T70 Links between Mesozoic Climate and Biodiversity

Sunday, 31 October 2010
1:30 PM - 5:30 PM
Room 603

COASTAL CRETACEOUS FOREST FIRES, PALEOSOLS, AND DINOSAUR PALEOECOLOGY FROM THE ARLINGTON ARCHOSAUR SITE, NORTH TEXAS

Paper number: T70-15
Program: Technical Sessions
Time: 5:15 PM – 5:30 PM

Authors

Abstract

This is the first reported occurrence of wildfires from the Cenomanian of Texas at the Arlington Archosaur Site (AAS). The AAS is a diverse fossil locality from the Cretaceous (95 Mya) Woodbine Formation of North Central Texas. The paleoenvironmental setting is a coastal, delta plain system from the southeastern interior seaway. The site preserves multiple components of a delta plain ecosystem within a 2m section consisting of a peat bed containing numerous, well preserved fossil turtle, crocodile (adult and juvenile) and logs. The logs are carbonized and vary from 2m - 4m in length. Overlying the peat is a fossil horizon containing mixed remains of vertebrates in a mudstone that demonstrates early pedogenesis from an inundated delta plain paleosol. The vertebrates occurring within this horizon include dinosaur, crocodile, turtle and lungfish. The dinosaurs recovered to date include a large herbivorous ornithopod and at least two theropods.

Overlying the fossil bearing horizon is a well developed, heavily rooted Histic Gleysol with numerous calcareous concretions. Within the concretions occur charcoal fragments and several large (28-36 cm length) burned tree stumps and roots. Concretion formation is indicative of seasonal dryness, and the burned tree stumps are evidence of wildfires. Charcoal conglomerate beds were mapped both below and above the paleosol, and dinosaur bone bearing horizon. The charcoal conglomerates contain numerous charcoal and fossil wood fragments (1-4cm length) bound in a Fe rich sand. The presence of charcoal conglomerates is typical of coastal, deltaic systems where burned materials were transported by river channels. The forest fire horizons occur below, within and above the vertebrate fossil horizon. Periodic forest fires are therefore thought to have been an influential part of the coastal ecosystem preserved at the Arlington Archosaur Site. Forest fires are not geographically random, they occur within paleoclimatic zones that are predisposed to fires. Continued study of forest fires may elucidate links between paleoclimate and the biodiversity of coastal Cretaceous ecosystems.