Program, Abstracts, and Guidebooks - University of Minnesota Duluth

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STOP 16
In the roadcut to the north of the second lookout, the following
features may be observed:
(1) Two thin Keweenawan diabase sills, partially replaced by
carbonate, cut across the poorly developed bedding plane at
a low angle.
(2) Finely lamiqated chert of the chert—stromatolite unit
cuts out below the lower sill. Up to six Inches of anthraxolitic
carbonate has accumulated at the base of the chert. An oily
smell may be detected when this anthraxolite is freshly broken!
(3) Limey red mudstoneabove this unit is marked by many
cream—coloured spots, (average diameter ½ inch)! Similar
spots are evident throughout this unit, and commonly have a
siiall amount of graphite or hydrocarbon at the center. In
thiii seçtion, the only apparent.mineralogical change in the
spots is the lack of hematite coa4ing on clay and carbonate
grains.
(4) Irregular, flame—shaped, bleached zones follow fractures
and bedding plane cleavage in the red lintey mudstone. Leaching
of hematite, and destruction of clay minerals and feldspar
has occurred along the fractures!
(5) Above the road cut and overlying talus slope, the purple
mudstone crops out. It is more highly fissile,a4 cokltains
approximately 4 per cent hematite, which coats.vexy fine
.grained corrensite and microcline, and forms blades of spec—
ularite in tiny vugs. Bleaching along fractures is common in
this rock!
End of Trip
For anyone interested in a more complete view of the Sibley Group,
two additional areas should be visited.
(1) From Rossport, a boat trip to Quarry Channel and Wilson
Islands, which lie one to two miles off shore, will allow the visitor
to see an almost complete section of Sibley rocks! Op Quarry Island,
Rove shale is overlain by a thick section of Sibley sandstone. Here,
crossbeds and ripple marks are abundant.
On Channel Island, the upper part of the sandston unit, sandy
red muçistone units are all exposed. The latter is disconformably over—
lain by Osler volcanic rocks.
(2) The stromatolites near Disraeli Lake may be reachdd by following
the Armstrong road noflhfrow Hurkett for 21.6 m.iles, to the Disraeli
Lake road, which connects the Armstrong road with the Spruce River road