Petrology of Upper Ordovician – Lower Silurian rocks of the Antigonish Highlands, Nova Scotia

1987 ◽  
Vol 24 (4) ◽  
pp. 752-759 ◽  
Author(s):  
J. B. Murphy
Keyword(s):  
Nova Scotia ◽  
Late Stage ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Late Ordovician ◽  
Geological History ◽  
Upper Ordovician ◽  
Marine Transgression ◽  
Lower Silurian ◽  
Clastic Rocks

Upper Ordovician to Lower Silurian rocks in the Antigonish Highlands consist of interlayered basalts, rhyodacites, arkoses, and conglomerates overlain by a thick sequence of marine clastic rocks and minor rhyolites. The stratigraphy documents a marine transgression. The volcanic rocks were deposited in a within-plate, continental, extensional environment. The basalts display alkalic and tholeiitic affinities, and the rhyodacites were formed by anatexis of the crust. The origin of the younger rhyolites is not clear: they are compositionally distinct from the rhyodacites but may be related to them as late-stage differentiates. At present, it is not possible to evaluate whether the tectonic setting and magmatic affinities are regionally or locally controlled.The geological history is very similar to that of Lower Silurian rocks immediately north of the Antigonish Highlands at Arisaig. In the simplest sense, this indicates these areas may have been juxtaposed prior to the Late Ordovician and limits cumulative post-Silurian movement on the boundary (Hollow) fault to about 40 km.

Origin of chert in the Upper Ordovician–Lower Silurian: implications for the sedimentary environment of North Qilian Orogen

2021 ◽  
pp. 1-16
Author(s):  
Qian HOU ◽  
Chuanlong MOU ◽  
Zuozhen HAN ◽  
Xiangying GE ◽  
Qiyu WANG
Keyword(s):  
Volcanic Ash ◽  
Tectonic Setting ◽  
Sedimentary Environment ◽  
Late Ordovician ◽  
Upper Ordovician ◽  
Lower Silurian ◽  
The North ◽  
Qilian Orogen ◽  
North Qilian ◽  
Deep Water Basin

ABSTRACT During the Upper Ordovician–Lower Silurian, chert was widely distributed in the Zhongbao Formation in the eastern part of the North Qilian Orogen. The origin and the tectonic setting of these chert were largely unknown. In order to analyse the material provenance, sedimentary environment, their formation and the tectonic setting, we present petrology and geochemical research on chert samples collected from Shihuigou Section. The evidence provided by radiolarite occurrences, Aluminium (Al)–iron (Fe)–manganese diagram and the silicon(Si)/Si + Al + Fe + calcium ratios suggesting a non-hydrothermal input and the biogenic origin chert. The geochemical features and the petrographic signatures have shown that the chert was also influenced by a terrigenous origin. It is considered that the deposition of the Late Ordovician chert is mainly affected by tectonic collision and volcanic ash events. During the Late Ordovician–Early Silurian transition, huge amounts of volcanic ash were released by massive volcanic activity that fell into the ocean, triggering the proliferation of radiolarians. Finally, in the Late Ordovician–Lower Silurian the tectonic setting of the North Qilian Orogen was not a typical deep-water basin, nor a typical continental margin, but a multi-island deep-water basin, which is closed to the mainland.

scholarly journals Effect of Hydrothermal Activity on Organic Matter Enrichment of Shale: A Case Study of the Upper Ordovician and the Lower Silurian in the Lower Yangtze, South China

Minerals ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 495 ◽  
Author(s):  
Yizhou Huang ◽  
Zhenxue Jiang ◽  
Kun Zhang ◽  
Yan Song ◽  
Shu Jiang ◽  
...  
Keyword(s):  
Organic Matter ◽  
Oxygen Isotope ◽  
Shale Gas ◽  
Organic Matter Content ◽  
Hydrothermal Activity ◽  
Late Ordovician ◽  
Sedimentary Organic Matter ◽  
Upper Ordovician ◽  
Lower Silurian ◽  
Activity Intensity

The effect of organic matter on hydrocarbon potential, storage space, and gas content of shale is well-known. Additionally, present-day content of sedimentary organic matter in shale is controlled by depositional and preservation processes. Therefore, a study of the enrichment mechanisms of sedimentary organic matter provides a scientific basis for the determination of favorable areas of shale gas. In this study the Upper Ordovician Xinkailing Fm. and the first member of the Lower Silurian Lishuwo Fm. were examined. Stratigraphic sequences were identified through conventional logs and elemental capture spectrum data. Oxygen isotope analysis was applied to recover paleotemperature of seawater in the study area. The excess silicon content was calculated and the origin of the silica was determined by the Fe-Al-Mn ternary plot. The enrichment mechanism of organic matter was analyzed by two aspects: redox conditions and paleoproductivity. As a result, the stratigraphic interval was divided into two 3rd-order sequences. Through oxygen isotope, the paleotemperature of seawater was 62.7–79.2 °C, providing evidence of the development of hydrothermal activity. Analysis of excess siliceous minerals identified two siliceous mineral origins: terrigenous and hydrothermal. It also revealed an upwards decreasing tendency in hydrothermal activity intensity. Strong hydrothermal activity during the Late Ordovician, recognized as TST1, formed a weak-oxidizing to poor-oxygen environment with high paleoproductivity, which promoted organic matter enrichment. During the Late Ordovician to the Early Silurian, identified as RST1, TST2, and RST2, weakening hydrothermal activity caused the decline of paleoproductivity and increased oxidation of bottom waters, leading to a relative decrease of organic matter content in the shale. Therefore, favorable areas of shale gas accumulation in the Upper Ordovician and Lower Silurian are determined stratigraphically as the TST1, with a high total organic carbonate content. Geographically, the hydrothermally-active area near the plate connection of the Yangtze and the Cathaysian is most favorable.

