An integrated petrographical and geochemical study of the Tredian Formation in the Salt and Trans‐Indus Surghar ranges, North‐West Pakistan: Implications for palaeoclimate

The Middle Triassic Tredian Formation is well exposed in the western region of the Salt Range. It is mostly composed of sandstone with minor alternations of shales and dolomite. This is the first integrated attempt using petrographical and geochemical features to reveal palaeoclimate during deposition of the Tredian Formation. This work sheds light on the petrographical and geochemical properties of the Tredian sandstone in order to date various layers and evaluate the palaeoclimate. The formation was sampled at two distinct stratigraphic layers for petrographic and geochemical analysis of major and trace elements. The sandstone of the Tredian Formation is sub‐feldspathic to feldspathic arenite with sub‐angular to rounded grains that are moderately to extensively sorted. The relative proportions of the quartz, feldspars and lithoclasts in the examined sandstone samples shows that the Tredian sediments originated from the interior of the craton during a transitional continental regime. Chemical index of alteration values of 59, chemical index of weathering values of 67, and plagioclase index of alteration values of 74.5 indicate a low to moderate degree of weathering in the Tredian sediment source region. Based on the silica content, SiO2/Al2O3 ratios (2.7–6.1; mean 4.1), and chemical maturity index, it is deduced that the Tredian Formation was deposited in chemically immature to sub‐mature and dry to semi‐arid conditions. Geochemical proxies indicate the acidic source of sediment and deposition on the passive margin of the Indian Plate. The trace element characteristics of the sediments, especially the Rb/Sr, Cu/Zn, Ni/Co, V/Cr and Sr/Ba ratios, indicate that the sediments originated from the first weathering cycle and support the notion that they were deposited in an oxidising continental environment. A semi‐arid to arid palaeoclimate predominated through the Middle Triassic at the north‐western passive continental margin of the Indian Plate in the south‐eastern Neo‐Tethys.


| INTRODUCTION
The Salt and Trans-Indus Surghar ranges of the Upper Indus Basin (UIB) are part of a foreland fold and thrust belt, and their sedimentary geological record ranges from the Precambrian (Salt Range Formation) to the Recent (Lei conglomerate; Bilal et al., 2022a).The Salt Range Thrust (SRT), which originated during the Eocene collision between the Indo-Pakistan and Eurasian plates, is the youngest and most southern of the foreland thrusts in Pakistan (Bilal et al., 2022b;Gardezi et al., 2021;Jaumé & Lillie, 1988).In comparison, the Kalabagh strike-slip fault defines the Salt Range's western limit.The Surghar Range is the easternmost part of the Trans-Indus Ranges (McDougall & Khan, 1990;Powell, 1979; Figure 1).The E-W structural trend of the Surghar Range becomes N-S as it approaches the eastern flank of the Bannu Basin (Abir et al., 2015;Bilal et al., 2022b).The bulk chemical composition of terrigenous sedimentary rocks was ultimately determined by factors such as source rock composition and sedimentary process type (McLennan et al., 1990).The geochemical examination of sedimentary rocks is used to determine palaeoclimate conditions and the sediments' chemical maturity (Armstrong-Altrin et al., 2013;Bilal et al., 2022b;Ogbahon & Olujinmi, 2019).Sandstone signatures of forelandrelated basins reflect the close changing nature of detrital composition during the growth of the orogenic belt and the flexure of the underplate (Critelli & Crinti, 2021;Dickinson & Suczek, 1979).
Researchers have worked on the individual aspects of the coeval formation in other areas of Pakistan (Malkani, 2014a(Malkani, , 2014b) ) although only reconnaissance studies were carried out in the study area and its environs (Khan et al., 2016;Saboor et al., 2021;Sarjeant, 1973).The Early to Mid-Triassic sequence (Mianwali and Tredian formations) was interpreted by Iqbal et al. (2014) as a prograding delta system.Basit et al. (2023) performed diagenetic studies on the Tredian Formation and identified its reservoir characteristics.
The suggested research sections at Landa Pasha (32°58′ 0.00″ N, 71°12′0.00″E) and Nammal Gorge (32°40′3.41″N, 71° 47′ 9.24″ E) provide good exposures of the Musakhel Group's Tredian Formation (Figure 1) although this section has been little studied, especially from a palaeodepositional and environmental point of view.Hermann et al. (2012) and Khan et al. (2016) have carried out pollen and spore analysis to determine the age and palaeoenvironments of the Tredian Formation.Whereas this work focusses on palaeoclimate conditions using petrographical and geochemical analyses during deposition of the Tredian Formation in the north-western passive margin of the Indian Plate.
1.1 | Regional geology and stratigraphic framework Pakistan has a complex geological history due to its location at the junction of the Indian and Eurasian plates.The collision of two main continental plates resulted in the Himalayan orogeny, which included the formation of significant suture zones such as the Main Karakoram Thrust (MKT) and Main Mantle Thrust (MMT; Ahmad et al., 2022;Zaheer et al., 2022).The substantial Himalayan deformation led to the development of new thrust systems farther south in Pakistan, namely the Main Boundary Thrust (MBT) and SRT (Figure 1; Bilal et al., 2022c).Tectonics began to form sedimentary basins.The Indus Basin, the Baluchistan Basin and the relatively smaller Pishin Basin are Pakistan's three major sedimentary basins (Ehsan et al., 2018).The Panjal-Khairabad fault, also known as the MBT, separates the Himalayan fold and thrust belt into the hinterland zone (in the north) and the foreland zone (in the south; DiPietro et al., 2021).The Himalayan crystalline nappe and thrust belt forms the hinterland zone, whereas the Kohat-Potwar fold belt, Hazara-Kashmir Syntaxis and Kurram-Cherat-Margalla thrust belts form the foreland zone.The current study is part of the Kohat-Potwar foreland fold belt (Figure 1).
Musakhel Group Triassic rocks are well exposed in both the Salt and Trans-Indus ranges (Alam et al., 2015).The lower contact is with the older Mianwali Formation and the upper contact with the younger dolomitic Kingriali Formation (Figure 2; Farid et al., 2018).The Middle Triassic Tredian Formation's thick clastic succession was deposited as a river dominated delta (Iqbal et al., 2014) and was divided into two lithostratigraphic units, the lower medium to fine-grained Landa Member and the upper coarse-grained Khatkiara Member.

