STYLOLITIZATION OF LATE EOCENE TO EARLY MIOCENE CARBONATE-BEARING LITHOLOGIES FROM IODP HOLE 317-U1352C (CANTERBURY BASIN)

Stylolites, recognized as irregular planes of discontinuity, are very common features in carbonate rocks. They result from physico-chemical processes induced by burial compaction or tectonic compression. Although the majority of the scientific community agrees that stylolites are caused by localized stress-induced dissolution of material along a fluid-filled interface, the genesis of stylolites is still a debated topic. Little is known on the controls on stylolitization and on the initiation of stylolite formation at a given site. For example, the role of clay and the role of grain size and grain fabric or lithology on stylolitization, are controversial and need more research. Also the interplay of stylolitization with fractures, porosity, cementation and fluid flow is complex. It is known that stylolites are closely related with local mass transfer of dissolved material, compaction and porosity reduction. All of the above are important diagenetic processes affecting intrinsic properties of the host rock.

The main focus of our study is the diagenetic aspect of pressure solution, and potentially related fracturation and cementation. Our approach has an emphasis on petrography and geochemistry. In order to gain a better understanding of the pressure solution process, the impact of several factors (such as burial depth, grain fabric and lithology and pore fluid characteristics) and the stylolite characteristics are assessed in late Eocene to early Miocene carbonate-bearing rock samples from the Integrated Ocean Drilling Program (IODP) Hole 317-U1352C (Canterbury Basin).

In addition, we assess fluid mobility during and after pressure solution. During pressure solution, carbonate is thought to dissolve, producing a fluid that could lead to fluid flow, which then could result in fluid escaping through fractures, or conversely in the cementation of pores or fractures if the fluid does not escape. Hence, we evaluate fluid flow and cementation and the role of fractures and the impact of insoluble residue along the stylolites by using a (quantitative) petrographic and geochemical approach.

A better understanding of what controls pressure solution and of the impact of stylolitization on fluid flow, derived from our study, will lead to a better prediction of diagenesis and heterogeneity in carbonate lithologies.