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1.
The Equotip surface hardness tester is becoming a popular method for rock and stone weathering research. In order to improve the reliability of Equotip for on‐site application this study tested four porous limestones under laboratory conditions. The range of stone porosity was chosen to represent likely porosities found in weathered limestones in the field. We consider several key issues: (i) its suitability for soft and porous stones; (ii) the type of probe required for specific on‐site applications; (iii) appropriate (non‐parametrical) statistical methods for Equotip data; (iv) sufficient sampling size. This study shows that the Equotip is suitable for soft and porous rock and stone. From the two tested probes the DL probe has some advantages over the D probe as it correlates slightly better with open porosity and allows for more controlled sampling in recessed areas and rough or curved areas. We show that appropriate sampling sizes and robust non‐parametric methods for subsequent data evaluation can produce meaningful measures of rock surface hardness derived from the Equotip. The novel Hybrid dynamic hardness, a combination of two measuring procedures [single impact method (SIM) and repeated impact method (RIM)], has been adapted and is based on median values to provide a more robust data evaluation. For the tested stones in this study we propose a sample size of 45 readings (for a confidence level of 95%). This approach can certainly be transferred to stone and rock with similar porosities and hardness. Our approach also allows for consistent comparisons to be made across a wide variety of studies in the fields of rock weathering and stone deterioration research. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

2.
A role of lithobionts in geomorphological processes is increasingly argued, but the spatio‐temporal scale of their impact is largely unexplored in many ecosystems. This study first characterizes in the temperate zone (northwest Italy) the relationships between lithobiontic communities including endolithic lichens and the hardness of their siliceous rock substrate (Villarfocchiardo Gneiss). The communities are characterized, on humid and xeric quarry surfaces exposed for decades and natural outcrops exposed for centuries, in terms of lichen and microbial constituents, using a combined morphological and molecular approach, and with regard to their development on and within the gneiss. A lichen species belonging to Acarosporaceae (Polysporina‐Sarcogyne‐Acarospora group, needing taxonomic revision) chasmoendolithically colonizes both the humid and xeric quarry surfaces, on which epilithic cyanobacterial biofilms and epilithic pioneer lichens respectively occur. Light and electron microscopic observations show the development of the endolithic thalli within rock microcracks and the hyphal penetration along crystal boundaries down to depths of 1 to 3 mm, more pronounced within the humid surfaces. Such colonization patterns are likely related to biogeophysical deterioration, while no chemical alteration characterizes minerals contacted by the endolithic lichen. By contrast, on natural outcrops, where the endolithic colonization is negligible, a reddish rind below epilithic lichens indicates chemical weathering processes. Schmidt Hammer measurements highlight that the endolithic lichens deeply affect the hardness of the gneiss (down to ?60% with respect to fresh controls and surfaces only colonized by cyanobacteria), exerting a significantly higher weakening effect with respect to the associated epilithic lithobionts. The phenomenon is more remarkable on humid than on xeric quarry surfaces and natural outcrops, where epilithic lichens are likely involved in long‐term hardening processes supporting surface stabilization. Endolithic lichens are thus active biogeomorphological agents at the upper millimetric layer of siliceous rocks in temperate areas, exerting their weakening action during the early decade‐scaled stages of surface exposure. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

3.
The identification of channel capacity associated with a particular frequency of peak discharges is necessary for discharge estimation for planning purposes at ungauged sites. Although lichen limits have been suggested to be useful for this purpose, previous studies have not elaborated their hydrological significance. Lichen limits are clearly defined on the sides of rock channels in New England. Australia and they are analyzed in relation to discharge at 6 gauging stations with up to 52 years of continuous record. It is demonstrated that the lowest lichen limit is maintained by peak discharges which occur on average at least once or twice each year. Recurrence intervals based on Annual Series and on Annual Exceedance Series are calculated and for the annual series are fairly consistent for the lowest lichen limit and range from 1·14 to 1·37 years. Lichenometry can be applied to the analysis of river channels in relation to the frequency of peak discharges. By reference to growth curves based upon lichens on Armidale tombstones it is shown that lichenometry may be employed to indicate dates for channel modification due to the removal of blocks and to dam construction and also to date the rock surface between lichen limits. Detailed analysis of the record from gauging stations indicates that where several lichen limits occur in a channel cross section each limit is related to periods when peak discharges exceeded the limits on at least 5 occasions. The lichen-free surfaces were then recolonized by Parmelia spp. and the size of the lichen thalli indicates the time elapsing since these frequent high discharges.  相似文献   

