Primera Generaión

A summary of the literature on the geology of the north-west Sydney Basin, in which Wybong Creek occurs, is covered first. The little which is known about hydrogeology in the area is then covered, followed by a review of the statistical procedures which will be used in this study.

1.3.1. Geological context

The Wybong Creek catchment lies within the Sydney-Gunnedah Basin complex, a sedimentary foreland basin lying between the New England Fold Belt in the north and the Lachlan Fold Belt in the south (Scheibner 1998). Publicly available geological mapping has not occurred in the Wybong Creek catchment beyond the Hunter Coalfield Regional 1:100 000 Geological Map (Glen and Beckett 1993), though detailed

descriptions of the local geology do occur in an environmental impact assessment (Umwelt Environmental Consultants 2006), and two drilling reports focused on geology in the mid-Wybong Creek catchment (Leary and Brunton 2003; Brunton and Moore 2004). A brief review of the literature regarding the geology of the north-western Sydney Basin and south-eastern Gunnedah Basin is presented, therefore, in order to give context to the conditions of groundwater flow in the Wybong Creek catchment.

The basement of the Sydney-Gunnedah Basin complex in the Wybong Creek area is made up of Late Carboniferous/Early Permian rocks (Scheibner 1998).Formation of the Sydney-Gunnedah Basin began in the Late Carboniferous, where volcanic rifting produced large quantities of ignimbrites and calc-alkaline volcanics. Thermal sag and subsidence then occurred, before the Sydney Basin truly developed into a foreland basin

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in the mid-Permian (Tadros 1993; Scheibner 1998). Large amounts of sedimentary material were eroded into the basin from the rising New England Fold Belt and the craton of the Lachlan Fold Belt at this time (Tadros 1993; Scheibner 1998). Thick, localised sequences of interbedded sandstones, conglomerates and coals were formed as lacustrine deposits in trough areas underlain by subsiding half-grabens. The upper-most of these Permian deposits is the Singleton Supergroup which includes the Wittingham Coal Measures, lying >300 m below the surface in the south of the Wybong Creek catchment, and 400 m below the surface in the mid-catchment (Leary and Brunton 2003; Brunton and Moore 2004). Eustatic sea rise led to marine deposition of the Denman Formation and the inundation of the Wittingham Coal Measures on which it formed (Tadros 1993; Scheibner 1998).

Large fluvial systems deposited one to two kilometres of organic and inorganic sediments and tuffs in the Sydney Basin during the Late Permian, before rapid

subsidence and felsic volcanism buried these sediments (Tadros 1993; Scheibner 1998). This formed what is now known as the Newcastle Coal Measures. These coal measures lie 100 – 200 m below the surface in the mid-Wybong Creek catchment and outcrop in the southeast (Leary and Brunton 2003; Brunton and Moore 2004). Major uplift, tilting and compression of the Sydney basin occurred in the Late Permian, with coal

sedimentation terminated and deep erosion of the Permian sediments occurring in the Wybong area. Alluvial fans prograding from the New England Fold Belt to the south- west produced the Narrabeen Group in the Early Triassic. This sedimentary deposition was terminated altogether in the mid-Triassic due to deformation and the formation of reverse-faults. Erosion since this period gave rise to the steep and deeply (>200 m) incised valleys seen in the catchment today, with the Quaternary alluvium within and adjacent to Wybong Creek derived from the Liverpool Range Volcanics and that further from the river channel and adjacent to the escarpments sourced from the Narrabeen Group (Kovac and Lawrie 1991).

The eastern part of the Liverpool Range forms the northern border of the Wybong Creek catchment, with the Liverpool Range being the largest lava-field province in New South Wales (Tadros 1993; Scheibner 1998). This part of the volcano is also the oldest, with K/Ar dating indicating formation in the late Eocene, around 38 – 40 Ma. The volcano is uniformly basic, with alkali olivine basalt the most common rock. Basanite, hawiite and mugearite are also common. Plagioclase makes up 35 – 60 % of the

Liverpool Range by volume, with K-feldspar rare and fluor apatite common. Mg and Na concentrations are relatively high (Schön 1985).

