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Geomorphological mapping using detailed morphometric analyses of newly available high-resolution (5 m) digital elevation datasets across more than 9000 km2 of southern Ontario shows that the Greater Toronto Area and its immediate environs, Canada's largest urban area, is built across the former till beds of two fast-flowing ice streams (the newly named Simcoe Ice Stream (SIS) and the Halton Ice Stream (HIS)) within the last Laurentide Ice Sheet (LIS). These formed during regional deglaciation sometime around 13 000 years before present and are directly analogous to fast-flowing (>3 km year−1) ice streams in today's Antarctic and Greenland ice sheets. Their subglacial footprint in southern Ontario consists of flow sets of highly elongated and closely spaced flow-parallel till ridges up to 4 km in length and 100 m in width (megascale glacial lineations) that converge on the Oak Ridges Moraine (ORM) from the north (SIS) and south (HIS). ORM is southern Ontario's largest glacial landform extending from the Niagara Escarpment to Kingston over some 160 km and was deposited as a series of en echelon glaciolacustrine fan deltas in a complexly evolving glaciolacustrine depocenter trapped between the converging ice streams; meltwater channels cut into the bed of the Simcoe Ice Stream suggest that glaciofluvial sediment was primarily supplied from the north. The sedimentology of the ORM is comparable to 'morainal banks' at the margins of ice streams terminating in water; some 70 km3 of sediment accumulated very rapidly (>300 years?) reflecting the ability of ice streams to move very large fluxes of sediment, combined with trapping of sediment between SIS and HIS. To date, more than 117 paleo ice streams have been recognized in the LIS and this study confirms the presence of additional corridors of fast-flowing ice in its eastern Great Lakes sector. The ice stream paradigm provides a uniformitarian foundation for a comprehensive re-evaluation of much existing glacial geologic mapping and stratigraphic work in southern Ontario that hitherto stressed the role of catastrophic regional subglacial megaflooding in the formation of the ORM and many other landforms. This paper advocates complete remapping of the glacial landscapes of southern Ontario using an 'ice stream landsystem' approach to determine the full number of ice streams in the eastern Great Lake sector of the last ice sheet. [ABSTRACT FROM AUTHOR]

A regional survey of Lower Paleozoic sedimentary strata (Ordovician–Silurian) exposed across some 7000 km 2 of Southern Ontario, Canada has identified the sedimentary record of paleo-seismicity at a time of known faulting and rapid subsidence of Appalachian foreland basins. Shallow marine shoreface sandstones and shales of the Lower Silurian Thorold Formation show laterally extensive beds of large (< 2 m) synsedimentary ball-and-pillow structures outcropping on the face of the Niagara Escarpment near Hamilton. It is argued that these are seismites produced by ground shaking caused by a moderate intracratonic earthquake. Other comparable deformation structures that can be attributed to seismic activity also occur within sandstone–shale shoreface successions of the Upper Ordovician Georgian Bay, Lower Silurian Grimsby and the dolostone DeCew Formations indicating recurring activity. Later seismic activity is recorded in carbonate strata by deformed rhythmically laminated lagoonal dolostones of the mid-Silurian Eramosa Member of the Guelph Formation consisting of intraformational syndepositional reverse faults and horizons of brecciated laminites indicating compressional stresses and mass flow. Deformation structures are exposed in several quarries and can be correlated in drill cores 15 km distant indicating widespread extent. Deformed dolostones are attributed to co-seismic slumping of lagoonal facies from bioherms and are similar to seismites of the same age in closely adjacent parts of the US. These were attributed to reactivation of underlying Precambrian basement structures such as the Grenville Front Tectonic Zone at times of rapid basin subsidence. Paleozoic seismites in Ontario occur close to basement structures that are seismically active at the present day supporting the emerging model for mid-continental seismicity involving reactivation of Precambrian structures. [ABSTRACT FROM AUTHOR]

