ABSTRACT

The origin of terra rossa and its relationship with its underlying carbonate rocks pose long-standing and controversial questions. This study focuses on one 5.4 m thick terra rossa profile on dolomite. The authors examined the quartz content, size distribution of quartz grains, mineral composition, surface micro-texture and crystal morphology of quartz, oxygen isotope ratios of quartz, and other tracers in the terra rossa and underlying dolomite to determine the derivation of terra rossa. The results indicate that terra rossa in the Dashandong profile on the Yunnan-Guizhou Plateau, China, is an in situ weathering solum. The terra rossa originates mostly from insoluble residues of the parent dolomite. The debris minerals (quartz and feldspar) derive completely from the parent dolomite. The clay minerals, and Al, Fe and Mn oxides and hydroxides likely have three origins. One portion derives from insoluble residues of the parent dolomite. A second portion converts from primary minerals in the parent dolomite. The last contribution comes from authigenic minerals from aqueous solutes transported by the water cycle. Authigenic minerals constitute the main components of the terra rossa. During weathering processes, the dolomite weathering functions as a “trap” against the escape of in situ insoluble residues and external aqueous solutes by means of poly-genetic chemical and physical barriers.