Carbon Isotope Chemostratigraphy of the Mid-Cretaceous Escucha Formation in Spain

The mid-Cretaceous represents a time of dramatic changes in global systems. A thorough understanding of this time period is essential for placing these distinct paleoclimatic, tectonic, and paleontological events into context. The Ocean Anoxic Event (OAE) 1b and the associated carbon isotope excursions (CIEs) combined with biostratigraphy have proven to be an effective tool for correlation of this time period on a global scale. The study stratigraphic interval, the Escucha Formation in Northern Spain, contains one of the noteworthy Aptian-Albian fossil sites of Europe. Our research objective is three-fold: to provide a chemostratigraphic context to the Escucha Formation, to verify if there are CIEs correlative to those in the literature, and to identify what environmental changes may be associated with this time period.

This study develops a high-resolution organic carbon isotope survey of the lower Escucha Formation. We collected 170 samples at 50 to 100 cm intervals across 108 meters of section in Arino, Teruel, Spain and measured their carbon isotopic compositions. Their values ranged from --28.4 to --20.3‰. The results of this chemostratigraphic survey allow for a compelling correlation to three sub-events of OAE1b. The results place the bonebed, Ar-1, in the late Aptian and give a precise stratigraphic context to the Escucha Formation. This correlation increases our understanding of how terrestrial delta13C records are related to their marine counterparts via ocean-atmosphere interaction. We propose a method for understanding the mechanisms behind carbon isotope perturbations by measuring their relation to the standard normal curve.