New Mexico Geological Society Annual Spring Meeting — Abstracts

Detecting Pennsylvanian Millennial-Scale Climate Changes Using Pollen Analysis of Marine Limestone-Shale Rhythmites

William Eldridge Ganter

Earth and Planetary Sciences, University of New Mexico

13510 Sunset Canyon Dr. NE, Albuquerque NM, 87111

wganter@unm.edu

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Abstract

Deep-water “rhythmites” are characterized by thin, rhythmically interbedded limestone layers alternating with shale layers. They are common in Precambrian through Cenozoic poorly oxygenated offshore marine deposits. Previous studies report that individual limestone-shale couplets represent 1000-3000 years and are the result of millennial-scale wetter to drier climate changes with shale layers indicating wetter climates and limestone layers representing drier climates. I am testing this millennial-scale climate change hypothesis by comparing the characteristics of eolian-derived pollen assemblages in limestone versus shale interbeds from two different Middle Pennsylvanian rhythmite successions in central New Mexico. If the pollen-producing terrestrial plant community changed in response to these climate changes, then the pollen diversity and abundance might be reflected in offshore deposits and different pollen morphotypes and abundances would occur in the limestone versus shale layers.

Preliminary results from a single section in the southern Sandia Mountains show four statistically significant pollen morphotypes including bissicate, alete, periporate, and trilete. Of these morphologies, bissicates are the most common in shale layers, whereas limestone layers contain greater abundances of the other three morphotypes. Additional samples from a coeval northern Sandia Mountain location are being processed to further substantiate these trends. If both locations record distinctly similar pollen abundances and diversity trends, then this research suggests that Paleozoic rhythmites as primary depositional features and millennial-scale climate changes affected both terrestrial vegetation patterns and offshore sediment input.