Shallow to Moderate Burial Diagenesis and Lithification Processes in a Mixed Carbonate/Siliciclastic Slope Succession in the Canterbury Basin, New Zealand

Abstract

At Integrated Ocean Drilling Program (IODP) Site U1352, drilled during Expedition 317 in the Canterbury Basin east of South Island, New Zealand, the 1927 m thick Holocene to Eocene section displays downhole changes in induration, from sandy sediment to calcareous sandstone. We document lithification processes in this continuously cored hole using a wide range of petrological, petrophysical and geochemical data sets measured on core and porewater samples. Porosity, mainly primary but also some secondary, decreases from around 50% at the sediment-water interface to ∼10% at the base of the hole (∼2km). with a corresponding increase in density from around 2 to 2.5 g cm³. Grain compaction is first seen in thin section at 347 m below the sea floor (mbsf). Pressure solution begins at 380 mbsf and is common below 1440 mbsf, with stylolite development below 1600 mbsf, and common glauconitic sediment-injection features below 1680 mbsf. Pore-water geochemistry and petrographic observations indicate two active zones of cementation, one shallow (eogenetic) down to ∼50 mbsf, as evidenced by micritic nodules, transitioning to another burial-related cementation zone (mesogenetic) starting at ∼300 mbsf. There are progressive mineral changes with depth: a decrease in quartz and clay content and an increase in carbonate, including carbonate cementing minerals. Our results quantify downhole diagenetic changes and verify depth estimates for these processes inferred from outcrop studies elsewhere in New Zealand and Australia, and they are likely applicable to other passive margin successions.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016