Road Log for Highway 566
Reset odometer to 0 at intersection of Second Line and Highway 17 N. Continuing north on Highway 17.
3.8 km. - 2.36 mi - Root River.
Stop 556-1. (Accessible only at low water levels)
At this point outcrops of mainly red sandstone of the Jacobsville Formation are found along the banks and bed of the Root River. Paleomagnetic studies have indicated that the Jacobsville rocks are only slightly younger that the 1.1 billion year old Keweenawan age basalts of the Mamainse Formation which outcrop along Highway 17 about 50 km north of Highway 556.
Red sandstones and conglomerates like the Jacobsville Formation are known as "redbeds". The origin of redbeds has been the subject of controversy in the past. But it is now believed that the red-colored, ferric oxide mineral, hematite (Fe2O3) of redbeds is transformed from drab-colored, ferrous iron minerals by a number of processes that are favoured by a desert environment under an oxidizing atmosphere.
4.0 km. - 2.49 mi - An unmarked road exiting east from Highway 17 allows parking and access to the Root River river where outcrops of the Jacobsville Formation can be observed when water levels in the river allow.
6.3 km. - 4.84 mi - Gravel pits near the highway expose gravels of a delta complex which hold an important commercial source of sand and gravel. These gravels were deposited from the melt-waters of the retreating ice front during a the warming period immediately after the most recent period of continental glaciation, known as the "Wisconsin Advance" which took place between 80,000 and 11,000 years ago.
7.8 km. - 0 4.84 mi - The predominantly granitic hills of " the Algoma Highlands" to the northeast.
8.9 km. - 12.5 km , 5.5 mi - 7.8 mi - Outcrops of granite and granite gneiss are seen along the highway. Absolute age measurements have yet to be made but these rocks of the Archean Eon are probably between about 2.60 Ga and 2.75 Ga (billion years) old.
12.8 km. - 7.9 mi - "Hayden Diabase" is a local name for a wide, nearly vertically dipping gabbro dike intruding granite and granite gneiss . The age of the gabbro dike has not been determined. It may be of Keweenawan age (1.1 bybp) or a Nipissing age (2.217 bybp). A mafic dike about 50 cm wide intrudes the diabase near the southern contact with the Archean granitic rocks. This younger dike may be a type of mafic rock known as "lamprophyre"
13.3 km. 8.2 mi -
Intersection of Highway 17 and Highway 566 at the Village of Hayden. - Reset odometer to 0 and proceed east on Highway 556.
Along this section Highway 556, north of Upper Island Lake, an important, northwest-southeast trending fault separates Archean granitic rocks to the north from the younger sedimentary rocks of the Aweres Formation of the Huronian Supergroup to the south.
Click here for a geological map of the area along Highway 556.
4.4 km. - 2.7 mi - Highway 552 at Highway 556. Continue on Highway 556.
5.6 km. - 3.5 - Fractured altered (Archean?) rocks.
5.9 km. - 3.6 mi - Arbour Road - Continue on 556
Click here to see a table of Formations of the Huronian Supergroup.
6.1 km. - 3.8 mi to 6.4 km - 4.0 mi
Rocks of the Island Lake Fault Zone (an ancient earthquake zone) are exposed along Highway 556 near Lower Island Lake. A good place to park and observe the effect of faulting can be found on the south side of the highway just west of the railroad crossing. In that area the rocks are highly fractured (brecciated) and crossed by zones of intense shearing up to a meter or so wide.
Click here to see a map of the geology along Highway 556.
The effect of the fault movement has been to obscure much of the original texture and composition of the rocks in and near the fault zone. The pinkish relatively, massive rocks, seen in the fault zone resemble younger (Keweenawan) intrusive rocks known as "felsite" (see my road log for Highway 17 north). However, the pink rocks may be older rocks much altered by fluids migrating along the fault. Some of the Archean granitic rocks north of the highway have been intensely altered to a chlorite-rich rock resembling a mafic volcanic rock. It requires examination of thin sections under the polarizing light microscope to reveal their true origin.
6.4 km. - 4.9 mi. - Railroad crossing
6.9 km. more fractured rocks with (quartz?) veins.
7.3 km. - More fractured altered rocks.
8.0 km. - Boundary marker between Vankoughnet and Aweres Twps.
N46deg. 41.186min W84deg 15.526min
8.1 km. 5.0 mi. - Park on shoulder just west of dark-gray outcrops. On south side of highway the rocks include dark-coloured conglomerate the Aweres Formation. At this location conglomerate of the Aweres Formation consists of tightly packed pebble to cobble-sized clasts of mafic volcanic rocks with a few clasts of pink granite. The matrix is commonly coarse, sand-sized quartz. In some places the interstices filled by brown weathering iron-carbonate (ankerite?).
The stratigraphic position of the Aweres Formation is uncertain. Geological mapping by the writer in the 1970's found that where the Aweres Formation directly overlays the metabasalts of the Thessalon Formation, the predominant clast type is that of the underlying volcanic rocks, but higher in the section granitic clasts increase in proportion. Outcrops of Aweres Formation near the top of the section around Trout Lake consist of predominantly granitic clasts with wisps of yellowish mudstone that I have interpreted as weathered mafic volcanic clasts.
These observations show that the Aweres Formation is stratigraphy above (therefore younger) than the volcanic rocks of the Thessalon Formation.
