WELL PRESERVED, ARAGONITIC PHYLLOID ALGAE (EUGONOPHYLLUM, UDOTEACEAE) FROM THE PENNSYLVANIAN HOLDER FORMATION, SACRAMENTO MOUNTAINS, NEW-MEXICO

Remarkably well-preserved fossils of the udoteacean alga Eugonophyllum occur in the Virgilian Holder Formation, Sacramento Mountains, south-central New Mexico in a 20-cm-thick packstone bed between two thick shale beds. Original aragonite is preserved in this bed as a felt-like mesh of needles in algal thalli, in mollusc shell fragments, in sponge walls, and in botryoidal and isopachous marine cements. The average Sr content of the algal aragonite (9091 ppm, n = 21, standard deviation = 1498) is comparable to reported values for modern Halimeda. Internal and cortical structures of Eugonophyllum are exceptionally well preserved. In the basal, heavily calcified portion of the alga the medullary (interior) region of the Eugonophyllum thallus is composed of an aragonitic felt interspersed by small (20 mum diameter), parallel siphons. In the distal, less calcified portion of the interior of the alga, siphons are larger and are irregularly arranged. As in modern udoteaceans, the bulbous tips of the utricles formed the outer surface of the organism. Where the outer cortex of our specimens is preserved by silicification, that cortex is similar to that of modern udoteacean algae (Halimeda and Udotea). This new morphologic information about Paleozoic phylloid algae substantiates earlier suggestions that at least some Pennsylvanian and Permian phylloid algae are related to modern green algae such as Halimeda and Udotea. These observations open new avenues for research on the lithologic similarities between Pennsylvanian/Permian phylloid algal mounds and Holocene Halimeda mounds as well as the factors that control the location of ancient and modern mounds.