4.
Some species of crustose lichens, such as Ochrolechia parella (L.) Massal., exhibit concentric marginal rings, which may represent an alternative technique of measuring growth rates and potentially, a new lichenometric dating method. To examine this hypothesis, the agreement and correlation between ring widths and directly measured annual radial growth rates (RaGR, mm a−1) were studied in 24 thalli of O. parella in north Wales, UK, using digital photography and image analysis. Variation in ring width was observed at different locations around a thallus, between thalli, and from year to year. The best agreement and correlation between ring width and lichen growth rates was between mean width of the outer two rings (measured in 2011) and mean RaGR (in 2009/10). The O. parella data suggest that mean width of the youngest two growth rings, averaged over a sample of thalli, is a predictor of recent growth rates and therefore could be used in lichenometry. Potential applications include as a convenient method of comparing lichen growth rates on surfaces in different environmental settings; and as an alternative method of constructing lichen growth-rate curves, without having to revisit the same lichen thalli over many years. However, care is needed when using growth rings to estimate growth rates as: growth ring widths may not be stable; ring widths exhibit spatial and temporal variation; rings may not represent 1-year's growth in all thalli; and adjacent rings may not always represent successive year's growth.  相似文献   

5.
Ian Metcalfe 《Island Arc》2016,25(2):126-136
Limestones exposed north of Raub, Pahang, Malaysia, and sandwiched between the Bentong‐Raub Suture Zone and the westernmost margin of the Sukhothai Arc terrane, yield a late Dienerian (late Induan) conodont fauna. The co‐occurrence of Neospathodus dieneri Sweet (morphotypes 1, 2 and 3) and Neospathodus pakistanensis Sweet represents the Neospathodus dieneri morphotype 3 sub‐zone of the Neospathodus dieneri Zone. The sampled limestones are interpreted as the northwards extension of the Jerus Limestone which crops out near Cheroh and Jerus villages, significantly extending the known outcrop of the Jerus Limestone northwards. The Jerus Limestone is interpreted as hemipelagic and formed in a foredeep or forearc setting on top of the accretionary complex formed by eastwards subduction of the Palaeo‐Tethys during the Lower to Middle Triassic.  相似文献   

6.
The effect of the weathering processes generated by Lecidea aff. Sarcogynoides (Koerb.) on the substrate was studied by means of a scanning electron microscope. The elements present in the substrate (Magaliesberg quartzite) and in the lichen thallus were determined by X-ray fluorescence spectrometry for the purpose of comparison. The elements present were mostly similar although a few were present in the thallus which were not observed in the quartzite. It is possible that those elements present in the lichen thallus which were not present in the substrate may have been extracted from the atmosphere. The occurrence of small hollows (weathering pits) in which the early stages of plant development occurs, and the disintegration of the rock indicate that Lecidea aff. sarcogynoides (Koerb.) contributes to the chemical weathering processes by chelation and mechanically by the penetration and expansion of hyphae. A model is proposed in which a possible mechanism for these weathering processes is suggested.  相似文献   

7.
Rapid, field‐based measurements of rock hardness are of use in investigating many geomorphological and heritage science problems. Several different methods are now available for taking such measurements, but little work has been done to assess their comparability and strengths and weaknesses. We review here the capabilities of two types of Schmidt Hammer (Classic N type and Silver Schmidt BL type) alongside two types of Equotip (standard type D and Piccolo) for investigating rock hardness in relation to rock weathering on various types of sandstone and limestone, as well as basalt and dolerite. Whilst the two Schmidt hammers and the two Equotips show comparable results when tested at 15 individual sites, interesting differences are found between the Equotip and Schmidt Hammer values which may reveal information about the nature of weathering on different surfaces. Operator variance is shown to be an issue in particular for the Equotip devices, which also exhibit higher variability in measurements and necessitate larger sample sizes. Carborundum pre‐treatment also has varying effects on the data collected, depending on the nature of the surface studied. The Equotip devices are shown to be particularly useful on smaller blocks and in situations where edge effects may affect Schmidt Hammer readings. We conclude that whilst each device contributes to geomorphological research, they do not necessarily produce comparable information. Indeed, using Schmidt Hammer and Equotip in combination and looking at any differences in results may provide invaluable insights into the structure of the near‐surface zones and the nature of weathering processes. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

