Biodetrital carbonates on the Adriatic continental shelf imprinted by oxidation of seeping hydrocarbons

Marco Taviani, Fulvio Franchi, Lorenzo Angeletti, Annamaria Correggiari, Matthias López-Correa, Vittorio Maselli, Claudio Mazzoli, Jörn Peckmann

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

The gas-productive Bonaccia area located at ca. 80-90 m below sea level offshore Ancona (Central Adriatic Sea) is site of hydrocarbon-derived carbonate production. The carbonates include large dm-sized slabs (bryozoan limestone), smaller concretionary aggregates, mudstones and pipes. The mudstones and botryoidal aragonite cements within limestones show δ13C values as low as -47.8‰ VPDB, consistent with seepage of isotopically light hydrocarbons (e.g. methane). These hydrocarbon-derived carbonates commonly incorporate abundant shell remains, deriving from the prevalently coarse bioclastic-rich muddy deposits from post-glacial transgressive units. It is, therefore, hypothesized that hydrocarbon-rich fluids permeated the post-glacial sediments, resulting in seafloor seeps that were inhabited by chemosymbiotic lucinid bivalves and burrowing callianassid shrimps; fossils and traces of which have been found in the Bonaccia carbonates. Microbial oxidation of the reduced compounds contained in the seep fluids led to a locally patchy carbonate cementation of the sediments at the seep sites. The pipes are interpreted as decapod burrows that subsequently served as conduits for hydrocarbon leakage. Seepage is probably still active at present as testified by gas production at the study site. Interestingly, seep carbonates exhumed by erosion served as hard substrate for fouling benthos (i.e., bryozoans, oysters and red algae) in the Holocene. The main products of the processes at the Bonaccia study site are composite bryozoan-dominated limestones, whose multi-step and complex history was unfold thank to radiocarbon dating of key components and precise stratigraphic control. The Bonaccia case-study can serve as a model for the interpretation of ancient analogs, such as bryozoan dominated limestones and mudstones of Paleozoic to Mesozoic age, which are not uncommon in the geological record. It further calls for caution in assuming that the presence of dominant macrobenthic fossil in old hydrocarbon-derived limestones implies its ecological connection to active seepage.

Original languageEnglish
Pages (from-to)511-531
Number of pages21
JournalMarine and Petroleum Geology
Volume66
DOIs
Publication statusPublished - Sep 1 2015

Fingerprint

continental shelves
limestone
continental shelf
carbonates
hydrocarbons
hydrocarbon
seepage
carbonate
oxidation
bryozoan
mudstone
fossils
Postglacial
sediments
pipe
Adriatic Sea
fossil
cementation
aragonite
fouling

All Science Journal Classification (ASJC) codes

  • Oceanography
  • Geophysics
  • Geology
  • Economic Geology
  • Stratigraphy

Cite this

Taviani, Marco ; Franchi, Fulvio ; Angeletti, Lorenzo ; Correggiari, Annamaria ; López-Correa, Matthias ; Maselli, Vittorio ; Mazzoli, Claudio ; Peckmann, Jörn. / Biodetrital carbonates on the Adriatic continental shelf imprinted by oxidation of seeping hydrocarbons. In: Marine and Petroleum Geology. 2015 ; Vol. 66. pp. 511-531.
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Taviani, M, Franchi, F, Angeletti, L, Correggiari, A, López-Correa, M, Maselli, V, Mazzoli, C & Peckmann, J 2015, 'Biodetrital carbonates on the Adriatic continental shelf imprinted by oxidation of seeping hydrocarbons', Marine and Petroleum Geology, vol. 66, pp. 511-531. https://doi.org/10.1016/j.marpetgeo.2015.03.015

Biodetrital carbonates on the Adriatic continental shelf imprinted by oxidation of seeping hydrocarbons. / Taviani, Marco; Franchi, Fulvio; Angeletti, Lorenzo; Correggiari, Annamaria; López-Correa, Matthias; Maselli, Vittorio; Mazzoli, Claudio; Peckmann, Jörn.

In: Marine and Petroleum Geology, Vol. 66, 01.09.2015, p. 511-531.

Research output: Contribution to journalArticle

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AU - Taviani, Marco

AU - Franchi, Fulvio

AU - Angeletti, Lorenzo

AU - Correggiari, Annamaria

AU - López-Correa, Matthias

AU - Maselli, Vittorio

AU - Mazzoli, Claudio

AU - Peckmann, Jörn

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AB - The gas-productive Bonaccia area located at ca. 80-90 m below sea level offshore Ancona (Central Adriatic Sea) is site of hydrocarbon-derived carbonate production. The carbonates include large dm-sized slabs (bryozoan limestone), smaller concretionary aggregates, mudstones and pipes. The mudstones and botryoidal aragonite cements within limestones show δ13C values as low as -47.8‰ VPDB, consistent with seepage of isotopically light hydrocarbons (e.g. methane). These hydrocarbon-derived carbonates commonly incorporate abundant shell remains, deriving from the prevalently coarse bioclastic-rich muddy deposits from post-glacial transgressive units. It is, therefore, hypothesized that hydrocarbon-rich fluids permeated the post-glacial sediments, resulting in seafloor seeps that were inhabited by chemosymbiotic lucinid bivalves and burrowing callianassid shrimps; fossils and traces of which have been found in the Bonaccia carbonates. Microbial oxidation of the reduced compounds contained in the seep fluids led to a locally patchy carbonate cementation of the sediments at the seep sites. The pipes are interpreted as decapod burrows that subsequently served as conduits for hydrocarbon leakage. Seepage is probably still active at present as testified by gas production at the study site. Interestingly, seep carbonates exhumed by erosion served as hard substrate for fouling benthos (i.e., bryozoans, oysters and red algae) in the Holocene. The main products of the processes at the Bonaccia study site are composite bryozoan-dominated limestones, whose multi-step and complex history was unfold thank to radiocarbon dating of key components and precise stratigraphic control. The Bonaccia case-study can serve as a model for the interpretation of ancient analogs, such as bryozoan dominated limestones and mudstones of Paleozoic to Mesozoic age, which are not uncommon in the geological record. It further calls for caution in assuming that the presence of dominant macrobenthic fossil in old hydrocarbon-derived limestones implies its ecological connection to active seepage.

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