Abstract Detail

Paleobotanical Section

Unger, Christa [1], Tomescu, Alexandru M.F. [1].

Reappraising the Early Cretaceous permineralized flora of the Chickabally Mudstone (Budden Canyon Formation, Barremian-Aptian, California).

The Budden Canyon Formation is a 6,700 meter thick unit spanning the Valanginian - Turonian interval (Cretaceous) in northern California. Lithologically, it comprises a variety of clastic marine deposits (mudstone- through conglomerate-grade) organized into seven members which are dated based on the ammonite fauna and nanofossils. The unit includes several sequences with near-shore deposits and is plant-fossiliferous throughout, with the richest sequences concentrated in Hauterivian - Aptian layers. The flora of the Budden Canyon Formation was first described at the turn of the twentieth century by Lester Ward, based on the morphology of compressed (and rare permineralized) material, which revealed 46 taxa including pteridophytes, gymnosperms, and angiosperms. This flora has received little attention since its original description –three studies added as many new taxa based on anatomically-preserved permineralized material: a pinaceous ovulate cone (Pityostrobus), an osmundaceous stem (Millerocaulis), and a dispersed seed or fruit (Onoana). Recent work in one of Ward’s localities in the Lower Chickabally Mudstone member (Barremian - early Aptian, ca. 120-125 Ma) has revealed a rich anatomically-preserved flora. The plant material is comprised of allochthonous fragments that range in size from large pieces of conifer trunks to minute bryophyte gametophytes. The plants are preserved by calcium carbonate permineralization which forms discontinuous fossiliferous beds and concretions close to the contact between the Lower Chickabally Mudstone and the overlying Huling Sandstone. Conifers form the bulk of the fossil material and are represented mostly by woody fragments and foliage, but cones are also present; at least two conifer types, one cupressaceous and the other pinaceous are recognized. The flora also includes numerous dispersed seeds, of which six types have been discovered. Filicalean ferns are represented by vegetative and fertile frond fragments, including some that exhibit Onoclea-type anatomy or indusiate sori. At least seven types of bryophyte gametophytes (mostly mosses) have also been recognized. Continued sampling will certainly broaden the diversity of this fossil flora. The flora of the Chickabally Mudstone is only slightly older (ca. 10-15 myr) than the intensely studied Apple Bay flora of Vancouver Island (Valanginian, 136 Ma), with which it shares the abundance of coniferous remains, the presence of filicalean ferns, and the high bryophyte diversity (leucobryaceous, polytrichaceous, and tricostate types have been identified in both floras). Together, these two floras will provide a more complete image of vegetation along the western seaboard of North America during the Early Cretaceous.

Broader Impacts:

1 - Humboldt State University, Department of Biological Sciences, 1 Harpst Street, Arcata, CA, 95521, USA

Keywords:
Cretaceous
California
fossil
bryophyte
Moss
Conifer
fern.

Presentation Type: Oral Paper:Papers for Sections
Session: 3
Location: Melrose/Riverside Hilton
Date: Monday, July 29th, 2013
Time: 9:00 AM
Number: 3004
Abstract ID:813
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award