Manganese-rich rock varnish does occur in Antarctica

doi:10.1016/0009-2541(92)90182-5

Chemical Geology

Volume 99, Issue 4, 15 September 1992, Pages 289-298

https://doi.org/10.1016/0009-2541(92)90182-5 Get rights and content

Abstract

Despite accounts to the contrary, we have found that Mn-rich rock varnish is present in Antarctica, as others have before. It is chemically and texturally similar to many varnishes found in lower latitudes. Antarctic varnishes show considerable potential as a dating and paleoenvironmental research tool.

References (51)

J.G. Bockheim et al.
Late Quaternary ice-surface fluctuations of Hatherton Glacier, Transantarctic Mountains
Quat. Res.
(1989)
T.A. Cahill et al.
Complete elemental analysis of aerosols: PIXE, FAST, LIPM, and MASS
Nucl. Instrum. Methods., Phys. Res.
(1984)
I.B. Campbell et al.
Landscape evolution in Antarctica
Earth-Sci. Rev.
(1988)
G.H. Denton et al.
Late Wisconsin and early Holocene glacial history, Inner Ross Embayment, Antarctica
Quat. Res.
(1989)
J.H. Johnston et al.
The characterization of the iron oxide phase in desert varnish from Antarctica using backscattered conversion electron and X-ray Mössbauer spectroscopy
Chem. Geol.
(1984)
J.H. Johnston et al.
Desert varnish in Antarctica: a nuclear microprobe and backscattered ⁵⁷Fe Mössbauer spectroscopic study
Chem. Geol.
(1984)
C.E. Jones
Characteristics and origin of rock varnish from the hyperarid coastal deserts of northern Peru
Quat. Res.
(1991)
D. Mittlefehldt et al.
Generation of abnormal trace element abundances in Antarctic eucrites by weathering processes
Geochim. Cosmochim. Acta
(1991)
R.M. Potter et al.
The manganese-and iron-oxide mineralogy of desert varnish
Chem. Geol.
(1979)
C.C. Allen
Desert varnish of the Sonoran Desert: optical and electron probe microanalysis
J. Geol.
(1978)

C.F. Boutron et al.

Lead concentration changes in Antarctic ice during the Wisconsin/Holocene transition

Nature (London)

(1986)

E.T. Brown et al.

Examination of surface exposure ages of terminal moraines with in situ produced beryllium-10

Eos (Trans. Am. Geophys. Union)

(1989)

T.A. Cahill

Particle-induced X-ray emission

I.B. Campbell et al.

Antarctica: Soils, Weathering Processes and Environment

G.G.C. Claridge

The clay mineralogy of some soils from Ross Dependency, Antarctica

N.Z. J. Geol. Geophys.

(1965)

R.I. Dorn

Rock varnish as an indicator of aeolian environmental change

R.I. Dorn

Cation-ratio dating: a geographic perspective

Prog. Phys. Geogr.

(1989)

R.I. Dorn et al.

Microbial origin of desert varnish

Science

(1981)

R.I. Dorn et al.

Rock varnish

Prog. Phys. Geogr.

(1982)

R.I. Dorn et al.

Accelerator mass spectrometry radiocarbon dating of rock varnish

Geol. Soc. Am. Bull.

(1989)

R.I. Dorn et al.

New approach to the radiocarbon dating of rock varnish, with examples from drylands

Ann. Assoc. Am. Geogr.

(1992)

G.R. Douglas

Manganese-rich rock coatings from Iceland

Earth Surf. Process. Land.

(1987)

C.D. Elvidge et al.

Regeneration of desert pavement and varnish

G.P. Glasby et al.

Desert varnish in southern Victoria Land, Antarctica

N.Z. J. Geol. Geophys.