F I G U R E 1
Location map of the studied sections in the Salt and Trans-Indus Surghar ranges (modified after Afzal, 1997).Also showing the correlation of detailed field logs.
Tredian Formation was measured (Figures 3 and 4).A total of 45 samples were collected for comprehensive petrographic and geochemical analyses based on observable differences in lithology and texture.Twenty-nine of the collected samples were chosen for petrographic investigation using standard thin sections prepared in the Hydrocarbon Development Institute of Pakistan's rock cutting laboratory (HDIP).The samples were impregnated with casting resin and blue dye to determine their visual porosity.A Gazzi-Dickinson point counting method was followed to determine the detrital mode of these sandstones.The Gazzi-Dickinson method is the preferred method in sedimentary petrology because it minimises the dependence of composition on grain size (Critelli et al., 2023;Ingersoll & Suczek, 1979).Quartz was differentiated into quartz-monocrystalline (Q m ) and quartz-polycrystalline (Q P ).Feldspar was categorised as alkali feldspar (Alk-F) and plagioclase (Plg; Table 1).Eight of the 29 petrographically studied samples from the formation's Landa and Khatkiara members were selected for major and minor (trace) elemental analysis using x-ray fluorescence (XRF) spectroscopy.The selected samples were evaluated using a Philips PW 1480 XRF at the National Center of Excellence in Geology (NCEG), University of Peshawar, Pakistan.The major elements were determined using glass (fusion) beads, whereas the trace and minor elements were determined using pressed powder pellets.

