Статті в журналах: "Precambrian-Cambrian boundary"

1

Fåhræus, Lars E. ✝. "The Precambrian-Cambrian Boundary - victim of parochialism." Newsletters on Stratigraphy 31, no. 1 (September 15, 1994): 1–19. http://dx.doi.org/10.1127/nos/31/1994/1.

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2

Fairchild, Ian. "The Precambrian-Cambrian boundary." Trends in Ecology & Evolution 4, no. 8 (August 1989): 251–52. http://dx.doi.org/10.1016/0169-5347(89)90175-4.

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3

Narbonne, Guy M., Paul M. Myrow, Ed Landing, and Michael M. Anderson. "A candidate stratotype for the Precambrian–Cambrian boundary, Fortune Head, Burin Peninsula, southeastern Newfoundland." Canadian Journal of Earth Sciences 24, no. 7 (July 1, 1987): 1277–93. http://dx.doi.org/10.1139/e87-124.

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The Burin Peninsula exhibits an exceptionally thick and essentially continuous succession of marine strata through the Precambrian–Cambrian transition. Fossils are abundant and include trace fossils, small shelly fossils, vendotaenid algae, soft-bodied megafossils, and microfossils. The Burin Peninsula is readily accessible and has long been considered a potential area for a Precambrian–Cambrian boundary stratotype.A continuous section through the upper part of member 1 and all of member 2 of the Chapel Island Formation is exposed at Fortune Head, and this section is herein proposed as a global stratotype for the Precambrian–Cambrian boundary. The boundary horizon is located 2.4 m above the base of member 2 of the Chapel Island Formation. This horizon marks the base of the basal Cambrian Phycodes pedum (ichnofossil) Zone and immediately overlies the top of the Late Precambrian Harlaniella podolica (ichnofossil) Zone. Shelly fossils (sabelliditids) first appear a few metres below the proposed boundary. Soft-bodied megafossils, carbonaceous impressions of vendotaenid algae, and organic-walled microfossils occur both below and above this boundary and enhance global correlation with this section.Fossils of the Rusophycus avalonensis (ichnofossil) Zone first appear midway through member 2 (approximately 135 m above the proposed boundary) and occur commonly throughout the upper part of the Chapel Island Formation and the overlying Random Formation. Calcareous small shelly fossils (?Circotheca sp.) appear near the top of member 2 (approximately 400 m above the proposed boundary), and a more diverse Aldanella attleborensis small shelly fossil assemblage characterizes the uppermost strata of member 3 and all of member 4 of the Chapel Island Formation (approximately 550–650 m above the proposed boundary). The lowest trilobites, representatives of the Callavia broeggeri Zone, first appear more than 1000 m above the proposed Precambrian–Cambrian boundary.

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4

Gamper, A., U. Struck, F. Ohnemueller, C. Heubeck, and S. Hohl. "Chemo- and biostratigraphy of the Gaojiashan section (northern Yangtze platform, South China): a new Pc-C boundary section." Fossil Record 18, no. 2 (June 10, 2015): 105–17. http://dx.doi.org/10.5194/fr-18-105-2015.

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Abstract. The widespread, terminal Ediacaran Dengying Formation (~ 551–~ 542 Ma) of South China hosts one of the most prominent negative carbonate carbon isotope excursions in Earth's history and thus bears on the correlation of the Precambrian–Cambrian boundary worldwide. The dominantly carbonate strata of the Dengying Formation are largely studied for their unique preservation of its terminal Ediacaran fauna but their geochemical context is poorly known. This study presents the first high-resolution stable isotope record (δ13C, δ18O) of calcareous siliciclastic shallow-water deposits of the Gaojiashan section (Shaanxi Province). The section includes (in ascending order) the Algal Dolomite Member, the Gaojiashan Member and the Beiwan Member of the Dengying Formation. Our data record a major δ13Ccarb negative excursion to −6 ‰ in the uppermost Gaojiashan Member which is comparable in shape and magnitude to the global Precambrian–Cambrian boundary negative δ13C excursion. Our data set is consistent with a "shallow-water anoxia" scenario which is thought to contribute to the "Cambrian explosion". The stratigraphic occurrence of Cloudina and a large negative δ13C excursion suggest that the Precambrian–Cambrian boundary is located near the top of the Gaojiashan Member and, consequently, that overlying carbonates and dolomites of the Beiwan Member are of earliest Cambrian age. Thus the Gaojiashan section may represent a new shallow-water section spanning the Precambrian–Cambrian boundary. Although bio- and chemostratigraphic data support this novel interpretation, we cannot exclude the possibility that the key excursions may represent a local perturbation indicating a restricted-basin environment.

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5

Jie-Dong, Yang, Sun Wei-Guo, Wang Zong-Zhe, and Wang Yin-Xi. "Sm—Nd isotopic age of Precambrian—Cambrian boundary in China." Geological Magazine 133, no. 1 (January 1996): 53–61. http://dx.doi.org/10.1017/s001675680000724x.

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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.

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6

Maithy, P. K., and Rupendra Babu. "Upper Vindhyan biota and Precambrian/Cambrian Boundary." Journal of Palaeosciences 46, no. (1-2) (December 31, 1997): 1–6. http://dx.doi.org/10.54991/jop.1997.1311.

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The upper age limit of the Vindhyan Supergroup is yet a point of debate. The evidences from structural biological remains, megafossils and organic-walled microfossils, from the Bhander Group support the view that the upper age limit of the Vindhyan Supergroup does not extend beyond Vendian. This fact also gets support by the absence of Ediacaran fauna and vendotaenids in Bhander. All the evidences now point to the fact that the deposition of the Vindhyan sediments ceased before the Precambrian/Cambrian Transition interval.

