Jasper conglomerate is an informal term for a very distinctive

Paleoproterozoic The Paleoproterozoic Era (also spelled Palaeoproterozoic) is the first of the three sub-divisions ( eras) of the Proterozoic eon, and also the longest era of the Earth's geological history, spanning from (2.5–1.6 Ga). It is further sub ...

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

and

jasper Jasper, an aggregate of microgranular quartz and/or cryptocrystalline chalcedony and other mineral phases, is an opaque, impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. The common red color is due to ...

pebble A pebble is a clastic rocks, clast of rock (geology), rock with a grain size, particle size of based on the Particle size (grain size), Udden-Wentworth scale of sedimentology. Pebbles are generally considered larger than Granule (geology), gra ...

conglomerate that occurs within the middle part of the Lorrain Formation of the Cobalt Group of the Huronian Supergroup. It is also known by other names including pebble jasper conglomerate, St. Joseph Island puddingstone, Drummond Island puddingstone, Michigan puddingstone. The jasper conglomerate occurs on St. Joseph Island and the St. Mary's River area north and northwest of the Bruce Mines of

Northern Ontario Northern Ontario is a primary geographic and quasi-administrative region of the Provinces and territories of Canada, Canadian province of Ontario, the other primary region being Southern Ontario. Most of the core geographic region is located on p ...

, about east of Sault Ste. Marie. This conglomerate consisted originally of gravelly

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

s and sandy

gravel Gravel () is a loose aggregation of rock fragments. Gravel occurs naturally on Earth as a result of sedimentation, sedimentary and erosion, erosive geological processes; it is also produced in large quantities commercially as crushed stone. Gr ...

s composed of subrounded pebbles of red jasper, white

quartzite Quartzite is a hard, non- foliated metamorphic rock that was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tecton ...

, semi-transparent quartz, and black

chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a prec ...

, with coarse-grained sand matrix. Typically it contains between about 30% to as much as 90% pebbles. It has been cemented and partially metamorphosed into a quartzitic conglomerate. The beds of jasper conglomerates fill erosional troughs and channels of what are interpreted to be either

alluvial fan An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to Semi-arid climate, semiar ...

braided river A braided river (also called braided channel or braided stream) consists of a network of river channel (geography), channels separated by small, often temporary, islands called ''braid bars'' or, in British English usage, ''aits'' or ''eyots''. ...

deposits of the Lorrain Formation.Lowey, G.W. (1985) ''Stratigraphy and Sedimentology of the Lorrain Formation, Huronian Supergroup (Aphebian), Between Sault Ste. Marie and Elliot Lake, Ontario, and Implications For Stratiform Gold Mineralization.'' Open File Report no. 1154. Geological Survey of Canada, Ottawa, Canada.Baumann, S.D.J., T. Arrospide, and A. E. Wolosyzn (2011) ''Preliminary Redefinition of the Cobalt Group (Huronian Supergroup), in the Southern Geologic Province, Ontario, Canada.'' Midwest Institute of Geosciences and Engineering, Chicago, Illinois. These deposits are interpreted to represent nonglacial deposits that immediately postdate the Makganyene glaciation.Williams, G. E., and P. W. Schmidt (1997) ''Paleomagnetism of the Paleoproterozoic Gowganda and Lorrain formations, Ontario: low paleolatitude for Huronian glaciation.'' Earth and Planelary Science Letters. 153:157- 169.Kopp R.E., J.L. Kirschvink, I.A. Hilburn, and C. Z. Nash (2005) ''The Paleoproterozoic snowball Earth: a climate disaster triggered by the evolution of oxygenic photosynthesis.'' Proceedings of the National Academy of Sciences. 102(32):11131–11136. Because of its distinctive nature, pebble- to

boulder In geology, a boulder (or rarely bowlder) is a rock fragment with size greater than in diameter. Smaller pieces are called cobbles and pebbles. While a boulder may be small enough to move or roll manually, others are extremely massive. In ...

-size fragments of jasper conglomerate can be recognized as

glacial erratic A glacial erratic is a glacially deposited rock (geology), rock differing from the type of country rock (geology), rock native to the area in which it rests. Erratics, which take their name from the Latin word ' ("to wander"), are carried by gla ...

s in

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

glacial

till image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...

s and drift within large parts of the

glaciated A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires d ...

Midwestern United States. Fragments of jasper conglomerate were eroded by continental

ice sheet In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacier, glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice s ...

s from Northern Ontario and spread across all of Michigan and as far south as Ohio and Kentucky during repeated glacial advances and retreats. For example, pebble to boulder-size fragments of jasper conglomerate are quite common on

Drummond Island, Michigan Drummond Township ( ) is a civil township of Chippewa County, Michigan, Chippewa County in the U.S. state of Michigan. The population was 973 at the 2020 United States census, 2020 census. The township encompasses the large Drummond Island and n ...

where it is called Drummond Island puddingstone.Slawson, C.B. (1933) ''The Jasper Conglomerate, an Index of Drift Dispersion.'' The Journal of Geology. 41(5):546-552.

References

External links

*Anonymous (2012a
''Guide to Rocks and Minerals of Illinois.''
Illinois State Geological Survey, Champaign, Illinois. *Anonymous (2012b
''Conglomerates.''(Illinois glacial erratics)
Illinois State Geological Survey, Champaign, Illinois. *Anonymous (2012c

The St. Joseph Island 1812 Bicentennial Committee, St. Joseph Island, Ontario. *Kelley, J.G., (2009
''Drummond Island Puddingstone.''
Drummond Island Tourism Association, Drummond Island, Michigan. {{DEFAULTSORT:Jasper Conglomerate Conglomerates (geology) Geology of Ontario

See also

References

External links