Moose River Basin: geology and mineral potential - Geology Ontario

Moose River Basin
vicinity of drillhole 75-04.
The Mistuskwia Beds appear to be restricted to the central part of the
Moose River Basin and extend no farther south than the Grand Rapids Arch
complex. Hamblin (this report) suggests a provenance in the northwest for the
Middle Jurassic sediments, i.e. a gross direction of transport from northwest to
southeast with passage finally halted by the Grand Rapids Arch.
The early phase of deposition of the Lower Cretaceous Mattagami Forma
tion, identified in drillhole 75-06, was restricted to the marginal areas of the
Moose River Basin, and the terrigenous sediments were derived from the
southern Precambrian uplands. Compared to the later depositional episodes,
the early phase was comparatively weak and extended no farther north than
the Grand Rapids Arch. The calcareous sands and clays accumulated in a nar
row east-west trough lying between the Precambrian escarpment and the
Grand Rapids Arch. This restricted depositional environment was conducive to
lignite accumulation, as evidenced by abundant detrital lignite found in drill
hole 75-06. The clays and lignites of the Mattagami Formation in the Onaka
wana area have been shown palynologically, to correlate with the early deposi
tional phase. As this area lies north of the Grand Rapids Arch, it is probable
that the deposition at Onakawana took place in a separate sub-basin.
The later phase of deposition of the Mattagami Formation was a stronger
and more widespread event. As in the early phase, the sediments were derived
from the southern Precambrian uplands. However, there may have been re
newed uplift of this region which resulted in increased erosional activity, and a
substantially greater supply of sediments to the Moose River Basin. The sands
and clays of the upper Mattagami Formation extended over the former barrier
of the Grand Rapids Arch and partly overlapped the older Mistuskwia Beds
(Figure 2.8).
More precise stratigraphic relationships between the Mattagami Forma
tion and underlying Mistuskwia Beds remain uncertain. The Mattagami For
mation is certainly thinning northwards and only just overlaps the Jurassic
unit before pinching out. The Grand Rapids Arch, while not forming a complete
barrier to transportation, retained some control over distribution of the Cre
taceous sediments. The palynologically defined hiatus between the Mistuskwia
Beds and Mattagami Formation may have considerable significance as a simi
lar disconformity between Middle Jurassic and Lower Cretaceous clastic sedi
ments has also been identified in the subsurface of southeastern Saskatchewan
(Playford 1977). An epeirogenic event of continental proportions is indicated.
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