Forcing of carbonate mounds and deep water coral reefs along the NW European continental margin (MOUNDFORCE)

Recent discoveries of carbonate mounds covered with cold water corals and related benthic communities along the NE Atlantic Ocean continental margin (Porcupine Bight and north of Porcupine Bank, southeast and southwest Rockall Trough Margin, Norwegian margin) and of actively venting mud volcanic areas along the continental margin surrounding the Gulf of Cadiz associated with authigenic carbonate crust formation and deep-water reef-like coral build-ups and carbonate chimneys margin, Galicia Bank as well as new discoveries of fossil and recent reef structures in the Mediterranean ), raises the question of their origin and development. A major objective of the proposed studies therefore is to establish the forcing conditions of carbonate mound formation and to test the hypothesis of a possible linkage between (hydrocarbon related) cold seeps and the development of carbonate mounds, cold water benthic communities and authigenic carbonate formation. This proposal is further directed towards a definition of the geological, geochemical and oceanographical conditions and processes forcing the development of carbonate mounds and establishing the benthic ecology and environmental conditions of carbonate mound andcold water coral reef formation in contrasting areas of the NE Atlantic Ocean and Mediterranean Sea. A third objective is to establish the factors governing lithification and stabilisation of carbonate mounds, and to use these as modern analogues of fossil carbonate build ups. Comparison between recent and past mound forcing conditions will allow development of a model of mound genesis in relation to tectonic, sedimentological, oceanographical and biological extant conditions.

MOUNDFORCE Presentation

The discovery of cold water coral and related benthic communities covered carbonate mounds along the NE Atlantic Ocean continental margin (Porcupine Bight and north of Porcupine Bank, southeast and southwest Rockall Trough Margin, Norwegian margin) and cold water coral communities at the Galicia Bank and in the Mediterranean and the presence of actively venting mud volcanic areas along the continental margin surrounding the Gulf of Cadiz associated with authigenic carbonate crust formation and deep-water reef-like coral build-ups and carbonate chimneys, raises the question of the origin and development of carbonate mounds and the possible relationship with cold water corals and hydrocarbon seepage.

A major objective of Moundforce is to establish the forcing conditions of carbonate mound formation and to test the hypothesis of a possible linkage between (hydrocarbon related) cold seeps and the development of carbonate mounds, cold water benthic communities and authigenic carbonate formation. Moundforce is further directed towards the comparison of carbonate mounds and cold water coral communities along the European margin. A third objective is to establish the factors governing lithification and stabilisation of carbonate mounds, and to use these as modern analogues of fossil carbonate build ups.

The morphology and internal structure of the carbonate mounds is studied by means of multibeam bathymetry, high resolution 2- and 3D seismics and side scan sonar. Photographic and video observations are used to choose sites for sea bed sampling (box and pistoncores). Environmental parameters (water temperature, currents, suspended matter, etc) are measured by means of CTD casts, moorings and benthic landers.

X-Ray, cathodeluminescence, fluorescence, SEM, microbial and biogeochemical analysis is performed to study the processes and products of microbial activity (carbonate crusts) that potential play an important role in stabilization of the steep flanked mounds. The study of stable carbon and oxygen isotopes gives information of possible seepage of fluids and the relationship with mound formation.

Figure 1

In the Gulf of Cadiz cold-water corals are mainly found on mud volcanoes and their slopes, but occasionally also on morphologic escarpments. Interestingly, the corals seem to be restricted to water depths shallower than 1200 m (Fig. 2).

 The occurrence of different species during different time intervals in the past points to distinct invasions of cold-water corals into the Gulf of Cadiz. Ongoing investigations aim to reconstruct the temporal development of cold-water corals in this region and to identify the dominant factors controlling their distribution and development under changing climatic and oceanographic conditions. A cruise planned by the Spanish Moundforce partners was unfortunately delayed.

Figure 3.

Existing data on diapirism and gas-venting structures along the continental slope of the Gulf of Cádiz (Fig. 3) was analysed and the gas hydrates in the Gulf of Cadiz and its relationships with fluid venting structures were modeled. In the area of Pobiti Kamani (Varna, northeast Bulgaria) massive fossil carbonate cemented columns (“chimneys”, up to 2.5 m diameter, 8 m high) were studied (Fig. 4). These chimneys occur with horizontal interbeds in seven dispersed groups and are organized in five superposed levels, within loose Lower Eocene sands. Field observations, petrographical and stable isotope geochemical characterisation revealed a relationship of these structures with processes of fossil hydrocarbon seepage.

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Figure 4.

 

 

Project Leader:

Tjeerdvan WeeringE-Mail
Royal Netherlands Institute for Sea Research (NIOZ)Marine Chemistry & Geology DepartmentDen Burg (Texel)Netherlands

Principal Investigators:

Wolf-ChristianDulloE-Mail
Christian Albrechts UniversitätLeibniz Institut für MeereswissenschaftenPaleo-OceanographyIFM - GEOMARKielGermany
AndréFreiwaldE-Mail
Universität TübingenInstitut für GeowissenschaftenTübingenGermany
DierkHebbelnE-Mail
MARUM - Center for Marine Environmental SciencesUniversity of BremenCenter for Marine Environmental SciencesResearch Center Ocean Margins (MARUM)BremenGermany
Jean-PierreHenrietE-Mail
Universiteit GentFaculty of SciencesDepartment of Geology and Soil ScienceRenard Centre of Marine Geology (RCMG)GentBelgium
LuisSomoza LosadaE-Mail
Geological Survey of Spain (IGME)MceMEC Science and Technology MinistryMarine Geology DivisionMadridSpain
Rudy Allin JozefSwennenE-Mail
Catholic University of LeuvenFaculty of Earth and Environmental SciencesAfdeling Fysico Chemische GeologieHeverleeBelgium
ConxitaTabernerE-Mail
Consejo Superior de Investigaciones Científicas (CSIC)Institute of Earth SciencesDept. Geologia AmbientalBarcelonaSpain
MarcoTavianiE-Mail
Institute of Marine Science - National Research CouncilIstituto di Geologia MarinaBolognaItaly