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Carbonate mounds that have been dragged up from the seafloor during fishing offshore the Northern Cape Breton Highlands are very distinctive in their nature. The carbonate mounds range in size from a few cm3 to larger than an m3 in size. Worldwide, other carbonate mounds have been documented, but they are either much larger or formed in different settings. By studying seismic sections and sampling the hand specimens, the process of their formation can be proposed. Using both Huntec and Airgun seismic data, distinct areas of hydrocarbon mixing with the sediments can be detected. The seismic data also showed a distinct layering between glacial deposits and more recent sediments. Carbon 13 values determined form isotope analysis of shelly debris encased in the mounds showed a distinct negative value in each of the samples. The range for the C13 values is -9.41 to -35.27, with one outlier at -61.38. Considering the isotopic analysis and the seismic data it seems likely that these carbonate mounds were formed by methanogenesis of hydrocarbon from slow seeps on the seafloor.

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Pages: 72
Supervisor: Peter Wallace