Lehman, T.M. , Wheeler, E.A. .
Cretaceous Conifers: Woods from Big Bend National Park, Texas.
Upper Cretaceous and lower Tertiary strata in the Big Bend region of Texas comprise a gradational sequence of marine, paralic, and terrestrial sediments. Conifer woods dramatically decrease in abundance from the Campanian Aguja Formation upward through the Maastrichtian Javelina and Paleocene Black Peaks formations, progressing from coastal to inland environments. There is an abrupt change from cupressoid/podocarpoid woods to araucariacean/cheirolepidiacean woods coincident with the transition from lowland flood-plain facies to well-drained inland flood-plain facies, reflecting changes in soil type, climate, and elevation that accompanied the change from lowland to inland facies. Conifer and dicot woods are not typically preserved together, suggesting that conifers and dicots normally grew in separate stands or in separate environments. The Big Bend conifer woods differ from those at other localities in the western interior and also document more variation in growth ring types than previously recognized for the whole of the Northern Hemisphere Late Cretaceous. The sizes of some logs and width of their growth rings suggests that some trees might have reached diameters of 1 meter in approximately 80 years. Woods of the Cupressaceae / Podocarpaceae type have juvenile wood with narrower tracheids and less distinct growth rings than mature wood. For those woods with distinct growth rings, it appears that formation of new cambial initials was more common near the latewood zone. The frequency of these divisions has potential for distinguishing whether wide growth rings are the result of a long growing season or an increased rate of tracheid production. The incidence of compression wood is relatively high and may reflect either growth on unstable substrate or frequent storms with high winds.
1 - N.C. State University, Wood & Paper Science, Raleigh, North Carolina, 27695-8005, U.S.A.
2 - Texas Tech University, Department of Geosciences, Lubbock, Texas, 79409-1053
Presentation Type: Paper
Location: Maybird (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 2:00 PM