Sedimentary calcium and magnesium carbonate minerals have recorded the evolution of life, climate, and CO₂ cycling for billions of years through their physical and chemical properties.  These largely depend on crystallization pathways related to fluid pH and supersaturation, biological processes, presence of additives and redox conditions.  As such, crystallization pathways define the properties of biominerals and abiotic carbonates that are used to reconstruct Earth’s history.

Crystallization pathways, often preserved in carbonate ultrastructures have been widely investigated for biominerals and bio-mediated calcium and Ca-Mg carbonates by using High-resolution Transmission Electron Microscopy (HRTEM).  Synchrotron micro-X-ray fluorescence facilitates trace element mapping highlighted heterogeneities in their distribution as related to fabrics. Nano and micro-scale investigations of biominerals and bio-mediated carbonates have revealed that they consist of crystalline, nanocrystalline and amorphous phases, which may co-exist in the same sample and influence the distribution of trace, minor and major elements. Critically, the clustering of nanoparticles is considered a marker of biotic Ca-Mg-carbonates, whereas monomer- by-monomer crystal growth seems to characterize abiotic minerals. However, HRTEM investigation of abiotic sabkha dolomicrite formed primarily by aggregation of nanoparticles as a response to fluctuating aqueous chemistry. Abiotic cave CaCO₃ minerals (speleothems), when observed by HRTEM also revealed that nanoparticle attachment is one of several crystallization pathways, that result in inter-and intracrystalline micro to nano-porosity and the formation of intracrystalline defects.   Critically, both inter- and intra-crystalline porosity and defects accommodate both organic macromolecules and inorganic colloids. The exploration of non-classical crystallization pathways, exemplified by particle attachment, explains the frequently observed non-equilibrium integration of trace elements. This phenomenon extends to the heterogeneous lateral distribution of both trace elements and organic molecules, providing insights into the intricate processes shaping the crystalline matrix.

Nano-scale observations further revealed that porosity follows crystallographic orientations, which leads to a hypothesis that sector zoning is responsible for lateral heterogeneity of organic and inorganic “impurities”. However, sector zoning largely stems from a classical monomer-by-monomer growth under pH and supersaturation ranges that are commonly lower than what expected for particle attachment. It is then plausible that local pH and supersaturation conditions as well as the presence of impurities result in changes in crystallization pathways. Nanoparticles participating in non-classical particle attachment may consist of amorphous calcium carbonate (ACC), whose uptake of trace elements differs from that of calcite. Transformation of ACC into calcite may ultimately result in an observed non-equilibrium partitioning of trace elements in the final phase. This phenomenon, in addition to the possibility that pores and crystal defects host impurities, suggests that multiple crystallization pathways explain kinetic effects that hinder a direct and constant link from proxy data to environmental parameters in carbonate archives of Earth’s history.

It is proposed that fabrics of abiotic carbonates, their ultrastructure and geochemistry should be granted the same level of investigation given to biominerals when interrogating their capability to accurately record climate (or environmental) change. Examples of how this can be achieved will be presented for case-studies including Triassic dolomicrite, Pleistocene subglacial carbonates from Antarctica and Holocene tropical stalagmites.

How to cite: Frisia, S.: Sedimentary carbonates: fabrics, ultrastructures and geochemistry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2710, https://doi.org/10.5194/egusphere-egu24-2710, 2024.

Taphonomy is a discipline dedicated to the analysis of the different processes that influence the mechanisms of fossilization, affecting both fossils and their environment. In this sense, this research is focused on the premortem and postmortem processes affecting animal bones found in archaeological sites. Studies related to human evolution can be approached from different perspectives, being paleontological analyses the best procedure for identifying ancestors through fossils. Paleo-environmental studies explore the past environment and climate, conditioning human evolution and adaptation. On the other hand, archaeological studies (the area of this research), examine the material culture and behaviour of ancient populations.

Sites can be exclusively paleontological, with no human intervention, or archaeological, with evidence of human activity. In the latter, bones may have been altered by humans, carnivores, or natural processes. In this context, taphonomy allows to classify the origin of this alteration, being even possible to define the intervention of several agents on the same animal, such as humans, carnivores, and rodents, and the order of such intervention.

Evidence of human intervention on animals from the past is found in the marks left when processing meat or marrow. The analysis of cut and percussion marks is used to reveal the applied tools and methods. The research here presented is based on the implementation of technologies such as photogrammetry and geometric morphometry to document these marks in a three-dimensional way. Machine learning, deep learning, and advanced statistics are then applied to answer specific questions. In particular, three main key questions about human behaviour in past populations have been addressed:

What tools were used to process animal meat, and were there any preferences in raw materials? Three-dimensional reconstructions are applied to identify the morphology of cut marks and, through repeated experiments, determine which materials, such as flint, quartz, or volcanic rock, were used in the past.

Which carnivores occupied the sites after they were abandoned by humans, and how does this affect the paleoecology? Tooth marks on bones are analysed to differentiate with high reliability which carnivore handled a bone, providing relevant information on the paleoecological implications depending on the specific carnivore.

How does trampling affect bones exposed at sites, and what relevant information does it provide? Through trampling analysis, it is possible to determine when this occurred, providing important data on how long the bones were exposed before burial and the degree of site disturbance.

All the previous lines of research enable to assess site integrity, identify the carnivores involved, and understand human behavioural strategies in the processing of animal carcasses.

How to cite: Maté González, M. Á.: New technologies applied to modelling taphonomic alterations of human origins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21896, https://doi.org/10.5194/egusphere-egu24-21896, 2024.