The undisclosed paleoclimatic record of northern mesoamerica: A pedostratigraphic approach for environmental reconstruction

Abstract

This article presents the results of a research on paleosols formation conditions in the Aguascalientes Valley, northern Mesoamerica, where paleoenvironmental reconstructions have been scarce. Records of environmental and climatic changes, as well as the alteration of the landscape are expressed in the memory of the soil. Soil micromorphology is the most efficient method to identify these changes. In paleosols, micromorphological features reflecting a certain soil forming process can be related to environments in which those processes took place. Paleoenvironmental reconstruction of the region consisted in identifying pedofeatures and other present soil attributes, grouping features into pedogenic facies under constant environmental conditions, examining the groundmass in order to detect features caused by erosion or sedimentation, and finally establishing a hierarchy between the different pedogenic facies, including erosional and sedimentary features if necessary. Specific statistical data analysis disclosed stratigraphical relationships. The results we obtained, such as illuvial clay coatings, redoximorphic nodules, and hypocoatings, revealed the most representative pedofeatures that developed under humid climate. Under a semiarid climate, representative pedofeatures that were revealed included micritic coatings and hypocoatings. A paleosol with ferruginous nodules and hypocoatings in groundmass, and at least one phase of dusty and high-birefringence yellow clay illuviation is proposed as stratigraphic marker for this area of the Aguascalientes Valley. Evidence indicates the sequence of events in the area was: (i) a large period of humid climate; (ii) a short period of climate change, from humid to semiarid, followed by subhumid; and (iii) a large period of semiarid climate, including the current one. The paleosols of the Aguascalientes Valley to a large extent preserve major trends in history and provide further evidence to define the 11 phases of stability (pedogenesis) in 8 cycles and to detect the interlayer phases of instability (sediment transport/deposition).