A Pedogenic Chronology for Kilbourne Hole, Southern New Mexico: II. Time of the Explosions and Soil Events Before the Explosions

Abstract

AbstractBecause tuff was emplaced as a result of explosions that produced Kilbourne Hole, soils formed in the tuff should provide important clues concerning time of the explosions. Pedogenic carbonate of illuvial origin was used to estimate the age of a soil in the tuff. Age was estimated by calculating the amount of pedogenic carbonate in a soil column 1 m2 in horizontal cross section, and by comparing this amount with the amount of carbonate in a soil with estimated age in the nearby Desert Soil‐Geomorphology Project. The amount of pedogenic carbonate for a soil in the tuff is 73 kg m−2. The Desert Project soil is estimated to be about 11000 yr old and has 34 kg m−2 of pedogenic carbonate that accumulated at a rate of 3.1 kg m−2 kyr−1. Using the same rate of carbonate accumulation, the soil in the tuff dates from about 24 000 yr BP and the explosions that produced Kilbourne Hole and the associated tuff are thought to have taken place at about that time. A lava flow preceded the explosions that produced Kilbourne Hole, but a time of sedimentation and soil formation occurred between the two events as evidenced by a postlava, pre‐tuff deposit in which a soil formed. This deposit is attributed to a localized cycle of sedimentation initiated by presence of the lava. The combined ages of the soil in the tuff and the soil in the post‐lava, pre‐tuff deposit are believed to represent the approximate age of the lava. Based on carbonate amount and morphology, the lava is estimated to be about 0.1 million yr old. This contrasts with the most recently obtained K‐Ar date of 0.53 ± 0.03 million yr for the lava. The amount of pedogenic carbonate in desert soils has potential for widespread application as a chronological tool and as a cross‐check for other dating techniques. However, lack of agreement on the age of soils at chronological benchmarks can indicate that some of the dates obtained by chronological extrapolation should be considered tentative, including the date obtained in this study.