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doi:10.2204/iodp.proc.317.204.2015

Introduction

In order to accurately reconstruct sea level history and subsequent depositional environments, it is necessary to test these sea level models against data from the geologic record. The occurrence of carbonate cements provides a method of understanding sea level history and the record of exposure because authigenic carbonate precipitation occurs in a wide range of conditions from marine to nonmarine. Outcrop studies would normally be used to study stratigraphy; however, these studies are difficult to employ with carbonate cements because of overprinting by burial and subaerial diagenesis. In order to obtain samples that have not been overprinted by later diagenetic events, material cored from modern shelf areas is necessary. Only a few shallow-shelf coring expeditions were carried out during the Deep Sea Drilling Project (DSDP), Ocean Drilling Program (ODP), and Integrated Ocean Drilling Program (IODP), and only one addressed the cementation history of siliciclastic shelf sediments. That study focused on the New Jersey shelf (Malone et al., 2002).

Recent drilling during IODP Expedition 317 on the Canterbury shelf provided important core records of shelf strata with local carbonate-cemented zones that may relate to seismic reflectors, including sequence boundaries (see the “Expedition 317 summary” chapter [Expedition 317 Scientists, 2011]). The purpose of this study is to further characterize the texture and chemical composition of the most indurated zones in the carbonate-cemented intervals in Expedition 317 cores. Understanding the conditions under which these zones formed is critical to enabling a more detailed interpretation of the seismic sequence stratigraphy of the Canterbury shelf and will contribute to additional testing of sea level models (Lu et al., 2005).

Geologic setting and Expedition 317 background

The Canterbury Basin is located on a passive margin that developed along the eastern portion of the South Island of New Zealand, which is a part of a continental fragment, the New Zealand Plateau, that rifted from Antarctica starting at ~80 Ma (Fulthorpe et al.,1996; Carter, 1998; Lu et al., 2005; see the “Expedition 317 summary” chapter [Expedition 317 Scientists, 2011]). The basin lies at the landward edge of the continental fragment and underlies the present-day onshore Canterbury plains and offshore continental shelf. The depositional history of the Canterbury Basin is a tectonically controlled transgressive–regressive cycle. The Cretaceous to Oligocene was a period of general transgression caused by relative sea level rise accompanied by postrift subsidence. Sequence boundaries suggest that the trend of sea level rise was punctuated by periods of sea level lowering or stillstand. In the Miocene, a regressive phase was initiated in response to increasing sediment supply that began with the mid-Cenozoic development of strike-slip motion along the boundary of the Pacific and Australian plates, the Alpine fault. Regression increased as the amount of convergence at the boundary increased. Convergence along this fault initiated the uplift of the Southern Alps around 8 Ma.

During Expedition 317 In 2009, four sites were cored in the Canterbury Basin at three sites on the continental shelf (Sites U1353, U1354, and U1351, landward to basinward) and one site (U1352) on the continental slope in water depths ranging from 85 to 344 m (Fig. F1) (see the “Expedition 317 summary” chapter [Expedition 317 Scientists, 2011]).

Drilling was performed using the advanced piston corer (APC), extended core barrel (XCB), and rotary core barrel (RCB) systems. Three holes were drilled at each of the three continental shelf sites (Sites U1351, U1353, and U1354), and material was recovered from the upper Miocene to the recent (Fig. F2). Drilling initiated at Site U1351 located on the outer shelf at a position thought to be near the historic lowstand shoreline (see the “Expedition 317 summary” chapter [Expedition 317 Scientists, 2011]). This would have placed Sites U1353 and U1354 onshore during the same lowstand. Four holes were drilled at Site U1352, on the upper continental slope, and the recovered cores represent a complete section from modern slope sediment down to Eocene limestone. Site U1352 was the deepest hole drilled in a single expedition and the second deepest hole in the history of scientific ocean drilling.

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