219 Paleontology, Diversity, Extinction, Origination (Posters)
Tuesday, 21 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1
Environmental Impacts on Encruster Abundance and Diversity: A Case Study from the Neogene San Joaquin Seaway of Central California
Paper number: 219-13
Program: Technical Sessions
Time: 10:45 AM – 11:00 AM
Authors
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Kayli StoweUniversity of California Berkeley, Berkeley, CA
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Lisa WhiteUniversity of California, Berkeley, Museum of Paleontology, Berkeley, CA
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Seth FinneganUC Berkeley Integrative Biology, Berkeley, CA
Abstract
Encrusting organisms are an important but often understudied component of benthic communities, and their fossil record can provide valuable insights into environmental conditions and biotic interactions through time. Many encrusters are sensitive to environmental factors such as salinity, and the density and diversity of encrusters may help to constrain changes in salinity when other proxies are not available. The San Joaquin Seaway, a Neogene continental sea in the San Joaquin Basin of central California, provides an ideal system to study the relationship between encrusters and salinity in the fossil record due to its limited geographic extent and a spatially and temporally dynamic salinity gradient reflecting varying inputs from Sierran freshwater drainage and the Pacific Ocean. From the Late Miocene through the Pliocene the connection between the Pacific Ocean and the San Joaquin Basin became gradually more restricted by a combination of tectonic and eustatic changes, leading to a progression from open marine to brackish to freshwater conditions. This long-term environmental transition is recorded by a thick sequence of very fossiliferous rocks that outcrop in the Kettleman Hills anticline, consisting in decreasing order age of the Etchegoin, San Joaquin, and Tulare formations.
Mollusc shells from Kettleman Hills collections housed in the University of California Museum of Paleontology were studied to document the distribution, density, and diversity of shell encrusters. Specimens were grouped by locality and biozone. The overall encruster presence observed on the mollusc shells is fairly consistent between the Etchegoin and the lower San Joaquin formations, but encruster presence increases in the mid to upper San Joaquin Formation. In overlying San Joaquin formation biozones the presence of encrusters again drops, and encrusters are nearly absent in the Tulare Formation. Specific encruster groups show varying temporal patterns, potentially linked to variation in salinity tolerance or sensitivity to other environmental conditions. Future work will incorporate insights from living relatives and potentially stable isotope measurements to better understand the factors influencing the distribution and density of shell encrusters in the Kettleman Hills sequence.
Geological Society of America Abstracts with Programs. Vol. 57, No. 6
doi: 10.1130/abs/2025AM-414201
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