23 Undergraduate Student Research (Posters)

Tuesday, 10 March 2020
8:30 AM - 5:00 PM
Ballroom B

STRATEGIES FOR RECOGNIZING PEDOGENIC LAYERS WHEN VAGUE IN OUTCROP: EXAMPLEFROM THE LOWER-MIDDLE SALAGOU FORMATION, LODÈVE BASIN, FRANCE

Paper number: 23-15
Program: Theme Sessions
Time: 8:30 AM – 5:00 PM

Authors

Abstract

The Permian redbeds of the Salagou Formation exposed in the Lodeve Basin, south-central France, have been interpreted to reflect fluvial floodplain or playa lake deposition. Recent work has shown that the characteristics of this strata are more consistent with eolian deposition and have ultimately been interpreted as paleo-loess deposits. Aside from uniformly fine (silt) grain size and massive bedding, loess deposits are characterized by the recurring paleosol layers that represent periods of wetter, interglacial climates within an overall arid trend. Determining the nature of paleosol-loess cyclicity in the Salagou Formation will (1) test our depositional interpretation (wind-deposited fines) and (2) deepen our understanding of the late Paleozoic paleoclimate of equatorial Pangea, but unfortunately, pedogenic features in this locality are weakly developed and difficult to characterize in outcrop (no abrupt color change, horizonation, root traces, etc).

Herein we apply new strategies to document pedogenic features at a high resolution, focusing on a section from the lower-middle Salagou Formation that includes an exposure of well developed, randomly oriented slickensides. Preliminary results from magnetic susceptibility data show increasing susceptibility from .051x10-3 to 0.45 x10-3 (2.1 to 5.7 meters) that can be interpreted to reflect a paleosol profile wherein the well-developed slicks are exposed (3-5.5 meters). Thin section attributes include circumgranular cracks, concentrations of birefringent clay, clay coatings on grains, wedge-shaped peds, and pedogenic fabrics (e.g. agglomeroplastic and porphyroskellic). Chemical index of alteration (CIA) values from the interpreted pedogenic horizon are higher on average than those from the parent loess (66 and 60, respectively). This combination of methods allows for a detailed observation of pedogenesis in a system where it is not easily recognized in outcrop. The vertic nature of these features represents wetter periods during an overall arid paleoclimate with significant deposition of fine-grained material. Application of these strategies in other cases where paleosols are poorly defined at the macroscale will allow for a better read on paleoclimatic conditions at the time of formation.

Geological Society of America Abstracts with Programs. Vol. 52, No. 1

doi: 10.1130/abs/2020SC-343669

© Copyright 2020 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.