Carbon and oxygen isotope profiles across Meso-Neoproterozoic limestones from central Brazil:

We present carbon and oxygen isotopic data on carbonates along three profiles of the Neoproterozoic Bambuı ́ group in central Brazil. This unit covers an area of more than 300 000 km2 and comprises carbonate–silicliclastic sediments at the base that grade into siliciclastic sediments towards the top. The Bambuı ́ group overlies by unconformity the Paranoa ́ group, which consists mostly of siltstone, quartzite and minor limestone. The data presented here improve the stratigraphic correlation within the Bambuı ́ basin and show that it evolved in an environment significantly different from that of the Paranoa ́ basin. Our data show large fluctuations of d13CPDB in limestones from the Bambuı ́ Group (from 0.8 to 13.5‰) in all the three studied areas. Some of these fluctuations represent stratigraphic markers that can be used as a chronostratigraphic tool within a basin scale. This observation is relevant considering the lack of fossil record and other stratigraphic markers in Neoproterozoic sequences. We also present the first isotopic profiles along the Paranoá–Bambuı ́ transition, which shows that the d13CPDB values grade from 1.0 ‰ in the Paranoa ́ group, to 2.6 ‰ in the lower portion of the Bambuı ́ group, increasing up to 12 ‰ in the upper part of this unit. Based on our carbon isotope data, as well as other geological, mineralogical and Nd isotope studies, we argue that the sediments of the Paranoa ́ group were deposited on an open platform that was fully connected to the ocean. On the other hand, the sediments of the Bambuı ́ group were deposited in an epicontinental sea and during a tectonic inversion in a forelan