Introduction

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R/V Pelagia Cruise GLOW
	Diary overview
Monday, 16 February
After transiting for several days we finished our first 24 hours of recording a south-north seismic profile along the strike of Davie Ridge offshore Tanzania. The Davie Ridge is a south-north feature running in the Mozambique Channel. In bathymetric profiles the ridge is a prominent feature causing quite some elevation of the sea floor. The ridge is not a simple monotonous south-north feature but it is dented in several places which gives it a somewhat irregular pattern. We aimed to produce a seismic profile over the top of the ridge to obtain an impression of the seismic sequences on top and to investigate the nature of the irregular features. These features are of interest to us, because they may represent areas without the upper seismic sequences, in other words sediments may be missing in these places, which would facilitate later drilling of deeper sequences.   We watched in shifts the seismic profile developing, sailing slowly to the north. The sound waves produced by the air gun penetrated for about a second, giving information on the upper sediment packages on the ridge for let's say the upper 700-800 meters. The reflectors were flat suggesting regular pelagic sedimentation on the ridge for tens of millions of years. These regular reflectors were interrupted at several places by canyon systems up to about 300-400 meters deep, which form the indentations on the ridge in bathymetric profiles. The nature of these canyons may be related to fault systems running to the northeast all the way from Tanzania, where a fault system is known with this geographical direction on land. The multibeam system revealed also enormous erosional, channel-like features on top of the ridge, at this stage it is not clear whether these channels are all fault bounded. The seismic profile, after processing, will reveal whether the canyons, and/or channels are fault controlled or not.   The erosional features on top of the ridge are enormously attractive for the objectives of this leg to find places where the deeper sediment package is exposed. Perhaps later in the cruise we will try to sample one of the canyons to date the outcropping sediments beyond the reach of gravity slides such as slumps. This would have the big advantage that we can date some of the reflectors directly.   We are now ready for seismic line 2 that will stretch perpendicular to our first line 1, thus we are heading to the shelf break of Tanzania. This is an important line to understand the structures perpendicular to the coast, and the line will also deliver correlation of the seismic packages of marine origin to the land based geology, with correlation patterns to onshore oil wells.   All in all we had an excellent first day with delivery of a beautiful seismic line across Davie Ridge! The shipboard party