Late Paleozoic conifers of North America: structure, diversity and occurrences

Abstract

Late Paleozoic conifer communities originated in moisture-stressed environments along the paleoequator on the Laurussian continent. By Late Permian time, northward movement of the continent displaced these communities toward subequatorial regions. North American deposits provide the most abundant and best preserved pre-Permian conifer fossils. They represent a wide spectrum of preservational modes including compression/impression, mold/cast, and cellular permineralization by carbonates, phosphates, iron sulfides, iron oxides and iron hydroxides. Some modes are associated with distinct biotic assemblages, and to some extent each can be correlated with certain depositional environments and taphonomic histories. Exceptional floras containing extensive conifer remains occur in the Rocky Mountains, the Midcontinent, and the Appalachian regions. These include: estuarine carbonates at Hamilton and Pomona, Kansas; transitional terrestrial to marine clastics at Kinney Brick Quarry, New Mexico, Garnett, Kansas and the 7–11 Mine in northeastern Ohio; and offshore marine shales in Kansas, Oklahoma and Texas that were deposited in dysoxic environments. Most specimens have been assigned to the form genus Walchia, but exceptionally well preserved specimens conform to species of Emporia (Emporiaceae) and to one or more undescribed species that may represent additional genera and/or families. These species add significantly to the growing diversity of Paleozoic conifers, and provide valuable data for testing hypotheses of conifer and coniferophyte relationships.