Epiphyton and Renalcis--Diagenetic Microfossils from Calcification of Coccoid Blue-Green Algae: ABSTRACT

Abstract

Epiphyton and Renalcis, and related microfossil genera, are very important but enigmatic framebuilding and encrusting components of many Paleozoic reefs. Study of numerous North American occurrences of various ages (Early Cambrian to Late Devonian) suggests that Epiphyton and Renalcis are end members of a continuous spectrum of diverse morphologies that commonly occur adjacent to or intergrown with each other. Salient morphotypes include (1) dendritic forms (typified by Epiphyton), (2) dendritic forms with finely septate branches (Gordonophyton), (3) robust branching forms with chambers (Chabokovia), (4) large unchambered branching tubes, (5) chambered and botryoidal aggregates (typified by Renalcis), and (6) arborescent grapelike clots which often lengthen into stubby br nches. Particularly noteworthy among common intergrowths and co-occurrences are Epiphyton branches attached to (sprouting from?) Renalcis chambers. Many well-preserved micrite walls, branches, and clots exhibit a faint dense peloidal microstructure. Figure The continuum of shapes and intergrowths indicates that these microfossils were likely not genetically distinct organisms. It is proposed that these fossils represent precipitation of high-Mg calcite around and within clumps of coccoid blue-green algal cells soon after death of the algae and in the environment of growth. Inferred rates of chamber addition and growth of branch tips suggest that many cells grew, died, and rotted away between successive times when biogeochemical conditions were right to promote calcite precipitation. The various forms, genera, and species resulted from environmentally related size variation of cells and cell clumps and whether or not calcification was episodic. These microfossils are therefore diagenetic taxa and, in a sense, can be considered microst omatolites. End_of_Article - Last_Page 619------------