Paleocene and early Eocene woods of the Denver Basin, Colorado Elisabeth A. Wheeler 1 * and Thomas C. Michalski 2 department of Wood and Paper Science, North Carolina State University, Box 8005, Raleigh, NC 27695-8005, U.S.A. 2 Core Research Center, U.S. Geological Survey, Denver, CO 80225, U.S.A. *Author to whom correspondence should be addressed: xylem@unity.ncsu.edu. ABSTRACT Silicified woods are common in the upper Dl (Paleocene — Puercan and Torrejonian) and D2 (Eocene — Wasatchian) sequences of the Denver Basin. Almost all derive from angiosperms. Woods from the upper Dl sequence are the second set of angiosperm woods described from Paleocene strata of the Rocky Mountain region. Wood assemblages from the upper Dl sequence differ from Paleocene wood assemblages of the San Juan Basin, New Mexico and the Big Bend region of Texas, indicating variation within the Western Interior. Lauraceous woods with oil cells are common in the Denver Basin assemblages while they are not known from the San Juan Basin or Big Bend. This initial survey suggests that the early Paleocene Dl (7 wood types) and early Eocene D2 (5 wood types) wood assemblages differ. Lauraceous woods with oil cells appar- ently are not common in the D2 sequence. The early Eocene Denver Basin wood assemblages differ from the early Eocene Yellowstone Fossil Forest wood assemblages in which conifers are common and phyllanthoid woods are rare. Growth rings are present but not well defined in the Dl and D2 sequence woods. The Denver Basin angiosperm woods are neither semi-ring porous nor ring porous, features that are common in present-day northern temperate forests and in angiosperm woods from the late Eocene Florissant Fossil Beds. KEY WORDS: fossil wood, paleobotany, Paleocene, Eocene, Lauraceae, Paraphyllanthoxylon, Platanaceae. INTRODUCTION There is little information about the internal structure of Paleocene trees of North America. Only four dicotyledonous angiosperm wood species are known from the western United States (two from Big Bend, Texas, Wheeler, 1991; two from the San Juan Basin, New Mexico, Wheeler et al., 1995); only 13 are known from the eastern U.S. (Williamsburg Formation, South Carolina; Melchior, 1998). The abundance of Paleocene (Puercan, earliest Paleo- cene) and Eocene (Wasatchian) angiosperm woods in the Denver Basin provides an unprecedented opportunity to study the anatomy of early Tertiary dicot trees from a relatively restricted geographic region where there is good stratigraphic control. Dicotyledonous trees (hardwoods) are charac- terized by: a) vessels for water conduction; b) fibers for support; and c) varying amounts of ray and axial parenchyma for storage of photosynthate and water as well as manufacture of secondary metabolites for wound responses. Variations in vessel charac- teristics (e.g., diameter, frequency, arrangement) are correlated with climatic variations in extant floras, particularly water availability and seasonal- ity (e.g., Baas, 1986; Carlquist, 1988; Wiemann etal., 1998). There has been limited success using fossil dicot wood to infer paleotemperature (Wiemann et al., 1999). Nonetheless, accumulating data on fossil wood from localities where leaf physiognomy and/ or isotopic analyses provide independent estimates of paleoclimate should be useful for refining ter- restrial paleoclimate models. Wood has particular Rocky Mountain Geology, v. 38, no. 1, p. 29-43, 5 figs., 1 table, May, 2003 29