Lower Paleozoic Rocks in Diatremes, Southern Wyoming and Northern Colorado

1969 ◽  
Vol 80 (1) ◽  
pp. 149 ◽  
Author(s):  
JOHN CHRONIC ◽  
MALCOLM E. McCALLUM ◽  
CLINTON S. FERRIS ◽  
DAVID H. EGGLER
Keyword(s):  
Lower Paleozoic ◽  
Northern Colorado ◽  
Paleozoic Rocks

scholarly journals A missing link in the peri-Gondwanan terrane collage: the Precambrian basement of the Moroccan Meseta and its lower Paleozoic cover

2018 ◽  
Vol 55 (1) ◽  
pp. 33-51 ◽  
Author(s):  
Dominik Letsch ◽  
Mohamed El Houicha ◽  
Albrecht von Quadt ◽  
Wilfried Winkler
Keyword(s):  
Carbonate Platform ◽  
Source Area ◽  
Source Rocks ◽  
Lower Paleozoic ◽  
Northern Margin ◽  
Precambrian Geology ◽  
The North ◽  
Late Cambrian ◽  
Paleozoic Rocks ◽  
Rifted Margin

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.

The last pteraspids (Vertebrata, Heterostraci): new material from the Middle Devonian of Alberta and Idaho

2020 ◽  
Vol 94 (4) ◽  
pp. 758-772
Author(s):  
David K. Elliott ◽  
Linda S. Lassiter ◽  
Kathryn E. Geyer
Keyword(s):  
Middle Devonian ◽  
New Genus ◽  
New Combination ◽  
Additional Material ◽  
Lower Paleozoic ◽  
Early Devonian ◽  
Red Sandstone ◽  
Large Channel ◽  
New Material ◽  
Paleozoic Rocks

AbstractThis report documents the last pteraspids, (armored, jawless members of the Heterostraci), which are otherwise only known from the Early Devonian of the Old Red Sandstone Continent. Tuberculate pteraspid heterostracans are described from the Middle Devonian beds of two formations in western North America. The late Givetian Yahatinda Formation of Alberta and British Columbia consists of channels cut into lower Paleozoic rocks and represents deposition in marine to littoral environments. Clavulaspis finis (Elliott et al., 2000a) new combination is redescribed from additional material from the Yahatinda Formation and reassigned to the new genus Clavulaspis because the original genus name is invalid. The Eifelian Spring Mountain beds of Idaho consist of a large channel that represents a clastic-dominated estuarine environment. It contains Scutellaspis wilsoni new genus new species, and the previously described species from the Spring Mountain beds is redescribed and reassigned to Ecphymaspis new genus, which was prompted by new material and a review of the validity of the original genus name. Phylogenetic analysis shows that these three new taxa form part of the derived clade Protaspididae.UUID: http://zoobank.org/9cf09b21-cec1-4ce4-bc2b-658d0b515e10

scholarly journals Hydrotermální mineralizace s dickitem v ordovických jílovcích bohdaleckého souvrství z tunelu metra linky D v Praze na Pankráci

2020 ◽  
Vol 28 (1) ◽  
pp. 116-125
Author(s):  
Zdeněk Dolníček ◽  
Petr Stöhr ◽  
Jana Ulmanová ◽  
Luboš Vrtiška ◽  
Radana Malíková
Keyword(s):  
Mineral Assemblage ◽  
Short Hair ◽  
Lower Paleozoic ◽  
Fault Structure ◽  
Friction Heat ◽  
Prague Basin ◽  
A Value ◽  
Paleozoic Rocks ◽  
Host Rocks ◽  
Thermal Overprint

Two types of hydrothermal veins were found in the Ordovician claystones of the Bohdalec Formation (Barrandian, Prague Basin) during the excavation of tunnel of subway Line D at Prague-Pankrác site. The first type is represented by short hair-thin veinlets of various directions fulfilled by dickite. The second type comprises thicker NNW - SSE trending veins with prevailing quartz, which cut the host rocks across the whole width of the gallery. In addition to quartz, they contain also dickite, chlorite (thuringite-chamosite), carbonates of dolomite-ankerite series (Dol37.5-44.0Ank42.0-46.8Ktn10.9-16.1), calcite, fluorapatite, pyrite (with up to 0.5 wt. % Mn), galena (with ~0.6 wt. % Se) and sphalerite (with ~1 wt. % Fe and up to 0.35 wt. % Sn and 0.36 wt. % Cu). Except for calcite, which forms younger veinlets in older quartz fill, all other mentioned minerals form minute inclusions enclosed in quartz, which are arranged parallel with outer margin of the vein. Based on mineral assemblage and chemical composition of individual minerals, highly variable crystallization temperatures (<100 - 350 °C) can be interpreted in various mineralogically distinct domains of the quartz vein. We assume a polyphase, episodic origin of individual domains of the vein fill, close to the crack-seal mechanism, which was bound to successive evolution of the adjacent fault structure. The maximum formation temperatures exceeding by a value of ca. 100 °C the highest reported temperatures of Variscan thermal overprint of Lower Paleozoic rocks of the Prague Basin are explained by production of friction heat in the fault structure. It is probable that part of parent fluids originated from sedimentary iron ores occurring in the host Ordovician sedimentary sequence.

