101-13 Terrestrial Paleotemperature and Phytolith Records Reveal Neotropical Mid to Late Miocene Cooling, Increased Humidity, and Non-Analog Forests

Session: Paleontology, Biogeography/Biostratigraphy & Phylogenetic/Morphological Patterns

Presenting Author:

Elena Stiles

Authors:

Stiles, Elena¹, Huntington, Katharine W.², Garzione, Carmala N.³, Strömberg, Caroline A.E.⁴, Montes, Camilo⁵, Escobar, Jaime⁶, Schauer, Andrew⁷, Wang, Zhennan⁸, Vanegas, Andrés Felipe⁹, Perdomo, César¹⁰, Góngora Blanco, Daniel Esteban¹¹, Li, Lin¹², Moreno, Federico¹³, Jaramillo, Carlos¹⁴, López Camacho, Rene¹⁵

Abstract:

For over a century, the mid to late Miocene vertebrate faunas of La Venta, Colombia, have been central to numerous studies and have served as key sources for paleoenvironmental reconstructions used to inform global climate and biosphere models. However, these paleoenvironmental interpretations are based on the vertebrate assemblages themselves rather than direct paleoclimate or paleobotanical evidence, which remains very limited in lower latitude terrestrial settings. This is problematic because as the Miocene receives increasing attention as a potential analog for future climate change, tropical environments on land are underrepresented and their long-term ecological responses to climate change remains poorly constrained. Here, we test previous paleoenvironmental reconstructions of La Venta and present one of the first terrestrial paleotemperature records from the Neotropics by coupling clumped isotope paleothermometry with phytolith (plant opaline biosilica) analysis in the mid-late Miocene La Ventan deposits (La Victoria and Villavieja formations) and overlying Gigante Formation, together spanning between 14 and 7 million years ago. Mean pedogenic carbonate temperatures decline from the middle Miocene La Victoria (42 ± 10 ºC) and Villavieja (32 ± 8 ºC) formations to the late Miocene Gigante Formation (21± 8 ºC), representing a substantial decline in soil temperature from the middle to late Miocene with respective propagated errors. This apparent cooling is likely amplified by increasingly dense vegetation and higher humidity interpreted from decreasing δ¹³C values in soil-respired CO₂ and meteoric water δ¹⁸O values. Together, these interpretations contrast with model predictions of widespread aridification in South America during this time. Phytolith assemblages from the late Miocene Gigante Formation indicate closed-canopy forests but differ from those of modern xerophytic and humid tropical vegetation, potentially reflecting non-analog biotic communities shaped by Miocene biogeography and climate. These findings provide one of the first combined climate and vegetation records from tropical South America between the middle and late Miocene and highlight the importance of regional terrestrial archives for testing model predictions towards and understanding of ecosystem responses to long-term climate change.

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

doi: 10.1130/abs/2025AM-9779

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