The pre-Mississippian "Neruokpuk Formation," northeastern Alaska and northwestern Yukon: review and new regional correlation

1991 ◽  
Vol 28 (10) ◽  
pp. 1521-1533 ◽  
Author(s):  
Larry S. Lane
Keyword(s):  
Lower Cambrian ◽  
Small Scale ◽  
Lower Paleozoic ◽  
Lower Silurian ◽  
Rock Types ◽  
Upper Proterozoic ◽  
Regional Correlation ◽  
Arctic Alaska ◽  
Lower Ordovician ◽  
Paleozoic Rocks

Since the early 1900's, regional reconnaissance in Alaska and the Yukon has failed to resolve the stratigraphy and structure of the pre-Mississippian Neruokpuk Formation. Its age and distribution have been defined and redefined as new data have slowly accumulated. In most recently published reconnaissance maps of the Yukon, the "Neruokpuk" includes nearly all of the pre-Mississippian strata in the British Mountains and is assigned a Precambrian age. In contrast, approximately half of contiguous strata in adjacent Alaska are interpreted as early Paleozoic in age and are excluded from the Neruokpuk. Recent detailed studies in the Firth River area of the Yukon have documented intense small-scale imbrication of fossiliferous Lower Cambrian to Devonian(?) units that were previously mapped as Precambrian Neruokpuk.A remarkable similarity between the lithologies of lower Paleozoic rocks in the British Mountains and the Selwyn Basin 1000 km to the southeast is strengthened by biostratigraphic ties in Lower Cambrian, Lower Ordovician, and Lower Silurian strata. This correlation between basin facies suggests that shelf and slope facies of upper Proterozoic through lower Paleozoic strata may also be correlatable between the two areas. The paleogeographic implications of these correlations indicate that pre-Mississippian strata in Arctic Alaska and the Yukon are part of a single Arctic–Pacific continental margin.The Neruokpuk Formation name should be restricted in Canada to the quartzite-dominant unit, contiguous with similar strata to which the restricted Neruokpuk definition applies in Alaska. The current broad definition, based on an assumed Proterozoic age but including many rock types, should be discontinued.

scholarly journals Characteristics of Pore Structure and Gas Content of the Lower Paleozoic Shale from the Upper Yangtze Plate, South China

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7603
Author(s):  
Xiaoyan Zou ◽  
Xianqing Li ◽  
Jizhen Zhang ◽  
Huantong Li ◽  
Man Guo ◽  
...  
Keyword(s):  
Organic Matter ◽  
Pore Structure ◽  
Shale Gas ◽  
Lower Cambrian ◽  
Gas Content ◽  
Lower Paleozoic ◽  
Lower Silurian ◽  
Surface Areas ◽  
Specific Surface Areas ◽  
Yangtze Plate

This study is predominantly about the differences in shale pore structure and the controlling factors of shale gas content between Lower Silurian and Lower Cambrian from the upper Yangtze plate, which are of great significance to the occurrence mechanism of shale gas. The field emission scanning electron microscopy combined with Particles (Pores) and Cracks Analysis System software, CO2/N2 adsorption and the high-pressure mercury injection porosimetry, and methane adsorption were used to investigate characteristics of overall shale pore structure and organic matter pore, heterogeneity and gas content of the Lower Paleozoic in southern Sichuan Basin and northern Guizhou province from the upper Yangtze plate. Results show that porosity and the development of organic matter pores of the Lower Silurian are better than that of the Lower Cambrian, and there are four main types of pore, including interparticle pore, intraparticle pore, organic matter pore and micro-fracture. The micropores of the Lower Cambrian shale provide major pore volume and specific surface areas. In the Lower Silurian shale, there are mesopores besides micropores. Fractal dimensions representing pore structure complexity and heterogeneity gradually increase with the increase in pore volume and specific surface areas. There is a significant positive linear relationship between total organic carbon content and micropores volume and specific surface areas of the Lower Paleozoic shale, and the correlation of the Lower Silurian is more obvious than that of the Lower Cambrian. The plane porosity of organic matter increases with the increase in total organic carbon when it is less than 5%. The plane porosity of organic matter pores is positively correlated with clay minerals content and negatively correlated with brittle minerals content. The adsorption gas content of Lower Silurian and Lower Cambrian shale are 1.51–3.86 m3/t (average, 2.31 m3/t) and 0.35–2.38 m3/t (average, 1.36 m3/t). Total organic carbon, clay minerals and porosity are the main controlling factors for the differences in shale gas content between Lower Cambrian and Lower Silurian from the upper Yangtze plate. Probability entropy and organic matter plane porosity of the Lower Silurian are higher than those of Lower Cambrian shale, but form factor and roundness is smaller.

