Observation of corer penetration and sample entry during gravity coring

Gravity core samples provide the basic data source for a wide range of geological, geotechnical and geochemical studies. However, the length of the core recovered is often less than the penetration achieved by the corer, such cores being described as shortened. If the penetration of the corer has been measured, and it is assumed that no dropout of the core occurs as the barrel is withdrawn from the seabed, it is present practice to reconstruct in situ dimensions using an overall correction factor based on this penetration and the length of core recovered. However, measurements, reported here, have been made of corer penetration and sample entry and these show that the entry deficit (penetration minus sample entry) develops in some instances continuously, and in others intermittently. These results indicate that an overall correction factor is unlikely to be appropriate to any given section of the core.