Rock fractures are a key contributor to a broad array of Earth surface processes due to their direct control on rock strength as well as rock porosity and permeability. However, to date, there has been no standardization for the quantification of rock fractures in surface process research. In this work, the case is made for standardization within fracture-focused research, and prior work is reviewed to identify various key datasets and methodologies. Then, a suite of standardized methods is presented as a starting “baseline” for fracture-based research in surface process studies. These methods have been shown in pre-existing work from structural geology, geotechnical engineering, and surface process disciplines to comprise best practices for the characterization of fractures in clasts and outcrops. This practical, accessible, and detailed guide can be readily employed across all fracture-focused weathering and geomorphology applications. The wide adoption of a baseline of data collected using the same methods will enable comparison and compilation of datasets among studies globally and will ultimately lead to a better understanding of the links and feedbacks between rock fracture and landscape evolution.

Rock fracturing sets the pace for a range of geomorphic processes. While experimental studies and modeling have provided invaluable insights into the mechanisms and rates of rock fracturing as a function of stress, time, and environmental conditions, field-based observations of subaerial fracturing evolution over geologic time are scarce. To address this knowledge gap, we conducted a systematic study of fractures that developed subaerially and in situ within clasts perched on abandoned late Quaternary alluvial surfaces (ca. 0, ca. 14, and ca. 62 ka in age) in the hyperarid Dead Sea Rift Valley, Israel. Using quantitative field observations, petrographic, and scanning electron microscopy, and micron-scale laser scans of fracture surfaces we found that fractures exhibit a consistent pattern of three distinctive weathering zones: (1) an “Outer Zone,” where fracture surface morphology resembles the clast exterior; (2) an “Accumulation Zone,” where fractures are infilled by “loose” accumulated particles; and (3) an “Inner Zone” where fractures extend inward to the crack-tip and preferentially follow grain boundaries. Crack-tips are characterized as a distinct micro domain that consists of fracture-parallel microcracks, chemical alteration, and dissolution morphologies. Altogether, the laboratory results indicate chemically enhanced fracturing and infiltration of water ahead of traction-free, open crack-tips. Field measurements also revealed an increase in fracture number density over geologic time. Our results highlight new details regarding the progressive nature of mechanical weathering through geologic time and the role of moisture as a potential rate-setting factor in the fracturing that allows mechanical weathering.

Abstract Rock fracturing drives and limits the evolution of Earth’s topography and life, the global carbon cycle, geologic hazards, and infrastructure stability. Yet there remains a paucity of constraints on long-term fracturing behavior. Here we use field observations to show that fracturing rates in natural surface rocks decrease exponentially over time. We present lab measurements showing that these results are consistent with rock mechanics experimental data and theory linking progressive fracturing to decreasing brittle strain response to stress. We characterize fracture evolution over periods of 1 – 100 kyr for three different field sites and three rock types. For rocks with less than ~5 kyr of exposure, fractures grow at rates on the order of 10 – 100 mm/kyr, then after ~10 – 15 kyr, fractures grow by less than 2 mm/kyr. Over similar timescales, the ‘appearance’ of visible fractures also decreases, dropping from 36 new fractures per m^2/kyr to <2 per m^2/kyr. We independently document similar fracturing deceleration trends using microfracture analyses, plus a novel application of infrared photoluminescence (IRPL) dating for three in situ fractures in a single clast. Our results contrast significantly with current landscape-scale conceptual models that assume fracturing rates and characteristics are invariant over time and are controlled by short term rock strength and external stress magnitudes alone. Instead, our findings indicate that, over geologic time, rock’s fracturing increases its toughness.

