Abstract
Faults commonly form loci for high fluid flux in sedimentary basins, where fluids, rocks and deformation processes frequently interact. Here, we elucidate the interaction of fluid flow, diagenesis and deformation near basin-bounding faults in sedimentary basins through a study in the vicinity (0–3.5 km) of the Dombjerg Fault in the NE Greenland rift system. Due to fault-controlled fluid circulation, fault-proximal syn-rift clastics underwent pervasive calcite cementation, whereas uncemented clastics at some distance from the fault remained highly porous and friable. Correspondingly, two distinct deformation regimes developed to accommodate continued deformation: discrete brittle fractures formed in calcite cemented rocks, whereas cataclastic deformation bands formed in uncemented deposits.We show that low-permeable deformation bands forming in highly porous rocks were associated with localized host rock alteration, and chemical reduction of porosity along bands. In rocks with cementation-induced low porosity, brittle fractures created new pathways for fluids, but were subsequently filled with calcite. Occasionally, veins comprise multiple generations of microcrystalline calcite, likely precipitated from rapidly super-saturated fluids injected into the fractures. This suggests cemented deposits sealed uncemented compartments, where fluid overpressure developed. We conclude that compartmentalized flow regimes may form in fault-bounded basins, which has wide implications for assessments of potential carbon storage, hydrocarbon, groundwater, and geothermal sites.
Highlights
Deformation, fluid flow and diagenesis are strongly interactive pro cesses that determine the evolution and properties of clastic sediments and rocks during and following deposition (e.g., Knipe, 1993; Laubach et al, 2010)
Deformation bands occur in the uncemented deposits outside the cementation zone, and within uncemented bodies of sedimentary rock inside the cementation zone (Figs. 2 and 4); deformation bands are ab sent in the cemented deposits within the cementation zone
Deformation bands are exclusively found in host rocks absent of calcite cement in outcrops both within and outside the cementation zone; no deformation bands are found within cemented deposits, suggesting that the bands likely formed after calcite cementation and establishment of the wider cementation zone
Summary
Deformation, fluid flow and diagenesis are strongly interactive pro cesses that determine the evolution and properties of clastic sediments and rocks during and following deposition (e.g., Knipe, 1993; Laubach et al, 2010). Increasing compaction and cementation leads to a reduction of porosity and permeability (e.g., Houseknecht, 1987; Lun degard, 1992; Pizzati et al, 2020), while at the same time to an increase of the tensile strength of the rock (e.g., Dyke and Dobereiner, 1991; Cook et al, 2015) The latter promotes a transition from grain scale defor mation processes of particulate/granular and cataclastic flow processes (see e.g. Menendez et al, 1996; Rawling and Goodwin, 2003) to discrete brittle failure, with fracture formation providing new pathways for fluids (e.g., Fisher et al, 2003; Williams et al, 2017). G., Bellani et al, 2004; Townend et al, 2017; Vanneste et al, 2005) and fluid circulation (e.g., Gibson, 1998; Eichhubl and Boles, 2000; Balsamo et al, 2013; Bense et al, 2013) The results of such influence have been showcased along the Dombjerg Fault, a major basin-bounding fault in the NE Greenland rift system (Kristensen et al, 2016; Salomon et al, 2020; Fig. 1). Syn-rift siliciclastic deposits in the hanging wall, juxtaposed against a footwall of crystalline basement, are affected by pervasive fault-proximal calcite cementation, which is interpreted to have resulted from fault-controlled fluid flow and diagenesis
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