Alan W. James e Graeme M. Philip. "THE GEOLOGY AND HYDROCARBON POTENTIAL OF THE NORTH-WESTERN OFFICER BASIN". APPEA Journal 25, n. 1 (1985): 52. http://dx.doi.org/10.1071/aj84004.
Testo completoAbstract (sommario):
Recent petroleum exploration in EP 186 and EP 187 in the north-western Officer Basin has greatly increased knowledge of the regional stratigraphy, structure and petroleum prospectivity of the region. This exploration programme has involved the drilling of two deep stratigraphic wells (Dragoon 1 and Hussar 1) and the acquisition of 1438 km of seismic data. Integration of regional gravity and aeromagnetic data with regional seismic and well data reveals that the Gibson Sub-basin primarily contains a Proterozoic evaporitic sequence. In contrast, the Herbert Sub-basin contains a Late Proterozoic to Cambrian clastic and carbonate sequence above the evaporites. This sequence, which was intersected in Hussar 1, is identified as the primary exploration target in the Western Officer Basin. The sequence contains excellent reservoir and seal rocks in association with mature source rocks. Major structuring of the basin has also been caused by compressive movements associated with the Alice Springs Orogeny. The northwestern Officer Basin thus has all of the ingredients for the discovery of commercial hydrocarbons.
23
Barr, Sandra M., Chris E. White, Sören Jensen, Teodoro Palacios e Deanne Van Rooyen. "Ediacaran and Cambrian rocks on Scatarie Island and nearby Hay Island, Avalonian Mira terrane, Cape Breton Island, Nova Scotia, Canada". Atlantic Geology 56 (22 ottobre 2020): 257–79. http://dx.doi.org/10.4138/atlgeol.2020.011.
Testo completoAbstract (sommario):
Scatarie Island and adjacent Hay Island, located 2 km east of the eastern tip of the Avalonian Mira terrane of southern Cape Breton Island, Nova Scotia, contain a succession of epiclastic and other sedimentary rocks of inferred Ediacaran to Cambrian age. The age assignment was based previously on lithological comparison with the Main-à-Dieu Group and overlying Bengal Road and MacCodrum formations of the Mira River Group. Detrital zircon grains from two sandstone samples from the Bengal Road Formation yielded typical Avalonian detrital zircon spectra with middle to late Neoproterozoic, Meso- to Paleoproterozoic (1300–2200 Ma) and Neoarchean ages. They indicate maximum depositional ages of 532.4 ± 4.2 Ma and 525.4 ± 2.4 Ma from essentially the same stratigraphic level, consistent with the interpretation that the rocks are Cambrian. The Bengal Road Formation also yielded scarce organic-walled microfossils including an acanthomorphic acritarch identified as Polygonium sp., also consistent with Cambrian age. The fine-grained siliciclastic succession on Hay Island, tentatively attributed to the MacCodrum Formation, yielded trace fossils, including Teichichnus isp. and Gyrolithes scintillus, that confirm Cambrian age. The Hay Island Gyrolithes scintillus expands the geographical distribution of this ichnospecies, previously known mainly from the Chapel Island Formation of Newfoundland, and represents a younger occurrence.
24
Al-Husseini, Moujahed I. "MIDDLE EAST GEOLOGIC TIME SCALE 2010: Early Cambrian Asfar Sequence". GeoArabia 15, n. 1 (1 gennaio 2010): 137–60. http://dx.doi.org/10.2113/geoarabia1501137.
Testo completoAbstract (sommario):
ABSTRACT This paper is the first in a series dedicated to the Phanerozoic Cambrian Period, and Neoproterozoic Ediacaran and Cryogenian periods, as represented in the Middle East Geologic Time Scale (ME GTS, see enclosed Chart). It introduces the term Asfar Sequence to represent a regional Early Cambrian time-rock unit, consisting mainly of continental quartz-rich arkosic sandstone, shale and siltstone, which attain a thickness of at least 750 m in Jordan and more than 700 m in Oman. The term “Asfar”, meaning yellow in Arabic, was chosen because it is the standard color for sandstone in ME GTS. To describe its stratigraphy, four representative formations are reviewed in lexicon format: Salib Arkosic Sandstone of Jordan, Siq Sandstone of Saudi Arabia, Amin Formation of Oman and Lalun Sandstone of Iran. The stratigraphic geometry of the lower boundary of the Sequence varies considerably by locality. In some regions in Iran it is conformable above the shales of the Zaigun Formation. In other regions, such as western Jordan, it is an onlap surface over Proterozoic and/or Lower and Middle Cambrian paleohighs, or a pronounced angular unconformity (e.g. central and southern Saudi Arabia). The paleo-relief represented by the unconformity surface, in many regions, forms a regional peneplain (e.g. central and eastern Jordan) implying erosion; in other paleohigh regions, the Sequence is absent by non-deposition. The age of the base Asfar Sequence is estimated at ca. 530 Ma, based on radiometric data and depositional rates in basinal areas. The top boundary of the Sequence, in Iran, Jordan, and northern and northeastern Saudi Arabia, is represented by a sequence boundary (or its correlative unconformity), above which marine, fine-grained siliciclastics and carbonates of late Early to early Mid-Cambrian age were deposited: Mila Formation in Iran, and Burj Formation in Jordan and Saudi Arabia, implying an age older than ca. 510 Ma in GTS 2004. In Oman, however, continental rather than marine deposition (Miqrat and coeval Mahwis formations) continued above the unconformity in ?Middle Cambrian. For the purpose of regional correlations it is proposed that the Angudan Unconformity of Oman be taken as the name for the basal boundary of the Sequence and the Burj Sequence Boundary for its top.
