Karst pocket valleys and their implications on Pliocene–Quaternary hydrology and climate: Examples from the Nullarbor Plain, southern Australia

Earth-Science Reviews 150 (2015) 1–13

Contents lists available at ScienceDirect

Earth-Science Reviews journal homepage: www.elsevier.com/locate/earscirev

Karst pocket valleys and their implications on Pliocene–Quaternary hydrology and climate: Examples from the Nullarbor Plain, southern Australia Matej Lipar a,⁎,1, Mateja Ferk b,⁎,1 a b

Environmental Geoscience, Department of Ecology, Environment & Evolution, La Trobe University, Melbourne (Bundoora), Victoria 3086, Australia Anton Melik Geographical Institute, Research Centre of the Slovenian Academy of Sciences and Arts, Gosposka ulica 13, SI-1000 Ljubljana, Slovenia

a r t i c l e

i n f o

Article history: Received 25 February 2015 Received in revised form 30 June 2015 Accepted 1 July 2015 Available online 6 July 2015 Keywords: Pocket valley Karst spring Steephead Geomorphology Palaeoclimate Palaeohydrology Palaeoenvironmental reconstruction Nullarbor Plain

a b s t r a c t Karst on the Nullarbor Plain has been studied and described in detail in the past, but it lacked the determination of the karst discharge and palaeo-watertable levels that would explain the palaeohydrological regime in this area. This study explores the existence of previously unrecognised features in this area – karst pocket valleys – and gives a review on pocket valleys worldwide. Initial GIS analyses were followed up by detailed field work, sampling, mapping and measuring of morphological, geological, and hydrological characteristics of representative valleys on the Wylie and Hampton scarps of the Nullarbor Plain. Rock and sand samples were examined for mineralogy, texture and grain size, and a U–Pb dating of a speleothem from a cave within a pocket valley enabled the establishment of a time frame of the pocket valleys formation and its palaeoenvironmental implications. The pocket valleys document the hydrological evolution of the Nullarbor karst system and the Neogene–Pleistocene palaeoclimatic evolution of the southern hemisphere. A review of pocket valleys in different climatic and geological settings suggests that their basic characteristics remain the same, and their often overlooked utility as environmental indicators can be used for further palaeoenvironmental studies. The main period of intensive karstification and widening of hydrologically active underground conduits is placed into the wetter climates of the Pliocene epoch. Subsequent drier climates and lowering of the watertable that followed sea-level retreat in the Quaternary resulted in formation of the pocket valleys (gravitational undermining, slumping, exudation and collapse), which, combined with periodic heavy rainfall events and discharge due to impeded drainage, caused the retreat of the pocket valleys from the edge of escarpments. © 2015 Elsevier B.V. All rights reserved.

Contents 1. 2. 3. 4. 5.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Regional setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pocket valleys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1. Pocket valleys on the Hampton and Wylie scarps and their formation . 5.2. Pocket valleys worldwide . . . . . . . . . . . . . . . . . . . . 6. Palaeoclimatological and palaeohydrological implications . . . . . . . . . 6.1. Early-mid Pliocene . . . . . . . . . . . . . . . . . . . . . . . . 6.2. Late Pliocene . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3. Quaternary . . . . . . . . . . . . . . . . . . . . . . . . . . . 7. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

1 2 3 3 6 6 8 9 9 9 11 11 11 12

1. Introduction ⁎ Corresponding authors. E-mail addresses: [email protected] (M. Lipar), [email protected] (M. Ferk). 1 Both authors contributed equally to this research and paper.

http://dx.doi.org/10.1016/j.earscirev.2015.07.002 0012-8252/© 2015 Elsevier B.V. All rights reserved.

Solution of limestone and underground drainage, all strongly related to climate, are defining characteristics of karst landscapes; in addition,

2

M. Lipar, M. Ferk / Earth-Science Reviews 150 (2015) 1–13

development of karst (karstification) influences topography and hydrology (Ford and Williams, 2007). Numerous detailed studies of karst features worldwide, especially cave deposits, have thus been used to provide an insight into landscape evolution, palaeohydrology and palaeoclimate (e.g., Wright, 1988; Ayliffe et al., 1998; Williams et al., 1999; Auler et al., 2009; Kenny, 2010; Lipar and Webb, 2015). Karst pocket valleys, however, have received relatively little attention in the scientific literature, and their utilities as tools for landscape and palaeoclimate interpretation are less well appreciated (Audra et al., 2004; Mocochain et al., 2011; Stepišnik et al., 2012). Detailed descriptions of the karst features on the Nullarbor Plain and its aquifer have been published (Lowry, 1968; Hunt, 1970; Webb and James, 2006; Doerr et al., 2012; Miller et al., 2012; Burnett et al., 2013), but these have not accurately determined the karst discharge and related palaeo-watertable levels that would explain the palaeohydrological regime in this area. The key findings of this paper are the occurrences of previously unrecognised small steep-headed valleys with amphitheatre-like shapes along the stretch of the Wylie and Hampton scarps (Fig. 1), recognised herein as karst pocket valleys (Gunn, 2004; Ford and Williams, 2007). Their discovery, and a comparison to the worldwide occurrence of pocket valleys, contributes to the overall understanding of the karst of the Nullarbor Plain by explaining the locations of the outflow from this vast underground palaeo-discharge system in the past. Advances in U–Pb dating techniques allowed us to determine the time frame of the pocket valley formation. This information provided an additional valuable source of data that allowed the palaeoenvironment of the Nullarbor Plain to be reconstructed in aspects of palaeohydrological evolution of the Nullarbor karst system and the Neogene–Pleistocene palaeoclimate in the southern hemisphere.

2. Regional setting The Nullarbor Plain (Fig. 1A) is one of the world's largest limestone outcrops and covers an area of more than 200,000 km2, stretching from the Great Victoria Desert in the north towards the Great Australian Bight in the south where it ends abruptly with 40 to 90 m high cliffs. The two low-lying areas of the Israelite and Roe plains were formed during the cliff retreat as a result of coastal erosion in the Pliocene (James et al., 2006), rising from sea level to ~30 and ~40 m inland, respectively. The former coastal cliffs were abandoned when the sea withdrew, forming the Wylie and Hampton scarps (Fig. 1), which stretch for about 100 and 300 km, respectively, and have a general relief of about 50 to 100 m. The rest of the Nullarbor Plain represents a vast area with relief less than 10 m (Gillieson et al., 1994), divided into extensive clay-floored depressions and low rocky ridges (Gillieson et al., 1994; Webb and James, 2006). At present the Nullarbor Plain has a semi-arid climate (Köppen BWk and BWh; Gillieson et al., 1994) with precipitation decreasing from the semi-arid coastal region (~ 400 mm per year) towards the very arid north with less than 150 mm rainfall per year. Potential evaporation increases from ~2000 mm near the coast to ~3000 mm inland (Bureau of Meteorology, 2014). The Plain is underlain by a series of Cenozoic limestones, deposited in the Eucla Basin and composed predominantly of sand-sized fragments of calcareous bioclasts, with three distinctive formations: • the white to grey, soft, poorly lithified, muddy to chalky bryozoan-rich middle to late Eocene Wilson Bluff Limestone, deposited in temperate water conditions on a drowned carbonate platform or ramp, and with

Fig. 1. Locality map of the Nullarbor Plain (A; satellite image downloaded from Google Earth) and digital elevation model images of Israelite (B) and Roe (C) plains showing locations of pocket valleys (examined in the field — red dots, observed only — blue dots). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) DEM downloaded from Shuttle Radar Topographic Mission website