The Developmental Biology of Brachiopods

2001 ◽  
Vol 7 ◽  
pp. 69-88
Author(s):  
Gary Freeman
Keyword(s):  
Developmental Biology ◽  
Life History ◽  
Fossil Record ◽  
Lower Cambrian ◽  
Comprehensive Treatment ◽  
Next Generation ◽  
Lower Paleozoic ◽  
Short Course ◽  
Invertebrate Paleontology ◽  
Lower Ordovician

The chapter on anatomy in the Treatise on Invertebrate Paleontology (Part H, Brachiopoda, revised) (Williams et al., 1997) is the most current and comprehensive treatment that we have of reproduction and development in these animals. My contribution to this short course is a commentary on and addendum to this review. The study of the developmental biology of extant brachiopods describes a large part of their life history and defines several of the parameters that have to be taken into account when thinking about how a given set of genes will make it to the next generation (Havenhand, 1995). Some extant brachiopod genera like Discinisca and Crania (Neocrania) belong to families that first appeared in the fossil record during the Lower Ordovician or, as in the case of Glottidia, to a superfamily that first appeared during the Lower Cambrian. Studies on the development of these extant animals provide a picture of what the development of their Lower Paleozoic ancestors might have been like.

Lower Ordovician (Arenig–Llanvirn) graptolites from the Notre Dame Subzone, central Newfoundland

1992 ◽  
Vol 29 (8) ◽  
pp. 1717-1733 ◽  
Author(s):  
S. Henry Williams
Keyword(s):  
Long Island ◽  
Middle Part ◽  
Black Shales ◽  
Head Group ◽  
Sedimentary Sequence ◽  
Lower Paleozoic ◽  
Lower Ordovician ◽  
The World ◽  
Paleozoic Rocks ◽  
Limestone Breccia

Many lower Paleozoic rocks in the Notre Dame Subzone of central Newfoundland are of unknown or imprecise age. Several new Lower Ordovician graptolite occurrences are here reported and earlier records revised. New graptolite localities in the Balsam Bud Cove Formation at Snooks Arm on the Baie Verte Peninsula, previously recorded as "early Ordovician (Arenig)" have yielded an assemblage identical to that found in the middle part of Bed 11 of the Cow Head Group, western Newfoundland, indicating a probable lower Didymograptus bifidus Zone age. At Corner Pond, southeast of Corner Brook, an abundant, diverse fauna from the Corner Pond formation indicates a marginally older age for the black shales than those at Snooks Arm (Pendeograptus fruticosus Zone, equivalent to lower Bed 11). Black shales associated with felsic volcanics and limestone breccia belonging to the Cutwell Group at Lushes Bight, on Long Island, western Notre Dame Bay, which were previously assigned to the widespread black shales of the Lawrence Harbour Formation and equivalents in the Exploits Subzone, contain a rich lower Llanvirn (Paraglossograptus tentaculatus Zone) graptolite assemblage. This agrees with ages established using other macrofossils and conodonts from the associated limestones. In contrast, a lower shale unit from older strata at Southern Head on the eastern end of the island yields a late Arenig Isograptus victoriae maximus Zone assemblage. These newly discovered graptolite faunas provide precise ages for the upper and lower parts of the volcano-sedimentary sequence on Long Island. Interestingly, all four graptolite assemblages discussed here are of open-ocean affinity, permitting accurate correlation with localities not only in western Newfoundland but also elsewhere in the world.

On the non-existence of a Cadomian basement in southern France (Pyrenees, Montagne Noire): implications for the significance of the pre-Variscan (pre-Upper Ordovician) series

2004 ◽  
Vol 175 (6) ◽  
pp. 643-655 ◽  
Author(s):  
Bernard Laumonier ◽  
Albert Autran ◽  
Pierre Barbey ◽  
Alain Cheilletz ◽  
Thierry Baudin ◽  
...  
Keyword(s):  
Lower Cambrian ◽  
Classical Model ◽  
Black Shales ◽  
High Grade ◽  
Upper Ordovician ◽  
Lower Paleozoic ◽  
Early Ordovician ◽  
Lower Ordovician ◽  
Montagne Noire ◽  
Back Arc