(1981)

M. Glazovskaya

Geochemical landscape and types of geochemical soil sequences

Cited by (44)

Calcium isotope fractionation associated with adsorption and desorption on/from δ-MnO<inf>2</inf>
2023, Geochimica et Cosmochimica Acta
Small mineral particles present in soils, such as clay minerals and some oxyhydroxides, constitute important nutrient reservoirs. This behavior is due to the negative charges and high specific surface areas of these particles allowing them to adsorb cations such as calcium (Ca), a macronutrient that occupies key physiological and structural functions in plant metabolism. Although the chemical reactivity of clay minerals is rather well-known in the literature, especially toward macronutrients such as Ca, that of oxyhydroxides such as phyllomanganate minerals remains largely unexplored.
To enhance our understanding of the mechanisms at the origin of the storage/release of the different isotopes of Ca in a soil solution, the possible fractionation between ⁴⁰Ca and ⁴⁴Ca during adsorption and desorption of Ca on a synthetic phyllomanganate, abiotically precipitated in the laboratory [synthetic analog of vernadite (δ-MnO₂)], was studied. Experiments were performed in batch (closed system), and several parameters (time, pH of the solution, Ca concentration and nature and concentration of the desorbent) were tested to cover a large range of physicochemical conditions.
This study demonstrated that the light ⁴⁰Ca isotope is preferentially adsorbed on δ-MnO₂, with Δ^44/40Ca (the apparent fractionation of the aqueous solution at the stationnary state of adsorption compared to the initial one) of the adsorbed Ca that can reach 1.19 ± 0.15‰. The results showed that this isotopic fractionation occurs at chemical equilibrium in a closed system and that the isotopic fractionation measured in this study during Ca adsorption on phyllomanganate is significantly higher than that reported in the literature during Ca adsorption on other soil constituents such as clay minerals. At pH below 4 Ca occupies only the interlayer/basal sites whereas above this pH Ca fills interlayer/basal sites (∼86%) and edges sites (∼14%). By combining the experimental data obtained at different pH values, initial Ca concentrations and interaction times, our results suggest that isotopic signature of the Ca adsorbed on δ-MnO₂ is dependent on the nature of the site involved in the adsorption step (i.e., enriched in ⁴⁰Ca in the interlayer with Δ^44/40Ca equal to −0.43‰ and enriched in ⁴⁴Ca when bound to the edges with Δ^44/40Ca equal to +3.5‰). As revealed by surface complexation modeling, such contrasting behavior between the two types of adsorption sites could be due to the bidendate nature of the Ca adsorption occurring on edges and to ion exchange of Ca²⁺ with H⁺ in the interlayer sites. Finally, desorption experiments point to total but not instantaneous Ca desorption, probably due to a partial collapse of the interlayer with some ions used to desorb Ca²⁺ (K⁺, NH₄⁺, hexaamine-cobalt). This suggests that the amount of bioavailable Ca in soils by simple ion-exchange reactions is highly dependent on the nature of the ions which could desorb Ca present in the soil solution.
Age estimation of tectonically exposed surfaces using cation-ratio dating of rock varnish
2021, Catena
Citation Excerpt :
In their study of RCD, Harrington and Whitney (1987) assumed that the cation exchange capacity was stable and that the cation-ratio linearly decreased with respect to the logarithm of its relative age (Dorn, 1983; Dorn et al., 1986, 1990, 1992; Nobbs and Dorn, 1988; Reneau and Raymond, 1991; Bierman and Harry, 1992; Watchman, 1992). Among the mathematical expressions developed for these dating methods, researchers have commonly applied the (Ca2+ + K+)/Ti4+ ratio, or in its initial form, the (Na+ + Mg2+ + K+ + Ca2+)/Ti4+ ratio (Dorn, 1983; Dorn et al., 1986, 1990, 1992; Reneau and Raymond, 1991; Bierman and Harry, 1992). Chemical cation analysis of rock varnish is performed using various methods (Dorn et al., 1990), including X-ray analysis associated with scanning electron microscopy (SEM).
Cation-ratio dating (R_CD) is a non-destructive and rapid means of dating rock varnish. This study explored that use of rock varnish R_CD as a means of aging tectonically exposed surfaces in a semi-arid region of northwestern Greece with varying degrees of tectonic activity. Tectonic structures in the study region were identified and aged using conventional dating techniques, and faults were classified as active, potentially active, or inactive. A stringent field sampling methodology was adopted which successfully determined the concentrations of calcium, potassium, and titanium cations in rock varnish on the exposed surfaces of these faults. Results showed that R_CD was a valuable tool for dating tectonic structures, and could be used to determine their activation age. The rapidly obtained results of this study could be used to expedite the identification of active and potentially active faults. Furthermore, these findings would contribute to neotectonic mapping efforts and other studies that relate to the tectonics of a specific area. The R_CD method was less destructive and more accurate compared to alternative numerical dating methods and was a rapid means of identifying tectonically active faults. It has the potential to be employed in managing future disasters and mitigating serious economic repercussions from tectonic activity.
