Characterisation and genesis of hypogene void systems in Mississippian carbonates, Derbyshire Platform, UK

Hypogene karst forms from upward-flowing fluids, but the processes governing its formation is still not well understood.  Mississippian strata on the Derbyshire Platform, UK, have experienced a complex diagenetic evolution including calcite cementation, compaction, dolomitisation, MVT mineralisation, and karstification. Epigenetic karst, formed from downward flowing groundwater, is well known and described and there is now also good evidence for hypogene karstification.

This study has documented the occurrence, fill, morphology, size, location, and geological context of hypogene caves, including association with faults, stratal architecture, and diagenetic phases. Three classes of have been identified. 1) Partially to completely mineralised; 2) calcite cemented and sediment filled; 3) open, vertical, and sub-vertical. Of particular interest are the very coarsely crystalline calcite cements that occur within type 1 & 2 voids.  Petrographical analysis of these coarsely crystalline calcite crystals reveals homogenous crystals with dull luminescence and an absence of zonation or chemical variation within the crystals. This suggests constant fluid composition, and redox, during crystal growth.

This geological analysis provides constraints for numerical models that aim to understand the genesis and evolution of hypogene void systems. Preliminary modelling results indicate complex patterns of dissolution and precipitation. Integration of all these data will be used to discuss the genesis of the hypogene voids, and implications to predicting where they might occur on other carbonate platforms.   The results also provide an important insight into potential flow behaviour and drilling risk during exploration and appraisal of targets for low enthalpy geothermal heat in the UK.

Cathy’s biography:

“I am a carbonate sedimentologist with a particular interest in diagenetic processes and their impact on the physical properties of sedimentary rocks.  I have a BSc in Geological Sciences from University of Birmingham (1990), and a PhD from University of Aberdeen (1995). I am currently President of the International Association of Sedimentologists, and I was Adjunct Professor of Carbonate Sedimentology at University of Bergen from 2020-2022.  I started my career as a carbonate geologist at Badley Ashton and Associates Ltd, working in the UK and the UAE.  In 2001, I joined Shell International Exploration and Production in The Netherlands as a production geologist before becoming Carbonate Research Team Leader (2005-2007).  I made the decision to return to the UK for an academic career in 2007, when I joined University of Manchester.  Over the last 15 years, I have led a team of post-graduate and post-doctoral researchers in carbonate sedimentary systems, especially basin-scale fluid – rock reactions.  I am particularly interested in dolomitization processes and reactions in the burial diagenetic realm, such as hypogene karstification and mineralization in sedimentary basins.  I enjoy fieldwork and have led studies in the UK, Canada, North Africa, Europe and the Middle East.”