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Scanning Electron Microscope Images of Sand and Silt from the Early MIS4–MIS3 Roxana Silt, Phillips Bayou, Arkansas

Scientific Investigations Report 2023-5062
By: , , , and 
https://doi.org/10.3133/sir20235062

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Abstract

The age and source of the late Pleistocene Roxana Silt in the Mississippi Valley have been studied since the middle 1800s. Published age and paleoenvironmental data for the Roxana Silt in the Mississippi Valley show that deposition occurred from late marine isotope stage 5 (MIS5) through late marine isotope stage 3 (MIS3) (80–30 kilo-annum [ka]), when the warm to hot interglacial climate of early to middle MIS5 (about 130 to about 80 ka) was transitioning to a considerably cooler and wetter climate. Scanning electron microscopy/energy dispersive X-ray (SEM/EDS) analysis of silt and sand grains from the Roxana Silt exposed in an abandoned borrow pit near Phillips Bayou, Arkansas, was performed as part of a 1990s study of late middle and late Pleistocene loess in the unglaciated lower Mississippi Valley. Results from that study were summarized in 1990s publications, but the data for sand and silt grain morphology and mineralogy were not published. Some of the SEM/EDS analyses of the Roxana Silt from that late 1990s study are presented in this report. Combined with previously published chronostratigraphic and pedostratigraphic data for the Roxana Silt at Phillips Bayou, the SEM/EDS data indicate some degree of syndepositional weathering and pedogenic alteration during and after gradual eolian deposition in late marine isotope stage 4 (MIS4) and MIS3 (about 60 to about 30 ka). Results from the SEM/EDS analyses support previously published paleoclimate interpretations indicating that at least as far south as northern Mississippi, the climate of the Mississippi Valley in MIS4 and MIS3 (about 70 to about 30 ka) was cool to cold and humid to wet.

Suggested Citation

Markewich, H.W., Wysocki, D.A., White, G.N., and Dixon, J.B., Scanning electron microscope images of sand and silt from the early MIS4–MIS3 Roxana Silt, Phillips Bayou, Arkansas: U.S. Geological Survey Scientific Investigations Report 2023–5062, 24 p., https://doi.org/10.3133/sir20235062.

ISSN: 2328-0328 (online)

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Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • Chronostratigraphy of Lower Mississippi Valley Eolian Silt Deposits
  • Roxana Silt Paleosol/Loess Chronostratigraphy at Phillips Bayou
  • SEM/EDS Investigations of the Roxana Silt at Phillips Bayou
  • Materials and Methods
  • Results of SEM/EDS Analysis
  • Summary of SEM/EDS analysis
  • Observations
  • References Cited
Publication type Report
Publication Subtype USGS Numbered Series
Title Scanning electron microscope images of sand and silt from the early MIS4–MIS3 Roxana Silt, Phillips Bayou, Arkansas
Series title Scientific Investigations Report
Series number 2023-5062
DOI 10.3133/sir20235062
Year Published 2023
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Florence Bascom Geoscience Center
Description vii, 24 p.
Country United States
State Arkansas
Other Geospatial Phillips Bayou
Online Only (Y/N) Y
Additional Online Files (Y/N) N
Google Analytic Metrics Metrics page
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