Mica Content Research Articles

Factors Affecting Potassium Pools Distribution in Calcareous Soils of Southern Iran

Different K pools in 197 surface and subsurface soil samples of southern Iran were determined to accurately assess factors affecting K pools distribution. Mineralogical analysis indicated that smectite, mica, chlorite, and palygorskite were the major minerals in the clay fractions. We obtained significant relationships between exchangeable, non-exchangeable, mineral, and total K with mica content, CEC, calcium carbonate equivalent, and clay content. Although many researchers have stated that mineralogical composition determines K status of soils, our studies indicated that some characteristics such as soil moisture and temperature regimes, soil orders, depth, agricultural activity, leaching, and some soil properties like particle size distribution, soil salinity, calcium carbonate equivalent, and cation exchange capacity could also affect K equilibration in the soils. Generally, Histosols and coarse-textured Entisols had the lowest contents of different K pools, and Alfisols and Vertisols had the highest values. On the other hand, soils with xeric moisture and mesic temperature regimes had the highest contents of different K pools. Further research is required to study the relationship between these findings with plant response and uptake of K.

Static and dynamic compressive properties of mica/polypropylene composites

The static and dynamic properties of mica/polypropylene composites, with a mica content of 10, 15, 20% by weight, were studied at different levels of strain rates (from 10s−4 to 10s2), using a conventional Universal Testing Machine and Split Hopkinson Pressure Bar apparatus. The results show, that the mechanical properties of mica/polypropylene composites, in terms of yield stress, fracture strain, compression modulus and compressive strength, were greatly affected by the level of strain rates applied and mica content. It was found that the Bergström model was both consistent and reliable, in evaluating the effect of the strain hardening mechanism of the composites, in respect to the applied strain rate. The relationship between the strain rate sensitivity and the thermal activation volume of the mica/polypropylene composites were successfully obtained at various mica contents, where the results show a contradicting pattern for both parameters.

The metamorphic history of rocks buried, accreted and exhumed in an accretionary prism: an example from the Otago Schist, New Zealand

AbstractAlthough subgreenschist facies metamorphic rocks are widespread in the upper crust, mineralogical processes affecting these rocks are poorly understood. Subgreenschist mineralogical transitions have been invoked as critical controls on the mechanical behaviour of rocks within the crustal seismogenic zone, calling for further study of very low‐grade metamorphic assemblages. In this study a multi‐technique thermobarometric study of the Chrystalls Beach Complex mélange, which is located within the Otago Schist accretion‐collision assemblage of the South Island of New Zealand, is presented. The Chrystalls Beach Complex comprises highly sheared trench‐fill sedimentary rocks and scattered pillow basalts, and is inferred to have formed during Jurassic subduction under the paleo‐Pacific Gondwana margin. Equilibrium mineral assemblages indicate peak P–T conditions in the range 400–550 MPa and 250–300 °C, which is supported by chlorite thermometry. Relatively high pressures of burial and accretion during foliation development are inferred from phengite content and b0 spacing analyses of white mica. Rare lawsonite occurs in a post‐foliation vein, and illite ‘crystallinity’ measurements indicate a thermal overprint during exhumation. These P–T estimates and their relative chronology indicate that the mineral assemblages developed along a clockwise P–T path. Based on variability in P–T estimates from different techniques, mineral assemblages developed during burial are largely overprinted during exhumation at similar or higher‐T than experienced along the prograde path. Observed subduction‐related subgreenschist assemblages are therefore likely to indicate lower‐P than experienced during subduction, as higher‐P mineral compositions re‐equilibrate during exhumation. The P–T path inferred in this study is similar in shape to P–T paths for higher grade parts of the Otago Schist, and other exhumed accretionary prisms around the world, and is therefore probably common for rocks buried, accreted and exhumed in accretionary prisms.