| Petrography
The Tredian Formation sandstone is cement-supported and moderately to well sorted.Quartz is the most abundant mineral in the studied sandstones, which are subangular to well-rounded (Figure 5A).Overgrowth of quartz cement forms on a few quartz grains that do not have a clay rim around their edges (Figure 5B).In addition, mica, rutile and zircon inclusions can be seen in a few quartz grains (Figure 5C).Calcite is the most common type of cement, along with quartz, dolomite, iron oxide/ hydroxide and chalcedony (Figure 5D,E).The modal percent abundances of the framework constituents are 49.4 (quartz), 14.3 (feldspar) and 0.08 (lithoclasts).The framework grains are sub-angular to well-rounded (Figure 5A).Two types of quartz grains were identified: monocrystalline and polycrystalline.Monocrystalline quartz is dominant.Potash feldspar is more prevalent than plagioclase (mostly microcline; Figure 5F,G).Plagioclase occurs as subrounded to well-rounded grains and displays polysynthetic twinning (Figure 5H).The rock fragments in the investigated samples are all sedimentary in origin and include bioclasts.Mica has an average abundance of 6%, with muscovite being dominant over biotite.The only heavy minerals identified in the Tredian sandstone are tourmaline, rutile and zircon.In addition, mica, rutile and zircon inclusions can be seen in a few quartz grains (Figure 5C).The major diagenetic signatures observed in the analysed materials are chemical and mechanical compaction, cementation, replacement, grain fracture and dissolution (Figure 5B,D,F).Petrographic composition characterises the sandstone samples of the Tredian Formation as quartz-feldspathic (Figure 6).Discriminatory plots were used to identify specific tectonic settings in the source region for the Tredian sediments.The relative proportions of quartz, feldspars and lithoclasts in the studied samples suggest that the Tredian sediments originated in the craton interior and transitional continental regime (Figure 7).

| Major element composition and geochemical classification of the Tredian sandstone
According to the petrographic classification, the chemical composition of the Tredian sandstone is feldspathic to subfeldspathic arenite (Table 1).The MgO and CaO concentrations of two of the examined samples, T-21 and T-22, do not, however, fall within the standard range.The higher MgO and CaO concentrations in samples T-21 and T-22 are a result of dolomitisation; hence, they are disregarded in geochemically based descriptions and interpretations.Roser et al. (1996) used the SiO 2 /Al 2 O 3 ratio to calculate the quartz and feldspar proportions, whereas Na 2 O/ K 2 O describes the chemical maturity index (CMI).Similarly, the Fe 2 O 3 /K 2 O ratio determines mineral stability (Ivanov et al., 2017).Figure 8 shows the chemical classification diagrams for Tredian sandstone after Pettijohn et al. (1987) and Herron (1988).All Tredian samples are classified as arkoses (Figure 8A).Two samples are arkoses, three are greywacke and one is shale (Figure 8B).The Tredian sandstone is divided by cement, feldspar and lithoclast components (Iqbal et al., 2021;Wadood et al., 2021).

| Index of alteration and weathering
The chemical index of alteration (CIA) and the chemical index of weathering (CIW) are widely used to determine the degree of chemical weathering (McHenry, 2009;McLennan et al., 1993;Minyuk et al., 2007;Qiu et al., 2015aQiu et al., , 2015b) ) The CIA, which measures the degree of weathering of feldspars relative to unweathered protoliths, is a widely used chemical index to ascertain the degree of source area weathering (Nesbitt & Young, 1982) and hence acts as a climate proxy (McLennan et al., 1993).The best way to understand the extent of source area weathering is by using the chemistry of the major elements.The (Harnois, 1988;Nesbitt & Young, 1982).The CaO is the amount of CaO present in silicates (Li et al., 2020;Nesbitt & Young, 1982;Qiu et al., 2015b).High CIA values commonly indicate intense chemical weathering conditions, which generally form in warm and humid climates with strong rainfall and continental runoff (Clift et al., 2014;Montero-Serrano et al., 2015).
A CIA value of 50 indicates unaltered plagioclase and K-feldspar, but values approaching 100 suggest complete T A B L E 1 Point counting data for the studied samples.Grain parameters (Dickinson, 1970;Graham et al., 1976;Ingersoll & Suczek, 1979).and rapid deposition, which leads to poor sorting of the resulting sediments.Only two of the investigated samples had CIA values of more than 75, indicating moderate weathering at the source location and the presence of considerable quantities of feldspar in the resultant sandstone.This conclusion is consistent with the petrographic results.Unlike the CIA, the CIW does not face the problem related to K-metasomatism (Harnois, 1988).The CIW is calculated as: Here, Al 2 O 3 , CaO* and Na 2 O are expressed in molar proportions.Potassium is excluded from this index as it may leach out or accumulate in the residue during weathering.As CIW increases, Ca and Na concentrations in sediments decrease in comparison to Al.The range of CIW values for the Tredian sandstone is 51 to 88 (averaging 67.2;Table 2), suggesting low to moderate source rock weathering conditions.
Similarly, another commonly used alteration index is the plagioclase index of alteration (PIA), which can also be used to estimate the degree of source rock weathering (Ngueutchoua et al., 2017).The PIA is calculated as follows: Unweathered plagioclase has a PIA value of 50, whereas completely altered material has a PIA value of 100.The PIA values for Tredian sediments vary from 59.9 to 92.3 (with an average of 74.5), indicating a modest degree of plagioclase source rock weathering.This result is also consistent with the interpretation inferred from the CIA and CIW.Therefore, evidence based on petrographic data, geochemical data and the CIW, CIA and PIA values consistently suggests low to moderate weathering of the Tredian sediments source rock.

