Geological Society of America

T153 Permian-Triassic Changes and Extinction Event: New Insights from Sedimentary, Geochemical, and Paleobiological Records and Modeling Approaches I

Tuesday, 11 October 2011
8:00 AM - 12:00 PM
Room 200FG

“OCHOAN” QUARTERMASTER FORMATION OF NORTH TEXAS, U.S.A., PART III: FIRST SIGN OF PLANT LIFE

Paper number: T153-7
Program: Technical Sessions
Time: 9:35 AM – 9:50 AM

Authors

Cynthia Looy Presenting Author
University of California, Berkeley, Berkeley, CA
Renske P.J. Kirchholtes
University of California, Berkeley, Berkeley, CA
Greg H. Mack
New Mexico State University, Las Cruces, NM
Tom B. van Hoof
Utrecht, N/A
Neil J. Tabor
Southern Methodist University, Dallas, TX

Abstract

Virtually nothing is known about the paleoenvironmental changes during the Permo-Triassic transition (PTB) in the western and central part of tropical Pangea, as we lack good macro- or microfloral fossil records. Sedimentary strata from the Panthalassan continental margin of tropical Pangea outcrop in Caprock Canyons State Park in northern Texas. Fluvial sandstones and overbank mudstones of the Quartermaster formation likely preserve the PTB, as determined by U-Pb dating of single crystal zircon analyses and Ar-dating of biotite in volcanic ashes. In addition, minute quantities of enclosed organic matter preserve chemostratigraphic d¹³C trends expected close to the PTB. Caprock Canyons’ sedimentary rocks, which are typical redbed formations deposited under oxidizing conditions, have yet to yield fossil pollen and are considered to be barren with respect to plant fossils. Yet, when the same samples were processed according to standard phytolith extraction techniques, numerous fossil vascular plant forms were discovered. In addition, we have recovered the first plant macrofossils from the Quartermaster fm in the form of wood petrifications.

Preliminary analysis of the samples revealed that almost all samples contain phytoliths. Twenty-three morphotypes were recognized, most notably those with imprints of circular boarded pits that are characteristic features of coniferous wood macrofossil petrifactions found in the same section, suggesting that conifer-containing vegetation was present along the coastal Panthalassa margin of Pangea during the Early Triassic, post-Permian mass extinction. These finds, both phytoliths and wood, are the first evidence for plant life in this region. If the Quartermaster fm would prove to be stratigraphically conformable, then these results imply that, contrary to what has been generally suggested, the Panthalassa margin of Pangea was not barren, but preserved woodland ecological elements throughout the time period crossing the PTB. For our future work we will focus on establishing the botanical affinity of the encountered phytolith morphotypes, increasing our sample set, and exploring the phytolith data set as a biostratigraphic tool.