Conceptualizing fluid-rock interaction diagenetic models with focus on tectonic settings

Abstract

A new conceptual diagenetic model is proposed to better understand the relationship between multi-scale tectonic and the ensuing diagenetic processes, whereby the physio-chemical fluid-rock interaction processes are linked to tectonic controls, in terms of creation or destruction of accommodation space, the evolution of overburden and compaction, exhumation, as well as fracturing and creation of fluid flow pathways. In our research, key processes involved in diagenetic fluid-rock interactions have been applied to a recent multi-scale tectonically induced sedimentation model in order to define a linked diagenetic-tectonic cyclicity concept. We demonstrate the applicability of this concept in various tectonic and depositional systems with worldwide examples. Four distinct diagenetic fluid types modify the properties of sedimentary systems, which are basinal fluids, compactional fluids, meteoric fluids, and fault-associated fluids. The related, time-independent, diagenetic facies and their extent in the subsurface defined as diagenetic facies tracts include the modified rock affected by a singular diagenetic fluid or process. The proposed diagenetic facies tracts are the basinal diagenetic facies tract, compactional diagenetic facies tract, meteoric diagenetic facies tract and fracture-associated diagenetic facies tract. Their subsurface extent is controlled by the tectonic evolution, and we demonstrate that quantification and prediction is possible using a previously defined tectonic successions model. Each diagenetic facies tract is associated with a set of diagenetic processes and resulting products, that ultimately impact the pore space of the host rock and its flow properties. The combinations of several diagenetic tracts (into diagenetic facies tracts complexes) have been assessed, showing that the optimal situation for enhanced flow is the one that combines meteoric diagenetic facies tracts with fracture-associated diagenetic facies tracts, where karst dissolution together with fracturing are common. Contrastingly, quiescent tectonic settings with a typical burial history result in excessive cementation and therefore reduced flow. These attributes are critical for the large-scale screening and quantification of subsurface geo-resources, conventional and particularly important for the sustainable ones (e.g., geothermal energy) and geological storage (e.g., CO₂ or energy) that are associated with enhanced fluid-rock interaction processes.