| Chemical maturity and weathering conditions
In general, the chemical maturity of sediments is characterised by their SiO 2 concentration, or CMI, which is equivalent to the CIW.This is governed by the ratio of SiO 2 /Al 2 O 3 (Zheng et al., 2012).The SiO 2 versus Al 2 O 3 + K 2 O + Na 2 O (A-CN-K) binary diagram is used to infer the source area (rock) weathering conditions and the chemical maturity of the sediments (Suttner & Dutta, 1986; Figure 9).The chemical maturity of sediments increases as the CMI increases.
The SiO 2 /Al 2 O 3 ratios in unaltered igneous rocks vary from 3.0 (for basic rocks) to 5.0 (for acidic rocks).Increasing sandstone maturity is indicated by CMI values higher than 5.0 (Bhattacharjee et al., 2018).The SiO 2 /Al 2 O 3 ratios of the Tredian sandstone range between 2.7% and 6.1% (averaging 4.1%), suggesting that the sediments are immature to moderately mature.Consequently, geochemical data on the Tredian sandstone indicates an arid to semi-arid source area, low to moderate chemical maturity, and a lack of evidence for intensive sediment recycling (Figure 6).On the ternary plot A-CN-K, the investigated samples fall into the category of weak to nearly strong weathering, that is, two samples plot in the weak weathering zone and the remaining samples plot in intermediate weathering conditions (Figure 10).The two samples plotted at the vertex CN showed no chemical alteration (Figure 10).The plotted samples in the illite-muscovite position suggest low to moderate chemical maturity with sediments reflecting the semi-arid to arid palaeoclimate.

Cox et al. (1995) proposed an index to measure variation in composition known as the index of compositional variability (ICV). It can be calculated as:
where CaO represents Ca from various sources and Fe 2 O 3 (t) symbolises the total iron concentration.The ICV is expressed as a weighted percentage of oxides.The ICV decreases as the degree of weathering increases.The ICV values of some common minerals are as follows: pyroxene and amphibole (10-100), biotite (8), alkali feldspar (0.8-1), plagioclase (0.6) and muscovite (0.3; Yousefifard et al., 2012).Compositionally immature sandstones have ICV values of over one, include unrecycled sediments, and were deposited in a tectonically active setting (Raza & Mondal, 2018).In contrast, compositionally mature deposits have an ICV value of less than one and show passive sediment recycling (Ghosh & Sarkar, 2010;Perri et al., 2012).Tredian sandstone ICV values vary from 0.33 to 1.18 (Table 2).Four samples show ICV values of less than one, indicating high maturity and sediment recycling, while two samples with ICV values larger than one represent immature sediments from the first weathering cycle.However, the ICV for the majority of the examined samples and, therefore, their average value (0.73) falls below 1 (with the exception of T-21 and T-22), indicating intermediate maturity and deposition in a tectonically quiescent or cratonic environment (Table 2).

| Trace element geochemistry
During the processes of weathering, the behaviour of trace elements such as Rb, Ba, Sr, U, Th and Cs is comparable to that of the associated major elements.During chemical weathering, Sr tends to leach out more often than Rb and Cs, which are typically integrated into clays (Guo et al., 2018).As a result, U and Th concentrations in the sandstone of the Tredian Formation are below the lower limits of detection (LLD), and they give no information on sediment recycling (Table 2).The average values of Rb, Sr, Ba and Cs are lower than those of UCC and PAAS (Tables 3 and 4), indicating conditions of moderate to mild weathering (Ray & Paul, 2021).The V/Cr ratio was employed by Dill et al. (1988) as a palaeo-oxygenation indicator suggesting oxic or anoxic conditions during sediment deposition.If the V/Cr ratio is greater than 2 it may imply anoxic conditions, whereas V/ Cr values of less than 2 indicate oxic conditions (Gallego-Torres et al., 2007).The average V/Cr ratio of 1.13 observed in Tredian sandstone samples implies deposition under oxidising circumstances (Table 5).
The ratio of Ni to Co has also been used to determine the quantity of oxygen present during deposition (redox; Neagu et al., 2015).If the Ni/Co ratio is 5, oxic environments are present, and if it is >5, sub-oxic to anoxic environments are prevalent (Guo et al., 2018).The Ni/ Co ratios of 5 in Tredian samples are indicative of oxic deposition.In general, high Cu/Zn ratios imply reducing conditions, while low ratios indicate oxidising situations (Ghandour, 2020).Low Cu/Zn ratios derived from the current research imply deposition of Tredian sediments under oxidising conditions (Table 5).From the relative amounts of Sr and Ba, the palaeosalinity conditions can  be deduced (Wei & Algeo, 2020).High Sr/Ba ratios suggest high salinity, while low ratios indicate less salty environments (Fathy et al., 2021).The low Sr/Ba ratios of the Tredian sandstone samples (0.12-0.35, with an average of 0.24) imply less salty conditions at the time of deposition with no marine influence.

