Strontium isotope (87Sr/86Sr) stratigraphy from the Coalcomana–Caprinuloidea rudist assemblage in the Greater Antilles (Puerto Rico, Dominican Republic and Jamaica)

Abstract

The stratigraphic range of the Coalcomana–Caprinuloidea rudist assemblage from Puerto Rico, the Dominican Republic and Jamaica has been revised based on numerical ages derived from strontium isotope (87Sr/86Sr) analyses of the calcitic outer shell of requieniid rudists. The extent of diagenetic alteration was assessed by cathodoluminescence microscopy and trace element concentration analyses (Sr, Mg, Fe and Mn), and only the least altered shells were selected for the 87Sr/86Sr analyses. The 87Sr/86Sr analyses from all the analyzed Antillean rudists resulted in average ages close to the Aptian/Albian boundary (112.56 Ma). These results show that the Antillean Coalcomana–Caprinuloidea rudist assemblage is correlative to the latest Aptian to early Albian Coalcomana interval zone from Texas and Mexico. There are, however, subtle differences in the orbitolinid foraminifer and rudist bivalve records of the Antillean Coalcomana–Caprinuloidea rudist assemblage that still need further revisions. In the Dominican Republic, for example, the orbitolinid fauna in the Central Cordillera include Coskinolinoides texanus (Keijzer), which is reported from middle Albian successions in Texas and Mexico. Moreover, the presence of primitive and advanced morphotypes of Caprinuloidea also suggests a possible bipartite division of the Coalcomana–Caprinuloidea rudist assemblage. Although the collected material from the localities with the foraminifer C. texanus and the advanced form of Caprinuloidea failed the preservation screening for 87Sr/86Sr analyses, we speculate about the possible extension of the Coalcomana–Caprinuloidea rudist assemblage from the Aptian/Albian boundary through the middle Albian.