Stratigraphy and depositional setting of the Sibley Group, Thunder Bay district, Ontario, Canada

1980 ◽  
Vol 17 (5) ◽  
pp. 633-651 ◽  
Author(s):  
J. M. Franklin ◽  
W. H. McIlwaine ◽  
K. H. Poulsen ◽  
R. K. Wanless
Keyword(s):  
Rift Valley ◽  
Lacustrine Environment ◽  
Saline Environment ◽  
New Name ◽  
Thunder Bay ◽  
Quartz Arenite ◽  
Lake Formation ◽  
Mud Flat ◽  
Depositional Setting ◽  
Red Bed

The Sibley Group is a Neohelikian (1339 ± 33 Ma, RbSr, 87Rb = 1.42 × 10−11 year−1) red bed sequence located in an elongate basin extending northward for 150 km from Nipigon, Ontario. The lowest unit, the Pass Lake Formation (new name), is 50 m thick and consists of quartz arenite, deposited primarily in a shallow, quiet lacustrine environment. It is overlain by the Rossport Formation (new name), a unit of 135 m thickness consisting of a lower arenaceous red dolomite member, central chert–carbonate and stromatolite member, and an upper argillaceous red dolomite member. The Rossport Formation was deposited in a shallow, highly saline environment, in a basin of fluctuating size. The Kama Hill Formation (new name) is 50 m thick, and consists of purple shale composed of smectite, authigenic microcline, and quartz. It was deposited in a periodically dry mud flat, and is characterized by desiccation cracks, evaporite casts, and mud-chip microbreccias.Both the Rossport and Kama Hill Formations have an increased arenite content near the basin margins. Breccias cut the Rossport Formation and consist of stoped blocks of Rossport and Kama Hill rocks; these breccias are cut by sandstone dykes. The Sibley Group is situated in, and was possibly deposited in, a "failed arm" which radiates from a paleo-plume in the Keweenawan rift valley.

Lead–zinc–barite veins of the Dorion Area, Thunder Bay District, Ontario

1977 ◽  
Vol 14 (9) ◽  
pp. 1963-1979 ◽  
Author(s):  
James M. Franklin ◽  
Roger H. Mitchell
Keyword(s):  
Lead Isotopes ◽  
Central Zone ◽  
Chloride Ion ◽  
Coarse Grained ◽  
Vein Wall ◽  
Sulphur Isotope ◽  
Thunder Bay ◽  
Basement Rocks ◽  
Lake Formation ◽  
Lead Zinc

The lead–zinc–barite deposits of the Dorion region are spatially associated with the unconformity between the Sibley Group (Helikian) and Archean and Aphebian basement rocks. The veins are coarse grained, and mineralogically zoned with galena–calcite in the central zone, sphalerite–quartz surrounding the central zone, and barite (±chalcopyrite) in the vein extremities. Veins occur near the pinch-out of the "Pass Lake formation" (basal Sibley Group), within the dolomite of the overlying "Rossport formation", or in nearby basement fractures. Rossport dolomite, where it forms a vein wall, is highly altered to metal-enriched chert and calcite. Archean wall rocks are not altered.Potassium–argon isotopic determinations on mica in Archean pegmatite immediately adjacent to a vein indicate that the transporting solutions were too cool to cause re-equilibration of the Ar within the mica. Sulphur-isotope data indicate equilibrium between galena and sphalerite yielding a depositional temperature range of 35–135 °C, and disequilibrium between sulphide–sulphate pairs. Lead isotopes are highly anomalous, yielding a secondary isochron which indicates either an Archean, or more probably a mixed Archean–Aphebian, source of lead.The deposits formed from metal leached from either basement rocks or breakdown of Sibley sandstone matrix. Metals and sulphate moved through the permeable sandstone, probably as chloride-ion complexes, and precipitated at the sandstone pinch-out. Reduced sulphur, possibly derived from organic decay, and probably held in a gas trap at the sandstone pinch out, caused precipitation of the sulphides by reaction with metal-bearing brines.

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."

Benjamin Henry Latrobe and the nomenclature of two North American fishes

1987 ◽  
Vol 14 (1) ◽  
pp. 85-88
Author(s):  
CHARLOTTE M PORTER
Keyword(s):  
United States ◽  
North American ◽  
The United States ◽  
American Shad ◽  
New Name ◽  
The Common ◽  
Fish Louse

A curious error affects the names of three North American clupeids—the Alewife, American Shad, and Menhaden. The Alewife was first described by the British-born American architect, Benjamin Henry Latrobe in 1799, just two years after what is generally acknowledged as the earliest description of any ichthyological species published in the United States. Latrobe also described the ‘fish louse’, the common isopod parasite of the Alewife, with the new name, Oniscus praegustator. Expressing an enthusiasm for American independence typical of his generation, Latrobe humorously proposed the name Clupea tyrannus for the Alewife because the fish, like all tyrants, had parasites or hangers-on.

Sign in / Sign up

Export Citation Format

Share Document