| Weathering and sediment recycling
Uranium and Th are good markers of weathering and sediment recycling and may be present in a variety of sedimentary rocks including as clay minerals, feldspars, heavy minerals, organic materials and phosphates (Ali et al., 2020;dos Santos et al., 2017dos Santos et al., , 2019)).The Th/U ratio rises as a result of repetitive cycles of weathering and redeposition (McLennan & Taylor, 1980).The Tredian sandstone samples had U and Th values below the detection limit and are thus insignificant (Table 3).In addition, the Rb/Sr ratio can be used as evidence that sedimentary recycling does not occur (Nielsen et al., 2018).The average value of 0.77 for the Tredian sandstone indicates no or a modest degree of recycling (Table 5).Zirconium and Sc are also commonly used trace elements for determining sedimentary recycling.However, the Sc concentration is below the detection threshold, so the Zr/Sc ratio cannot be used.

| Regional correlation
The Tredian Formation from the Salt Range area revealed the existence of a heterolithic-proximal, oxic shelf depositional environment during the Lower Middle Triassic (Anisian; Figure 11; Khan et al., 2016).Iqbal et al. (2014) and Khan et al. (2016) also argued that deposition in the western Salt Range region occurred in a prograding delta although Saboor et al. (2021) interpreted the palaeoenvironment as a shallow marine depositional setting.Basaltic lava flows of the Bagh Complex in the Baluchistan Basin indicate rifting in that domain (Siddiqui et al., 2017).The Yerrapalli Formation in India is coeval with the Tredian Formation.For these sediments, Dasgupta et al. (2022) proposed a fluvio-lacustrine depositional environment based on mineralogical and geochemical investigations.In Nepal, the Mukut Limestone Formation is the stratigraphic counterpart of the Tredian Formation.Petrological studies revealed low oxygenated shallow marine shelf conditions in the Neo-Tethys Sea hinterland (Fuchs et al., 1988).The Tongchuan Formation is found coeval with the Tredian Formation in China's Ordos Basin.This formation is composed of organic-rich shale, indicating that these sediments might be a possible hydrocarbon source rock in the basin.Comprehensive research indicated that the formation was deposited in a lacustrine palaeoenvironment (Zhao et al., 2021).However, the Leikoupo Formation is found coeval with the Tredian Formation in China's Sichuan Basin, where it is also a prospective gas resource.
The palaeoenvironment during deposition of the Leikoupo Formation is proposed to be a carbonate platform with open marine conditions (Ding et al., 2014).Based on petrographical and geochemical data, this study reveals that the Tredian Formation was deposited in an arid to humid continental palaeoenvironmental setting near a coastal region with moderate rain fall.The surrounding regional coeval strata, on the other hand, were deposited in a completely shallow marine depositional environment.The ammonoid-rich sediments of the Lower Triassic Mianwali Formation may indicate subsidence, followed by the sandstone of the Middle Triassic Tredian Formation which provides evidence for the sudden increase in siliciclastic supply in the Salt Range.
The lower portion of the Tredian Formation is characterised by syn-depositional slumps, which provide evidence of possible tectonic activity.This clearly indicates that the study domain underwent an uplifting event shortly before deposition of the Tredian Formation owing to rifting in the Baluchistan regions.As a result, the strata are located in a continental-arid palaeoenvironmental setting.However, further geochemical analyses of Rock-Eval Pyrolysis and total organic content are recommended for future research to validate the lack or presence of organic matter in the formation.

