PRELIMINARY CENSUS OF FOSSIL WOOD, KAIPAROWITS FORMATION (UPPER CAMPANIAN-CRETACEOUS), GRAND STAIRCASE-ESCALANTE NATIONAL MONUMENT, UTAH

Lacustrine and crevasse splay deposits of the Upper Campanian Kaiparowits Formation yield an abundant, highly diverse, and somewhat unique foliage assemblage dominated by platanoid angiosperms and several species of cupressoid-taxodioid conifers. Analysis of palynomorphs also shows cupressoid-taxodioid conifers co-dominant with a highly diverse angiosperm assemblage. Fossil wood, which typically occurs in fluvial channel facies, is also abundant, but prior to this has never been systematically surveyed. Fourteen samples of silicified wood were collected from a variety of stratigraphic levels within the formation and processed into thin sections oriented into the three standard views; tangential, radial and transverse. Samples were assessed to determine the presence of distinguishable growth rings, the presence/absence of resin ducts, the number of ray cells, arrangement of border pits, cross pitting, and septation between cells and can be categorized into three general groups based on border pit morphology and vessel element presence/absence. Twelve samples exhibit uniseriate border pits characteristic of cupressoid wood. One sample displays multiseriate border pits which we believe indicate it’s a taxodioid. The remaining sample lacks tracheids and based on the pitting arrangement of the vessel elements and configuration of ray cells we refer it to the angiosperm family Platanaceae. While we stress the preliminary nature of these results, it could be concluded that the Kaiparowits Formation’s forest overstory was completely dominated by cupressoid conifers. This is at variance with both the foliage and palynological records. Interestingly, the platanoid sample shows extensive evidence of fungal hyphae attacking the wood, which was not observed in any of the conifer samples. We speculate platanoid trees may have been a significant component of the forest overstory, but that their wood did not fossilize in abundance proportional to their foliage record because of its relatively rapid decay in fluvial settings.