Platy layer silicate minerals for controlling residual strength in landslide soils of different origins and geology

We use a ring-shear apparatus to examine the relationship between the residual strength and mineralogical properties of landslide soils and find a significant relation between the residual strength parameter, φr, and the total content of layer silicate minerals prone to preferred orientation within the bulk soil. In this context, the total content of smectite, vermiculite, chlorite, and mica in the sub-425-μm soil fraction is a suitable mineralogical parameter for estimating the magnitude of φr. Plotting φr as a function of total mineral content forms a chair-shaped curve, based on which we classify landslide soils into three groups. In the first group of soils, sliding appears to be controlled by minerals such as quartz, feldspar, calcite, dolomite, and layer silicate minerals other than smectite, vermiculite, chlorite, and mica and their φr is almost constant at ∼32°. In the second group of soils, the controlling mineralogical factor for sliding quickly shifts from nonpreferred-orientation minerals to preferred-orientation minerals and φr decreases from 30° to 10°. In the third group of soils, sliding is well controlled by preferred-orientation layer silicate minerals and φr gradually decreases from 10° to 5°. The results show that the relationship can be used for predicting φr of a wide range of landslide soils that differ in geology, soil type, mineralogical properties, and shear strength.

Near infrared spectra of white mica in the Belt Supergroup and implications for metamorphism

The wavelength of the white mica (illite and muscovite) Al-OH absorption band near 2200 nm in 1036 samples from the Belt Supergroup and associated metasedimentary rocks was determined with a portable visible and near infrared reflectance spectrometer. The Al-OH wavelength decreases from 2225 nm in sub-biotite-zone samples to 2194 nm in sillimanite-zone samples; this decrease corresponds with an increase in total Al content of white mica from ~2.0 to ~2.8 atoms per 11 O atoms. These observations indicate that: (1) the frequency of the Al-OH vibration is controlled by the aluminoceladonite exchange reaction [ IV Si+ VI (Mg,Fe 2+ ) = IV Al+ VI Al], and (2) the reaction proceeds toward more Al-rich composition with increasing metamorphic grade. In these circumstances, Al-OH wavelength provides an indirect monitor of compositional variation and metamorphic grade. Metamorphic grade in most of the study area is in the biotite zone or lower, yet Al-OH wavelengths in low-grade rocks define systematic patterns that correlate with depth of burial and later structural displacements. In higher grade areas, wavelengths generally decrease from the garnet isograd through the sillimanite zone; however, anomalies occur locally, and it is not clear whether these result from differences in bulk composition and mineral assemblage or whether they point to actual metamorphic or structural discontinuities. These findings indicate that reflectance spectroscopy can yield valuable information on metamorphic intensity in rocks containing white mica, particularly in low-grade sequences where conventional indicators of metamorphic grade are lacking. Furthermore, this information can be obtained with field-portable spectrometers and the potential exists to obtain comparable results from airborne and spaceborne imaging spectrometers.

40Ar/ 39Ar analyses of artificially mixed micas and the treatment of complex age spectra from samples with multiple mica populations

Artificial mixtures of two age populations of muscovite and of biotite were prepared at relative weight percents of 3:1, 1:1, and 1:3 and analyzed by the 40Ar/ 39Ar vacuum furnace step-heating method. The original micas are Late Jurassic and Late Cretaceous samples that yield flat age spectra, with plateau ages defined by 97–100% of the gas release and no evidence for excess argon. The age spectra from mica mixtures yield patterns that systematically decrease with decreasing Jurassic mica content and increasing Cretaceous component. However, the mixed muscovite spectra are relatively flat, consistent with the two original samples showing similar degassing patterns during vacuum furnace heating. In contrast, the mixed biotite spectra are highly discordant with an overall decrease in age during the step-heat analysis. This is consistent with the degassing patterns of the original mica samples, which indicate the Jurassic biotite (high Fe/Mg) outgases at lower temperatures and the Cretaceous biotite (low Fe/Mg) remains retentive until the higher temperature steps. The individual degassing patterns and compositions show consistencies with known compositional controls on argon diffusivity indicating that micas may maintain argon retention characteristics rooted in crystal chemistry during vacuum furnace heating. All but one of the mixed samples failed to yield ages reflecting the age of the original micas. These results imply that complex age spectra obtained for multiply-deformed rocks with multiple mica populations may define geologically meaningless ages as a result of simultaneous degassing (i.e. mixing of sample reservoirs) during heating. Comparison of laboratory degassing rates and crystal chemistry indicates compositional controls on argon retention are likely preserved during vacuum furnace step heating and micas may degas/retain argon in a predictable manner. These conclusions support assertions that recovery of fossil age gradients in slowly cooled samples may be possible using furnace step heating.

