I left industry to undertake a PhD Thesis in Carbonate Sedimentology at the University of Barcelona (Spain) which was funded by REPSOL Exploration (2009-2013). During this project, I gained in depth understanding of the basin-scale mechanisms controlling the macro-morphologies and facies architecture of the Triassic microbial carbonates in the Catalan Basin (Spain). I established how the inter-relationship between sequence stratigraphy, basin configuration and paleoenvironmental conditions controlled the distribution of these deposits and the overall carbonate platform architecture. The findings allowed me, for the first time, to predict the sequential framework of these microbial carbonate accumulations (stromatolites and thombolites), and develop a refined approach to understand the analogous South Atlantic Cretaceous Presalt carbonate occurrences (Brazil and Angola).


Carbonate Microbial Sedimentology Triassic Catalan Basin Ramp
Left: Sampling laminated carbonates of the Middle Triassic (Ladinian) basin near Querol area (Tarragona). Right: Me and Concha Arenas analysing the metre-thick domal stromatolite succession near Querol village. These buildups were deposited in the restricted parts of the inner carbonate ramp during the Middle Triassic in the Catalan Basin. All the images have a CCBY attribution.


During my interaction with REPSOL, I recognised a knowledge deficit regarding the role of aqueous geochemistry and microbial influence in the development of carbonate textures of apparently microbial origin. Thus, my strategy during my BP funded post-doctoral project (2014-2017) was to widen my expertise in analytical and laboratory techniques (SEM, TEM, Nano-SIMS, stable isotopes, ICP-MS/OES, PHREEQC modelling, flume design) to better constrain the hydrochemistry, petrography, sedimentary environment, and geobiology of continental carbonate-precipitating systems (lakes, hot-springs, and rivers).

Carbonate Microbial Sedimentology Mono Lake Travertine Hotspring
Left: Me in Mono Lake (California, USA) standing with a lacustrine carbonate chimney outcropping in the surroundings of the recent lake. The growth of these striking Pleistocene metre-scale constructions was affected by the presence of centrimetre-thick tubular and vertically oriented microbial mats. Right: Enrico Capezzuoli showing the facies architecture of the travertine deposits at Rapolano Quarry (Siena, Italy), a world-class site to study the geology of ancient hot-spring carbonate systems. All the images have a CCBY attribution.

So far, I have developed a novel laboratory experimentation to assess the impact that microbial-derived organic molecules, solution chemistry and Mg-rich clay minerals have in the growth of unusual lacustrine carbonate textures. My ambition lies in having an holistic process-product understanding of non-skeletal carbonate factories by combining classical methodologies (outcrop-petrographic data and geochemical modelling and analysis), innovative laboratory approaches (geomicrobiology, high-resolution biomarker analyses), and experimental designs (flume and batch tests).

Why studying the microbial influence on mineral formation/ deposition?

Microbes play fundamental roles shaping Earth’s biogeochemical cycles, recycling organic matter, and they promote the precipitation and dissolution of sedimentary minerals throughout complex metabolic-mineral-water interactions.

Therefore, clarify the physico-chemical and biological influences on mineral deposition is of pivotal importance to:

i) understand the formation and diagenesis of sedimentary minerals (carbonates, phosphates, silicates, sulphates);

ii) recognise the geochemical and petrographical signatures of Life on Earth substrates and in the Solar System, and

iii) propose refined climatic and environmental models that can explain the depositonal heterogeneity of the ancient and Recent sedimentary record.

Petrography Calcite Crystal Spherulite Carbonate Kirkton Experiment
Left: Calcite crystals nucleated under tightly-controlled laboratory conditions mimicking waters found in hypersaline, alkaline lakes. Right: East Kirkton laminites (Scotland) are made up of a sub-millimetre alternation of carbonate, organic and silica laminae showing evidence of soft-sediment deformation. Calcite spherules are recognised intermingled between these laminated sediments. These facies was sedimented in a hyperalkaline, saline and volcanic lake during the Carboniferous. All the images have a CCBY attribution.
Ramon Mercedes-Martín