Deep-basin/deep-water carbonate-evaporite deposition of a saline giant: Loch Macumber (Visean), Atlantic Canada

Abstract

The Carboniferous saline giant of Atlantic Canada is approximately 500 m thick and extends over an area of 250 x 10 3 km', It consists of three lithologies: 1. a relatively thin (usually less than 5 m) extensive carbonate sheet containing buildups, 2. an overlying thick (up to 400 m) evaporite complex of sulphates and chlorides, and 3. wedge-shaped units of conglomerate, breccia, and sandstone (up to 200 m). The latter interfinger with the preceding lithologies but locally may underlie the carbonate sheet. The basal carbonate occurs mainly as fine, laminar couplets of alternating peloidal grainstones and bituminous films; these pass laterally into peloidal marlstones and mounds. Laminites andmarlstones have incipient brecciation, recumbent folds, siliciclastic and carbonate turbidites, rubble, and olistostromes.Fossils are rare. They are restricted in space to the basal decimeter and in diversity to conodonts and crustaceans. A Nereites ichnofauna occurs at one locality. Mounds consist mainly of turbid fans of fascicular-optic calcite and botryoids of laminated calcite. Their fauna shows low diversity but high density of some species; tube worms and microbial growths are noteworthy. The overlying evaporites are mainly anhydrite with lateral and vertical transition into halite and potash. Siliciclastic sediments thicken toward boundary faults. Both the base and top of the giant are unconformities, the former abrupt, the latter karsdc,The basal carbonate accumulated subaqueously in deep, physically and chemically stratified water. Initially, the desert floor of the complex rift 'basin was below ambient sea level. After catastrophic submergence, basal waters were at first dysaerobic and restricted marine, but changed to anoxic and pene-to hypersaline as the water column became stratified. Its sedimentary record corresponds to a giant, meromictic, saline lake -Loch Macumber. The laminite records either seasonal changes in rainfall and temperature, or episodic storms punctuating normal chemical sedimentation. Sulphate-reducing bacteria fed on terrestrial organic matter preserved in anoxic bottom water, and precipitated peloidal calcite. Concentrations of bacteria over hot springs may also have supported chemosynthetic organic communities and precipitated petroliferous and sulphide-rich mounds. Siliciclastic rocks increase toward basin margins. Locally steep depositional surfaces caused mass movements of sediment down basin margins. A long term increase in salinity resulted in precipitation of initially corroded and subsequently euhedral crystals of gypsum. Thick sulphates and chlorides followed. Sedimentary rock of Loch Macumber records topographic filling of a deep rift basin. Isostatic analysis suggests thatboth depth of the subaerial desert basin and initial water depth after submergence were considerably less than the preserved thickness of the saline giant. Its record corresponds closely to that expected from Schmaltz's model of deep-basin/deep-water carbonate-evaporite deposition.

Gradual encroachment of a rocky shoreline by an invasive sea during the Mississippian at the southeastern margin of the Maritimes Basin, Nova Scotia, Canada

“…This conclusion challenges the thesis of von Bitter et al (1992) that all Gays River Formation buildups may have formed in deep-water conditions. Moreover, contrary to studies conducted in southern Newfoundland and northern Cape Breton Island (von Bitter et al 1990(von Bitter et al , 1992Schenk et al 1994Schenk et al , 2001, we found no evidence of hydrothermal activity as a control to bank development in the Gays River Formation of central Nova Scotia. (4) According to core correlations, clastic sedimentation of the Meaghers Grant Formation along river deltas was synchronous with bank development in the Gays River Formation, away from these deltas and along the southeast margin of the Windsor Sea.…”

“…According to von Bitter et al (1990,1992) and Schenk et al (1994Schenk et al ( , 2001, mounds of the Big Cove and Gays River formations in southern Newfoundland and northern Cape Breton Island ( Fig. 1; inset) were formed around deep-water hydrothermal vents.…”

“…In the present paper, the sedimentology of two significant exposures is combined with the study of 14 core logs and the paleontology of 23 basal Windsor biohermal banks to add detail to the previously proposed paleogeographic reconstructions and paleoenvironments of deposition. The main objectives of this study are (i) to understand the dynamics of the transgression, (ii) to differentiate Viséan paleotopographic elements from subsequently formed basement highs, (iii) to understand lateral variations in basal beds of the Windsor Group, and (iv) to compare the paleoenvironments and paleogeography of the Lower Windsor Group in central Nova Scotia with those of other studied areas in eastern Canada (McCutcheon 1988;Dix and James 1989;von Bitter et al 1990von Bitter et al , 1992Schenk et al 1994Schenk et al , 2001).…”

Major erosion at the end of the Messinian Salinity Crisis: evidence from the Levant Basin, Eastern Mediterranean

“…An evaporite load of 1.8 km (i.e. the maximum thickness recorded in the study area) could produce subsidence due to isostatic adjustment in excess of 1000 m (Allen & Allen, 1990; Schenk et al , 1994). At the same time, significant sea‐level falls led to rapid water unloading and erosion on the margin.…”

Carbonates and associated sedimentary rocks of the Upper Viséan to Namurian Mabou Group, Cape Breton Island, Nova Scotia: evidence for lacustrine deposition

“…Schenk et al (1994) illus trated how the interaction of evaporite precipitation and subsidence, during the first cycle of marine sedimentation in the Windsor Group in Middle Vis^an time, would have readily filled much of the initial relief in the basin. The regional distribution of the lower Windsor evaporites of Cycle 1 (Giles, 1981) suggests that this process of early basin fill ing operated over an area at least as large as the present Gulf of St. Lawrence.…”