Geochemical insights into the relationship of rock varnish and adjacent mineral dust fractions
2020, Chemical Geology
Citation Excerpt :
“Rock varnish” describes μm-thin, brown to black, Mn-rich crusts with metallic luster coating the surfaces of rocks (Broecker and Liu, 2001; Dietzel et al., 2008; Dorn and Oberlander, 1982; Liu and Broecker, 2000; Perry and Adams, 1978; Potter and Rossman, 1977). Rock varnish-like crusts form in all climate zones and on a wide range of lithologies, with growth rates in the range of few μm per ka (Dorn, 1984; Dorn et al., 1992; Dorn et al., 2012; Dorn and Oberlander, 1982; Liu and Broecker, 2007; Perry and Adams, 1978). It consists of ca. 70% clay minerals cemented together by ca. 30% Mn oxyhydroxides intermingled by detrital mineral grains (Potter and Rossman, 1977; Potter and Rossman, 1979; Thiagarajan and Lee, 2004).
Rock varnishes are μm-thin, dark, manganese(Mn)-rich crusts that accrete in the order of few μm/ka on weathering-resistant lithologies. Although these crusts can form in all climates, they are best known in arid to semi-arid settings. Aeolian dust is understood as a major contributor to the distinct trace metal and REE enrichments in rock varnish. However, the exact proportions of abiotic and biotic formation mechanisms that may explain the oxidation-reactions of Mn²⁺ to Mn⁴⁺, present as Mn oxyhydroxides in the varnish, are still a matter of ongoing debate.
We present here the first systematic study of trace element enrichment processes between the uppermost layer of the varnish sequence and their adjacent <50 μm and >50 μm dust fractions across a selection of 41 major and trace elements. This approach is used to investigate samples from three fully arid deserts: the An Nafud in Saudi Arabia, the Negev in Israel, and the Mojave in the USA, which are compared to the significantly different environment of the semi-arid Knersvlakte in South Africa. A new in situ trace element analysis protocol was developed to perform femto- and nanosecond sector-field LA-ICP-MS microanalyses at high-spatial resolution, which allows us to measure the most recent varnish layers for their comparison with recent dust. In agreement with previous studies, all varnishes are enriched in Mn, Pb, Ce, Co, Ba, Zn, Ni, and the Rare-Earth Elements (REE). Here we demonstrate that fine (<50 μm) dust is characterized by similar trace element trends as the varnishes, at overall lower mass fractions. Dust >50 μm has low trace element mass fractions, and enrichment patterns plotting distinctly away from varnish and fine dust. Based on these geochemical patterns, our results indicate a general enrichment mechanism from fine dust to varnish. Previous studies suggested dust to play an integral role in providing the trace elements that are incorporated into the varnish by pH-Eh fluctuations in short-term rain and fog events. We amalgamate and refine previous growth models by providing direct evidence that leaching of about 10% of the Mn and other trace elements from clay minerals in rain or fog droplets at pH ~5 and subsequent scavenging on varnish surfaces at pH ~8 leads integrated over time to the distinct enrichment patterns of the varnish, while initial Mn oxyhydroxide formation is suggested to follow pathways of metal oxide mediated photo-catalysis.
For the semi-arid occurrence in the Knersvlakte we present a distinct growth model as both environment, varnish, and dust composition differ significantly from the arid settings. Here, thick, metallic-looking varnish occurs mainly on the rim of quartz pebbles, lacks microlamination, and likely has upscaled growth processes. Among other aspects, we suggest a more complex interplay between photo-catalysis, nocturnal condensation events on quartz pebbles with subsequent water trapping at the rock-soil-atmosphere interface, due to a salic top-soil layer, to mainly account for these differences.
Nanoscale structure and compositional analysis of manganese oxide coatings on the Smithsonian Castle, Washington, DC
2020, Chemical Geology
The Smithsonian Castle is a historic building in Washington, D.C. that was erected 165 years ago and served as the first home for the Smithsonian Institution. Currently, the building exhibits dark surface discoloration due to manganese-rich coatings that are growing in patches across its Seneca sandstone exterior. Bulk and microanalysis of this coating indicate that it is consistent with rock varnish, but the coating is difficult to analyze without contribution from the underlying minerals that comprise the sandstone. To address this limitation, SEM/FIB-prepared cross-sections of the coating were analyzed using HRTEM, STEM-EDX, and SAED analyses in order to study the nanoscale structure and composition of the Mn-rich coating in isolation, without convolution from the sandstone. Structurally, the coating is <1 μm thick, polycrystalline, and composed primarily of birnessite, a layered manganese oxide. High spatial resolution data reveal that the coating is Ca-bearing, with only minor quantities of Fe, Si, and Al, distinguishing it compositionally from typical manganese rock varnish and classifying it instead as a manganese skin. TEM revealed layers of aeolian detritus below and a thin silica glaze above the Mn-rich coating, providing a relative timeline of formation. Nanoscale particulates of barite found within the Mn-rich coating, along with the micro- and nanoscale detritus below the coating, indicate atmospheric deposition as the main source for both Mn and Ba. The compositional and structural information gathered from these analyses helps constrain mechanisms of formation towards a biological origin; however, no direct evidence for Mn oxide producing microorganisms was observed.
