Weathering Rind Research Articles

The Development of Limestone Weathering Rind in a Proglacial Environment of the Hallstätter Glacier

The contemporary retreat of glaciers results in the development of glacial forelands which constitute excellent areas for studies on the initial stages of weathering. This research concentrates on weathering rinds developed on glacially abraded Dachstein limestone surfaces (Eastern Alps) liberated from glacial ice since LIA (mid-19th century). We performed measurements of rock surface micro-roughness and strength (Schmidt hammer), spectral reflectance, and petrographic and microbiological analyses in SEM. There was a time-dependent increase in micro-roughness, decrease in rock strength and decrease in spectral reflectivity, but only within visual light. Rock surfaces on older sites reflected infrared radiation significantly better than younger ones. SEM analysis revealed that angular micro-structures inherited from glacial abrasion dominated in younger sites, eventually giving way to more rounded micro-structures. The structure of rock (micrite versus spar, phlogopite veinlets, etc.) plays a significant role. On older sites, microorganisms were detected within the studied weathering rinds, which probably results in better infrared reflectivity. We advocate the potential role of microorganisms (mainly heterotrophic) in the dissolution of limestone, and the role of cyanobacteria in the formation of the secondary porous limestone layer (extracellular biomineralization).

The Structural Characteristics and Chemical Composition of Serpentine Jade Weathering Rinds: Implications for the Formation Process

Weathering rind retains the greatest extent of the mineralogical and chemical composition information of the original mineral. Recently, we found some brownish-yellow or khaki serpentine jade weathering rinds with a thickness of 0.2–0.6 cm in Ji’an. The purpose of this paper is to explore differences in structural characteristics and chemical composition between weathering rinds and unweathered cores and summarize the formation of weathering rinds. In terms of structural characteristics, weathering rinds have smaller a0, b0, β values than unweathered cores; the specific surface area is 13.3987 m2/g; the pore volume is 0.0314 cm3/g; and the pore size distribution is characterized as more mesoporous (2–10 nm). The weathering rind shows partial dissolution of serpentine grains, increased porosity, and loosening structure. In terms of chemical composition, the weathering rind is characterized by the decrease of some serpentine major elements (Si, Mg, and Fe) and the increase of some impurity elements (Al, Ca, K, Na, and Cl). The weathering rind is the result of further alteration of serpentine jade, accompanied by the reduction of the Fe3+/Fe2+ ratio and the generation of the clay mineral (chlorite). In addition, it was also found that Ji’an serpentine jade belongs to Mg-bearing carbonate rock genesis, which are derived from marine deposits.

Change in composition and potential functional genes of microbial communities on carbonatite rinds with different weathering times.

Organisms and time are important factors for rock weathering to form soils. However, weathering time is usually difficult to quantitatively study, and the potential microorganisms involved in rock weathering are difficult to identify qualitatively. Currently, there is no clear conclusion on how ecological strategies of carbonatite weathering rind microorganisms change with weathering time, and how the microbial composition and functional genes involved in element cycling change over two century-scale weathering time. In this study, we selected abandoned carbonate tombstones as the subject and used the date when the tombstones were erected by humans as the onset of weathering. Using metagenome sequencing methods, we investigated the trends in the composition of fungal, bacterial and archaeal communities of carbonate weathering rind and related elemental cycle functional genes during a weathering time of 19 to 213 years. The results showed that: (1) with the increase in weathering time, at the phylum level, microbial taxa gradually shifted from r-strategists (faster turnover rates, higher mortality rates, higher reproduction, lower competition rate) to K-strategists (slower turnover rates, lower mortality rates, lower reproduction, higher competition rate), which correspondingly increased the abundance of functional genes related to C and N cycles. (2) The properties of the parent rock layer determines the colonization and distribution of weathering rind microorganisms (especially prokaryotic microorganisms) and the corresponding functional gene abundance. Our study provides new insights into the weathering process of carbonate rocks.

