The Geology of the Torlesse Supergroup, Southern Tararua Range, North Island, New Zealand

<p>Basement rocks in the southern Tararua Range are part of the Torlesse Supergroup, possibly Late Triassic to Late Jurassic in age, and form two distinct associations. The sedimentarv association consists mainly of quartzo-feldspathic sandstone and argillite with minor olistostrome, calcareous siltstone and microsparite. The sandstone and argillite were deposited as turbidites in a mid- to outer- submarine fan environment. The sediment was derived from a heavily dissected active continental margin that was shedding sediment of mainly plutonic and metamorphic origin. The volcanic association consists mainly of metabasite and coloured argillite with minor chert and limestone. Geochemical data indicate that the metabasites were erupted in an oceanic intraplate environment. The nature of amygdules in amygdaloidal metabasites suggests eruption in less than 800m of water. Coloured argillites have two distinct origins, namely sediments formed by the degredation of basalt; and also pelagic material modified by metal-rich effluent either from hydrothermal systems associated with mid-ocean ridges or intraplate volcanism. The rocks of the volcanic association indicate formation in an environment similar to present day mid-ocean islands. Nowhere were rocks of the two associations observed to be conformable. Coupled with this, the nature of the two associations suggests that they were formed in separate environments. The following structural history is proposed: 1) Early veining; 2) Isoclinal folding and development of a NNE striking cleavage; 3) Faulting both at low and high angles to bedding, extreme amounts of which have resulted in mélange; 4) NE-SW trending close to open folds; 5) E-W trending open to gentle folds; 6) Recent faulting, predominantly NE trending strike-slip faults. The nature of the two associations and the deformational style and history supports an accretionary prism model for the development of the Torlesse Supergroup. Rocks of the southern Tararua Range show many similarities with, and probably represent a northward continuation of, the Esk Head Mélange of the South Island.</p>

The Geology of the Torlesse Supergroup, Southern Tararua Range, North Island, New Zealand

<p>Basement rocks in the southern Tararua Range are part of the Torlesse Supergroup, possibly Late Triassic to Late Jurassic in age, and form two distinct associations. The sedimentarv association consists mainly of quartzo-feldspathic sandstone and argillite with minor olistostrome, calcareous siltstone and microsparite. The sandstone and argillite were deposited as turbidites in a mid- to outer- submarine fan environment. The sediment was derived from a heavily dissected active continental margin that was shedding sediment of mainly plutonic and metamorphic origin. The volcanic association consists mainly of metabasite and coloured argillite with minor chert and limestone. Geochemical data indicate that the metabasites were erupted in an oceanic intraplate environment. The nature of amygdules in amygdaloidal metabasites suggests eruption in less than 800m of water. Coloured argillites have two distinct origins, namely sediments formed by the degredation of basalt; and also pelagic material modified by metal-rich effluent either from hydrothermal systems associated with mid-ocean ridges or intraplate volcanism. The rocks of the volcanic association indicate formation in an environment similar to present day mid-ocean islands. Nowhere were rocks of the two associations observed to be conformable. Coupled with this, the nature of the two associations suggests that they were formed in separate environments. The following structural history is proposed: 1) Early veining; 2) Isoclinal folding and development of a NNE striking cleavage; 3) Faulting both at low and high angles to bedding, extreme amounts of which have resulted in mélange; 4) NE-SW trending close to open folds; 5) E-W trending open to gentle folds; 6) Recent faulting, predominantly NE trending strike-slip faults. The nature of the two associations and the deformational style and history supports an accretionary prism model for the development of the Torlesse Supergroup. Rocks of the southern Tararua Range show many similarities with, and probably represent a northward continuation of, the Esk Head Mélange of the South Island.</p>

Principal component analysis of textural characteristics of fluvio-lacustrine sandstones and controlling factors of sandstone textures

