Paleosol occurrences along the Archean-Proterozoic contact in the Aravalli craton, NW India

The Archean-Proterozoic contact (APC) comprises a large scale folded surface around Udaipur in NW India. The APC is exposed on both eastern and western flanks of a synclinorium formed during thick skinned thrusting of the Archean basement and the Paleoproterozoic cover units. Paleosol occurrences on both the limbs of this structure imply an originally continuous paleoweathering horizon and not individual pockets of paleosol as seen today. Preservation of paleosol sections along the Archean-Proterozoic interface in the Aravalli craton is strongly controlled by the structural grain. Complete paleosol sections are recognized in the eastern flank of the Udaipur synclinorium in low strain regions with respect to the regional F1 and F2 folding. In this sector the Tulsi Namla paleosol section represents an ancient lateritic weathering profile with an iron depleted pallid lower zone (lithomarge) and an iron enriched upper zone (mottled zone to ferricrete). Original kaolinite in the saprolite and pallid zone has been transformed into kyanite during metamorphism and subsequently to white mica during retrograde overprint, while Fe rich clay and goethite were probably the primary minerals for the chloritoid and hematite which now constitute the upper zone. At the western flank of the synclinorium the contact is heavily sheared and Archean basement and Proterozoic units show interfingering on a small scale. Here, the paleosol sections are incomplete. The weathering interval can be inferred by the stabilization of the craton at similar to 2.5 Ga and deposition of rift related sequences of the Aravalli basin (Delwara formation) at similar to 2.15 Ga. The Udaipur paleosols, especially in the eastern flank, represent the most complete Archean-Paleoproterozoic paleosol sections in India. (C) 2012 Elsevier B.V. All rights reserved.