Morphology and Structure of Buried Cold-Water Coral Banks from Combined High-Resolution 2-D with 3-D Seismic Data: Examples from the Porcupine Basin, Offshore Ireland

Pieter Van Rensbergen
Ghent University, Ghent, Belgium

Coral mounds in the Porcupine basin consist mainly of framework-building corals Lophelia pertusa and Madrepora occulata, clogged with sediment. Coral mounds reach spectacular sizes at the sea floor, up to 200 m high and 5 km wide, while a large part is buried by hemi-pelagic sediment. In the Porcupine Basin, a nearly 2000 mounds have been identified on seismic data but a vast majority is buried and only about 60 mounds still have a surface expression. The morphology and the internal structure of these mounds is completely unknown, simply because tools to image them are missing. Subsurface data at coral mounds is limited to high-resolution 2D seismic data, industrial 3D seismic data, and short cores of a maximum length of 20 m. High resolution seismic data document a wide variety of shapes but 3D mapping is hampered by line spacing and a fresnel zone of about 40 m wide, which makes mounds seem larger then they actually are. 3D seismic data shows the distribution of buried coral banks but gives very little information about their shape or internal structure. For this purpose, a technique was developed to use the high-resolution seismic facies from 2D lines in a multi-attribute analysis of the 3D seismic data. The calculated 3D data volume thus distinguishes coral bank facies from stratified sediment and coral-to-sediment transition facies. It shows that coral banks are not solid coral facies but are ring-shaped and that complex build-ups evolve from discrete coral alignments to wide build-ups with multiple crests.

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