The Holocene Becher Point Cuspate Foreland, Western Australia – an Internationally Signiﬁcant and Globally Unique Potential Geopark

Home , Becher Point Wetlands, Cuspate foreland

International Journal of Geoheritage and Parks 8 (2020) 1–17

Contents lists available at ScienceDirect

International Journal of Geoheritage and Parks journal homepage: http://www.keaipublishing.com/en/journals/ international-journal-of-geoheritage-and-parks/

The Holocene Becher Point Cuspate Foreland, Western Australia – An internationally signiﬁcant and globally unique potential geopark

V. Semeniuk a,b,c,⁎, C.A. Semeniuk a,M.Brocxc a V & C Semeniuk Research Group, Warwick, Western Australia b School of Arts & Sciences, Notre Dame University, Fremantle, Western Australia c Environmental and Conservation Sciences, Murdoch University, Perth, Western Australia article info

Article history: Located in south-western Australia in a distinctive setting sedimentologically, oceanographi- Received 19 October 2019 cally, climatically, biologically, and sea-level history context, the Becher Point Cuspate Foreland Accepted 14 February 2020 is globally unique, and is a site of International Geoheritage Signiﬁcance that has the potential Available online 18 February 2020 to be developed as a Geopark. The cuspate foreland is part of an extensive shore-parallel Ho- locene coastal sand system that forms the seaward edge of the Swan Coastal Plain and eastern border of the Rottnest Shelf. It is the largest cuspate foreland complex in Western Australia and one of the largest in the World. Sedimentary accretion in the region began some 7000 years BP with a sea level + 2 m AHD. Since then, attended by a progressive climate change, sea level has steadily fallen to its present position, and sedimentation has built a coastal plain of low beach ridges with wetlands in the swales. Sedimentologically and stratigraphically, the cuspate foreland developed by seagrass bank accretion shoaling to the strand to form beach and beach- ridge/dune deposits capped in the swales by wetland deposits. Key features of the Cuspate Foreland are (1) the accreted Holocene beach-ridge plain, (2) the evolution of Holocene swale wetlands, (3) the Holocene sea level history, (4) Holocene climate history as recorded in the wetlands, and (5) a host of small-scale geological phenomena. The complex of beach ridges and swale wetlands is the basis of a geopark in which coastal plain evolution, wetland evolution, Holocene sea level history, and Holocene climate changes can be explored and explained essentially in an outdoor Museum. To illustrate the richness of the natural history information, from macroscale to microscale, embedded in the Becher Point Cuspate Foreland, we choose, as case studies, two aspects of the area and describe them in a holistic and multi-scalar manner for education and research, and potential thematic geotours. © 2020 Beijing Normal University. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction

The Becher Point Cuspate Foreland is located in south-western Australia in a distinct setting sedimentologically, oceanographically, climatically, and biogeographically and, with a distinct Holocene Western Australian sea-level history (Searle & Semeniuk,

⁎ Corresponding author. E-mail addresses: [email protected],(V.Semeniuk),[email protected]. (M. Brocx). https://doi.org/10.1016/j.ijgeop.2020.02.001 2577-4441/© 2020 Beijing Normal University. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/). 2 V. Semeniuk et al. / International Journal of Geoheritage and Parks 8 (2020) 1–17

1985; Searle, Semeniuk, & Woods, 1988). Situated along the south-eastern margin of the Indian Ocean, the Becher Point Cuspate Foreland receives and experiences intra-annual, annual, and inter-decadal oceanic and coastal oceanographic and meteorologic signals and sea temperature changes that are recorded in the coastal landforms, biota, sediment types, and stratigraphy (cf. Brocx & Semeniuk, 2009), with sea temperature changes and gradients recorded in the extant and fossil macrobiota and micro- biota (T A Semeniuk, 2000, 2001; Smale, Wernberg, & Vanderklift, 2017). As such, for this part of world, ocean setting, and climate, it presents a globally unique ensemble of coastal geomorphology, seagrass bank development, stratigraphy, and microscale geological features all evolved within a changing Holocene climate. Seagrass bank influenced sedimentation in this region is an important component of coastal sedimentation patterns, and the Becher Point Cuspate Foreland presents a distinct and different seagrass bank sedimentary system to elsewhere. Seagrass- influenced sedimentation, sedimentary shoaling, and coastal progradation have resulted in diagnostic bank to beach to beachridge stratigraphy, and a prograded coastal plain up to 10 km wide (Searle et al., 1988). In addition, in comparison to seagrass banks elsewhere in Australia and globally, those of the Becher Point area commonly are founded on cuspate forelands that shoal to the level of the strand and are capped by beach ridges and dunes. In contrast, seagrass bank sedimentation and stratigraphy elsewhere in Shark Bay (Western Australia) are fringing and/or barrier banks (Davies, 1970; Hagan & Logan, 1974; Read, 1974), those in Spencer Gulf (South Australia) are meadows (sheets) (Gostin, Hails, & Belperio, 1984), those in Florida are reticulate mud mounds (Enos & Perkins, 1979; Scholl, 1966; Wanless & Tagett, 1989), and in the Mediterranean Sea are meadows (sheets) (Hemminga and Duarte, 2000). However, the Becher Point Cuspate Foreland presents more than just shoaling a seagrass bank leading to development of a beach-ridge plain - it is quite holistic in that its geological characteristics of climate record, sea level history, wetland development and stratigraphy, and a host of small-scale geological features are integrated and interdependent (Semeniuk & Searle, 1986; Semeniuk, 1985; Semeniuk, 1986;CASemeniuk, 2007; Semeniuk, Semeniuk, Trend, & Brocx, 2015), and the ensemble of these features renders the Becher Point Cuspate Foreland globally unique. Designated firstly as an assemblage of Nationally Significant Wetlands in 1993 (Environment Australia, 2001), it was later recognised as being of international importance under the Ramsar Convention on Wetlands and inscribed as Ramsar Site 1048 on 5th January 2001 (Department of Parks and Wildlife, 2014). The importance of the Becher Point Ramsar site lies in the occurrence of unique wetlands via staggered development in the swales in response to rising water tables, to the dissolution and sinking of wetland basins, to climate history preserved in the wetland stratigraphy, amongst others. Additionally, Semeniuk et al. (2015) also show how this area provides an excellent example of how foraminifera, pollen and charophyte fructifications and dissolution are important markers and signatures within the Holocene history of the beach ridge plain and wetlands and, as such, represent significant geoheritage values at the smallest scale. However, the importance of Becher Point extends beyond its value as a Ramsar site and the occurrence of unique wetlands, because, holistically, it presents a range of geological features from the large scale to small scale, and presents features that are internationally to nationally significant; these include a stratigraphy of seagrass bank sediments succeeded by beach and dune sediments. In a wider context, focused on the Rockingham-Becher Plain beyond and northwards of the Becher Point Cuspate Foreland, there are additional significant Holocene geological features such as lagoons formed by barrier spits, and stromatolites fringing the shores of lakes (Searle et al., 1988;CASemeniuk, 2007), but these are outside the scope of this paper. In this paper, in a context of national parks and natural heritage protection, we present the extent of information available on this globally significant coastal-marine system and coastal-plain system of the Becher Point Cuspate Foreland by providing a description of the area and how that information might be used for a Science and Education Centre and Thematic Geotours, thereby providing a case study of an approach to present natural history information in a holistic and multi-scalar manner for education, research, and geotourism.

