Alluvial–playa sedimentation in the lower Keweenawan Sibley Group, Thunder Bay District, Ontario

1986 ◽  
Vol 23 (4) ◽  
pp. 527-542 ◽  
Author(s):  
Burns A. Cheadle
Keyword(s):  
Depositional Environments ◽  
Midcontinent Rift ◽  
North Shore ◽  
The North ◽  
Thunder Bay ◽  
Lake Formation ◽  
Playa Lake ◽  
Main Period ◽  
Sand Flats ◽  
Middle Proterozoic

The Middle Proterozoic Sibley Group is a mixed clastic–carbonate red bed sequence located in the Thunder Bay – Nipigon area on the north shore of Lake Superior. The lowest unit, the Pass Lake Formation, consists of a basal paraconglomerate member, of probable alluvial debris-flow origin, overlain by 20–80 m of plane-bedded and cross-bedded quartz arenites, which were probably deposited by sheetfloods and eolian processes on alluvial outwash sand flats. The overlying Rossport Formation is dominated by red and buff dolomicritic mudstone. The association of these mudstones with relatively pure massive carbonate beds and sheetflood sandstone units is strongly suggestive of a playa lake depositional environment. Fluctuations in playa lake levels may have resulted in oscillations between carbonate-dominated and clastic-dominated sedimentation. The upper unit, the Kama Hill Formation, consists of horizontally laminated purple shales and ripple cross-laminated buff siltstones to fine sandstones. The presence of stacked "powering-down" sequences and abundant dessiccation features is suggestive of sheetflood deposition on a distal alluvial floodplain.The sequence of depositional environments suggests that the Sibley Basin formed by stretching and sagging of the Middle Proterozoic crust preceding the main period of volcanic activity along the Keweenawan Midcontinent Rift Zone. In this sense, the Sibley Group red beds represent the earliest products of Keweenawan rifting. They were not, however, deposited in a classical aulacogen or "failed arm."

Depositional environments of a thick Proterozoic sandstone: the (Huronian) Mississagi Formation of Ontario, Canada

1978 ◽  
Vol 15 (2) ◽  
pp. 190-206 ◽  
Author(s):  
Darrel G. F. Long
Keyword(s):  
Depositional Environments ◽  
Stratified Medium ◽  
River Systems ◽  
North Shore ◽  
The North ◽  
Lake Region ◽  
Braided Stream ◽  
Major River ◽  
Flowing System ◽  
Mixed Load

The Mississagi Formation is a thick (up to 3.4 km) Proterozoic arenite sequence that forms part of the Huronian (lower Aphebian [Formula: see text]) succession of the north shore of Lake Huron, Ontario. The formation is characterized by planar and to a lesser extent trough cross-stratified medium to coarse feldspathic arenites, with only minor amounts of argillite and conglomerate. Although the formation lacks any regular systematic cyclicity, both thinning upward and fining upward sequences can be recognized in some sections. Paleocurrent roses for individual outcrops are typically unimodal, although some bimodal distributions are recognized. The bulk of the formation is interpreted to be the result of deposition in a fluvial environment, principally from bed load and mixed load streams. These rivers were probably marked by a braided stream pattern in which channels were characterized by intermediate to low sinuosities and high width to depth ratios. Regional paleocurrent and petrographic trends indicate that two major river systems were operative. One system flowed east and south from the Sault Ste. Marie – Elliot Lake region to meet a second, southwesterly flowing system originating in the Cobalt Plain. These systems met in the southern Huronian area, from where the coalescing river systems flowed south.

Lower Huronian Sandstones; Correlation Problems and Uranium; Morin Township Area, Ontario

1975 ◽  
Vol 12 (2) ◽  
pp. 237-251
Author(s):  
F. W. Chandler
Keyword(s):  
Lake Huron ◽  
North Shore ◽  
The North ◽  
Stratigraphic Subdivision ◽  
Lake Formation ◽  
Stratigraphic Position

