Using δ18O and δ2H in mean transit time (MTT) modeling can ensure the verifiability of results across catchments. The main objectives of this study were to (i) evaluate the δ18O- and δ2H-based behavioral transit time distributions and (ii) assess if δ18O and δ2H-based MTTs can lead to similar conclusions about catchment hydrologic functioning. A volume weighted δ18O (or δ2H) time series of sampled precipitation was used as an input variable in a 50,000 Monte Carlo (MC) time-based convolution modeling process. An observed streamflow δ18O (or δ2H) time series was used to calibrate the model to obtain the simulated time series of δ18O (or δ2H) of the streamflow within a nested system of eight Prairie catchments in Canada. The model efficiency was assessed via a generalized likelihood uncertainty estimation by setting a minimum Nash–Sutcliffe Efficiency threshold of 0.3 for behavioral parameter sets. Results show that the percentage of behavioral parameter sets across both tracers were lower than 50 at the majority of the studied outlets; a phenomenon hypothesized to have resulted from the number of MC runs. Tracer-based verifiability of results could be achieved within five of the eight studied outlets during the model process. The flow process in those five outlets were mainly of a shallow subsurface flow as opposed to the other three outlets, which experienced other additional flow dynamics. The potential impacts of this study on the integrated use of δ18O and δ2H in catchment water storage and release dynamics must be further investigated in multiple catchments within various hydro-physiographic settings across the world.
This study petrologically and mechanically assesses and compares five of the seven stratigraphic units of the Sekondi Group comprising Elmina sandstone from Central region; Ajoa, Takoradi, Takoradi Harbour and Essipong shales from the Western region in Ghana. All the studied shales were detrital clastic sedimentary rocks observed to have angular, near rounded and elongated crystal habits which are randomly distributed within fine-grained clay minerals as cementing matrix. These characters were clearly observed in the Ajua shales than the others. Unlike the shales, no chlorite, organic materials or foliations were observed in the Elmina sandstone. Also, the most consisted minerals in the shales were the feldspars (K- and plagioclase) and quartz, whereby the K-feldspar dominated the other crystals in the sandstone. The finer texture of the shales may be inferred that the shales have undergone longer times and distances of transportation process. The UCS test carried out on the Elmina sandstone reveals it to be a weak rock with a strength value of 37.3 MPa whilst the Schmidt Hammer test carried out on the four shale rock samples define the shales to be delaminated with the average rebound value of zero (0) each. Both results confirm the megascopic and microscopic petrological results, since both revealed the occurrences of laminated sections within the rocks, and the fissile property of all the shales. It also proves megascopic observation of Elmina sandstone being the hardest of the rocks observed, although the sandstone is still relatively weak from the rock hardness classification.
Main purpose of this paper is to determine the mineralogical composition and mechanical properties of the Tarkwaian Supergroup and compare them. This project will help determine whether the rock units of the Tarkwaian Supergroup are competent based on their mineral contents and strength of the rocks to be quarried and used as aggregates for construction and also determine the structural features that were formed in the various rock units due to the deformation that took place. Values obtained from the Unconfined Compressive Strength (UCS) test were (21.50-77.10) N/mm2 with the Kawere conglomerate having the lowest, and Tarkwa Phyllite having the highest strength. The Huni sandstone, Banket Quartzite and Kawere conglomerate were classified as weak rocks, but the Tarkwa Phyllite was classified as a medium rock, according to Attewell and Farmer’s (1976) classification. The Huni sandstone, Banket Quartzite and Kawere conglomerate are made up of grains of varying degrees of roundness and maturity. The Huni sandstone, Banket Quartzite, and Tarkwa Phyllite exhibit foliation. Micro-folding is also observed in the Kawere conglomerate. Petrographic studies of the rocks classify them as metasedimentary rocks weathering. Based on the weak strengths of the various rock units, they are not suitable to be used as aggregates for construction but can be used for other purposes such as construction sand and dimension stones.
This research leads to identifying the microstructures, the deformation episodes (D) and foliation grades (S) of rocks in the study area. Different geological structures such as shear zones, foliations, micro-faults, crack-seal events, etc. have been identified in the study area. Different phases of deformation episodes and foliation grades have been studied to determine the deformation environments. Senses of shear such as dextral, CS, and CS’ as well as antithetic and synthetic micro-faults and boudins may be identified at the north-west New Drobo. Three (3) main deformational (D) events and foliation grades (S) in both the Tarkwaian sandstones and Birimian volcanic rocks may be identified as D1, D2 and D3 as well as S1, S2 and S3. Recrystallization of quartz and feldspar through bulging (BLG), subgrain boundary rotation (SBR) and grain boundary migration (GBM) have been observed at the study area. The overprinting relationships in the Birimian Supergroup may be identified with three (3) different deformational phases. The first deformation (D1) defines the formation of a vertical shortening, whilst the second deformation (D2) defines oblique shortening. Moreover, the third deformation (D3) is due to high strain rate causing brittle faulting.
The petrographic and geochemical studies of Birimian Supergroup meta-volcanic rocks in the New Drobo environs in Ghana help to decipher the tectonic settings at the study area. Twenty thin sections were prepared with rock samples from the field at the KNUST Geological Engineering Laboratory and petrographic microscope used to determine the different types of minerals in the samples and also the rock type. Whole rock geochemical analysis was done, using both X-Ray Fluorescence and Inductively Coupled Plasma Mass Spectrometer methods at Australian Laboratory Services in Canada. The main volcanic rock types at the study area comprise of basalt, andesite, dacite and rhyo-dacite with porphyritic mineralogical composition such as plagioclase feldspar, augite, olivine, hornblende, biotite, quartz, rutile, chlorite. The average concentrations of Zr < 150 ppm, TiO2 < 1.5 % and P2O5 < 0.25 % and the ratios of Nb/Y < 1.2 and Y/Nb > 1 reveal the magma type in the study area to be continental tholeiitic basalt in nature. The mafic volcanic basalt is from a plate margin tectonic setting and thus of normal MORB and volcanic arc basalts. Also, the low basaltic values of the ratios of Ti/Y and Nb/Y confirm the tectonic setting of the area to be of plate margin. Zr is highly incompatible with respect to Ti and renders the ratio of Zr/TiO2 to be influenced by partial melting and causes heterogeneity in the mantle. The heterogeneity in the source of the mantle can be confirmed with the high value of the ratio of Zr/Y.
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