2. Regional setting and formation of the Becher Point Cuspate Foreland

The cuspate foreland at Becher Point in south-western Australia is part of an extensive shore-parallel Holocene coastal sand system (of beach/dunes, barriers, cuspate forelands, and tombolos) that is the seaward edge of the Swan Coastal Plain and the shore of the Rottnest Shelf (Fig. 1; Searle & Semeniuk, 1985; Semeniuk, Cresswell, & Wurm, 1989). In a regional setting, coastal sand has been transported northwards at a flux of 100,000 m3/annum alongshore by swell and south-westerly to southerly wind waves from eroding coasts further south (Searle & Semeniuk, 1985; Semeniuk, 1985; Semeniuk & Meagher, 1981). While a large component of sand has been delivered to the coast to north by this longshore drift, locally, sand also is derived from and delivered onshore both from seagrass banks and from erosion of semi-lithified offshore limestone barriers (Searle & Semeniuk, 1985, 1988). Following the post-glacial marine transgression, sea level reached +2 m (Australian Height Datum, or AHD) approximating its present position some 7000 years ago, and these three sources of sand contributed to the development of sand bodies in central and northern parts of the coast. Where there are offshore islands and perforated linear limestone reefs, the energy shelter pro- vided by these structures results in cuspate forelands and tombolos. Additionally, strong onshore sea breezes transport sand inland to form beach ridges, moderate-relief coastal dunes, and inland ingressing parabolic dunes (Semeniuk et al., 1989). Much of the south-western coast of Western Australia between Geographe Bay and Cape Bouvard/Halls Head has no limestone barriers and thus is directly exposed to receive swell from the Indian Ocean, refracted swell from the Southern Ocean, as well as sea-breeze generated wind waves (Searle & Semeniuk, 1985). The northwards transport of sand is unimpeded until the occurrence of the first of the shore-parallel (perforated) limestone barriers (north of Cape Bouvard/Halls Head; Fig. 1; Searle & Semeniuk, 1985; Semeniuk, 1996). Thereafter, northward-moving sand accumulated in lower-energy ‘shadows’ accreting from V. Semeniuk et al. / International Journal of Geoheritage and Parks 8 (2020) 1–17 3

Fig. 1. Regional and geological setting of the Becher Point Cuspate Foreland. A & B. Location along coastal Western Australia. C. Large scale geomorphic setting showing location of Rottnest Shelf and Swan Coastal Plain. D. Geomorphic setting of the Quindalup Dunes in the context of the Swan Coastal Plain. E. The double cuspate foreland in the region; this map also shows the three consanguineous wetlands suites of C A Semeniuk, (1988) - the wetlands of this paper belong to the Becher Suite; also shown are the spit-barred lagoons (Lake Richmond, Lake Cooloongup, and Lake Walyungup, that are outside the scope of this paper); the wetlands of the paper located on the Becher Point cuspate foreland are clearly evident. F. Details of the wetlands of this paper located on the Becher Point Cuspate Foreland showing their alignment along beach-ridge swales (as linear basins and linearly-arranged wetland basins). Diagram collated and modified after C A Semeniuk, 2007. 4 V. Semeniuk et al. / International Journal of Geoheritage and Parks 8 (2020) 1–17 a palaeo-shoreline (cut as cliffs into Pleistocene limestone) forms cuspate forelands leeward of the limestone barriers and limestone islands. But leaving aside the abandoned, buried, and eroded early Holocene cuspate sedimentary accumulation at Cape Bouvard (Semeniuk, 1996), the cuspate foreland at Becher Point is now the first major trap for the northward-moving sand and, here, leeward of a limestone reef complex (Penguin Island, Point Peron, and Garden Island; Fig. 1) sand has accreted to form a large sedimentary accumulation (termed the Rockingham-Becher Plain - a beach-ridge coastal plain accreted some 10 km from the palaeo-shoreline cut into the Pleistocene limestone). This accumulation formed leeward of two limestone islands/reefs and formed a double cuspate accumulation – the southern one is the cuspate foreland at Becher Point, and the northern one is the cuspate foreland at Point Peron (Fig. 1). The Rockingham-Becher Plain is the first sediment trap for the northward- migrating sand emanating from southern areas and, as such, is the largest cuspate foreland complex in Western Australia. Our focus is on the southern part of this double cuspate accumulation viz., that at Becher Point. Sedimentologically and stratigraphically, the cuspate foreland at Becher Point developed by seagrass bank accretion shoaling to a level of the strand to form beach deposits and beach-ridges (Semeniuk et al., 1989). Thus, the cuspate foreland comprises

