ABSTRACT: Generic Identity and Diagenesis of Pennsylvanian Phylliod Algae Revealed by Cathodoluminescence

Stephen O. Moshier, Brenda Kirkland

The late Paleozoic phylloid algae are of problematic, although likely diverse, affinity. Phylloids in the Pennsylvanian Providence Limestone (Desmonesian) in western Kentucky are typical in appearance: millimeter-long leaf forms composed of a calcite mosaic lacking relict fabrics. Petrography with cathodoluminescence, however, reveals details of internal features that enable generic identification of these phylloids as the ancestral coralline Archeolithophyllum. Nonluminescent cellular material and luminescent pore-fill calcite delineate clearly defined polygonal hypothallial and perithallial tissue. Backscattered electron imaging is also helpful in distinguishing skeletal and diagenetic material in the algae. Hypothallial pores are 25 × 50 µ and commonly are ar anged in arcuate layers (referred to as coaxial tissues). Cellular walls are thin (5 µ) and contain scattered holes or pits (1 µ diameter), some filled with pyrite. Low magnesium and high strontium contents of the skeletal material suggest an aragonitic precursor mineralogy (Mg average, 519; range 0-2016 ppm; Sr average, 4461; range, 388-10549 ppm). These phylloids do indeed share morphological, structural, and compositional characteristics with Holocene Squamariacean genera composed of aragonite.

Generations of calcite-filling cellular pores change from bright yellow to dull red luminescence. Electron microprobe data indicate continuous enrichment in the magnesium, manganese, and iron content of the diagenetic fluids. Iron content of the last pore-fill calcite ranges to 22,875 ppm but averages 12,296 ppm. Strontium is progressively depicted in these cements.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990