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. 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. Both escarpment and stepped margins were stable in position, and accreted with time. In contrast, ramp margins consisted of prograding shelf-margin skeletal-sand banks and shoals interdigitating with low-energy lime mudstone and black terrigenous mudstone on the slope.--Modified journal abstract.

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