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KOUCHINSKY, ARTEM, STEFAN BENGTSON, YVES GALLET, IGOR KOROVNIKOV, VLADIMIR PAVLOV, BRUCE RUNNEGAR, GRAHAM SHIELDS, JAN VEIZER, EDWARD YOUNG e KAREN ZIEGLER. "The SPICE carbon isotope excursion in Siberia: a combined study of the upper Middle Cambrian–lowermost Ordovician Kulyumbe River section, northwestern Siberian Platform". Geological Magazine 145, n. 5 (23 maggio 2008): 609–22. http://dx.doi.org/10.1017/s0016756808004913.
Testo completoAbstract (sommario):
AbstractAn integrated, high-resolution chemostratigraphic (C, O and Sr isotopes) and magnetostratigraphic study through the upper Middle Cambrian–lowermost Ordovician shallow-marine carbonates of the northwestern margin of the Siberian Platform is reported. The interval was analysed at the Kulyumbe section, which is exposed along the Kulyumbe River, an eastern tributary of the Enisej River. It comprises the upper Ust'-Brus, Labaz, Orakta, Kulyumbe, Ujgur and lower Iltyk formations and includes the Steptoean positive carbon isotopic excursion (SPICE) studied here in detail from upper Cambrian carbonates of the Siberian Platform for the first time. The peak of the excursion, showing δ13C positive values as high as +4.6‰ and least-altered87Sr/86Sr ratios of 0.70909, is reported herein from the Yurakhian Horizon of the Kulyumbe Formation. The stratigraphic position of the SPICE excursion does not support traditional correlation of the boundary between the Orakta and Labaz formations at the Kulyumbe River with its supposedly equivalent level in Australia, Laurentia, South China and Kazakhstan, where theGlyptagnostus stolidotusandG. reticulatusbiozones are known to immediately precede the SPICE excursion and span the Middle–Upper Cambrian boundary. The Cambrian–Ordovician boundary is probably situated in the middle Nyajan Horizon of the Iltyk Formation, in which carbon isotope values show a local maximum below a decrease in the upper part of the Nyajan Horizon, attributed herein to the Tremadocian Stage. A refined magnetic polarity sequence confirms that the geomagnetic reversal frequency was very high during Middle Cambrian times at 7–10 reversals per Ma, assuming a total duration of about 10 Ma and up to 100 magnetic intervals in the Middle Cambrian. By contrast, the sequence attributed herein to the Upper Cambrian on chemostratigraphic grounds contains only 10–11 magnetic intervals.
26
Brasier, M. D., e P. Singh. "Microfossils and Precambrian–Cambrian boundary stratigraphy at Maldeota, Lesser Himalaya". Geological Magazine 124, n. 4 (luglio 1987): 323–45. http://dx.doi.org/10.1017/s0016756800016666.
Testo completoAbstract (sommario):
AbstractAn assemblage of problematical microfossils of Precambrian–Cambrian boundary age is redescribed from the Chert–Phosphorite Member, at the base of the Lower Tal Formation of Maldeota in the Lesser Himalaya of India. This assemblage has previously been ascribed to various ages, from Precambrian to Cretaceous, but is held by us to contain:Maldeotaia bandalica, Protohertzina anabaricagroup, trumpet-shaped elements, acicular elements A & B, ?Conothecasp.,Ovalithecacf.multicostata, allathecid sp. A,Barbitositheca ansata, Hexangulaconulariacf.formosa, Coleoloidesaff.typicalis, Hyolithellusaff.insolitus, H.cf.isiticus, H. vladimirovae, Spirellus shankariandOlivooides multisulcatus. These compare closely with assemblages found above the base of the first,Anabarites trisulcatus–Protohertzina anabaricaZone in China and in the second,Pseudorthotheca costataZone of southern Kazakhstan. The stratigraphic setting of the Krol–Tal succession is reviewed and several similarities are noted between the Precambrian–Cambrian boundary successions of Lesser Himalaya in India and of Yunnan and Sichuan in Southwest China, indicating that correlation between them is possible at several levels.
27
Letsch, Dominik, Mohamed El Houicha, Albrecht von Quadt e Wilfried Winkler. "A missing link in the peri-Gondwanan terrane collage: the Precambrian basement of the Moroccan Meseta and its lower Paleozoic cover". Canadian Journal of Earth Sciences 55, n. 1 (gennaio 2018): 33–51. http://dx.doi.org/10.1139/cjes-2017-0086.
