Clumped isotopes in Pennsylvanian brachiopods and macropore cements: Timing, temperature, and tectonic drivers of cementation

Carbonate clumped isotope (Δ47) thermometry can provide unique records of burial temperature and changes in fluid chemistry during the evolution of sedimentary basins. Here, we unravel the diagenetic, cementation, and thermal history of the Late Pennsylvanian Madera Group at contrasting localities in north-central New Mexico, USA, using Δ47 microanalysis of articulated brachiopod shells and a series of internal macropore calcitic cements. Brachiopod shells yield Δ47 temperatures [T(Δ47)] of 26–46 °C and calculated δ18OH2O values of −1.8‰ to 2.8‰ Vienna standard mean ocean water (VSMOW), whereas calcitic macropore cements reveal T(Δ47) values ranging from 44 °C to 85 °C and δ18OH2O values of 1.4‰–3.6‰ VSMOW. Elevated T(Δ47) values for brachiopod shells and cements from the Jemez Springs (JS) locality, compared with the Manzano Mountain (MM) brachiopod shells (~45 °C vs. ~28 °C), are consistent with clumped isotope reordering associated with geothermal heating in the JS area. In contrast, the δ18OH2O-T(Δ47) trend for the MM cements match that of formation waters in US petroleum basins. T(Δ47) values, combined with burial history, suggest regional cementation events at ca. 166 Ma and ca. 18 Ma. These correspond to the opening of the Atlantic Ocean or the Cordilleran Orogeny, and volcanism associated with the Rio Grande Rift, respectively. Application of a Δ47 reordering model-based Monte Carlo simulation and a time-temperature sensitivity test to the JS shells and cements yields temperatures of ≥135 °C in response to geothermal heating associated with the Rio Grande Rift.