M. Lipar, M. Ferk / Earth-Science Reviews 150 (2015) 1–13

an average thickness up to 150 m in South Australia and about 300 m in Western Australia (Playford et al., 1975; James and Bone, 1991; Benbow et al., 1995b), • the yellowish grainy, skeletal and bryozoan-rich Oligocene to early Miocene Abrakurrie Limestone, deposited in cool to temperate water on a partly to completely drowned platform, and with a variable thickness of less than 10 m in South Australia to up to 100 m in Western Australia (Playford et al., 1975; James and Bone, 1991; Benbow et al., 1995b; Li et al., 1996), and • the grainstone to rudstone bioclastic and micritic middle Miocene Nullarbor Limestone, deposited in subtropical to warm temperate water in a shallow platform setting, with an average thickness between 20 and 35 m and with a maximum of 45 m (Lowry, 1970; Playford et al., 1975; Hocking, 1990; James and Bone, 1991; Benbow et al., 1995b; Webb and James, 2006; Miller et al., 2012; O'Connell et al., 2012). Uplift and global eustatic lowering of sea level caused regression of the sea ~15 Ma ago, exposing the Nullarbor Limestone. The stronger denudation to the south has since removed most of the Nullarbor Limestone to expose the underlying Abrakurrie Limestone at the southern margin of the plain (Lowry and Jennings, 1974; Gillieson and Spate, 1992). The late Pliocene Roe Calcarenite with a maximum thickness about 8 m forms the low-lying Roe Plain (James et al., 2006). It was deposited during a period when sea level was approximately 30 m higher than today (Playford et al., 1975). The Roe Calcarenite is in places covered by the Semaphore Sand (Holocene aeolian and beach quartz–carbonate sand), which also predominantly covers the Israelite Plain (Stewart et al., 2008). There are no permanent surface streams on the Nullarbor Plain (Gillieson and Spate, 1992). The Nullarbor karst aquifer has varied through time as a response to sea-level fluctuations (James et al., 1991). At present, the mostly brackish or saline underground water is encountered between 30 and 45 m depth in the northern part of the Nullarbor, between 100 and 120 m beneath the Hampton Range, and between 5 and 40 m beneath the Roe Plain (James et al., 1991). Rainfall (often as intense storms) is the main recharge of the aquifer (Gillieson and Spate, 1992; Gillieson et al., 1994). Surface and subsurface karst features developed during changeable environmental conditions after the uplift of the Eucla Basin in the middle Miocene (Jennings, 1962; Grodzicki, 1985; Goede et al., 1990; Gillieson and Spate, 1992; Benbow et al., 1995a; James et al., 2006; Webb and James, 2006; Woodhead et al., 2006). Despite the relatively flat surface, the remarkable karst features are caves (Sexton and Tech, 1965; Hunt, 1970), often divided into shallow (generally less than 30 m below the surface) and deep (generally 50–150 m below the surface, and often intersecting the watertable) caves (Jennings, 1962, 1963; Grodzicki, 1985; Gillieson and Spate, 1992; Webb and James, 2006; Burnett et al., 2013), blowholes (Lowry, 1968; Doerr et al., 2012; Burnett et al., 2013), collapse dolines (Jennings, 1962; Gillieson and Spate, 1992; Webb and James, 2006) and dryland solutional depressions — dayas (Jennings, 1962; Gillieson and Spate, 1992; Goudie, 2010). The calcreted surface on the Nullarbor Plain also shows solution etching, e.g., small-scale irregular shallow solution pits and pans (Jennings, 1962; Lowry and Jennings, 1974). The major dissolutional process currently active in the water filled passages of the deep Nullarbor caves is mixing corrosion at the vadose–brackish water interface (James et al., 1991), and this is also suggested for the formation of the shallow caves (Burnett et al., 2013). Nevertheless, the karst geomorphology of the escarpments at the edge of the Plain has received only minor attention (Waddell, 2010). 3. Methods Initial geographic information system (GIS) analyses of digital elevation models (Shuttle Radar Topographic Mission) and satellite data

3

(Google Earth) of both escarpments and associated valleys were followed up by detailed field-work, sampling, mapping and measuring of the morphological, geological and hydrological characteristics of 25 representative valleys on the Wylie and Hampton scarps (Fig. 1). Thin sections of collected rock and sand samples were examined for mineralogy and texture, and grain size analysis was performed on sand samples (≤ 2 mm) using a Malvern Mastersizer 2000 particle analyser at La Trobe University (Melbourne, Australia); full details of the latter analytical procedure are provided in Sperazza et al. (2004). The mineral composition of samples was determined by X-ray powder diffraction (XRD) analysis, using the La Trobe University Siemens D5000 equipped with a Cu-Kα source, operating at 40 kV and 30 mA in continual scan mode with a speed of 1°/min from 4° to 70° 2Ɵ. Eva software was used for qualitative mineralogical analysis. Two 5 cm thick samples of horizontally laminated flowstone were collected for dating from the top of a ~ 1 m thick exposed block in the pocket valley on the western part of the Hampton Scarp, about 70 m above present sea level. In recent years the U–Pb method has been used to date carbonate speleothems beyond the range of the previously employed U–Th method (600 ka) (Richards et al., 1998; Woodhead et al., 2006). U–Pb geochronology was conducted at the University of Melbourne using the methods outlined in Woodhead et al. (2006). The U and Pb abundances and isotope ratios are provided in Table 1.

4. Results Approximately 140 steep-headed valleys occur within the Nullarbor and Abrakurrie limestones on both escarpments, and are absent on the ocean cliffs. Approximately 4 valleys per 10 km appear on the Wylie Scarp, and approximately 3 valleys per 10 km appear on the Hampton Scarp (Figs. 1B, C). They are relatively evenly distributed on the Wylie Scarp, but on the Hampton Scarp their distribution increases from ~ 1 valley per 10 km in the west to ~ 5 valleys per 10 km in the east (Fig. 1C). The comparison to the surficial geology did not provide any correlation with their variable distribution. The valleys generally penetrate 100 to 500 m from the edge of escarpments into the Nullarbor Plain and are about 120 to 180 m wide (Fig. 2A). An amphitheatre-like morphology is often present (Fig. 2B): valley slopes with colluvium on the foothills (Fig. 2B) form semicircular upstream ends up to 40 m deep with occasional cliffs and overhangs. Alluvial fans occur where the valleys open on to the Roe and Israelite plains, but are undetectable in areas close to the present coast due to burial by active sand deposition, especially evident as eastward to north-eastward moving sand dunes on the Israelite Plain. On the Roe Plain, the alluvial fans are often interconnected and merge with the colluvial zone downslope from the escarpment. Alluvial fans are generally from 500 m to more than 1 km long and up to 1 km wide with inclinations from 3° to 7°. They appear to be mostly composed of material physically eroded from the pocket valleys and contain clasts and pebbles (generally up to 20 cm in diameter; mostly comprising calcrete, limestone, and occasional flowstone), sand, silt and clay. XRD analyses of b2 mm particles show the dominant and constant presence of lowMg calcite and quartz, however, montmorillonite was identified within some alluvial fans on the Roe Plain, and aragonite within alluvial fans closest to the present coast (Table 2). Table 1 U and Pb data for the sample considered in this study. U Pb (ppm) (ppm)

206

0.174 0.199 0.200 0.184

40.469 41.400 35.515 26.912

0.0005 0.0004 0.0005 0.0009

Pb/204Pb

238

U/206Pb % error (2σ)

799.03 1004.38 902.38 566.95

5.1 5.3 5.6 3.4

207

Pb/206Pb % Error error correlation (2σ)

0.49106 0.40811 0.45529 0.59776

4.5 6.5 5.5 1.8

−0.9317 −0.9989 −0.9999 −0.9970

4

M. Lipar, M. Ferk / Earth-Science Reviews 150 (2015) 1–13

Fig. 2. Morphology of the pocket valleys. A, B, C: pocket valleys on the Hampton Scarp showing overall morphology including alluvial fans (A; see Fig. 1A for location), extensive colluvium and exposed walls with solutional voids containing flowstone (arrow) (B), and exposed pocket (C) with cave (ca), flowstone (f), flowstone covered with calcrete (fc), and calcrete-covered Nullarbor Limestone (nc). D, E: Characteristically short steep-headed karst pocket valleys (white arrows) and fluvial valleys with long fluvial catchments (black arrows) on the southern part of the Israelite Plain on satellite (D) and DEM (E) images (see Fig. 1A for location). DEM downloaded from Shuttle Radar Topographic Mission website; the satellite map is based on Google Earth imagery

Impassable solutional voids (often honeycombing the limestone) are found in the steep-headed walls of all the examined valleys (i.e. 25) and, in the upstream ends of six of the valleys (65–75 m above sea level), caves and/or speleothems occur (Fig. 2C). Caves are defined

as natural underground openings enterable for humans (Ford and Williams, 2007), whilst initial solution openings are much smaller (i.e. from 1 cm to several tens of cm). However, both share the same genesis without significant differences related to size (Goudie, 2006). The caves,

Table 2 XRD identification of selected minerals in alluvial fan and cave sediments. Sample no.

