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Cold Water Carbonate Mounds and Sediment Transport on the Northeast Atlantic Margin

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Cold Water Carbonate Mounds and Sediment Transport on the Northeast Atlantic Margin Intergovernmental Oceanographic Commission technical series 52 Cold water carbonate mounds and sediment transport on the Northeast Atlantic margin Preliminary results of geological and geophysical investigations during the TTR-7 cruise of R/V Professor Logachev in co-operation with the CORSAIRES and ENAM 2 programmes July-August, 1997 Editors: N.H. Kenyon M. K. lvanov A.M. Akhmetzhanov UNESCO 1998 The designations employed and the presentation of the material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariats of UNESCO and IOC concerning the legal status of any country or territory, or its authorities, or concerning the delimitations of the frontiers of any country or territory. For bibliographic purposes, this document should be cited as follows: Cold water carbonate mounds and sediment transport on the Northeast Atlantic margin IOC Technical Series No. 52, UNESCO 1998 (English) Published in 1998 by the United Nations Educational, ‘Scientific and Cultural Organization 7, place de-Fontenoy, 75352 Paris 07 SP Printed in UNESCO’s Workshops 0 UNESCO 1998 Printed in France IOC Technical Series No. 52 Page 1 TABLE OF CONTENTS Page ABSTRACT .................................................................................................. 3 ACKNOWLEDGEMENTS ............................................................................ 4 INTRODUCTION ......................................................................................... 5 TECHNICAL REPORT ................................................................................. 10 I. Seismic data aquisition and processing.......................................................... 10 II. OKEAN and OREtech sidescansonars and sonographprocessing .......................... 11 III. Underwater photo and television system ......................................................... 12 IV. Bottom sampling technique ........................................................................ 13 V. Geochemical sampling............................................................................... 15 VI. Sampling of benthos ................................................................................ 20 SCIENTIFIC REPORT .................................................................................. 21 I. PORCUPINE SEABIGHT (Leg I). ..................................................................... 21 1.1. Objectives and geological setting ................................................................ 21 1.2. Seismic profiling data ............................................................................. 25 1.3. Long-range sidescansonar data ................................................................. 34 1.4. OREtech sidescansonar data .................................................................... 40 1.5. Bottom sampling results ........................................................................... 59 1.6. Biological data ....................................................................................... 102 1.7. Conclusions ........................................................................................... 107 II. ROCKALL TROUGH (Leg II) ......................................................................... 108 11.1.Geological setting and objectives ............................................................... 108 11.2.Seismic data ......................................................................................... 110 II. 2. a. Southeastern Rockall Trough ............................................................... 110 11.2.b. Southwestern Rock-all Trough .............................................................. 115 11.3.OKEAN and OREtech data ..................................................................... 121 II.3.a. Southeastern Rockall Trough ............................................................... 121 II.3.b. Southwestern Rockall Trough .............................................................. 126 11.3.~.Seismic and OREtech line ties and interpretation: SE Rockall Trough ............................................................................ 131 II.3.d. Interpretation of seismic and sidescan sonar data: SW Rockall Trough ........................................................................... 132 11.4.Bottom sampling results ......................................................................... 134 II.4.a. Southeastern Rock-all Trough ............................................................... 134 II.4.b. Southwestern Rockall Trough .............................................................. 142 11.5.Biological data ...................................................................................... 149 11.6.Conclusions .......................................................................................... 158 I v-- - 1- IOC Technical Series No. 52 Page 2 III. FAEROE MARGIN (Leg II) . .. 159 111.1.Objectives and geological setting ............................................................. 159 111.2.Seismic data ....................................................................................... 160 III.3 OKJZAN and OREtech sidescansonar data ................................................ 164 111.4.Bottom sampling results ........................................................................ 167 III.5 Conclusions ......................................................................................... 175 REFERENCES . , . 176 IOC Technical Series No. 52 Page 3 ABSTRACT The seventh Training-through-Research(TTR-7) international cruise of the R/V Professor Logachev was carried out in the northeast Atlantic in July - August 1997. As in previous years the cruise was conducted within the UNESCO/IOC “Floating University” Programmebut this year in co- operation with the CORSAIRES and ENAM programmes of the European Commission. The expedition aimed to solve some outstandingproblems in the field of geological processeson a passive continental margin and particularly to shed light on the nature and ecology of carbonate mounds recently discovered west off Ireland, which were thought to be due to hydrocarbons migrating upward. Modem analoguesof hydrocarbon reservoirs were the other important objective of the cruise. A well developed system of tributary channels that runs from the margin south of Ireland to the Porcupine Abyssal Plain, and the potential area of sandy contourites lying to the west of the Faeroe Bank Channel were consideredto be of interest as such analogues. Comprehensive investigations resulted in the realisation that there are huge quantities of carbonatewithin cold water carbonatemounds. They are of enormous size (up to 400 m high, 5 km long) and have great diversity of shape.Over 150 moundswere mappedon just a small portion of the slopes of the Rockall Trough and Porcupine Seabight. Advances in understanding why carbonate mounds occur came from the biological, geochemicaland sedimentologicalstudies. The importance of fast flowing currents to the growth of cold water corals, the main growth builder of the mounds, was clearly demonstrated.Moulding of moundsby prevailing currents was also seen. Contour currents are one of the main ways that slopesin the region are fashioned. In spite of the fact that sandy contourites are rarely recognisedin studies of either ancient or modem sediments they were shown to be very significant in this part of the Atlantic. Sidescansonar proved the most effective way to map the pathways of strong currents. By this method, a hitherto unknown, strong northward directed current was discovered in the Porcupine Seabight. Strong currents were also sweeping sands along the upper slope east of Rockall Bank and along the slope west of Porcupine Bank. Complex, sand filled channels shapedby the cold, salty overflow water from the Norwegian Sea were mappedin the Iceland Basin. A new Tertiary igneous centre is believed to have been discovered at the foot of the Porcupine Bank. The deep sea turbidite channel system in the Porcupine Seabight was shown to be inactive during the Holocene. (This is in contrast to the situation in nearby submarinecanyons in the Bay of Biscay, which during the same period appear to have been the conduits for sands that have been brought to the shelf edge by tidal currents). Terraces had developedalong the channel, probably by a slumping process. IOC TechnicalSeries No. 52 Page4 ACKNOWLEDGEMENTS Financial support for the seventhTraining-through-Research cruise came from various sourcesamong which were the CORSAIRES and ENAM- projects of the EuropeanCommission, the IntergovernmentalOceanographic Commission (IOC) of UNESCO, the Ministry of Scienceand Technology and the Ministry of Natural Resourcesof the RussianFederation. Additional support was provided by national funding institutions and universities in Belgium, Denmark, Ireland and the United Kingdom. The cruise would not come to reality without the efforts of severalpeople in different organisationsacting in support of the Training-through-ResearchProgramme. Credit should be given to Prof. Dr. I. F. Glumov (Ministry of Natural Resourcesof the RussianFederation), Dr. A. Suzyumov (UNESCO), and Dr. G. Kullenberg (Executive Secretaryof IOC). We gratefully appreciateassistance provided by C. van Bergen Henegouw of the Netherlands Institute for Sea Researchfor logistic support and Prof. Dr. V. T. Trofimov (Moscow State University) for administrative support. The port calls in Lisbon and Dublin were made possible with kind assistanceof
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