Data report: coring disturbances in advanced piston cores from IODP Expedition 398, Hellenic Arc Volcanic Field

Coring disturbances can affect the properties and interpretations of advanced piston cores collected during International Ocean Discovery Program (IODP) expeditions. IODP Expedition 398 in the Hellenic arc, Greece, used piston cores for unconsolidated and commonly thick volcaniclastic successions ranging from fine ash to lapilli intervals that are interbedded with cohesive carbonate oozes. The occurrence of thick intervals of loose, low-density clasts (pumice) and ash made coring operations difficult. Several instances of partial strokes were recorded by the drilling data, and flow-in coring disturbances occur over multiple cores, particularly where the volcaniclastic sediment is not confined by carbonate oozes. Moreover, strong rheological contrast between intervals favored midcore flow-in and, to a lesser extent, liquefaction and shearing. Collapse of the borehole enabled coring of fall-in that was recovered at the top of some cores. In addition, some cores experienced further disturbances during horizontal storage after recovery, affecting physical properties. These various disturbances in piston cores are important to identify because they affect the nature of the core, mix multiple strata, modify stratigraphy, and affect the shipboard analyses of physical properties and hence how geophysical data are interpreted. Visual identification of the coring disturbances presented in this report is based on core photographs that were reviewed by a single person over a few days to ensure uniformity in data acquisition. This report was produced to inform and guide current and future interpretations of data from these cores, which can affect stratigraphy and hence the reconstruction of eruption chronology, deposit thickness, and emplacement mechanisms.