Testo completoAbstract (sommario):
This article provides stratigraphic and geochronological data from a central part of Gondwana’s northern margin — the Moroccan Meseta Domain. This region, located to the north of the Anti-Atlas area with extensive outcrops of Precambrian and lower Paleozoic rocks, has hitherto not received much attention with regard to its Precambrian geology. Detrital and volcanic zircon ages have been used to constrain sedimentary depositional ages and crustal affinities of sedimentary source rocks in stratigraphic key sections. Based on this, a four-step paleotectonic evolution of the Meseta Domain from the Ediacaran until the Early Ordovician is proposed. This evolution documents the transition from a terrestrial volcanic setting during the Ediacaran to a short-lived carbonate platform setting during the early Cambrian. The latter then evolved into a rifted margin with deposition of thick siliciclastic successions in graben structures during the middle to late Cambrian. The detritus in these basins was of local origin, and a contribution from a broader source area (encompassing parts of the West African Craton) can only be demonstrated for postrifting, i.e., laterally extensive sandstone bodies that seal the former graben. In a broader paleotectonic context, it is suggested that this Cambrian rifting is linked to the opening of the Rheic Ocean, and that several peri-Gondwanan terranes (Meguma and Cadomia–Iberia) may have been close to the Meseta Domain before drifting, albeit some of them seem to have been constituted by a distinctly different basement.
28
Sim, Min Sub, e Yong Il Lee. "Sequence stratigraphy of the Middle Cambrian Daegi Formation (Korea), and its bearing on the regional stratigraphic correlation". Sedimentary Geology 191, n. 3-4 (ottobre 2006): 151–69. http://dx.doi.org/10.1016/j.sedgeo.2006.03.016.
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LI, DA, HONG-FEI LING, SHAO-YONG JIANG, JIA-YONG PAN, YONG-QUAN CHEN, YUAN-FENG CAI e HONG-ZHEN FENG. "New carbon isotope stratigraphy of the Ediacaran–Cambrian boundary interval from SW China: implications for global correlation". Geological Magazine 146, n. 4 (26 marzo 2009): 465–84. http://dx.doi.org/10.1017/s0016756809006268.
Testo completoAbstract (sommario):
AbstractThe Yangtze Platform preserves relatively thick carbonate successions and excellent fossil records across the Ediacaran–Cambrian boundary interval. The intensely studied Meishucun section in East Yunnan was one of the Global Stratotype Section candidates for the Precambrian–Cambrian boundary. However, depositional breaks were suspected in the section and the first appearance of small shelly fossils could not be verified. The Laolin section located in NE Yunnan is more continuous and shows great potential for global correlation of carbon isotope features across the Precambrian–Cambrian boundary. However, the stratigraphic framework and correlations were controversial. We studied and systematically sampled the Laolin section and present here new carbon isotope data for this section. The Laolin section consists of, in ascending order, the Baiyanshao dolostone of the Dengying Formation, the Daibu siliceous dolostone, Zhongyicun dolomitic phosphorite, lower Dahai dolostone and upper Dahai limestone of the Zhujiaqing Formation, and the black siltstone of the Shiyantou Formation. Our data reveal a large negative δ13C excursion (−7.2‰, L1′) in the Daibu Member, which matches the previously published data for the Laolin section, and a large positive excursion (+3.5‰, L4) in the Dahai Member, which was not shown in the published data. The excursion L1′ correlates well with the similarly large negative excursion near the first appearance of small shelly fossils in Siberia and Mongolia. Similar magnitude excursions are also known from Morocco and Oman, for which there are no robust fossil constraints but from where volcanic ash beds have been dated precisely at 542 Ma, thus confirming a global biogeochemical event near the Ediacaran–Cambrian boundary. Our data also indicate that deposition was more continuous at the Laolin section compared with the Meishucun section, where there are no records of a comparable negative excursion near the Ediacaran–Cambrian boundary, nor any comparable positive excursion in the Dahai Member. Therefore, the Laolin section has proven potential to be a supplementary Global Stratotype Section for the Ediacaran–Cambrian boundary on the Yangtze Platform.
30
Hutchinson, Peter J., e Maggie H. Tsai. "Stratigraphic Analysis with Refraction Tomography". Environmental and Engineering Geoscience 25, n. 3 (2 agosto 2019): 245–54. http://dx.doi.org/10.2113/eeg-2127.
Testo completoAbstract (sommario):
ABSTRACT Near-surface seismic refraction tomography imaged the basal contact of the Upper Cambrian silica-rich Mount Simon Formation with that of the underlying Precambrian granite in central Wisconsin. The discrimination between the Mount Simon and underlying non-conformable contact with Precambrian rocks was based upon a p-wave velocity of 1,700 m/s. Refraction tomography imaged deep, broad tidal channels within the Mount Simon consistent with the inference that Mount Simon was deposited in a high-energy near-shore, probably fluvial environment. The Mount Simon is an arenite that has high commercial value.
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Korobkin, V. V., A. Ye Chaklikov, A. A. Ismailov e Zh S. Tulemissova. "LATE PALEOZOIC – MESOZOIC TECTONIC EVOLUTION AND PROSPECTS OF HYDROCARBON EXPLORATION IN THE ALAKOL SEDIMENTARY BASIN (KAZAKHSTAN)". Geodynamics & Tectonophysics 14, n. 5 (17 ottobre 2023): 0717. http://dx.doi.org/10.5800/gt-2023-14-5-0717.