8.
Lichenometric dating represents a quick and affordable surface exposure dating method that has been widely used to provide a minimum age constraint on tectonic and geomorphic landscape changes as well as buildings and anthropogenic landscape changes in various settings during the late Holocene. Despite its widespread usage, this method has several limitations. Major problems relate to the sampling of lichen population on any given rock surface and the modeling of growth curves. In order to overcome these issues, it has been suggested to subdivide the rock surface into some areas and measure the largest lichen thallus on each one. However, how to express the data in terms of a probability distribution function and link it to an age of last exposure of the rock surface are still a matter of debate. Here, we propose a novel approach to the modeling of lichen growth curves by treating lichen growth as a continuous-time Markov process with a time-varying rate and additive Brownian noise. Given the growth rates, the probability distribution of the lichen population at any time can then be obtained by solving the Fokker–Planck equation. This method is illustrated using a dataset from the Huashan area of eastern China, which consists of measurements of the largest thalli on 12 rock surfaces of known age. We first build up the probability distribution of the lichen population for each rock surface based on extreme value theory and then use these to optimize the growth curve by minimizing the Jensen–Shannon divergence. A new method is also proposed to use the growth curve to map a sample of size data from an undated rock surface to the calendar age domain so as to yield a fully probabilistic estimate of the exposure age of the undated rock surface rather than a point estimate.  相似文献   

9.
The development of cavernous weathering features such as tafoni remains poorly understood. In particular, the roles played by internal moisture and case hardening remain unclear. In this study, Electric Resistivity Tomography (ERT) has been used to map moisture distribution within inner walls of tafoni developed in sandstone, and an Equotip device used to measure rock surface hardness as a proxy measure of the degree of weathering and case hardening. Seven large tafoni in the Golden Gate Highlands National Park (South Africa), varying in size and degree of development have been monitored. A dynamic relationship between surface hardness, degree of weathering and internal moisture regimes has been found. We propose a new conceptual model which illustrates the complex interaction between case hardening and internal moisture and suggests a new direction for cavernous weathering research. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

10.
Data are reported demonstrating the potential role of microscale morphologies, induced by endolithic lichen communities, specifically Verrucaria baldensis, in the initiation and development of mesoscale solution basin formation on limestone in the Burren, County Clare. A biophysical model is proposed outlining the different microscale stages leading to solution basin initiation with a progression from initial lichen colonization and growth, associated perithecial biopitting followed by biopit coalescence to form biotroughs, their subsequent enlargement and eventual incipient solution basin formation. This model provides one explanation for solution basin development as this end state may also be achieved through simple solutional means without biological input. The complexity of interactions at the lichen–rock interface are identified with emphasis on the spatial and temporal variability of these underlining the point that, as with macrotopographies at the landscape scale, rock surface microtopographies also reflect historical weathering legacies. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

11.
A traversing micro‐erosion meter was used to measure rock surface micro‐topography over 40 cm2 on a supra‐tidal cliff face from early morning to late evening in late spring. From 06:00 hours to 22:00 hours the relative heights of 188 coordinates were obtained using the meter at 2‐hour intervals, resulting in a data set of 1607 readings. Monitoring shows that rock surfaces are dynamic entities, with significant rise and fall relative to the first measurement at shorter timescales than previously reported. The maximum positive rise between readings was 0·261 mm and lowering was 0·126 mm. The pattern of change did not relate as expected to environmental variables such as temperature or insolation. Rather, the surface showed greater surface change in the early morning and late afternoon. It is hypothesized that this pattern relates to the expansion and contraction of lichen thalli as moisture is absorbed during higher humidity in the morning and late afternoon. The implications of these results for weathering studies are considered. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

12.
This research characterizes the weathering of natural building stone using an unsteady‐state portable probe permeameter. Variations between the permeability properties of fresh rock and the same rocks after the early stages of a salt weathering simulation are used to examine the effects of salt accumulation on spatial variations in surface rock permeability properties in two limestones from Spain. The Fraga and Tudela limestones are from the Ebro basin and are of Miocene age. Both stone types figure largely in the architectural heritage of Spain and, in common with many other building limestones, they are prone to physical damage from salt crystallization in pore spaces. To examine feedbacks associated with salt accumulation during the early stages of this weathering process, samples of the two stone types were subjected to simulated salt weathering under laboratory conditions using magnesium sulphate and sodium chloride at concentrations of 5% and 15%. Permeability mapping and statistical analysis (aspatial statistics and spatial prediction) before and after salt accumulation are used to assess changes in the spatial variability of permeability and to correlate these changes with salt movement, porosity change, potential rock deterioration and textural characteristics. Statistical analyses of small‐scale permeability measurements are used to evaluate the drivers for decay and hence aid the prediction of the weathering behaviour of the two limestones. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