| CONCLUSIONS
A petrographic and geochemical examination of the sandstone of the Tredian Formation has been carried out in a newly explored area.A pioneer integrated study was used to reveal the palaeoclimate of the hypothesised source region during the Triassic period.The indices such as CIA, PIA, CIW and ICV provide valuable information on the chemical maturity and weathering of sediments.The average values of CIA, PIA and CIW for the Tredian sandstone in the Western Himalayan Foreland Basin (Salt and Surghar ranges) indicate low to moderate weathering conditions.The SiO 2 /Al 2 O 3 ratio shows that the chemical maturity of the sandstone is low to moderate, while the SiO 2 versus A-CN-K plot suggests that the sediments originated from arid to semi-arid source areas.In addition, the range of the ICV summary shows a tectonically quiescent or cratonic environment with low to intermediate maturity.The Rb/Sr ratio suggests that sedimentary recycling is either absent or extremely low.Finally, the Cu/Zn, Ni/Co and V/Cr ratios concluded that the sediments of the Tredian Formation from the Salt Range area were deposited under oxidising conditions.Compared to regional coeval F I G U R E 1 1 Regional correlation of the Tredian Formation with the coeval strata of the surroundings (modified after Bilal et al., 2022b).
formations that are deposited in shallow marine and lacustrine depositional settings, the palaeoenvironment of the Tredian Formation is suggested to be arid to semiarid near coastal, with moderate rainfall.The Indian Plate's north-northwest margin experienced passive margin settings as a result of the Neo-Tethys opening.An elevated passive margin was created by tectonic activity as this passive margin developed in the eastern Salt Range and in an area farther to the east on the Indian Plate.Triassic-Jurassic strata from Pakistan's UIB demonstrate that the Neo-Tethyan passive margin has extended westward and that the Tethyan Himalayan Succession may have occurred in the Salt Range.Geochemical proxies indicate the acidic source of sediment and deposition on the passive margin of the Indian Plate.A semi-arid to arid palaeoclimate predominated through the Middle Triassic at the northwestern passive continental margin of the Indian Plate in the south-eastern Neo-Tethys.Further study, including isotopic geochronology, is suggested in order to more accurately establish the parent rock for these deposits.

F
Generalised stratigraphic column of the Salt Range.F I G U R E 3 Lithological log of Tredian Formation, Landa Pasha Section, Surghar Range, Pakistan.
of feldspars into clay and other minerals (e.g.kaolinite;Perri et al., 2012Perri et al., , 2016)).The CIA values for the Tredian sandstone vary from 45.5 to 78.2.The mean value (59.4) is higher than upper continental crust (UCC; 52.7) but lower than post-Archean Australian shale (PAAS; 70.4), indicating a modest degree of source rock weathering(Zhao et al., 2017).The range of CIA values shows that the source area of sediments has experienced physical breakdown with low chemical weathering.Low CIA values imply a fast rate of erosion, limited transport F I G U R E 5 Photomicrograph of the Tredian sandstone.(A) Rounded quartz grains with empty fracture (indicated by yellow arrows).(B) Quartz grain with overgrowth.(C) Zircon present as inclusion in quartz grain.(D) Dolomite rhomb present as cement between the grains.(E) Floating grains texture with calcite cement present between grains and dissolved grains.(F, G) Microcline (yellow arrows).(H) Plagioclase (indicated by yellow arrow).

F
I G U R E 6 QFL diagram for the Tredian sandstone after Pettijohn et al. (1987) based on framework element proportions.F I G U R E 7 Qt-F-Lt plot of the Tredian sandstone after Dickinson et al.

R E 8
Chemical classification diagram discriminating sediments on the basis of their logarithmic ratios of SiO 2 /Al 2 O 3 versus Na 2 O/K 2 O (A; after Pettijohn et al., 1987) and Fe 2 O 3 /K 2 O (B; after Herron, 1988).F I G U R E 9 Bivariant plot of SiO 2 versus Al 2 O 3 + K 2 O + Na 2 O showing chemical maturity and corresponding conditions of deposition of sandstone.F I G U R E 1 0 Chemical compositional variations in the studied samples in the Al 2 O 3 − (CaO* + Na 2 O) − K 2 O ternary diagram to infer the degree of weathering.T A B L E 2 Major element composition (wt%) of the Tredian sandstone, PAAS (post-Archean Australian shales) and UCC (upper continental crust).
Trace element composition (ppm) of the Tredian sandstone.