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AAPG Bulletin

Abstract


Volume: 68 (1984)

Issue: 1. (January)

First Page: 1

Last Page: 17

Title: Tectonic Control of Silurian Carbonate-Shelf Margin Morphology and Facies, North Greenland

Author(s): John M. Hurst, Finn Surlyk (2)

Article Type: Meeting abstract

Abstract:

On the basis of profile and topography, three carbonate-shelf margin configurations in North Greenland are identified as having been formed during the Silurian. They include escarpment margins which are abrupt and characterized by slope angles of 35° to 40°; stepped margins consisting of blocks downstepping into the deep-water basin and with the slope angle inclined from a few up to 40°; and ramp margins characterized by gentle slopes and lack of a pronounced break between carbonate shelf and deep-water basin.

The carbonate-shelf margins are related to the Navarana Fjord fault and Permin Land flexure. The escarpment margin is not a fault scarp but represents a sedimentary escarpment, constructed by vertical carbonate-shelf accretion, and controlled by faults that delineate the boundary between the carbonate shelf and the deep-water basin. The stepped margin had a similar origin and relation to controlling faults, but later shelf-margin downdropping of blocks may have been contemporaneous with shelf sedimentation. Ramp margins result from differential subsidence related to deep-seated faults.

In the late Llandoverian (Lower Silurian) escarpment, shelf margins were drowned except for small carbonate buildups and grainstone shoals; the slope was an erosional bypass zone, and thick, chaotic, carbonate conglomerate wedges accumulated at the base-of-slope. Stepped-shelf margins were similar to escarpment margins, but isolated pinnacle buildups indicating drowning occur locally on the carbonate shelf, possibly related to foundering of the shelf-margin blocks. Some parts of the slope were similar to that of the escarpment margin, whereas other parts were depositional with small buildups and hemipelagic black terrigenous mudstones. Both escarpment and stepped margins were stable in position, and accreted with time. In contrast, ramp margins consisted of prograding shelf-margin ske etal-sand banks and shoals interdigitating with low-energy lime mudstone and black terrigenous mudstone on the slope.

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