Prediction of Mechanical Properties of Mica-filled Epoxy Composite Using Various Mechanical Models

This paper reports an investigation on the prediction of tensile properties of mica-filled epoxy composites. Various mechanical models were used to predict the tensile properties of mica-filled epoxy composites at several mica concentrations (5-30 vol%). The tensile properties of mica-filled epoxy at various mica contents were determined experimentally and modeled using Nielsen, Nicolais-Narkis, Verbeek, Halpin-Tsai, Guth, and Novak models. It was found that the tensile modulus of epoxy increases with increasing mica content, whereas the elongation at break and tensile strength decrease. Predictions, which have been offered by the models on tensile strength, elongation at break, and Young’s modulus, are in good agreement with experimental data over the range of mica contents studied. The Halpin-Tsai model shows best agreement in predicting the Young’s modulus (accuracy > 93 %), and Novak curve fitting shows best prediction for elongation at break (accuracy > 99%) for mica-filled composites. In the case of tensile strength, good agreement with Nicolais-Narkis models (accuracy > 99%) was obtained.

Grafted Polyolefin-Coated Synthetic Mica-Filled Polypropylene-co-ethylene Composites: A Study on the Interfacial Morphology and Properties

Purified maleic anhydride grafted isotactic polypropylene (iPP-MA) and maleic anhydride grafted polyolefin elastomer (POE-MA) were used to coat synthetic mica, which was added to block polypropylene-co-ethylene (cPP) to prepare composites with 10 wt% mica content. The effect of the kinds of grafted polyolefin, their contents and composition ratios on the interfacial morphology, mechanical properties, crystallization behavior, and essential work of fracture parameters for the composites were studied. The results showed that the coating of synthetic mica with grafted polyolefin could effectively lower the surface polarity of the mica and improve the interfacial adhesion between mica and cPP. The sedimentation volume of mica reached a minimum, and the interface adhesion of the composites was comparatively good when the grafted polyolefin was 3 wt% of the weight of the mica. When the content of grafted polyolefin was fixed at 3–5 wt% of the weight of the mica, the sedimentation volume of mica decreased and the interface adhesion of the composites improved with increasing POE-MA content. The coating with grafted polyolefin and the composition change of the grafted polyolefin had little effect on the mechanical properties and crystallization behavior of the mica-filled composites. However, the coating with grafted polyolefin increased the special essential work of fracture (we ) of the composites significantly, whereas the special non-essential work of fracture (βwp ) showed a slight decrease. When the total grafted polyolefin was fixed, the we decreased and the βwp increased a little as the POE-MA content was increased.

Stabilized Dredged Material. III: Mineralogical Perspective

The prior two papers in this series reported on the geoenvironmental and geomechanical properties of 20 stabilized dredged material (SDM) blends using dredged material (DM) from the U.S. Army Corps of Engineers Craney Island confined disposal facility. The pozzolans included lime, cement kiln dust (CKD), class F fly ash, and two cements (portland and slag cement). This paper reports on the mineralogical evolution of the SDM blends over a 6-month curing period using techniques new to mainstream geotechnical engineering: X-ray diffraction (XRD) with Rietveld quantification analysis which allows direct quantitative mineralogical comparisons between soil samples. Despite being classified as a high plasticity clay-organic clay (CH/OH soil), XRD showed that the DM contained no montmorillonite, illite or kaolinite, and was thus mineralogically unreactive. The quartz, feldspar, and mica contents were numerically tracked and were shown to remain stable 6 months after blending. The chlorite (in DM) content decrease...

