16 Radionuclides: Biogeochemistry, Transport, and Geological Applications II

Friday, 20 March 2020
1:30 PM - 3:30 PM
Regency Ballroom A

COSMOGENIC EROSION RATES IN CENTRAL AND WESTERN CUBA

Paper number: 16-5
Program: Symposia Sessions
Time: 2:50 PM – 3:10 PM

Authors

Abstract

Characterization of the rates of landscape change in the tropics remains limited, particularly at the basin scale and over geologically meaningful timescales. Here, we present the first erosion rates for Cuba inferred from in-situcosmogenic nuclide analyses of detrital sediment and couple them with chemical denudation rates derived from chemical analysis of stream waters. 10Be-derived erosion rates for 25 basins in central Cuba range from 1.5-81 m/My (average = 25.5 m/My, median = 19.4); 10Be-derived erosion rates from western Cuba are comparable, ranging from 10.6-27.3 m/My (average = 17.3 m/My, median = 17.1). Measured cosmogenic erosion rates are similar to, but slightly lower than, those measured elsewhere in the tropics. We observed a lithologic dependence in measured erosion rates; rates in basins underlain by metamorphic and igneous rocks were ~7X lower than in sedimentary basins. 10Be-based erosion rates in central Cuba are positively correlated with slope and mean annual precipitation. We find no correlation between cosmogenic erosion rates and basin area or elevation.

Although cosmogenic erosion rates are often interpreted as total landscape denudation, we find in some Cuban drainage basins that 10Be-based erosion rates underestimate total landscape denudation. Considerable discordance (12-60X) between erosion rates and chemical denudation rates in five central Cuban basins suggests that significant mass loss by solution is not reflected by cosmogenic-based erosion rates. In 2 of these basins, erosion rates calculated from duplicate measurements of 10Be (1.4 & 2.5 m/My) and 26Al (1.7 & 2.9 m/My) were ~50X lower than chemical denudation rates (89 & 108 m/My). Both 26Al and 10Be concentrations indicate long term, near-surface (>>100 ky) sediment residence; stream water geochemical data are consistent with the presence of evaporite deposits. We suspect that rapid chemical denudation enriches remaining sediment in quartz, which lingers at or near the surface in these low slope (0.5°) basins.

Geological Society of America Abstracts with Programs. Vol. 52, No. 2

doi: 10.1130/abs/2020SE-345442

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