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7

VALENTINE, J. W. "A Biotic Transition: The Precambrian-Cambrian Boundary." Science 245, no. 4922 (September 8, 1989): 1126. http://dx.doi.org/10.1126/science.245.4922.1126.

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8

Kimura, Hiroto, and Yoshio Watanabe. "Oceanic anoxia at the Precambrian-Cambrian boundary." Geology 29, no. 11 (2001): 995. http://dx.doi.org/10.1130/0091-7613(2001)029<0995:oaatpc>2.0.co;2.

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9

AWRAMIK, STANLEY M. "The Precambrian-Cambrian boundary and geochemical perturbations." Nature 319, no. 6055 (February 1986): 696. http://dx.doi.org/10.1038/319696a0.

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10

MORRIS, SIMON CONWAY, and STEFAN BENGTSON. "The Precambrian-Cambrian boundary and geochemical perturbations." Nature 319, no. 6055 (February 1986): 696–97. http://dx.doi.org/10.1038/319696b0.

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11

HSÜ, KENNETH J. "The Precambrian-Cambrian boundary and geochemical perturbations." Nature 319, no. 6055 (February 1986): 697. http://dx.doi.org/10.1038/319697a0.

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12

Cowie, J. W. "Continuing Work on the Precambrian-Cambrian Boundary." Episodes 8, no. 2 (June 1, 1985): 93–97. http://dx.doi.org/10.18814/epiiugs/1985/v8i2/003.

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13

Brasier, Martin, John Cowie, and Michael Taylor. "Decision on the Precambrian-Cambrian boundary stratotype." Episodes 17, no. 1-2 (June 1, 1994): 3–8. http://dx.doi.org/10.18814/epiiugs/1994/v17i1.2/002.

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14

Crimes, T. P., and Jiang Zhiwen. "Trace fossils from the Precambrian–Cambrian boundary candidate at Meishucun, Jinning, Yunnan, China." Geological Magazine 123, no. 6 (November 1986): 641–49. http://dx.doi.org/10.1017/s0016756800024158.

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AbstractThe Precambrian–Cambrian boundary candidate section at Meishucun, China, has yielded trace fossils which are abundant at some horizons. The earliest occur in Unit 3 of the Zhongyicun Member approximately 8 m above the lower selected stratotype reference point for the boundary and includeArenicolitessp.,Asteriacitessp.,Neonereites biserialis, N. uniserialisandSellaulichnus meishacunensis. The next trace-fossil-bearing horizon is in Unit 6 of the Zhongyicun Member whereCochlichnussp.,Monomorphichnussp.,Neonereites biserialisandN. uniserialisoccur. Immediately above, in Unit 7, areCruzianasp.,Didymaulichnus miettensis, Monomorphichnussp. andRusophycussp. In the Badaowan Member at the top of the section there areDidymaulichnussp. andTaphrhelminthopsis circularisin Unit 9,Arenicolitessp.,Diplocraterionsp.,Gordia molassica, Skolithossp. andT. circularisin Unit 11, andGordia meandria, ?Plagiogmussp.,Skolithossp. andT. circularisin Unit 12.Comparison of this trace-fossil distribution with that in key Precambrian–Cambrian boundary sections in other countries indicates that the ranges of a few trace fossils cross the boundary (e.g.Didymaulichnus, Neonereites, Planolites) but most appear only in the Cambrian. Different ichnogenera seem to appear at various levels above the boundary.ArenicolitesandAsteriacitesare among the first, whileTaphrhelminthopsis circularisis only encountered higher in all sequences. Some have only been recorded at much higher levels and relatively close to the first appearance of trilobites (e.g.Cruziana, Diplocraterion, Rusophycus). This suggests that the first appearance of specific trace fossils or groups of trace fossils may be valuable for locating the boundary in some sections and for correlating late Precambrian and early Cambrian strata.

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15

Knoll, Andrew H., and Keene Swett. "Micropaleontology across the Precambrian—Cambrian boundary in Spitsbergen." Journal of Paleontology 61, no. 5 (September 1987): 898–926. http://dx.doi.org/10.1017/s0022336000029292.

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Paleobiological studies of early metazoan evolution are critically dependent on the accurate stratigraphic subdivision and correlation of uppermost Proterozoic and Lower Cambrian sequences. Planktonic microfossils evolved rapidly during this period and are widely distributed and abundant in Vendian and Lower Cambrian rocks; therefore, they provide what is potentially one of the best means of correlating successions of this age. In Ny Friesland, Spitsbergen, tillite-bearing detrital rocks of the uppermost Proterozoic Polarisbreen Group are overlain without apparent unconformity by the Tokammane Formation, a tripartite lithologic sequence consisting of quartzarenites (Blårevbreen Member) overlain by dark shales with subordinate sandstone (Topiggane Member) and dolomites (Ditlovtoppen Member).Salterella, hyoliths, and other invertebrate remains occur in the upper part of the Tokammane succession; trace fossils are found in the Tokammane quartzarenites and shales, as well as in the uppermost few meters of the Polarisbreen sequence. Planktonic microfossils occur throughout the succession. They indicate that the Polarisbreen Group is Vendian in age and that a hiatus corresponding in time to the latest Vendian and (perhaps) earliest Cambrian coincides with the Polarisbreen/Tokammane boundary. Lower Topiggane shale samples contain acritarchs comparable to those found in the sub-HolmiaLontova Beds of Eastern Europe. Upper Topiggane samples contain diverse acritarch assemblages that indicate a lateHolmiaorProtolenusage, suggesting the presence of a second hiatus within the Tokammane Formation. Planktonic microfossils allow biostratigraphic correlation with other sequences both within (East Greenland) and between (East European Platform) paleocontinents. Like those from other areas, diversity trends exhibited by late Proterozoic and Early Cambrian acritarchs from Spitsbergen indicate a major Vendian episode of extinction followed by Early Cambrian rediversification of planktonic microfossils.