Characteristics of desert varnish from nanometer to micrometer scale: A photo-oxidation model on its formation
2019, Chemical Geology
Citation Excerpt :
However, it should be noted that our photo-oxidation model may only account for the formation of varnish in desert regions. Although arid and semi-arid regions are most famous sites for the occurrence of varnish, rock varnish in places where there is no strong solar light irradiation has also been reported, like Antarctica (Dorn et al., 1992), Iceland (Douglas, 1987), caves (Spilde et al., 2006), humid regions (Krinsley et al., 2012; Dorn et al., 2012), etc. Other kinds of Mn coatings like Mn cutan in subsurface regions and Mn dendrite in bedding surface of rocks are also very common, and there have been different hypotheses for their formation (Chopard et al., 1991; Huang et al., 2008).
Rock varnish is a widespread Mn-rich rock coating commonly developed in arid environments, but the mechanism for its formation is still under debate. In this study, rock varnish and adjacent soil dust collected from Gobi Desert were analyzed for exploring the possible abiotic oxidation mechanism of Mn oxides. The occurrence of rock varnish shows a direct and close relationship with strong irradiation of sunlight, giving the first evidence of photochemical genesis. Abundant caves and tunnels with average diameter of ~1–5 μm are observed on varnish surface regions, which facilitate the penetration of sunlight and water. Metal (oxyhydr)oxides, including birnessite, hematite, goethite, rutile and anatase, account for the major components of rock varnish, which are all solar light-responsive semiconducting minerals. The trace elements enrichment patterns revealed by LA-ICP-MS provide the indication of an aqueous origin. The positive Ce anomalies in varnish in contrast to the rock substrate, as well as the positive correlation between Ce and Mn suggest a strong oxidizing environment in the genesis of rock varnish. Therefore, the photo-generated holes and reactive oxygen species (ROSs) on metal oxides in varnish can promote Mn(II) oxidation, which are further demonstrated from thermodynamic and kinetic considerations. ROSs including ¹O₂ and OH with strong oxidizing capability are detected by EPR in varnish suspension, providing the direct evidence for Mn(II) oxidation. Laboratory experimental simulations show the photocatalysis of metal oxides in rock varnish greatly promote Mn(II) oxidation by 2.10–7.97 times in comparison with homogenous solution oxidation. All these lines of evidence suggest that light-induced abiotic process may play important roles in the formation of rock varnish together with other abiotic and biotic pathways, which can even provide implications for the evolution of Mn oxides on surface of terrestrial planets.
Characterization and differentiation of rock varnish types from different environments by microanalytical techniques
2017, Chemical Geology
We investigated rock varnishes collected from several locations and environments worldwide by a broad range of microanalytical techniques. These techniques were selected to address the challenges posed by the chemical and structural complexity within the micrometer- to nanometer-sized structures in these geological materials. Femtosecond laser ablation-inductively coupled plasma-mass spectrometry (fs LA-ICP-MS), scanning transmission X-ray microscopy-near edge X-ray adsorption fine structure spectroscopy (STXM-NEXAFS) in combination with scanning electron microscopy (SEM) of focused ion beam (FIB) ultra-thin (100–200 nm) sections, conventional and polarization microscopy, as well as electron paramagnetic resonance (EPR) measurements were used to obtain information about these rock varnishes.
Rock varnishes from different environments, which cannot readily be distinguished based on their macroscopic appearance, differ significantly in their constituent elemental mass fractions, e.g., of Mn, Fe, Ni, Co, Ba, and Pb, and their rare earth element (REE) patterns. Structural characteristics such as the particle sizes of embedded dust grains, internal structures such as layers of Mn-, Fe-, and Ca -rich material, and structures such as cavities varied between varnishes from different environments and regions in the world. The EPR spectra were consistent with aged biogenic Mn oxides in all samples, but showed subtle differences between samples of different origin.
Our observations allow us to separate rock varnishes into different types, with differences that might be indicators of distinct geneses. Five different types of rock varnish could be distinguished, Type I–V, of which only Type I might be used as potential paleoclimate archive. Each varnish type has specific characteristics in terms of their elemental composition, element distribution, and structures. The combination of element ratios (Mn/Ba, Al/Ni, Mn/REY, Mn/Ce, Mn/Pb, La_N/Yb_N, and Ce/Ce*), total REE contents, and structures can be used to separate the different types of rock varnish from each other.

