Abstract
Fluid flow in the subsurface is fundamental in a variety of geological processes including volcanism, metamorphism, and mineral dissolution and precipitation. It is also of economic and societal significance given its relevance, for example, within groundwater and contaminant transport, hydrocarbon migration, and precipitation of ore-forming minerals. In this example-based overview, we use the distribution of iron oxide precipitates as a proxy for palaeofluid flow to investigate the relationship between fluid flow, geological structures, and depositional architecture in sedimentary rocks. We analyse and discuss a number of outcrop examples from sandstones and carbonate rocks in New Zealand, Malta, and Utah (USA), showing controls on fluid flow ranging from simple geological heterogeneities to more complex networks of structures. Based on our observations and review of a wide range of the published literature, we conclude that flow within structures and networks is primarily controlled by structure type (e.g., joint and deformation band), geometry (e.g., length and orientation), connectivity (i.e., number of connections in a network), kinematics (e.g., dilation and compaction), and interactions (e.g., relays and intersections) within the network. Additionally, host rock properties and depositional architecture represent important controls on flow and may interfere to create hybrid networks, which are networks of combined structural and stratal conduits for flow.
Highlights
It is well known that besides the intrinsic rock and fluid properties, geological structures such as faults, fractures, and deformation bands may strongly influence fluid flow (e.g., [1,2,3,4])
Understanding the interaction between fluid flow and geological structures is key for the comprehension of flow-and-reaction-related phenomena that tend to localize around faults and fractures (e.g., [5, 6]), and fundamental for a variety of geological processes such as volcanism and metamorphism, as well as mineral dissolution and precipitation
We study a variety of geological structures, both fractures, joints, and deformation bands, from New Zealand, Malta, and Utah (Figure 1), where Iron oxide precipitates (IOPs) represent a record of paleofluid flow in sandstones and limestones
Summary
It is well known that besides the intrinsic rock and fluid properties (i.e., porosity, permeability, fluid density, and viscosity), geological structures such as faults, fractures, and deformation bands may strongly influence fluid flow (e.g., [1,2,3,4]). Different types of structures have different effects on flow. Open fractures, such as joints, may be highly conductive, whereas cemented fractures (veins) or deformation bands may be nonconductive or have very low permeability (e.g., [18,19,20]). Being able to identify and separate between different types of structures is essential since they may have different effects on flow. Numerous studies have offered insight into how single structures, or pairs of interacting faults and their damage zones, may affect flow [13, 31, 32]
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