“Comment on: Genesis of subtropical soils with stony horizons in NE Argentina: Autochthony and polygenesis”. H. Morras, L. Moretti, G. Piccolo, W. Zech. Quaternary International (2009), vol. 196 (1-2): 137-159”. Forum Comment.

Abstract

We feel it necessary to comment the paper of Morras et al. (2009) in this journal. The authors presented there a re-interpretation about the origin of the “red materials-soils” outcropping in the Province of Misiones, northeastern Argentina. Particularly, they discussed the ‘‘tropical loess’’ theory (Iriondo, 1996; Iriondo and Kröhling, 1997, 2007, 2008 and Iriondo et al., 1998) focusing their research on the premise that all the materials covering the landscape of Misiones are a product of the weathering of the K-basalt and a subsequent pedogenesis, mainly using a pedological criteria. With specific regard to the province of Misiones, the origin of the red materials was originally investigated by as (Iriondo and Kröhling, 1997, 2008), also our works are the first in the Quaternary of northeastern Argentina. From the first part of the paper, the authors question the validity of that papers largely on the basis of all of their “complex outcropping profiles” are a solum (with thicknesses of several meters above weathered basalt) and discussed the autochthonous or allochthonous origin of materials based on the study of “stone lines”, ‘‘ferruginous nodular horizons’, ‘‘siliceous horizons’’ and ‘‘blocky structured horizons’’ (sic). Especially for the origin of surface material above the ‘‘stone lines’’ they failed to make a comprehensive study. The authors seek to discredit geology (mainly physical stratigraphy and sedimentology) as the main basis for Quaternary studies of the tropical-subtropical regions. Their approach adopted is, in essence, a reinterpretation of the data and ideas presented in our original papers, with the addition of data not very suitable for discussing in proof the theme. In fact, the statements of Morras et al. (2009) misrepresent our geological descriptions of the region and misquote our work resulting from examine every natural outcrop at the region (also extending to the southern Brazil and to the NW of Uruguay), and support varied sedimentological data (Iriondo and Kröhling, 2008). In conclusion, we believe that the investigators are incorrect in some of their assumptions or interpretations in this study. They dismisses our study with the ad hoc explanation that “all” the red earth of Misiones are soils (but may be the parent material of any soils); yet they uses no objective criteria, presents no representative sedimentological analyses and cites no field evidences to support this conclusion. In other words, the autochthony theory of Morras et al. (2009) of all red earths of Misiones lacked geological control. The validity of the data cited by the authors cannot be judged rigorously because the localization of samples and the selection of the profiles studied (clearly observed in the photographs included in their paper) are not convenient for discussing our theory. Until the geochemistry of the correct profiles and a detailed micromorphological and sedimentological data were accomplished and well understood the result will be remain dependent on the individual sampled profile (regolith or structured horizons or tropical loess).