I am thinking of the noun "refuse" (stress on the first syllable), which has nothing to do with the verb to refuse or with refusal, but means garbage, rubbish, junk, which could be covering the sea bed. This is a mistake which is not likely to be made by a native English speaker, but maybe the writer of this is not one.

I think it should read:

These cores were collected at locations where ***refuse was encountered on the gravel***.

("Met" means much the same as "encountered", but the latter is what one would use in English here, if my theory is right).

It sounds like the initial 'coring' was done by a modern technique relying on acoustics to penetrate soil layers and to return an accurate assessment of the lower layers. When gravel broke up the acoustics, i.e. the acoustic probe 'met refusal' at the gravel layer, the traditional drill was sent down to bring up a physical sample.

See http://www.state.me.us/doc/nrimc/mgs/explore/marine/saco-san...

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