26-5 Using δ18O composition of a modern microvertebrate assemblage to assess spatial resolution of the fossil record

Session: Interdisciplinary Paleontology: New approaches to solving complex paleontological problems (Posters)

Poster Booth No.: 33

Presenting Author:

Remilla Olivola

Authors:

Olivola, Remilla L.¹, Moore, Jason Richard², Redman, Cory M.³, Atudorei, Viorel N.⁴

(1) University of New Mexico, Earth and Planetary Science, Albuquerque, New Mexico, USA, (2) University of New Mexico, Honors College, Albuquerque, NM, , (3) Grand Rapids Public Museum, Grand Rapids, Michigan, USA, (4) Univ New Mexico, Earth and Planetary Sciences, Albuquerque, NM, ,

Abstract:

The degree of temporal and spatial averaging in terrestrial fossil assemblages has proven frustratingly difficult to assess due, in part at least, to the absence of direct modern analogs for many modes of preservation. A major complexity this introduces is uncertainty about whether the fossil record is recording ecological data (low temporal and spatial averaging), or is more akin to evolutionary data (high temporal and spatial averaging), or some combination. Here we hope to begin to address some of these questions for terrestrial microvertebrate assemblages using isotopic data gathered from what we believe to be the first modern fluvial microsite, discovered recently from the Pilcomayo Megafan in Pozo Hondo, western Paraguay. Variations in the ratio of δ18O, driven by gradual changes in precipitation across the land surface (becoming lighter to the west) allow us to assess the spatial resolution of different types of vertebrates and invertebrates in this microsite. Higher variance in isotopic composition of the terrestrial portion of the Pilcomayo assemblage will correlate with higher spatial averaging. In this preliminary study we have measured the oxygen isotope composition from bone carbonate of 10 microvertebrate samples from the Pozo Hondo assemblage, and from 8 local water samples from both river- and precipitation-fed sources across the Pilcomayo Fan. These preliminary data will allow us to ascertain the range of variation in the oxygen isotopic composition of the modern microvertebrate assemblage, and we can compare this range to similar data from ancient microvertebrate assemblages. We will also be able to assess how closely these compositions match the compositions of the water sources from which the bone carbonate is drawn. This comparison will provide a first test of whether the environment in which the microvertebrates resided prior to death is close to where they were deposited or not. Furthermore, if the range of isotope ratio measurements of these modern microvertebrates are similar to those of ancient assemblages, it implies that the preservation of these deep time assemblages will likely be similar to that of our modern data, strengthening its use as an analog. We also aim to assess the degree of short-term time averaging in the assemblage using low-background gamma spectroscopy for 137Cs.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4, 2026

doi: 10.1130/abs/2026RM-14763

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