Quantifying weathering rind formation rates using in situ measurements of U-series isotopes with laser ablation and inductively coupled plasma-mass spectrometry

Abstract To quantify chemical weathering processes, it is essential to develop and utilize new geochemical tools that can provide information about chemical weathering in the field. U-series isotopes have emerged as a useful chronometer to directly constrain the rates and duration of chemical weathering. However, the conventional solution-based MC-ICPMS method involves a long and expensive sample processing procedure that restricts the numbers of measurements of samples by U-series analysis that can be completed. Here, we report in situ measurements of U-series disequilibria obtained with laser ablation (LA)-MC-ICPMS on weathering rinds collected from the tropical island of Basse-Terre in the archipelago of French Guadeloupe. We characterized two weathering rinds for U-series isotope compositions and elemental distributions with LA-MC-ICPMS and LA-Q-ICPMS. The in situ measurements of U-series disequilibria were consistent with the previous bulk measurements obtained by conventional solution MC-ICPMS despite the larger analytical uncertainties. The LA technique allowed a greater number of measurements that accelerated sample throughput and improved spatial resolution of measurement. The rind formation age, weathering rates, and U-series mobility parameters modeled in this study are comparable to the results from previous studies conducted on the same clasts, and also reveal new insights on rind formation such as the impact of micro-fractures on weathering history and U-series ratios. The improved spatial resolution available with LA Q-ICPMS helps distinguish between linear and power law rind thickness-age relationships that were unresolvable using conventional solution-based MC-ICPMS. In situ measurements with LA-Q-ICPMS in these weathering rinds also elucidates the sequences of mineral reactions during chemical weathering. The LA-Q-ICPMS maps of major and trace elements and elemental ratios reveal details about the rind formation processes at the weathering interfaces of clasts such as dissolution of primary phases, formation of new phases, development of porosity, and mobility behavior of U. This study demonstrates a new analytical method for determining weathering rates in rinds rapidly and accurately that can be used in a large number of rinds, providing key information at the clast scale.

From unweathered core to regolith in a single weathering andesitic clast: Rates and trends of in situ chemical weathering on a tropical volcanic island (Basse Terre Island, French Guadeloupe)

We conduct X-ray microprobe, chemical and U-series isotope analyses on an oriented weathering clast collected from the regolith of a weathered Quaternary volcanoclastic debris flow on Basse Terre Island, French Guadeloupe. The sample consists of an unweathered basaltic andesite core surrounded by a weathering rind, and an indurated crust that separates the rind from the overlying soil matrix. U/Th disequilibria dating indicates that rind age increases away from the core-rind boundary to a maximum of 66 ka. This translates to a rind-advance rate of ~0.2 mm kyr−1, broadly consistent with rind advance rates calculated elsewhere on Basse Terre Island. The overlying indurated crust is 72 ka, indicating a possible minimum duration of the rind formation. Elemental variations are constrained by a bulk chemical analysis along a vertical transects from the core to the overlying soil matrix and parallel electron microprobe analyses. The hierarchy of elemental loss across the core-rind boundary varies in the order Ca > Na ≈ Mg > K > Mn > Si > Al > Ti = 0 > P > Fe, consistent with the relative loss of phases in the clast from plagioclase ≈ glass ≈ pyroxene > apatite > ilmenite. The abrupt, <900 μm wide, Ca, Na and porosity reaction fronts at the core-rind boundary approximately equal the length of the long dimension of plagioclase phenocrysts observed in the unweathered core. The <1000 μm wide reaction front at the rind-soil interface is marked by an indurated horizon with Fe and Mn enrichment that spans into enrichment of Mn, Ba, Al, Mg and K in the soil matrix. Unlike previously studied clasts, the preservation of the rind-soil interface permits characterization of weathering reactions and material exchanges between the weathering core, the rind, and the surrounding soil matrix, shedding insights into communication between the enveloping weathering rind and host regolith. The lack of an enrichment signal of Mn within the weathered rind suggests that weathering processes active within clasts are distinct from surrounding soil formation processes.

Steinmetzite, Zn2Fe3+(PO4)2(OH)·3H2O, a new mineral formed from alteration of phosphophyllite at the Hagendorf Süd pegmatite, Bavaria