&lt;p&gt;Fractures in rock are ubiquitous; from cold dry planetary bodies to the hottest, wettest climates on Earth, and from km-scale tectonic fractures deep in Earth&amp;#8217;s crust to microcracks in surficial rocks. Yet, many of these fractures propagate progressively over geologic timescales, making their development complex and enigmatic. Therefore, to measure how fractures have developed in rocks exposed at Earth&amp;#8217;s surface over millennia, and how this consequently changes rock physical properties, we collected ten ~25 cm diameter granitic boulders from two sites in the Eastern Sierra, California, USA. The boulders were deposited on the surface of alluvial terraces and fans during geologically instantaneous glacial and alluvial events at different times since about 148ka BP, then the depositional surfaces were subsequently abandoned. The &lt;em&gt;chronosequences &lt;/em&gt;of geomorphic surfaces provide a natural laboratory in which rocks of consistent lithology have been exposed to similar environmental conditions for different lengths of time, allowing us to compare rock property evolution on the order of 0 to 10&lt;sup&gt;5&lt;/sup&gt; years of environmental exposure; an approach that allows us to better understand and characterize mechanical weathering processes, especially long-term changes in rock fracturing. Note that &lt;em&gt;fresh&lt;/em&gt; (time-zero) rocks in this study are represented by boulders found within active channels, and that the measured changes in rocks with longer exposure times are interpreted by comparison with the fresh rocks. Focusing only on similarly sized boulders removes any ambiguities in tectonic and exhumation history that might arise in outcrop samples, thus ensuring that rocks from each site have experienced similar stress conditions; namely those restricted to the environment.&lt;/p&gt;&lt;p&gt;We performed laboratory measurements on 10 granitic boulders (four from Lundy Canyon, with exposure ages of ~0 to ~148 ka; six from Shepherd Creek, with exposure ages of ~0 to ~117 ka) to quantify how rock physical properties changed as a function of environmental exposure age. We measured key parameters commonly used as proxies for crack damage, including porosity, compressional wave velocity (Vp), and shear wave velocity (Vs). We hypothesize that changes in crack damage are likely to affect rock mechanical properties, so we also measured tensile strength, uniaxial compressive strength (UCS), and Young&amp;#8217;s modulus (E). We find that all measured parameters evolve as a function of exposure age, with systematic increases in porosity, and systematic decreases in Vp, Vs, tensile strength, UCS, and E. For example, porosity increases from 0.5 &amp;#8211; 1.0 % in the fresh rock to 2.6 &amp;#8211; 3.2 % in the oldest rocks. We interpret these changes as reflecting progressive subcritical crack growth that arises due to ubiquitous, but relatively low magnitude, environmental stresses continuously acting on the boulders, as opposed to differences inherited before their erosion from bedrock.&lt;/p&gt;&lt;p&gt;Apart from demonstrating the importance of environmentally driven cracking in rock weathering, these observations of progressive crack damage accumulation also have significant implications for the interpretation of any measurements made on rocks exposed at Earth&amp;#8217;s surface, even if the age of exposure is relatively short compared to the age of the geologic deposit itself.&lt;/p&gt;

Abstract. Rock fracturing comprises a key component of a broad array of Earth surface processes due to its direct control on rock strength as well as rock porosity and permeability. However, to date, there has been no standardization for the quantification of rock fractures in surface processes research. In this work, we make the case for standardization within fracture-focused research and review prior work to identify various key datasets and methodologies. We then present a suite of standardized methods that we propose as ‘baseline’ for fracture-based research in surfaces processes studies. These methods have been shown in preexisting work from structural geology, fracture mechanics, and surface processes disciplines to comprise best practices for the characterization for cracks, clasts, and outcrops. These practical, accessible and detailed methods can readily be employed across all fracture-focused weathering and geomorphology applications. The wide adoption of a baseline of data, all collected using the same methods, will enable comparison and compilation of data among studies globally, and ultimately will lead to a better understanding of the links and feedbacks between rock fracture and landscape evolution.

Agricultural terraces are the most widespread archaeological landforms worldwide. Despite their far-reaching prevalence in many inhabited parts of the world, archaeological soils in terraces (hereafter 'terrace soils') are scarcely studied and their nature is poorly defined. This study aims to depict a space-time framework for the development of calcareous soils in archaeological stone-wall bench terraces and suggest modifications to their soil classification and mapping. To do so, we examined soils at the forefront of five terraces in Catalonia (Spain), that had been previously dated with optically stimulated luminescence to periods from Medieval-Late Middle Ages (1200 +/- 60 CE) to Modern (1810 +/- 15 CE). Local soils surrounding the terraces are Entisols and Inceptisols in the relatively drier areas and Mollisols in the moister areas. Methods applied are field survey, standard physico-chemical analyses, and soil micromorphology. CaCO3 content, P, OM and CEC show irregularly trending values throughout the profiles. Micromorphology shows abundant content of charred components throughout the profiles and slight discontinuous carbonate recrystallization, mostly biogenic. Based on these observations, the main parent material was determined to be local soil that was redeposited by workforce as fill material for terracing. We further interpret that pedogenesis mainly involved structure development under the influence of anthroturbation and bioturbation, inheritance of ex situ aggregates from parent soil, reaggregation with little occurrence of organic matter, and low levels of lessivage and CaCO3 redistribution. We found that pedogenesis in these terraces started in a chaotic manner, considerably faster than pedogenesis in natural soils, primarily influenced by the act of terracing, the maturity of its inherited parent soil material, and relatively large depth. Therefore, early stages of terrace soil development can differ greatly from known soil models, questioning paradigms of pedogenic 'time zero' and 'maturity' in terrace soil. We suggest four terrace fill settings for terrace material and propose a model for the state of entropy and development of terrace soils. We classify the studied soils as Archaeo-Anthroportic Xerorthents, (Anthrosols (Calcaric, Escalic)), and Archaeo-Anthroportic Typic Haploxerolls (Anthrosols (Calcaric, Escalic, Relocatic, Anthromollic)), both overlying buried Inceptisols (Cam-bisols). Our primary conclusion is that terrace soils should be separately classified and mapped by treating terracescapes as distinct morpho-stratigraphic units in which age is the same as the age of their geomorphic surface. This study advances the pedological understanding of archaeological stone-wall bench terraces and identifies gaps in the understanding of terrace soils.

