21-4 The Paleogene Planktonic Foraminiferal Diversification: Structure & Forcing Factors

Session: Insights from Microfossils and Their Modern Analogs: From Traditional to Emerging Approaches

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Identification of factors responsible for biotic diversification across deep time requires access to high-resolution, globally representative and taxonomically up-to-date species-richness data. These criteria can be met by the fossil records of many microfossil groups. As part of a larger study of planktonic foraminiferal evolutionary history, the Paleogene interval represents an intriguing example data-analysis strategies that could be applied to, and results that could be obtained for, other organismal groups and time intervals. Drawing on data from the Neptune and Triton databases, species-richness patterns from 105 deep-sea cores, representing all major ocean basins, were assembled and updated taxonomically. These core-specific data were then compared to infer the most well-supported global sequence of species occurrences using the sCONOP approach. This analysis yielded an average temporal resolution for taxonomic occurrences of c. 97.8 kyr. The overall Paleogene planktonic foraminiferal richness pattern exhibited an Early Paleocene peak, a sustained radiation throughout the Late Paleocene, an Early Eocene plateau, a Middle Eocene radiation, and a two-phase extinction from the Middle Eocene through the Oligocene, interrupted by a sustained, early Oligocene radiation. Factor analysis of species-richness histories indicated this pattern reflects the rise and fall of four polyphyletic component faunas: (1.) disappearance of post-K/Pg "Cretaceous" taxa, (2.) an early Eocene Morozovella/Globanomalina-dominated fauna, (3.) a late Eocene Globigerinatheka/Hantkenina/Turborotalia-dominated fauna, and (4.) an Oligocene Dentoglobigerina/Paragloborotalia/Globoturborotalia-dominated fauna with the species-rich genera Acarinina and Subbotina being present more-or-less continuously through the interval. These Paleogene planktonic foraminiferal component faunas are reminiscent of Sepkoski’s Phanerozoic “evolutionary” faunas. While this overall diversification pattern does not appear associated closely with any major Paleogene oceanographic or climate event, it does exhibit a statistically significant negative correlation with global δ¹⁸O data, but not with global δ¹³C data. More interestingly though, statistically, significant associations with global δ¹⁸O and δ¹³C data are present for each component fauna where their moderately positive/negative polarities switch between faunas 1 & 2 and faunas 3 & 4. These results suggest (i.) species richness data often have an informative subsidiary structure, (ii.) different component faunas appear to be associated with different physical driving-factor proxies in different ways and (iii.) temperature/precipitation and productivity/carbon-cycling factors alone cannot explain the diversification dynamics of Paleogene planktonic foraminifera fully.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6335

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