Mesoproterozoic deep‐water reefs from Borden Peninsula, Arctic Canada

Abstract

A superbly exposed stromatolite reef complex occurs in the Victor Bay Formation near Strathcona River on northern Baffin Island. Individual reefs are up to 130 m thick and nearly 1 km in length, and their development was clearly related to their position in the facies spectrum and to sea-level dynamics. In the first sea-level cycle, metre-scale reefs grew amongst mid-ramp calcarenites and outer-ramp shales during slow sea-level rise; a 25-m-thick oblate reef tract, separating mid-ramp and outer-ramp facies, formed during the highstand. The greatest period of reef growth was during the second sea-level cycle. Pinnacle reefs nucleated on the karsted upper surface of the oblate reef tract and aggraded rapidly in response to rising sea-level, producing structures with more than 75 m of depositional relief. A gradual symmetrical succession of stromatolite growth forms, from stratiform to cylindrical columns to conical columns and then back through cylindrical columns to stratiform, is mirrored by evidence in offreef deposits for deepening to a maximum flooding surface and then shallowing. The tops of these high-standing reefs were karsted during the following regression, while dolomite 'cryptodomes' grew as sheets on their submerged flanks and as progradational tongues extending basinward of the reefs. Continued sea-level fall resulted in subaerial exposure of the entire reef complex and the extensive formation of surface and subsurface karst.These Proterozoic slope buildups are similar to Phanerozoic deep-water reefs in size, shape, prevalence of synsedimentary lithification, presence of Neptunian dykes and in their well-developed vertical zonation of reefbuilders. However, they differ in being constructed exclusively by stromatolites rather than being mud mounds with small skeletal elements, and in lacking halos of perireefal sand-and gravel-sized calcareous debris. Their responses to changes in sea-level were strikingly similar to those shown by their younger counterparts, and suggest that sequence-stratigraphic concepts derived from studies of Phanerozoic reefs can also be applied to the Proterozoic.

Reconstructing sea-level change from the internal architecture of stromatolite reefs: an example from the Mesoproterozoic Sulky Formation, Dismal Lakes Group, arctic Canada

“…In contrast, decreasing accommodation space driven by tectonic uplift, depositional filling of available accommodation space, or sea-level fall, commonly results in progradation of the reef over basinal sediments and the eventual infilling and subaerial exposure of the reef top. Proterozoic stromatolitic and calcimicrobial reef architectures exhibit comparable relationships between large-scale changes in reef geometry and changes in relative sea level (Grotzinger 1989;Narbonne and James 1996;Turner et al 1997;Lemon 2000). In particular, several Mesoproterozoic (Narbonne and James 1996) and Neoproterozoic (Turner et al 1997;Lemon 2000) reefal deposits reveal vertical stacking of reef packages that record expansion, contraction, progradation, backstepping, and subaerial exposure of the reef system in response to major fluctuations in relative sea level.…”

“…Proterozoic stromatolitic and calcimicrobial reef architectures exhibit comparable relationships between large-scale changes in reef geometry and changes in relative sea level (Grotzinger 1989;Narbonne and James 1996;Turner et al 1997;Lemon 2000). In particular, several Mesoproterozoic (Narbonne and James 1996) and Neoproterozoic (Turner et al 1997;Lemon 2000) reefal deposits reveal vertical stacking of reef packages that record expansion, contraction, progradation, backstepping, and subaerial exposure of the reef system in response to major fluctuations in relative sea level. In these cases, coeval facies changes in off-reef strata support reconstructions of reef growth in response to changing sea level.…”

“…The morphological irregularity of stromatolitic and calcimicrobial framework components (Turner et al 2000), frequent lack of distinctive morphological end members, and a "self-similarity" in the hierarchical scaling of stromatolitic growth forms (Narbonne and James 1996) typically obscures reef architecture. Here, we examine a relatively thin (<40 m) yet laterally extensive (>2400 km 2 ) reef complex within the Mesoproterozoic Dismal Lakes Group.…”

δ<SUP>13</SUP>C stratigraphy of the Proterozoic Bylot Supergroup, Baffin Island, Canada: implications for regional lithostratigraphic correlations

“…The Athole Point Formation is present only in the eastern regions of Borden Basin; it interfingers with and is replaced by siliciclastic facies of the Strathcona Sound Formation to the north and west (Jackson and Ianelli 1981) and is separated from underlying formations by a regional unconformity Jackson and Ianelli 1981;Narbonne and James 1996). In central Borden Basin, the lower Athole Point consists of recessively weathered calcareous shale and shaley limestone and subordinate quartz-rich, calcareous turbidites.…”

“…The Victor Bay Formation comprises a variety of carbonate and siliciclastic lithologies deposited in a range of peritidal shelf to subtidal shelf and slope environments (Jackson and Iannelli 1981;Narbonne and James 1996). The transition from peritidal carbonates of the Society Cliffs is marked by an abrupt transition to black to dark grey calcareous shales (Jackson and Iannelli 1981).…”