Longstanding goals of scientific ocean drilling include determining the timing and amplitudes of global sea-level change, as well as the role of eustacy in the generation and preservation of continental margin stratigraphy. However, continental margin sedimentation is a function of both allogenic and autogenic processes, and extracting a eustatic record requires an understanding of local sedimentary processes and their influence on strata formation. IODP Expedition 317 to Canterbury Basin, New Zealand provides an opportunity to identify the regional processes involved in the formation of sedimentary sequences where temporally evolving across-shelf and along-margin sediment sources potentially interact with both eustasy and tectonics to generate margin stratigraphy. This study defines sedimentary petrofacies using petrographic and X-ray diffraction techniques and combines them with lithofacies to characterize sedimentation within unconformity-bounded sequences. Differentiating the relative influence of each sediment source is made possible by the unique aspects of the onshore geology and sediment supplied by the rivers of South Island, New Zealand: in this system sediment composition is a proxy for transport mode/direction, with mica-rich schist detritus being brought in from the south, and graywacke Torlesse detritus from the west. Higher-resolution analyses will target specific seismic sequences from the Pliocene to Recent that represent changing climatic and eustatic conditions. A primary hypothesis tested is that recurring lithofacies motifs that likely formed during high-amplitude Pleistocene sea-level cycles can be linked to sediment provenance, and even where less lithologically distinct, a recognizable signal may remain in the detrital fraction. Another hypothesis is that the formation of Plio- Pleistocene sequences along the Canterbury Margin is strongly influenced by the relative sediment supply from alongshore/shelf (Clutha/Waitaki rivers) versus cross-margin (Rangitata-Ashburton-Rakaia braided system) transport, with the latter becoming more dominant in the later Pleistocene, potentially leading to an autogenic increase in accommodation space that lead to increased sequence preservation. A holistic approach is used to test these hypotheses, similar to that applied in the MARGINS Source-to-Sink focus site on North Island, New Zealand. This methodology links newly acquired data from onshore outcrops, stream and coastal deposits (collected in conjunction with New Zealand colleagues) to Expedition 317 results in order to evaluate potential basin-wide changes in sediment supply and distribution. Temporal changes in the relative timing and routing of sediment to the Canterbury margin are determined from comparisons between the cross-shelf (U1351, U1353, U1354) and the two Canterbury slope sites (ODP Site 1119 and U1352). Discrete mineralogical observations from this study eventually will be compared to and combined with high-resolution elemental and carbonate analyses proposed by Fulthorpe et al. to provide key petrologic and mineralogic constraints on core and seismic data interpretation for the margin, including distinguishing lithologic changes that might correspond to Milankovitch cyclicity. The history of global sea level change and the impact of future sea-level rise related to global warming are one of the foremost issues facing society. Drilling results from the Canterbury Margin represent a key global component of a comprehensive IODP program to extract sea-level information from continental margin stratigraphy. Our data and results will be made publically available through the IODP portal as part of the IODP Sample, Data, and Obligations Policy and through presentations at meetings and publications. This study will provide educational opportunities for a number of high school, undergraduate and graduate students at CSU Northridge and the University of Florida. One high school student from Florida will participate as part of the UF Student Science Training Program (UF-SSTP), a seven-week residential research program for junior and senior-level high schools students considering science careers. Two undergraduate and two graduate students will participate in this project from CSUN and UF, including students from underrepresented groups and it is expected this participation will form the basis for their theses (BS/MS) or dissertation. The project includes an educational outreach program at UF as part of the UF Geogator program that provides presentations to local K-12 programs about Earth and our environment. The program will make the research on global sea-level change accessible to the local Florida community, where rising sea level and the hazards associated with it are a growing societal concern.
A major aim of Integrated Ocean Drilling Program (IODP) Expedition 317 on the Canterbury Margin was to obtain the sea-level history of a Pacific passive margin that was well-characterized seismically, in order to create a global model of eustasy (global sea-level change) and its record in continental margin stratigraphy. Understanding eustasy, in turn, has great societal relevance in light of climate change and potential impacts on coastal infrastructure, as well as important applications in hydrocarbon exploration. In this study we documented the compositional variation and provenance of sandy terrigenous sediment at a transect of drill sites across the Canterbury Margin system to help decipher the roles of eustasy and tectonics in generating the continental margin shelf-to-slope stratigraphy at this location. This work takes advantage of the unique onshore geological variation in rock types to evaluate along strike vs. along shelf/slope input of sandy sediment. South Island river sediment composition can be used a proxy for transport mode/direction, with mica-rich schist detritus being fed into the system from the south and greywacke (Torlesse) detritus from the west, directly onshore of the Expedition 317 drilling transect. Our study is holistic, looking at river, coastal, shelf, slope settings that comprise the Canterbury sedimentary system, and sediments from Modern to Miocene in age, spreading north along strike in a deeper-water current transported (contourite) section at ODP Site 1119. It tests and expands on concepts developed within the NSF MARGINS Source-to-Sink Initiative, extending them past the Pleistocene (glacials/interglacials) back into deep time (Miocene). We define distinct compositional signatures associated with Pleistocene rapid sealevel change on shelf/slope systems, with long-distance current transport of terrigenous debris, and with tectonic events such as uplift and magmatism. Transect sites show non-uniform changes, suggesting that each part of the system (inner vs. outer shelf vs. slope) is variably affected at any given timeframe. In sum, this margin succession is product of strong current activity, tectonic activity associated with evolution of the Alpine Fault plate boundary, and Pleistocene glaciation, each of which leaves a fingerprint in the clastic record. This project has greatly enhanced diversity of the geoscience workforce and academia through its support of student researchers from underrepresented groups who have gone on to obtain or seek MS and PhD degrees.
