Depositional environments along a carbonate ramp to slope transition in the Silurian of Washington Land, North Greenland

Abstract

During the earliest Silurian, subsidence and tilting of a relatively flat carbonate platform produced a homoclinal carbonate ramp transitional to the slope of a deep-water basin. Further subsidence, associated with a flexure, differentiated the slope from the carbonate ramp. Subsequently, a linear reef tract developed along part of the flexure, producing a steep reef-scarp slope at the outer homoclinal carbonate ramp margin and accentuating the initial basin slope. Isolated reefs also developed on the slope. The reef tract, which influenced slope depositional environments considerably, marked the transition from the shallow homoclinal carbonate ramp facies to the deeper slope environments. Background slope sedimentation was primarily temgenous mudstone deposited out of suspension and by very dilute muddy turbidity flows. Superimposed were calcarenites and conglomerates, derived from the carbonate ramp margin and reefs, deposited by low-to high-density turbidity flows, debris flows, and possibly grain and liquefied flows. Sedimentation patterns along the incipient slope reflect both shallow carbonate ramp and deep basinal influences. With continued subsidence and differentiation of slope and ramp, slumping of carbonate blocks occurred at the ramp margin. Disorganized talus wedges developed as circular fringes around reefs on the slope, and a fine-grained talus wedge developed along the base of the main precipitous reef scarp at the ramp margin. A large channel cut down and across the slope and eventually became choked with ramp-margin reef and top-of-slope material. Finally, abrupt subsidence, which generated an olistostrome containing a minimum of f km3 of debris, drowned all reefs and the slope became essentially starved of resedimented carbonate debris. N s le d6but du Silurien une subsidence et un basculement d'une plate-forme de carbonates relativement plane ont engendr6 la formation d'une rampe de carbonates homoclinale transitionnelle avec le talus d'un bassin profond. La poursuite de mouvement de subsidence, associ6e B une flexure, a favoris6 la diffkrentiation du talus avec la rampe de carbonates. SubsCquemment, un I alignement de rCcifs construits Ie long d'une partie de la flexure a produit un escarpement abrupt rCcifs-talus a la zone exteme de la marge de la rampe de carbonates homoclinale et a accentu6 la raideur du talus. Les rCcifs alinnCs ont influence considkrablement les milieux de sedimentation du talus, ils ont marque la transition entre le faciks d'eau peuirofonde de la rampe de carbonates homoclinale et les milieux plus profonds du talus. Les sCdiments B I'arrikre-plan du talus sont composts principalement de mudstones temghnes provenant de suspensoides et de coul6es boueuses de turbidit6 t&s diluks. On observe en superposition des calcarenites et des conglomerats d6rivCs de la marge de la rampe de carbonates et des rCcifs, et d6pods par des coulks de turbidit6 de densit6 faible B 6levCe, par des coulCes de dCbris et possiblement par des coul6es granulaires et liqu6fiCes. Les motifs sairnenta...

Explanatory notes to the Geological map of Greenland, 1:500 000, Humboldt Gletscher, Sheet 6

“…the Morris Bugt, Washington Land and Peary Land Groups -respectively, Smith et al (1989), Hurst (1980a) and Hurst & Surlyk (1982) -but not for the older part, the Ryder Gletscher Group of Ineson & Peel (1987. The Silurian shelf-slope transition on the map sheet is well known from sedimentological and palaeogeographical analyses (Hurst 1981;Hurst & Surlyk 1983). For the setting of the Franklinian Basin strata in the context of regional basin evolution in Greenland, the reviews of Hurst (1980b), Hurst & Surlyk (1984), Sønderholm & Harland (1989a) and Higgins et al (1991a, b) are relevant.…”

“…Other literature. Hurst (1980bHurst ( , 1981, Hurst & Kerr (1982b), Hurst & Surlyk (1983), Sønderholm et al (1987), Sønderholm & Harland (1989a), Higgins et al (1991a, b), de Freitas & Nowlan (1998), Dawes et al (2000a). Age.…”

Isolated carbonate bodies composed of stacked debris-flow deposits on a fine-grained carbonate lower slope of Devonian age, Antelope Peak, Elko County, Nevada

“…are common in carbonate turbidite sequences (Markello and Read, 1981;Cook and others, 1983;Hurst and Surlyk, 1983).…”

Origin of fine‐grained carbonate and siliciclastic sediments in an Early Palaeozoic slope sequence, Cow Head Group, western Newfoundland

“…Such an origin, although a possibility, is not likely to have resulted in deposits that are sufficiently distinct from lime mudstone turbidites to be recognizable. The even, continuous bedding and general absence of sedimentary structures and scour in these beds could instead be interpreted as suspension settling of periplatform muds through the water column, from nepheloid layers, or from turbidity currents which spread out over mid-water pycnoclines (Wilson, 1969;Cook & Taylor, 1977;Keith & Friedman, 1977;Hurst & Surlyk, 1983). From the above, it appears that deposition from turbidity currents and hemipelagic settling are the two most plausible primary depositional origins for the deep-water lime mudstones.…”

“…Most conglomerates were deposited from unconfined, viscous debris flows on palaeoslopes that were inclined only a few degrees seaward (Hiscott & James, 1985). Massive and graded calcarenites accumulated as suspension fall-out from highdensity turbidity currents (Coniglio, 1985), similar to proximal turbidites described by Hurst & Surlyk (1983). Turbidite calcarenites characterized by parallel and ripple laminations were deposited by residual flows.…”