LATE PLIOCENE CHANGES IN MACRO AND MICROFAUNA COMMUNITY ASSOCIATION DUE TO NUTRIENT AVAILABILITY

This study documents changes in marine community diversity and abundance in response to a hypothesized decrease in SST and increase in nutrient availability. Foraminifera biostratigraphy confirmed a Late Pliocene date for the San Diego Formation, Tourmaline Surf Park, San Diego County, CA location and samples were collected from 9 fossil beds. Specimens were identified to the species level and diversity and abundance were calculated. While diversity declined through time, abundance levels varied sporadically. To determine the variables controlling changes in diversity and abundance, we tracked SST, via stable isotope analysis, and nutrient availability, via Ba/Ca ratios calculated through Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). SST decreased during this interval, while nutrient availability increased. NMDS, clustering analysis, and ANOSIM were used to statistically determine differences between the San Diego Formation Pliocene fossil beds and known Pleistocene fossil sites in Orange and Los Angeles Counties. The statistical results confirm that there are major differences between the Pliocene and Pleistocene horizons.