AbstractSteinmetzite, ideally Zn2Fe3+(PO4)2(OH)·3H2O, is a new mineral from the Hagendorf-Süd pegmatite, Hagendorf, Oberpfalz, Bavaria, Germany. Steinmetzite was found in a highly oxidized zone of the Cornelia mine at Hagendorf-Süd. It has formed by alteration of phosphophyllite, involving oxidation of the iron and some replacement of Zn by Fe. Steinmetzite lamellae co-exist with an amorphous Fe-rich phosphate in pseudomorphed phosphophyllite crystals. The lamellae are only a few μm thick and with maximum dimension ∼50 μm. The phosphophyllite pseudomorphs have a milky opaque appearance, often with a glazed yellow to orange weathering rind and with lengths ranging from sub-mm to 1 cm. Associated minerals are albite, apatite, chalcophanite, jahnsite, mitridatite, muscovite, quartz and wilhelmgümbelite.Goethite and cryptomelane are also abundant in the oxidized zone. The calculated density is 2.96 g cm–3. Steinmetzite is biaxial (–) with measured refractive indices α = 1.642(2), β = 1.659 (calc.), γ = 1.660(2) (white light). 2V(meas) = 27(1)°; orientation isY≈b,X^c≈ 27°, with crystals flattened on {010} and elongated on [001]. Pleochroism shows shades of pale brown;Y&gt;X≈Z. Electron microprobe analyses (average of seven crystals) with Fe reported as Fe2O3and with H2O calculated from the structure gave ZnO 31.1, MnO 1.7, CaO 0.5, Fe2O321.9, Al2O30.3, P2O532.9, H2O 14.1 wt.%, total 102.5%. The empirical formula based on 2 P and 12 O, with all iron as ferric and OH–adjusted for charge balance is Zn1.65Fe1.193+Mn0.112+Ca0.03Al0.023+(PO4)2(OH)1.21·2.79H2O. The simplified formula is Zn2Fe3+(PO4)2(OH)·3H2O.Steinmetzite is triclinic,P1̄, with unit-cell parameters:a= 10.438(2),b= 5.102(1),c= 10.546(2) Å, α = 91.37(2), β = 115.93(2) and γ = 94.20(2)°.V= 502.7(3) Å3,Z= 2. The strongest lines in the powder X-ray diffraction pattern are [dobsin Å (I) (hkl)] 9.313(65) (100), 5.077(38) (010), 4.726(47) (002), 4.657(100) (200), 3.365 (55) (3̄02), 3.071(54) (11̄2) and 2.735(48) (3̄1̄2). The structure is related to that of phosphophyllite.

Weathering crusts on peridotite

Chemical weathering of dark-green massive peridotite, including partly serpentinized peridotite, produces a distinct and remarkable brown weathering rind when exposed to the atmosphere long enough. The structure and mineral composition of crusts on rocks from the Ronda peridotite, Spain, have been studied in some detail. The generic overall weathering reaction serpentinized peridotite + rainwater = weathering rind + runoff water describes the crust-forming process. This hydration reaction depends on water supply from the outcrop surface to the reaction front separating green peridotite from the brown crust. The reaction pauses after drying and resumes at the front after wetting. The overall net reaction transforms olivine to serpentine in a volume-conserving replacement reaction. The crust formation can be viewed as secondary serpentinization of peridotite that has been strongly altered by primary hydrothermal serpentinization. The reaction stoichiometry of the crust-related serpentinization is preserved and reflected by the composition of runoff waters in the peridotite massif. The brown color of the rind is caused by amorphous Fe(III) hydroxide, a side product from the oxidation of Fe(II) released by the dissolution of fayalite component in olivine.

Weathering rind formation in buried terrace cobbles during periods of up to 300ka

Weathering rinds formed in Mesozoic sandstone and basalt cobbles buried in terrace deposits for up to 300 ka have been investigated. The aim was to determine the formation process and elemental mass balances during rind development. The ages of terraces distributed in the western part of Fukui prefecture, central Japan have been determined as 50 ka, 120 ka and 300 ka based on a tephro-stratigraphic method. Detailed investigations across the weathering rinds, consisting of microscopic observations, porosity measurements, and mineralogical and geochemical analyses using X-ray diffractometry (XRD), X-ray fluorescence (XRF), secondary X-ray analytical microscopy (SXAM), scanning electron microanalyser (SEM) and electron probe microanalysis (EPMA) have been carried out. The results revealed that the Fe concentrations in the weathering rind of a basalt cobble slightly decreased from the cobble’s surface (rim) towards the unweathered core. In contrast, in a sandstone cobble formed under the same environmental conditions over the same period of time there is an Fe-rich layer at some distance below the cobble’s surface. Elemental mass balances across the rinds were determined by using open system mass balance (τi,j) calculations and show that the Fe was precipitated as Fe-oxyhydroxides in the basalt cobbles, although Fe was slightly removed from the rims. In sandstone cobbles, on the other hand, Fe migrated along a Fe concentration gradient by diffusion and precipitated as Fe-oxyhydroxide minerals to form the weathering rinds. Presumably, precipitation was due to the relatively higher pH conditions caused by mineral dissolution within the pores, principally involving calcite, but probably also silicates including feldspar. The detailed characterization of the weathering rinds revealed the influence of lithology on the accumulation and dissolution of Fe-oxyhydroxides, causing weathering rinds with different characteristics to develop in different kinds of buried cobbles under the same conditions. Relatively large climatic changes in the study area did not cause discernable variations in the mean formation rates of the studied rinds, which were in the order of 10−8 m/a for both basalt and sandstone cobbles. These rates are 1–2 orders of magnitude slower than those reported for tropical areas elsewhere, most probably due to the lower rainfall in the studied area.

