Deep-Water Coral Mounds from Rockall Trough: A Modern Analogue for Hydrocarbon Reservoir Carbonate Mounds?

Conxita Taberner¹, Th. Richter², H. De Haas², F. Mienis², A. Stadniskaia², H. Vonhof³, and T. Van Weering^2
1 Institute of Earth Sciences, CSIC, Barcelona, Spain
² Royal Netherlands Institute for Sea Research, Den Burg, Netherlands
³ Vrije Universiteit Amsterdam, Amsterdam, Netherlands

Carbonate mounds of up to 300 m height and with diameters of 5-10 km at their base, are found as single mounds and in clustered complexes at the SW and SE Rockall Trough margin (NE Atlantic). At the SE margin (Porcupine Bank) they occur at depths between 600 and 1200 m. These carbonate mounds formed in cold deep waters and constitute an exceptional recent analogue of deep water carbonate mounds from the fossil record.

High resolution seismic surveys, complemented with bottom sampling and seabed observations by using ROV, underwater video and photography and by lander operations were carried out to establish their mode of formation and the present-day hydrodynamic conditions on and near the mounds. Cores from the top-most part of the coral mounds and dredged samples provide constraints to understand carbonate growth and development patterns, facies and early diagenetic evolution.

Aragonite dissolution and carbonate lithification are the main processes controlling porosity redistribution during early diagenesis. Hardground formation during glacial stages appears to be the main control for extensive cementation at specific levels of the carbonate mound. Alternation of cemented hardground levels and more permeable sediments are predicted as main constraints of flow-units and permeability barriers during late diagenesis.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005