Indicators for identifying aquic conditions in paleosols: First approximation

Abstract

Identifying paleosols with aquic conditions is essential for understanding the evolution and distribution of ancient wetland systems. Yet there are no guidelines for paleopedologists for writing field descriptions to target properties that indicate wetness. Here we provide field indicators for aquic conditions modified from the U.S. Soil Taxonomy based on organic materials, matrix color, and iron redoximorphic features. These field-based soil morphological properties have been correlated to numerous hydrological monitoring stations. The universal indicators presented here were developed from four of the eleven mineral soil orders and are the most conservative for identifying aquic conditions across paleosol types. If aquic conditions are not met with these indicators, others are provided for specific taxonomic orders where it is difficult to form or observe aquic indicators; for example, iron rich paleo-Oxisols. Strategies are provided to help separate paleosol properties that may be diagenetically altered from those representing environmental conditions during soil formation prior to burial. The aquic indicators were tested 102 paleosols showing that more than one-fourth were originally mis-identified. However, testing of a stratigraphic succession of two paleosol studies indicated that between 25 and 50 % failed to meet the interpretations of the original investigators. Testing also showed the difficulty of identifying aquic conditions in seasonally wet paleosols, but the indicators provide consistency in how those decisions were made. The aquic condition criteria may be applied to paleosols classified by any taxonomic scheme. This is a first approximation and will require further testing of the indicators provided here.