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16

Brasier, M. D., and P. Singh. "Microfossils and Precambrian–Cambrian boundary stratigraphy at Maldeota, Lesser Himalaya." Geological Magazine 124, no. 4 (July 1987): 323–45. http://dx.doi.org/10.1017/s0016756800016666.

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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.

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17

Wen, Hanjie, Jean Carignan, Yuxu Zhang, Haifeng Fan, Christophe Cloquet, and Shirong Liu. "Molybdenum isotopic records across the Precambrian-Cambrian boundary." Geology 39, no. 8 (August 2011): 775–78. http://dx.doi.org/10.1130/g32055.1.

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18

Corsetti, Frank A. "Carbon isotope stratigraphy of the Neoproterozoic-Cambrian transition: An introduction." Paleontological Society Papers 10 (November 2004): 17–34. http://dx.doi.org/10.1017/s108933260000231x.

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Carbonate units deposited during the Precambrian-Cambrian transition records a unique δ13C profile that is useful for chemostratigraphic correlation. However, the Precambrian-Cambrian boundary is currently defined within siliciclastic units where δ13C data are not available. The mixed siliciclastic-carbonate succession from the southern Great Basin, USA, records the appropriate fossils in the siliciclastic strata interbedded with carbonate strata that record the appropriate shifts in δ13C to facilitate correlation between the lithologic end-members. Ultimately, the integrated dataset demonstrates that vertical burrowing and the onset of widespread biomineralization was essentially synchronous.

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19

Brasier, M. D. "Global ocean—atmosphere change across the Precambrian—Cambrian transition." Geological Magazine 129, no. 2 (March 1992): 161–68. http://dx.doi.org/10.1017/s0016756800008256.

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AbstractThe late Precambrian and Cambrian world experienced explosive evolution of the biosphere, including the development of biomineral skeletons, and notably of phosphate and siliceous skeletons in the initial stages of the adaptive radiation. Ongoing research indicates profound changes in climate and atmospheric carbon dioxide over this span of time. Glacial conditions of the Varangian epoch occur enigmatically at low latitudes, associated with carbonate rocks. Later changes in palaeogeography, sea level rise and salinity stratification encouraged prolonged ‘greenhouse’ conditions in both latest Precambrian and Cambrian times, with indications of relatively low primary production in the oceans. The Precambrian–Cambrian boundary interval punctuated this trend with evaporites, phosphogenic events and carbon isotope excursions; these suggest widespread eutrophication and conjectured removal of carbon dioxide from the atmosphere. Whatever the cause, nutrient–enriched conditions appear to have coincided with the development of phosphatic and siliceous skeletons among the earliest biomineralized invertebrates.

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20

Tucker, Maurice E. "Carbon isotope excursions in Precambrian/Cambrian boundary beds, Morocco." Nature 319, no. 6048 (January 1986): 48–50. http://dx.doi.org/10.1038/319048a0.

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21

BRASIER, M. D. "Evolutionary and geological events across the Precambrian-Cambrian boundary." Geology Today 1, no. 5 (September 1985): 141–46. http://dx.doi.org/10.1111/j.1365-2451.1985.tb00316.x.

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22

VIDAL, G., and M. MOCZYD£OWSKA. "Patterns of phytoplankton radiation across the Precambrian-Cambrian boundary." Journal of the Geological Society 149, no. 4 (July 1992): 647–54. http://dx.doi.org/10.1144/gsjgs.149.4.0647.

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23

Landing, Ed. "Precambrian-Cambrian boundary global stratotype ratified and a new perspective of Cambrian time." Geology 22, no. 2 (1994): 179. http://dx.doi.org/10.1130/0091-7613(1994)022<0179:pcbgsr>2.3.co;2.

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24

Palacios, Teodoro, and Gonzalo Vidal. "Lower Cambrian acritarchs from northern Spain: the Precambrian-Cambrian boundary and biostratigraphic implications." Geological Magazine 129, no. 4 (July 1992): 421–36. http://dx.doi.org/10.1017/s0016756800019518.

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AbstractAcritarchs are reported from basal Cambrian rock units inthe Cantabrian region of northern Spain that are known to contain archaeocyathan and trilobite faunas. Biostratigraphic correlation of the Iberian sequences with other regions has been hampered by the strong provincialism of these faunas. However, this report of evidently cosmopolitan acritarch taxaestablishes the time equivalence of early Cambrian trilobite faunas from Iberia, Baltoscandia and the East European Platform (EEP). Our data suggest that the detrital deposition of the Lower Cambrian Herreria Formation embraces at least three (and possibly four) Lower Cambrian acritarch zones previously identified in the EEP, eastern Siberia, Baltoscandia, Scotland, Greenland, Svalbard and western North America. The early Cambrian transgression in northern Spain was probably initiated in Talsy times (Schmidtiellus mickwitzi trilobite Zone in Baltoscandia and the EEP), in part corresponding to the Dokidocyathus regularis archaeocyathian Zone of the Middle Tommotian in Siberia.

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25

Brasier, M. D., M. M. Anderson, and R. M. Corfield. "Oxygen and carbon isotope stratigraphy of early Cambrian carbonates in southeastern Newfoundland and England." Geological Magazine 129, no. 3 (May 1992): 265–79. http://dx.doi.org/10.1017/s001675680001921x.

