Editing Hudson Bay (section)

==Geology==
Hudson Bay occupies a large [[Depression (geology)|structural basin]], known as the Hudson Bay basin, that lies within the [[Canadian Shield]]. The collection and interpretation of outcrop, seismic and drill hole data for [[Hydrocarbon exploration|exploration for oil and gas reservoirs]] within the Hudson Bay basin found that it is filled by, at most, {{cvt|2500|m}} of [[Ordovician]] to Devonian [[limestone]], [[Dolomite (rock)|dolomite]], [[evaporite]]s, black [[shale]]s, and various [[Clastic rock|clastic]] [[sedimentary rock]]s that overlie less than {{cvt|60|m}} of Cambrian [[Stratum|strata]] that consist of [[wiktionary:unfossiliferous|unfossiliferous]] [[quartz arenite|quartz sandstone]]s and [[Conglomerate (geology)|conglomerate]]s, overlain by sandy and [[Stromatolite|stromatolitic]] dolomites. In addition, a minor amount of terrestrial [[Fluvial sediment processes|fluvial]] sands and gravels of the [[Cretaceous]] period are preserved in the fill of a prominent ring-like depression about {{cvt|325–650|km}} across created by the dissolution of [[Silurian]] evaporites during the Cretaceous period.<ref name="Burgess2008a">Burgess, P.M., 2008, ''Phanerozoic evolution of the sedimentary cover of the North American craton.'', in Miall, A.D., ed., ''Sedimentary Basins of the United States and Canada'', Elsevier Science, Amsterdam, pp. 31–63.</ref><ref name="LavoieOthers2015a">Lavoie, D., Pinet, N., Dietrich, J. and Chen, Z., 2015. ''The Paleozoic Hudson Bay Basin in northern Canada: New insights into hydrocarbon potential of a frontier intracratonic basin.'' ''American Association of Petroleum Geologists Bulletin'', 99(5), pp. 859–888.</ref><ref name="Roksandic1987a">Roksandic, M.M., 1987, ''The tectonics and evolution of the Hudson Bay region'', in C. Beaumont and A. J. Tankard, eds., ''Sedimentary basins and basin-forming mechanisms.'' Canadian Society of Petroleum Geologists Memoir 12, p. 507–518.</ref><ref name="SanfordOthers1998a">Sanford, B.V. and Grant, A.C., 1998. ''Paleozoic and Mesozoic geology of the Hudson and southeast Arctic platforms.'' ''Geological Survey of Canada Open File 3595'', scale 1:2 500 000.</ref>

From the large quantity of published geologic data that has been collected as the result of hydrocarbon exploration, academic research, and related [[geological map]]ping, a detailed history of the Hudson Bay basin has been reconstructed.<ref name="LavoieOthers2015a"/> During the majority of the [[Cambrian]] Period, this basin did not exist. Rather, this part of the Canadian Shield area was still topographically high and emergent. It was only during the later part of the Cambrian that the rising sea level of the [[Sauk sequence|Sauk]] [[marine transgression]] slowly submerged it. During the Ordovician, this part of the Canadian Shield continued to be submerged by [[sea level rise|rising sea levels]] except for a brief middle Ordovician [[marine regression]]. Only starting in the Late Ordovician and continuing into the Silurian did the gradual regional [[subsidence]] of this part of the Canadian Shield form the Hudson Bay basin. The formation of this basin resulted in the accumulation of black [[Bitumen|bituminous]] [[oil shale]] and evaporite deposits within its centre, thick basin-margin limestone and [[Dolomite (rock)|dolomite]], and the development of extensive [[reef]]s that ringed the basin margins that were [[Tectonic uplift|tectonically uplifted]] as the basin subsided. During Middle Silurian times, subsidence ceased and this basin was uplifted. It generated an emergent arch, on which reefs grew, that divided the basin into eastern and western sub-basins. During the [[Devonian]] Period, this basin filled with terrestrial [[red beds]] that interfinger with marine limestone and dolomites. Before deposition was terminated by marine regression, Upper Devonian black bituminous shale accumulated in the south-east of the basin.<ref name="Burgess2008a"/><ref name="LavoieOthers2015a"/><ref name="Roksandic1987a"/><ref name="SanfordOthers1998a"/>

The remaining history of the Hudson Bay basin is largely unknown as a major [[unconformity]] separates Upper Devonian strata from [[Glacial period|glacial deposits]] of the [[Pleistocene]]. Except for poorly known terrestrial Cretaceous fluvial sands and gravels that are preserved as the fills of a ring of subsided strata around the centre of this basin, strata representing this period of time are absent from the Hudson Bay basin and the surrounding Canadian Shield.<ref name="Burgess2008a"/><ref name="SanfordOthers1998a"/>