Role of lichens in granite weathering in cold and arid environments of continental Antarctica

Abstract The mechanical and chemical effects of lichens on the outer and inner surfaces of tafoni features were investigated through a multidisciplinary approach at two locations (Oasi 74°42′S, 164°07′E, 40–250 m a.s.l.; Mount Keinath, 74°32′S; 163°58′E; 850 m a.s.l.) close to the Italian Antarctic station (Mario Zucchelli). Outer tafoni roof surfaces show low values of effective porosity coupled with pervasive hyphal penetration and an extensive reddish-brown weathering rind. Inner tafoni surfaces show higher values of effective porosity, which correspond with an almost absent weathering rind and low hyphal penetration. Our observations indicate that: (a) iron oxy-hydroxides, particularly concentrated where hyphal patches and bundles contact biotite, consist of hematite; (b) the microcosms of lichen hyphae and their precipitates fill voids to form case hardening on outer surfaces; and (c) on inner surfaces biological action is less active, most likely because of more intense thermal stress and salt action.

Geochemistry of a New Zealand nephrite weathering rind

A dark-green nephrite boulder collected from Pleistocene glacial outwash gravels, West Coast of New Zealand, has a 6.1 cm thick weathering rind composed of an inner pale-green-white bleached zone (3.5 cm) and an outer brown oxidised zone (2.6 cm). The primary mineralogy of the boulder is monomineralic actinolite with small amounts of secondary Al-substituted goethite within the weathering-rind. Outwards from the unweathered nephrite core, SiO2, FeO, MgO, CaO, Na2O and density decrease, while Fe2O3, Al2O3, Cr, H2O+, H2O− and bulk oxidation ratio increase. The generalised weathering reaction can be characterised as: actinolite+H2O+H+=Fe-hydroxide+silicic acid+(Ca2+, Mg2+, Na+)aq. Assuming that alumina was immobile during weathering, isocon analysis indicates a mass decrease of −24% and a volume change of −26% in the bleached zone and a mass decrease of −52% and volume change of −58% in the oxidised zone with 7–84% depletion of all elements except Fe3+ and H2O− which indicates gains of 47–51% and 42–64%, respectively. Using H2O− values to estimate relative porosity, increasing Fe2O3, Al2O3, Cr and oxidation ratio and decreasing SiO2, FeO, CaO, MgO and rock density occur with increasing H2O−. Non-linear trends suggest that higher porosity created by actinolite dissolution results in an exponential increase in the amount of weathering (consistent with dissolution and secondary precipitation). An abrupt change in nephrite density at H2O+ values between ~2.38 and 2.55 wt % is probably related to incipient dissolution and cation loss as well as lower amounts of Fe-hydroxide formation. Depending on the deposition age of the gravels from which the nephrite boulder was derived, the weathering rind may be the result of 360–250 ka of weathering. The intensity of the green colouration of the nephrite reflects total iron content and oxidation ratio (mol.2Fe2O3×100/[2Fe2O3+FeO]). Combined with compositional data of other West Coast nephrites, a colour change from green or dark-green (unweathered) to pale-green-white (weathered) occurs where the oxidation ratio is >7; a change to brown colour occurs where oxidation ratios are >17.

