Abstract Detail

Paleobotanical Section

BAGHAI-RIDING , NINA LUCILLE [1], Davis, Kendal [2], Hotton, Carol [3], Myrow, Paul [4], Dangles, Lauren [4].

Palynomorphs from the Base of the Late Jurassic Morrison Formation, Colorado Springs, Colorado, U.S.A.

The Late Jurassic Morrison Formation, deposited across much of the western interior of the U.S, supported a diverse fauna of dinosaurs and other terrestrial reptiles, as well as terrestrial and freshwater invertebrates. Plant fossils, especially megafossils, however, are rarely preserved, so the plant component of this complex ecosystem remains poorly understood. As part of a long-term study on Morrison floristics and phytogeography through palynology, we report here on palynomorphs from the base of the formation just east of Manitou Springs, Colorado. The samples were derived from thin coal and carbonaceous shale beds immediately underlying a thin chert-bearing unit, a widely recognized marker at or near the base of the Morrison Formation. This bed, recognized for the first time in the Colorado Springs area, marks a significant shift in facies from restricted marine basin deposits to freshwater terrestrial conditions. The palynomorph assemblage resembles others previously recovered from elsewhere in the Morrison Formation, but is much less diverse. It is dominated by two species of fern spores, Ischyosporites marburgensis (Schizaeaceae) and Cyathidites minor (possibly the tree fern family Cyatheaceae), and the extinct conifer taxon Classopollis (Cheirolepidaceae). Other rare taxa include Araucariacites spp. (Araucariaceae), Exesipollenites tumulus (?Taxodiaceae), and bisaccates (?Pinaceae or ?Voltziales, ?Podocarpaceae), as well as the dinoflagellates Spiniferites and Odontochitina. The abundance of spores, unusual for Morrison floras, undoubtedly reflects the local wetland that gave rise to the coal beds, but the abundance of Classopollis, usually indicative of drier conditions in the Morrison, is somewhat surprising. The depositional environment may represent an alkaline or brackish wetland, which could explain the low diversity of the assemblage and the presence of dry and wetland plants as well as dinoflagellates. This depauperate assemblage contrasts markedly with a rich palynomorph assemblage associated with abundant plant megafossils, vertebrates and invertebrates previously reported from a lacustrine/wetland limestone unit in Temple Canyon Park, about 50 miles SW of the Manitou Springs locality. The Temple Canyon locality is near the base of the Morrison as well, but almost certainly stratigraphically above the Manitou Springs locality, although precise correlation is unclear. Throughout the Morrison, local depositional environment appears to be a major factor affecting the composition of palynomorph assemblages, often overwhelming other signals such as climate

1 - Delta State University, Department of Biological Sciences, Caylor Hall Room 235, Cleveland, MS, 38733, USA
2 - Delta State University, Department of Biological Sciences, Cleveland, MS, 38733
3 - National Museum of Natural History, Smithsonian Institution, Department of Paleobiology, MRC-121, Washington , DC, 20560, USA
4 - Colorado College, Geology, Colorado Springs, CO, 80903, USA

Keywords:
Morrison Formation
Manitou Springs
Temple Canyon
palynomorphs
Ischyosporites.

Presentation Type: Poster:Posters for Sections
Session: P
Location: Eyrie/Boise Centre
Date: Monday, July 28th, 2014
Time: 5:30 PM
Number: PPB004
Abstract ID:529
Candidate for Awards:None