On Aphebian stromatolites and Riphean stromatolite stratigraphy

Abstract

New occurrences of typical Riphean stromatolite and microphytolite groups are reported and illustrated from typical Aphebian sequences in Canada. These include Minjaria, Colonnella, and Kussiella from the Mistassini Group of central Quebec, Gymnosolen, Jacutophyton garganicum, Minjaria, Colleniella, Kussiella, Tungussia, Lenia, Osagia, and Vesicularites from the Belcher Supergroup in Hudson Bay, and Asterosphaeroides ( Nelcanella) and Radiosus from the Manitounuk Supergroup of the southeastern coast of Hudson Bay. These occurrences are at variance with prevailing views of Riphean “biostratigraphy”. They call into question the validity of age assignments based only on stromatolite groups, as well as the premise that prokaryotic evolution is mainly responsible for observed trends in gross morphology. The systematics of stromatolites is re-examined in the second part of the paper, and a more objective, morphometric (stereometric) approach is discussed. Example illustrate how differences and similarites whitin and between stromatolite groups can be expressed quantitatively. The morphologic attributes chosen comprise the shapes of lamina profiles, cross sections (plan views), and longitudinal sections (silhouettes). Microstructures are illustrated photographically; they were not analysed morphometrically and await further study.