View all citing articles on Scopus

View full text

Research paperManganese-rich rock varnish does occur in Antarctica

Abstract

Quat. Res.

Nucl. Instrum. Methods., Phys. Res.

Earth-Sci. Rev.

Quat. Res.

Chem. Geol.

Chem. Geol.

Quat. Res.

Geochim. Cosmochim. Acta

Chem. Geol.

Desert varnish of the Sonoran Desert: optical and electron probe microanalysis

J. Geol.

Lead concentration changes in Antarctic ice during the Wisconsin/Holocene transition

Nature (London)

Examination of surface exposure ages of terminal moraines with in situ produced beryllium-10

Eos (Trans. Am. Geophys. Union)

Particle-induced X-ray emission

Antarctica: Soils, Weathering Processes and Environment

The clay mineralogy of some soils from Ross Dependency, Antarctica

N.Z. J. Geol. Geophys.

Rock varnish as an indicator of aeolian environmental change

Cation-ratio dating: a geographic perspective

Prog. Phys. Geogr.

Microbial origin of desert varnish

Science

Rock varnish

Prog. Phys. Geogr.

Accelerator mass spectrometry radiocarbon dating of rock varnish

Geol. Soc. Am. Bull.

New approach to the radiocarbon dating of rock varnish, with examples from drylands

Ann. Assoc. Am. Geogr.

Manganese-rich rock coatings from Iceland

Earth Surf. Process. Land.

Regeneration of desert pavement and varnish

Desert varnish in southern Victoria Land, Antarctica

N.Z. J. Geol. Geophys.

Geochemical landscape and types of geochemical soil sequences

Research paper
Manganese-rich rock varnish does occur in Antarctica