Central Canada experiences numerous intraplate earthquakes but their recurrence and source areas remain obscure due to shortness of the instrumental and historic records. Unconsolidated fine-grained sediments in lake basins are ‘natural seismographs’ with the potential to record ancient earthquakes during the last 10,000 years since the retreat of the Laurentide Ice Sheet. Many lake basins are cut into bedrock and are structurally-controlled by the same Precambrian basement structures (shear zones, terrane boundaries and other lineaments) implicated as the source of ongoing mid-plate earthquake activity. A regional seismic sub-bottom profiling of lakes Gull, Muskoka, Joseph, Rousseau, Ontario, Wanapitei, Fairbanks, Vermilion, Nipissing, Georgian Bay, Mazinaw, Simcoe, Timiskaming, Kipawa, Parry Sound and Lake of Bays, encompassing a total of more than 2000 kilometres of high-resolution track line data supplemented by multibeam and sidescan sonar survey records show a consistent sub-bottom stratigraphy of relatively-thick lowermost lateglacial facies composed of interbedded semi-transparent mass flow facies (debrites, slumps) and rhythmically-laminated silty-clays. Mass flows together with cratered (‘kettled’) lake floors and associated deformations reflect a dynamic ice-contact glaciolacustrine environment. Exceptionally thick mass flow successions in Lake Timiskaming along the floor of the Timiskaming Graben within the seismically-active Western Quebec Seismic Zone (WQSZ), point to a higher frequency of earthquakes and slope failure during deglaciation and rapid glacio-isostatic rebound though faulting continues into the postglacial. Lateglacial faulting, diapiric deformation and slumping of coeval lateglacial sediments is observed in Parry Sound, Lake Muskoka and Lake Joseph, which are all located above prominent Precambrian terrane boundaries. Lateglacial sediments are sharply overlain by relatively-thin rhythmically-laminated and often semi-transparent postglacial silty-clay laminations. Postglacial neotectonic activity is recorded by co-seismic water-escape structures, faults, slumps and debris flows in Lake Simcoe (above a terrane boundary) and especially within lakes Timiskaming and Kipawa, recording ongoing deformation within the WQSZ. High resolution seismo-stratigraphic data presented here support the model that ongoing mid-plate earthquake activity is a consequence of brittle deformation of the upper crust of the North American plate. Such activity appears to have been greatest during deglaciation but continues today. [ABSTRACT FROM AUTHOR]

Abstract: The Western Quebec Seismic Zone (WQSZ) of eastern North America is characterised by frequent moderate magnitude intracratonic earthquakes (e.g., 1732, M5.8; 1935, M6.2 and 1944, M5.2). The WQSZ is centered along the Timiskaming and Ottawa-Bonnechere grabens, which form part of a complex aulacogen (St.Lawrence Rift) within the Canadian Shield. The WQSZ includes the urban areas of Montreal and Ottawa but seismic risk analysis is challenged by short instrumental records and long recurrence intervals. The M6.2 1935 Timiskaming Earthquake is the largest recorded to date and was felt over some 1.3millionkm2 of eastern North America with many aftershocks of magnitude 4 to 5. Its epicenter lies below the western margin of Lake Kipawa, Quebec in the area where a major Proterozoic crustal boundary (the Grenville Front Tectonic Zone) crosses the Timiskaming Graben. A high-resolution ‘chirp’ seismic reflection survey of the lateglacial and postglacial sediment infill of Lake Kipawa reveals a clear record of recent ground shaking that is attributed to the 1935 earthquake. Widespread large slumps record down slope failure of the lateglacial and postglacial sediment fill indicating that the 1935 temblor was the largest in this area since deglaciation some 8000years ago. Systematic mapping of landslides shows that they extend across an area of 600km2 around the earthquake''s epicenter. Lakes cover a large area of eastern Canada; a regional-scale survey of lake floors could constrain historic epicenters and postglacial seismic history of the heavily populated WQSZ. [Copyright &y& Elsevier]

Abstract: Two prominent episodes of Neoproterozoic glaciation in Australia are recorded in the Cryogenian (Sturtian<725 Ma) and during the Ediacaran (Elatina

The Paraná Basin (1 600 000 km[SUP2]) is the largest intracratonic basin in southern South America and contains a thick (1300 m) Permo-Carboniferous glacial succession (the Itararé Group). This paper describes over 1700 m of drill core recovered during recent exploration for oil and gas. Itararé Group sediments consist of massive and stratified diamictites interbedded with massive and graded sandstones, and massive and laminated mudstones. Facies are interpreted as the product of sethment gravity flows in a glacially influenced marine basin. Three stratigraphic formations can be defined across the basin, each consisting of a lowermost sandstonerich member overlain by a diamictite-rich member. Examination of Itararé Group rocks both in core and outcrop shows that depositional processes were influenced by active faulting and downslope resedimentation on relatively steep and unstable substrate slopes. Primary glacial deposits such as tillites and associated striated pavements occur along the present eastern outcrop belt which probably coincidod with the eastern basin margin during deposition of the Itararé Group. Ice masses fringing the eastern (southern African) and western (Bolivian) basin margins supplied sediment to the basin in the form of fluvio-glacial deltas, fans and floating ice tongues. This sediment was then resedimented downslope as debris flows and turbidites. Both stratigraphic relationships and the regional distribution of facies types identify a clear pattern of basin subsidence and step-wise expansion by outward faulting within Late Proterozoic mobile belts. The position of successive basin margins can be related to specific lineament structures in the underlying basement. Asymmetric expansion of the Paraná Basin occurred along the northern and southern basin margins during deposition of the Itararé Group; this expansion probably reflects shallow crustal adjustments activated by collisionat... [ABSTRACT FROM AUTHOR]