Chapter Three – Aquifers and groundwater bodies in the Wybong Creek catchment 55

Magma intrusion caused the folding and coking of coal throughout the Sydney – Gunnedah Basin complex, with hydrated clay minerals and carbonates such as calcite currently filling fractures and cavities (Tadros 1993). Jurassic intrusions in the south of the Wybong Creek catchment are associated with the break-up of Gondwana during the Jurassic, though intrusions may also be of Tertiary age closer to the Liverpool Range. Dikes and sills have been mapped in the south-east of the Wybong Creek catchment where economic deposits of the Newcastle Coal Measures occur (Umwelt

Environmental Consultants 2006).

Sparse drilling and thick alluvial cover precludes the delineation and magnitude of faults in this north-western part of the Sydney – Gunnedah Basin complex, though many cores contain thick breccia and slickensiding (Tadros 1993). Lineaments which have been interpreted as faults have been identified, however, and can be grouped into those trending north-north east and north-west, and those east-north-east and west-north west (Tadros 1993). They occur with near vertical orientation and seldom any

displacement, though different structural development on either side of lineaments does take place. These lineaments have been interpreted as transfer faults, shear zones, fault zones or zones of weakness, and penetrate the lithosphere to great (though unquantified) depths. Lineaments trending north-west are associated with rift-related extension, and are expressed as mesoscale fracturing, normal faults and dykes. The north-north-east and north-western lineaments instead appear to reflect the Late Carboniferous volcanic basement underlying the basin. East-west compression of the Newcastle Coal Measures has resulted in frequent and complex faulting in the south-eastern Wybong Catchment.

1.3.1.1. Hydrogeological context

Regional hydrochemical studies have been conducted in the upper Hunter Valley, although hydrogeology has not been addressed specifically within the Wybong Creek catchment (Kellett et al. 1987; Creelman 1994). Eight hydrochemical regions with distinctive chemistry occur in the upper Hunter Valley, with these groups distinguished by canonical and principle component analyses (Kellett et al. 1987). Wybong Creek was placed in the TRIAS group in this study, with the low to moderate salinity of this Na-Mg-Cl-HCO3 dominated group related to chemical weathering of the Triassic

Narrabeen Group. The Na-Cl dominated saline groundwater of Big Flat Creek, which occurs in the south-eastern Wybong Creek catchment, was instead related to

groundwater discharge from the Wittingham Coal Measures (Group WI2) and/or other units deposited or influenced by marine conditions.

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Uplift and erosional unloading has lead to fracturing within the Permian Coal Measures, with groundwater flow lines in the coal measures related to faulting, fracturing, structure-jointing, thrusting and cleat directions (Creelman 1994). Halite (NaCl), bloedite (Na2Mg(SO4)2·4(H2O)), and thenardite (Na2SO4) occur as salt

efflorescences in the Wittingham Coal Measures, despite the occurrence of a regional groundwater body (Kellett et al. 1987). The presence of these highly soluble minerals is anomalous with the age of the 300 million year old coal measures and led Kellett et al. (1987) to the conclusion that groundwater was trapped within the coal measures until they were tectonically uplifted during the Tertiary, allowing molecular diffusion towards fractures to drain salts from the coal.

1.3.2. Statistical theory

Statistics and numerical analyses have traditionally been the domain of

psychologists and biologists (Davis 1973), however, their utilisation by hydrologists is increasingly common (e.g., Gűler et al. 2002; McNeill et al. 2005; O'Shea and

Jankowski 2006; Papatheodorou et al. 2007). The principle types of analyses useful to hydrologists are those which group samples according to their hydrochemical

characteristics. Such analyses encompass both statistical (MANOVA, ANOVA, etc.) and numerical (fuzzy logic, hierarchical cluster analysis, etc.) techniques. Analyses used in this study were focused on the grouping of samples into hydrochemical groups, and were largely numerical rather than statistical. The following review is therefore relevant to these types of analyses.