Testo completoAbstract (sommario):
Based on the analysis of stratigraphic, lithofacies, and geological and geophysical data, consideration is being given to the main stages in the formation of the basement and cover structures of the Alakol sedimentary basin. For this region, there was developed the substantiation of a scheme of tectonic zoning and there were proposed structural characteristics of faults and lithofacies features of the section. Evidence was found of a complex, multi-stage tectonic evolution. There were discovered potentially promising stratigraphic oil and gas complexes of the Late Paleozoic and Mesozoic. The deep-seated structure of the region is illustrated by a geological and geophysical section, spatially coincident with the "Turkestan" seismic profile. Based on the lithological and paleogeographic reconstructions, there were identified four major tectonic boundaries: Cambrian-Ordovician, Devonian-Carboniferous, Permian-Early Triassic, and Middle Triassic-Cretaceous. The correlation of the stratigraphic range of the hydrocarbon potential of the Alakol basin has been carried out. The criteria for forecasting hydrocarbon accumulations were substantiated.
32
ŻYLIŃSKA, ANNA, e MONIKA MASIAK. "Cambrian trilobites from Brzechów, Holy Cross Mountains (Poland) and their significance in stratigraphic correlation and biogeographic reconstructions". Geological Magazine 144, n. 4 (16 aprile 2007): 661–86. http://dx.doi.org/10.1017/s0016756807003366.
Testo completoAbstract (sommario):
A revision of the trilobite fauna from Brzechów in the Holy Cross Mountains (Poland) shows that the assemblage consists of Palaeolenus medius (Bednarczyk), Issafeniella orlowinensis (Samsonowicz), Kingaspidoides sanctacrucensis (Czarnocki), Paradoxides (Acadoparadoxides) oelandicus Sjögren, P. (A.) cf. mureroensis Sdzuy and P. (A.) sp. It is earliest Middle Cambrian in age according to the West Gondwana standard of Geyer & Landing (2004) and can be correlated with the Cephalopyge notabilis Zone of Morocco. Moreover, the co-occurrence of the ranges of P. (A.) oelandicus with P. (A.) cf. mureroensis might suggest that P. (A.) oelandicus appears earlier in the Brzechów sandstones than in Scandinavia, thus the strata exposed here do not find their correlative in the Scandinavian succession. As a result, the Banian/Agdzian boundary (Lower–Middle Cambrian boundary according to the West Gondwana standard) probably lies within the Kamieniec Formation, and also below the Brzechów sandstones, in the upper part of the Ociesęki Formation. Close similarity of the discussed assemblage with contemporaneous assemblages from Morocco, Jordan or New Brunswick indicates that the fauna is generally of peri-Gondwanan and Gondwanan aspect.
33
HUGHES, NIGEL C., PAUL M. MYROW, N. RYAN MCKENZIE, D. A. T. HARPER, O. N. BHARGAVA, S. K. TANGRI, K. S. GHALLEY e C. M. FANNING. "Cambrian rocks and faunas of the Wachi La, Black Mountains, Bhutan". Geological Magazine 148, n. 3 (14 settembre 2010): 351–79. http://dx.doi.org/10.1017/s0016756810000750.
Testo completoAbstract (sommario):
AbstractThe Pele La Group in the Wachi La section in the Black Mountains of central Bhutan represents the easternmost exposure of Cambrian strata known in the Himalaya. The group contains a succession of siliciclastic rocks with minor amounts of carbonate, the uppermost unit of which, the Quartzite Formation, bears age-diagnostic trilobite body fossils that are approximately 493 Ma old. Trilobite species includeKaolishania granulosa, Taipaikia glabraand the new speciesLingyuanaspis sangae.A billingsellid brachiopod,Billingsellacf.tonkiniana, is co-occurrent. This fauna is precisely correlated with that of a specific stratigraphic horizon within the upper part of theKaolishaniaZone, Stage 9 of the Cambrian System, Furongian Epoch of the North China block, and thus represents the youngest Cambrian sedimentary rocks yet known from the Himalaya. The faunal similarity suggests proximity between North China and the Himalayan margin at this time. This unit was deposited in a predominantly storm-influenced shelf and shoreface environment. U–Pb geochronological data from detrital zircon grains from the fossil-bearing beds of the Quartzite Formation and strata of the underlying Deshichiling Formation show grain age spectra consistent with those from Cambrian rocks of the Lesser and Tethyan Himalaya in Tibet, India and Pakistan. These data support continuity of the northern Gondwanan margin across the Himalaya. Prominent peaks of approximately 500 Ma zircons in both the Quartzite and Deshichiling formations are consistent with the Furongian (late Cambrian) age assignment for these strata. The presence of these relatively young zircon populations implies rapid post-cooling erosion of igneous bodies and subsequent deposition which may reflect the influence of a widespread Cambro-Ordovician orogenic event evident in the western Himalaya.