Description & location

Quartz

Calcite

Aragonite

SA 4 SA 7 SA 10 SA 16 SA 17 SA 18 SA 3 SA 23

Alluvial fan sediment (Israelite Plain) Alluvial fan sediment (Israelite Plain) Alluvial fan sediment (Israelite Plain) Alluvial fan sediment (Roe Plain) Alluvial fan sediment (Roe Plain) Alluvial fan sediment (Roe Plain) Cave sediment (Abrakurri) Cave sediment (Mullamullang)

x x x x x x x x

x x x x x x x x

x

Montmorillonite

x x x x

M. Lipar, M. Ferk / Earth-Science Reviews 150 (2015) 1–13

which have not been previously documented, are up to 8 m wide, 2 m high and 5 m long. Fissures and cracks are observed in caves within pocket valleys, indicating joint-controlled passage formation. Any initial phreatic features (e.g., scallops) are not preserved or are covered with cave sediments that block the major parts of the caves. Consequently, the primary dimensions of the caves cannot be determined in detail. Porous to compact horizontal-laminar flowstone deposits often partly or completely fill the cave entrances below the steep-headed walls (Fig. 2C). They form up to 1.5 m thick outcrops that have been exposed due to recent collapses removing the younger calcrete. They are generally light to dark brown in colour (most likely due to iron,

5

manganese and organic compounds; Caldwell et al., 1982). Thinsection examination shows that generally 5–10 mm thick layers of columnar compact and columnar open low-Mg calcite crystals (terminology after Frisia, 2015) are periodically intersected by layers of variable thickness (10 μm–10 mm) of microbially influenced low-Mg micritic calcite with stromatolite-like structures and occasional bioclasts (e.g., bryozoans) between different crystal growth segments (Fig. 3). The columnar fabric has rhombohedral terminations at these intersections (below the micrite layer; columnar microcrystalline type). Microsparite and blocky mosaic calcite crystals occur on the top of the micrite layer. In the growth direction, these blocky mosaic crystals

Fig. 3. Microphotographs of speleothem (flowstone) deposit within the pocket valleys. A, B: different cement layers within the laminar flowstone; microstratigraphic logs showing the prevailing type of fabrics (C = columnar, Co = columnar open, Cm = columnar micro-crystalline, M = micrite, Ms = microsparite, Mc = mosaic calcite, P = porosity). C, D (D in cross-polarised light): microphotographs showing bioclast (bryozoan; white arrow) cemented within the speleothem and surrounded by calcite cement with microsparite and mosaic fabric. E, F (F in cross-polarised light): isopachous columnar calcite (black arrows) and occasionally blocky mosaic calcite crystals (white arrows) within a layer of flowstone with predominantly micrite (M) fabrics (P = porosity). G, H (H in cross-polarised light): columnar fabrics of speleothem, showing large elongated calcite crystals.

6

M. Lipar, M. Ferk / Earth-Science Reviews 150 (2015) 1–13

Fig. 4. U–Pb data for the flowstone sample plotted using the Tera–Wasserburg or ‘semitotal Pb–U isochron’ construction. The quasi-horizontal line in this plot represents a disequilibrium Concordia plotted for [230Th/238U]i = 0, [234U/238U]i = 1. A linear regression with its associated 2σ uncertainty envelope is shown passing through the individual blank-corrected U–Pb analyses. The calculated age is derived from the intersection of the two.

progressively change into columnar calcite. Some pores within the micrite layers are filled with additional isopachous radial fibrous (columnar) calcite and sometimes blocky mosaic calcite crystals. One sample of horizontally laminated flowstone was dated by U–Pb as 3.60 ± 0.12 Ma (Fig. 4). A second sample of flowstone could not be dated by U–Pb due to its high porosity. Up to 1 m thickness of calcrete has formed in the pocket valleys, covering the valley floors (including rubble and colluvial material) and walls (including flowstone deposits) (Fig. 5A). Small water gullies are evident on the surface of this calcrete, and occasionally also erode into the colluvium material as well as into alluvial fans (Fig. 5B). Thinsection examination of calcrete samples shows fragments of the parent rock, cemented together by micritic calcite. Detailed studies of these calcretes have been presented by Miller et al. (2012). 5. Pocket valleys 5.1. Pocket valleys on the Hampton and Wylie scarps and their formation Pocket valleys were first defined and interpreted by Cvijić (1893), who classified karst valleys into pocket, blind, semi-blind

and dry valleys. Sweeting (1973), Gams (1974), Jennings (1985, using the alternative name “steephead”), Gunn (2004) and Ford and Williams (2007) have described pocket valleys as short valleys with amphitheatre-like steepheads (pockets), with their formation as the result of a trigger process, which is usually the emergence of water from a karst aquifer when it can no longer flow underground, and later processes that include retreat of the valley either by gravitational undermining (spring sapping) and slumping of a slope or by irregular collapse of a cave roof above a subterranean water flow. The overall morphology of the valleys on the Hampton and Wylie scarps (Fig. 2A), including the abrupt upstream ending as a cliffed pocket, strongly suggests a karst origin and their definition as karst pocket valleys. The absence of fluvial catchments past the steep-walled upstream ends of the valleys additionally strengthens the argument for their karst origin; they are clearly distinct from fluvial valleys (Huggett, 2007) containing extensive fluvial catchments (and no pockets) forming on the non-karstic substrate of the Cenozoic sand or gravel plains (Stewart et al., 2008) on the southern part of the Israelite Plain (Fig. 2D, E). U–Pb dating of a thick flowstone material from the pocket valleys has produced an age of 3.6 Ma, which is in a good accordance with U– Pb dating of flowstones from other caves on the Nullarbor (Woodhead et al., 2006; Blyth et al., 2010), and therefore indicates that the most favourable period for speleothem growth (i.e. humid climate) on the Nullarbor was occurring in the mid Pliocene (~3–4 Ma). Flowstone is a type of speleothem (i.e. cave sediment), formed as a subterranean precipitate from thin water films flowing over the rock (Flügel, 2010) and is therefore a feature for recognising karstification (Frisia et al., 2000). Flügel (2010) described laminar flowstone consisting of several cement layers (i.e. similar to the ones found in the pocket valleys) as a distinctive criteria of palaeospeleothems, growing directly on a host rock. Micrite fabrics of a flowstone are usually associated with the presence of organic compounds (e.g. Morse et al., 2003; Frisia, 2015) and in continental environments often associated with calcretes and tufas (Alonso-Zarza and Wright, 2010). Periodical interchange between micrite and columnar calcite crystals and the lack of macro-flora input indicate that these speleothems deposited before the outflow — i.e. are not tufa. Micrite may also be a destructive fabric (Cañaveras et al., 2001) formed by biomechanical micritization and/or condensation–corrosion, usually associated with aragonite (Frisia, 2015). However, stromatolite-like structures (such as in the flowstone in this study) rather indicate a primary fabric (Frisia, 2015). Microsparite that overlies the micrite layer within the flowstone of the pocket valleys is most probably due to neomorphism of micrite into microsparite; aggradation would occur when a flow of saturated solutions enters in contact with

Fig. 5. Calcrete covering the floor of the pocket valley (A), and fluvial gully (arrows), extending from the pocket valley across the alluvial fan on the Roe Plain (B).

M. Lipar, M. Ferk / Earth-Science Reviews 150 (2015) 1–13

micrite, and organic additives (especially typical for underlying micrite) may influence its precipitation (Frisia, 2015). These flowstone deposits and related caves, accessible within the pockets only ~40 m of the foot of escarpments, therefore indicate the initial karst environment in sections now eroded to form pocket valleys, and probably relate to the “shallow caves” on the Nullarbor (Gillieson and Spate, 1992; Webb and James, 2006; Miller et al., 2012; Burnett et al., 2013). Faulting and associated joints (Jennings, 1962; Playford et al., 1975; Hou et al., 2008; Sandiford et al., 2009; Miller et al., 2012) most probably controlled the distribution and contributed to the formation of the caves and consequently the pocket valleys. However, the main fault-scarps on the Nullarbor Plain (Fig. 1C) with a relief from 10–20 m are not related to the distribution of the pocket valleys. Biostratigraphic and Sr-isotope dating methods applied to the Roe Calcarenite suggest its deposition in the late Pliocene (James et al., 2006), when the escarpment was subject to shoreline erosion. The cliff-retreat at that time (2 to 3 m per year; discussed in James et al., 2006) was at least as fast as the possible retreat of pocket valleys, which prevented their formation at that stage. Similar shoreline erosion is present today along the Great Australian Bight and the retreat of the cliffs most probably contributes to the absence of pocket valleys in these regions. The initiation and upstream retreat of pocket valleys on both escarpments therefore began at the last stage of the overall escarpments retreat and continued in the following period as the sea retreated from