The Cenozoic geodynamics of the north‐eastern Mediterranean Basin have been dominated by the subduction of the African Plate under Eurasia. A trench‐parallel crustal‐scale thrust system (Misis–Kyrenia Thrust System) dissects the southern margin of the overriding plate and forms the structural grain and surface expression of northern Cyprus. Late Eocene to Miocene flysch of the Kythrea (Değirmenlik) Group is exposed throughout northern Cyprus, both at the hanging‐wall and foot‐wall of the thrust system, permitting access to an extensive Cenozoic sedimentary record of the basin. We report the results of a combined examination of detrital zircon and rutile U–Pb geochronology (572 concordant ages), coupled with Th/U ratios, Hf isotopic data and quantitative assessment of grain morphology of detrital zircon from four formations (5 samples) from the Kythrea flysch. These data provide a line of independent evidence for the existence of two different sediment transportation systems that discharged detritus into the basin between the late Eocene and late Miocene. Unique characteristics of each transport system are defined and a sediment unmixing calculation is demonstrated and explained. The first system transported almost exclusively North Gondwana‐type, Precambrian‐aged detrital zircon sourced from siliciclastic rock units in southern Anatolia. A different drainage system is revealed by the middle to late Miocene flysch sequence that is dominated by Late Cretaceous–Cenozoic‐aged detrital zircon, whose age range is consistent with the magmatic episodicity of southeast Anatolia, along the Arabia–Eurasia suture zone. Deposition of these late Miocene strata took place thereupon closure of the Tethyan Seaway and African–Eurasian faunal exchange, and overlap in time with a pronounced uplift of eastern Anatolia. Our analytical data indicate the onset of prominent suture‐parallel sediment transport from the collision zone of south‐eastern Anatolia into the Kyrenia Range of northern Cyprus, marking the drainage response to the continental collision between Arabia and Eurasia.

Rock fracturing can be slow and steady, comprising physiochemical processes that involve the chemical breaking of bonds that are weakened in response to local stress loading. Whereas subaerial cracking of surface boulders is universally observed in desert environments, the rates and specific mechanisms that drive crack propagation in such conditions are yet to be completely understood.Here, we present new field and petrographic observations from mode-1 (tensional) incipient (rocks are not yet split) fractures in alluvial boulders from the hyperarid southern Negev desert (Israel). Over 100 carbonate boulders embedded in a well-developed, 70 ka desert pavement that held visible fractures were forced apart along the incipient cracks. Doing so revealed a systematic recurring tri-zone pattern in crack morphology whose boundaries consistently paralleled the crack propagation front: Zone 1 – A weathered (as evidenced by incipient patina) zone proximal to the boulder surface; Zone 2 – A relatively fresh crack zone partly filled with aeolian particles and salts medial from the boulder up-facing surface; Zone 3 – A chemically altered (as evidenced by petrographic analyses) zone of otherwise intact rock at the crack tip. The occurrence of such micro-morphological crack zonation suggests slow sub-critical crack propagation at sufficiently long geologic timescales that support development of differential weathering within the crack. The petrographic analyses of sections perpendicular to the plane of the crack indicate chemical alteration that precedes the crack propagation in both space and time (i.e., extends in front of the crack tip), also indicates slow piecemeal propagation of the crack. This linkage between chemical weathering processes at the crack tip and slow subcritical propagation of the crack into the boulder provides additional support for first-order control of environmental and climatic conditions on boulder cracking rates, regardless of the physical stress-loading mechanism.