Astrobiological Implications of Rock Varnish in Tibet

The study of terrestrial geomicrobiology and its relationship to rock weathering processes is an essential tool in developing analogues for similar processes that may have occurred on Mars. Most studies of manganese-enhanced rock varnish have focused on samples taken from warm arid desert regions. Here, we examine samples obtained from eolian-abraded lava flows of the 4700-4800 m high Ashikule Basin in Tibet. Because it receives approximately 300 mm of precipitation annually, this site is nowhere near as dry as Atacama Desert locales. However, the dusty, sulfate-rich, high-altitude and high-UV flux environment of the Tibetan locale offers new insight into rock varnish formation processes in a terrestrial environment that displays some attributes similar to those expected on early Mars. Microprobe measurements reveal that Mn enhancements in varnish are two orders of magnitude above the dust source, but Fe is only enhanced by a factor of three. Manganese-enhancing bacterial forms are not abundant but are still approximately 3 times more common than in Mojave and Sonoran Desert varnishes. In addition to its occurrence in subaerial positions, Tibetan varnish also occurs in micron-scale "pods" enveloped by silica glaze and as remobilized constituents that have migrated into the underlying weathering rind. A lack of surficial Mn-rich varnish, therefore, might not imply the absence of varnish. In contrast to suggestions that silica glaze might be a good source of microbial fossils and a key to varnish formation, we did not observe any clear microfossil forms entombed in silica glaze; further, there is no gradation between varnish and silica glaze but only distinct contacts.

Incipient weathering rind development on introduced machine‐polished granite discs in an Arctic alpine environment, northern Scandinavia

AbstractWeathering rinds, zones of alteration on the exterior surfaces of rock outcrops and coarse unconsolidated surficial debris are widely used by geomorphologists and Quaternary geologists as indicators of the relative age of landforms and landscapes. Additionally they provide unique insights into the earliest stages of rock and mineral weathering, yet the origin of these alteration zones is relatively poorly understood. This lack of understanding applies especially to the initial stages of rind formation. The study reported in this paper has two principal objectives. The first is to use lightly polished granite discs inserted in soil profiles under several different plant communities in an Arctic alpine environment for a period of four or five years to investigate the nature of incipient weathering rind development. The second is to investigate the factors responsible for spatial variability in the nature and rates of rind formation.Incipient weathering rind development on the outer edges of the granite discs is observable and measurable over a period of time as short as four years in the mild Arctic alpine environment of Swedish Lapland. The earliest stages of rind development involve the development of a porous structure consisting of a combination of pits and fractures which have been solutionally enlarged and modified. Solution appears to be preferentially concentrated on the surfaces of feldspars and, to a lesser extent, quartz. In addition, iron oxides are present along grain boundaries and in grain interiors and are interpreted to have been derived from the oxidation of ferromagnesian minerals. Spatial variability in weathering rind development appears to be particularly driven by differences in moisture but is not related to soil pH. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Rates of weathering rind formation on Costa Rican basalt

Weathering rind thicknesses were measured on ∼ 200 basaltic clasts collected from three regionally extensive alluvial fill terraces (Qt 1, Qt 2, and Qt 3) preserved along the Pacific coast of Costa Rica. Mass balance calculations suggest that conversion of unweathered basaltic core minerals (plagioclase and augite) to authigenic minerals in the porous rind (kaolinite, allophane, gibbsite, Fe oxyhydroxides) is iso-volumetric and Ti and Zr are relatively immobile. The hierarchy of cation mobility (Ca ≈ Na > K ≈ Mg > Si > Al > Fe ≈ P) is similar to other tropical weathering profiles and is indicative of differential rates of mineral weathering (anorthite > albite ≈ hypersthene > orthoclase ⪢ apatite). Alteration profiles across the cm-thick rinds document dissolution of plagioclase and augite and the growth of kaolinite, with subsequent dissolution of kaolinite and precipitation of gibbsite as weathering rinds age. The rate of weathering rind advance is evaluated using a diffusion-limited model which predicts a parabolic rate law for weathering rind thickness, rr, as a function of time, t(rr =κt), and an interface-limited model which predicts a linear rate law for weathering rind thickness as a function of time (rr = kappt). In these rate laws, κ is a diffusion parameter and kapp is an apparent rate constant. The rate of advance is best fit by the interface model.Terrace exposures are confined to the lower reaches of streams draining the Pacific slope near the coast where the stream gradient is less than ∼3 m/km, and terrace deposition is influenced by eustatic sea level fluctuations. Geomorphological evidence is consistent with terrace deposition coincident with sea level maxima when the stream gradient would be lowest. Assigning the most weathered regionally extensive terrace Qt 1 (mean rind thickness 6.9 ± 0. 6cm) to oxygen isotope stage (OIS) 7 (ca. 240 ka), and assuming that at time = 0 rind thickness = 0, it is inferred that terrace Qt 2 (rr = 2.9 ± 0.1 cm) is coincident with stage 5e (ca. 125 ka) and that Qt 3 (rr = 0.9 ± 0.1 cm) is consistent with OIS 3 (ca. 37 ka). These assignments yield a value of kapp of 8.6 × 10−13 cm s−1 (R2 = 0.99). Only this value satisfies both the existing age controls and yields ages coincident with sea level maxima. Using this value, elemental weathering release fluxes across a weathering rind from Qt 2 range from 6.0 × 10−9 mol Si m−2 s−1 to 2.5 × 10−11 mol K m−2 s−1. The rate of rind advance for the Costa Rican terraces is 2.8 × 10−7 m yr−1. Basalt rind formation rates in lower temperature settings described in the literature are also consistent with interface-controlled weathering with an apparent activation energy of about 50 kJ mol−1. Rates of rind formation in Costa Rica are an order of magnitude slower than reported for global averages of soil formation rates.