Geochemistry and tectonic setting of some Upper Ordovician volcanic rocks in east and southeast Ireland

1979 ◽  
Vol 42 (2) ◽  
pp. 288-310 ◽  
Author(s):  
C.J. Stillman ◽  
C.T. Williams
Keyword(s):  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Upper Ordovician

A probable glacio-marine deposit of Late Ordovician—Early Silurian age from the north central Newfoundland Appalachian Belt

1974 ◽  
Vol 111 (6) ◽  
pp. 549-564 ◽  
Author(s):  
A. M. McCann ◽  
M. J. Kennedy
Keyword(s):  
North Atlantic ◽  
Late Ordovician ◽  
Mobile Belt ◽  
North Atlantic Region ◽  
Upper Ordovician ◽  
Atlantic Region ◽  
North Central ◽  
Marine Deposits ◽  
Lower Silurian ◽  
The North

SummaryConglomerate beds occur in an Upper Ordovician—Lower Silurian clastic sequence on the northeastern side of the Newfoundland Central Paleozoic Mobile Belt. They contain scattered pebbles and cobbles dispersed in a finely laminated sandstone and siltstone matrix. Laminations are generally 5–20 mm thick and the clasts 10–300 mm across. The laminations are locally disrupted by the clasts. These laminations have subsequently been tectonically flattened into augen around the clasts and locally disrupted by boudinage. It is concluded that these conglomerate beds represent icerafted glacio-marine deposits interbedded with turbidites which were probably deposited in a locally restricted marine environment. The deposits are interpreted on the basis of scattered fossil localities as being of Late Ordovician–Early Silurian age. They are compared with deposits of similar age elsewhere in the North Atlantic region.

Kimberlite from Somerset Island, District of Franklin, N.W.T.

1973 ◽  
Vol 10 (3) ◽  
pp. 384-393 ◽  
Author(s):  
Roger H. Mitchell ◽  
Peter Fritz
Keyword(s):  
Late Stage ◽  
Country Rock ◽  
Canadian Arctic ◽  
Upper Ordovician ◽  
Lower Silurian ◽  
Rock Types ◽  
Immiscible Phase ◽  
Somerset Island

A new occurrence of kimberlite located on Somerset Island in the Canadian Arctic is described. The intrusion is in the form of a diatreme showing evidence of fluidization and is emplaced in Ordovician sediments. Kimberlitic breccia containing rounded xenoliths of country rock and massive kimberlite are the dominant rock types. The massive kimberlite contains phenocrysts of olivine (Fo90–Fo93), chrome-pyrope (7–12 mol.% uvarovite), and phlogopite together with xenocrysts of pyrope-almandine (28–36 mol.% pyrope, 58–64 mol.% almandine) set in a groundmass of olivine (Fo89.5), magnetite, perovskite, and serpentine. Abundant dolomitic carbonate, which replaces the silicate groundmass, is considered to be primary and to represent a late stage immiscible phase. Emplacement of the diatreme is thought to have been controlled by a crustal lineament defined by the Boothia Uplift. An Upper Ordovician or Lower Silurian age is postulated on the basis of the lack of country rock xenoliths older than Upper Ordovician age within the diatreme.

Parallel geological development in the Dunnage Zone of Newfoundland and the Lower Palaeozoic terranes of southern Scotland: an assessment

1992 ◽  
Vol 83 (3) ◽  
pp. 571-594 ◽  
Author(s):  
S. P. Colman-Sadd ◽  
P. Stone ◽  
H. S. Swinden ◽  
R. P. Barnes
Keyword(s):  
Volcanic Rocks ◽  
Foreland Basin ◽  
Late Ordovician ◽  
Marine Transgression ◽  
Early Ordovician ◽  
Sedimentary Sequences ◽  
Structural Regime ◽  
Lower Palaeozoic ◽  
Back Arc ◽  
Combined Data