Huronian feldspathic sandstones 30 km north of Thessalon (the Morin Township area) rest noncomformably upon Archean rocks and are overlain by the Huronian Gowganda Formation. They contain uraniferous pyritic quartz-pebble orthoconglomerate, similar to the uraniferous conglomerate ore of the Elliot Lake – Blind River area. The sandstones also contain paraconglomerate units at several stratigraphic levels which are lithologically similar to the Ramsay Lake and Bruce Formations.Trends in Huronian stratigraphy on the North Shore of Lake Huron suggest that in the Morin Township area the Quirke Lake Group is absent and the McKim and Pecors Formations, which contain much argillite, are likely to be very thin or absent. Thus the feldspathic sandstones of the Morin Township area are assigned to the Matinenda and the Mississagi Formations. The most continuous paraconglomerate unit might be correlated with the Ramsay Lake Formation.Huronian feldspathic sandstones lying nonconformably upon Archean rocks 16 km northeast of Sault Ste Marie (the 'Soo Series') and 50 km north of Sudbury, have many features in common with the sequence of the Morin Township area. Stratigraphic subdivision of these two sequences and finer delimitation of potential uraniferous units may be aided by using paraconglomerates such as the Ramsay Lake Formation as marker units. Such subdivision however will be uncertain until the number, exact stratigraphic position and the areal continuity of these paraconglomerates can be assessed better.

Geochemistry of North Shore Hypabyssal dikes and sills in the Midcontinent Rift of Minnesota: an example — the 47th Avenue sill

2004 ◽  
Vol 41 (7) ◽  
pp. 829-842 ◽  
Author(s):  
Karl E Seifert ◽  
James F Olmsted
Keyword(s):  
Lake Superior ◽  
Geochemical Data ◽  
Rift System ◽  
Midcontinent Rift ◽  
North Shore ◽  
Volcanic Group ◽  
The North ◽  
Midcontinent Rift System ◽  
Basalt Composition

This study presents geochemical data for several of the numerous small to large dikes and sills, including the 47th Avenue sill, exposed along the shore of Lake Superior in and north of Duluth, Minnesota. These intrusions are late magmatic features of the Proterozoic Midcontinent Rift System and together form the North Shore Hypabyssal Group. The dikes are geochemically distinct from the sills, and, when the two are exposed together, the younger dike intrudes the older sill. Dikes are primitive with Mg# up to 68, have positive εNd values, and are oriented approximately north–south with steep westerly or near vertical dips. The older sills are more evolved, usually have εNd values near or below 0, and have the same gentle easterly dip as the thick sequence of North Shore Volcanic Group flows they intrude. Dike compositions correlate best with a mixture of widespread basalt compositions types 4 and 5, with primitive geochemistry and positive εNd values, whereas sill compositions are similar to widespread basalt composition type 4 typical of most North Shore Volcanic Group flows. The 47th Avenue sill in Duluth is an evolved single intrusion North Shore Hypabyssal Group diabase sill with trough banding, sharp lower and upper contacts, and a spectacular fractured and undulating roof zone containing blocks of the overlying ferroandesite flow.

On Riccia marginata and related species (Ricciaceae, Marchantiophyta)

2012 ◽  
Vol 46 ◽  
pp. 298-305 ◽  
Author(s):  
A. D. Potemkin ◽  
T. Ahti
Keyword(s):  
Related Species ◽  
Lake Ladoga ◽  
Leningrad Region ◽  
Sem Images ◽  
North Shore ◽  
The North ◽  
Molecular Studies ◽  
The Future ◽  
The Town

Riccia marginata Lindb. was described by S. O. Lindberg (1877) from the outskirts of the town of Sortavala near the north shore of Lake Ladoga, Republic of Karelia, Russia. The species has been forgotten in most recent liverwort accounts of Europe, including Russia. Lectotypification of R. marginata is provided. R. marginata shares most characters with R. beyrichiana Hampe ex Lehm. It differs from “typical” plants of R. beyrichiana in having smaller spores, with ± distinctly finely areolate to roughly papillose proximal surfaces and a narrower and shorter thallus, as well as in scarcity or absence of marginal hairs. It may represent continental populations of the suboceanic-submediterranean R. beyrichiana, known in Russia from the Leningrad Region and Karelia only. The variability of spore surfaces in R. beyrichiana is discussed and illustrated by SEM images. A comparison with the spores of R. bifurca Hoffm. is provided. The question how distinct R. marginata is from R. beyrichiana needs to be clarified by molecular studies in the future, when adequate material is available. R. marginata is for the time being, provisionally, included in R. beyrichiana.

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