仙丈が岳，薮沢圏谷におけるれきの風化皮膜厚からみた完新世の岩石氷河流動の可能性

Weathering rind thickness of stones was measured on a crescentic ridge and on its surrounding low ridges and slopes in Yabusawa cirque (35° 43' N, 138° 11' E, 2, 885 m a.s.l.; est. MAAT-2.3°C) in the Akaishi Mountains, central Japan. Although a numerical time scale has not been established, the crescentic ridge, which is most likely of rock glacier origin, is considered to be the oldest at the study site from weathering rind data. Meanwhile, the debrismantled valley floor is estimated to be younger in the late Holocene. This fact suggests that more recent movement of rock glacier is proposed for the occurrence on landforms of the debrismantled valley floor.

Micromorphological Characterization and Microchemical Quantification of Weathering in an Alkali Basalt Pebble

Optical and submicroscopical techniques enable in situ chemical and mineralogical quantification of weathering and neoformation of minerals. A mass balance can be set up if the neoformed minerals can be related to their source. In thin section, a partially weathered basalt pebble enclosed by a weakly anisotropic, partially isotropic nonlaminated clay coating was examined. Such coatings were absent around any other adjacent grain surface and voids. Both observations indicated that the clay coating formed from precipitation of constituents weathered from the pebble. Weathering was considered isovolumetric because original shapes and volumes of the dissolved phenocrysts and groundmass of the pebble are maintained. The weathering rind closest to the unaltered core was characterized by weathering of glass. The strongly altered outer weathering rind was characterized by intensive pyroxene alteration. Chemical trends of various zones were in good agreement with micromorphological observations and mineralogical calculations. Mass balance calculations indicated that all elements except Fe were leached from the entire weathering rind. Essentially all Na and K, a considerable part of the Mg (44%), Ca (58%), and Si (29%), and a small amount of the Ti (15%) were leached from the rind. Only Si, Al, and a small amount of Ca were found in the neoformed coating. More Al was found in the coating than may have been leached from the rind, suggesting an external Al source when isovolumetric weathering is assumed. Sensitivity analysis of the calculation method concerning the consequences of changes in bulk density of core, rind, and coating showed similar trends in the elemental chemical amounts, except for Al. The isovolumetric method was successfully applied in this microscale weathering study.

Aranuian vegetation history of the Arrowsmith Range, Canterbury II. Revised chronology for moraines of the Cameron Glacier

Abstract The chronology for the younger Marquee and Arrowsmith moraine sets of the Cameron Glacier is revised. This is done by using new lichen growth curves for Rhizocarpon geographicum and R. candidum, developed for moraines of the Mueller Glacier at Mount Cook and calibrated with ages determined from rock weathering rind thicknesses. A new rock weathering rind curve was established for this purpose. The new lichenometric dates (greatest age estimated by either lichen, years B.P.) for the Cameron Glacier moraines are: Arrowsmith set: A1 c.170|A2 c.410|A2b c.480|A3 c.1010;A4 c. 1480|A5 c. 1960|Younger Marquee set: B1 c. 2320|B2 c. 3080|B3 c. 4480|B4 c. 5390. The kinds of vegetation and soils on the morainic time series are briefly indicated.