7

the Roe and Israelite plains (late Pliocene/early Pleistocene) (Fig. 6). Mixing-zone corrosion at the foot of the coastal scarp most likely contributed to their solutional formation at this stage. Back et al. (1984) showed that differential dissolution in the mixing zone produces extremely high porosity, often expressed as honeycomb-like solutional voids. It is expected that corrosion at the saltwater–freshwater interface caused solutional honeycombing (similar as observed on the higher elevations of the pocket valleys) in lower elevations of pocket valleys on the Nullarbor Plain. However, the occurrence of solutional voids and caves limited to the higher levels of pocket valleys is due to the rubble material and calcrete formation within the valleys, covering any existing voids (or caves) below the zone of ~65 m above sea level. Alluvial fans are, on the other hand, not a defining feature of the pocket valleys as they are the product of erosion rather than dissolution. Their morphostratigraphic position on the Roe Plain (i.e. they were deposited on top of the Roe Calcarenite after the sea level – and consequently the water table – dropped) suggests their deposition in hydrological settings (see Section 6.3.) characterised by occasional high rainfall events that eroded material from the pocket valleys. Nevertheless, flowstone clasts within the alluvial fans clearly indicate the degradation of caves and solutional voids within the pocket valleys. Furthermore, montmorillonite, a weathering-derived clay mineral often associated with caves (Polyak, 2000; Gunn, 2004; Onac, 2005), also previously reported from Nullarbor caves by Caldwell et al. (1982) and additionally found within the sediment in caves on the

Fig. 6. A diagram illustrating main stages of pocket valley formation on the Hampton Scarp. Note that the diagram does not account for general denudation of the plateau.

8

M. Lipar, M. Ferk / Earth-Science Reviews 150 (2015) 1–13

Hampton Range (Table 2), may also be related to the cave systems of pocket valleys. However, aragonite and probably some other clays within the alluvial fans close to the coast most probably represents an additional and relatively recent aeolian input from the Holocene Semaphore Sand; aeolian transport processes have been also reported by Gillieson et al. (1994). The angular shape of the clasts suggests that they were not transported far, which is in accordance with the transport distance of clasts (generally 0.5 to 1 km) from the pocket valleys to the alluvial fans estimated from DEM. 5.2. Pocket valleys worldwide Pocket valleys have been reported worldwide in various karst/rock types: Australia (Gentilli and Scott, 1963; Jennings, 1968; Goudie et al., 1990), United States (Herrick and LeGrand, 1964), Slovenia (Gams, 1974; Lipar and Ferk, 2011; Stepišnik et al., 2012; Tičar, 2012), Mexico (Back et al., 1984; Ford and Williams, 2007), Italy (Sauro, 2001), France (Audra et al., 2004; Frachon, 2004), Great Britain (Ford and Williams, 2007), Romania (Tîrlă and Vijulie, 2013). Large semicircular features measuring kilometres across, ascribed to the emergence of groundwater and therefore related to pocket valleys have been termed makhteshim (erosion cirques) (Issar, 1983; Zilberman, 2000). However, pocket valleys have rarely been a specific subject of discussion and, consequently, their utility as environmental indicators is often overlooked. Nevertheless, Audra et al. (2004) used the pocket valleys of the Calanques massif in France to explain the effect of the low sea level of the Mediterranean (Messinian Deep Stage) on karst development around the Mediterranean Sea, and Stepišnik et al. (2012)

studied sediments preserved on high levels in pocket valleys in Slovenia to reconstruct Holocene flood events. Both studies show that the dynamics of karst aquifers may clearly be expressed in features such as pocket valleys. A review of pocket valleys in different climatic and geological settings suggests that their basic characteristics (spring-related pockets, caves and associated flowstones) remain the same (Ladišič, 1999; Tičar, 2012; Tîrlă and Vijulie, 2013), and that variations in size, morphology and distribution occur depending on bedrock lithology, general morphological predisposition, and climate. For instance, Frachon (2004) studied pocket valleys in France and concluded that the inclinations of slopes depend largely on the rock characteristics (e.g., mostly vertical in limestone, and less inclined in marl). In comparison, the slopes of the pocket valleys on the Nullarbor have been largely modified by gravitational processes that became dominant after the Pliocene due to the drop of the water table. The extent (length, width and depth) of pocket valleys also strongly depends on morphological characteristics of the spring area and can vary enormously. Within the edges of relatively low plateaus, pocket valleys tend to develop more typical amphitheatre-like shapes and long extents, whilst higher (in altitude) slopes prevent a fast retreat. An example are the pocket valleys on the alpine limestone ridges studied by Tîrlă and Vijulie (2013) where extensively active overall erosion of the slope and high general relief inhibited the pocket valley from developing in its length. On the other hand, geomorphologically similar tectonically controlled multiple pocket valleys, as on the Nullarbor, appear at the edge of the massif in Causse de Gramat, France (Fig. 7A, B, C), also often associated with alluvial fans (Frachon, 2004; Tičar, 2012). The continual appearance of pocket valleys on the edge of the plateau

Fig. 7. (A) DEM (downloaded from Shuttle Radar Topographic Mission website) of multiple pocket valleys in Causse de Gramat, France, and (B) photo of the largest one — Autorie (photo: Tičar, 2012), compared to (C) similar pocket valley on the Wylie Scarp (note imbedded photograph of its pocket). (D) DEM of the pocket valley of Kostanjeviška Jama Cave (arrow), and (E) photo of the rubble after the strong rainfall event in 2014 (photo: Matjaž Čuk), compared to (F) the alluvial fan rubble in front of the pocket valley on the Hampton Scarp.

M. Lipar, M. Ferk / Earth-Science Reviews 150 (2015) 1–13

(escarpment) on the Nullarbor Plain is therefore not unique, and nor are the fluvial processes to form alluvial fans. However, the source of material transported as alluvial fans in France has been highly influenced by glaciation processes, which were absent on the Nullarbor. Another analogy to the pocket valleys and related alluvial fans on the escarpments on the Nullarbor Plain can be observed in a pocket valley in southern Slovenia (Fig. 7D). An intensive rainfall event in 1937 caused an extreme rise of the karst water table in the hinterland of the springs, which resulted in reactivation of ~10 m higher springs and opening of the entrance to Kostanjeviška Jama Cave (Eržen, 1964; Ladišič, 1999). The gravel material that was previously blocking the cave entrance and the springs was washed to lower parts of the pocket valley and accumulated in form of an alluvial fan. A comparable event occurred in 2014, during which the higher springs were reactivated again and large amounts of colluvial material, piled up in the previous eight decades, and various cave sediments were redeposited in an alluvial fan below the pocket valley (Fig. 7E). Similarly, when the watertable on the Nullarbor in the late Pliocene to early Pleistocene dropped and karst springs at the escarpment ceased to be permanently active, the slope processes became dominant, and the occasional high rainfall events removed the colluvial material as well as sediment from the caves and deposited it as alluvial fans (Fig. 7F).

6. Palaeoclimatological and palaeohydrological implications Global cooling has been demonstrated by oxygen isotope records and palynological data throughout the past 15 Myr (Flower and Kennett, 1994; Lear et al., 2000; Zachos et al., 2001; Udeze and Oboh-Ikuenobe, 2005) accompanied by increased aridity globally (Haywood et al., 2000) as well as in Australia (Macphail, 1997; Gallagher et al., 2001, 2003; Megirian et al., 2004; Martin, 2006; Woodhead et al., 2006; Metzger and Retallack, 2010). However, the transition between the humid and non-seasonal conditions of the earlier Tertiary to the subhumid-arid and strongly seasonal climates characteristic of the Quaternary was not uniform (Macphail, 1997): Cerling et al. (1997) showed the relatively rapid change in global vegetation at the Miocene/Pliocene boundary, and increased aridity was described from western South America and southern Africa (15–14 Ma, 9 Ma, 6.5 Ma; Hartley and Chong, 2002), as well as in southwestern Australia (2.9 and 2.56 Ma; Dodson and Macphail, 2004). However, global trends do not necessarily apply to all areas, and the southern margin of Australia was effectively more humid and warmer during the early Pliocene than at present and had less temperate conditions during the late Miocene and late Pliocene (Macphail, 1997). Deposition of the Nullarbor Limestone in subtropical to warmtemperate water (Benbow et al., 1995b; O'Connell et al., 2012) during the early Miocene indicates a warmer and more humid climate than at present (Benbow et al., 1995b). The long time span between the exposure of the Nullarbor Limestone in the middle Miocene until the (shallow) cave formation in the Pliocene was probably still characterised by a relatively warm and humid climate (similar to central Australia; Metzger and Retallack, 2010), but due to the lower sea level (i.e. greater distance to the coast), the climate could have been more continental and therefore less humid, as reported by Benbow et al. (1995a). The formation of pocket valleys can be incorporated into the landscape evolution of the Nullarbor Plain that spans from the early Pliocene to the Holocene (~5.5 Myr) (Figs. 8, 9). Three stages of their formation provide explanation for certain hydrological and climatic conditions in the past: the early-mid Pliocene characterised by formation of jointcontrolled solutional channels predating the pocket valleys, the late Pliocene characterised by commenced retreat of the pocket valleys, the Quaternary characterised by reforming of the pocket valleys due to variable gravitational and hydrological processes.