Fig. 2. Age structure in 14C years of the double cuspate foreland of the Rocking-Becher plain. (Modiﬁed from C A Semeniuk, 2007) V. Semeniuk et al. / International Journal of Geoheritage and Parks 8 (2020) 1–17 5 seagrass-bank sediments, succeeded by beach facies, and capped by beachridge/dune sediments. Swales between the beach ridges are ﬁlled with wetland sediments (C A Semeniuk, 2007). Today, the climate of Becher Point is subhumid with seasonal rainfall in winter. With an annual rainfall of 700–900 mm, and annual evaporation of 1500–1600 mm, rainfall directly recharges the groundwater so there is a seasonal rise and fall in the water table.

3. Key features of the Becher Point Cuspate Foreland - what makes it globally unique

The cuspate forelands of Rockingham-Becher began forming some 7000 years BP with a sea level + 2 m AHD, and the Becher system began 5000 years BP and accreted to form cuspate forelands leeward of islands and rocky reefs (Fig. 2). Since then, sea level has steadily fallen to its present position (Semeniuk & Searle, 1986). Concomitantly, with Earth-axis precession, the climate changed from semi-arid to humid (Semeniuk, 1986, 1996). The accretion of the foreland formed a landscape of shore-parallel

Fig. 3. Beach ridges in the Becher Point Cuspate Foreland. A. Aerial photograph. B. Map showing beachridges and those spaced on 45-year interval compared to those spaced on 250-year interval (from Semeniuk Semeniuk, 2012). 6 V. Semeniuk et al. / International Journal of Geoheritage and Parks 8 (2020) 1–17 low-relief beach ridges and swales. With progradation, a rising water table resulted in a landscape-and-stratigraphic system that records wetland development, Holocene sea level history, and climate changes. The key features of the Becher Point Cuspate Foreland are as follows:

1. a stratigraphy of seagrass bank sediments succeeded by beach and dune sediments 2. westward younging beach ridges showing 45-year cycles and 250-year cycles 3. complex sedimentary dynamics at the point of the cuspate foreland 4. beach ridges and wetland formation 5. staggered insertion of wetlands in the swales in response to rising water tables 6. younging sequence and age-structured wetland sediments 7. the sedimentary ﬁll of the wetlands 8. differential hydrology of the wetlands depending on their sedimentary ﬁll

Table 1 Description of the various geological features of Becher Point Cuspate Foreland.

Stratigraphy of seagrass bank, beach and The shoaling stratigraphy of seagrass bank, beach to dune is globally unique and presents a stratigraphic standard dune sediments of marine sediment shoaling through beaches to beach ridges (dunes) (Semeniuk, 1997, Semeniuk, Searle, & Woods, 1988) Younging beach ridges showing 45-yr Growth of the cuspate foreland from east to west was via accretion of low-relief beachridges on a 45-year pattern and 250-yr cycles (the Double Hale Cycle), and the large beachridges on a 250-year cycle; this chronological spacing effectively records cycles of climate (Semeniuk, 1995; Semeniuk & Semeniuk, 2012) Complex sedimentary dynamics at the With a southerly derived and northward migrating shoreline ribbon of sand, the cusp tip of the Becher Point point Cuspate Foreland shows a complex history of alternating erosion and accretion (Semeniuk, 1995) Beach ridges and wetland formation As beachridges accrete on a generally 45-year and/or 250-year cycle the prograded coast is a series of shore-parallel beach ridges and intervening linear swales; as the prograding edge of the coastal plain migrates seawards, the regional water table becoming more distant from the shore begins to rise (Fig. 3), and the older inland swales between the ridges, being low-relief terrain, become progressively flooded by the rising water table (C A Semeniuk, 2007); the result is a series of linear beachridges separating linear wetlands Staggered insertion of wetlands Because swales (which will become wetland basins) between the beachridges are not always at a regular diminishing height above sea level from east to west, and because a given swale does not have an even (flat) floor along its basin length, the flooding of swales is not a regular east to west process nor a consistent phenomenon along the length of swale – rather, the development of wetlands is staggered in time and space, responding to the irregularities of the swales intersecting the rising water table (C A Semeniuk, 2007)(Figs. 4 & 5) Younging sequence/age-structured While insertion of wetlands is staggered, in an overall and general pattern, there is a younging of wetlands from wetland sediments east to west and, within a given wetland basin that has filled with wetland sediment, there is a younging upwards with sediment accretion (C A Semeniuk, 2007) Sedimentary fill of the wetlands There are four types of sediments that fill the wetland basins (C A Semeniuk, 2007); the dominant type is calcilutite that derives from disintegration of calcareous charophytic algae; where mixed with the underlying sand that forms the floor of the incipient wetland, there is developed a bioturbated calcilutaceous muddy sand; the margins of the wetland basin have bioturbated lenses and wedges of quartzose calcareous sand and calcilutaceous muddy sand developed by sheet wash of beachridge sand into the wetland margins, with calcilutite bioturbated into the beachridge sand to form calcilutaceous muddy sand; and locally, peat Differential hydrology of wetlands Given the various types of sediments in and bordering wetland basins, given the differential heights of the incipient wetland floors above a water table, and given the extent (thickness) wetland sediment can fill the basin, there are different hydrological patterns from east to west across the range of basins and even within a single wetland swale; this results in variable vegetation in response to hydrology, hydrochemistry, and various substrate types (C A Semeniuk, 2007); hydrochemically, this differential hydrology results in differential diagenesis Short-term climate history in wetland Short-term inter-decadal and intra-centurial changes in climate driven by Sun-spot activity, and Lunar Nodal stratigraphy Periodicity, which result in alternating wetter and drier periods, as evident in changes in wetland vegetation and wetland stratigraphy (Semeniuk, 1995, 2012, Semeniuk & Semeniuk, 2012); these alternating wet and dry episodes result in times when peat is developed, then peat is fire-excavated, and when wetlands replenished with water can support charophytes (and carbonate mud production) Long-term climate history in wetland The pollen record in wetland stratigraphy (C A Semeniuk, Milne, Semeniuk, & Ladd, 2006), corroborates the stratigraphy climate change determined by calcrete (Semeniuk, 1986) as driven by Earth-axis precession; the pollen record indicates a late Holocene inter-millennial climate change manifest by the encroachment into the basins of the grass tree (Xanthorrhoea preissii) at circa 1500 14C years BP, implying its incursion into wetland margins (regardless of the individual vegetation history of a wetland) was broadly synchronous in the region, implicating a climate change Dissolution/dissolutional sinking of Although the wetlands sediments are calcilutaceous, organic matter and decaying plants generate weakly acidic wetland basins groundwater and this results in dissolution of calcilutite within the basins and dissolution of the carbonate grains in the sand underlying the wetland basins leading to removal of carbonate and ‘sinking’ (deepening) of the wetland basins (Figs. 6 & 7)(CASemeniuk, 2007) Fire excavation of wetlands During dry episodes of the inter-decadal and intra-centurial climate changes, peat (developed during the wet phase) is ignited by vegetation fires and combusted, and removed to create small cliffs, steep basin margins, and deepening of the wetland basins (cf. Semeniuk & Semeniuk, 2005)(Fig. 8) Sea level history in the stratigraphy Using sea-level indicators such as swash-zone sedimentary structures, bubble sand, and storm-level indicators of the floating shells (Sepia, and Spirula spirula)(Semeniuk, 1997; Semeniuk & Johnson, 1982), Searle and Woods (1986) and Semeniuk and Searle (1986) reconstructed the Holocene sea level history of the Rockingham-Becher Plain showing that the post-glacial transgression sea level reached a maximum height of +2 m AHD and then steadily fell to its present position); this sea-level record contrasts with others in Western Australia (see later) V. Semeniuk et al. / International Journal of Geoheritage and Parks 8 (2020) 1–17 7

