Alfred A. Hartling

B. Sc. Honours Thesis

Paleoenvironment of a Small Portion of the Gay's River Carbonate Complex (Carboniferous), Gay's River Nova Scotia.

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In the past, the Gay's River Carbonate Complex, Gay's River, Nova Scotia, has been largely described as an ecologic reefal buildup. This now appears to be a false use of terminology, as the carbonate complex is found to comply favourably with typical lime mud mound development in modern and ancient environments.

The detailed study of three diamond drill cores, provided by Imperial Oil Ltd., has outlined four distinct stratigraphic units, identified by faunal assemblage, lithology, and/or textural criteria: (1) Basal Siliceous Unit, (2) Algal-Skeletal Unit; (3) Fenestral Unit; and (4) Cap Unit. The thin, basal unit is found overlying an erosional contact which offers approximately 35 feet of relief. This unit has been isolated on the basis of a higher content (greater than 15%) of siliceous material. The Basal Siliceous Unit grades abruptly into the thick Algal-Skeletal Unit. The Algal-Skeletal Unit is dominantly composed of algal-skeletal wackestones and algal boundstones. The skeletal grains, found floating in a carbonate mud, are mostly thin shelled brachiopods and bryzoa, with gastropods, corals, and ostracods often associated. Gradationally overlying the Algal-Skeletal Unit is the thick Fenestral Unit, dominated by fenestral-algal boundstones. Fenestral fabrics are abundant throughout the unit, with skeletal grains, similar to those of the underlying unit, occasionally present. The upper Fenestral Unit has been eroded by Pleistocene glacial activity over most of the study area. A thin Cap Unit is found gradationally overlying the Fenestral Unit at one locality. The Cap Unit is dominated by skeletal wackestones. Thin shelled, generally fragmented gastropods and brachiopods form the bulk of the skeletal grains found.

The succession of stratigraphic units is interpreted as a transgressive mud mound buildup. As Windsorian sea level rose, a paleotopographic ridge system, with associated talus debris, was flooded. The physiographic nature of the ridge system resulted in the formation of a small, semi-restricted bay. Thus, the talus slope, inside the bay, was reworked by tidal currents and infrequent storm activity. The reworked talus material combined with carbonate deposition in formation of the Basal Siliceous Unit.

The colonization of the sea floor by corals, brachiopods, bryzoa, and Porostomata baffled the tidal currents active within the bay. The accumulation of carbonate mud around the initial baffles lead to the formation or small, localized mounds. As these small mounds grew and were colonized by an increasing number of baffling organisms, current restriction increased. Mounds began to merge, and eventually a large bank-like structure was formed. This bank is defined as the Algal-Skeletal Unit in the stratigraphic succession.

As sediment continued to accumulate, the bank began to shoal, and a tidal flat developed. An increase in salinity nearshore restricted the occurrance of grazing organisms, and algal mats grew relatively unhampered. These algal mats aided the formation of fenestral fabrics in the intertidal-supratidal zone. This intertidal-supratidal zone is present in the stratigraphic section, and is defined as the Fenestral Unit.

As sea level continued to rise, the bay became subjected to increasing wave activity. The baffling organic communities were destroyed, and salinity decreased nearshore. wave activity piled up beach ridges, rimming the supratidal flat. These supratidal beach ridges are found within the Cap Unit.

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Pages: 134
Supervisor: Paul Schenk