60-5 Fluvial Paleoenvironments and Root-Based Water Table Indicators in the Coll De Montllobar Formation

Session: 2YC and 4YCU Geoscience Student Research Poster Showcase

Presenting Author:

Authors:

Abstract:

Fluvial strata of the Paleocene Montllobar Formation in the Coll de Montllobar cliffs of the Tremp Basin, in the frontal Spanish Pyrenees, contain abundant root models that record oxidation and reduction from root penetration along the depositional dip of the bar. Since root distribution on bar surfaces and root penetration generally is tied to standing water levels, the depth of these fossilized roots in channel stories is a proxy for past water table positions. This study examines root density vertically toward the bottom of the channels, indicating the depth of sustained flow drop between bankfull floods. The channel depth where roots dissipate is thus indicative of discharge fluctuation. Our findings contribute to understanding past climatic hydrological conditions in this region.

To test this, root density was measured every two feet down seven bar sections using image-based color analysis. Black pixels, representing traced roots, were used to calculate root density percentages. These values were plotted on a chart, where each line represents a different bar section within the Coll de Montllobar. The X-axis shows depth, and the Y-axis shows root density. When interpreting the results, if multiple bars show peaks at similar depths, it may suggest stable past water table levels and consistent environmental conditions during deposition.

The presence of roots nearly down to the channel base suggests prolonged periods of very low water stage. This implies strong seasonal discharge variation, with brief high-flow events separated by long low-flow intervals. Such flashy discharge is consistent with a warm, semi-arid climatic local setting during the Paleocene. These findings support previous interpretations that this stratigraphic interval reflects the later stages or extension of the Paleocene–Eocene Thermal Maximum (PETM)—a global warming event already well documented in slightly younger strata nearby. By using root distribution as a gauge of stage variation, this study provides insight into ancient fluvial hydrology and enhances our understanding of climate-driven environmental changes in the Tremp Basin.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6245

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