9. short term climate history recorded in wetland stratigraphy 10. long term climate history recorded in wetland stratigraphy 11. dissolution and dissolutional sinking (deepening) of wetland basins 12. ﬁre excavation of the wetlands 13. sea level history in the younging stratigraphy A brief description of these features in presented in Table 1. Each of these features can form the basis of dedicated geotours or can be amalgamated into thematic geotours. To illustrate the richness of the natural history information at macroscale to microscale embedded in the Becher Point Cuspate Foreland, we focus in part on two thematic geotours (to be described below): 1. evolution of wetlands in the Becher Point system, and 2. stratigraphic evolution of seagrass banks to beach ridge.

4. Thematic geotour - evolution of wetlands in the Becher Point system – a 5000 year journey

The evolution of wetlands in the Becher Point system essentially is a journey over 5000 years of progressive wetland development, wetland basin filling, and post-sedimentary modification of the stratigraphy by dissolution and by fires. Progressing from

Fig. 4. Idealised cross-section of the Becher Point Cuspate Foreland showing, with water-table rising, the progressive insertion of wetland in swale basins across the beach-ridge plain. Chronological order of wetland insertion labelled as (1) to (4). Modified from C A Semeniuk (2007). 8 V. Semeniuk et al. / International Journal of Geoheritage and Parks 8 (2020) 1–17 the west to the east, that is, from the coast where the youngest wetland basins that are simply underlain by beach-ridge sand are located inland to the oldest wetlands that are underlain by the full complement of wetland sedimentary fill and exhibit the full complement of margins and intra-basinal complications, the story of wetland evolution can be viewed more-or-less chronologi- cally in terms of changes in geomorphology, sediments, stratigraphy, hydrology, and hydrochemistry, and climate history. There are several stages in the evolution of wetlands in the Becher Point system (Fig. 6), and it begins with the construction of a beach ridge. At the coast, successive beach ridges are separated by linear swales and their interior basins which, as the water table rises with coastal progradation (C A Semeniuk, 2007), become seasonally flooded to become a linear wetland or a series of wetland basins. The length of a swale is not a plain and flat surface but has undulations and, consequently, consists of a series of small basins along the length of the swale depression. As a result, water-table rise results in differential seasonal depths of surface water and different degrees of waterlogging along the length of the linear depression - at one extreme there are damplands and, at the other, there are sumplands (wetland terms after Semeniuk & Semeniuk, 2016). This results in differential array of vegetation types that reflect sediment types, water sources, and water longevity (Fig. 9). As the coast progrades, the near-coastal

Fig. 5. Idealised map of the Becher Point Cuspate Foreland showing the progressive insertion of wetland in swale basins across the beach-ridge plain. (Modified from C A Semeniuk, 2007). V. Semeniuk et al. / International Journal of Geoheritage and Parks 8 (2020) 1–17 9 basins are stranded further inland. Also, as the coast progrades and the regional water table rises to sufficient and appropriate heights, the more inland basins that initially were not flooded eventually may be intersected by the rising water table. Overall, though, there is a general younging of wetland insertion into the beach-ridge plain as the coast progrades but young wetlands (i.e., newly inserted wetlands) can be developed inland if the rising water table intersects a stranded swale basin. This phenomenon is illustrated in Figs. 4 & 5. Once the basin becomes a wetland, it begins to accrete carbonate mud through the seasonal growth and disintegration of calcareous charophytes. Initially, the carbonate mud is mixed (bioturbated) into the sandy floor of the wetland and the basin begins to function to perch rainwater to a limited extent. Thereafter, with seasonal inundation and more prolific carbonate mud production by charophytes, the basin begins filling with calcilutite and begins to more consistently perch rainwater. The basal calcilutaceous muddy sand is overlain stratigraphically by calcilutite. During the wetter phases of the wet-to-dry alternations of the climate cycles, peat may develop as the uppermost sedimentary layer. However, during the drier phases of the wet-to-dry alternations of the climate cycles, the peat may be ignited by scrub fires and be removed by combustion leaving cliff scars and causing a lowering of the wetland floor. During the wet versus dry phases of the climate cycles, the wetland margin may expand during the wet phase and contract during the dry phase. Further, during the dry phases, sheet wash can deliver sandy sediment from the adjoining beach ridge to