AbstractThe Notre Dame and Exploits subzones of Newfoundland's Dunnage Zone are correlated with the Midland Valley and Southern Uplands of Scotland, using detailed comparisons of two key Lower Palaeozoic successions which record similar histories of extension and compression. It follows that the Baie Verte Line, Red Indian Line and Dover Fault are equivalent to the Highland Boundary Fault, Southern Upland Fault and Solway Line, respectively.The Betts Cove Complex and overlying Snooks Arm Group of the Notre Dame Subzone are analogous to the Ballantrae Complex of the Midland Valley, both recording the Arenig evolution and subsequent obduction of an arc and back-arc system. The Early Ordovician to Silurian sequence unconformably overlying the Ballantrae Complex is poorly represented in the Notre Dame Subzone but important similarities can still be detected suggesting corresponding histories of continental margin subsidence and marine transgression.In the Exploits Subzone, Early Ordovician back-arc volcanic rocks are overlain by Llandeilo mudstones and Late Ordovician to Early Silurian turbidites. A similar stratigraphy occurs in the Northern and Central Belts of the Southern Uplands and both areas have matching transpressive structural histories. Deeper erosion in the Exploits Subzone reveals Cambrian and Early Ordovician volcano-sedimentary sequences structurally emplaced on the Gander Zone, and such rocks are probably present beneath the Southern Uplands. Combined data from the Notre Dame Subzone and Midland Valley suggest an Arenig southeast-dipping subduction zone. Early Ordovician volcanic rocks in the Exploits Subzone and Southern Uplands have back-arc basin geochemistry and support the model of the Southern Uplands as a transition from back-arc to foreland basin. Preferential emergence of the Dunnage Zone and contrasts between Exploits Subzone and Southern Uplands turbidite basins are attributed to collision of Newfoundland with a Laurentian promontory and Scotland with a re-entrant. This hypothesis also explains the transpressive structural regime common to both areas.

Geochemistry and tectonic discrimination of Late Proterozoic arc-related volcaniclastic turbidite sequences, Antigonish Highlands, Nova Scotia

1993 ◽  
Vol 30 (12) ◽  
pp. 2273-2282 ◽  
Author(s):  
J. Brendan Murphy ◽  
Deborah L. MacDonald
Keyword(s):  
Nova Scotia ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Widespread Application ◽  
Isotopic Signatures ◽  
Late Proterozoic ◽  
Felsic Volcanic ◽  
Clastic Sedimentary ◽  
End Members

The Late Proterozoic (ca. 618–610 Ma) Georgeville Group of northern mainland Nova Scotia lies within the Avalon Composite Terrane and consists of subgreenschist- to greenschist-facies mafic and felsic volcanic rocks overlain by volcaniclastic turbidites that were deposited in an ensialic basin within a rifted volcanic arc. Geochronological data indicate that the volcanic and sedimentary rocks are coeval. The geochemical and isotopic signatures of the sedimentary rocks are attributed to erosion of the coeval Avalonian volcanic rocks that flank the basin and are consistent with synorogenic deposition. There is no evidence of significant chemical contribution from Avalonian basement.Knowledge of the tectonic setting facilitates the testing of published geochemical discriminant diagrams for clastic sedimentary rocks. Discrimination diagrams using ratios such as K2O/Na2O and Al2O3/(CaO + Na2O) give inconclusive results, probably due to elemental mobility during secondary processes. Plots involving MgO, TiO2, and Fe2O3 detect the chemical contribution of mafic detritus, give much tighter clusters of data, and plot between Aleutian- and Cascade-type arc-derived sediments, suggesting a moderate thickness of continental crust beneath the arc.The arc-related signature of the Georgeville sedimentary rocks is clearly recognizable on ternary plots involving inter-element ratios of high field strength elements (e.g., Ti–Y–Zr, Nb–Y–Zr, and Hf–Ta–Th) in which the samples plot as mixing trends between mafic and felsic end members. Diagrams of this type may have widespread application to tectonic discrimination of sedimentary rocks because in most suites these ratios are relatively insensitive to sedimentary and metamorphic processes.

Radiometric Age of the Keppoch Formation, Browns Mountain Group, Northern Mainland of Nova Scotia

1974 ◽  
Vol 11 (9) ◽  
pp. 1325-1329 ◽  
Author(s):  
R. F. Cormier
Keyword(s):  
Nova Scotia ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Initial Ratio ◽  
Lower Paleozoic ◽  
Middle Cambrian ◽  
Lower Silurian

The lower Paleozoic Browns Mountain Group of volcanic and sedimentary rocks underlies much of the Antigonish Highlands on the northern mainland of Nova Scotia. The rocks are apparently unfossiliferous and pre-Lower Silurian in age. Volcanic rocks belonging to the Keppoch Formation give a Rb–Sr whole-rock isochron age of 528 ± 40 m.y.; the indicated value for the initial ratio 87Sr/86Sr is 0.7032 ± 0.0020. The apparent stratigraphic age of the lower part of the Browns Mountain Group then is Cambrian with a middle Cambrian age favored.

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