Globular layer silicates of the glauconite–illite composition in Upper Proterozoic and Lower Cambrian rocks

2015 ◽  
Vol 50 (6) ◽  
pp. 452-477 ◽  
Author(s):  
T. A. Ivanovskaya ◽  
B. B. Zviagina ◽  
B. A. Sakharov ◽  
T. S. Zaitseva ◽  
E. V. Pokrovskaya ◽  
...  
Keyword(s):  
Lower Cambrian ◽  
Layer Silicates ◽  
Upper Proterozoic

The initiation of the early Paleozoic Cordilleran miogeocline: evidence from the uppermost Proterozoic – Lower Cambrian Hamill Group of southeastern British Columbia

1988 ◽  
Vol 25 (1) ◽  
pp. 1-19 ◽  
Author(s):  
William J. Devlin ◽  
Gerard C. Bond
Keyword(s):  
British Columbia ◽  
Lower Cambrian ◽  
Direct Evidence ◽  
Thermal Anomaly ◽  
Passive Margin ◽  
Early Paleozoic ◽  
Upper Proterozoic ◽  
Windermere Supergroup ◽  
Depositional Setting ◽  
Thermal Subsidence

The uppermost Proterozoic–Lower Cambrian Hamill Group of southeastern British Columbia contains geologic evidence for a phase of extensional tectonism that led directly to the onset of thermally controlled subsidence in the Cordilleran miogeocline. Moreover, the Hamill Group contains the sedimentological record of the passage of the ancient passive margin from unstable tectonic conditions associated with rifting and (or) the earliest phases of thermal subsidence to post-rift conditions characterized by stabilization of the margin and dissipation of the thermal anomaly generated during the rift phase (the rift to post-rift transition). Widespread uplift that occurred prior to and during the deposition of the lower Hamill Group is indicated by an unconformable relation with the underlying Windermere Supergroup and by stratigraphic relations between Middle and Upper Proterozoic strata and unconformably overlying upper Lower Cambrian quartz arenites (upper Hamill Group) in the southern borderlands of the Hamill basin. In addition, the coarse grain size, the feldspar content, the depositional setting, and the inferred provenance of the lower Hamill Group are all indicative of the activation of basement sources along the margins of the Hamill basin. Geologic relations within the Hamill Group that provide direct evidence for extensional tectonism include the occurrence of thick sequences of mafic metavolcanics and rapid vertical facies changes that are suggestive of syndepositional tectonism.Evidence of extensional tectonism in the Hamill Group directly supports inferences derived from tectonic subsidence analyses that indicate the rift phase that immediately preceded early Paleozoic post-rift cooling could not have occurred more than 10–20 Ma prior to 575 ± 25 Ma. These data, together with recently reported isotopic data that suggest deposition of the Windermere Supergroup began ~730–770 Ma, indicate that the rift-like deposits of the Windermere Supergroup are too old to represent the rifting that led directly to the deposition of the Cambro-Ordovician post-rift strata. Instead, Windermere sedimentation was apparently initiated by an earlier rift event, probably of regional extent, that was part of a protracted, episodic rift history that culminated with continental breakup in the latest Proterozoic – Early Cambrian.

Palynology of uppermost Proterozoic and lowermost Cambrian formations, central Mackenzie Mountains, northwestern Canada

1989 ◽  
Vol 26 (1) ◽  
pp. 129-148 ◽  
Author(s):  
D. Baudet ◽  
J. D. Aitken ◽  
M. Vanguestaine
Keyword(s):  
Rocky Mountains ◽  
Lower Cambrian ◽  
Russian Platform ◽  
Blue Flower ◽  
Flower Formation ◽  
Early Cambrian ◽  
Canadian Rocky Mountains ◽  
Structural Units ◽  
Upper Proterozoic ◽  
Lithostratigraphic Correlation

The acritarch assemblages of strata from the base of the Upper Proterozoic Sheepbed Formation to the base of the Lower Cambrian (Atdabanian) Sekwi Formation are described. The sections sampled are in southwestern (internal) structural units where erosion beneath the "sub-Cambrian"(?) unconformity is least evident. Problems of lithostratigraphic correlation of post-Sheepbed, pre-Backbone Ranges formations remain. Acritarchs indicate the age of the Sheepbed Formation and the Blue-flower Formation above it is latest Proterozoic (Vendian), whereas that of the Vampire Formation is Early Cambrian (Atdabanian). The Backbone Ranges Formation has not yielded datable acritarchs, but it is for the most part Cambrian in age, based on other fossil evidence. Comparisons are made with the Russian Platform and southern Canadian Rocky Mountains successions. The total number of acritarch genera increases markedly across the Precambrian–Cambrian transition.