Fig. 6. Four chronological stages of wetland development from initial wetting of the swale ﬂoor by water-table rise to the ﬁlling of the swale by wetland sediments (a ‘mature’ wetland basin). 10 V. Semeniuk et al. / International Journal of Geoheritage and Parks 8 (2020) 1–17

Fig. 7. Details of Stage 4, the final filling of a mature wetland basin; annotations show the processes operating in and around the wetland illustrating a generally shoaling stratigraphy of calcilutite but with a basal layer where basement sand was mixed with calcilutite. The stratigraphy also shows evidence of basement solution, basin widening and contraction responding to Holocene climate changes, and the effects of fire in deepening the basin. Diagram modified from C A Semeniuk (2007). Wetland nomenclature after Semeniuk and Semeniuk (2016).

encroach into the wetland margins creating (with alternating wet versus dry phases) an interfingering of wetland sediment and beach-ridge sediment. As mentioned earlier, the geomorphology, stratigraphy, hydrology, and hydrochemistry of the wetlands in their chronological sequence presents: a story of staggered insertion of wetlands across the beach-ridge plain, a long-term climate history in wetland stratigraphy, a short-term climate history in wetland stratigraphy, a record of sedimentary fill, a younging age-structured sequence of wetland sediments, a story of dissolution and dissolutional-sinking of wetland basins, and the consequences of fire excavation of wetlands. The complicated history of expansion and contraction of wetland basins, the sedimentary sequences, the fire excavation, and the dissolutional-deepening of the basins following wet-and-dry climate cycles is illustrated diagrammatically in Fig. 8.

5. Thematic geotour - stratigraphic evolution of seagrass banks to beach ridge

Unlike the evolution of the wetlands, the sedimentary evolution and resulting stratigraphy of the cuspate foreland is relatively consistent and less complicated. Seagrass banks underlain by skeletal quartzose sand (with locally generated skeletons dominantly of bryozoans, calcareous algae, foraminifera, and molluscs; Searle & Semeniuk, 1988;TASemeniuk, 2000, 2001) and quartz sand, limestone lithoclasts, and remanié fossils derived from southwards from longshore drift, and from offshore limestone barriers and islands) generate sedimentary wedges and prisms of bioturbated sand that are overlain by a sheet of lam- inated shelly skeletal quartzose sand (beach sand) and this is stratigraphically succeeded by beach-ridge and dune sands. The structures therein and the stratigraphic sequence is illustrated in Fig. 10. The processes and products along a beach to dune proﬁle are illustrated in Fig. 11. The resulting region-speciﬁc stratigraphy generated by shoaling of the seagrass bank to beach to beach ridge with their diagnostic molluscan fauna is illustrated in Fig. 12. This style and detail of stratigraphy appears to be globally unique. A transect from east to west (oldest sequence to youngest sequence) across the beach-ridge plain will illustrate sheet-like ge- ometry of the shoaled sedimentary sequence. The extra advantage of this east to west transect is that it will illustrate the progressive fall in sea level over 7000–5000 years (using four relative sea-level indicators, viz., 1. the subtidal contact of seagrass bank facies with the beach facies that is circa 2 m below MSL, 2. the swash zone facies, 3. bubble sand, if it is preserved, that signals high-water mark, and 4. the zone of Sepia and Spirula that signal storm water level), and it will illustrate the changes in diagenesis and pedogenesis of the beach-ridge sands from 5000 years BP to the present. The sea level indictors have been used to construct the diagnostic sea level history curve for the Holocene in this area is illustrated in Fig. 13, and the comparative sea level curves for elsewhere in Western Australia are illustrated in Fig. 14. V. Semeniuk et al. / International Journal of Geoheritage and Parks 8 (2020) 1–17 11

Fig. 8. Idealised diagram showing the complex history of a mature wetland basin; there is a complicated history of expansion, contraction, marginal sediment encroachment, dissolution and sinking, and ﬁre excavations. (Modiﬁed from C A Semeniuk, 2007).

6. A geopark - a Western Australian perspective - the Becher Point Cuspate Foreland

There are a number of deﬁnitions or concepts associated with the term ‘geopark’. In its original and simplest form, a geopark is auniﬁed area that advances the protection and use of geological heritage in a sustainable way and promotes the economic well- being of the resident community (McKeever & Zouros, 2005). There are UNESCO Global Geoparks and National Geoparks. Follow- ing McKeever and Zouros (2005), Brocx and Semeniuk (2011) and Semeniuk and Brocx (2019),thetermgeoparkhasbeenused in its original sense as outlined above. Where an area has not yet been inscribed as a UNESCO Geopark but has potential to be a UNESCO “Aspiring Geopark” or a potential National Geopark we add the appropriate descriptors, viz. aspiring geopark or potential geopark. 12 V. Semeniuk et al. / International Journal of Geoheritage and Parks 8 (2020) 1–17

Fig. 9. A. Map of location of wetland WAWA within the array of swale wetlands. B Map of vegetation complexes across the basin. C. Profile showing vegetation structure and asymmetry in vegetation structure and composition across the basin. Modified from C A Semeniuk (2007).Intheprofile, mud is calcilutite, muddy sand is calcilutaceous muddy sand, and sand is skeletal quartzose sand.