Textures are important features of sandstones; however, their controlling factors are not fully understood. We present a detailed textural analysis of fluvio-lacustrine sandstones and discuss the influences of provenance and depositional environments on sandstone textures. The upper Permian – lowermost Triassic Wutonggou sandstones in the Bogda Mountains, NW China, are the focus of this study. Sandstone thin-sections were studied by point counting and their textures were analysed using statistical and principal component analysis. Fluvial lithic, fluvial feldspathic, deltaic lithic, deltaic feldspathic, littoral lithic and littoral feldspathic sandstone were classified and compared. These comparisons indicate that lithic and feldspathic sandstones from the same depositional settings have significant differences in graphic mean, graphic standard deviation and roundness; in contrast, sandstones from different depositional settings but with similar compositions have limited differences in textures. Moreover, three principal components (PCs) are recognized to explain 75% of the total variance, of which the first principal component (PC1) can explain 44%. In bivariate plots of the PCs, sandstones can be distinguished by composition where lithic and feldspathic sandstones are placed in different fields of the plots along the axis of PC1. However, sandstones from different depositional settings overlap and show no clear division. These results indicate that provenance, mainly the source lithology, is the most significant controlling factor on sandstone texture, whereas the depositional environment has limited influence. This study improves our understanding of textural characteristics of fluvio-lacustrine sandstones and their controlling factors, and shows the potentiality of principal component analysis in sandstone studies.

Influences of water chemical property on infiltration into mixed soil consisting of feldspathic sandstone and aeolian sandy soil

Water infiltration into the soil profile are related to the condition of the soil texture, soil bulk density, and water intensity, it is also affected by the physicochemical properties of the water. In this study, we tested the effect of two different chemical properties of water (groundwater for irrigation and naturally accumulated water) on water infiltration in seven different mixed soil consisting of different ratios of feldspathic sandstone and aeolian sandy soil (1:0, 5:1, 2:1, 1:1, 1:2, 1:5, 0:1) through laboratory soil column testing. Our results show that when the textures of the mixed soils are silty loam and sandy loam (ratios of feldspathic sandstone to aeolian sandy soil 1:0, 5:1, 2:1, 1:1 and 1:2), the infiltration time of the naturally accumulated water is significantly longer than the infiltration time of the groundwater for irrigation. When the mixed soil texture is loamy sand and sand (the ratio of feldspathic sandstone to sandy soil is 1:5 and 0:1), there was no significant difference in the infiltration time of the naturally accumulated water and of the groundwater for irrigation. Using water with the same chemical properties, the infiltration time in different ratios of mixed soil decreases from 1:0, 5:1, 2:1, 1:1, 1:2, 1:5, to 0:1. Using the same feldspathic sandstone to aeolian sandy soil ratio, the cumulative infiltration using naturally accumulated water is greater than that using groundwater for irrigation, and the difference in cumulative infiltration is greatest when the ratio of feldspathic sandstone to sandy soil is 2:1. The relationship between the cumulative infiltration and elapsed time is consistent with the Logarithmic model. The changes in wetting front migration distance are consistent with the changes in the cumulative infiltration. The infiltration characteristics of water in the mixed soil are affected by a combination of water chemical property and soil texture.

The Bigrlyi Tabular Sandstone-Hosted Uranium–Vanadium Deposit, Ngalia Basin, Central Australia

The Bigrlyi deposit is a tabular, sandstone-hosted, uranium–vanadium deposit of Carboniferous age located in the Ngalia Basin of central Australia. The deposit is similar to the continental, fluvial Saltwash-type of sandstone-hosted U-V deposits which are well known from the Colorado Plateau, USA. Most mineralization at Bigrlyi occurs as thin, multiple-stacked, stratiform lenses at the base of fluvial channels near the contact between a grey sandstone succession and a hematitic, purple–red sandstone succession. A larger halo of lower grade vanadium mineralization extends beyond the main U-V-mineralized zone. The host is an immature, feldspathic sandstone, grading into arkose and lithic-rich variants. Lithic ‘rip-up’ clasts of clay-rich sediments are common in the basal parts of fluvial channels, and are frequently the focus of, and have acted as sites for, U-V mineralization. Coffinite and uraninite are the main uranium minerals, with the former dominant. Vanadium is mainly hosted by Fe-V-bearing clays and chlorite, including roscoelite, grading into vanadian illite, the interlayer mineral corrensite, and altered detrital biotite. The V-Fe–oxyhydroxide minerals montroseite, haggite and doloresite, and altered detrital Fe-Ti oxides, are minor V-hosts. Mineralized zones correlate with enrichments in Se, Li, Ba, Be, Mo, Mg and Fe, and elevated Se/S ratios are characteristic of U-mineralized zones. Petrographic studies show that a heterogeneous mixture of variably mineralized lithic clasts is present; in the same rock, some clasts are Fe-rich and only weakly U-V-mineralized, while other clasts are strongly V- and/or U-mineralized. These observations point to mineralization processes that did not take place in-situ in the host sandstone at the site of deposition as required by conventional groundwater models. Lead isotope results provide evidence of the open-system mobility of radiogenic elements in parts of the deposit. In V-bearing zones, radiogenic Pb contents were found to be unsupported by current U levels, suggesting that over time U has been mobilized from these zones and redistributed, resulting in U-enrichment in other parts of the deposit. Mobility pathways were likely open over time from early in the history of the Bigrlyi deposit. A hybrid mineralization model, involving an interplay between solution-precipitation processes, detrital transport and post-depositional U remobilization, is proposed for Bigrlyi. Ferrous-ion-bearing clay minerals and pyrite are considered to be the most likely primary reductants/adsorbents, while the deposit is lacking carbonaceous matter.

