THE YELLOW POINT FORMATION AND ITS RELATIONSHIP TO PERIDOTITE CARBONATION, LOBSTER COVE HEAD, WESTERN NEWFOUNDLAND, CANADA

The Yellow Point formation (YPF) comprises a unique Lower-Middle Ordovician dolostone-shale-chert assemblage within the Humber Arm Allochthon of western Newfoundland. The YPF conformably rests on a limestone conglomerate and ribbon limestone of the Cow Head Group, and has been interpreted as a terminal passive margin facies deposited adjacent to a drowned portion of the Laurentian platform. It underlies, either conformably or disconformably, chromite-bearing sandstones of the Lower Head Formation (LHF). We here propose an alternative distal foreland basin setting in which the dolomite was detrital. Supporting arguments include: 1) elsewhere in the LHF, elevated Cr and Ni values and ophiolitic Cr/Ni ratios in shales appear below the lowest chromite-bearing sandstones; 2) within the YPF, the trend of basal cherts overlain by hemipelagic black and green shales with dolostone beds increasing in thickness and abundance upwards suggests a basin controlled by contraction rather than extension; 3) uncompacted silicified burrows indicate high-silica waters and chemical weathering (versus oligotrophic carbonate platform); 4) across several small thrust sheets, an eastward increase in the proportion of dolostone relative to hemipelagic shale and chert may suggest an eastern source; and 5) along-strike variations envisioned in the original model seem unrealistic. A distal foreland basin setting for the dolostones would be similar to that documented for barzamanites forming today by replacement of peridotite sediments west of the Samail ophiolite. If so, the sequestering of atmospheric CO₂ in YPF dolostones likely contributed to the coeval increase in δ¹⁸O and decrease in ⁸⁷Sr/⁸⁶Sr in global seawater during this interval.