13.
The Equotip rebound tester is a simple, non-destructive technique to measure the surface hardness of materials. Having a low impact energy gives the Equotip advantages over the commonly used Schmidt Hammer on weathered rock and stone. In this study we have investigated the influence of different parameters (sample size, moisture content and surface roughness) on the surface hardness values obtained from freshly cut blocks of four types of sandstone. In a series of laboratory experiments both Single Impacts (SIM) and Repeat Impacts (RIM) methods have been used with C and D probes (which have different impact energies). Our results show that whilst sample size is of great importance we find that smaller samples can be reliably evaluated than previously reported. Moisture contents are also found to exert a more important influence on both SIM and RIM results than previously thought, with up to 26% lower hardness values recorded on saturated vs dry sandstone. Conversely, we find that surface roughness (over Sz values of 100 to 800 microns) does not have a significant impact on SIM measurements collected using the D probe. Both SIM and RIM data are found to be good proxies for compressive strength and open porosity, with SIM data collected with the C probe showing the best fits. Data collected using 3D microscopy helps visualize and quantify the small impact marks created by the Equotip and confirms that these are much reduced when using the C vs D probe. The results highlight the benefits of the Equotip to studies of the nature and deterioration of sandstone, the need for careful evaluation of any confounding factors which might influence the values obtained, and illustrate the different advantages of C and D probes. © 2019 John Wiley & Sons, Ltd.  相似文献   

14.
A study carried out on Carboniferous limestone in the north and west of Ireland supports the idea that rock substrate is removed by the direct mechanical action of lichens. An experiment in which the lichen Collema auriforma was subjected to a number of wetting-drying cycles, showed, using scanning electron microscopy, that contraction of the lichen thallus during the drying phase plucked rock fragments from the substrate surface. This process could contribute to the formation of karstic features including solution basins.  相似文献   

15.
Tafone‐like depressions have developed on the Aoshima sandstone blocks used for a masonry bridge pier in the coastal spray zone. A thin layer of partial granular disintegration was found on the surface in depressions. To evaluate quantitatively the strength of the thin weathered layer, the hardness was measured at the surface of the sandstone blocks using both an Equotip hardness tester and an L‐type Schmidt hammer. Comparison of the two testing results indicates that the Equotip hardness value is more sensitive in evaluating the strength of a thin layer of weathered surface rock than the Schmidt hardness value. By applying two methods, i.e. both the repeated impact method and the single impact method, the Equotip tester can evaluate the strengths of fresh internal and weathered surficial portions of rocks having a thin weathering layer. Comparison of the two strengths enables evaluation of strength reduction due to weathering. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

16.
Historic structures can be viewed as exposure trials of the stone of which they are constructed. As such, they represent a geomorphological weathering experiment. Several structures of Henrician (sixteenth century) and greater age on the coast of southwest England have been exposed to coastal salt weathering for 500–600 years. Long‐term weathering rates on five different rock groups are derived from careful study of weathering depths and forms. There is significant variation in weathering rate between five major rock groups. Rank ordering of weathering rate values reveals a durability order of these rock groups, which is confirmed by local juxtapositions. Controls on rock durability in the coastal weathering environment include both mechanical and mineralogical characteristics. Specific density, and combined quartz and muscovite content, are positively related to durability; high feldspar and chlorite content are associated with low durability. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

17.
The Schmidt Hammer (SH) method is used to quantify the rock weathering degree and has been proposed as a relative dating tool. Terrestrial Cosmogenic Nuclide (TCN) methods provide absolute exposure ages for erosive surfaces. Few works combine both methods for surfaces older than the Holocene. We compare data obtained by both methods for c. 150 ka bp glacial and fluvial erosive granite surfaces from northwest Spain. Rebound values (R) have been firstly compared with the rock density to assess the correlation with the rock strength, independently from influence of factors such as wetness and roughness in the R‐values. For erosive glacial surfaces older than 100 ka R‐values are confined in a narrow range, with no differences within errors. Stepped fluvial surfaces of 700 m to 70 m above present sea level show an inverse correspondence between TCN ages and R‐values, although no age predictions can be done on the basis of the R‐values. Thus, age inferences exclusively based on R‐values may not be realistic, but SH studies could be a useful tool for selecting surfaces for TCN dating. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

