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Christodoulou, Dimitris
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Christodoulou, Dimitris
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- PublicationOpen AccessGas Seepage-Induced Features in the Hypoxic/Anoxic, Shallow, Marine Environment of Amfilochia Bay, Amvrakikos Gulf (Western Greece)(2021-01-05)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; Amfilochia Bay (Eastern Amvrakikos Gulf, Western Greece), a complex marine area affected by tectonism, was investigated for seabed seepage manifestations and for possible inter-relationships between shallow gas accumulations and hypoxia. For this purpose, an integrated research methodology that combined geophysical, geochemical, and hydrographic surveys was applied. Marine geophysical and bathymetric surveys led to the discovery of a gas-induced pockmark group in the study area. Oceanographic surveying confirmed that the bay is hypoxic/anoxic below a depth of 15 m (dissolved oxygen from ~4 to 60 μM). Very weak CH4 seepage was detected in correspondence to the pockmark group that seemed to slightly enhance the hypoxic environment locally and close to the seabed, with no effect in shallower waters and the oxycline. Methane isotopic analysis showed variable carbon isotopic composition (from −41‰ to −86‰) which could be either related to differential CH4 oxidation or mixing between microbial and thermogenic gas. However, the pathway of degassing is clearly related to the fault-controlled pockmark group. A protrusion mound, which has erroneously been reported as a submarine “volcano” since 1876, could be the result of mud volcanism based on the geophysical data of this study.174 46 - PublicationRestrictedMethane and hydrogen sulfide seepage in the NW Peloponnesus petroliferous basin (Greece): origin and geohazard(2006-05)
; ; ; ; ; ; ;Etiope, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Papatheodorou, G.; Department of Geology, University of Patras, Greece ;Christodoulou, D.; Department of Geology, University of Patras, Greece ;Ferentinos, G.; Department of Geology, University of Patras, Greece ;Sokos, E.; Seismological Laboratory, Department of Geology, University of Patras, Greece ;Favali, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; ; ; ; ; Gas seepages along the Ionian coast of the northwestern Peloponnesus (Greece), at Killini, Katakolo, and Kaiafas reflect deep hydrocarbon-generation processes and represent a real hazard for humans and buildings. Methane microseepage, gas concentration in offshore and onshore vents, and gas dissolved in water springs, including the isotopic analysis of methane, have shown that the seeps are caused by thermogenic methane that had accumulated in Mesozoic limestone and had migrated upward through faults, or zones of weakness, induced by salt diapirism. A link between local seismicity and salt tectonics is suggested by the analyses of hypocenter distribution. Methane acts as a carrier gas for hydrogen sulfide produced by thermal sulfate reduction and/or thermal decomposition of sulfur compounds in kerogen or oil. Methane seeps in potentially explosive amounts, and hydrogen sulfide is over the levels necessary to induce toxicological diseases and lethal effects.171 25 - PublicationRestrictedThe geological links of the ancient Delphic Oracle (Greece): A reappraisal of natural gas occurrence and origin(2006)
; ; ; ; ; ;Etiope, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Papatheodorou, G.; Department of Geology, University of Patras, Rio, 26500 Patras, Greece ;Christodoulou, D.; Department of Geology, University of Patras, Rio, 26500 Patras, Greece ;Geraga, M.; Department of Geology, University of Patras, Rio, 26500 Patras, Greece ;Favali, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; ; ; ; Recent studies have speculated that the prophetic powers of Pythia, the woman of the Delphic Oracle, at the Temple of Apollo in Greece, were induced by hydrocarbon vapors, specifically ethylene, rising from bedrock fissures at the intersection of the E-W Delphi fault with the NNW-SSE Kerna fault, and producing neurotoxic effects, including trance and delirium. New surveys including gas flux from soil, gas in groundwater, and isotopic analyses of spring scales, provide the experimental confirmation of the gas release in the Delphi area. Presently, methane, ethane, and carbon dioxide are being released from a thermogenic (catagenetic) hydrocarbon-prone environment. This environment is not prone to biogenic production of ethylene in amounts inducing neurotoxic effects (hundreds or thousands of ppmv). A WNW-ESE–trending subsidiary fault within the Delphi fault zone, extending for 2 km, passes under the Temple of Apollo and shrine of Athena. The Temple of Apollo, located above this fault, may have been the site of enhanced degassing in the past. If gas-linked neurotoxic effects upon Pythia need to be invoked, they should be sought in the possibility of oxygen depletion due to CO2-CH4 exhalation in the indoor temple. Alternatively, a plausible geological explanation behind the natural presence of sweet scents could be the occurrence of aromatic hydrocarbons, such as benzene, dissolved in the groundwater spring.205 58 - PublicationRestrictedMonitoring of a methane-seeping pockmark by cabled benthic observatory (Patras Gulf, Greece)(2006)
