Introduction
The geology of Jordan presents a compelling case study for understanding the interplay between tectonic motion and rock deformation. While regional tectonics are well documented, the focus here is on the less obvious, yet equally important, nontectonic deformation processes that affect friable sedimentary formations. This article examines tectonic structures and their consequential nontectonic deformations in the Friable Lower Cretaceous sandstones found in parts of Jordan. By integrating structural geology with sedimentology, we can better predict how these rocks respond to stress, weathering, and unloading, with broad implications for engineering, groundwater management, and hazard assessment.
Geologic setting and material properties
The Lower Cretaceous sandstones in Jordan occur within a complex stratigraphic framework that records long-term tectonic quiet interspersed with episodic deformation. The friable nature of these sandstones—characterized by relatively weak cementation and coarse grain textures—renders them particularly sensitive to deformation mechanisms. In this context, tectonic structures such as faults, folds, and fracture sets create anisotropy in strength and permeability. The interplay between rock fabric, grain contacts, and pore-fluid pressures governs how the sandstone responds to stress, whether through brittle fracture, dilatancy, or more subtle nontectonic adjustments driven by near-surface unloading and surface processes.
Tectonic structures shaping deformation patterns
Several structural elements are crucial to understanding deformation in these rocks:
- Fault networks: Normal, strike-slip, and oblique faults can develop because of horizontal tectonic movements and vertical loading. In friable sandstones, faulting often localizes deformation, promoting zones of weakness that direct subsequent weathering and erosion.
- Fracture sets and joints: A pervasive system of fractures increases permeability and creates preferential pathways for fluid movement. The spacing and orientation of joints influence mechanical stability, particularly under fluctuating moisture and temperature.
- Folding and flexural slip: Regional compression can produce gentle to moderate folds. The associated flexural slip can generate shear zones within the sandstone, contributing to nontectonic deformation over geological timescales.
- Unconformities and bedding planes: Bedding and lithologic contrasts act as planes of weakness. This layering controls how stresses are transmitted and dissipated, affecting both deformation intensity and pattern.
Nontectonic deformation: the secondary response
Nontectonic deformation in friable Lower Cretaceous sandstones arises as a secondary response to tectonic forcing and surface processes. Key drivers include:
- <strongUnloading and diurnal cycles: Exhumation and seasonal drying can cause differential shrinkage, promoting crack widening and prong-like pull-apart features along pre-existing fractures.
- Weathering and osmotic moisture changes: Repeated wetting and drying cycles alter pore pressures and reduce effective stress, leading to gradual compaction, differential settlement, or localized subsidence in unconsolidated zones.
- Hydro-mechanical coupling: Groundwater flow along fracture networks can alter the effective stress regime, accelerating fragmentation and porosity changes in the friable sandstone matrix.
<h2Case implications for engineering and hazard assessment
Understanding the balance between tectonic structures and nontectonic deformation is essential for infrastructure planning, groundwater management, and hazard mitigation in Jordan. Engineering projects must account for anisotropic strength and potential progressive failure along fracture corridors. Sustainable groundwater extraction requires models that incorporate fracture connectivity and changes in permeability driven by nontectonic processes. Moreover, nontectonic deformation can influence slope stability, roadbed integrity, and building foundations, especially in areas with friable sandstone layers near the surface.
Methodological approaches
Researchers approach this topic by combining field structural mapping with petrographic analysis, geomechanical testing, and geophysical surveys. High-resolution imaging of fracture networks, together with pore-pressure monitoring and climate data, helps distinguish primary tectonic signals from secondary, nontectonic responses. Numerical models that simulate coupled hydro-mechanical behavior are increasingly used to predict deformation patterns under varying tectonic and environmental scenarios.
Concluding remarks
The Friable Lower Cretaceous sandstones in Jordan offer a clear window into how tectonic structures set the stage for nontectonic deformations. Recognizing and characterizing these processes improves our ability to forecast deformation, manage resources, and reduce risk in sedimentary basins affected by both long-term tectonics and surface-driven changes. As research advances, integrated, multidisciplinary studies will be essential to untangle the complex history recorded in Jordan’s sandstones and to apply these insights to neighboring regions with similar geological fabrics.