34
Grazhdankin, Dmitriy, Konstantin Nagovitsin, Elena Golubkova, Galina Karlova, Boris Kochnev, Vladimir Rogov e Vasiliy Marusin. "Doushantuo-Pertatataka–type acanthomorphs and Ediacaran ecosystem stability". Geology 48, n. 7 (27 aprile 2020): 708–12. http://dx.doi.org/10.1130/g47467.1.
Testo completoAbstract (sommario):
Abstract Large (100 to ∼700 µm diameter) spheroidal carbonaceous microfossils ornamented with regularly arranged spinose or branched processes are globally distributed in the Ediacaran (635–542 Ma). These microfossils, collectively known as the Doushantuo-Pertatataka–type acanthomorphs, have been variously interpreted as a polyphyletic assortment of resting stages of eukaryotes, including animals. The stratigraphic range of the acanthomorphs has long been thought to be restricted to the interval between the uppermost Cryogenian glacial deposits and the largest-known carbon isotope excursion in Earth’s history, the Shuram event. The mid-Ediacaran disappearance of the acanthomorphs was puzzling until they were discovered in younger strata in south China, in northwestern Russia, and in Mongolia. Here, we report Doushantuo-Pertatataka–type acanthomorphs coeval with Cambrian-type small skeletal fossils. It appears that neither the Shuram event nor the emergence of macro-organisms, eumetazoans, and biologically controlled mineralization significantly affected the acanthomorphs, suggesting a marked stability of Ediacaran ecosystems up to the very beginning of the Cambrian.
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Pelechaty, Shane M., John P. Grotzinger, Vladimir A. Kashirtsev e Vladimir P. Zhernovsky. "Chemostratigraphic and Sequence Stratigraphic Constraints on Vendian-Cambrian Basin Dynamics, Northeast Siberian Craton". Journal of Geology 104, n. 5 (settembre 1996): 543–63. http://dx.doi.org/10.1086/629851.
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Parcha, S. K., e Birendra P. Singh. "Stratigraphic significance of the Cambrian ichnofauna of the Zanskar region, Ladakh Himalaya, India". Journal of the Geological Society of India 75, n. 3 (marzo 2010): 503–17. http://dx.doi.org/10.1007/s12594-010-0040-x.
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Shahkarami, Setareh, Luis A. Buatois, M. Gabriela Mángano, James W. Hagadorn e John Almond. "The Ediacaran–Cambrian boundary: Evaluating stratigraphic completeness and the Great Unconformity". Precambrian Research 345 (agosto 2020): 105721. http://dx.doi.org/10.1016/j.precamres.2020.105721.
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Chen, Qiong, Guochun Zhao e Min Sun. "Protracted northward drifting of South China during the assembly of Gondwana: Constraints from the spatial-temporal provenance comparison of Neoproterozoic–Cambrian strata". GSA Bulletin 133, n. 9-10 (19 gennaio 2021): 1947–63. http://dx.doi.org/10.1130/b35791.1.
Testo completoAbstract (sommario):
Abstract Neoproterozoic to Paleozoic sedimentation shows systematic temporal-spatial variations within South China, which must be considered in reconstructing geological evolution of South China in response to global plate reorganization from the breakup of Rodinia to the assembly of Gondwana. We use >1000 new U-Pb and Hf isotopic data for detrital zircons from Neoproterozoic–Cambrian strata across the western (i.e., Longmenshan) and eastern (i.e., Wuyishan) margins of South China, coupled with compiled stratigraphic and magmatic information, to constrain change in provenance through time. First-order conclusions are as follows: (1) detrital zircons from the Neoproterozoic strata of the two margins were mainly sourced from the Panxi-Hannan arc and the Jiangnan orogen, signaling a rough self-sufficient sedimentary system; (2) newly identified Cambrian molasse-like sediments in the western margin, in which abundant detrital zircons are 550–500 Ma old with positive εHf(t) values, were mainly derived from the 580–500 Ma Cadomian arc belt along the Iran-Turkey margin; and (3) the Cambrian sediments in the eastern margin document more increased contributions from the Grenvillian-age provinces most possibly in Australia. Such spatial-temporal provenance variations signal the northward drifting of South China, from a position connecting with Iran-Turkey and northern India to that approaching Australia during the late Neoproterozoic–Cambrian period. We highlight that the activity of oblique oceanic-continental convergence accreted Asian terranes onto the northern margin of Gondwana, hence contributing to the ultimate Gondwana architecture under global plate reorganization.
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Moynihan, David P., Justin V. Strauss, Lyle L. Nelson e Colin D. Padget. "Upper Windermere Supergroup and the transition from rifting to continent-margin sedimentation, Nadaleen River area, northern Canadian Cordillera". GSA Bulletin 131, n. 9-10 (8 marzo 2019): 1673–701. http://dx.doi.org/10.1130/b32039.1.
