CALCARENITE PROVENANCE BY STABLE ISOTOPE GEOCHEMISTRY

Traditional petrographic methods of provenance analysis are of limited applicability to calcarenites, for which they yield results of low resolution due to the difficulty of linking carbonate detritus to specific source units. Given the large secular variations in marine carbonates' δ¹³C and δ¹⁸O over the Phanerozoic, the provenance of calcarenites derived from such source units may be resolvable to a higher precision by the use of these ratios as provenance indicators. While this is potentially a powerful tool, it is unclear whether the unstable carbonate clasts will retain the isotopic signatures of their sources through weathering, transport, and diagenesis. We test the efficacy of this provenance method by analyzing the basin-fill of the southeastern Ebro Basin in northeastern Spain, a foreland basin succession composed largely of calcarenites and carbonate-clast conglomerates derived from a Mesozoic carbonate platform succession in the nearby Catalán Coastal Ranges. δ¹³C and δ¹⁸O were determined by gas source mass spectrometry for a representative suite of source rocks, whole-rock sandstone samples from throughout the succession, as well as single clasts associated with several conglomerate and sandstone units. In addition, abundances of certain elements (Mn, Sr) were determined by ICP-AES for all whole-rock and source samples. We find that our whole-rock basin-fill samples and source samples differ only insignificantly in Mn and Sr concentrations, indicating minimal differential chemical alteration between the two. Our basin succession's isotopic compositions can all be realistically created by a mixture of differing proportions of source units, with at least one transition among differing sources apparent. The development of this new procedure for determining calcarenite provenance by stable isotopic ratios will allow for the analysis of exhumational histories in carbonate-rich regions previously inaccessible to provenance studies.