An insight on the polyphase thermal history of the Ghomarides and Upper Sebtides in the Internal Rif (North Morocco) by means of Raman spectroscopy on organic matter

2021 ◽  
Author(s):  
Andrea Schito ◽  
Achraf Atouabat ◽  
Rocco Calcagni ◽  
Sveva Corrado ◽  
David Muirhead ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Thermal Structure ◽  
Carbonaceous Material ◽  
Stability Field ◽  
Lower Paleozoic ◽  
Suitable Alternative ◽  
History Of ◽  
Maximum Temperatures ◽  
Paleozoic Rocks ◽  
Metamorphic Core

&lt;p&gt;The correct assessment of maximum temperatures experienced by rocks is an essential tool to unravel the evolution of the thermal structure of the crust during the main phases of an orogenesis. Given to broad P-T stability field of classical metamorphic mineralogical indicators, maximum temperatures derived from the analyses of carbonaceous material dispersed in rocks by means of Raman spectroscopy has shown to be a suitable alternative to classical geothermometer. Initially developed for high metamorphic rocks the use of this tools has recently been extended also at lower metamorphic degree and diagenesis. This allowed us to extend the analyses of paleotemperatures experienced by rocks from Ghomarides and Sebtides from the Internal Rif in North Morocco with respect to previous works. Ghomaride and Sebtides in this portion of the Rif-Betic-Tell chain, represent respectively the upper and lower plates of a metamorphic core complex&amp;#160; and are composed, the first, by Paleozoic rocks with a partially preserved Mesozoic-Cenozoic cover and the second by lower Paleozoic to Triassic deep-crustal mica-schists, migmatites and granulites associated with peridotites (Beni Bousera complex).&lt;/p&gt;&lt;p&gt;Our data suggest that the uppermost Tiszgarine Unit of the Upper Sebtides experienced warmer condition than previously observed. Moreover, we calculate the maximum temperatures experienced by the Ghomarides&amp;#160; during both the Eo and Late Variscan cycles showing that differences in temperature exist among the vary units that compose the complex. Finally, in the southern area our data suggest a less severe alpine heating related to the emplacement of the Beni Bousera peridotite, than previously calculated.&lt;/p&gt;

Medusoid Impressions in the Lower Paleozoic Rocks of Eastern Newfoundland

1973 ◽  
Vol 10 (6) ◽  
pp. 1016-1020 ◽  
Author(s):  
Avinash Ch. Nautiyal
Keyword(s):  
Southeastern Part ◽  
Lower Paleozoic ◽  
Bay Area ◽  
Island Group ◽  
Paleozoic Rocks ◽  
Conception Bay

Two medusoid impressions of discoidal form with radial ridges and striations were collected from the Lower Paleozoic rocks (Bell Island Group) of Kelly s and Bell Islands in the southeastern part of the Conception Bay area.

Application géophysique à l'interprétation structurale de la région du lac Bécancour, Thetford Mines, Québec

1983 ◽  
Vol 20 (8) ◽  
pp. 1327-1339
Author(s):  
Maurice K. Seguin
Keyword(s):  
Structural Unit ◽  
Bouguer Anomaly ◽  
Positive Anomaly ◽  
Ophiolite Complex ◽  
Lower Paleozoic ◽  
Polyphase Deformation ◽  
Magnetic Mass ◽  
Anomaly Map ◽  
Bouguer Anomaly Map ◽  
Paleozoic Rocks

The present study, based on detailed gravity anomaly (Bouguer and residual) and magnetic maps of the Thetford Mines area, seeks to explain the mechanism by which the Lac Bécancour structural unit was emplaced. The Bouguer anomaly map shows: (1) generally more positive anomalies toward the northwest; (2) local positive anomalies in the southwest and north-northwest; and (3) a small local positive anomaly in the east. Residual anomalies are characterized by a weak high of the order of 2–3 × 10−5 m/s2 (2–3 mgal) over the center of the structure. The magnetic map shows: (1) negative to neutral intensities over the center of the structure; (2) two small positive anomalies on the inner border of the structure; (3) a large magnetic mass (the ophiolite complex) in the west-northwest; and (4) small and isolated magnetic masses to the southwest and east.The hypothesis of diapir-like rise caused by an underlying serpentinite mass, as proposed by some geologists, is refuted by the absence of a positive magnetic anomaly over the structure. A second hypothesis, which calls on post-nappe granitization of the core of the structure at depth, is unlikely as gneiss is now here exposed in the area and the structure is bounded by faults. Instead, the geophysical data suggest that the Lac Bécancour structural unit is an old (Early Cambrian or Eocambrian) block that has undergone polyphase deformation during the Taconic Oxogeny rather than being a horst-like body emplaced by vertical rise. Identical overthrust slices of Hadrynian basement in the centers of imbricated blocks and nappes of lower Paleozoic rocks are commonly observed in the Caledonides of Norway and Sweden where they generally have the appearance of antiforms or synforms. [Journal Translation]

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