Abstract Detail

Paleobotanical Section

Baghai-Riding, Nina Lucille [1], Hotton, Carol [2], Davis, Kendal [1], Davidson, Taylor [1].

Palynological Evidence from New Mexico for a Latitudinal Moisture Gradient in the Late Jurassic Morrison Formation.

The faunistically rich Late Jurassic Morrison Formation was deposited over much of the Western Interior, from central New Mexico into equivalent units in Canada, probably under seasonally dry conditions. Hotton & Baghai-Riding (2010) tentatively suggested, based on a very small number of samples, that the southern reaches of the Morrison Formation, especially in New Mexico and Arizona, may have been drier overall compared to more northerly regions. This inference was based primarily on the abundance of Classopollis spp. and the relative low diversity and abundance of spores. We present here analysis of an additional nine samples from the upper Salt Wash and lower Westwater Canyon Members of north western New Mexico. Samples are well-preserved and relatively diverse, containing typical Late Jurassic pollen and spore types. Spores typically comprise from less than 1% to about 10% of a given sample, and only about 20 distinct taxa are recognized among the nine samples. These include spores of bryophytes, Lycopodiaceae, Isoetaceae, Equisetum, Dicksoniaceae/Dipteridaceae, Osmundaceae, Schizeaceae, as well as taxa of unknown affinity. Classopollis (Cheirolepidaceae) and Exesipollenites (?Taxodiaceae) dominate all samples; bisaccates (representing Pinaceae, ?Podocarpaceae, and perhaps seed ferns) and pollen of Araucariaceae are subdominant. Gnetophyte pollen (Ephedripites spp.) and Cycadopites (Ginkgophyta, Cycadales or Bennettitales) are present but rare. The extinct conifer family Cheirolepidaceae is considered xerophytic on the basis of morphologic features (highly reduced leaves, thick cuticle, sunken stomata) and sedimentological occurrence (often associated with evaporites and red beds), so Classopollis is often treated as an indicator of aridity. Exesipollenites is sporadically abundant through the Morrison, so its status as an indicator of aridity is uncertain. Araucariaceae and other conifers are considered to indicate more mesic conditions, based primarily on analogy with modern representatives. The more mesic conifers and pteridophytes may have occupied sites near water in New Mexico, whereas Classopollis and perhaps Exesipollenites may have represented ecologically dominant vegetation. Morrison palynofloras in New Mexico support the inference of drier conditions in that region, in contrast to samples from Utah, Colorado and Wyoming, where Classopollis is quite subordinate and spores usually display greater abundance and diversity. Inference of precipitation from palynology is supported by recent elemental analysis of Morrison paleosols by Myers et al. (2014).

1 - Delta State University, Department of Biological Sciences, PO Box 3262 DSU, Cleveland, MS, 38733, USA
2 - National Museum of Natural History, Smithsonian Institution, Palebiology- MRC 121, Proceedings of the Biological Society of Washington, Washington, DC, 20560, USA

Keywords:
Morrison Formation
palynomorphs
Classopollis
New Mexico
Exesipollenites.

Presentation Type: Poster:Posters for Sections
Session: P
Location: Hall D/The Shaw Conference Centre
Date: Monday, July 27th, 2015
Time: 5:30 PM
Number: PPB002
Abstract ID:342
Candidate for Awards:None