The evolution of the early Paleozoic deep-water basin of North Greenland

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 km 3 . 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 km 3 . 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 km 2 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.