The Transformation of Sediment Into Rock: Insights From IODP Site U1352, Canterbury Basin, New Zealand

Abstract

At Integrated Ocean Drilling Program (IODP) Expedition 317 Site U1352, east of the South Island New Zealand, we continuously cored a 1927-m-thick Holoceneto-Eocene section where we can uniquely document downhole changes in induration and lithification in siliciclastic to calcareous fine-grained sediment using a wide range of petrological, physical-property, and geochemical data sets. Porosity decreases from around 50% at the surface to 5-10% at the base of the deepest hole, with a corresponding increase in density from ~ 2 to ~ 2.5 g cm 3. There are progressive bulk mineral changes with depth, including an increase in carbonate and decrease in quartz and clay content. Grain compaction is first seen in thin section at 347 m below sea floor and intensifies downhole. Pressure solution (chemical compaction) begins at 380 m and is common below 1440 m, with stylolite development below 1600 m, and sediment injection features below 1680 m. Porewater geochemistry and petrographic observations document two active zones of cementation, one shallow (eogenetic) down to ~ 50 m, as evidenced by micritic nodules and pore-water geochemistry driven by methane oxidation by sulfate, and another burial-related cementation zone (mesogenetic) starting at ~ 300 m. A transitional zone occurs between 50 and 300 m. Our results quantify downhole diagenetic changes and verify depth estimates for these processes inferred from outcrop studies, and provide an actualistic example of cementation and compaction trends in a slope setting.

Sedimentary architecture of a Late Cretaceous under‐filled rift basin, Canterbury Basin, New Zealand

“…The increase in plate convergence rates and possible initiation of the Alpine Fault during the Early Miocene triggered uplift, erosion and marine regression throughout the majority of central Zealandia, including the South Island and much of the onshore Canterbury Basin (Barrier et al., 2019; King et al., 1999; Mortimer et al., 2014). The Miocene to Recent was dominated by an increase in sediment supply from newly created topography to the west of the basin, generated by uplift of the Southern Alps in the central south (Browne & Naish, 2003; Bull et al., 2019; Lu & Fulthorpe, 2004; Lu et al., 2003, 2005; Marsaglia et al., 2017; Wellman, 1979). This recent tectonic phase and associated uplift were partly responsible for the often thin (<500 m) and discontinuous preservation of Cretaceous rift and post‐rift sedimentary rocks onshore, whereas offshore they are extensively preserved and only mildly deformed.…”

The erosionally confined to emergent transition in a slope‐derived blocky mass‐transport deposit interacting with a turbidite substrate, Ventimiglia Flysch Formation (Grès d’Annot System, north‐west Italy)

“…The sedimentary character of the marlstone conglomerate (for example, normal grading and roundness of component clasts) and its association with the underlying marlstone megabreccia, suggest that most of its clasts originally were early cementation nodules characterizing the less compacted and less cemented upper part of the failed Blue Marl section. Such early cementation nodules, documented elsewhere in a relatively shallow (eogenetic) diagenetic zone in similar argillaceous marlstones (Marsaglia et al ., 2017), may have become smaller, less frequent, less interlocked, and less indurated up‐section, alongside the decrease in carbonate content characterizing the Blue Marl (Bodelle et al ., 1971). Two processes may have acted, either exclusively or in combination, to generate the parent flow that deposited the marlstone conglomerate.…”