Methane-Derived Authigenic Carbonates (MDAC) in northern-central Adriatic Sea: Relationships between reservoir and methane seepages

Rossella Capozzi, Francesco L. Guido, Davide Oppo, Giovanni Gabbianelli

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

In the Adriatic basin, gas venting characterized by pockmarks, gas bubbling and other fluid escape related features, is diffused and has been linked or to shallow gases trapped in the Late Pleistocene and below the Holocene maximum flooding surface or to leakage from more deeply buried Pliocene to Pleistocene foredeep succession. Some seepages are associated with carbonate crusts, but a possible correlation between methane leakage and carbonate precipitation in this basin never reached a clear definition. Carbonate concretions recovered by different areas of the Adriatic Sea (northern, central and southern) at different depths (from ca 30 to ca 300m) have been analysed. Different fabrics, petrography and mineralogy can be evidenced for the different sets of samples; all of them show a carbonate content mainly represented by high-Mg calcite: up to 66% in weight of total carbonates for the samples from central Adriatic (close to Bonaccia gas field, offshore Ancona), and 79 to 96% of the total carbonate weight for the other samples that are mainly biogenic. These differences are also reflected by the ??13C values, ranging between -19??? and -29??? VPDB, for the samples collected in the Bonaccia area and moderately positive values for all the other samples. Bonaccia samples contain carbonate cements that record the contribution of methane-derived carbon and have been interpreted as formed below the sea floor, in correspondence of the Sulphate-Methane Transition Zone. Carbonates recovered from the southern and northern Adriatic basin, do not show clear evidence of methane-derived carbon and are mainly made up by organisms typically recovered in the Adriatic coralligenous assemblage. Nonetheless micro-morphological evidences suggest influence of bacterial sulphate reduction and methanogenesis in precipitation of some of these carbonates. ?? 2012 Elsevier B.V.
Original languageEnglish
Pages (from-to)174-188
Number of pages15
JournalMarine Geology
Volume332-334
DOIs
Publication statusPublished - 1 Dec 2012

Fingerprint

Carbonates
Methane
Seepage
seepage
methane
carbonate
Gases
Sulfates
leakage
Carbon
gas
basin
Pleistocene
Petrography
sulfate
pockmark
sea
Mineralogy
Calcium Carbonate
concretion

Keywords

  • Adriatic Sea
  • Methane seepage
  • Methane-Derived Authigenic Carbonates
  • Reservoir

Cite this

Methane-Derived Authigenic Carbonates (MDAC) in northern-central Adriatic Sea: Relationships between reservoir and methane seepages. / Capozzi, Rossella; Guido, Francesco L.; Oppo, Davide; Gabbianelli, Giovanni.

In: Marine Geology, Vol. 332-334, 01.12.2012, p. 174-188.

Research output: Contribution to journalArticle

Capozzi, Rossella ; Guido, Francesco L. ; Oppo, Davide ; Gabbianelli, Giovanni. / Methane-Derived Authigenic Carbonates (MDAC) in northern-central Adriatic Sea: Relationships between reservoir and methane seepages. In: Marine Geology. 2012 ; Vol. 332-334. pp. 174-188.
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N1 - Acknowledgements We wish to thank Prof. Luis Menezes Pinheiro and Dr. Vitor Hugo Magalhães for the fruitful discussion on the topic of this paper and for supporting the re-processing of the deep crustal seismic line of the CROP Project and the SEM-EDAX analysis, at Marine Geophysics Laboratory of the University of Aveiro, Portugal. We are indebted with ENI Spa (Italy) for the permission to use the offshore seismic data. Funding provided by the PRIN 2009 Project (University of Bologna, research grants to Prof. R. Capozzi).

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N2 - In the Adriatic basin, gas venting characterized by pockmarks, gas bubbling and other fluid escape related features, is diffused and has been linked or to shallow gases trapped in the Late Pleistocene and below the Holocene maximum flooding surface or to leakage from more deeply buried Pliocene to Pleistocene foredeep succession. Some seepages are associated with carbonate crusts, but a possible correlation between methane leakage and carbonate precipitation in this basin never reached a clear definition. Carbonate concretions recovered by different areas of the Adriatic Sea (northern, central and southern) at different depths (from ca 30 to ca 300m) have been analysed. Different fabrics, petrography and mineralogy can be evidenced for the different sets of samples; all of them show a carbonate content mainly represented by high-Mg calcite: up to 66% in weight of total carbonates for the samples from central Adriatic (close to Bonaccia gas field, offshore Ancona), and 79 to 96% of the total carbonate weight for the other samples that are mainly biogenic. These differences are also reflected by the ??13C values, ranging between -19??? and -29??? VPDB, for the samples collected in the Bonaccia area and moderately positive values for all the other samples. Bonaccia samples contain carbonate cements that record the contribution of methane-derived carbon and have been interpreted as formed below the sea floor, in correspondence of the Sulphate-Methane Transition Zone. Carbonates recovered from the southern and northern Adriatic basin, do not show clear evidence of methane-derived carbon and are mainly made up by organisms typically recovered in the Adriatic coralligenous assemblage. Nonetheless micro-morphological evidences suggest influence of bacterial sulphate reduction and methanogenesis in precipitation of some of these carbonates. ?? 2012 Elsevier B.V.

AB - In the Adriatic basin, gas venting characterized by pockmarks, gas bubbling and other fluid escape related features, is diffused and has been linked or to shallow gases trapped in the Late Pleistocene and below the Holocene maximum flooding surface or to leakage from more deeply buried Pliocene to Pleistocene foredeep succession. Some seepages are associated with carbonate crusts, but a possible correlation between methane leakage and carbonate precipitation in this basin never reached a clear definition. Carbonate concretions recovered by different areas of the Adriatic Sea (northern, central and southern) at different depths (from ca 30 to ca 300m) have been analysed. Different fabrics, petrography and mineralogy can be evidenced for the different sets of samples; all of them show a carbonate content mainly represented by high-Mg calcite: up to 66% in weight of total carbonates for the samples from central Adriatic (close to Bonaccia gas field, offshore Ancona), and 79 to 96% of the total carbonate weight for the other samples that are mainly biogenic. These differences are also reflected by the ??13C values, ranging between -19??? and -29??? VPDB, for the samples collected in the Bonaccia area and moderately positive values for all the other samples. Bonaccia samples contain carbonate cements that record the contribution of methane-derived carbon and have been interpreted as formed below the sea floor, in correspondence of the Sulphate-Methane Transition Zone. Carbonates recovered from the southern and northern Adriatic basin, do not show clear evidence of methane-derived carbon and are mainly made up by organisms typically recovered in the Adriatic coralligenous assemblage. Nonetheless micro-morphological evidences suggest influence of bacterial sulphate reduction and methanogenesis in precipitation of some of these carbonates. ?? 2012 Elsevier B.V.

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