Abstract The deepest Hercynian metamorphic terrains in the Pyrenees and in the nearby Montagne Noire are made up of medium-grade orthogneisses and micaschists, and of high-grade, often granulitic, paragneisses. The existence of a granitic-metamorphic Cadomian basement and of its sedimentary Lower Paleozoic cover was advocated from the following main arguments: (i) a supposed unconformity of the Lower Cambrian Canaveilles Group (the lower part of the Paleozoic series) upon both granitic and metamorphic complexes; (ii) a ca. 580 Ma U-Pb age for the metagranitic Canigou gneisses. A SE to NW transgression of the Cambrian cover and huge Variscan recumbent (“penninic”) folds completed this classical model. However, recent U-Pb dating provided a ca. 474 Ma, early Ordovician (Arenigian) age for the me-tagranites, whereas the Vendian age (581 ± 10 Ma) of the base of the Canaveilles Group was confirmed [Cocherie et al., 2005]. In fact, these granites are laccoliths intruded at different levels of the Vendian-Lower Cambrian series. So the Cadomian granitic basement model must be discarded. In a new model, developed in the Pyrenees and which applies to the Montagne Noire where the orthogneisses appear to be Lower Ordovician intrusives too, there are neither transgression of the Paleozoic nor very large Hercynian recumbent folds. The pre-Variscan (pre-Upper Ordovician) series must be divided in two groups: (i) at the top, the Jujols Group, mainly early to late Cambrian, that belongs to a Cambrian-Ordovician sedimentary and magmatic cycle ; the early Ordovician granites pertain to this cycle; (ii) at the base, the Canaveilles Group of the Pyrenees and the la Salvetat-St-Pons series of the Montagne Noire, Vendian (to earliest Cambrian?), are similar to the Upper Alcudian series of Central Iberia. The Canaveilles Group is a shale-greywacke series with rhyodacitic volcanics, thick carbonates, black shales, etc. The newly defined olistostromic and carbonated, up to 150 m thick Tregurà Formation forms the base of the Jujols Group, which rests more or less conformably on the Canaveilles Group. The high-grade paragneisses which in some massifs underlie the Canaveilles and Jujols low- to medium grade metasediments are now considered to be an equivalent of the Canaveilles Group with a higher Variscan metamorphic grade; they are not derived from metamorphic Precambrian rocks. So, there is no visible Cadomian metamorphic (or even sedimentary) basement in the Pyrenees. However, because of its age, the Canaveilles Group belongs to the end of the Cadomian cycle and was deposited in a subsident basin, probably a back-arc basin which developed in the Cadomian, active-transform N-Gondwanian margin of this time. The presence of Cadomian-Panafrican (ca. 600 Ma) zircon cores in early Ordovician granites and Vendian volcanics implies the anatexis of a thick (> 15 km?) syn-Cadomian series, to be compared to the very thick Lower Alcudian series of Central Iberia, which underlies the Upper Alcudian series. Nd isotopic compositions of Neoproterozoic and Cambrian-Ordovician sediments and magmatites, as elsewhere in Europe, yield Paleoproterozoic (ca. 2 Ga) model-ages. From the very rare occurrences of rocks of this age in W-Europe, it can be envisionned that the thick Pyrenean Cadomian series lies on a Paleoproterozoic metamorphic basement. But, if such a basement does exist, it must be “hidden”, as well as the lower part of the Neoproterozoic series, in the Variscan restitic granulites of the present (Variscan) lower crust. So a large part of the pre-Variscan crust was made of volcano-sedimentary Cadomian series, explaining the “fertile” characteristics of this crust which has been able to produce the voluminous Lower Ordovician and, later, Upper Carboniferous granitoids.

Detrital zircon geochronology and regional correlation of metasedimentary rocks in the Coast Mountains, southeastern Alaska

1998 ◽  
Vol 35 (3) ◽  
pp. 269-279 ◽  
Author(s):  
G E Gehrels ◽  
P A Kapp
Keyword(s):  
Continental Margin ◽  
Detrital Zircon ◽  
Lower Paleozoic ◽  
Coast Mountains ◽  
Detrital Zircon Geochronology ◽  
Metasedimentary Rocks ◽  
Upper Proterozoic ◽  
Regional Correlation ◽  
Upper Paleozoic ◽  
Detrital Zircon Ages