Testo completoAbstract (sommario):
AbstractNeoproterozoic–Cambrian rocks of the Windermere Supergroup and overlying units record the breakup of Rodinia and formation of the northwestern Laurentian ancestral continental margin. Understanding the nature and timing of this transition has been hampered by difficulty correlating poorly dated sedimentary successions from contrasting depositional settings across Mesozoic structures. Here we present new litho- and chemo-stratigraphic data from a Cryogenian–lower Cambrian succession in east-central Yukon (Canada), establish correlations between proximal and distal parts of the upper Windermere Supergroup and related strata in the northern Canadian Cordillera, and consider implications for the formation of the northwestern Laurentian margin. The newly defined Nadaleen Formation hosts the first appearance of Ediacaran macrofossils, while the overlying Gametrail Formation features a large negative carbon isotope anomaly with δ13Ccarb values as low as –13‰ that correlates with the globally developed Shuram-Wonoka anomaly. We also define the Rackla Group, which includes the youngest (Ediacaran) portions of the Windermere Supergroup in the northern Cordillera. The top of the Windermere Supergroup is marked by an unconformity above the Risky Formation that passes into a correlative conformity in the Nadaleen River area. This surface has been interpreted to mark the top of the rift-related succession, but we draw attention to evidence for tectonic instability through the early-middle Cambrian and argue that the transition from rifting to post-rift thermal subsidence is marked by a widespread unconformity that underlies upper Cambrian carbonate rocks. This is younger than the interpreted age of the rift to post-rift transition elsewhere along the ancestral western Laurentian continental margin.
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Makarova, A. L. "Middle–Upper Cambrian Trilobites of the Genus Nganasanella Rosova, 1963 and Their Stratigraphic Significance". Russian Geology and Geophysics 62, n. 07 (1 luglio 2021): 746–64. http://dx.doi.org/10.2113/rgg20194101.
Testo completoAbstract (sommario):
Abstract —This paper presents a revision for the genus Nganasanella Rosova, 1963, first described in the stratotype of the Kulyumbean Regional Stage of the Kulyumbe River section (northwest of the Siberian Platform). This section is typical of the upper Cambrian sediments of the Kotuy–Igarka facies region, formed in a shallow marine shelf. As shown by the study, the genus comprises seven species. The species N. nganasanensis Rosova, 1963 (type species), N. tavgaensis Rosova, 1963, N. glabella (Kobayashi), 1943, N. granulosa Rosova et Makarova, 2009, and N. vernacula Rosova et Makarova, 2009 are found in the Siberian Platform. The species N. australica sp. nov. occurs in northeastern Australia. The species N. trisulcatus (Ergaliev), 1980 is widespread in southern Kazakhstan. Some species (N. granulosa and N. vernacula) are found in open marine facies sediments along with the cosmopolitan agnostid species Glyptagnostus reticulatus (Angelin), 1851, serving as a marker of the lower boundary of upper Cambrian strata in the International Chronostratigraphic Chart and the General Stratigraphic Chart of Russia. The species N. trisulcatus and N. australica are found slightly above Glyptagnostus reticulatus. Representatives of the genus Nganasanella are a link between strata of different facies containing different trilobite associations. Their stratigraphic position can serve as an argument for the correlation of the Kulyumbean Regional Stage with units containing Glyptagnostus reticulatus, i.e., the Omnian and Idamean regional stages, the lower parts of the Kutugunian Horizon and the Sakian Regional Stage, and the Paibian Stage of the International Chronostratigraphic Chart.
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Mel’nikov, N. V., Yu Ya Shabanov e O. S. Shabanova. "Stratigraphic chart of Cambrian deposits in the Turukhansk–Irkutsk–Olekma region, Siberian Platform". Russian Geology and Geophysics 51, n. 6 (giugno 2010): 672–83. http://dx.doi.org/10.1016/j.rgg.2010.05.008.
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Smith, Emily F., Francis A. Macdonald, Tanya A. Petach, Uyanga Bold e Daniel P. Schrag. "Integrated stratigraphic, geochemical, and paleontological late Ediacaran to early Cambrian records from southwestern Mongolia". Geological Society of America Bulletin 128, n. 3-4 (2 settembre 2015): 442–68. http://dx.doi.org/10.1130/b31248.1.
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Lu, Chaojin, Zhen Liu, Haibo Jia, Haiqin Tian, Huayao Zou, Quanqi Dai e Bo Han. "The eogenetic karst of the Cambrian Longwangmiao Formation in the Yangtze Platform: Implications for the eustatic and stratigraphic correlations of Toyonian (Cambrian)". Geological Journal 54, n. 6 (26 novembre 2018): 3720–36. http://dx.doi.org/10.1002/gj.3352.
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Read, J. J. "Seismic reflection investigations of the Hellyer orebody and Que-Hellyer volcanics, North West Tasmania". Exploration Geophysics 20, n. 2 (1989): 159. http://dx.doi.org/10.1071/eg989159.
Testo completoAbstract (sommario):
Two separate seismic reflection surveys have been conducted over Aberfoyle Resources Hellyer orebody and the enclosing Cambrian Que-Hellyer volcanics. The initial survey, conducted as a test case to determine if seismic reflection techniques could detect massive sulphide orebodies at depth, successfully identified the Hellyer orebody, which was found to have a characteristic seismic expression. Identification and mapping of stratigraphic units within the Que-Hellyer volcanics was also possible due to the good geological control available.The second survey did not successfully identify the Hellyer orebody, although some information relating to the structure of the enclosing basin could be inferred from the seismic data. Due to data degradation conventional seismic interpretation techniques could not be applied to the second survey.High resolution seismic surveys can detect massive sulphide orebodies if low velocity overburden problems are eliminated and high frequency data is collected. High resolution surveys can also provide structural and stratigraphic information between widely spaced drill holes in volcanic terrains.
