Development of a Pleistocene calcrete over a sequence of marine terraces at Tongoy (north-central Chile) and its paleoenvironmental implications.

摘要

The importance of the Norte Chico region in north-central Chile has long been recognized for the paleoclimates recorded in its soils. This area lies in an extreme climate gradient between the hyper-arid Atacama Desert in the north and a Mediterranean climate in the south, which has made it very sensitive to past climate changes. Nevertheless, few paleoclimate studies have been undertaken in the region, and these were mostly concentrated on the Holocene. We studied Pleistocene climate changes recorded in soils that formed over a series of marine terraces near Tongoy about 60 km south of La Serena. The calcrete and soil development took place on four marine terraces associated with Marine Isotope Stages MIS 11, MIS 7e, MIS 5e, and MIS 1. The different types of calcretes that developed on the three oldest terraces containing calcareous material indicate that they developed during different periods, and that climatic conditions favorable for the development of these soils existed in the area at least from MIS 11 (412 ka) until post-MIS 5e (125 ka). The calcrete horizons show well-defined development stages recording cyclic climate changes varying between arid and more humid during the late Pleistocene. These climate changes recorded in the Tongoy soils are reflected by sedimentological, geomorphological and pedogenic processes. Climate cycles have only been recorded previously for the post-MIS 5e stage in the area, this study being the first to include climate variations reaching MIS 11.