At this point the clasts of the Aweres Formation are at least 90% of basaltic rocks of the Thessalon Formation, with minor granitic and quartz clasts. The granitic
clasts are commonly well-rounded and predominantly reddish in colour. The conglomerate of the Aweres Formation is overlain by massive, grey, pebbly sandstone of the Gowganda Formation.
The contact is abrupt and can be recognized in outcrops along both sides of the highway in this area. In places the contact is marked by a thin (0.1 to 1 cm thick) brown-weathering iron-carbonate.
Similar carbonate locally forms the "matrix" of the Aweres conglomerate, and is also found as veinlets in the overlying Gowganda Formation.
This is is an erosional contact - an unconformity - not a fault or sedimentary contact.
This interpretation is supported by the irregular form of the contact and general lack of deformation adjacent to the contact. At one location a large boulder (2 X 0.5 m) of fine-grained, gray sandstone with quartz veins lies within the Aweres conglomerate. A few cobbles of similar sandstone were noted near the block.
A few large (> 1 m) boulder-size, megaclasts of Thessalon metabasalt were also seen this part of the outcrop. The lithology is identical to the lowermost part of the Aweres Formation as seen directly overlying the Thessalon Formation in the Jarvis Township about 10 km southeast of this point. In this region, the Aweres Formation overlies an erosional contact the Thessalon Formation (Bennett et al. 1974).
The Aweres Formation has a similar stratagraphic position as the Ramsay Lake Formation but Bennett et al (1974) proposed the Aweres Formation was deposited as an alluvial fan while the Ramsay Lake Formation has features of a glaciogenic deposit.
Rocks at the east end of the outcrop appears to be mainly siltstone and mudstone with some sandstone of the Gowganda Formation. East end of outcrop at Zone 16, 709849 E, 5175464 N.
Stop 556-6
9.1 km - 5.6 mi - Zone 16 - 710458E; 5176002N
N46.42.266 W84deg 14.81min
Outcrop of laminated argillite of the Gowganda Formation on the south side of the highway contains pebbles or cobbles within thinly bedded (laminated) mudstone or siltstone. The geological significance of these much larger clasts (pebbles in this case) within siltstone, mudstone or metamorphosed equivalents. dropstones are the important indicators of paloclimate in Precambrian rocks because they indicate the presence of floating ice that carried large clasts over much more fine-grained sediment.
9.2 km. more or less continuous outcrops of Gowganda siltstone etc.
Stop 556-6a
Zone 16, 710962 E, 5176051 N.
46deg 42.283 min, 84deg. 14.413 min
9.5 km. - 6.9 mi. - Park on shoulder just west of outcrop.
Dark green, pebbly sandstone (wacke) and , conglomerate with abundant granite clasts
(Gowganda Formation) in sharp fault contact with dark grey Huronian basalt flows
to the east. At the west end of the Gowganda outcrop is a unit of pinkish
sandstone striking 160 and dipping 40W. The contact between the volcanics on the
east and the Gowganda conglomerate on the west strikes 135 dips 65 W. Bedding in
Gowganda Formation at contact is in essentially the same direction. There is
minor fracturing parallel to the contact in the volcanics but no deformation is
noticeable in the conglomerate. Zone 16, 710962 E, 517605 1 N. at the contact.
The Huronian volcanics (Thessalon Formation) contains clots of altered
plagioclase crystals (glomeroporphyritic texture).
10.7 km. - 6.6 mi - Bellevue Valley Road. Z16 - 712022E, 5176019N.
46deg.42.28min 84deg.15.01 min
10.8 km. - railroad trestle.
Stop 556-7
11.3 km. 7.2 mi - Sharp Corner - Archean granitic rocks (syenite to syenodiorite) at the east end of this outcrop are unconformably overlain by clast-supported, granite-cobble conglomerate of the Gowganda Formation seen at the west end of the outcrop. A few mafic (dark-coloured) dikes intrude the granitic rocks. The contact between the plutonic rocks and conglomerate is covered at this location. However an unconformable (erosional) relationship is suggested by the presence of angular to subrounded cobbles of adjacent syenitic rocks in the conglomerate which are similar the adjacent syenite. Can you think of additional evidence for an unconformity vs an intrusive contact?
12.6 km. - 7.9 mi - Quartzite - metaquartz arenite of the Lorrain Formation. Fractured reddish quartzite (A little varved clay?)
13.5 km. - 8.7 mi -Nipissing Diabase - No contacts visible.
14.4 km. - 8.9 Quartzite of the Lorrain Formation
Stop 556-8
46deg.38.288min W84deg.18.287min
14.9 km. - 9.2 mi - Good exposure of "puddingstone"; More correctly termed the "Jasper-pebble Conglomerate Member of the Lorrain Formation " This well-known member of the Lorran Formation is about the middle of the Lorrain Formation (Frarey, 1967). The dip of the bedding here is vertical or nearly so.
15.1 km. Pinkish Lorrain quartzite
Stop 9
16.4 km. - Northland Lake Road.
16.6 km. Rail crossing.
17.5 km. Outcrops of Archean amphibolite. Most dark-coloured rocks east of the rail crossing are medium grade metamorphic rocks known as "amphibolite". These were originally mafic volcanic rocks (basalt) the original minerals in which have been converted to amphibole and plagioclase feldspar by heat and pressure from the Archean granitic intrusions.
Log ends at 19.2 km lot 3977. G. Bennett June-Oct. 1999. Modified June 2003, photography 2003, 2014
g.bennett@geoben.ca