Late Paleozoic and Mesozoic tectonostratigraphic terranes are exposed in New Zealand and New Caledonia but their original positions and tectonic configuration along the eastern Gondwanan margin are not well understood. To better constrain Mesozoic reconstructions, we sampled marine and non-marine sandstones in the Murihiku Terrane (New Zealand) and obtained 935 new U-Pb detrital zircon ages and trace-element data. Our results show that late Permian to Early Triassic volcaniclastic successions in the Murihiku Terrane are characterized by unimodal age spectra (260-245 Ma), indicating a proximal arc source. In contrast, a mixed provenance is recognized in Middle Triassic to Late Jurassic rocks, containing Devonian-Triassic (380-240 Ma) and Triassic-Jurassic (240-145 Ma), as well as minor early Paleozoic-Proterozoic (500-1000 Ma) detrital zircon ages. The detrital zircon age spectra from the Murihiku Terrane match magmatic pulses in the adjacent Tuhua Intrusives (Median Batholith), which is thus interpreted as the main source of the detrital sediments. Our petrochronological data show that a prominent change in the sandstone provenance occurred at 235-230 Ma, simultaneously with the transition from the Longwood Suite (261-252 Ma) to the Darran Suite (232-125 Ma) magmatism in the Median Batholith. The transitional period at 235-230 Ma also overlaps with an episode of magmatism, deformation, and uplift in New Caledonia and eastern Australia (Hunter-Bowen Orogeny). We therefore conclude that this ubiquitous tectonic episode, during the Late Triassic, marks a large-scale secular change within the Gondwanide Orogen, which was possibly driven by increased convergence rates following a plate reorganization event. (C) 2020 Elsevier B.V. All rights reserved.

Archean and Proterozoic zircon grains are commonly found in much younger clastic sedimentary rocks, but the geological significance of these ages is often overlooked. Here we demonstrate that the age spectra of early Precambrian sedimentary recycled and/or magmatic inherited zircon grains form a unique pattern (detrital fingerprint) that can be used to test connectivity or indicate sediment recycling between terranes. Using the island of New Caledonia as a case study, we compiled 212 (published and new) concordant ages that are older than 1400 Ma from samples that represent contemporary sediments (this study), an allochthonous nappe sequence, and Paleozoic–Mesozoic metasedimentary rocks. By comparing these data with an equivalent dataset of Precambrian zircon ages (n>1400 Ma = 2636) from Paleozoic eastern Australia (Tasmanides), we test connectivity and disjunction of New Caledonia with crustal domains within the Tasmanides. Results show that the early Precambrian detrital fingerprint of New Caledonia is similar to the southern Tasmanides (and possibly East Antarctica), but is significantly different than the detrital fingerprint of the northern Tasmanides. The results thus provide an independent constraint on the origin of the late Paleozoic to early Mesozoic New Caledonian continental basement, shedding new light on the tectonic evolution of the southwestern Pacific region, and demonstrate the capabilities of the methodological approach.

The Paleozoic tectonic history of the Tasmanides in eastern Australia was dominated by subduction‐related processes along the margin of eastern Gondwana. The earliest deformation event, Delamerian Orogeny, took place in the middle‐late Cambrian and is recorded in rocks within the Delamerian and Thomson orogens. The Cambrian‐Ordovician Warburton Basin covers the boundary between the Delamerian and Thomson Orogens, but very little is known about its origin and deformation history. Here we interpret geophysical data, including 2‐D seismic reflection transects, Bouguer gravity, and aeromagnetic data that provide new insights into the deformation in the eastern Warburton Basin and the kinematics of major faults. Our results show that curvilinear NE‐trending faults in the eastern Warburton Basin are basement reverse faults that experienced multiple phases of contractional deformation. Evidence for a syn‐kinematic Cambrian package (Kalladeina Formation) suggests that faulting commenced in response to the Delamerian Orogeny. A subsequent Early Devonian deformation in the eastern Warburton Basin is evident from K‐Ar geochronology of low‐grade (subgreenschist) metasedimentary rocks. We suggest that the NE‐trending Cambrian fold‐thrust belt within the eastern Warburton Basin marks the continuation of the curved Delamerian Orogen into the Thomson Orogen. This oroclinal structure may have developed in the Early Devonian in response to dextral transpression along the northern boundary of the Delamerian Orogen. Our results provide a demonstration for the complex interactions that can take place during the evolution of convergent plate boundaries, involving deformation in the fold‐thrust belt, development of sedimentary basins, and oroclinal bending.

The island of New Caledonia is the second largest rock exposure of the continent Zealandia. The New Caledonian basement rocks have been interpreted as representing a late Paleozoic to Mesozoic intra-oceanic arc system that was possibly correlative to contemporaneous terranes in eastern Australia and New Zealand. In order to understand tectonic relationships between the basement rocks of New Caledonia and other eastern Gondwanan terranes, we obtained >2200 new U-Pb ages of detrital zircon grains from New Caledonia. Our new results, combined with a synthesis of previously published geochronological data, show abundant pre-Mesozoic zircon ages, but an absence of Early Permian to Middle Triassic ages characteristic of eastern Gondwana magmatism. The results thus suggest that the detritus of the New Caledonian basement was derived from a local Paleozoic continental fragment that was rifted from the margin of Gondwana, most likely in the Early Permian. The results imply that dispersal of the Gondwanan margins started earlier than the Late Cretaceous opening of the Tasman and Coral seas, consistent with the Mesozoic endemism of both New Caledonia and New Zealand.