On the delimitation of the carbonate burial realm

Abstract

Over the past decades, the burial realm, the most prolonged and arguably the least well-understood diagenetic environment, has received significant research attention. Despite remarkable progress driven by exploratory drilling, outcrop analogue studies and experimental work, the scientific theories defining the burial sub-domains are inconsistently presented in the literature. This paper reviews the concepts, processes and products that characterise the burial realm from the viewpoint of the carbonate geoscientist. Typical features of carbonate burial (fluid types, porosity evolution, diagenetic fabrics, patterns in isotope geochemistry) in epicontinental and marine basins are presented and discussed. A step towards an improved conceptual delimitation and a subdivision of the carbonate burial realm is taken, and an intuitive terminology is proposed. The very shallow limit of the burial realm is placed within the upper sediment column (redox boundary; centimetres to tens of metres). In the shallow (marine) burial domain (down to depths of many hundreds of metres), carbonate dissolution and reprecipitation, sediment dewatering and grain reorganisation take place. Interstitial waters are mainly marine (and subordinate meteoric) in origin and the system is fluid-dominated. Under ongoing burial, physical and chemical compaction reduces pore space. At burial depths of ca 750 m, initial sediment porosities (40–80%) are reduced to about 30%. The intermediate burial domain (hundreds of metres to about 2 km; T < 100°C) is characterised by the transition from fluid-buffered to rock-buffered diagenesis. In the deep-burial domain (ca 2–12 km; T > 100°C), marine formation fluids are increasingly modified by rock–fluid interaction and replaced by saline brines. The transition from the deep burial to the very low-grade metamorphic domain is placed at depths of 12–15 km (T > 250°C). Here, carbonates undergo recrystallisation into meta-carbonate and equigranular marble fabrics.