The carbonate-derived δ¹³C and δ¹⁸O records as proxies for Mid-Carboniferous climate in northwestern Mexico

The Paleozoic climate variations are preserved in δ ¹³ C and δ ¹⁸ O records from marine carbonate rocks. These records can be modified by diagenesis derived from the environmental processes of a particular region. The simultaneous evaluation of δ ¹³ C _carb and δ ¹⁸ O _carb can help to identify alterations and to improve environmental interpretations. The Late Paleozoic Ice Age began during the Carboniferous and coincided with the early stages of the Pangea assembly. The paleoceanographic and paleoclimatic changes affected the region of central Sonora, Mexico, at the westernmost embayment of the Rheic Ocean. To explore the relationship between local environmental processes and the early diagenesis imprint in the isotopic records, we estimate the δ ¹³ C _carb and δ ¹⁸ O _carb values in 54 rock samples from Sonora. 38 samples were from the Sierra Agua Verde region, and 16 samples from the Cerro Las Rastras southern area. The early diagenetic imprint of the environmental variations suggests periods characterized by: (a) lower δ ¹⁸ O _carb values which indicates heavy rains and/or riverine discharges; (b) higher δ ¹⁸ O _carb values associated with droughts; (c) lower δ ¹³ C _carb values related to enhanced upwellings and/or riverine discharges; and (d) higher δ ¹³ C _carb values, reflecting a high productivity period. The δ ¹³ C _carb and δ ¹⁸ O _carb records from central Sonora rocks are consistent with those reported in the western USA, a region closely correlated with NW Mexico. The results of this study offer an approximation of how the environmental conditions were during the MPB in the westernmost Rheic Ocean area, and how they were related to global climatology.