A Pedogenic Chronology for Kilbourne Hole, Southern New Mexico: I. Soils in the Tuff

Kilbourne Hole, in southern New Mexico, was formed by steam explosions and is a maar volcano surrounded by tuff, most of which is prominently stratified. Although a few carbonate nodules are in unstratified materials of soils at stablest sites, a banded carbonate horizon is the most prominent and extensive pedogenic feature and has formed in stratified tuff. The carbonate bands are commonly about 1 to 2 mm thick, have formed along some of the primary strata of the tuff, and are separated from each other by tuff with little or no macroscopic carbonate. Development of the carbonate bands is attributed to the character of the parent materials, which are stratified, cohesive sands deposited by base surge and differing considerably in size and consistence. These factors have caused pedogenic carbonate to accumulate in banded form instead of the nodules and cylindroids that are more common in other materials which have little or no gravel. The bands consist of both laminar and nonlaminar types. The stratified tuff constitutes a special case in which the laminar horizon would form much faster than in the conventional sediments of basin floors, alluvial fans, and fan piedmonts that dominate many arid regions. Most of the studied soils are sandy Entisols that have been classified as Typic Torriorthents, sandy, mixed, thermic. They have been classified as Orthents instead of Psamments because hazards are minimal for blowing and for the support of wheeled vehicles. An exclusion for soils of stratified, cohesive sands of base surge origin is needed in the definition of Psamments. Minor areas of Typic Haplargids, coarse‐loamy, mixed, thermic, are also present.