Abstract

A major early Paleozoic carbonate shelf–deep-water basin system is exposed in North Greenland over a length of 800 km, with a maximum preserved width of about 200 km and a thickness reaching 8 km. The successive southern deep-water basin margin was controlled by four major west-southwest– and east-northeast–trending fault zones or flexures. Nine deep-water basin evolutionary stages are recognized. (1) The oldest sequence consists of at least 500 m of sandstones and mudstones, but little is known about the depositional environment. (2) Incipient basin: 1 km of (late Precambrian?) Early(?) Cambrian dark gray or yellow limestones, turbiditic siltstones and mudstones, and resedimented carbonate conglomerates deposited in slope and relatively deep-water basin environments. (3) Narrow turbiditic basin: 2 to 3 km of Early(?) Cambrian turbiditic sandstones, deposited on westerly deflected submarine fans, alternating with dark or varigated interfan and slope mudstones, deposited following a major episode of shelf-margin back-stepping. (4) Basin expansion and initial starvation: about 1 km of Cambrian-Ordovician basin-plain anoxic dark mudstones, black and green cherts, and turbidites were deposited. Small borderland fans prograded into the deep basin, and upper-slope slumping resulted in a debris sheet of at least 45 km3. Eventual fan abandonment resulted in basin starvation and periodic stagnation reflected by the fine-grained deposits. The base of slope is dominated by resedimented conglomerates, the main sheet about 375 km3. This coincides with increased uplift, tilting, nondeposition, and erosion of the eastern carbonate shelf. (5) Longitudinal turbidite basin: an elongate, east-northeast, west-southwest–sand-rich, longitudinal, turbidite fan-to-basin system developed at the Ordovician-Silurian transition. This was punctuated by several episodes of lateral conglomerate deposition from the southern shelf margin. (6) Basin expansion and starvation: more than 30,000 km2 of the eastern carbonate shelf foundered at the Llandoverian-Wenlockian boundary and a thick mudstone unit was deposited on top. (7) Wide turbidite basin: turbidite deposition rapidly resumed, and an elongate submarine fan system prograded toward the west-southwest parallel to the shelf margin. (8) Middle Wenlockian Caledonian thrusting and conglomerate deposition: chert-pebble conglomerates prograded westward eroded from uplifted Ordovician chert sequences in the Caledonian nappes. (9) Transpression or gravity sliding related to the advancing Caledonian front: a remarkable series of imbricate thrust sheets occurring in the axial, eastern part of the basin is interpreted as caused by large-scale gravity sliding or by transpression due to sinistral transcurrent movements along the Harder Fjord fault zone. A Late Silurian age is tentatively suggested for this event.

The North Greenland basin may represent a gradually opening, narrow ocean basin, with the mid-oceanic ridge to the north forming a northern barrier to the basin. Conversely, the basin may be fully ensialic and may have formed during the early rifting stages preceding true back-arc spreading. Alternatively, the basin may be an aulacogen extending deeply into an old continent at a right angle to the Caledonian front to the east.

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