Abstract
The Middle Ordovician Shoal Arm Formation in the central volcanic belt of north-central Newfoundland consists of hematitic argillites overlain by grey cherts, then black shales directly underneath a Late Ordovician/Early Silurian flysch sequence. Using principal component analysis, geochemically definable components within related lithologie groups are: (1) biogenic, (2) mixed detrital, (3) hydrothermal, and (4) Mn, Ca-carbonate. Close sampling of the whole 350-m thick sequence provides reconstruction of variations among the sediment components through time. At the base of the hematitic section, a sharp increase in the hydrothermal component (enrichment in Mn, Fe, Ni, Pb, and Zn) decreases stratigraphically upward and disappears in the upper red Shoal Arm Formation. The Mn, Ca-carbonate component also decreases upward but persists into the grey cherts, indicating an additional source of Mn. The clastic component is largely mixed mafic/pelagic clay-like detritus with a strong pulse of Zr-, Nb-, and Y-rich ...
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