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Khomentovsky, V. V. "The Vendian System of Siberia and a standard stratigraphic scale". Geological Magazine 123, n. 4 (luglio 1986): 333–48. http://dx.doi.org/10.1017/s0016756800033422.
Testo completoAbstract (sommario):
AbstractIn Siberia Vendian is equated with a Yudoma Complex or Yudomian. Yudomian deposits of the Siberian Platform and adjacent geosynclines differ greatly in facies and thickness. According to the composition and structure of Yudomian deposits, four facies provinces may be recognized on the platform. Local stratigraphic charts for each province are presented and their correlation and possibility to subdivide the Vendian System in Siberia into three horizons or stages are substantiated. The upper stage (Nemakit–Daldyn), on the basis of palaeontological evidence, is in its turn subdivided into two zones: Anabarites trisulcatus and Purella antiqua.The most important Early Baikalian rearrangement is proved to take place around 800±50 Ma. The pre-Vendian (Late Baikalian) movements, though less intensive, make the determination of the Yudomian lower boundary easier.The specific character of Vendian biostratigraphy is discussed involving all groups of the organic remains, that causes the necessity of recognition, subdivision and correlation on the basis of the whole complex of data.The boundary between the Vendian System and the Lower Cambrian Tommotian Stage (in type section) is proved to conform to the base of the Pestrozvet Formation, which divides the A. sunnaginicus and P. antiqua zones.
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Evans, James E., Joshua T. Maurer e Christopher S. Holm-Denoma. "Recognition and significance of Upper Devonian fluvial, estuarine, and mixed siliciclastic-carbonate nearshore marine facies in the San Juan Mountains (southwestern Colorado, USA): Multiple incised valleys backfilled by lowstand and transgressive systems tracts". Geosphere 15, n. 5 (9 agosto 2019): 1479–507. http://dx.doi.org/10.1130/ges02085.1.
Testo completoAbstract (sommario):
Abstract The Upper Devonian Ignacio Formation (as stratigraphically revised) comprises a transgressive, tide-dominated estuarine depositional system in the San Juan Mountains (Colorado, USA). The unit backfills at least three bedrock paleovalleys (10–30 km wide and ≥42 m deep) with a consistent stratigraphy of tidally influenced fluvial, bayhead-delta, central estuarine-basin, mixed tidal-flat, and estuarine-mouth tidal sandbar deposits. Paleovalleys were oriented northwest while longshore transport was to the north. The deposits represent Upper Devonian lowstand and transgressive systems tracts. The overlying Upper Devonian Elbert Formation (upper member) consists of geographically extensive tidal-flat deposits and is interpreted as mixed siliciclastic-carbonate bay-fill facies that represents an early highstand systems tract. Stratigraphic revision of the Ignacio Formation includes reassigning the basal conglomerate to the East Lime Creek Conglomerate, recognizing an unconformity separating these two units, and incorporating strata previously mapped as the McCracken Sandstone Member (Elbert Formation) into the Ignacio Formation. The Ignacio Formation was previously interpreted as Cambrian, but evidence that it is Devonian includes reexamined fossil data and detrital zircon U-Pb geochronology. The Ignacio Formation has a stratigraphic trend of detrital zircon ages shifting from a single ca. 1.7 Ga age peak to bimodal ca. 1.4 Ga and ca. 1.7 Ga age peaks, which represents local source-area unroofing history. Specifically, the upper plate of a Proterozoic thrust system (ca. 1.7 Ga Twilight Gneiss) was eroded prior to exposure of the lower plate (ca. 1.4 Ga Uncompahgre Formation). These results are a significant alternative interpretation of the geologic history of the southern Rocky Mountains.
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Cooper, R. A., J. B. Jago e J. G. Begg. "Cambrian trilobites from Northern Victoria Land, Antarctica, and their stratigraphic implications". New Zealand Journal of Geology and Geophysics 39, n. 3 (settembre 1996): 363–87. http://dx.doi.org/10.1080/00288306.1996.9514720.
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ZHU, MAOYAN, e XIAN-HUA LI. "Introduction: from snowball Earth to the Cambrian explosion–evidence from China". Geological Magazine 154, n. 6 (27 ottobre 2017): 1187–92. http://dx.doi.org/10.1017/s0016756817000644.
