Chemostratigraphic correlation of Neoproterozoic successions in South America

Abstract

The Neoproterozoic successions of South America largely accumulated during extensional events associated with the breakup of Rodinia. These units are preserved as thick carbonate and siliciclastic strata in epicontinental seaways and shallow marine environments on passive cratonal margins, which have been intensely deformed in mobile belts surrounding the craton. Volcaniclastic and siliciclastic materials are associated with some of the marginal fold belts. Three mega-sequences are represented in the cratonal area: glaciogenic, carbonate and molasse. At least two transgressive-regressive sea level cycles occurred during the evolution of the carbonate mega-sequence, which lies above iron-cemented glacio-marine diamictite of probable Sturtian age. We report high resolution carbon, oxygen, strontium and sulfur isotope trends from analyses of well-preserved sample sets and use principally strontium and carbon isotopes from the best preserved samples in concert with lithostratigraphic and biostratigraphic observations to provide detailed correlations of the South American Neoproterozoic successions. Lead–zinc deposits, some of which with important metal reserves seem to be restricted to the Sturtian carbonate succession and associated with a sequence boundary at the end of the first transgressive–regressive cycle. Phosphate deposits are found in both Sturtian and Varangerian/Marinoan carbonate successions, above glaciogenic sequences.