Cryptotephra studies applied to a deep marine sedimentary record in the northern Hikurangi Trough, Aotearoa New Zealand

The study of ‘non-visible’ tephra layers (cryptotephra) can provide insight into the volcanic history of the Taupō Volcanic Zone (TVZ). The tephrochronological record of the TVZ has typically relied on macroscopic terrestrial or marine tephra deposits, which leaves big gaps in the record. This thesis uses non-destructive detection methods to identify cryptotephra deposits in the upper 500 m of core U1520D from the northern Hikurangi Trough as part of International Ocean Discovery Program (IODP) Expedition 375 in order to develop a more comprehensive record of TVZ volcanic activity for the past ~1.2 Myrs. First, the methodology used to incorporate magnetic susceptibility, density, and x-ray fluorescence data through the use of statistics and coding to identify potential cryptotephra deposits is presented. Then, the methods used to correlate and interpret cryptotephra deposits are presented with key characteristics being the major element geochemistry, glass shard morphology, shape of the shard concentration profile, and proximity to macroscopic tephra deposits. Finally, the results from these cryptotephra deposits are presented, showing the non-destructive detection technique to have a success rate of 85% for position identification and confidence levels applied to interpretations made. Within the upper 500 m of core U1520D, a total of five primary cryptotephra deposits and seven reworked cryptotephra deposits were identified within tephra barren regions of core. These results show is it possible to detect cryptotephra deposits in long core section using non-destructive detection, and that it is possible to make interpretations regarding method of emplacement from key characteristics.