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AbstractCarbonate rocks have been sampled through predominantly siliciclastic sediments above the Precambrian-Cambrian global stratotype level in southeastern Newfoundland to assess their potential for oxygen and carbon isotope stratigraphy. Comparable successions were sampled at Nuneaton and Comley in England. Greatly depleted δ18O signals are attributed to widespread thermal alteration during deep burial and granitic intrusion, including within the stratotype region. Carbon isotope ratios appear to have been less affected and these are described from nine sections. A provisional, composite δ13C curve is based on non-ferroan, pink nodular and bedded micrites. Several δ13C excursions occur in the fossiliferous Bonavista Group and allow the position of the Tommotian-Atdabanian boundary to be identified. Chemostratigraphic correlation of the new Precambrian-Cambrian boundary stratotype may, however, prove difficult because of the lack of suitable, well-preserved carbonates. The search must begin for a comparable reference section allowing global correlation of the boundary level using chemostratigraphy as well as biostratigraphy.

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26

LI, DA, HONG-FEI LING, SHAO-YONG JIANG, JIA-YONG PAN, YONG-QUAN CHEN, YUAN-FENG CAI, and HONG-ZHEN FENG. "New carbon isotope stratigraphy of the Ediacaran–Cambrian boundary interval from SW China: implications for global correlation." Geological Magazine 146, no. 4 (March 26, 2009): 465–84. http://dx.doi.org/10.1017/s0016756809006268.

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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.

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27

Hamdi, B., M. D. Brasier, and Jiang Zhiwen. "Earliest skeletal fossils from Precambrian–Cambrian boundary strata, Elburz Mountains, Iran." Geological Magazine 126, no. 3 (May 1989): 283–89. http://dx.doi.org/10.1017/s0016756800022378.

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AbstractThe lithological and biotic succession across the late Precambrian to early Cambrian interval is outlined for the Dalir and Valiabad successions of the Elburz Mountains of Iran. The Lower Dolomite Member contains an assemblage of phosphatic tubes and other poorly preserved remains. The succeeding Lower Shale Member bears macroscopic chuariamorphid algae. Early skeletal fossil diversity rises through the Middle Dolomite Member, with the successive appearance ofProtohertzina anabarica, Cambrotubulus decurvatusandAnabarites trisulcatus, culminating near the top of the dolomites with the appearance ofPurellasp.,Maikhanella multa, Tiksitheca licisand circothecids. This succession is compared with lower to upper parts of the Nemakit-Daldyn Formation of Siberia. The overlying Upper Shale Member bears phosphatic beds at its base with allathecids and an uncoiled pelagiellid (?Aldanellasp.) that suggest comparison with lower Tommotian strata and the Precambrian–Cambrian boundary phosphorite event of southern and central Asia. A rich assemblage of molluscs appears high in the Upper Shale Member, including theLatouchella korobkovigroup and thePelagiella lorenzigroup. The succession is broadly homotaxial with those from the Siberian Platform and Mongolia and those platforms bordering Gondwana (India, Kazakhstan, South China).

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28

Al-Husseini, Moujahed, Joachim Amthor, John Grotzinger, and Joerg Mattner. "Arabian Plate Precambrian-Cambrian Boundary interpreted in Oman’s Ara Group." GeoArabia 8, no. 4 (October 1, 2003): 578–80. http://dx.doi.org/10.2113/geoarabia0804578.

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29

Vannier, Jean, Ivan Calandra, Christian Gaillard, and Anna Żylińska. "Priapulid worms: Pioneer horizontal burrowers at the Precambrian-Cambrian boundary." Geology 38, no. 8 (August 2010): 711–14. http://dx.doi.org/10.1130/g30829.1.

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30

Kumar, Gopendra, Ravi Shanker, V. K. Mathur, P. K. Maithy, S. K. Bhattacharya, and R. K. Jain. "Terminal Proterozoic-Cambrian sequences in India: a review with special reference to Precambrian-Cambrian Boundary." Journal of Palaeosciences 46, no. (1-2) (December 31, 1997): 19–31. http://dx.doi.org/10.54991/jop.1997.1314.

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The Terminal Proterozoic marine sequences, grading into Cambrian, are present in the Krol Basin (Lesser Himalaya), the Kashmir, Spiti-Zanskar and Kumaun Basins (Higher Himalaya) and in Marwar Basin (western India). These sequences postdate a major tectono-thermal event associated with Cadomian Orogeny and rest on eroded older successions which include well-dated Malani Igneous Suite (Malani Rhyolite 745 ±10 Ma; Siwana Granite 731± 14 Ma) in Western India and over the Salkhala Group with granites (745 ± 50 Ma) or the Simla Group in the Himalaya. This cycle of sedimentation terminated with Pan-African Orogeny in Late Cambrian. These sequences are dominantly siliciclastic in basins in Higher Himalaya while those in Krol Basin and Marwar Basin show development of thick carbonate-evaporite facies with or without phosphorite. From the Upper Vindhyan and Bhima Groups in central and south India, respectively a Chuaria-Tawuia Assemblage along with sphaeromorphida Acritarch of Early Neoproterozoic age has been recorded. The δ13C values range from +1.3 to +4.0 ‰ PDB and that of δ 18O from -5 to -9‰ PDB. These are, thus, not considered part of this sequence. In absence of age-determinating biota and radiometric dates from the basal part of the succession, the lower boundary of the Terminal Proterozoic cannot be delineated and dated. However, a significant depletion in values may be taken to mark the lower boundary. The upper boundary of the Terminal Proterozoic (Precambrian-Cambrian Boundary) cannot be demarcated in terms of GSSP due to the absence of trace fossils of Zone-1 (Harlaneilla podolika Zone) and Zone-II (Phycodes pedum Zone) in carbonate facies in Krol Basin and poor documentation of siliciclastic facies in Kashmir and Spiti-Zanskar Basins. The trace fossils correlative with ichnozone-III occur in all sections in the Himalayas and are useful for regional and global correlations. However, a significant depletion in δ13C values has been recorded in the carbonate facies of the Krol Basin between the horizons yielding Ediacaran and small shelly fossils of Meishucunian Zone-I. This has also been recorded in the Marwar Basin below the Phosphorite Bed. This depletion may be correlated with that recorded from the Precambrian-Cambrian transition in Siberian Platform, Anti Atlas Mountains, Morocco, China, etc. It may be taken into consideration to define and mark the boundary in the absence of trace fossils.