; ; ; ; ; ; ; ; ; ; ; ;Marinaro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Etiope, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Lo Bue, N.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Favali, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Papatheodorou, G.; Department of Geology, University of Patras, Greece ;Christodoulou, D.; Department of Geology, University of Patras, Greece ;Furlan, F.; TECNOMARE-ENI SpA, ;Gasparoni, F.; TECNOMARE-ENI SpA, ;Ferentinos, G.; Department of Geology, University of Patras, Greece ;Masson, M.; Franatech GmbH, 21339 Luneburg, Germany ;Rolin, J. F.; IFREMER, France; ; ; ; ; ; ; ; ; ; A new seafloor observatory, the gas monitoring module (GMM), has been developed for continuous and long-term measurements of methane and hydrogen sulphide concentrations in seawater, integrated with temperature (T), pressure (P) and conductivity data at the seafloor. GMM was deployed in April 2004 within an active gas-bearing pockmark in the Gulf of Patras (Greece), at a water depth of 42 m. Through a submarine cable linked to an onshore station, it was possible to remotely check, via direct phone connection, GMM functioning and to receive data in nearreal time. Recordings were carried out in two consecutive campaigns over the periods April–July 2004, and September 2004–January 2005, amounting to a combined dataset of ca. 6.5 months. This represents the first long-term monitoring ever done on gas leakage from pockmarks by means of CH4+H2S+T+P sensors. The results show frequent T and P drops associated with gas peaks, more than 60 events in 6.5 months, likely due to intermittent, pulsation-like seepage. Decreases in temperature in the order of 0.1–1°C (up to 1.7°C) below an ambient T of ca. 17°C (annual average) were associated with short-lived pulses (10–60 min) of increased CH4+H2S concentrations. This seepage “pulsation” can either be an active process driven by pressure build-up in the pockmark sediments, or a passive fluid release due to hydrostatic pressure drops induced by bottom currents cascading into the pockmark depression. Redundancy and comparison of data from different sensors were fundamental to interpret subtle proxy signals of temperature and pressure which would not be understood using only one sensor.554 45 - PublicationRestrictedOffshore and onshore seepage of thermogenic gas at Katakolo Bay (Western Greece)(2013-02-15)
; ; ; ; ; ;Etiope, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Christodoulou, D.; Laboratory of Marine Geology and Physical Oceanography, Department of Geology, University of Patras, Greece ;Kordella, S.; Laboratory of Marine Geology and Physical Oceanography, Department of Geology, University of Patras, Greece ;Marinaro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Papatheodorou, G.; Laboratory of Marine Geology and Physical Oceanography, Department of Geology, University of Patras, Greece; ; ; ; Considerable seepage of natural gas occurs throughout the Katakolo Bay, both at sea and on land, along the Ionian coast of Peloponnesus (Western Greece). Explosive levels of CH4 and toxic concentrations of H2S accumulating in the ground, pose a severe hazard for humans and tourist infrastructures. A wide offshore and onshore gas survey, including marine remote sensing, underwater exploration by a towed instrumented system, compositional and isotopic analyses, and flux measurements of gas, allowed us to assess that: (a) gas seepage takes place along two main normal faults; (b) offshore side-scan sonographs recorded at least 823 gas bubble plumes over an area of 94,200 m2, at depths ranging from 5.5 to 16 m; (c) offshore and onshore seeps release the same type of thermogenic gas (δ13CCH4~−34 to −36‰); (d) offshore gas showed increased stable carbon isotopic ratio of CO2 and propane, which suggests enhanced biodegradation of hydrocarbons; (e) isotopic data combined with thermogenic gas generation modeling and maturity plots, suggest that the gas is related to a deep Petroleum System with Jurassic carbonate reservoirs, Triassic source rocks, and Triassic evaporites; (f) H2S (δ34S: +2.4‰) is produced by thermochemical sulfate reduction in deep anhydrites, in contact with hydrocarbon-rich carbonates; (g) due to the shallow depth, more than 90% of CH4 released at the seabed enters the atmosphere, consistent with theoretical bubble dissolution