U-Pb ages have been determined for 55 detrital zircon grains from a metasedimentary sequence along the west flank of the Coast Mountains in southeastern Alaska. These rocks belong to the Port Houghton assemblage, which consists of upper Paleozoic pelitic and psammitic schist, metaconglomerate, metabasalt, and marble. The Port Houghton assemblage rests unconformably(?) on metamorphosed and deformed mid-Paleozoic arc-type volcanics (Endicott Arm assemblage), which gradationally overlie upper Proterozoic(?) - lower Paleozoic continental margin strata (Tracy Arm assemblage). Three main clusters of ages are present: 330-365 Ma (19 grains), 1710-2000 Ma (27 grains), and 2450-2680 Ma (6 grains). Additional grains are approximately 2334, 2364, and 3324 Ma. Comparison of these ages with detrital zircon ages in other Cordilleran assemblages supports previous interpretations that metasedimentary rocks in the Coast Mountains (i) form a southwestern continuation of the Yukon-Tanana terrane of eastern Alaska and Yukon, (ii) are not correlative with strata of the Alexander terrane, and (iii) contain detritus that was probably shed from cratonal rocks in the Canadian Shield to the east. Several scenarios exist to explain the occurrence of these continental margin rocks west (outboard) of arc-type and ocean-floor assemblages such as the Stikine, Cache Creek, Quesnel, and Slide Mountain terranes.

scholarly journals Age of lower Paleozoic rocks composing erosional outliers on Manpupuner Ridge (Northern Urals)

2017 ◽  
Vol 92 (2) ◽  
Author(s):  
A. A. Soboleva ◽  
◽  
V. A. Saldin ◽  
P. P. Yukhtanov ◽  
J. K. Hourigan ◽  
...  
Keyword(s):  
Detrital Zircons ◽  
Clastic Material ◽  
Lower Paleozoic ◽  
Northern Urals ◽  
Lower Ordovician ◽  
Paleozoic Rocks

The article presents the first U-Pb data on the age of the rocks composing scenic erosional outliers located on the Manpupuner Ridge in the Northern Urals. Based on the analysis of the ages of detrital zircons micaceous quartzites exposed on the Manpupuner Ridge are thought to belong to Lower Ordovician Telpos Formation. Sources of clastic material are supposed.

The mid-Paleozoic deformation in the Hazen fold belt, Ellesmere Island, Arctic Canada

1990 ◽  
Vol 27 (10) ◽  
pp. 1359-1370 ◽  
Author(s):  
Eva M. Klaper
Keyword(s):  
Large Scale ◽  
Ellesmere Island ◽  
Small Scale ◽  
Northwestern Part ◽  
Fold Belt ◽  
Southeastern Part ◽  
Lower Paleozoic ◽  
Slip Mechanism ◽  
Fold Belts ◽  
Surface Geology

The mid-Paleozoic deformation of lower Paleozoic subgreenschist-facies sediments of the Hazen fold belt in northern Ellesmere Island is represented predominantly by chevron-style folding. Folded multilayers display cleavage fans suggesting synchronous fold and cleavage formation. Bedding-parallel slip indicates a flexural slip mechanism of folding. The geometry of several large-scale anticlinoria has been interpreted as being due to formation of these structures over detachments and thrust ramps.The constant fold geometry, the parallel orientation of faults and large- and small-scale folds, and the axial-plane foliation are related to a single phase of folding with a migrating deformation front in the Hazen fold belt during the mid-Paleozoic orogeny. The minimum amount of shortening in the Hazen and Central Ellesmere fold belts has been estimated from surface geology to increase from 40–50% of the original bed length in the external southeastern part to 50–60% in the more internal northwestern part of the belts.The convergent, thin-skinned nature of the Hazen and Central Ellesmere fold belts indicates that the postulated transpressive plate motions during the accretion of Pearya did not affect the study area.

scholarly journals The Souss lagerstätte of the Anti-Atlas, Morocco: discovery of the first Cambrian fossil lagerstätte from Africa

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Gerd Geyer ◽  
Ed Landing
Keyword(s):  
South China ◽  
Lower Cambrian ◽  
Northern Slope ◽  
Sea Floor ◽  
Upper Cambrian ◽  
Exceptional Preservation ◽  
West Gondwana ◽  
Regional Correlation ◽  
Animal Remains ◽  
Stratigraphic Interval

AbstractEpisodic low oxygenated conditions on the sea-floor are likely responsible for exceptional preservation of animal remains in the upper Amouslek Formation (lower Cambrian, Stage 3) on the northern slope of the western Anti-Atlas, Morocco. This stratigraphic interval has yielded trilobite, brachiopod, and hyolith fossils with preserved soft parts, including some of the oldest known trilobite guts. The “Souss fossil lagerstätte” (newly proposed designation) represents the first Cambrian fossil lagerstätte in Cambrian strata known from Africa and is one of the oldest trilobite-bearing fossil lagerstätten on Earth. Inter-regional correlation of the Souss fossil lagerstätte in West Gondwana suggests its development during an interval of high eustatic levels recorded by dark shales that occur in informal upper Cambrian Series 2 in Siberia, South China, and East Gondwana.

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