Title: Evolution of deformation and fault-related fluid flow within an ancient methane seep system (Eocene, Varna, Bulgaria)
Authors: De Boever, Eva ×
Muchez, Philippe
Swennen, Rudy
Dimitrov, L. #
Issue Date: May-2011
Publisher: Blackwell Science
Series Title: Geofluids vol:11 issue:2 pages:166-183
Abstract: Faults are often important in fuelling methane seep systems; however, little is known on how different components
in fault zones control subsurface fluid circulation paths and how they evolve through time. This study provides
insight into fault-related fluid flow systems that operated in the shallow subsurface of an ancient methane
seep system. The Pobiti Kamani area (NE Bulgaria) encloses a well-exposed, fault-related seep system in unconsolidated
Lower Eocene sandy deposits of the Dikilitash Formation. The Beloslav quarry and Beloslav N faults displace
the Dikilitash Formation and are typified by broad, up to 80 m wide, preferentially lithified hanging wall
damage zones, crosscut by deformation bands and deformation band zones, smaller slip planes and fault-related
joints. The formation of a shallow plumbing system and chimney-like concretions in the Dikilitash Formation was
followed by at least two phases of fault-related methane fluid migration. Widespread fluid circulation through the
Dikilitash sands caused massive cementation of the entire damage zones in the fault hanging walls. During this
phase, paths of ascending methane fluids were locally obstructed by decimetre-thick, continuous deformation
band zones that developed in the partly lithified sands upon the onset of deformation. Once the entire damage
zone was pervasively cemented, deformation proceeded through the formation of slip planes and joints. This created
a new network of more localized conduits in close vicinity to the main fault plane and around through-going
slip planes. 13C-depleted crustiform calcite cements in several joints record the last phase of focused methane
fluid ascent. Their formation predated Neogene uplift and later meteoric water infiltration along the joint network.
This illustrates how fault-related fluid pathways evolved, over time, from ‘plumes’ in unconsolidated sediments
above damage zones, leading to chimney fields, over widespread fluid paths, deflected by early
deformation structures, to localized paths along fracture networks near the main fault.
ISSN: 1468-8115
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Division of Geology
× corresponding author
# (joint) last author

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