Necoslie breccia: mixed conodont fauna-bearing neptunian dyke in Carboniferous-Permian seamount-capping oceanic buildup (Pope succession, Cache Creek Complex, central British Columbia)

Abstract

A mixed conodont fauna-bearing limestone breccia, informally designated as Necoslie breccia, crops out as an internal sediment hosted by the Lower Moscovian limestone unit of the Pope limestone succession (Bashkirian to Asselian) of Cache Creek Complex in central British Columbia, reconstructed as a mid-oceanic buildup upon a seamount, or an oceanic plateau. Necoslie breccia consists predominantly of limestone fragments derived from the host rocks, with subordinate isolated skeletal debris, all embedded in a matrix of fine-grained clastic carbonates. The mixed conodont fauna yields the youngest element indicative of Carnian. Our microscopic examination and conodont paleontological data show that Necoslie breccia is better defined as a neptunian dyke formed by infilling sedimentation of carbonates in a fracturing-generated submarine cavity, rather than a karstic cave-fill deposit. We postulate that infilling sedimentation took place immediately after the formation of the cavity, most likely in a transgression period during Carnian time.