Determining Geoheritage Values

Definitions

Geoheritage. The heritage value assigned to features of a geological nature encompasses globally, nationally, statewide to regionally, and locally significant features of earth science that are intrinsically important or culturally important, offering information or insights into the evolution of the earth or into the history of earth science, or that can be used for research, teaching, or reference (Brocx, 2008). It encompasses the variety of rocks types, stratigraphy, structural geology, geomorphology, and hydrology and covers a large variety of processes and products across a wide range of scales, from global tectonics, mountain building, landscape evolution to local surface processes and products such as weathering, erosion and sedimentation, cliff faces, fossils sites and mineral localities, and, at the microscale, diagenesis and deformation.

Geoconservation. This term refers to an action that works toward the preservation of sites of geoheritage significance for heritage, science, or education purposes. It can encompass all important geological features from the regional scale to the individual crystal, involving specific sites (special sites), or ensembles of geological sites. A “specific site” is where a significant geological feature occurs in isolation or may have historical or cultural significance; these have been formally identified in the British Isles as (geological) site(s) of special scientific interest (SSSI) or regionally important geological/geomorphologic sites (RIGS) (Ellis et al., 1996).

Geodiversity. Geodiversity is the natural variety of geological, geomorphological, pedological, and hydrological features of a given area and geological processes forming them (Brocx and Semeniuk, 2007). Use of the term, which etymologically means “the diversity of geological features,” should be applied only in a region-specific or site-specific sense, i.e., not as a synonym for geology.

Geosite. This is a term used to denote small sites of geoheritage significance used for education, science, geotours, and reference.

Geopark. Geopark is used to denote large sites of geoheritage significance, usually an ensemble of geosites used for education, science, geotours, and reference.

Introduction

Estuaries stand as a distinct environment along the coast in that they bridge the aquatic hydrochemical environmental gap between freshwater and seawater. They can bring another aspect in addition to this hydrochemical setting because the landscape and geomorphic/sedimentologic setting of an estuary provide variability to the “mixing bowl” where freshwater and seawater interact. The emphasis on the landscape and geomorphic/sedimentologic settings of estuaries has resulted in their being classified according to a geomorphic framework or according to their origin (Fairbridge, 1980; Nichols and Biggs, 1985; Perillo, 1995). In this context, with their geologic, geomorphic, and sedimentologic characteristics and variability, they fall into the realm of geodiversity and geoheritage. As such, estuaries, in addition to the complexities and variability of styles of hydrochemical mixing, which is their first tier criterion of identification, provide a rich assortment of geologic, geomorphic, sedimentologic, mineralogic, and biogenic attributes such as shell deposits and bioturbation structures, not only in regard to the features within the estuaries themselves but also in the geology, geomorphology, and hydrology of the immediately surrounding landscape that frames or that has built them. Consequently, they hold potential to contain features and sites of geological significance or geoheritage value and lend themselves to qualifying as sites of geoheritage significance. This is especially the case in that estuaries, as sedimentary repositories, reside in various types of geologic and geomorphic settings, from rias to coastal plains to structural controlled (Fairbridge, 1980; Perillo, 1995), which results in a variety of geomorphic and sedimentologic estuarine types, and occur in a wide range of climates from tropical to temperate and from humid to arid, which also results in a variety of geologic/geomorphic, sedimentologic, and geochemical/mineralogic expressions. A large diversity (or geodiversity) of estuary types can be expected therefore from the perspective of the earth sciences.

Before a description is provided of the procedure to determine geoheritage values, the terms “geoheritage,” “geoconservation,” “geodiversity,” “geosite,” and “geoparks” are defined. They are associated with the concept of geoheritage, the enactment of geoconservation, and the inscription of geosites/geoparks.