Precambrian—Cambrian boundary and correlation from southwestern and central part of Spain

1984 ◽  
Vol 121 (3) ◽  
pp. 221-228 ◽  
Author(s):  
E. Liñán ◽  
T. Palacios ◽  
A. Perejón
Keyword(s):  
Iberian Peninsula ◽  
Lower Cambrian ◽  
First Record ◽  
Trace Fossils ◽  
Middle Part ◽  
Early Cambrian ◽  
Upper Proterozoic ◽  
Upper Vendian ◽  
General Series ◽  
Calcareous Microfossils

AbstractThis paper comprises the first palaeontological correlation between the Upper Proterozoic–Lower Cambrian Series of Ossa-Morena, Luso-Oriental-Alcúdica and Galaico-Castellana Zones of the Iberian Peninsula.The authors show the palaeontological events on acritarchs, stromatolites, cyanophyta, soft-bodied metazoa, trilobites, archaeocyathans and skeletal microfossils from three representative sequences of the above mentioned zones and discuss the position of the Precambrian–Cambrian boundary in the sequences. The Sierra de Córdoba general Series (Ossa-Morena Zone) has an erosive discontinuity between the rocks with the first record of Cambrian metazoan activity (Skolithos sp., Monomorphichnus sp., Phycodes pedum and Rusophycus sp.) and the rocks with a palynological association (Bavlinella faveolata, Protosphaeridium flexosum, Trachisphaeridium sp., aff. Octoedryxium truncatum, Phycomicetes? sp. and cf. Ooidium sp.) which suggests a Lower–Middle Vendian age. For this reason we suggest that the Precambrian–Cambrian boundary be placed at this unconformity.The upper part of the Sierra de Guadalupe Series (Luso-Oriental-Alcúdica Zone) includes detrital beds with Phycodes pedum, Planolites sp. and Treptichnus sp. which are also the first record of Cambrian metazoan activity. In the middle part of the sequences, acritarchs attributed to the genus Micrhystridium are found at the top of the Calcareous Beds. This is taken to indicate an early Cambrian age. Vendotaenids and Bavlinella faveolata are found in abundance, thus indicating a Late Vendian age for the middle part of this unit. Thus, we propose the Precambrian–Cambrian boundary be located in the upper part of the Calcareous Beds.In the Rio Uso Series (Galaico-Castellana Zone), the Azorejo Sandstones contain Rusophycus gr. radwanskii, Planolites sp. and Gordia sp. Trace fossils produced by trilobite-like arthropoda (Monomorphichnus) have been cited in the upper part of the underlying Pusa Shales. Moreover, Octoedryxium truncatum and Bavlinella faveolata are found in the lower part of this unit which suggest that the Precambrian–Cambrian boundary could be situated in the Pusa Shales.Calcareous microfossils related to annelid polychaetes are found associated with Upper Vendian acritarchs in the Calcareous Beds of Sierra de Guadalupe. They are the oldest record of skeletal metazoa in the Spanish Series.The medusoids found are associated with a Vendian flora and they are also the oldest non-skeletal metazoa record known in the Iberian Peninsula.

THE SUBSURFACE GEOLOGY OF THE WESTERN OFFICER BASIN — RESULTS OF SHELL'S 1980-1984 PETROLEUM EXPLORATION CAMPAIGN

1985 ◽  
Vol 25 (1) ◽  
pp. 34 ◽  
Author(s):  
W.G. Townson
Keyword(s):  
Lower Cambrian ◽  
Oil And Gas ◽  
Source Rocks ◽  
Petroleum Exploration ◽  
Gas Generation ◽  
Upper Proterozoic ◽  
Magnetic Basement ◽  
Complex Structural ◽  
Proterozoic Basement ◽  
The 1960S

The Officer Basin described in this paper includes four Proterozoic to Lower Palaeozoic sub-basins (Gibson, Yowalga, Lennis, Waigen) which extend in a northwest to southeast belt across 200 000 sq. km of central Western Australia. These sub-basins are bounded by Archaean to Proterozoic basement blocks and are almost entirely concealed by a veneer of Permian and Cretaceous sediments. Depth to magnetic basement locally exceeds eight kilometres.Until recently, information on the sub-surface geology was limited to shallow levels, based on the results of a petroleum exploration campaign in the 1960s and the work of State and Federal Geological Surveys. In 1980, the Shell Company of Australia was awarded three permits (46 200 sq. km) covering the Yowalga and Lennis Sub-basins. The results of 4700 km of seismic data and three deep wildcat wells, combined with gravity, aeromagnetic, Landsat, outcrop and corehole information, has led to a better understanding of the regional subsurface geology.The Lennis Sub-basin appears to contain Lower to Middle Proterozoic sediments, whereas the Yowalga Sub- basin is primarily an Upper Proterozoic to Lower Cambrian sequence which comprises a basal clastic section, a middle carbonate and evaporite sequence and an upper clastic section. Widespread Middle Cambrian basalts cap the Upper Proterozoic to Lower Cambrian prospective sequence. Late Proterozoic uplift resulted in salt- assisted gravity tectonics leading to complex structural styles, especially in the basin axis.Despite oil shows, organic matter in the oil and gas generation windows and reservoir-quality sandstones with interbedded shales, no convincing source rocks or hydrocarbon accumulations have yet been located. The area remains, however, one of the least explored basins in Australia.