9

6.1. Early-mid Pliocene The caves and associated flowstone on the escarpment above the Roe Plain are about 70 m above the present sea level (hwp) and indicate an active underground water drainage in the early-mid Pliocene. Assuming that the sea level during the early Pliocene was ~30 m higher than today (Playford et al., 1975), caves and flowstone occurred about 40 m above the sea level during that time (hwPl). They functioned as an underground discharge system, draining water from the Nullarbor Plain towards the palaeo-coastline. Higher watertable levels within the Nullarbor aquifer are in accordance with previous reports (James et al., 1991), and the wet phase in the Pliocene (needed for cave formation and flowstone deposition) also corresponds with the climate interpretation based on the Nullarbor Limestone diagenesis by Miller et al. (2012) as well as with extensive fluvial and lacustrine sedimentation along palaeochannels around the Eucla Basin (Benbow et al., 1995a). However, different crystal segments of the flowstone, i.e. layers that show a periodical alternation between big columnar crystals (slow flow rate) and micrite layers with a high input of organic compounds from the surface including occasional wind-blown marine bioclasts washed underground through the vadose zone (fast flow rate), indicates seasonality in rainfall events during the generally humid early-mid Pliocene. The present hydraulic gradient beneath the Nullarbor Plain ranges from 1:650 in the west to 1:2400 in the east (Webb and James, 2006). It would be expected that the hydraulic gradient in the early-mid Pliocene was different due to higher precipitation. Calculations can be made by comparing the elevations of the belt of shallow cave systems with that of the caves within pocket valleys in regards to their distance from the coast at the time of shallow cave formation. Burnett et al. (2013) described a belt of caves over 75 km inland from the coast at about 145 m.a.s.l. (in the area north from the Hampton Scarp) with a median depth of ~7.5 m (i.e. 137.5 m.a.s.l.; hwi). This altitude is considered to correspond to the water table at that time. The distance of this belt from the escarpment is ~45–85 km (average ~65 km; de), meaning that the water table gradient in the early-mid Pliocene would be 1:963. The equation to calculate the distance of the coastline (dc) from the present-day escarpments is: dc ¼ de = hwi –hwp





 hwPl :

Using the above numbers and the early-mid Pliocene gradient, we calculate that the coastline was ~38 km away from the present-day escarpment. James et al. (2006) proposed a cliff retreat of ~85 km in a ~3 million year interval (5.5–2.5 Ma). This suggests that the discharge of the karst water (springs) from the Nullarbor Plain during (or before) the time of the speleothem formation was located on the palaeocoastline; the scarp and pocket valleys as we see today are thus younger and were able to form when the cliff retreat reached its final stage (~2.5 Ma). However, despite the potential of these calculations, further research is needed before stating final conclusions. For instance, a median depth of ~7.5 m for the shallow caves (Burnett et al., 2013) includes all types of caves including blowholes, and the real elevation of phreatic passages would probably be lower than a median depth. Furthermore, a tectonic uplift is likely to have occurred at ~ 2.5–1.5 Ma (Li et al., 2004; James et al., 2006), but the amount of uplift is unknown and therefore cannot be used in the calculations. Lastly, different suggestions of Pliocene sea-level highstand exist (e.g. Playford et al., 1975; James et al., 2006; Hou et al., 2008), making the calculation at this stage only theoretical. 6.2. Late Pliocene The lack of late Pliocene ages of flowstone formation in the Nullarbor caves (Woodhead et al., 2006; Blyth et al., 2010) suggests the

10

M. Lipar, M. Ferk / Earth-Science Reviews 150 (2015) 1–13

Fig. 8. The timeline of major events accompanied with palaeoclimate. Palaeotemperature curve derived from Zachos et al. (2001); simplified general sea level curve derived from Haq et al. (1987). Climate by other authors includes Miller et al. (2012; blue line), Hartley and Chong (2002; red line) and Dodson and Macphail (2004; green marks). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

progressive drying trend at this period. Seismic, facies, foraminiferal proxy data and palaeobotanical data from the marine and terrestrial deposits indicate a similar trend through the Pliocene also in southeastern Australia (Gallagher et al., 2003). Escarpment retreat until ~2.5 Ma (James et al., 2006) most probably caused a continuous drop of the water table; if not, the elevation would suggest that there would have been ~40 m waterfalls (or trickles) cascading down the sea cliff at the time, which is highly unlikely. Instead, by the late Pliocene the karst drainage was probably lowered, and the spring sapping that formed the pocket valleys may have been from voids and caves at a lower level (scarp foot), which are now hidden under the rubble and not accessible to collect exact elevation and

morphometrical data. The persisting spring activity related to pocket valleys after the drop of the water table is probably due to the same joint control as on the upper levels. Since the coast was most likely at the base of the cliffs when pocket valleys started to form in the late Pliocene, they probably experienced the mixing-zone corrosion effects as discussed above. Similar hydrological settings (e.g., seawater encroachment into coastal aquifers) resulting in crescent-shaped beaches and related coves and caves are observed in Pleistocene limestones on the Yucatan Peninsula, Mexico (Back et al., 1984). These authors interpreted mixing-zone corrosion at the saltwater–freshwater interface to be the trigger process for incipient coves to form at the coastal discharge points of groundwater flows, followed by

M. Lipar, M. Ferk / Earth-Science Reviews 150 (2015) 1–13

11

Fig. 9. Simplified diagram showing the Pliocene–Holocene situation on the general section of the Hampton Scarp. Note that elevations and distances are not to scale. WT: water table.

inland expansion of the dissolution zone along joint-controlled solution channels.

6.3. Quaternary The stratigraphic position of alluvial fans on top of the Roe Calcarenite suggests that the events (or periods) of high rainfall were present from the beginning of the Pleistocene to remove some of the material from the pocket valleys and redeposit it as alluvial fans. In addition, calcrete clasts within the alluvial fans simultaneously indicate the increasing overall aridity and seasonality (calcretes are characteristic of semiarid climates with limited and/or seasonal precipitation; Goudie, 1983; Alonso-Zarza and Wright, 2010). The onset of aridity in southern Australia, occurring in the late Pliocene to Pleistocene, was also reported by Goede et al. (1990), Sesiano and Hedley (1996), Woodhead et al. (2006), and McLaren and Wallace (2010). The semiarid conditions of the late Pleistocene–Holocene are indicated by formation of calcrete layers on exposed surfaces of the pocket valleys, representing the latest event as they cover both the flowstone and colluvial deposits. Miller et al. (2012) similarly described the increasing aridity in the Quaternary with periods of dry and wet seasons alternating with extremely dry periods. Additional processes involved in the present formation of pocket valleys are therefore probably also exudation — crystal wedging due to gypsum and halite crystallization, which contributed also to cave collapses on the Nullarbor Plain as suggested by Lowry (1968), Gillieson and Spate (1992) and Webb and James (2006). Active solutional voids are seen within some pocket valleys. These indicate that higher levels of pocket valleys are occasionally reactivated in present-day conditions and most probably act as an impeded drainage, discussed also by James et al. (1991) and Webb and James (2006). The reactivation occurs during daily or seasonal high rainfall events, especially due to intrusion of atmospheric depressions of tropical origin. These occur on the Nullarbor two to three times per decade and have the capacity to deliver large amounts of water onto the plain (from 25 to 48 mm a day; Gillieson and Spate, 1992; Gillieson et al., 1994; Bureau of Meteorology, 2014). Even though the Nullarbor Plain at present has a semi-arid climate, the karstification (and hence the formation of pocket valleys) is not inactive but only retarded. Generally wetter interglacial and generally drier glacial Quaternary climatic regimes in southern Australia (Parkin, 1974; Molina-Cruz, 1977; Wyrwoll, 1979, 1993; Zheng et al., 2002; Tapsell et al., 2003; Pickett et al., 2004; Lipar and Webb, 2014; Stuut et al., 2014) have probably caused periods of stronger karstification and relatively rapid formation of pocket valleys, intersected by periods of weaker karstification favourable for slope processes to form colluvium, and calcrete formation.