In a Western Australian context, given the political climate where mineral exploration and exploitation are paramount as a national ethos and the State of Western Australia and Australia itself lag behind the World in matters of geoconservation (Brocx, 2008; Brocx & Semeniuk, 2018), there has been a resistance to the inscription of UNESCO Geoparks. The only geopark in Australia, Kanawinka (declared Australia's First UNESCO Assisted Geopark in 2008, was delisted in 2012; Mackay, 2017). We circumvent (in part) the issue of the Australian resistance to geoconservation by utilising the term geopark in the sense of McKeever and Zouros (2005) and preparing for the future when the Australian Federal Government ethos and priorities change with regard to UNESCO Geoparks, we add the descriptor ‘potential’ to denote the area in question has the attributes of a geopark. V. Semeniuk et al. / International Journal of Geoheritage and Parks 8 (2020) 1–17 13

Fig. 10. A. Environments, surface sediments and stratigraphy of a seagrass bank to beach to beachridge system. B. Dynamics/processes that lead to the development of the stratigraphy.

On the other hand, we plan to utilise the area of the Becher Point Cuspate Foreland as a unified area (i.e., a geopark) to advance the protection and use of geological heritage that has been described above in a sustainable way for education, promotion and celebration of its globally significant geological features, for research, and for geotourism, at the same time promoting the economic well-being of the resident community. However, while the area of the Becher Point Cuspate Foreland, in principle, has the potential to be developed as a Western Australia geopark, the promotion, protection and use of geological heritage for education, promotion, for research, and for geotourism, and for the celebration of the globally significant geological features of this area are intended to be housed and admin- istered from the Becher Science Park and Education Centre, as described below.

7. A proposed Becher Science Park and Education Centre

Given the global scientiﬁc importance and the multiplicity of natural geological features on the Becher Point Cuspate Foreland, The Wetlands Research Association Inc. (a non-government organisation in Western Australia), in consultation with government and other non-government community organisations, is proposing to construct and operate a world-class Science Park (Becher Science Park) which will be the only Science Theme Park in Australia. The Science Park will comprise two major facilities: 1. The Bernard Bowen Wetland Centre – designed to attract world-class researchers and support education and training, and 2. a Science Theme Park - an outdoor family-oriented commercial park based on the Earth Sciences. The proposed Becher Science Park will be unique in Western Australia as it will be developed in keeping with internationally established Geopark principles. It will focus on developing four strategic areas: 1. Tourism and Local Business development, 2. Environmental Management, 3. Community Engagement, and 4. Education and Training. For the Becher Science Park and Education Centre there will be lasting Education/Scientiﬁc outcomes as this is an inter- generational project based on the Earth Sciences and Biological Sciences. Educational programmes will include pre-primary school to postgraduate level, community workshops, and school holiday programmes. It will be developed to stimulate interest and ed- ucate up-and-coming scientists and will ensure that the local and regional communities understand the values of the site. At the 14 V. Semeniuk et al. / International Journal of Geoheritage and Parks 8 (2020) 1–17

Fig. 11. Processes and products on a sandy beach (graded across the beach and related to the slope gradient). Waves, tides, wind, fresh-water seepage, and biota interact with a sloping sandy shore producing a range of sedimentary products and sediment types. (Modiﬁed from Brocx & Semeniuk, 2009).

Research level, as an outdoor classroom, that is highly relevant to today's focus on climate change, the proposed Becher Science Park and Wetland Education Centre will be linked to any number of multidisciplinary educational programmes from the Marine Sciences, to the Earth Sciences, Biological Sciences, and Social Sciences. Guiding Principles will be developed to address the conservation of sites of geoheritage significance as well as internationally significant wetlands as a model for community management for other Ramsar sites in Western Australia, Australia, and globally, in association with the scientific community. Income generated from the Becher Science Park and tourist-based activities will be utilised to ensure that the site is managed according to its scientificandintrinsicvalues.

8. Discussion and conclusions

Application of the geoheritage evaluation methods of Brocx and Semeniuk (2007, 2015) shows most of the geological features described above to be globally signiﬁcant in that they do not occur elsewhere as an integrated natural history ensemble with the same range of diversity. Further, this part of south-western Australia located in the south-eastern part of the Indian Ocean is, of V. Semeniuk et al. / International Journal of Geoheritage and Parks 8 (2020) 1–17 15

Fig. 12. The shoaling stratigraphy of seagrass bank to beach to beachridge; also shows the shelly fauna diagnostic of each stratigraphic unit. (From Semeniuk, 1997). course, unreplicated globally, and the Leeuwin Current deriving from northern water and feeding the oceanic waters to the south is not a recurring world-wide phenomenon. As such, this part of south-western Australia oceanographically is globally unique with attendant consequences for biota, and oceanographic phenomena. Even though there are beach-ridge plains elsewhere globally (Bowman & Harvey, 1986; Otvos, 2000; Stapor, 1975; Tanner, 1995), the beach ridges, comprising the Becher Point Cuspate Foreland, stand distinct from the others because of their geo- graphic/oceanographic and biogeographic setting, climate setting and history, and the Holocene sea level history. As such, the

Fig. 13. History of Holocene mean sea level in the Rockingham-Becher area. (After Semeniuk & Searle, 1986). 16 V. Semeniuk et al. / International Journal of Geoheritage and Parks 8 (2020) 1–17

Fig. 14. For comparison with the mean sea level curve in the Rockingham-Becher area, collation of Holocene sea level history from Semeniuk and Searle (1986), Semeniuk (1996, 2008) and Semeniuk and Semeniuk (1990). This illustration compares the open marine Holocene sea level history for Rockingham-Becher with other locations studied by Semeniuk and colleagues. Insets B & C show that the Rockingham and Peel Inlet curves (north of a tectonic ‘axis’) are similar, though the latter is estuarine, while the Preston Beach and Leschenault curves are broadly similar; the Harvey Estuary data falls in line with the 7000–6000 year pattern of sites south of the tectonic ‘axis’.