Coastal exposures of Late Plcistocene sediments deposited after 19,000 yr BP near Dublin, Ireland, provide a window into the infill of a subglacially-cut tunnel valley. Exposures close to the steeply dipping bedrock wall of the valley show boulder gravels within multi-storey U-shaped channels cut and filled by subglacial meltwaters driven by a high hydrostatic head. Gravels are truncated by poorly sorted ice-proximal glaciomarine sediments that record the pumping of large volumes of subglacial debris along the tunnel valley to a tidewater ice sheet margin. The sedimentary succession is dominated by sediment gravity flow facies comprising interbedded diamict and massive, poorly sorted gravel facies interpreted as subaqueous debris flow deposits. Gravel beds show local inverse and normal coarse-tail graded facies recording the restricted development of turbulent flow. Sediment gravity flow deposits fill broad (<2 km) shallow (10 m) and overlapping channels. Penetrative deformation structures (e.g. dykes) are common at the base of channels. The same subglacially-eroded topography and glaciomarine infill stratigraphy can be identified on high resolution seismic profiles across nearly 60 km[sup2] of the western Irish Sea. Tunnel valleys are argued to have been exposed to glaciomarine processes by the rapid retreat of a calving tidewater ice sheet margin in response to marine flooding caused by glacio-isostatic downwarping below the last British Ice Sheet. The facies associations described in this paper comprise an event stratigraphy that may be found on other glaciated continental shelves. [ABSTRACT FROM AUTHOR]

Presents comments on the study "Analysis and Reinterpretation of Deformation Features in the Rouge River Valley, Scarborough, Ontario." Presence and significance of major bedrock lineaments; Identification of significant data gaps regarding environmental setting and impact of Pickering Nuclear Generating Station; Important advances in understanding the geology of the Rouge Valley area.

Glaciers and ice sheets are important agents of bedrock erosion, yet the precise processes of bedrock failure beneath glacier ice are incompletely known. Subglacially formed erosional crescentic markings (crescentic gouges, lunate fractures) on bedrock surfaces occur locally in glaciated areas and comprise a conchoidal fracture dipping down-ice and a steep fracture that faces up-ice. Here we report morphologically distinct crescentic scars that are closely associated with preexisting joints, termed here joint-bounded crescentic scars . These hitherto unreported features are ca. 50–200 mm deep and involve considerably more rock removal than previously described crescentic markings. The joint-bounded crescentic scars were found on abraded rhyolite surfaces recently exposed (< 20 years) beneath a retreating glacier in Iceland, as well as on glacially sculpted Precambrian gneisses in NW Scotland and various Precambrian rocks in Ontario, glaciated during the Late Pleistocene. We suggest a common formation mechanism for these contemporary and relict features, whereby a boulder embedded in basal ice produces a continuously migrating clast-bed contact force as it is dragged over the hard (bedrock) bed. As the ice-embedded boulder approaches a preexisting joint in the bedrock, stress concentrations build up in the bed that exceed the intact rock strength, resulting in conchoidal fracturing and detachment of a crescentic wedge-shaped rock fragment. Subsequent removal of the rock fragment probably involves further fracturing or crushing (comminution) under high contact forces. Formation of joint-bounded crescentic scars is favoured by large boulders at the base of the ice, high basal melting rates, and the presence of preexisting subvertical joints in the bedrock bed. We infer that the relative scarcity of crescentic markings in general on deglaciated surfaces shows that fracturing of intact bedrock below ice is difficult, but that preexisting weaknesses such as joints greatly facilitate rock failure. This implies that models of glacial erosion need to take fracture patterns of bedrock into account. [ABSTRACT FROM AUTHOR]