PALEOENVIRONMENTAL RECONSTRUCTION OF THE MIDDLE MIOCENE HONDA GROUP (LA VENTA FAUNA) OF COLOMBIA USING STABLE ISOTOPE PROXIES

The Neogene history of the Neotropics presents a dynamic story, including major climatic, environmental, and biological events such as the closure of the Central American Seaway, the uplift of the Andes, and the Great American Biotic Interchange. While these events have been the subject of much interest and study, major questions remain regarding the terrestrial climate and ecosystem structure of northern South America during this interval. We present carbon and oxygen stable isotope records from the uppermost La Victoria through the Baraya (lower) member of the Villavieja Formations from the Mid-Miocene Honda Group in Colombia, including 1) δ¹⁸O (PO₄, CO₃) and δ¹³C (CO₃) of mammalian bioapatite, 2) δ¹⁸O and δ¹³C (CO₃) of pedogenic carbonates, and 3) δ¹⁸O (PO₄) of fish teeth.

The Mid-Miocene ecological structure of the region was affected by the climate changes related to both global trends and the early stages of Andean and Central American uplift, but the details of the extent, timing, and character of these effects has not yet been resolved. A combination of δ¹⁸O (PO₄) measurements from endotherm (mammalian) and ectotherm (fish) bioapatite enable mean annual temperature (MAT) estimates. Our data indicate MAT between 30-34°C. These reconstructions are sensitive to the model parameterization; however, independent lines of evidence can help to more firmly resolve these parameters. δ¹⁸O (PO₄) is similar between the lowermost and uppermost sites sampled in the sequence, which suggests that MAT was stable for the Honda Group over this interval.

Seasonality is another very important climate factor in terrestrial ecosystems, as the same MAT and mean annual precipitation (MAP) can result in both grasslands and rainforests depending on the amount of seasonal variation. Serial sampling of mammalian tooth enamel provides a useful record of seasonal variability. δ¹⁸O shows very little variation along the length of the mammal teeth, which indicates a climate low in variation in both temperature and the amount of precipitation. δ¹³C indicates that the diets of the large mammalian herbivores were comprised of plants from a somewhat open, but humid, vegetation structure. These data help to fill gaps in our knowledge of low latitude continental paleoclimate.