Becher Point Cuspate Foreland presents an integrated ensemble of geomorphic, stratigraphic, diagenetic, and wetland features that are intrinsic to south-western Australia. The Becher Point Cuspate Foreland clearly stands as globally unique. Consequently, it can form a globally signiﬁcant classroom for natural history science that explores and explains its signiﬁcant features. As described above, the complex of beach ridges and swale wetlands is the basis of a geopark in which coastal plain evolution, wetland evolution, Holocene sea level history, and Holocene climate changes can be explored and explained essentially in an outdoor Museum. At present there are plans to present these in a proposed Becher Science Park and Education Centre to explore dune and wetland formation, explore Holocene sea level history, and exploring Holocene climate history and the details of phenomena that occur within these four broad areas of natural history.

References

Bowman, G., & Harvey, N. (1986). Geomorphic evolution of a Holocene beach-ridge complex, Le Fevre Peninsula, South Australia. Journal of Coastal Research, 2, 345–362. Brocx, M. (2008). Geoheritage: From global perspectives to local principles for conservation and planning. WA Museum (Monograph). 175p. ISBN 978-1-920843-35-9 http://museum.wa.gov.au/store/museum-books/geology/geoheritage-global-perspectives-local-principles-conservation-and-plannin. Brocx, M., & Semeniuk, V. (2007). Geoheritage and geoconservation – History, definition, scope and scale. Journal of the Royal Society of Western Australia, 90,53–87. Brocx, M., & Semeniuk, V. (2009). Coastal geoheritage: Encompassing physical, chemical, and biological processes, shoreline landforms and other geological features in the coastal zone. Journal of the Royal Society of Western Australia, 92,243–260. Brocx, M., & Semeniuk, V. (2011). Assessing geoheritage values: A case study using Leschenault Peninsula and its estuarine lagoon, south-western Australia. Proceedings of the Linnaean Society of New South Wales, 132,115–130. Brocx, M., & Semeniuk, V. (2015). Using the Geoheritage Tool-Kit to identify inter-related geological features at various scales for designating geoparks: Case studies from Western Australia. In E. Errami, M. Brocx, & V. Semeniuk (Eds.), From geoheritage to geoparks - Case studies from Africa and beyond (pp. 245–259). Amsterdam: Springer. Brocx, M., & Semeniuk, V. (2018). Impacts of ports along the Pilbara Coast, Western Australia – a coastline of global geoheritage significance that services a mineral-rich hinterland. Annals of Geophysics, 60(2017). https://doi.org/10.4401/AG-7495 Fast Track 7. Davies, G. R. (1970). A recent seagrass bank, Shark Bay, Western Australia. In Logan (Eds.), Carbonate sedimentation and environments. 13.(pp.85–168). Shark Bay, W.A.: American Association of Petroleum Geologists Memoir. Department of Parks and Wildlife 2014. Information Sheet on Ramsar Wetlands - Becher Point Wetlands. http://www.environment.gov.au/water/topics/wetlands/da tabase/pubs/54-ris.pdf. Enos, P., & Perkins, R. D. (1979). Evolution of Florida Bay from island stratigraphy. Bulletin Geological Society of America, 90,59–83. Environment Australia (2001). A directory of important wetlands in Australia (3rd ed.). Canberra: Environment Australia. https://www.environment.gov.au/system/ files/resources/18f0bb21-b67c-4e99-a155-cb5255398568/files/directory.pdf. Gostin, V. A., Hails, J. R., & Belperio, A. P. (1984). The sedimentary framework of northern Spencer Gulf, South Australia. Marine Geology, 61,111–138. V. Semeniuk et al. / International Journal of Geoheritage and Parks 8 (2020) 1–17 17