Improving water retention capacity of an aeolian sandy soil with feldspathic sandstone

The Mu Us sandy land in China’s Shaanxi Province faces a critical water shortage, with its aeolian sandy soil endangering the regional eco-environment. Here we investigated the effects of feldspathic sandstone on water retention in an aeolian sandy soil from the Mu Us sandy land. Feldspathic sandstone and aeolian sandy soil samples were mixed at different mass ratios of 0:1 (control), 1:5 (T1), 1:2 (T2), and 1:1 (T3). Soil-water characteristic curves were determined over low- to medium-suction (1–1000 kPa) and high-suction (1000–140 000 kPa) ranges, by centrifuge and water vapor equilibrium methods, respectively. Results showed that the addition of feldspathic sandstone modified the loose structure of the aeolian sandy soil mainly consisting of sand grains. The van Genuchten model described well the soil-water characteristic curves of all four experimental soils (R2-values > 0.97). Soil water content by treatment was ranked as T2 > T3 > T1 > control at the same low matric suction (1–5 kPa), but this shifted to T2 > T1 > T3 > control at the same medium- to high-suction (5–140 000 kPa). T2 soil had the largest saturated water content, with a relatively high water supply capacity. This soil (T2) also had the largest field capacity, total available water content, and permanent wilting coefficient, which were respectively 17.82%, 11.64%, and 23.11% higher than those of the control (P-values < 0.05). In conclusion, adding the feldspathic sandstone in an appropriate proportion (e.g., 33%) can considerably improve the water retention capacity of aeolian sandy soil in the study area.

Effects of Mixing Feldspathic Sandstone and Sand on Soil Microbial Biomass and Extracellular Enzyme Activities—A Case Study in Mu Us Sandy Land in China

Microbial biomass, extracellular enzyme activity, and their stoichiometry in soil play an important role in ecosystem dynamics and functioning. To better understand the improvement of sand soil quality and the limitation of soil nutrients after adding feldspathic sandstone, we investigated changes in soil microbial activity after 10 months of mixing feldspathic sandstone and sand, and compared the dynamics with soil properties. We used fumigation extraction to determine soil microbial biomass carbon (MBC), nitrogen (MBN), phosphorus (MBP), and microplate fluorometric techniques to measure soil β-1,4-glucosidase (BG), β-1,4-xylosidase (BX), β-D-cellobiohydrolase (CBH), N-acetyl-β-glucosaminidase (NAG), and Alkaline phosphatase (AKP). We also measured soil organic carbon (SOC), pH, electrical conductivity (EC), soil inorganic carbon (SIC), and soil water content (SWC). Our results showed that the soil microbial biomass C, N, P, and individual extracellular enzyme activities significantly increased in mixed soil. Similarly, the soil microbial biomass C:N, C:P, N:P, MBC:SOC, and BG:NAG significantly increased by 54.3%, 106.3%, 33.1%, 23.0%, and 65.4%, respectively. However, BG:AKP and NAG:AKP decreased by 19.0% and 50.3%, respectively. Additionally, redundancy analysis (RDA) and Pearson’s correlation analysis showed that SWC, SOC, porosity and field capacity were significantly associated with soil microbial biomass indices (i.e., C, N, P, C:N, C:P, N:P in microbial biomass, and MBC:SOC) and extracellular enzyme activity metrics (i.e., individual enzyme activity, ecoenzymatic stoichiometry, and vector characteristics of enzyme activity), while pH, EC, and SIC had no correlation with these indices and metrics. These results indicated that mixing feldspathic sandstone and sand is highly susceptible to changes in soil microbial activity, and the soil N limitation decreased while P became more limited. In summary, our research showed that adding feldspathic sandstone into sand can significantly improve soil quality and provide a theoretical basis for the development of desertified land resources.