ICHNOPEDOLOGIC SIGNATURES OF PALEOCLIMATE: LINKING ICHNOFOSSILS, PALEOSOLS, AND PALEOLANDSCAPES TO INTERPRET THE SEASONALITY AND AMOUNT OF PRECIPITATION AND OTHER PALEOCLIMATIC INDICATORS

A well-defined relationship exists between climate, hydrology, soils, and biodiversity, expressed as net primary productivity (NPP). The major control on NPP and biotic distribution in modern settings is climate. Biota is distributed laterally and vertically in alluvial, lacustrine, and eolian environments as conterminous biotopes. Major factors controlling biotic distribution are temperature, precipitation, evapotranspiration, solar radiation, soil moisture and water-table level, and trophic resources. Similar factors impact soil formation: time, topography, climate, parent material, and biologic activity. Biota are related to the substratum via feeding, dwelling, locomotion, reproductive, and searching behaviors manifested as tracks, trails, burrows, nests, and roots. These behaviors, preserved as trace fossils, have various impacts on the formation and destruction of soil features. The distribution of soil biota, soils, and NPP can also be linked by the soil-water budget, which indicates the distribution of climate factors. Preliminary work suggests that ichnofossil tiering in paleosols or ichnopedologic units shows distinct paleoclimate patterns, particularly when calibrated to modern climate zones. Ichnofossils in dry climates occur as rare, intensely bioturbated bedding-plane exposures with very little vertical tiering. This pattern represents bursts of activity due to episodic precipitation. As precipitation and moisture in a system increase, so do ichnofossil abundance, diversity, and tiering. Ichnopedologic units in wet-dry climates are characterized by shallow to intermediate tiering with an increase in tiering diversity and depth. These characters increase with greater moisture in the wetter climate range. Wet climates are characterized by all tiers and range from deep to shallow depending on the amount of water in the system. As the amount of perennial water increases, the more compressed become the tiers. Ever-wet climates have very shallow tiering where all tiers are compressed to the paleosurface.