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31

Lindsay, J. F., M. D. Brasier, D. Dorjnamjaa, R. Goldring, P. D. Kruse, and 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, no. 4 (July 1996): 417–28. http://dx.doi.org/10.1017/s0016756800007585.

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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.

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32

Kumar, Gopendra, D. K. Bhatt, and B. K. Raina. "Skeletal microfauna of Meishucunian and Qiongzhusian (Precambrian–Cambrian boundary) age from the Ganga Valley, Lesser Himalaya, India." Geological Magazine 124, no. 2 (March 1987): 167–71. http://dx.doi.org/10.1017/s0016756800015995.

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AbstractThe earliest skeletal microfauna of Precambrian-Cambrian age recovered from the ‘Lower Tal’ sequence (Chert-Phosphorite to Calcareous members) of the Tal Formation, exposed in the Ganga Valley, Lesser Himalaya, Uttar Pradesh, India, has been grouped into three assemblages. In ascending order these are: assemblage I, containing Anabarites trisulcatus Missarzhevsky, Tiksitheca korobovi (Miss.). Circotheca sp., Turcutheca sp., Spirellus columnorus Jiang and Olivooides alveus Qian; assemblage II, yielding Allonia erromenosa Jiang, A. sp. cf. A. erromenosa Jiang, Dimidia simpleca Jiang, D. sp. cf. D. simpleca Jiang and Hyolithellus sp.; and assemblage III, comprising Pelagiella lorenzi Kobayashi, Auriculatespira madianensis Zhou & Xiao and A. andunca He & Pei. The assemblages I and II are correlatable to the Meishucunian Zone I and Zone III respectively, and the assemblage III to the Qiongzhusian Stage of China. Thus the ‘Lower Tal’ sequence is assigned to Precambrian–Cambrian age.

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33

Peter Crimes, T. "Trace fossils and correlation of late Precambrian and early Cambrian strata." Geological Magazine 124, no. 2 (March 1987): 97–119. http://dx.doi.org/10.1017/s0016756800015922.

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AbstractTrace fossils are abundant and diverse in many clastic sequences spanning the Precambrian-Cambrian boundary and may prove to be the most useful palaeontological method for global correlation in this stratigraphic interval. The ichnofaunas of the latest Precambrian (Vendian) rocks include some forms whose range does not extend into the Cambrian (e.g.Bilinichnus, Intrites, Palaeopascichnus, Vendichnus, Vimenites) and others which continue throughout most or all of the Phanerozoic (e.g.Arenicolites, Aulichnites, Cochlichnus, Didymaulichnus, Gordia, Neonereites, Planolites, Skolithos). At least 50 ichnogenera make their first appearance below the lowest trilobites in sections with broad geographic spread. A few of these appear to have a short time range, extending to about the incoming of the trilobites (e.g.Astropolichnus, Didymaulichnus miettensis, Plagiogmus, Taphrhelminthopsis circularis), but the majority continue through most or all of the Phanerozoic.For correlation of Precambrian-Cambrian boundary sequences it is therefore possible to use both the occurrence of those ichnogenera with a short time range and the incoming of those with an extended range. Three stratigraphical zones can be recognized with respect to the incoming of trace fossils. Zone I is of Upper Vendian age and includesArenicolites, Bilinichnus, Cochlichnus, Didymaulichnus, Gordia, Harlaniella, Intrites, Nenoxites, Neonereites, Palaeopascichnus, Skolithos, VendichnusandVimenites.In Zone II, of Lower Tommotian age, the earliest examples ofBergaueria, Phycodes, TeichichnusandTreptichnusare encountered. Many trace fossils appear in Zone III, which extends from Upper Tommotian to Lower Atdabanian, but the most important are:Astropolichnus, Cruziana, Diplichnites, Diplocraterion, Dimorphichnus, Plagiogmus, RusophycusandTaphrhelminthopsis circularis.This vertical zonation of trace fossils allows an attempt at world-wide correlation, from which the most significant conclusions are that the Vendian/Tommotian boundary can probably be placed: (i) near the middle of the McNaughton Formation in the Rocky Mountains, Canada; (ii) at the base of the Deep Spring Formation or in the underlying Reed Dolomite in the White Inyo Mountains, California, U.S.A.; (iii) low in the Chapel Island Formation in the Burin Peninsula, Newfoundland, Canada; (iv) at or close to the base of the Candana Quartzite in North Spain; (v) at or below the base of the Breivik Member in Finnmark, Norway; and (vi) near or below the base of the Zhongyicun Member at Meischucun, China.The sections in the Burin Peninsula, Newfoundland and Meischucun, China are favoured candidates for the global stratotype for the Precambrian-Cambrian boundary. In the Burin Peninsula, the trace fossils suggest that the Tommotian/Atdabanian boundary may be within or at the base of the Random Formation, thereby implying that the Tommotian may include a thickness of 500 m of sediment comprising at least most of the Chapel Island Formation. At Meishucun, the ichnofaunal evidence implies that the Tommotian/Atdabanian boundary is probably no higher than the top of the Zhongyicun Member. The thickness of the Tommotian is therefore possibly only about 20 m here, implying a very condensed sequence, a conclusion consistent with an abundance of phosphorites. Two stratotype reference points for the Precambrian-Cambrian boundary have been suggested in this section. The lower point (0.8 m above the base of the Xiawaitoushan Member) may be near the Vendian/Tommotian boundary or younger, while the higher point (base of Unit 7 of the Zhongyicun Member) is probably Upper Tommotian or even Lower Atdabanian. The higher point would place the boundary above the world-wide dramatic increase in trace fossil abundance and diversity but probably before the first trilobites. This would almost certainly have advantages for correlation. The inference that the Meishucun section is younger than most Chinese work suggests should not therefore, by itself, prejudice its adoption as global stratotype.In general, where comparative data are available, the trace fossil correlations agree well with pre-existing proposals based on small shelly fossils. The degree of resolution of the two methods would appear at present to be similar but trace fossils, being found mainly in clastic facies, may benefit from more frequent occurrence.

