Overview

I am a geochemist interested especially in the use of biominerals formed by marine invertebrates to understand palaeoenvironments. My work fits into the themes of analytical geochemistry, modern analogue studies and proxy development, diagenesis, and palaeoenvironmental reconstruction. The ultimate goal of my work is to create reliable geochemical datasets that allow us to accurately reconstruct temperature, ocean chemistry and carbon cycle through time, and to determine how animals co-evolved with the planet. My work is multidisciplinary and I particularly enjoy learning from experts in related fields, allowing to conduct research that is of broad relevance for the Earth Science community and beyond.

You can find my publications here:

Clemens V. Ullmann - Google Scholar profile

Clemens V. Ullmann - Web of Science profile

Clemens V. Ullmann - Researchgate profile

Please feel free to reach out to me if you are interested in a research collaboration or in undertaking a research project under my guidance.

Analytical Geochemistry

My speciality is the use of quantitative analytical instrumentation to derive geochemical proxy information from biological calcite. This includes major and trace element concentrations, as well as traditional and non-traditional isotope systems. Over the years I have worked with various instruments, including ICP-OES, ICP-MS, TIMS, GS-IRMS and MC-ICP-MS and managed several analytical laboratories. At CUG (Wuhan) I am taking care of the Thermal Ionisation Mass Spectrometry (TIMS) facility housed at the State Key Laboratory of Geomicrobiology and Environmental Changes, Future City Campus.

Modern analogue studies and proxy development

Marine macrofossils are key to understanding Paleozoic and Mesozoic environments and are often used for geochemical analysis, but the understanding of isotopic and chemical composition of fossil shells is still comparatively limited. I am working on charting chemical fingerprints of shells of modern and extinct species and test which parameters control chemical and isotopic variability and broader chemical patterns in their calcite. This work has for instance looked into the chemistry of modern barnacles (Ullmann et al., 2018) and more recently the distribution of elements in brachiopod shells (Ullmann et al., 2026).

Diagenesis

No palaeoenvironmental study based on fossil geochemistry can be carried out without first assessing whether the analysed specimens are preserved well, but limited efforts have been undertaken in recent years to refine and update approaches to testing for fossil preservation. This is of particular relevance for novel geochemical tools which are often very vulnerable to shell alteration and contamination and thus require especially high confidence in the preservation of fossil material. I have been active in this field, summarising typical approaches to testing for preservation (Ullmann and Korte, 2015), giving recommendations for suitable sampling and analytical strategies for macrofossil calcite (Ullmann, 2024). I have also contributed to the understanding of Li isotope diagenesis (Ullmann et al., 2013), and proposed new tracers for alteration such as the variability of element/Ca ratios and co-variation of Mg/Ca with S/Ca ratios in brachiopod calcite (Ullmann et al., 2026).

Palaeoenvironmental reconstruction

An important benefit of macrofossil calcite is that its preservation can be tested with high confidence. However, animals that form this calcite are complex and geochemical indices encoded in fossils can therefore be complicated, for instance by so-called vital effects, but also by high-frequency changes in environmental conditions such as seasonality which can sometimes be resolved due to rapid secretion of the biological calcite. My contributions have led to a more refined understanding of the role of ecology in controlling geochemical signals in cephalopods (Ullmann et al., 2014) and brachiopods (Ullmann et al., 2020) and I am working on improvements in the reconstruction of past seawater chemistry (Ullmann et al., 2013).

In recent years I have been increasingly involved in supporting the creation of integrated stratigraphic schemes for the Early Jurassic, based on multiple stratigraphic techniques. This work has led to the creation of key datasets that can be used for global correlation of Early Jurassic strata, for instance for the Early Jurassic in the Cardigan Bay Basin, UK (Ullmann et al., 2022) and Hettangian Stage in the Cheshire Basin, UK (Ullmann et al., 2026).