Weathering, dust, and biocycling effects on soil silicon isotope ratios

Silicon isotope ratios (δ 30Si) of bulk mineral materials in soil integrate effects from both silicon sources and processing. Here we report δ 30Si values from a climate gradient of Hawaiian soils developed on 170 ka basalt and relate them to patterns of soil chemistry and mineralogy. The results demonstrate informative relationships between the mass fraction of soil Si depletion and δ 30Si. In upper (<1 m deep) soil horizons along the climate gradient, Si depletion correlates with decreases of residual δ 30Si values in low rainfall soils and increases in high rainfall soils. Strong positive correlation between soil δ 30Si and dust-derived quartz and mica content show that both trends are largely controlled by the abundance of these weathering-resistant minerals. The data also lend support to the idea that fractionation of Si isotopes in secondary phases is controlled by partitioning of silicon between dissolved and precipitated products during the initial weathering of primary basalt. Secondary mineral δ 30Si values from lower (>1 m deep) soil horizons generally correlate with the isotope fractionation predicted by a study of dissolved Si in basalt-watershed rivers and driven by preferential 28Si removal from the dissolved phase during precipitation. In contrast, after correcting for the influence of dust, secondary mineral Si depletion and δ 30Si values in shallow (<1 m deep) soil horizons showed evidence of biocycling induced Si redistribution and substantially lower δ 30Si values than predicted. Low δ 30Si values in shallow soil horizons compared to predictions can be attributed to repeated fractionation as secondary minerals undergo additional cycles of dissolution and precipitation. Primary mineral weathering, secondary mineral weathering, dust accumulation, and biocycling are major processes in terrestrial Si cycling and these results demonstrate that each can be traced by δ 30Si values interpreted in conjunction with mineralogy and measures of Si depletion.

Mica, deformation fabrics and the seismic properties of the continental crust

Seismic anisotropy originating within the continental crust is used to determine kinematic flow lines within active mountain belts and is widely attributed to regionally aligned mica. However, naturally deformed micaceous rocks commonly show composite (e.g. S–C) fabrics. It is necessary therefore to understand how both varying mica content and differing intensities of multiple foliations impact on seismic interpretations in terms of deformation fields. An outcrop analogue for granitic mid-crustal deformed zones is used here to calibrate the seismic response against both parameters. Seismic responses are modelled using crystallographic preferred orientations for polymineralic, micaceous granitic gneisses, measured using Electron Back-Scatter Diffraction. The sample results are generalised by modelling the effects of variations in modal composition and the relative importance of deformation fabrics of variable orientation, so-called rock and fabric recipes. The maximum P- and S-anisotropy are calculated at 16.6% and 23.9% for single-foliation gneisses but for mixed (i.e. S–C) foliation gneisses these values reduce to 5.8% and 7.5% respectively. Furthermore, mixtures of multiple foliations generate significant variations in the geometry of the seismic anisotropy. This effect, coupled with the geographical orientation of fabrics in nature, can generate substantial variations in the orientation and magnitude of seismic anisotropy (especially for shear waves) as measured for the continental crust using existing receiver function and teleseismic near-vertical incidence methods. Thus, maps of seismic anisotropy varying with depth in deforming continents need not imply necessarily depth-varying deformation kinematics and tectonic decoupling.

Barrier properties of biodegradable composite films based on kappa-carrageenan/pectin blends and mica flakes

In this work, the enhancement of the barrier properties to water vapour and gases (CO 2 and O 2) of a polymeric matrix composed by kappa-carrageenan and pectin (66.7% kappa-carrageenan), with the inclusion of mica flakes, was studied. The effect of the films mica content on the water vapour permeability (WVP) was dependent on the driving force applied. A higher WVP reduction (of about 40% for a mica content of 10%, mass of mica per mass of dry polymer), was observed when the films were more homogenously hydrated throughout their thickness. A significant decrease was also observed for both CO 2 and O 2 permeabilities (73% and 27%, respectively), in conditions where the films were plasticized with water (25% of water, dry basis), for which there is a depletion of the good barrier properties characteristic of dry polysaccharide films. In addition, the composition of 10% of mica flakes in the polymer matrix represented a critical volume fraction of inorganic particles, above which there was a decrease of the films barrier properties, for all components tested.

Clast-based kinematic vorticity gauges: The effects of slip at matrix/clast interfaces

Clast-based methods for estimating the mean kinematic vorticity number W m are compromised by strain localization at the clast margins. Localization increases with modal matrix mica content as determined with samples from the Sandhill Corner mylonite zone – a crustal-scale, high-strain, strike-slip shear zone in Maine. Using these samples, we estimate W m with the oblique quartz shape-preferred orientation and rigid-clast rotation methods. The rigid-clast rotation method yields much lower values for W m than the quartz method. To investigate whether or not slip at the matrix/clast interface can explain the discrepancy in calculated W m, we conducted numerical modeling of rigid clasts enveloped by a low viscosity layer, both embedded within a shearing viscous matrix. Within this dynamic framework, we carried out numerical sensitivity analyses in which we varied the viscosity ratio between the lubricating layer and the surrounding matrix, the thickness of the lubricating layer, and the kinematic vorticity number of the bulk flow. Our data and numerical results succeed in explaining why W m estimates from clast-based rotational methods are typically lower than estimates from other methods, and this has implications for testing hypotheses related, for example, to vorticity partitioning in oblique convergent settings, crustal-scale extrusion or channel flow, and exhumation of ultra-high pressure rocks, all of which rely on robust estimates of W m. The relation between the shape preferred orientations of clasts and modal mica content lead to the hypothesis that mica is the cause of the lubrication at clast/matrix interfaces. If so, then we surmise that mica fish should be self-lubricating and would therefore form an end-member shape preferred orientation, regardless of matrix modal mica content. The unique role of mica allows us to speculate about the bounds on viscosity contrast between the matrix and lubricated clast interfaces.

