Neogene Shallow-marine Paleoenvironments and preliminary strontium isotope chro...

• Author(s): Kirby, Michael X. ; Jones, Douglas S. ; Ávila, Sérgio P.
• Date: 2007
• Persistent ID: http://hdl.handle.net/10400.3/817
• Origin: Repositório da Universidade dos Açores
• Subject(s): Fóssil; Neogene Shallow-Marine; Santa Maria Island (Azores); Preliminary Strontium Isotope Chronostratigraphy; Azores
• Document Type: Article
• Language: English

Description

The fossils of Santa Maria Island in the Azores archipelago represent one of the few shallow-marine communities of Neogene age between Europe and North America. Before the evolutionary and biogeographic implications of these fossils can be understood, however, their associated depositional environments and geologic ages must be determined. Here we present preliminary results from sedimentary facies analysis and strontium isotope chronostratigraphic analysis of sediments and fossils from two localities on Santa Maria Island that provide a window into shallow-marine environments and communities within the mid-Atlantic Ocean during the Neogene. Pedra-que-Pica on the southeastern corner of Santa Maria contains strata of fine-grained lithic calcarenite, coquina, and fine- to medium-grained lithic wacke that represent a regressive sequence from transition-zone to foreshore environments. The second locality at Pedreira do Campo on the southwestern-side of Santa Maria contains limestone and fine- to coarse-grained lithic arenite that represent a regressive sequence from shallow bank to shoreface-foreshore environments. Strontium isotopic results from Pedra-que-Pica and Pedreira do Campo indicate that these localities contain fossils that range from late Miocene to late Pliocene in age. Three molluscs collected from the coquina at Pedra-que-Pica have an average 87Sr/86Sr composition of 0.709018±0.000008 that represents an average estimated age of 5.51±0.21 Ma. Three pectinid bivalves collected from the limestone at Pedreira do Campo show a wide range in 87Sr/86Sr ratios, from 0.708885 to 0.709078, which represent estimated ages from 10.03 to 2.24 Ma, respectively. These results help to place the shallow-marine communities of Santa Maria Island into a geologic context that will aid our understanding of how these communities relate to the broader evolutionary and biogeographic history of the Atlantic basin during the Neogene.