Basal Cambrian reworked phosphates from Spitsbergen (Norway) and their implications

1989 ◽  
Vol 126 (1) ◽  
pp. 79-88 ◽  
Author(s):  
D. L. Kidder ◽  
K. Swett
Keyword(s):  
Soviet Union ◽  
Calcium Phosphate ◽  
Lower Cambrian ◽  
Single Unit ◽  
The Arctic ◽  
Western North America ◽  
Upper Proterozoic ◽  
The Soviet Union ◽  
Lower Palaeozoic ◽  
Phosphate Deposits

AbstractSeveral phosphatic zones are associated with the oldest remains of shelly fossils on the arctic island of Spitsbergen. The phosphate occurs as reworked nodules and layers associated with a disconformity. A gap in the acritarch biostratigraphic record supports a hiatus associated with the phosphatic zone. Palaeogeographic positions for Svalbard, both (1) as a single unit, and (2) as three isolated parts prior to Caledonian tectonism are consistent with conditions favourable to at least minimal amounts of upwelling. However, upwelling may not have been a prerequisite for development of these phosphate deposits. These phosphates were deposited in a nearshore shelf environmnt which contrasts with the outer shelf setting of many modern and recent phosphate deposits.Geochemistry of the Lower Cambrian phosphates of Spitsbergen varies with the mode of phosphate occurrence. Concretionary phosphate clasts are chemically zoned such that their centres are enriched in P2O5 and CaO and are depleted in A12O3, SiO2, and K2O. Laminated and thinly bedded phosphate shows no chemical zonation within clasts. Phosphate cements are the most pure with respect to calcium phosphate.This thin phosphatic zone of Svalbard is minor when compared with thicker and richer Lower Cambrian phosphate deposits, particularly those in the Soviet Union, Southeast Asia, and Australia. Coupled with the near absence of phosphate in some extensive Proterozoic to Lower Palaeozoic successions (e.g. western North America), this emphasizes the fact that widespread Lower Cambrian phosphate deposition was unevenly distributed. Althouth the Upper Proterozoic and Lower Cambrian are characterized by enhanced phosphogenesis, palaeogeographic position was also apparently critical to deposition of phosphatic sediments.

PALAEOZOIC HISTORY OF THE ST. VINCENT GULF REGION, SOUTH AUSTRALIA

1972 ◽  
Vol 12 (1) ◽  
pp. 9 ◽  
Author(s):  
William J. Stuart ◽  
A.T. von Sanden
Keyword(s):  
Lower Cambrian ◽  
Regional Metamorphism ◽  
South Australia ◽  
Lower Permian ◽  
Gulf Region ◽  
Middle Cambrian ◽  
Upper Proterozoic ◽  
Marginal Areas ◽  
Major Fault ◽  
Yorke Peninsula

The St. Vincent Gulf Region comprises portions of the Gawler Craton and Adelaide Geosyncline. It extends from Yorke Peninsula and a portion of Investigator Strait (within the craton) to the Mt. Lofty — Kangaroo Island fold belt (inclusive). An area of potential hydrocarbon accumulation exists in a marginal area of the geosyncline adjacent to the craton.After latest Precambrian deformation of Proterozoic strata, Lower Cambrian deposition commenced with transgressive arkoses, overlain by carbonates. The upper portion of the carbonates near or on the craton grade eastwards into mudstones in the geosyncline proper. A major retreat of the sea from marginal areas of the craton and geosyncline occurred during late Lower Cambrian time. The exposed land mass constituted a source for clastics deposited in the remainder of the geosyncline, which was undergoing strong downwarping movements. Intercalated carbonates and clastics of latest Lower Cambrian and Middle Cambrian age document return of the sea to the craton.Deposition in the geosyncline probably terminated during Middle Cambrian time, with pronounced earth movements and regional metamorphism culminating during Ordovician time. The Palaeozoic and Proterozoic rocks are unconformably overlain by Lower Permian and Cainozoic sediments.Three major fault patterns can be recognized in the region. Within most of the western portion, the fault pattern is similar to that of the Gawler Craton. Two later patterns of faulting in the remainder of the region evolved during Upper Proterozoic-Cambrian and Cambro-Ordovician times respectively, as the consequence of pronounced folding. Episodic movements of blocks bounded by faults in the western and northwestern portions of the region were the result of strong compressional forces directed towards the craton. Weaker earth movements also occurred during Lower Permian-Eocene time rejuvenating some of the old structures.

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