models, with a mean plume output of 0.12 kg d−1; total offshore CH4 output was estimated in the range of 33 to 120 t y−1; and (h) in the onshore area at least 50 gas vents in the harbor and a large seep on the adjacent Faros hill, emit in total about 89 t CH4 y−1. Katakolo results to be one of the biggest thermogenic gas seepage zones in Europe.688 80 - PublicationOpen AccessGeophysical and Geochemical Exploration of the Pockmark Field in the Gulf of Patras: New Insights on Formation, Growth and Activity(2023)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ; ; ;The Patras Gulf Pockmark field is located in shallow waters offshore Patras City (Greece) and is considered one of the most spectacular and best-documented fluid seepage activities in the Ionian Sea. The field has been under investigation since 1996, though surveying was partially sparse and fragmentary. This paper provides a complete mapping of the field and generates new knowledge regarding the fluid escape structures, the fluid pathways, their origin and the link with seismic activity. For this, data sets were acquired utilising high-resolution marine remote sensing techniques, including multibeam echosounders, side-scan sonars, sub-bottom profilers and remotely operated vehicles, and laboratory techniques focusing on the chemical composition of the escaping fluids. The examined morphometric parameters and spatial distribution patterns of the pockmarks are directly linked to tectonic structures. Acoustic anomalies related to the presence of gas in sediments and in the water column document the activity of the field at present and in the past. Methane is the main component of the fluids and is of microbial origin. Regional and local tectonism, together with the Holocene sedimentary deposits, appear to be the main contributors to the growth of the field. The field preserves evidence that earthquake activity prompts the activation of the field.49 11 - PublicationRestrictedMethane flux and origin in the Othrys ophiolite hyperalkaline springs, Greece(2013)
; ; ; ; ; ; ;Etiope, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Tsikouras, B. ;Kordella, S. ;Ifandi, E. ;Christodoulou, D. ;Papatheodorou, G.; ; ; ; ;The occurrence and origin of methane (CH4) generated by serpentinization of ultramafic rocks is of current timely interest in planetary geology, astrobiology and energy resource exploration, as it may contribute, in particular, to decipher the source of methane on Mars, the origin of life and the potential of abiotic hydrocarbon synthesis. Methane of dominant abiotic origin in serpentinized peridotites on continents (ophiolites or igneous intrusions) has been documented so far, with complete carbon and hydrogen isotope composition, in six countries, in the Philippines, Turkey, Oman, New Zealand, Japan and Italy. We report the discovery of two new sites in Greece, at Archani and Ekkara, located in the Othrys ophiolite massif. Portable sensors based on Fourier Transform InfraRed spectrometry (FTIR) and Tunable Diode Laser Absorption Spectroscopy (TDLAS) allowed to realize that out of 21 ophiolitic springs, methane is released only by four hyperalkaline (pH from 10.7 to 11.3) and calcium hydroxide (Ca–OH) type waters; all other 17 springs with pH b 8.7 and magnesium-rich waters in the Pindos, Vourinos and Veria ophiolites, do not show methane. This correlation between gas occurrence and water type seems to occur worldwide; accordingly, CH4 production appears to be intimately related to the depth and residence time of the circulating meteoric waters. Methane is emitted into the atmosphere also from the soil surrounding the hyperalkaline springs, with fluxes of the same order of magnitude (~102–103 mg m−2 day−1) of seepage typically observed over conventional petroleum systems. Othrys CH4 has an isotopic composition (δ13C from −27‰ to −37.3‰ VPDB, δ2H from −250‰ to −311‰ VSMOW) similar to that reported in ultramafic rocks in New Zealand and Japan, and in Precambrian crystalline shields, which were considered dominantly abiotic and probably derived from Fischer–Tropsch Type reactions. The paucity of CO2, which is the norm in hyperalkaline waters, and of other hydrocarbons prevents from evaluating possible mixing of gas of different sources, including microbial methanogenesis. Also the H2 content is trivial, notwithstanding it being a typical product of serpentinization; this could be due to complete H2 consumption by CO2 reduction in a limited or decreased H2 production system due, for example, to a late stage of increased silica activity, as suggested by preliminary petrographic observations. The low geothermal gradient of the area and the present-day serpentinization imply that,whatever the CH4 production mechanism, it took place at temperatures below those traditionally considered for the origin of abiotic methane in hydrothermal systems.196 58