Archaean stromatolites from the Steep Rock Group, northwestern Ontario, Canada

Reinvestigation of the late Archaean stromatolites of the Steep Rock Group has shown that a wide variety of forms is present, including domed and tabular bioherms and biostromes. Both columnar and noncolumnar structures are present. Branching is common in some columnar forms. Facing directions in the stromatolites are consistent with other field evidence showing that the base of the Steep Rock Group is an unconformity.

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Archean rocks from the eastern Lac Seul region of the English River Gneiss Belt, northwestern Ontario, part 1. Petrology, chemistry, and metamorphism

Canadian Journal of Earth Sciences ◽

10.1139/e76-121 ◽

1976 ◽

Vol 13 (9) ◽

pp. 1201-1211 ◽

Cited By ~ 7

Author(s):

N. B. W. Harris ◽

A. M. Goodwin

Keyword(s):

Complex Structure ◽

Granulite Facies ◽

Metamorphic Grade ◽

Amphibolite Facies ◽

Northwestern Ontario ◽

Southern Margin ◽

Field Evidence ◽

Facies Metamorphism

The eastern Lac Seul region of the English River Gneiss Belt is divided into two domains defined by contrasting petrology and structure. The northern domain is underlain by east-trending, steeply south-dipping, migmatized metasediments, intruded by occasional granite sills, and the southern domain by gneissic tonalite and trondhjemite, with abundant amphibolite inclusions, intruded by granite dykes and diapirs: this domain has a complex structure with gently east-plunging open folds of about 5 km wavelength. Field evidence suggests that metasediments of the northern domain have been deposited on the tonalite trondhjemite basement, which was subsequently mobilized, thereby producing the steeply dipping paragneiss belt of the northern domain.The grade of metamorphism throughout the region lies in the upper amphibolite facies, rising locally to the granulite facies. Within 15 km of the southern margin of the gneiss belt, the metamorphic grade decreases to the greenschist facies.U–Pb dating of zircons indicates that the tonalite gneiss was emplaced at least 3040 m.y. ago, and the granite plutons at 2660 m.y., coeval with migmatization and upper amphibolite facies metamorphism. Late pegmatites were emplaced at 2560 m.y.

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The Yorkshire Dogger

Geological Magazine ◽

10.1017/s001675680007463x ◽

1949 ◽

Vol 86 (4) ◽

pp. 201-225 ◽

Cited By ~ 6

Author(s):

R. H. Rastall ◽

J. E. Hemingway

Keyword(s):

Economic Value ◽

Black Shales ◽

Limited Extent ◽

Rock Group ◽

Field Evidence ◽

Sedimentary Deposit ◽

Facies Variation

AbstractThe Lias-Oolite junction in Rosedale and Farndale is defined. The underlying Lias is folded into a pre-Oolite complex of shallow Caledonoid folds, wherein are preserved about 55 square miles of Yeoyilian strata in the Cleveland region. The Rosedale East and Sheriff's Pit ironstones, now exhausted, are included on field evidence with the Yeovilian and not the Dogger. They occur in the troughs of two structural basins of limited extent in the fold complex, while other basins hold ironstones of no economic value. It is unlikely that the depositional basin of the Rosedale ironstones extended far beyond the present limits of the dale. Within Rosedale its distribution was materially reduced by erosion from the crests of minor pre-Dogger folds, pebbles now phosphatised derived from the crests occurring in the base of the Dogger.A three-fold sub-division of the Dogger is recognized. The Glaisdale Oolite is here of little importance; the lenticular Rosedale Sandstone represents sand trapped in the continued down-warping over Rosedale in early Dogger times. The most widely spread rock group, the Blakey Series, includes the important Black Shales at its base. Marked facies variation is recognized in the sandy upper part, which includes the Ajalon facies, the Green Flag facies, etc., which were earlier incorrectly regarded as in chronological succession.The Rosedale magnetite-oolite is regarded as a sedimentary deposit underlying the Dogger.The petrography of the several beds of the Lias-Oolite junction is briefly described.

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