Hagan, G. M., & Logan, B. W. (1974). Development of carbonate banks and hypersaline basins, Shark Bay, Western Australia. In B. W. Logan (Ed.), Evolution and diagenesis of Quaternary carbonate sequences, Shark Bay, Western Australia. 22.(pp.61–139). American Association of Petroleum Geologists Memoir. Hemminga, M. A., & Duarte, C. M. (2000). Seagrass Ecology: An Introduction. 298.Cambridge: Cambridge University Press ISBN:0521661846. Mackay, R. (2017). Australia state of the environment 2016: Heritage, independent report to the Australian government minister for the environment and energy, Australian Government Department of the Environment and. Canberra: Energy. McKeever, P. J., & Zouros, N. (2005). Geoparks: Celebrating Earth heritage, sustaining local communities. Episodes (pp. 274–278) December 2005. Otvos, E. G. (2000). Beach ridges - definitions and significance. Geomorphology, 32,83–108. Read, J. F. (1974). Carbonate bank and wave built platform sedimentation, Edel Province. Shark Bay, Western Australia. In B. W. Logan (Ed.), Evolution and diagenesis of Quaternary carbonate sequences, Shark Bay, Western Australia. 22.(pp.1–60). American Association of Petroleum Geologists Memoir. Scholl, D. W. (1966). Florida Bay: A modern site of recent limestone formation. In R. W. Fairbridge (Ed.), The encyclopedia of oceanography (pp. 282–288). New York: Reinholt Publishing Co. Searle, D. J., & Semeniuk, V. (1985). The natural sectors of the Rottnest Shelf Coast adjoining the Swan Coastal Plain. Journal of the Royal Society of Western Australia, 67, 116–136. Searle, D. J., & Semeniuk, V. (1988). Petrology and origin of beach sand along Rottnest Shelf coast. Journal of the Royal Society of Western Australia, 70,119–128. Searle, D. J., Semeniuk, V., & Woods, P. J. (1988). The geomorphology, stratigraphy and Holocene history of the Rockingham - Becher plain. Journal of the Royal Society of Western Australia, 70,89–109. Searle, D. J., & Woods, P. J. (1986). Detailed documentation of Holocene sea-level record in the Perth region, South Western Australia. Quaternary Research, 6,299–308. Semeniuk, C. A. (1988). Consanguineous wetlands of the Darling system. Journal of the Royal Society of Western Australia, 70,69–87 In this issue. Semeniuk, C. A. (2007). The Becher Wetlands - A Ramsar site. Evolution of wetland habitats and vegetation associations on a Holocene coastal plain, South-Western Australia. The Netherlands: Springer ISBN-10 1-4020-4671-5. Semeniuk, C. A., Milne, L. A., Semeniuk, V., & Ladd, P. (2006). Holocene palynology of five wetland basins in the Becher Point area, southwestern Australia. Journal of the Royal Society of Western Australia, 89,129–154. Semeniuk, C. A., & Semeniuk, V. (2012). The response of basin wetlands to climate changes: A review of case studies from the Swan Coastal Plain, south-western Australia. Hydrobiologia, 708(1), 45–67. https://doi.org/10.1007/s10750-012-1161-6 (May 2013). Semeniuk, C. A., & Semeniuk, V. (2016). Wetland classification: The geomorphic-hydrologic system. In M. Finlayson, & A. van Dam (Eds.), The wetlands book (pp. 1–10). Amsterdam: Springer. https://doi.org/10.1007/978-94-007-6172-8. Semeniuk, T. A. (2000). Spatial variability in epiphytic foraminifera from micro-to regional scale. Journal of Foraminiferal Research, 30,99–109. Semeniuk, T. A. (2001). Epiphytic foraminifera along a climatic gradient, Western Australia. Journal of Foraminiferal Research, 31,191–200. Semeniuk, V. (1985). The age structure of a Holocene barrier dune system and its implication for sea-level history reconstructions in south-western Australia. Marine Geology, 67,197–212. Semeniuk, V. (1986). Holocene climate history of coastal SW Australia using calcrete as an indicator. Palaeogeography, Palaeoclimatology, Palaeoecology, 53,289–308. Semeniuk, V. (1995). The Holocene record of climatic, eustatic and tectonic events along the coastal zone of Western Australia - A review. Chapter 21 Journal of Coastal Research Special Issue. In C. W. Finkl (Ed.), Holocene cycles: Climate, sealevel rise, and sedimentation. Vol. 17.(pp.247–259). Semeniuk, V. (1996). An early Holocene record of rising sealevel along a bathymetrically complex coast in southwestern Australia. Marine Geology, 131,177–193. Semeniuk, V. (1997). Pleistocene coastal palaeogeography in southwestern Australia - Carbonate and quartz sand sedimentation in cuspate forelands, barriers and ribbon shoreline deposits. Journal of Coastal Research, 13,468–489. Semeniuk, V. (2008). Sedimentation, stratigraphy, biostratigraphy, and Holocene history of the Canning Coast, north-western Australia. Journal of the Royal Society of Western Australia, 91,53–148. Semeniuk, V. (2012). Predicted response of coastal wetlands to climate changes – a Western Australian model. Hydrobiologia, 708(1), 23–43. https://doi.org/10.1007/ s10750-012-1159-0 May 2013. Semeniuk, V., & Brocx, M. (2019). The Archaean to Proterozoic igneous rocks of the Pilbara region, Western Australia – internationally significant geology of a globally unique potential geopark. International Journal of Geoheritage and Parks, 7 (2), 56–71. Semeniuk, V., Cresswell, I. D., & Wurm, P. A. S. (1989). The Quindalup dunes: The regional system, physical framework and vegetation habitats. Journal of the Royal Society of Western Australia, 71,23–47. Semeniuk, V., & Johnson, D. P. (1982). Recent and Pleistocene beach and dune sequences, WA. Sedimentary Geology, 32,301–328. Semeniuk, V., & Meagher, T. D. (1981). The geomorphology and surface processes of the Australind - Leschenault Inlet coastal area. Journal of the Royal Society of Western Australia, 64,33–51. Semeniuk, V., & Searle, D. J. (1986). Variability of Holocene sealevel history along the southwestern coast of Australia - Evidence for the effect of significant local tec- tonism. Marine Geology, 72,47–58. Semeniuk, V., Searle, D. J., & Woods, P. J. (1988). The sedimentology and stratigraphy of a cuspate foreland, southwestern Australia. Journal of Coastal Research, 4, 551–564. Semeniuk, V., & Semeniuk, C. A. (1990). Radiocarbon ages of some coastal landforms in the Peel-Harvey estuary. Journal of the Royal Society of Western Australia, 73, 61–71. Semeniuk, V., & Semeniuk, C. A. (2005). Wetland sediments and soils on the Swan Coastal Plain, southwestern Australia: Types, distribution, susceptibility to combustion, and implications for fire management. Journal of the Royal Society of Western Australia, 88,91–120. Semeniuk, V., Semeniuk, C. A., Trend, F., & Brocx, M. (2015). Microscale geology and micropalaeontology of the Becher Point Cuspate Foreland, Australia: Significant geoheritage values at the smallest scale – A model for identifying similar features in Geosites and Geoparks. In E. Errami, M. Brocx, & V. Semeniuk (Eds.), From geoheritage to geoparks - Case studies from Africa and beyond (pp. 261–269). Amsterdam: Springer. Smale, D. A., Wernberg, T., & Vanderklift, M. A. (2017). Regional-scale variability in the response of benthic macroinvertebrate assemblages to a marine heatwave. Marine Ecological Progress Series, 568,17–30. https://doi.org/10.3354/meps12080. Stapor, F. W. (1975). Holocene beach ridge plain development, northwest Florida. Zeitschrift für Geomorphologie, 22,116–144. Tanner, W. F. (1995). Origin of beachridges and swales. Marine Geology, 129,149–161. Wanless, H. R., & Tagett, M. G. (1989). Origin, growth and evolution of carbonate mudbanks in Florida bay. Bulletin of Marine Science, 44,454–489.