7. Conclusion This is the first study to document previously unrecognised pocket valleys on the escarpments of the Nullarbor Plain and to use their characteristics for palaeoenvironmental reconstruction. There are two main morphographic characteristics indicating their karst origin. First, they lack fluvial catchments — their sudden transition into steep walls at their upstream end that usually form amphitheatre-like pockets is a specific element that conflicts with the laws of fluvial erosion. Second, they show evidence of an underground outflow of water within pockets, demonstrated by solutional voids and caves. These significant topographic features of the Hampton and Wylie scarps offer the potential for a reconstruction of the Nullarbor environmental history. Three stages of their formation are proposed: (1) the early-mid Pliocene characterised by the formation of joint-controlled solutional channels predating the pocket valleys, (2) the late Pliocene characterised by commenced retreat of the pocket valleys, (3) the Quaternary characterised by reshaping of the pocket valleys due to variable gravitational and hydrological processes. Caves, formed in the early-mid Pliocene, provided an ideal environment that preserved the cave sediments. A speleothem U–Pb age places the initial solutional formation and deposition of flowstone in the generally wetter climate of the Pliocene. The locations of the caves and speleothems clearly indicate the palaeohydrological conditions at that time, and their relation to shallow caves on the Nullarbor Plain allow estimating hydraulic gradients and the distance of the palaeo-cliffs and related springs to the coastline. The retreat of the pocket valleys from the edge of the escarpment by gravitational undermining, exudation and slope processes began with the sea regression from the Israelite and Roe plains in the late Pliocene and the simultaneous drop of the water table. Solutional formation of pocket valleys was probably enhanced by mixing-zone corrosion at the saltwater–freshwater interface. The occurrence of pocket valleys is limited to the Hampton and Wylie scarps, but caves and springs probably also occurred throughout the escarpment of the Great Australian Bight. However, any pocket valley that may have formed along the Nullarbor cliffs would have been eroded away by the active retreat of these cliffs. Apart from the high rainfall events that formed alluvial fans in front of the pocket valleys in the Quaternary, the calcrete clasts within the fan material as well as calcrete layer on top of them imply the onset of aridity in southern Australia. The pocket valleys are at present predominantly subject to slope processes and occasional fluvial erosion on their side walls and downstream ends. Acknowledgement We wish to thank Blaž Komac, John Webb and Ken Grimes for comments on the early draft of the text, and an anonymous peer-reviewer as

12

M. Lipar, M. Ferk / Earth-Science Reviews 150 (2015) 1–13

well as peer-reviewers Jo De Waele, Susan White and editor André Strasser for improving the manuscript. Ann-Marie Meredith assisted with the extensive field work on the Roe and Israelite plains for which we are very grateful. Jon Woodhead is thanked for providing the U–Pb age data on the speleothem sample. The research was carried out whilst M. Lipar was supported by a La Trobe University Postgraduate Research Scholarship and a La Trobe Postgraduate Writing-Up Award (Web of Science), and whilst M. Ferk was supported by a Scholarship for Research Work from the Research Centre of the Slovenian Academy of Sciences and Arts.

References Alonso-Zarza, A.M., Wright, V.P., 2010. Calcretes. Dev. Sedimentol. 61, 225–267. Audra, P., Mocochain, L., Camus, H., Gilli, É., Clauzon, G., Bigot, J.-Y., 2004. The effect of the Messinian Deep Stage on karst development around the Mediterranean Sea. Examples from Southern France. Geodin. Acta 17 (6), 27–38. Auler, A.S., Smart, P.L., Wang, X., Piló, L.B., Edwards, R.L., Cheng, H., 2009. Cyclic sedimentation in Brazilian caves: mechanisms and palaeoenvironmental significance. Geomorphology 106 (1–2), 142–153. Ayliffe, L.K., Marianelli, P.C., Moriarty, K.C., Wells, R.T., McCulloch, M.T., Mortimer, G.E., 1998. 500 ka precipitation record from southeastern Australia: evidence for interglacial relative aridity. Geology 26 (2), 147–150. Back, W., Hanshaw, B.B., Van Driel, J.N., 1984. Role of groundwater in shaping the Eastern Coastline of the Yucatan Peninsula, Mexico. In: LaFleur, R.G. (Ed.), Groundwater as a Geomorphic Agent. Allen & Unwin, Boston, pp. 280–293. Benbow, M.C., Alley, N.F., Callen, R.A., Greenwood, D.R., 1995a. Geological history and palaeoclimate. In: Drexel, J.F., Preiss, W.V. (Eds.), The Geology of South Australia. Vol. 2, The Phanerozoic. South Australia. Geological Survey. Bulletin 54, pp. 208–218. Benbow, M.C., Lindsay, J.M., Alley, N.F., 1995b. Eucla Basin and palaeodrainage. In: Drexel, J.F., Preiss, W.V. (Eds.), The Geology of South Australia. Vol. 2, The Phanerozoic. South Australia. Geological Survey. Bulletin 54, pp. 178–186. Blyth, A.J., Watson, J.S., Woodhead, J., Hellstrom, J., 2010. Organic compounds preserved in a 2.9 million year old stalagmite from the Nullarbor Plain, Australia. Chem. Geol. 279, 101–105. Bureau of Meteorology, Australian Government, 2014. Climate statistics for Australian locations. URL: http://www.bom.gov.au (October, 2014). Burnett, S., Webb, J.A., White, S., 2013. Shallow caves and blowholes on the Nullarbor Plain, Australia — flank margin caves on a low gradient limestone platform. Geomorphology 201, 246–253. Caldwell, J.R., Davey, A.G., Jennings, J.N., Spate, A.P., 1982. Colour in some Nullarbor Plain speleothems. Helictite 20 (1), 3–10. Cañaveras, J., Sanchez-Moral, S., Soler, V., Saiz-Jimenez, C., 2001. Microorganisms and microbially induced fabrics in cave walls. Geomicrobiol J. 18, 223–240. Cerling, T.E., Harris, J.M., MacFadden, B.J., Leakey, M.G., Quade, J., Eisenmann, V., Ehleringer, J.R., 1997. Global vegetation change through the Miocene/Pliocene boundary. Nature 389, 153–158. Cvijić, J., 1893. Das Karstphänomen. Geogr. Abh. Wein 5 (3), 218–329. Dodson, J.R., Macphail, M.K., 2004. Palynological evidence for aridity events and vegetation change during the Middle Pliocene, a warm period in Southwestern Australia. Glob. Planet. Chang. 41, 285–307. Doerr, S.H., Davies, R.R., Lewis, A., Pilkington, G., Webb, J.A., Ackroyd, P.J., Bodger, O., 2012. Origin and karst geomorphological significance of the enigmatic Australian Nullarbor Plain ‘blowholes’. Earth Surf. Process. Landf. 37, 253–261. Eržen, M., 1964. Kostanjeviška Jama. Naše Jame 6, 17–19. Flower, B.P., Kennett, J.P., 1994. The middle Miocene climatic transition: East Antarctic ice sheet development, deep ocean circulation and global carbon cycling. Palaeogeogr. Palaeoclimatol. Palaeoecol. 108, 537–555. Flügel, E., 2010. Microfacies of Carbonate Rocks — Analysis, Interpretation and Application. 2nd edition. Springer, Heidelberg, Dordrecht, London, New York (984 pp.). Ford, D., Williams, P., 2007. Karst Hydrogeology and Geomorphology. John Wiley and Sons, Chichester (562 pp.). Frachon, J.-C., 2004. Les reculées du Jura lédonien. Étude géomorphologique. Spéléo-Club du Jura, Colonne, France (135 pp.). Frisia, A., 2015. Microstratigraphic logging of calcite fabrics in speleothems as tool for palaeoclimate studies. Int. J. Speleol. 44 (1), 1–16. Frisia, A., Borsato, A., Fairchild, I.J., McDermott, F., 2000. Calcite fabrics, growth mechanisms, and environments of formations in speleothems from the Italian Alps and southwestern Ireland. J. Sediment. Res. 70, 1183–1196. Gallagher, S.J., Smith, A.J., Jonasson, K., Wallace, M.W., Holdgate, G.R., Daniels, J., Taylor, D., 2001. The Miocene palaeoenvironmental and palaeoceanographic evolution of the Gippsland Basin, Southeast Australia: a record of Southern Ocean change. Palaeogeogr. Palaeoclimatol. Palaeoecol. 172, 53–80. Gallagher, S.J., Greenwood, D.R., Taylor, D., Smith, A.J., Wallace, M.W., Holdgate, G.R., 2003. The Pliocene climatic and environmental evolution of southeastern Australia: evidence from the marine and terrestrial realm. Palaeogeogr. Palaeoclimatol. Palaeoecol. 193, 349–382. Gams, I., 1974. Kras - zgodovinski, naravoslovni in geografski oris. Slovenska Matica, Ljubljana (358 pp.). Gentilli, J., Scott, D.R., 1963. The Yanchep Area. Geographical Society of Western Australia, Nedlands (25 pp.).

