Abstract

GUZZY-ARREDONDO, Gabriela Sara et al. High-temperature dolomite in the Lower Cretaceous Cupido Formation, Bustamante Canyon, northeast Mexico: petrologic, geochemical and microthermometric constraints. Rev. mex. cienc. geol [online]. 2007, vol.24, n.2, pp.131-149. ISSN 2007-2902.

The Lower Cretaceous Cupido Formation, a carbonate system developed in northeastern Mexico, like many ancient carbonate platforms contains numerous dolomite bodies. These diagenetic features are particularly -well exposed at Bustamante Canyon (Nuevo Leon State) -where the Cupido Formation crops out from base to top along 6 km. Dolomitization affected practically all fades and crosscuts bedding planes; dolomite bodies are irregular in outer and margin platform fades and tabular/subhorizontal in inner platform fades. Most dolomite is replacive and also occurs as cement in small amounts. Crystal shape of replacement dolomite varies from nonplanar, planar-s toplanar-e, whereas the dolomite cement consists mostly of saddle dolomite. Dolomite is nonferroan and shows dull red luminescence, its ¹⁸ O_PDB varies from -4.2 to -6.4‰ and its ¹³C_PDB from 1.8 to 3.4‰. ⁸⁷Sr / ⁸⁶Sr ratios of replacement dolomite vary from 0.70754 to 0.70770. Homogenization temperatures in dolomite from fluid inclusion analysis range from 190 °C to 200 °C and are interpreted as the minimum temperatures for the dolomite formation. Petrographic data, geometries and distribution of dolomite bodies, microthermometric results from fluid inclusions and geochemical information suggest that the dolomitization occurred under deep-burial diagenetic conditions. Similar homogenization temperatures were determined in dolomite and post-dolomite calcite cement of the Cupido Formation from southern locations including Potrero Chico and Potrero Minas Viejas. The high temperatures recorded in the Cupido Formation dolomites are the result of a regional thermal anomaly developed probably around salt structures. ⁸⁷Sr / ⁸⁶ values, oxygen stable isotopes, and trace element composition of dolomite suggest that the dolomitizing fluid was perhaps a hot mixture of formation water (modified sea water) of the Cupido Formation and brines derived from the updip La Virgen Formation, a carbonate-evaporite succession equivalent in age to the Cupido Formation. Dolomite distribution was apparently not controlled by major tectonic features (e.g., faults orfractures); the dolomitizing fluid seems to have followed subhorizontal or lateral flowing circulating patterns controlled by the former porosity and permeability of the calcareous facies.

Keywords : dolomite; high-temperature; thermal anomaly; Cupido Formation; Lower Cretaceous.