Testo completoAbstract (sommario):
The Neoproterozoic–Palaeozoic transition (NPT) around 600 Ma ago was a critical time interval when the Earth experienced fundamental change, manifested as climatic extremes – ‘snowball Earth’ – followed by the emergence and rapid diversification of animals – ‘Cambrian explosion’. How animals and environments co-evolved, and what caused these fundamental changes to the Earth system during the NPT, is a great scientific puzzle, which has been a rapidly developing frontier of interdisciplinary research between bio- and geosciences. South China preserves a complete stratigraphic succession of the NPT developed in various facies ranging from shallow to deep marine realms with extraordinarily well-preserved, successive fossil biotas in various taphonomic settings (Zhu, 2010; Fig. 1), making it a key area and global focus of studies in the field over recent decades. Indeed, the current narrative of early animal evolution has largely been based on the fossil biotas from South China. These include: (1) the world's oldest microscopic animal fossils with cellular details from the early Ediacaran Weng'an biota (Doushantuo Formation); (2) putative macroscopic animal fossils preserved as carbonaceous imprints from the early Ediacaran Lantian, Wenghui and Miaohe biotas (also Doushantuo Formation); (3) typical late Ediacaran faunas, preserved in dark limestone (Shibantan biota) and as large and poorly mineralized tubular animal fossils (Gaojiashan biota), both from the Dengying Formation; (4) phosphatized small shelly and soft-bodied animal fossils from the early Cambrian Meishucun and Kuanchuanpu faunas; and (5) Cambrian fossil Lagerstätten (Chengjiang, Guanshan and Kaili faunas) with typical Burgess Shale-type soft-bodied preservation.
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Evans, D. A., A. Yu Zhuravlev, C. J. Budney e J. L. Kirschvink. "Palaeomagnetism of the Bayan Gol Formation, western Mongolia". Geological Magazine 133, n. 4 (luglio 1996): 487–96. http://dx.doi.org/10.1017/s0016756800007615.
Testo completoAbstract (sommario):
AbstractOriented samples of the Lower Cambrian Bayan Gol Formation from Salaany Gol, Mongolia, were collected at roughly 5 m stratigraphic intervals for palaeomagnetic analysis. Progressive alternatingfield and thermal demagnetization isolated two magnetic components: a present-field overprint, typically removed by 10 mT fields and ~200°C heating; and a high-coercivity, high-unblocking-temperature (550–600 °C), predominantly single-polarity component that was imparted to the rocks prior to early or middle Palaeozoic deformation. Single-polarity magnetization at Salaany Gol contrasts with results from Lower Cambrian rocks on the Siberian platform, previously considered correlative with the Bayan Gol Formation, which show a prominent change in polarity bias near the top of the Tommotian Stage. Two hypotheses can explain this discrepancy. First, the entire Bayan Gol Formation may correlate with the predominantly reversely polarized, lower half of the Tommotian Stage in Siberia. This model is consistent with plausible interpretations of δ13C profiles for the Zavkhan basin and the Siberian platform. Alternatively, the characteristic magnetic direction from our samples may be a pre-fold overprint. If post-accretionary, then comparison with Siberian palaeomagnetic results suggest a Silurian–Devonian remagnetization age, and existing bioand chemostratigraphic correlations provide the most reliable spatial and temporal links between the Zavkhan basin and the Siberian platform. If the observed magnetic directions are primary or an immediate overprint then they may be used to constrain the early Cambrian palaeogeography of the Zavkhan basin and the Palaeo-Pacific Ocean. Mean inclination of 62 ±4° corresponds to a palaeolatitude of 44 ±5°, several thousand kilometres from the equatorial Siberian craton
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Khomentovsky, V. V., e A. S. Gibsher. "The Neoproterozoic–lower Cambrian in northern Govi-Altay, western Mongolia: regional setting, lithostratigraphy and biostratigraphy". Geological Magazine 133, n. 4 (luglio 1996): 371–90. http://dx.doi.org/10.1017/s001675680000755x.
Testo completoAbstract (sommario):
AbstractThis paper provides a framework for the stratigraphy and correlation of key sections through the Neoproterozoic–lower Cambrian of the Govi-Altay area, western Mongolia, studied by members of IGCP Project 303. Dzabkhan Formation volcanic rocks at the base of the succession are suggested to have formed during rifting of the Baydrik–Tarbagatay microcontinent in the Baykalian interval (c. 850–650 Ma). Pre-Vendian accretion transformed this rift and adjacent microcontinental fragments into a marginal marine back-arc basin, in which accumulated relatively uninterrupted Neoproterozoic and earliest Palaeozoic sediments. Lithostratigraphy for the latter is defined, with detailed maps, at five sections (Bayan Gol northern and southern blocks, Tsagaan Gol, Salaany Gol and Tayshir). The Tsagaan Oloom Formation lower member contains two diamictites of possible Sturtian age. Middle and upper carbonates are compared with the Yudomian (Vendian) of Siberia, the former ending with a unit ofBoxonia grumulosastromatolites. In the upper member, phosphorite-shale is followed mainly by limestones, with the earliest skeletal fauna. The Bayan Gol Formation comprises siliciclastic–limestone intercalations with increasingly diverse invertebrate biota. Correlation of lithological marker beds across the study area produces a composite stratigraphic section to which the earliest skeletal fossil occurrences are tied. TheAnabarites trisulcatusZone of the Nemakit-Daldynian Stage begins near the base of the Tsagaan Oloom Formation upper member (unit 11). ThePurella antiquaZone begins near the base of the Bayan Gol Formation (unit 18). Assemblages typical of theNochoroicyathus sunnaginicusZone (base of the Tommotian Stage) range through units 19 to 23. Elements typical of theDokidocyathus regularisZone (middle Tommotian) appear in unit 24 near the top of the Bayan Gol Formation.