Gillieson, D.S., Spate, A., 1992. The Nullarbor Karst. In: Gillieson, D.S. (Ed.), Geology, Climate, Hydrology and Karst Formation: Field Symposium in Australia; GuidebookSpecial Publication 4. Department of Geography and Oceanography, University College, Australian Defence Force Academy, Canberra, pp. 65–99. Gillieson, D.S., Cochrane, J.A., Murray, A., 1994. Surface hydrology and soil movement in an arid karst: the Nullarbor Plain, Australia. Environ. Geol. 23, 125–133. Goede, A., Harmon, R.S., Atkinson, T.C., Rowe, P.J., 1990. Pleistocene climatic change in southern Australia and its effect on speleothem deposition in some Nullarbor caves. J. Quat. Sci. 5, 29–38. Goudie, A.S., 1983. Calcrete. In: Goudie, A.S., Pye, K. (Eds.), Academic Press, pp. 93–131. Goudie, A.S., 2006. Encyclopedia of Geomorphology. Routledge, Taylor & Francis Group, London, New York (1202 pp.). Goudie, A.S., 2010. Dayas: distribution and morphology of dryland solutional depressions developed in limestones. Z. Geomorphol. 54 (2), 145–159. Goudie, A.S., Viles, H., Allison, R., Day, M., Livingstone, I., Bull, P., 1990. The geomorphology of the Napier Range, Western Australia. Trans. Inst. Br. Geogr. 15 (3), 308–322. Grodzicki, J., 1985. Genesis of the Nullarbor Plain caves in southern Australia. Z. Geomorphol. 29 (1), 37–49. Gunn, J. (Ed.), 2004. Encyclopedia of Caves and Karst Science. Fitzroy Dearborn, an imprint of the Taylor and Francis Group, New York, London (1940 pp.). Haq, B.U., Hardenbol, J., Vail, P.R., 1987. The new chronostratigraphic basis of Cenozoic and Mesozoic sea level cycles. Special Publications — Cushman Foundation for Foraminiferal Research 24, pp. 7–13. Hartley, A.J., Chong, G., 2002. Late Pliocene age for the Atacama Desert: implications for the desertification of western South America. Geology 30 (1), 43–46. Haywood, A.M., Valdes, P.J., Sellwood, B.W., 2000. Global scale palaeoclimate reconstruction of the middle Pliocene climate using the UKMO GCM: initial results. Glob. Planet. Chang. 25, 239–256. Herrick, S.M., LeGrand, H.E., 1964. Solution subsidence of a limestone terrane in southwest Georgia. Bull. Int. Assoc. Sci. Hydrol. 9 (2), 25–36. Hocking, R.M., 1990. Eucla Basin. Geological Survey of Western Australia, Memoir 3 pp. 548–561. Hou, B., Frakes, L.A., Sandiford, M., Worrall, L., Keeling, J., Alley, N.F., 2008. Cenozoic Eucla Basin and associated palaeovalleys, southern Australia — climatic and tectonic influences on landscape evolution, sedimentation and heavy mineral accumulation. Sediment. Geol. 203, 112–130. Huggett, R.J., 2007. Fundamentals of Geomorphology (Routledge Fundamentals of Physical Geography). second edition. Routledge, New York (458 pp.). Hunt, G.S., 1970. The origin and development of Mullamullang Cave N37, Nullarbor Plain, Western Australia. Helictite 8, 3–26. Issar, A.S., 1983. Emerging ground water: a triggering factor in the formation of the mekhteshim (erosion cirques) in the Negev and Sinai. Isr. J. Earth Sci. 32 (1/2), 53–61. James, N.P., Bone, Y., 1991. Origin of a cool-water Oligo-Miocene deep-self limestone, Eucla Platform, southern Australia. Sedimentology 60, 323–341. James, J.M., Pilkington, G., Rogers, P., Spate, A., 1991. The Nullarbor carbonate aquifer, Australia: the impact of man and suggestions for future management. Proceedings of the International Conference on Environmental Changes in Karst Areas, IGU-IUS Italy. Universita di Padova, pp. 205–214. James, N.P., Bone, Y., Carter, R.M., Murray-Wallace, C.V., 2006. Origin of the Late Neogene Roe Plains and their calcarenite veneer: implications for sedimentology and tectonics in the Great Australian Bight. Aust. J. Earth Sci. 53, 407–419. Jennings, J.N., 1962. The limestone geomorphology of the Nullarbor Plains (Australia). Proceedings 2nd International Congress of Speleology 1, pp. 371–386. Jennings, J.N., 1963. Some geomorphological problems of the Nullarbor Plain. Trans. R. Soc. S. Aust. 87, 41–62. Jennings, J.N., 1968. Syngenetic karst in Australia: contributions to the study of karst. The Australian National University, Research School of Pacific Studies, Department of Geography, Publication, pp. 41–110 (G/5). Jennings, J.N., 1985. Karst Geomorphology. Basil Blackwell, Oxford, New York (293 pp.). Kenny, R., 2010. Continental palaeoclimate estimates from the late Mississippian Redwall karst event: northern and north-central Arizona (USA). Carbonates Evaporites 25 (4), 297–302. Ladišič, B., 1999. Nova Kostanjeviška jama. Naše Jame 41, 82–88. Lear, C.H., Elderfield, H., Wilson, P.A., 2000. Cenozoic deep-sea temperatures and global ice volumes from Mg/Ca in benthic foraminiferal calcite. Science 287, 269–272. Li, Q., James, N.P., Bone, Y., McGowran, B., 1996. Foraminiferal biostratigraphy, and depositional environments of the mid-Cenozoic Abrakurrie Limestone, Eucla Basin, southern Australia. Aust. J. Earth Sci. 43, 437–450. Li, Q., Simo, J.A., McGowran, B., Holburn, A., 2004. The eustatic and tectonic origin of Neogene unconformities from the Great Australian Bight. Mar. Geol. 203, 57–81. Lipar, M., Ferk, M., 2011. Eogenetic caves in conglomerate: an example from Udin Boršt, Slovenia. Int. J. Speleol. 40 (1), 53–64. Lipar, M., Webb, J.A., 2014. Middle–Late Pleistocene and Holocene chronostratigraphy and depositional history of the Tamala Limestone, Cooloongup and Safety Bay Sands, Nambung National Park, southwestern Western Australia. Aust. J. Earth Sci. 61, 1023–1039. Lipar, M., Webb, J.A., 2015. The formation of the pinnacle karst in Pleistocene aeolian calcarenites (Tamala Limestone) in southwestern Australia. Earth Sci. Rev. 140, 182–202. Lowry, D.C., 1968. The origin of blow-holes and the development of domes by exsudation in caves of the Nullarbor Plain. Geological Survey of Western Australia Annual Report: 1967. Geological Survey of Western Australia, Perth, pp. 40–44. Lowry, D.C., 1970. Geology of the western Australian part of the Eucla Basin. Bulletin, Geological Survey of Western Australia 122. Geological Survey of Western Australia, Perth (199 pp.). Lowry, D.C., Jennings, J.N., 1974. The Nullarbor karst, Australia. Z. Geomorphol. 18, 35–81.