The Capillarity of Mica-Rich Base-Course Aggregates

In regions of temperate climate, the destructive influence of frost is the main contributor to damage of a road structure. Commonly, the frost susceptibility of base-course aggregates is often ignored in road construction. However, a number of studies on aggregates for construction purposes, and field observations of road failures, indicate a negative influence of mica-rich rock aggregates (used in unbound applications) on the service life of road construction. The scope of the current work investigates the capillary properties of unbound base-course aggregates with varying free mica grains. The materials studied in this research are commercially available road construction aggregates, and originate from different regions of Sweden. The mineral composition of the samples has been determined by polarizing microscopy using a point-count method. The parameter characterizing the capillarity was measured using the test for determining capillary rise (VVMB24). The results show that there is a direct correlation between mica content of the aggregates and water suction by capillary forces. Therefore, mica-rich materials susceptible to frost heave, thus confirming the tendency for frost damage of unbound aggregates.

Herpes Simplex Virus Infection Downmodulates NKG2D Ligand Expression

Herpes simplex virus (HSV) type 1 infection may cause orofacial infections in humans. The virus resides in a latent form in neural ganglia and occasionally reactivates and infects epithelial cells. Natural killer (NK) cells have been implicated in immune control of herpes virus infections, possibly by downmodulating major histocompatibility complex (MHC) class I and by other, as yet unidentified, mechanisms. Upon HSV-1 infection of cell lines, surface levels of NKG2D ligands MHC class I related proteins (MIC) A and UL16 binding protein 2 were downmodulated due to late viral gene product(s). As also MHC class I levels were reduced by HSV-1, NK cell recognition of HeLa cells was not affected by infection. Total cellular MICA contents remained unchanged, suggesting masking, internalization or intracellular retention of MICA as possible mechanisms of viral downregualtion of MICA surface levels. Furthermore, NK cells from patients with active HSV-1 infection had a tendency towards increased expression level of the activating receptor NKG2D. These data support a role for NKG2D-MICA interactions in immune responses to HSV-1 reactivation.

Determination of the Test Methods Sensitive to Free Mica Content in Aggregate Fine Fractions

The detrimental influence of mica rich aggregates on structural deterioration of road pavement has been discussed in the literature for over a half century. This negative effect is of great importance especially for regions with crystalline, mica-rich bedrock and temperate, subarctic climates. Recent investigations reveal that elevated fractions of free mica particles in unbound granular materials, used in road constructions, greatly reduce bearing capacity and influence the hydraulic behavior of the road structure. Despite the awareness of mica’s potential harmful effect, the absence of properly adapted analytical methods is noticeable. The scope of the current study was to test two possible analytical methods which, are susceptible to mica content and could be used as an indicating technique for quantitative determination of free mica particles in unbound granular materials. Two standard methods: Sand equivalent test and methylene blue (MB) test were assumed as the most sensitive to mica presence. The rock samples used in the tests are representative for the common crushed rock aggregates for construction purposes with different contents of mica. Both methods showed susceptibility to mica content and gave strong correlation in terms of mica content. The result of the MB test can be explained by the schistose structure of mica particles and the ability of mica to absorb liquids. Another important explanation is the increased reaction surface of mica particles, which leads to an increase in the total reaction surface of the sample. The receptiveness of the sand equivalent test to mica content could be caused by the ability of mica to stay in suspension due to its flake-shaped grains.

