Introduction
Jordan’s geologic history presents a compelling puzzle for researchers: a tapestry woven from Precambrian basement rocks, Mesozoic sedimentation, and successive tectonic regimes. The focus of this article is the interplay between pronounced tectonic structures and the subsequent nontectonic deformations observed in friable Lower Cretaceous sandstones. By examining these formations, scientists gain insight into how brittle rocks respond to regional stress, carving a pathway to understand deformation mechanisms that occur without direct faulting or significant tilting. This synthesis highlights the importance of structural geology for both academic inquiry and practical applications in engineering geology, resource exploration, and hazard assessment.
Geological Setting in Jordan
Jordan’s crust offers a layered story: a Precambrian granitic basement exposed in parts of the southern regions, overlain by sedimentary sequences that span the Paleozoic to the Cretaceous. The Lower Cretaceous sandstone units are of particular interest due to their friable nature and sensitivity to stress changes. In this context, “friable” implies a brittle, easily disaggregated material that records deformation through microfracturing, grain rotation, and reorganization of pore spaces. The regional tectonics—driven by plate boundary dynamics and mantle processes—impose complex stress fields that influence deformation patterns in these sands, sometimes independent of large-scale faulting.
Mechanical Behaviour: Tectonic vs Nontectonic Deformation
Structural geology distinguishes between tectonic deformations, which are driven by plate motions and are often accompanied by faulting and folds, and nontectonic deformations, which arise from localized processes such as diagenetic cementation changes, pore-fluid pressure fluctuations, compaction, and aquifer–cap rock interactions. In the friable Lower Cretaceous sandstones of Jordan, nontectonic deformation can dominate the texture and structure of outcrops and cores, especially where cementation is weak and grain contacts are minimal. These rocks may exhibit pressure solution seams, stylolites, and grain rounding that signal diagenetic adjustment rather than lateral displacement. Understanding the balance between tectonic stress and nontectonic adjustments helps explain observed anisotropy, permeability trends, and rock fabric evolution over geological timescales.
Case Studies: Deformation Signatures in Friable Sandstones
Several field sections across Jordan reveal a spectrum of deformation indicators. In zones of reduced cementation, fractures propagate along bedding planes and grain boundaries, yet remain non-penetrative by major faults. In these areas, stress relief through microcracking can be extensive, often accompanied by grain-scale rearrangements that reduce porosity and alter permeability. Conversely, locally elevated pore pressures during diagenesis may promote vein-like cement infillings that artificially strengthen certain pockets of rock, masking underlying tectonic strain. The net effect is a heterogeneous fabric where nontectonic processes imprint a distinctive signature on the sandstone’s mechanical and hydraulic properties.
Implications for Reservoirs, Hazards, and Engineering
For tailorable resource assessments and hazard mitigation, recognizing nontectonic deformation is critical. Friable Lower Cretaceous sandstones may display variable porosity and anisotropy patterns that challenge conventional reservoir models. Engineers must account for diagenetic history, cementation heterogeneity, and stress-induced microfracturing when designing foundations, slope stability analyses, or groundwater models. In civil and mining projects, nontectonic deformation indicators can guide the placement of boreholes, the estimation of rock mass strength, and the prediction of long-term settlement or unexpected subsidence. The integration of field observations, thin-section petrography, and geomechanical testing yields a more reliable picture of how Jordan’s sandstones respond to present-day and paleo-stress fields.
Methodological Approaches
Investigations combine stratigraphic correlation, petrography, and geomechanical experiments. High-resolution logging, micro-CT imaging, and scan-line analysis enable quantification of fracture density, orientation, and connectivity. Coupled with diagenetic zoning maps and in situ stress measurements, researchers can reconstruct the deformation history of friable sands and distinguish between tectonic and nontectonic signatures. Geographic information systems (GIS) facilitate the synthesis of regional datasets, while modeling efforts simulate the interplay between grain-scale processes and large-scale stress regimes.
Concluding Thoughts
The case of the friable Lower Cretaceous sandstones in Jordan illustrates how nontectonic processes can leave a lasting imprint on rock fabric, sometimes independent of classic tectonic events. A nuanced understanding of these deformation pathways enriches our interpretation of Jordan’s geology, informing exploration strategies, hazard assessments, and engineering decisions. As structural investigations advance, the boundary between tectonic and nontectonic deformation becomes a continuum rather than a dichotomy, urging geoscientists to integrate multiple lines of evidence for a fuller picture of crustal deformation.
