Abstract The stable isotopic composition of pedogenic carbonate forms in equilibrium with environmental parameters and, thus, records palaeoenvironmental signals. The aims of this study are to synthesize available data on the stable isotopic composition of Quaternary pedogenic carbonates in calcareous parent materials of Iran and to decipher paleoenvironmental implications of the isotopic data for the country. Isotopic composition and microfabric of pedogenic carbonates in 18 pedons in both gravelly (calcareous alluvium in central Iran) and non-gravelly deposits (calcareous loess in northeastern Iran) have been investigated. The results indicate that in limestone-derived soils of central Iran in situ weathering of calcareous pebbles is a major source of Ca for genesis of the carbonates, and carbonate features consist of micritic calcite crystals. In the loessic soils of northeastern Iran, pedogenic carbonates show a dominance of nodule morphology and are classified as orthic nodules. Microfabric analysis reveals that most of the carbonates have not been altered by diagenetic processes, especially the Holocene carbonates, and are suitable for isotopic study and palaeoreconstructions. In limestone-derived soils within the arid region of central Iran, the δ 18 O and the δ 13 C values of carbonates indicate their enrichment due to the effects of evaporative water loss, a decline in plant density and the entrance of atmospheric CO 2 into the soils. In semi-arid ecosystems of central and northeastern Iran, most of the Holocene carbonates have formed in equilibrium with the ambient environment and are suitable for palaeoenvironmental reconstructions. The combination of carbon and oxygen isotopic data demonstrates the dominant role of climate in determining the δ 13 C values of carbonates. There is a strong relationship between the δ 13 C values of carbonates and rainfall, and between O isotopes and aridity indices. Stable isotope patterns in Holocene soils appear to provide data for models that can then be used to interpret the many localities where Pleistocene-aged soils and associated carbonate exist.

No particular division between soil science and geology existed as the two sciences emerged at the end of the Enlightenment. An institutional chasm emerged at the end of the nineteenth century, when soil-related research and mapping were placed within the U.S. Department of Agriculture—despite interesting efforts to combine the two led by Eugene Hilgard of Berkeley and John Wesley Powell of the U.S. Geological Survey. It is likely that the resulting institutional separation contributed to an academic divergence between the fields, an unfortunate division for both sciences as they contend with emerging problems of societal significance. Soil is the derma of the Earth. It has been suggested that the key attributes that define a soil's quality are its texture, mineralogy, and organically derived components. These are in turn controlled by the variables of lithology, climate, biota, topography, and landform age. The Earth is tectonically active, and thus stable, level landscapes are rare. The rates and processes by which soil is eroded from sloping lands, and replaced by the disruption of underlying rock into soil material contribute to the nature of the soil composition. James Hutton long ago recognized that these counteracting processes are largely in balance in many locations, leading to a local quasi-steady state, or in the terms of environmental vernacular: sustainability. Soils on hillslopes also have certain features characteristic of resilience, a feature where changes in the relative rates of either erosion or soil production produce feedbacks that in turn control the rate of the opposing process. The major geological force capable of disrupting the soil and geomorphic resilience is the array of human activities, particularly cultivation. Cultivation removes vegetative cover and changes the mechanisms of soil transport, which can then rapidly accelerate erosion beyond the capability of soil production. Cultivation also greatly changes the rates of organic matter inputs and losses, generally resulting in large reductions in the soil's store of C, N, and other elements associated with humus. Yet much remains to be understood about these and other problems. Multidisciplinary work involving the reconnection of the geosciences and soil science will result in more holistic means of sustainably managing a cultivated planet.

Mima mounds, often associated with vernal pools, have historically been shrouded in genetic uncertainty. Nevertheless, emerging from the array of explanations proposed, a biological mechanism for mound formation has steadily gained strength. We use innovations in remote sensing and geomorphic modeling to develop a new approach to evaluate the microtopography. Using a digital elevation model created from LIDAR (light detection and ranging) data, morphometric values—average mound diameters, heights, slopes, and curvatures—were calculated across an 18 km 2 sector of a mound-pool region that covers an ancient river terrace near Merced, California. The terrain information was applied to a sediment transport model to estimate mound erosion and swale deposition rates. The mean net erosion rate was 38 cm kyr −1 , using a diffusion coefficient of 50 cm 2 yr −1 . At steady state, erosion must be balanced by a restorative upslope transport, and this estimate of erosion is comparable to observed rates of sediment mounding via pocket gopher burrowing (61 cm kyr −1 ). These data suggest that bioturbation may play a dominant role in maintaining Mima mound terrain. LIDAR measurements were also used to develop a model that approximates the energy required for the formation of Mima mounds (shearing, pushing, and uplifting soil) and their maintenance (counteractions to erosion). This energy estimate was compared to estimates of energy available to gopher populations in the region. Our results indicate that gophers have ample energy to build typical Mima mounds in as little as 100 years, thus strongly supporting a biotic mechanism of Mima mound development and maintenance.