M. Lipar, M. Ferk / Earth-Science Reviews 150 (2015) 1–13 Macphail, M.K., 1997. Late Neogene climates in Australia: fossil pollen- and spore-based estimates in retrospect and prospect. Aust. J. Bot. 45, 425–464. Martin, H.A., 2006. Cenozoic climatic change and the development of the arid vegetation in Australia. J. Arid Environ. 66, 533–563. McLaren, S., Wallace, M.W., 2010. Plio-Pliestocene climate change and the onset of aridity in southeastern Australia. Glob. Planet. Chang. 71, 55–72. Megirian, D., Murray, P., Schwartz, L., Von Der Borch, C., 2004. Late Oligocene Kangaroo Well Local Fauna from the Ulta Limestone (new name), and climate of the Miocene oscillation across central Australia. Aust. J. Earth Sci. 51 (5), 701–741. Metzger, C.A., Retallack, G.J., 2010. Paleosol record of Neogene climate change in the Australian outback. Aust. J. Earth Sci. 57, 871–885. Miller, C.R., James, N.P., Bone, Y., 2012. Prolonged carbonate diagenesis under an evolving late cenozoic climate; Nullarbor Plain, southern Australia. Sediment. Geol. 261–262, 33–49. Mocochain, L., Audra, P., Bigot, J.-Y., 2011. Base level rise and per ascensum model of speleogenesis (PAMS). Interpretation of deep phreatic karsts, vauclusian springs and chimney-shafts. Bull. Soc. Geol. Fr. 182 (2), 87–93. Molina-Cruz, A., 1977. The relation of the southern trade winds to upwelling processes during the last 75,000 years. Quat. Res. 8, 324–338. Morse, J.W., Gledhill, D.K., Millero, F.J., 2003. CaCO3 precipitation kinetics in waters from the great Bahama bank: implications for the relationship between bank hydrochemistry and whitings. Geochim. Cosmochim. Acta 67, 2819–2826. O'Connell, L.G., James, N.P., Bone, Y., 2012. The Miocene Nullarbor Limestone, southern Australia; deposition on a vast subtropical epeiric platform. Sediment. Geol. 253–254, 1–16. Onac, B.P., 2005. Minerals. In: Culver, D.C., White, W.B. (Eds.), Encyclopedia of Caves. Elsevier Academic Press, Burlington, San Diego, London, pp. 371–378. Parkin, D.W., 1974. Trade-winds during the glacial cycles. Proc. R. Soc. Lond. A Math. Phys. Sci. 337 (1608), 73–100. Pickett, E.J., Harrison, S.P., Hope, G., Harle, K., Dodson, J.R., Kershaw, A.P., Prentice, I.C., Backhouse, J., Colhoun, E.A., D'Costa, D., Flenley, J., Grindrod, J., Haberle, S., Hassel, C., Kenyon, C., Macphail, M., Martin, H., Martin, A.H., McKenzie, M., Newsome, J.C., Penny, D., Powell, J., Raine, J.I., Southern, W., Stevenson, J., Sutra, J.-P., Thomas, I., van der Kaars, S., Ward, J., 2004. Pollen-based reconstructions of biome distributions for Australia, Southeast Asia and the Pacific (SEAPAC region) at 0, 6000 and 8,000 14 C yr BP. J. Biogeogr. 31, 1381–1444. Playford, P.E., Cope, R.N., Cockbain, A.E., Low, G.H., Lowry, D.C., 1975. Phanerozoic. Geology of Western Australia. West. Australia Geol. Survey, Mem. 2, pp. 223–433. Polyak, V.J., 2000. Clays in caves of the Guadalupe Mountains, New Mexico. J. Cave Karst Stud. 62 (2), 120–126. Richards, D.A., Bottrell, S.H., Cliff, R.A., Strohle, K., Rowe, P.J., 1998. U–Pb dating of a speleothem of Quaternary age. Geochim. Cosmochim. Acta 62, 3683–3688. Sandiford, M., Quigley, M., de Broekert, P., Jakia, S., 2009. Tectonic framework for the Cenozoic cratonic basins of Australia. Aust. J. Earth Sci. 56 (1), 5–18. Sauro, U., 2001. Aspects of contact karst in the Venetian Fore-Alps. Acta Carsolog. 30 (2), 89–102. Sesiano, J., Hedley, I., 1996. Preliminary datation by paleomagnetism of a speleothem in Nullarbor Plain, southern Australia. Arch. Sci. 49, 127–136. Sexton, R.T., Tech, B., 1965. Caves of the coastal areas of South Australia. Helictite 3 (3), 45–59. Sperazza, M., Moore, J.N., Hendrix, M.S., 2004. High-resolution particle size analysis of naturally occurring very fine-grained sediment through laser diffractometry. J. Sediment. Res. 74, 736–743.

13

Stepišnik, U., Ferk, M., Gostinčar, P., Černuta, L., 2012. Holocene high floods on the Planina Polje, classical Dinaric Karst, Slovenia. Acta Carsolog. 41 (1), 5–13. Stewart, A.J., Sweet, I.P., Needham, R.S., Raymond, O.L., Whitaker, A.J., Liu, S.F., Phillips, D., Retter, A.J., Connolly, D.P., Stewart, G., 2008. Surface geology of Australia 1:1,000,000 scale, Western Australia (Digital Dataset), Canberra, The Commonwealth of Australia, Geoscience Australia. URL: http://www.ga.gov.au. Stuut, J.-B.W., Temmesfeld, F., De Deckker, P., 2014. A 550 ka record of aeolian activity near North West Cape, Australia: inferences from grain-size distributions and bulk chemistry of SE Indian Ocean deep-sea sediments. Quat. Sci. Rev. 83, 83–94. Sweeting, M.M., 1973. Karst Landforms. Columbia University Press, New York (362 pp.). Tapsell, P., Newsome, D., Bastian, L., 2003. Origin of yellow sand from Tamala Limestone on the Swan Coastal Plain, Western Australia. Aust. J. Earth Sci. 50, 331–342. Tičar, J., 2012. Geomorphological Characteristics of Pocket Valleys in Slovenia and France Bachelor's degree, Department of Geography, Faculty of Arts, University of Ljubljana (111 pp.). Tîrlă, L., Vijulie, I., 2013. Structural–tectonic controls and geomorphology of the karst corridors in alpine limestone ridges: Southern Carpathians, Romania. Geomorphology 197, 123–136. Udeze, C.U., Oboh-Ikuenobe, F.E., 2005. Neogene palaeoceanographic and palaeoclimatic events inferred from palynological data: Cape Basin off South Africa, ODP Leg 175. Palaeogeogr. Palaeoclimatol. Palaeoecol. 219, 199–223. Waddell, P.A., 2010. Geomorphology. In: Waddell, P.A., Gardner, A.K., Hennig, P. (Eds.), An inventory and condition survey of the Western Australian part of the Nullarbor regionTechnical Bulletin No. 97. Department of Agriculture and Food, South Perth, pp. 80–99. Webb, J.A., James, J.M., 2006. Karst evolution of the Nullarbor Plain, Australia. In: Harmon, R.S., Wicks, C. (Eds.), Perspectives on Karst Geomorphology, Hydrology, and Geochemistry — A Tribute Volume to Derek C. Ford and William B. White. Geological Society of America Special Paper 404, pp. 65–78. Williams, P.W., Marshall, A., Ford, D.C., Jenkinson, A.V., 1999. Palaeoclimatic interpretation of stable isotope data from Holocene speleothems of the Waitomo district, North Island, New Zealand. The Holocene 9 (6), 649–657. Woodhead, J., Hellstrom, J., Maas, R., Drysdale, R., Zanchetta, G., Devine, P., Taylor, E., 2006. U–Pb geochronology of speleothems by MC-ICPMS. Quat. Geochronol. 1, 208–221. Wright, V.P., 1988. Paleokarsts and paleosols as indicators of paleoclimate and porosity evolution: a case study from the Carboniferous of South Wales. In: James, N.P., Choquette, P.W. (Eds.), Paleokarst. Springer-Verlag, New York, Berlin, Heidelberg, London, Paris, Tokyo, pp. 329–341. Wyrwoll, K.H., 1979. Late Quaternary climates of Western Australia: evidence and mechanisms. J. R. Soc. West. Aust. 62, 129–142. Wyrwoll, K.H., 1993. An outline of Late Cenozoic palaeoclimatic events in the Cape Range region. In: Humphreys, W.F. (Ed.), The Biogeography of Cape Range, Western Australia. Western Australian Museum, Perth, pp. 39–50. Zachos, J., Pagani, M., Sloan, L., Thomas, E., Billups, K., 2001. Trends, rhythms, and aberrations in global climate 65 Ma to present. Science 292 (5517), 686–693. Zheng, H., Powell, C.M., Zhao, H., 2002. Eolian and lacustrine evidence of late Quaternary palaeoenvironmental changes in southwestern Australia. Glob. Planet. Chang. 35, 75–92. Zilberman, E., 2000. Formation of makhteshim unique erosion cirques in the Negev, southern Israel. Isr. J. Earth Sci. 49 (3), 127–141.