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 terrigenous 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 [Formula: see text] of debris, drowned all reefs and the slope became essentially starved of resedimented carbonate debris.