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34

SAPPENFIELD, AARON D., LIDYA G. TARHAN, and MARY L. DROSER. "Earth's oldest jellyfish strandings: a unique taphonomic window or just another day at the beach?" Geological Magazine 154, no. 4 (June 13, 2016): 859–74. http://dx.doi.org/10.1017/s0016756816000443.

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AbstractDiscoidal macrofossils reported herein from the lower Cambrian Zabriskie Quartzite (Great Basin, western United States) record the oldest Phanerozoic medusozoan body fossils, as well as the oldest medusozoan stranding event on record. Moreover, these fossils provide evidence of a significant shift in the taphonomic mode characteristic of preservation of nonmineralized taxa in coarse-grained siliciclastic successions near the onset of the Phanerozoic. Taphonomic and sedimentological evidence recorded by these and younger examples of stranded Cambrian medusae is consistent in suggesting that several of the requirements for preservation of these fossils were holdovers from the Ediacaran Period, including the presence of microbial mats and a lack of carcass disturbance by scavenging and/or bioturbating taxa. To shed further light upon the taphonomic factors necessary for the preservation of Cambrian medusae, we compared the biostratinomy and sedimentology of Cambrian medusa strandings to those of Ediacara Biota assemblages from lithologically similar successions. We find key secular disparities in the taphonomic histories of these two types of fossil assemblage. Inconsistencies between the preservational styles characteristic of fossil assemblages preserved in sandstone lithofacies on each side of the Precambrian–Cambrian boundary are explained by a considerable change in the preferred depositional setting in which these macrofossil assemblages are preserved. Thus, rather than documenting a single taphonomic continuum through the Precambrian–Cambrian transition, the Zabriskie and younger medusozoan body fossil assemblages record the advent of an entirely new, yet still very rarely exploited, taphonomic window exclusive to the Cambrian Period.

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35

Wille, Martin, Thomas F. Nägler, Bernd Lehmann, Stefan Schröder, and Jan D. Kramers. "Hydrogen sulphide release to surface waters at the Precambrian/Cambrian boundary." Nature 453, no. 7196 (May 28, 2008): 767–69. http://dx.doi.org/10.1038/nature07072.

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36

Brasier, M. D. "Phosphogenic events and skeletal preservation across the Precambrian-Cambrian boundary interval." Geological Society, London, Special Publications 52, no. 1 (1990): 289–303. http://dx.doi.org/10.1144/gsl.sp.1990.052.01.21.

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37

Khomentovsky, V. V., and G. A. Karlova. "Biostratigraphy of the Vendian-Cambrian beds and the lower Cambrian boundary in Siberia." Geological Magazine 130, no. 1 (January 1993): 29–45. http://dx.doi.org/10.1017/s0016756800023700.

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AbstractGeneral agreement exists that the position of the base of the Cambrian (Precambrian–Cambrian boundary) should coincide with a biostratigraphic marker that can be widely traced and is linked to the evolution of the small shelly fauna. On the Siberian platform the presence of distinct facies during the Vendian–Cambrian interval has made biostratigraphic correlation based on palaeontological data highly contentious. A solution to this problem appears to exist with the recognition of an almost uninterrupted profile in the Aldan–Uchur watershed where key sections expose the eastern and transitional facial region. On this basis we present a general biostratigraphic scheme for the Vendian–Cambrian across the southern Siberian platform that connects separate facies. Further correlation with key sections in northern Siberia leads to the recognition of three biostratigraphic zones for the Vendian–Cambrian interval. These are: Anabarites trisulcatus Zone; Purella antiqua Zone; Aldanocyathus sunnaginicus Zone. The abundance of Chinese-type small shelly fossils in the region of the eastern facies suggest correlation of the A. sunnaginicus Zone with the Siphogonuchites–Paragloborilus Zone of China, and the P. antiqua Zone with the Circotheca–Anabarites–Protohertzina Zone. In places, at the base of the Circotheca–Anabarites–Protohertzina Zone in China, analogies to the A. trisulcatus Zone can be identified. It is proposed that in Siberia the base of the A. sunnaginicus Zone (= base of Tommotian Stage) be taken as the base of the Cambrian. This would correspond with Marker B of the Meishucunian in China

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38

Rozanov, A. Yu, and Ed Landing. "Precambrian-Cambrian boundary global stratotype ratified and a new perspective of Cambrian time: Comment and Reply." Geology 23, no. 3 (1995): 285. http://dx.doi.org/10.1130/0091-7613(1995)023<0285:pcbgsr>2.3.co;2.

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39

KOUCHINSKY, ARTEM, STEFAN BENGTSON, VLADIMIR PAVLOV, BRUCE RUNNEGAR, PETER TORSSANDER, EDWARD YOUNG, and KAREN ZIEGLER. "Carbon isotope stratigraphy of the Precambrian–Cambrian Sukharikha River section, northwestern Siberian platform." Geological Magazine 144, no. 4 (April 16, 2007): 609–18. http://dx.doi.org/10.1017/s0016756807003354.

