Bone diagenesis and stratigraphic implications from Pleistocene karst systems

Area of Science:

• Paleontology
• Geochemistry
• Materials Science

Background:

• Bone diagenesis significantly alters bone composition and structure post-burial.
• Understanding these diagenetic changes is crucial for accurate fossil classification and deposit formation analysis.
• Stratigraphic context is key to interpreting diagenetic pathways in bone material.

Purpose of the Study:

• To investigate bone diagenetic processes across a complete stratigraphic sequence at the Galería site, Sierra de Atapuerca.
• To evaluate the effectiveness of chemometric indices and machine learning algorithms for classifying bone diagenesis and stratigraphy.
• To elucidate the environmental conditions associated with different diagenetic pathways in bone apatite.

Main Methods:

• Combined X-ray diffraction with Rietveld refinement and infrared spectroscopy.
• Analysis of eleven chemometric indices related to bone components (phosphates, carbonates, organic phase).
• Application of nine machine learning algorithms for classification using apatite unit cell parameters and cell volume.

Main Results:

• Observed gradual shifts in apatite unit cell volume (531.9 to 526.1 ų), correlating with stratigraphic units (GII to GIV).
• Identified distinct diagenetic pathways: GII shows leaching and carbonate loss (acidic, wet environment), while GIII-GIV show F⁻ and CO₃ incorporation (alkaline, drier environment).
• Demonstrated changes in apatite structure chemistry, including F⁻ and OH⁻ variations, linked to dissolution-precipitation processes.

Conclusions:

• The study successfully developed classification models for bone diagenesis and stratigraphy using geochemical and machine learning approaches.
• Distinct burial environments were inferred based on the identified diagenetic pathways.
• The findings enhance the understanding of deposit formation dynamics and facilitate the recontextualization of fossil remains.