The Precambrian Shield underlying Hudson Bay and in which Hudson Bay basin formed is composed of two [[Archean]] proto-continents, the [[Churchill craton|Western Churchill]] and [[Superior cratons]]. These [[craton]]s are separated by a tectonic collage that forms a [[Suture (geology)|suture zone]] between these cratons and the [[Trans-Hudson orogeny|Trans-Hudson Orogen]]. The Western Churchill and Superior cratons collided at about 1.9–1.8 Ga in the Trans-Hudson orogeny. Because of the irregular shapes of the colliding cratons, this collision trapped between them large fragments of juvenile crust, a sizable [[Continental fragment|microcontinent]], and [[island arc]] [[terrane]]s, beneath what is now the centre of modern Hudson Bay as part of the Trans-Hudson Orogen. The [[Belcher Islands]] are the eroded surface of the Belcher Fold Belt, which formed as a result of the tectonic [[Compression (geology)|compression]] and folding of sediments that accumulated along the margin of the Superior Craton before its collision with the Western Churchill Craton.<ref name="DarbyshireOthers2010a">Darbyshire, F.A., and Eaton, D.W., 2010. ''The lithospheric root beneath Hudson Bay, Canada from Rayleigh wave dispersion: No clear seismological distinction between Archean and Proterozoic mantle'', ''Lithos''. 120(1–2), 144–159, doi:10.1016/j.lithos.2010.04.010.</ref><ref name="EatonOthers2010a">Eaton, D.W., and Darbyshire, F., 2010. ''Lithospheric architecture and tectonic evolution of the Hudson Bay region'', ''Tectonophysics''. 480(1–4), 1–22, doi:10.1016/j.tecto.2009.09.006.</ref>

[[File:PGR Paulson2007 Rate of Lithospheric Uplift due to PGR.png|thumb|upright=1.4|Map of post-glacial rebound. Hudson Bay is in the region of the most rapid uplift.]]

=== Free-air gravity anomaly ===
Hudson Bay and the associated structural basin lie within the centre of a large [[free-air gravity anomaly]] that lies within the Canadian Shield. The similarity in areal extent of the free-air gravity anomaly with the perimeter of the former [[Laurentide ice sheet]] that covered this part of [[Laurentia]] led to a long-held conclusion that this perturbation in the Earth's gravity reflected still ongoing [[Post-glacial rebound|glacial isostatic adjustment]] to the melting and disappearance of this ice sheet. Data collected over Canada by the [[GRACE and GRACE-FO|Gravity Recovery and Climate Experiment]] (GRACE) satellite mission allowed [[Geophysics|geophysicists]] to isolate the gravity signal associated with glacial isostatic adjustment from longer–time scale process of [[mantle convection]] occurring beneath the Canadian Shield. Based upon this data, geophysicists and other [[Earth science|Earth scientists]] concluded that the Laurentide Ice Sheet was composed of two large domes to the west and east of Hudson Bay. Modelling glacial isostatic adjustment using the GRACE data, they concluded that ≈25 to ≈45% of the observed free-air gravity anomaly was due to ongoing glacial isostatic adjustment, and the remainder likely represents longer time-scale effects of mantle convection.<ref name="TamisieaOthers2007a">Tamisiea, M.E., Mitrovica, J.X. and Davis, J.L., 2007. ''GRACE gravity data constrain ancient ice geometries and continental dynamics over Laurentia''. ''Science'', 316(5826), pp. 881–883.</ref>

===Southeastern semicircle===
Earth scientists have disagreed about what created the semicircular feature known as the [[Nastapoka arc]] that forms a section of the shoreline of southeastern Hudson Bay. The Nastapoka arc forms a 155 degree curve and appears to be very circular.<ref name=":1">{{Cite web |date=28 November 2022 |title=Hudson Bay's Nastapoka Arc |url=https://earthobservatory.nasa.gov/images/150665/hudson-bays-nastapoka-arc |access-date=10 October 2023 |website=earthobservatory.nasa.gov}}</ref> Noting the paucity of impact structures on Earth in relation to the Moon and Mars, [[Carlyle S. Beals]]<ref name="Beals1968a">Beals, C.S., 1968. ''On the possibility of a catastrophic origin for the great arc of eastern Hudson Bay.'' In: Beals, C.S. (Ed.), pp. 985–999. ''Science, History and Hudson Bay'', Vol. 2, Department of Energy Mines and Resources, Ottawa.</ref> proposed that it is possibly part of a [[Precambrian]] extraterrestrial impact structure that is comparable in size to the [[Mare Crisium]] on the Moon. In the same volume, [[John Tuzo Wilson]]<ref name="Wilson1968a">Wilson, J.T., 1968. ''Comparison of the Hudson Bay arc with some other features.'' In: Beals, C.S. (Ed.), pp. 1015–1033. ''Science, History and Hudson Bay'', Vol. 2. Department of Energy Mines and Resources, Ottawa.</ref> commented on Beals' interpretation and alternately proposed that the Nastapoka arc may have formed as part of an extensive Precambrian continental collisional [[orogeny|orogen]], linked to the closure of an ancient [[Oceanic basin|ocean basin]]. The current general consensus is that it is an arcuate boundary of tectonic origin between the Belcher Fold Belt and undeformed basement of the Superior Craton created during the Trans-Hudson orogeny. This is because no credible evidence for such an [[impact structure]] has been found by regional magnetic, [[Bouguer anomaly|Bouguer gravity]], or other geologic studies.<ref name="DarbyshireOthers2010a"/><ref name="EatonOthers2010a"/> However, other Earth scientists have proposed that the evidence of an Archean impact might have been masked by deformation accompanying the later formation of the Trans-Hudson orogen and regard an impact origin as a plausible possibility.<ref name="GoodingOthers1992a">Goodings, C.R. & Brookfield, M.E., 1992. ''Proterozoic transcurrent movements along the Kapuskasing lineament (Superior Province, Canada) and their relationship to surrounding structures.'' ''Earth-Science Reviews'', 32: 147–185.</ref><ref name="BleekerOthers2004a">Bleeker, W., and Pilkington, M., 2004. ''The 450-km-diameter Nastapoka Arc: Earth's oldest and largest preserved impact scar?'' ''Program with Abstracts – Geological Association of Canada; Mineralogical Association of Canada: Joint Annual Meeting, 2004'', Vol. 29, pp. 344.</ref>