Impact of mica content on water sensitivity of asphalt concrete

It is well known that mineral fillers have an important influence on the performance of bituminous mixtures. Properties of filler are depending on the type and the nature of mineral filler. Experience has shown that presence of mica in the filler material has reduced the asphalt concrete resistance against water influence and freeze and thaw cycles. The purpose of the present work is to clarify the effect of free mica in the filler material on the durability of bituminous mixtures. Presence of free mica results in a tremendous increase of the total surface area of aggregate, which is intended to be covered by a bitumen film. It is concluded that making mix design in respect to surface area of the filler will almost vanish the disadvantage of using mica in production of asphalt mixtures. It will also result in using less amount of mineral filler.

Modelling damping ratio and shear modulus of sand–mica mixtures using genetic programming

This study presents two Genetic Programming (GP) models for damping ratio and shear modulus of sand–mica mixtures based on experimental results. The experimental database used for GP modelling is based on a laboratory study of dynamic properties of saturated coarse rotund sand and mica mixtures with various mix ratios under different effective stresses. In the tests, shear modulus, and damping ratio of the geomaterials have been measured for a strain range of 0.001% up to 0.1% using a Stokoe resonant column testing apparatus. The input variables in the developed NN models are the mica content, effective stress and strain, and the outputs are damping ratio and shear modulus. The performance of accuracies of proposed NN models are quite satisfactory (R2=0.95 for damping ratio and R2=0.98 for shear modulus).

Modelling damping ratio and shear modulus of sand–mica mixtures using neural networks

This study proposes two neural network (NN) models for damping ratio and shear modulus of sand–mica mixtures based on experimental results. The experimental database used for NN modelling is based on a laboratory study of dynamic properties of saturated coarse rotund sand and mica mixtures with various mix ratios under different effective stresses. In the tests, shear modulus, and damping ratio of the geomaterials have been measured for a strain range of 0.001% up to 0.1% using a Stokoe Resonant Column testing apparatus. The input variables in the developed NN models are the mica content, effective stress and strain, and the outputs are damping ratio and shear modulus. The performance of accuracies of proposed NN models are quite satisfactory ( R 2 = 0.97 for damping ratio and R 2 = 0.99 for shear modulus). Moreover the proposed NN models are also presented as simple explicit mathematical functions for further use by researchers.

Crack density tensor inversion for analysis of changes in rock frame architecture

SUMMARY This paper presents a development of the use of multi-axial ultrasonic data for the quantification of extrinsic, crack or grain-contact induced elastic anisotropy in core samples with application to a UKCS oil field. An approach for inversion of multi-axial velocity measurements is presented, which extends the previous work by Sayers (2002) for the determination of secondand fourth-order crack density tensors from inversion of multi-axial ultrasonic velocity data. The extensions to the inversion approach provide improved consideration of data uncertainties, by using all available P- and S-wave data and also permit the inclusion of an orthorhombic background anisotropy in the inversion [e.g. due to intrinsic lattice preferred orientation(LPO) effects]. The latter aspect leads to estimates of the extrinsic anisotropy, that is, the quantified crack density tensors, that are ‘unpolluted’ by the effects of the intrinsic anisotropy, thus permitting extrinsic and intrinsic anisotropies to be distinguished. For the samples considered, the extrinsic crack-induced anisotropy is strong relative to that of the intrinsic LPO effects, and the pre-dominant crack-set is commonly aligned parallel to the depositional fabric (which is generally horizontal). However, the LPO and extrinsic anisotropies are in general aligned, which indicates a linked origin. Furthermore, a strong correlation is observed between the degree of VTI anisotropy and the modal content of micas in the samples, which cannot be explained solely by the LPO effect. In fact, it is shown that increased horizontal (grain parallel) crack densities are associated with higher mica content. These horizontal cracks in the mica-rich samples often show moderate-to-strong variations in crack density with loading that might be detected in situ with non-hyperbolic moveout. Additionally, three samples show significant pressure sensitivity of the vertical crack sets indicating that loading-induced azimuthal anisotropy might also exist in some layers in situ and be detectable using azimuthal AVO type analyses. Analysis of the fourth-order crack density tensor allows insight into the relative sizes of the normal and tangential crack compliances, B N and B T . For one case it is found that B N ≥ B T (i.e. the crack-sets are more compliant in compression than in shear). For another sample B N < B T ; this sample had been cleaned prior to the analysis, which appears to facilitate shear in the cracks. This conclusion may have significant implications for the use of analogue samples acquired at the surface where organic products, which lead to the reduced shear compliance, are not present.