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A high-resolution carbon isotope profile through the uppermost Neoproterozoic–Lower Cambrian part of the Sukharikha section at the northwestern margin of the Siberian platform shows prominent secular oscillations of δ13C with peak-to-peak range of 6–10 ‰. There are six minima, 1n–6n, and seven maxima 1p–7p, in the Sukharikha Formation and a rising trend of δ13C from the minimum 1n of − 8.6 ‰ to maximum 6p of + 6.4 ‰. The trough 1n probably coincides with the isotopic minimum at the Precambrian–Cambrian boundary worldwide. Highly positive δ13C values of peaks 5p and 6p are typical of the upper portion of the Precambrian–Cambrian transitional beds just beneath the Tommotian Stage in Siberia. A second rising trend of δ13C is observed through the Krasnoporog and lower Shumny formations. It consists of four excursions with four major maxima that can be correlated with Tommotian–Botomian peaks II, IV, V, and VII of the reference profile from the southeastern Siberian platform. According to the chemostratigraphic correlation, the first appearances of the index forms of archaeocyaths are earlier in the Sukharikha section than in the Lena–Aldan region.

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40

Conway Morris, Simon. "Ediacaran survivors." Paleontological Society Special Publications 6 (1992): 69. http://dx.doi.org/10.1017/s2475262200006298.

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Ediacaran taxa are a characteristic element of latest Precambrian biotas, with an effectively global distribution. Their time range is not well understood, but with one possible exception from western Canada Ediacaran faunas appear always to post-date the late Precambrian glaciations. There is also growing evidence that many Ediacaran taxa disappeared before the Precambrian-Cambrian boundary. These disappearances traditionally have been ascribed to changes in taphonomic circumstances, but a series of extinctions is a plausible alternative. Ediacaran fossils pose two major problems: Notwithstanding the reasons for their disappearance shortly before the Precambrian-Cambrian boundary, was their demise total or did some forms persist into the Cambrian? Second, is the traditional view that Ediacaran taxa are metazoans, many of a cnidarian grade, correct? Recently Seilacher, Bergström and others have argued that the Ediacaran organisms have a distinctive bauplan, difficult to reconcile with known phyla and possibly different from any metazoan.In the Cambrian, Burgess Shale-type faunas are the principal source of information on soft-bodied metazoans. The differences between them and Ediacaran assemblages are largely self-evident, but there is now unequivocal evidence for at least one Ediacaran survivor from the Middle Cambrian Burgess Shale of British Columbia. This is a sea-pen-like animal, known from three specimens (one adult about 20 cm in length, and two juveniles). The fossils consist of a broad frond, with branches arising from a central axis on one side, while the opposite side is smooth apart from longitudinal ridges. The frond extends into a blunt holdfast that presumably was embedded in the muddy silt of the sea floor. This fossil is strikingly similar to the Ediacaran taxon Charniodiscus, best known from South Australia. The Burgess Shale example shows two important features. The first are pustule-like structures, possibly zooids, both on the branches and adjacent to the axis. The second feature is evidence for connections between the branches and axis, possibly representing canals. These features both support a comparison with extant pennatulaceans, and suggest that at least some Ediacaran taxa are correctly assigned to the metazoans.Also occurring in the Burgess Shale is an enigmatic bag-like organism Mackenzia costalis. Clear evidence exists for it being benthic, but its mode of feeding is uncertain. The interior appears to have consisted largely of a spacious cavity, probably sub-divided by longitudinal partitions. In addition, an elongate strand may represent a discrete organ, perhaps connected with digestion or reproduction. No exact equivalent to Mackenzia appears to occur in Ediacaran assemblages, but bag-like taxa are a common component. These include erniettids, best known from Namibia, and Platypholina, from the White Sea region of Russia.

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Amthor, Joachim E., John P. Grotzinger, Stefan Schröder, Samuel A. Bowring, Jahandar Ramezani, Mark W. Martin, and Albert Matter. "Extinction of Cloudina and Namacalathus at the Precambrian-Cambrian boundary in Oman." Geology 31, no. 5 (2003): 431. http://dx.doi.org/10.1130/0091-7613(2003)031<0431:eocana>2.0.co;2.

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42

Magaritz, Mordeckai, William T. Holser, and Joseph L. Kirschvink. "Carbon-isotope events across the Precambrian/Cambrian boundary on the Siberian Platform." Nature 320, no. 6059 (March 1986): 258–59. http://dx.doi.org/10.1038/320258a0.

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43

Brasier, M. D. "Nutrient flux and the evolutionary explosion across the Precambrian‐Cambrian boundary interval." Historical Biology 5, no. 2-4 (December 1991): 85–93. http://dx.doi.org/10.1080/10292389109380392.

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44

Latham, Andrew, and Robert Riding. "Fossil evidence for the location of the Precambrian/Cambrian boundary in Morocco." Nature 344, no. 6268 (April 1990): 752–54. http://dx.doi.org/10.1038/344752a0.

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45

Strauss, Harald, Stefan Bengtson, Paul M. Myrow, and Gonzalo Vidal. "Stable isotope geochemistry and palynology of the late Precambrian to Early Cambrian sequence in Newfoundland." Canadian Journal of Earth Sciences 29, no. 8 (August 1, 1992): 1662–73. http://dx.doi.org/10.1139/e92-131.

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A sequence of clastic sediments in southeastern Newfoundland straddling the Precambrian–Cambrian boundary has been investigated for its stable isotope geochemistry of carbon and sulfur and acid-resistant organic-walled microfossils. A detailed study of the Chapel Island Formation, which includes the boundary interval, has revealed fluctuations in the isotopic composition of organic carbon. These are largely interpreted as caused by differences in the depositional environments. Highly variable sulfur isotopic compositions indicate bacterial sulfate reduction as a pyrite-forming process, sometimes under sulfate-limited conditions. Palynological results are quite limited with respect to diagnostic microfossils.

