Jasper conglomerate
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Jasper conglomerate is an informal term for a very distinctive
Paleoproterozoic The Paleoproterozoic Era (;, also spelled Palaeoproterozoic), spanning the time period from (2.5–1.6  Ga), is the first of the three sub-divisions ( eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's ...
quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
and
jasper Jasper, an aggregate of microgranular quartz and/or cryptocrystalline chalcedony and other mineral phases,Kostov, R. I. 2010. Review on the mineralogical systematics of jasper and related rocks. – Archaeometry Workshop, 7, 3, 209-213PDF/ref> ...
pebble 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 Canadian province of Ontario, the other primary region being Southern Ontario. Most of the core geographic region is located on part of the Superior Geological Pro ...
, 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 defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class o ...
s and sandy gravels composed of subrounded pebbles of red jasper, white
quartzite Quartzite is a hard, non- foliated metamorphic rock which 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 tec ...
, 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 ...
, 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 semiarid climates, but a ...
or braided river 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-size fragments of jasper conglomerate can be recognized as
glacial erratic A glacial erratic is glacially deposited rock differing from the type of rock native to the area in which it rests. Erratics, which take their name from the Latin word ' ("to wander"), are carried by glacial ice, often over distances of hundre ...
s in
Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...
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 (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such as ...
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 glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are in Antarctica and Greenland; during the Last Glacial Period at La ...
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 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.


See also

* Puddingstone (rock) *
Hertfordshire puddingstone Hertfordshire puddingstone is a conglomerate sedimentary rock composed of rounded flint pebbles cemented together by a younger matrix of silica quartz. The distinctive rock is largely confined to the English counties of Buckinghamshire and Hertf ...
*
Roxbury puddingstone The Roxbury Conglomerate, also informally known as Roxbury puddingstone, is a name for a rock formation that forms the bedrock underlying most of Roxbury, Massachusetts, now part of the city of Boston. The bedrock formation extends well beyond ...


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 Rocks Sedimentary rocks Conglomerates (geology) Geography of Algoma District Geology of Ontario