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| Hills Supergroup | |
|---|---|
| Name | Hills Supergroup |
| Type | Supergroup |
| Age | Neoproterozoic–Cambrian |
| Period | Neoproterozoic |
| Pr | sedimentary and volcanic |
| Region | Global analogue occurrences (Laurentia, Baltica, Gondwana) |
| Country | Canada, Scotland, Scandinavia, Australia, Namibia |
| Underlies | younger Cambrian sequences |
| Overlies | crystalline basement or older Proterozoic rocks |
Hills Supergroup The Hills Supergroup is a broadly distributed Neoproterozoic–Cambrian supracrustal sequence first characterized in classic field studies of northern Canada and subsequently correlated with strata in Scotland, Australia, Scandinavia and southern Africa. It has been the focus of multidisciplinary work by researchers associated with institutions such as the Geological Survey of Canada, the British Geological Survey, the Australian Geological Survey Organisation, and universities including Oxford University, University of Cambridge, and University of Toronto. Debates about its correlation and tectonic significance have involved comparisons with assemblages described from the Wopmay Orogen, the Trans-Hudson Orogen, the Caledonides, and the Nama Group.
The Hills Supergroup occurs on multiple cratonic margins and orogenic belts including portions of Laurentia, Baltica, and the perimeters of Gondwana where it overly Archean and Paleoproterozoic basement such as the Canadian Shield and the Fennoscandian Shield. Mapping campaigns by teams from the United States Geological Survey and the Geological Survey of Canada have documented outcrops from the Mackenzie Mountains through the Sverdrup Basin to exposures correlated in the Broken Hill Block of Australia and the Namaqualand region of Namibia. Its regional distribution links it to rifted margins and astringent orogens like the Ross Orogeny and the Grenville Orogeny in terms of basin architecture and provenance signals.
Stratigraphically the Supergroup comprises multiple formations and groups, typically including basal conglomerates, mature quartz arenites, subordinate shales, carbonate intervals, and mafic to felsic volcanic units comparable to those described in the Jasper Supergroup and the Windermere Supergroup. Key lithologies include arkosic breccias akin to the Flin Flon belt megabreccias, laminated mudstones similar to the Ediacara Member-style successions, and carbonate platforms with stromatolitic fabrics reminiscent of the Dwyka Group and the Kapp Toscana Group. Stratigraphic subdivisions have been formalized by regional surveys such as the British Geological Survey nomenclature and correlated using biostratigraphic frameworks developed at institutions like the Natural History Museum, London.
Depositional models invoke rift-related continental margin basins, shallow-marine carbonate platforms, tidal flats, and deltaic systems comparable to facies interpreted in the Sverdrup Basin and Williston Basin. Provenance studies employing detrital zircon populations link sediments to sources in the Slave Craton, Superior Province, and recycled orogens such as the Grenville Province, with geochemical fingerprints matching volcanic inputs from arcs analogous to the Iapetus Ocean margin and the Pannotia breakup. Sedimentological features include cross-bedded quartzites, wave-rippled carbonates, and turbiditic successions analogous to those in the Torngat Orogen and Otago Schists.
Geochronological constraints derive from U–Pb zircon dating, Ar–Ar dating of volcanic tuffs, and chemostratigraphic correlations tied to global events such as the Sturtian glaciation and the Marinoan glaciation. Radiometric ages from detrital and igneous zircons reported by research groups at Massachusetts Institute of Technology, ETH Zurich, and the Geological Survey of Canada place deposition largely between ca. 750 and 520 million years ago, overlapping the terminal Neoproterozoic and early Cambrian periods. Chemostratigraphic excursions comparable to documented signals in the Marinoan and correlations with datums used in the International Commission on Stratigraphy aid interregional correlation.
The Supergroup records a complex deformational history tied to rifting, passive margin subsidence, and later contractional events related to orogenies such as the Caledonian Orogeny, the Hercynian/Variscan Orogeny, and transpressional phases linked to assembly of Pangaea. Structural styles include extensional half-grabens, listric normal fault systems akin to those in the North Atlantic Craton, and later thrusts and folds comparable to structures in the Appalachians and Scandinavian Caledonides. Metamorphic overprints range from low-grade greenschist to amphibolite facies in proximity to plutons like those emplaced during the Pan-African Orogeny.
Fossil assemblages are generally sparse but include microbial mats, stromatolites, and Ediacaran-style macrofossils comparable to communities in the Ediacara Hills and Mistaken Point. Trace fossils and small shelly fossils related to early Cambrian radiation have been reported in horizon-equivalents correlated with the Sirius Passet and Chengjiang biotas, though diversity is lower and preservation style differs regionally. Palaeoecological interpretations draw on comparisons with assemblages studied at Smithsonian Institution collections and specialist groups at the University of California, Santa Barbara and University of Adelaide.
The Supergroup hosts mineralization styles including volcanogenic massive sulfide analogues, stratiform base metal concentrations, iron formations similar to the Banded Iron Formation occurrences, and placer gold and heavy mineral sands similar to deposits in the Klondike and Pilbara. Hydrocarbon potential has been evaluated in rifted margin analogues investigated by energy companies like BP and Shell and by national agencies such as the Norwegian Petroleum Directorate. Groundwater reservoirs in quartzite aquifers and low-grade metamorphic rocks have local economic importance in regions administered by authorities like the Government of Canada and the Australian Government.
Category:Neoproterozoic geology Category:Stratigraphic units