『Abstract
　Poorly documented yet spectacularly thick and extensive outcrops of calcrete hardpan occur on gneiss in the semiarid region of Coimbatore, South India. The hardpan caps a series of residual plateaux forming the present-day continental divide and grades into large expanses of Vertisols. Characteristic calcrete and Vertisol profiles were logged along toposequences and sampled for macro- and micromorphological study, and for chemical and mineralogical composition. strontium isotopic analyses revealed that the calcrete is derived from in situ weathering of Ca-bearing primary minerals of the saprolite, which is rich in ankerite, Ca-amphiboles and Ca-plagioclase. The macroscale analysis revealed a range of facies developed within the gneiss saprolite, but in terms of relative chronology the nodular hardpan has the longest history. Two evolutionary pathways leading to nodular hardpan formation have been established. The first occurs entirely within a vadose environment, whereas the second begins within a phreatic environment before continuing to develop in vadose conditions. The ability to identify and map these generic categories of calcrete constitutes a potential tool for reconstructing paleotopography and paleogroundwater levels. The bedrock-weathering-derived nodular hardpan is blanketed by a laminar facies that correlates with an eolian event with marine Sr signatures. This suggests influx of Ca dust from the Arabian Sea continental shelf during a Pleistocene sea-level low-stand. It defines an important benchmark in the chronology of the area and highlights the potential antiquity of the thick calcrete profiles.

Keywords: Calcrete; Chemical weathering; Petrography; Isotopic tracing; Landscape chronology; Groundwater; Quaternary; India』

1. Introduction
2. Present-day environmental setting
3. Materials and methods
4. Results
　4.1. Calcrete diversity at topographic scale
　4.2. Facies characteristics of the calcrete at exposure scale
　　4.2.1. Hardpan
　　4.2.2. Laminar facies
　　4.2.3. Massive facies
　　4.2.4. Brecciated facies
　　4.2.5. Nodular facies
　　4.2.6. Coalescent nodules (‘popcorn’ or ‘honeycomb’ horizon)
　　4.2.7. Isolated nodules
　　4.2.8. Joints, cracks and their fillings
　4.3. Stratigraphic relations between the different facies
　　4.3.1. Distribution of carbonate in the weathering profile
　4.4. Chemical and mineralogical characterization
　　4.4.1. Mineralogy
　　4.4.2. Chemistry
　4.5. Micromorphological features
　　4.5.1. Type I laminar facies (hardpan)
　　4.5.2. Brecciated facies (hardpan)
　　4.5.3. Massive facies (hardpan)
　　4.5.4. Nodular facies (hardpan)
5. Discussion
　5.1. Pathways of nodular hardpan genesis: an observation-based evolutionary model
　　5.1.1. Degradational sequence of nodular hardpan development
　　5.1.2. Accretionary sequence of nodular hardpan development
　　5.1.3. Model implications
　5.2. Pathways of laminar horizon genesis
　5.3. Calcium provenance: local origin vs. allochthonous input
6. Conclusions
Acknowledgements
References