High‐resolution topography and albedo of the south polar layered deposits on Mars

Using a new photoclinometric technique with high‐resolution Mariner 9 images, maximum slopes of 10°–20° are found to occur on an exposure of layered deposits within the south polar residual cap of Mars. Stereophotogrammetry is used to constrain the photoclinometric solutions, which resolve layer thicknesses of 100–300 m. Albedo variations are correlated with slope, indicating that frost is present on level areas. There is evidence for temporal changes in frost distribution in the 7 days (4° of LS) between the two images used in this study. The magnitude of the slopes derived here and consideration of the stability of water ice at the surface of the layered deposits strongly suggest the presence of a competent weathering rind. The weathered surface may be composed of dark filamentary sublimation residue particles that protect the underlying ice from solar heating. This hypothesis is consistent with previous studies of the regional color and albedo of the layered deposits, which indicate that the deposits are slightly darker and less red than the bright dust that mantles much of the south polar region. Furthermore, the proposed weathering mechanism provides a plausible source of dark, saltating material for the Martian polar dune fields.

Adjustments by the Charwell River, New Zealand, to uplift and climatic changes

Major climatic changes and rapid local and regional tectonic movements were common in New Zealand during the late Quaternary and caused a diversity of adjustments in the drainage-basin and piedmont reaches of the Charwell River, which are separated by the Hope Fault. The onset of semi-arid, frigid climates during the latest Pleistocene probably greatly increased hillslope sediment yields in a periglacial environment, and the piedmont reach aggraded as much as 42 m on top of a broad strath. With the return of humid, mesic climates in the Holocene sediment yields decreased as dense forests again mantled the slopes, and the piedmont reach degraded as mush as 81 m. Dating of eleven cut-and-strath terraces by radiocarbon-calibrated weathering rind measurements on greyawake cobbles shows the degradation rates varied greatly during the last 14 ka (1 ka = 1000 yr). Initial degradation rates of < 4 m ka −1 increased to 30 m ka −1 by 6 ka ago during a mid-Holocene climatic optimum. Since 4 ka ago degradation rates have been only 1.2 m ka −1, comparable to uplift rates in the piedmont reach inferred from marine-terrace studies, and the river is again cutting a broad strath. Each broad strath represents equilibrium conditions attained by this powerful stream during interglacial times despite episodes of being overwhelmed by climatically induced sediment-yield increases during full-glacial climates and having to maintain a long-term degradation rate equal to the uplift rate. The 75–81 m of degradation since formation of the latest Pleistocene fill-terrace tread is the sum of the amount of late Pleistocene valley-floor aggradation and the amount of regional uplift that occurred between the estimated times of major strath formation at about 30 and 0 ka. The 39 m of tectonically induced degradation below the pre-aggradation strath is sufficiently large that post-30 ka uplift may have doubled Holocene degradation rates. Each of the eleven degradation terraces represents pauses of a few centuries in Holocene downcutting. Brief equilibrium conditions were attained by streambed armoring and concurrent growth of riparian plants; both processes progressively increased hydraulic roughness and the shear stresses needed to entrain streambed materials. Occasional floods, possibly from rare cyclones derived from tropical moisture sources, destroyed streambed armor and channel downcutting was renewed. Thus the formation of eleven equilibrium terraces can be accounted for without postulating additional tectonic perturbations or secular climatic changes.

Lichenometry as a relative-age dating method in Mount Cook National Park, New Zealand

Abstract A study of the Holocene glacial sequence at Mount Cook National Park, New Zealand lead to revision of proposed chronology and re-examination of lichenometric dates for the area. Glacial deposits were up to one order of magnitude older than was previously thought and the original lichen record has been re-calibrated using the new dates. Additional measurements of lichens were collected from the eastern end of the Park and compared with ages of the moraines. A revised lichen growth curve was produced for glacial deposits formed during the last 1000 years. The rate of lichen growth declined on some older surfaces with increased competition from vascular plants. Calibration of the lichen growth curve was only possible where independent dates were available. Rates of rock weathering rind development, soil development, and plant succession were all useful for the re-calibration. Many radio-carbon dates greatly aided the construction of the chronology.