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46

MOCZYDŁOWSKA, M. "Proterozoic and Cambrian successions in Upper Silesia: an Avalonian terrane in southern Poland." Geological Magazine 134, no. 5 (September 1997): 679–89. http://dx.doi.org/10.1017/s0016756897007504.

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All Cambrian series and several Cambrian biozones have been recognized using acritarch biochronology within the siliciclastic successions underlying Upper Silesia in southern Poland. The entire Cambrian succession is around 580 m thick and contains rare Lower Cambrian trilobites of the Acado-Baltic faunal province. Acritarch associations are taxonomically comparable to those recorded in Baltica, Laurentia and Gondwana, but their closest taxonomic affinity is with Iberia. The Cambrian succession accumulated in a shallow shelf environment and is almost flat-lying, unmetamorphosed, uncleaved and in normal stratigraphic order. It underlies paraconformably Lower Devonian deposits and overlies unconformably steeply dipping metasediments of undetermined Precambrian age. Tectonic deformation and metamorphism to greenschist grade in these Precambrian strata must have occurred in the Proterozoic, and are attributed to the Cadomian orogeny because similar Cadomian basement complexes occur in the adjoining Brno Massif and in the East Avalonian and Armorican terranes. Upper Silesia appears to be a stable crustal block bordered by deep faults whose sedimentary cover has not been affected by tectonic deformation other than faulting. Based on the recognition of Cadomian age basement, the distribution of trilobites and acritarchs and the tectonostratigraphic relationships to adjacent areas, the Upper Silesia terrane is interpreted to be a distal segment of East Avalonia that in Cambrian times faced Iberia. An extension of the Tornquist Suture from the Intra-Sudetic Fault is seen in the Kraków-Myszków Fault Zone at the margin of Upper Silesia. The Intra-Sudetic Fault zone and the Kraków-Myszków Fault Zone contain Early Palaeozoic rocks deformed during the Caledonian orogeny, and mark the boundary between the Caledonian accretionary belt and areas unaffected by this orogeny.

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47

Long, D. G. F. "Kennedy Channel Formation: key to the early history of the Franklinian continental margin, central eastern Ellesmere Island, Arctic Canada." Canadian Journal of Earth Sciences 26, no. 6 (June 1, 1989): 1147–59. http://dx.doi.org/10.1139/e89-098.

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The Franklinian sequence in the Canadian Arctic Islands may have been initiated by rifting in Late Proterozoic or Early Cambrian times. Unfortunately, no record of this early phase of basin evolution is exposed; the oldest known strata are weakly metamorphosed mudstones, limestones, and sandstones of the Kennedy Channel Formation. Although these have previously been considered late Precambrian in age, the presence of minor trilobite and brachiopod debris indicates an Early Cambrian age, possibly corresponding to a pre-Olenellus trilobite zone. Strata of the Kennedy Channel Formation reflect repeated progradation of shallow-water facies into a slowly subsiding basin that developed in response to subsidence at a late stage of rift development along the Franklinian shelf margin. The first two cycles involve storm- and tide-influenced clastics derived from the Precambrian Shield to the southeast, whereas the third and fourth cycles involve progradation of carbonate ramp and rimmed platform facies. The contact with overlying dolostones of the Ella Bay Formation represents a depositional and diagenetic facies boundary and not an unconformity.

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Brasier, M. D., J. K. Ingham, and A. W. A. Rushton. "Cambrian." Geological Society, London, Memoirs 13, no. 1 (1992): 13–18. http://dx.doi.org/10.1144/gsl.mem.1992.013.01.05.

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AbstractAspects of the history of the Cambrian System, and especially its usage in the British Isles, are discussed by Holland (1974). Rushton (1974), Cowie (1974) and Dhonau & Holland (1974) give general accounts of Cambrian stratigraphy in the British Isles, with extensive bibliographies, and the correlation is discussed by Cowie et al. (1972)The limits of the Cambrian System are still unsettled. The Precambrian/ Cambrian boundary has been the subject of much recent research, concentrated especially on strata of Tommotian and Meishucunian age (Cowie & Brasier 1989). These stages are characterized by faunas of small shelly fossils but biostratigraphical correlation based on them is still rather insecure and a consensus on the basal Cambrian stratotype has yet to be reached (Brasier 19896)The upper limit of the Cambrian (the base of the Ordovician System) is likewise unsettled. Cowie et al. (1972) took the base of the Ordovician at the base of the Arenig Series, thereby including the Tremadoc Series in the Cambrian. Nowadays a level at the base of the Tremadoc, for long adopted in continental Europe and elsewhere, is more widely accepted in Britain, and is employed here. However, the exact horizon for the base of the Ordovician, and the locality at which it is to be defined, are still under debate.There are no standard series defined in the Cambrian System. It has long been customary to speak of Lower, Middle and Upper Cambrian, and treat these as series, but they are employed in different senses in different

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49

Parnell, John, Darren F. Mark, Robert Frei, Anthony E. Fallick, and Rob M. Ellam. "40Ar/39Ar dating of exceptional concentration of metals by weathering of Precambrian rocks at the Precambrian–Cambrian boundary." Precambrian Research 246 (June 2014): 54–63. http://dx.doi.org/10.1016/j.precamres.2014.02.012.

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50

Walker, D., and S. G. Driese. "Constraints on the position of the Precambrian-Cambrian boundary in the Southern Appalachians." American Journal of Science 291, no. 3 (March 1, 1991): 258–83. http://dx.doi.org/10.2475/ajs.291.3.258.

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