Abstract
Abstract. Microbial life in the continental deep biosphere is closely linked to geodynamic processes, yet this interaction is poorly studied. The Cheb Basin in the western Eger Rift (Czech Republic) is an ideal place for such a study because it displays almost permanent seismic activity along active faults with earthquake swarms up to ML 4.5 and intense degassing of mantle-derived CO2 in conduits that show up at the surface in form of mofettes. We hypothesize that microbial life is significantly accelerated in active fault zones and in CO2 conduits, due to increased fluid and substrate flow. To test this hypothesis, pilot hole HJB-1 was drilled in spring 2016 at the major mofette of the Hartoušov mofette field, after extensive pre-drill surveys to optimize the well location. After drilling through a thin caprock-like structure at 78.5 m, a CO2 blowout occurred indicating a CO2 reservoir in the underlying sandy clay. A pumping test revealed the presence of mineral water dominated by Na+, Ca2+, HCO3−, SO42− (Na-Ca-HCO3-SO4 type) having a temperature of 18.6 °C and a conductivity of 6760 µS cm−1. The high content of sulfate (1470 mg L−1) is typical of Carlsbad Spa mineral waters. The hole penetrated about 90 m of Cenozoic sediments and reached a final depth of 108.50 m in Palaeozoic schists. Core recovery was about 85 %. The cored sediments are mudstones with minor carbonates, sandstones and lignite coals that were deposited in a lacustrine environment. Deformation structures and alteration features are abundant in the core. Ongoing studies will show if they result from the flow of CO2-rich fluids or not.
Highlights
Microbial processes in the “deep biosphere” and their interaction with geological processes are a matter of ongoing debate
In deep saline aquifers intended for CO2 capture and geological storage (CCS), changes in the microbial community caused by injected CO2 can induce mineral dissolution and precipitation or the formation of biofilms
Our main interests are to determine to which extend the microbial communities are conditioned by the mantle-derived CO2, how the microbial activity is potentially affected by seismic activity such as earthquake swarms, and if active fault zones, due to an intensified substrate support, lead to significantly accelerated microbial activity compared to other deep subsurface ecosystems
Summary
Microbial processes in the “deep biosphere” and their interaction with geological processes are a matter of ongoing debate. Our main interests are to determine to which extend the microbial communities are conditioned by the mantle-derived CO2, how the microbial activity is potentially affected by seismic activity such as earthquake swarms, and if active fault zones, due to an intensified substrate support, lead to significantly accelerated microbial activity compared to other deep subsurface ecosystems. Cuni.cz/uhigug/icdp; Dahm et al, 2013) focuses on the interaction between lithospheric geodynamic activity driven by magma generation and magma/fluid escape beneath the Cheb Basin in the western Eger Rift and the microbial communities of the deep biosphere in the upper crust. Because of the potential risk of a spontaneous gas/fluid blowout during drilling, extra safety measures including the application of a blowout gas preventer, highdensity bentonite-based drill mud and gas alarm techniques had to be employed
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