1.3.2.1. Factor analyses

Factor analyses reduce data sets to those variables or samples which account for the greatest variability (Razack and Dazy 1990; Meng and Maynard 2001;

Papatheodorou et al. 2007). Frequently used factor analyses include Q-mode analyses and R-mode analyses. All assess the relationship between groundwater samples by constructing variance-covariance matrices of a multivariate data set, before extracting eigenvalues and eigenvectors from the matrix thus produced (Davis 1973). R-mode factor analyses specifically investigate the inter-relationship between variables (ions in this case). Q-mode factor analyses instead determine the relationship between

Chapter Three – Aquifers and groundwater bodies in the Wybong Creek catchment 57 1.3.2.1.1. Principle component analyses

Principal Component Analysis (PCA) is based upon R-mode analysis and reduces the number of factors in a data set to those which describe the greatest differences between samples (Gűler et al. 2002). It is most often used with varimax rotation in hydrochemical studies (e.g., Suk and Lee 1999; Meng and Maynard 2001; Singh et al. 2004; Sikdar and Chakraborty 2008). Correlation or covariance matrices are produced by PCA, with coefficients of the eigenvectors (or loadings) representing the relative contribution each factor (in this case of each ion) makes to the variation of each

principle component of the test (Davis 1973). Correlation matrices are necessary if data values occur on different scales, however, covariance analyses are more useful in the case of hydrogeochemical data sets which contain significant differences in the variance of ions (i.e., when there is a large range in the concentrations of different ions). Unlike many other forms of multivariate analysis, PCA does not require the normalisation of data for reliable results.

1.3.2.1.2. Hierarchical cluster and discriminant analyses

Hierarchical Cluster Analyses (HCA) places samples into groups based upon their similarity. The closer samples plot to each other on a dendrogram produced by HCA the more similar they are, with Euclidean distance and Ward’s method for linkage being the most frequently used means of creating dendrograms in hydrogeochemical studies (e.g., Suk and Lee 1999; Gűler et al. 2002; Singh et al. 2004; O'Shea and Jankowski 2006). Other methods may also be used to group similar samples in other types of cluster analyses, such as the cosine theta similarity coefficient in R-mode analysis, and the product-moment correlation coefficient used in Q-mode analyses (Meng and Maynard 2001). The dendrogram produced from HCA is projected on to two-dimensional space with the proximity of two samples reflecting their chemical rather than spatial

similarity. HCA is a visual rather than statistical test, albeit utilising more data than stiff and piper diagrams (Gűler et al. 2002).

2. Materials and Methods

The methods used for the analyses of O, H and Sr isotopes are described in Chapter Two (Section 2.2).

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2.1. Sample collection

Groundwater was sampled from as many bores and piezometers as possible across the Wybong Creek catchment (Figure 3.1). Sampling occurred on three dates during the low rainfall conditions of 2001-2007: the 21st_-22nd _{April; the 21-23}rd _{July 2006, where}

samples were collected by Ben Macdonald; and the 1st _{June 2007. Average rainfall}

occurred in the catchment from mid-2007 onwards, with groundwater samples collected on the 5th-7th July 2007; the 17-18th June 2008; and the 20th January, the 14th– 15th May, and the 30th June 2009.

Bores and piezometers were purged of at least one well volume the day before sampling. Samples were then collected after groundwater had attained constant

chemistry. Water quality parameters were measured on unfiltered water samples using Orion Gel-Filled pH and Eh electrodes and pH and Eh meters; an Orion DuraProbe ™ 4-electrode conductivity cell and conductivity meter; and an Orion dissolved oxygen probe and dissolved oxygen meter, with instrument calibration conducted as described in Chapter Two (Section 2.2). Alkalinity was measured on filtered water in the field by titration with a Hach digital titrator, HCl and methyl orange as an indicator (Franson 2005). Rainwater samples were collected 13 km south of the catchment at Denman on June 14th _{2007, and July 18}th _{2008. All other rainwater samples were collected 20 km}

west of Wybong Creek in Muswellbrook.

2.1.2. Sample preparation

Samples collected for isotope and ion analyses were filtered through 0.45 µm Millipore® _{nitrocellulose filters on site. Samples selected for anion, δ}2_{H, δ}18_{O, and} 14_C

analyses were stored in refrigerators prior to further laboratory preparation and/or analyses. Sample volumes of 50 mL were collected for cation and Sr isotope analyses and were acidified in the field with 2 mL 50% HNO3. Barium chloride (BaCl) was

added to select samples to precipitate BaSO4for δ34SSO4 analyses, with BaSO4 separated

from the supernatant by filtration in the laboratory. At least one blank sample was made per field trip, whereby milli-Q water was prepared for analyses as per groundwater samples.