Conical-Columnar Stromatolites and Subtidal Environment: ABSTRACT

Abstract

Several distinct varieties of stromatolites are present in dolostones of the Proterozoic Dismal Lakes Group, Great Bear Lake region, Northwest Territories. Comparison of the stromatolite types with respect to abundance of associated sedimentary structures (cross-laminations, ripple marks, oolites, desiccation cracks, evaporite casts, intraformational conglomerates) supports the concept that stromatolite morphology is closely related to environment. As in modern analogues, water turbulence appears to be a particularly significant determinant of morphology. On the basis of textures, associated sedimentary structures, and comparison with modern algal stromatolites, most stromatolites of the Dismal Lakes Group appear to have formed in either supratidal or intertidal environments. However, conical-columnar stromatolites (Conophyton), for which a modern analogue is lacking, are confined largely to a prominent dolostone unit in which sedimentary structures indicative of turbulence are almost totally absent. The paucity of such structures, coupled with consideration of the stromatolite morphology during growth, suggests that conical-columnar stromatolites may be characteristic of a subtidal environment. Maintenance of a vast field of conical surfaces in an intertidal or supratidal environment without reduction or fragmentation of the apices eems unlikely. The relation of the conical-columnar stromatolites to flat-bedded subjacent strata renders interpretation of origin by deformation untenable, and continuity of lamination within and between the columns refutes a diagenetic origin. The Dismal Lakes dolostone unit consisting mainly of conical-columnar stromatolites is interpreted as a Proterozoic subtidal algal reef of unusual persistence in space and time. End_of_Article - Last_Page 614------------