18.
A simulation was undertaken within a climatic chamber to investigate limestone dissolution under varied carbonic acid (H2CO3) strengths as a possible analogue for future increases in atmospheric CO2 arising from global warming. Twenty‐eight samples cut from a block of Bath (Box Hill) limestone from Somerville College, Oxford, which had been removed during restoration after 150 years in an urban environment, were weighed and placed in closed bottles of thin plastic containing varying concentrations of H2CO3. Half of the stone samples were derived from exposed surfaces of the stone block (weathered) while the others were obtained from the centre of the block on unexposed surfaces (unweathered). The purpose of this was to compare dissolution of previously weathered versus unweathered surfaces in strong (pH 4·73) versus weak (pH 6·43) solutions of H2CO3. A temperature of c. 19 °C was maintained within the chamber representing a plausible future temperature in Oxford for the year 2200 given current warming scenarios. The simulation lasted 25 days with a few stone samples being removed midway. Stone samples show reduced weight in all cases but one. There was greater dissolution of stone samples in a strong H2CO3 solution as conveyed by higher concentrations of total hardness and Ca2+ in the water samples as well as enhanced microscopic dissolution features identified using SEM. The simulation confirms that enhanced atmospheric CO2 under global warming, given adequate moisture, will accelerate dissolution rates particularly of newly replaced limestone building stones. However, previously weathered surfaces, such as those on historical stone exposed for a century or more, appear to be less susceptible to the effects of such increased rainfall acidity. Conservation techniques which remove weathered surfaces, such as stone cleaning, may accelerate future decay of historical limestone structures by increasing their susceptibility to dissolution. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

19.
Despite numerous investigations on substrate‐inhabiting microflora, especially lichens, very little is known about the colonization of coastal escarpments by lithobiontic micro‐organisms, inland of a retreating coastline in Africa. Reported herein are the results of a combined field observation and microscopy study focusing on the connection between microrelief of the substrate, colonies of lithobiontic micro‐organisms (in particular the lichen Xanthoria parietina) and microstructures of putative bacterial origin. The occurrence of weathering pits in which the early stages of the biotic development occurs, and the subsequent disintegration of the rock indicate that lichens, mosses and fungi act synergistically by alternating chemical and mechanical weathering. Penetration of grains by expansion and contraction of the hyphae depletes the rock matrix and contributes to the mechanical breakdown of the rock. Calcite rhombs on the weathered surfaces of the calcite‐cemented sandstones are severely etched with well‐developed rhomb‐shaped etch pits (‘spiky calcite’), holes, or has one or more of the faces removed, and their cores exposed and leached. Nanofilaments (c. 100–700 nm) and ‘nanomicrobial’ fruiting bodies (c. 250 nm) emanating from micropores appear to be common on affected crystalline structures. Weddellite present immediately below the thallus is a strong indicator of biomineralization. Quartz responds differently to chemical weathering by producing peeling structures and microbrecciation features. The dissolution of these crystals appears to be a surface reaction‐controlled process mediated by microbial microfilaments and nanofilaments. A model is proposed, firstly indicating early‐stage biochemical weathering, followed by biophysical weathering. Disintegration of the rock outcrops in due to a complex interplay of several events, probably beginning at the nanoscale with penetration of sites on crystal faces. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

20.
Determining the rates of rock weathering is difficult because, firstly, the weathering rate of rocks is usually so slow that it is difficult to measure; secondly, it is also difficult to determine the start time and duration of weathering. The Shanxi River Valley in Fujian, China dried up after a reservoir was built upstream in 1959, and became a stone quarry site. Quarrying ceased in 1977, so a large amount of quarry wastes with artificially excavated surfaces were left in the valley. The concave-upward curved rocky surface, broken by manual excavation, easily contains rainwater in its central part, which was easily weathered into a more concave surface. Plaster mould casting was performed in situ on such a concave surface of an excavated stone rock in the valley and scanned with a high-precision 3D scanner to obtain 3D data of the concave-upward rock surface and its more concave middle part, which was considered as an initial weathering pit. The 3D model provided an in-depth understanding of the initial formation process of weathering pits, indicating that: (1) the average weathering rate of a weathering pit is 10.8 ± 0.49 cm ka−1; (2) weathering pits are generally formed by standing water in depressions on a flat near-horizontal rock surface due to weathering actions involving water; (3) the deepening rate of a weathering pit is about four times greater than that of the surrounding area; (4) the growth of a weathering pit can begin in some small concavities on the flat rock surface without pre-existing depressions and gradually expands; (5) a weathering pit is generally wider than deep or with a flat bottom due to expansion with a lateral weathering rate that is greater than that of the vertical, and the lamination of the host rock is not necessary for the formation of flat-floored weathering pits. © 2020 John Wiley & Sons, Ltd.  相似文献   

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