Abstract Detail

Paleobotanical Section

Miller, Lauren [1], Smith, Selena [2], Stromberg, Caroline [3], Sheldon, Nathan [1].

A high-resolution record of deep-time vegetation dynamics from the Eocene of Montana.

Reconstructing past vegetation at high resolution is key to understanding ecological dynamics and links with earth processes on geological time scales. Macrofossil florasprovide important data on vegetation types, but are limited in terms of geographic and temporal coverage. Phytoliths (plant silica bodies) offer an opportunity to study vegetation in the absence of macrofossils. While phytoliths have previously been used for examining vegetation on broad spatial and temporal scales, we wanted to test the ability of phytoliths and other biosilica (e.g., diatoms) to reconstruct vegetation dynamics on a shorter (<1 million years) time scale for a single locality. In addition, this study represents the first to compare directly phytolith and paleosol data. We examined vegetation patterns inferred from phytoliths from a section of the Renova Formation, Timberhills region, Montana dated to 39.2 ± 3 Ma. The sectionis composed of Alfisols, Entisols, Inceptisols, and composite paleosols superimposed onto floodplain sediments that were deposited under generally low-energy conditions. Phytoliths from 27 paleosol horizons were extracted to reconstruct a high-resolution vegetation history for this section. Phytolith morphotypes are predominantly from forest plants, confirming the presence offorests in Montana ~40 Ma. Tropical elements such as palms (Arecaceae) and gingers (Zingiberales) are present throughout the section, suggesting this was a paratropical forest. The high-resolution sampling demonstrates vegetation shifts between three main dominant plant types: closed forest, moderately open forest (forest gaps, edges, and woodland; represented by Zingiberales), and grasses. The heterogeneity is likely due to succession and vegetation patchiness. Grasses are interpreted as early-successional and tolerant of relatively drier conditions, but are out-competed by forest vegetation on longer time-scales. At some stratigraphic horizons, there is poor correspondance of paleosol type and phytolith assemblages, reflecting changing vegetation along a soil depth profile. This study demonstrates that high-resolution sampling and multiple lines of evidence are necessary for capturing vegetation dynamics in time and across microhabitats in deep time.

Broader Impacts:

1 - University of Michigan, Geological Sciences, 2534 CC Little Bldg , 1100 North University Ave, Ann Arbor, MI, 48109-1005, USA
2 - University Of Michigan, Department Of Geology, 1100 North University Avenue, 2534 CC Little Building, Ann Arbor, MI, 48109, USA
3 - University of Washington, Biology, 24 Kincaid Hall, Box 351800, Seattle, WA, 98195-1800, USA

Keywords:
phytoliths
paleosols
paleoecology
Eocene
Montana
Poaceae
Zingiberales
Succession
vegetation dynamics.

Presentation Type: Poster:Posters for Sections
Session: P
Location: Khorassan Ballroom/Chase Park Plaza
Date: Monday, July 11th, 2011
Time: 5:30 PM
Number: PPB005
Abstract ID:610