Identifying and assessing sites of geoheritage value using the geoheritage tool kit

Identifying estuaries in different geological regions and the geoheritage essentials (i.e., the geological features that characterize an area) of these estuaries provides the first step in identifying sites for geoheritage. Clearly not all aspects of estuaries on earth are present in the one region, and not all aspects of an estuary in a region may be of geoheritage significance – the former recognizes the uniqueness, rarity, or representativeness of some estuarine features, and the latter requires some measure of assessment of significance. There are a number of ways that sites of geoheritage significance may be identified, and the British and European literature provides a history of how this has been achieved, with the final outcome being an inventory-based approach (Doyle et al., 1994; Wimbledon et al., 1995; Wimbledon, 1996; ProGEO, 2002; for discussion see Brocx, 2008).

The British and European approach to compiling an inventory of features of significance in the realm of geology has been successful in that numerous and varied aspects of geology have been identified and secured, but the approach has been thematic within a context of known geology and nationally specific geology. This is largely because the geology of European countries is reasonably well known, and these countries are relatively small (compared to, say, Australia, an island continent with a surface are of ∼7.7 million km², and Africa with a surface area of ∼30 million km²). Australia has its own geological history with a vast array of geological features, from Archaean terranes to Proterozoic rock systems to Phanerozoic stratigraphy, lithology, paleontology, mineralization, etc., representing a wide diversity of processes and products developed under igneous, sedimentary, metamorphic, pedogenic, metallogenic, hydrologic, and diagenetic conditions. As such, Australia’s estuaries also present exceptional geodiversity, reflecting the range of their geologic, oceanographic, and climatic settings. Therefore, to provide the framework for a category-based inventory of sites of geoheritage significance, Brocx and Semeniuk (2009, 2011) developed the geoheritage tool kit, to systematically identify and categorize sites of geoheritage significance. This method has been adapted to determine the geoheritage values of estuaries. The geoheritage tool kit uses six steps to identify geological features across various geological regions and at various scales, assign geological sites to various categories of geoheritage, and assess their levels of significance, and case studies are used here to illustrate the diversity of Australia’s estuaries (Figure 1; Brocx and Semeniuk, 2009).

• Step 1 identifies geological regions, providing a natural boundary to the estuary being investigated in terms of geological and geoheritage features, and an indication of the types of geological features that may be expected. It also ensures that comparisons in assessing significance are undertaken wholly within similar regions. Figure 2, for instance, shows the main regions of estuaries in Australia.

• Step 2 identifies the geological essentials of a region and requires listing those geological features that characterize or are peculiar to a given natural region. For an estuary, it involves listing aspects such as the geological setting, estuary type, effects of climate, oceanography, and tidal range and interior features (such as flood-tidal deltas, shoals, tidal flats, deltas, basin type) and small-scale features (such as mineral precipitations, bioturbation types, and unusual or distinct sedimentary structures). The geological essentials of a region can be identified by drawing on the literature, interviewing scientists and, after identifying gaps in information, systematically obtaining further information from fieldwork. The list is termed the “geoheritage essentials” of an area.

• Step 3 allocates each unit of the inventory to a category of geoheritage, viz., a reference site, cultural site, geohistorical site, or a modern active landscape, so that comparisons in assessing significance are undertaken within similar categories. In regard to reference sites and/or type locations, once estuaries have been classified as to a type, the reference locations of end-member type or best example of an estuary can be identified and allocated as an international or national heritage locality. In this context, for comparisons of estuaries for geoheritage evaluation, it is important to have a worldwide applicable estuarine classification and nomenclature scheme that can be used systematically and comparatively to differentiate types based on landform/coastal setting, climate, shape and size of estuary, tidal and wave regime, sediment assemblages, seawater/ freshwater mixing style, and biota. A selection of estuaries that stand out globally as distinct and geomorphically significant because of either their size, internal landforms, representativeness, or naturalness and that could be used as estuarine reference sites and/or type locations are Lake St. Lucia (Natal, South Africa), Solway Firth (Scotland), Gironde Estuary (France), the Elbe (Germany), the deltaic complex of the Ganges-Brahmaputra (Sundarbans National Park, India), Walpole-Nornalup Inlet Estuary (Western Australia), Fitzroy River Estuary (Queensland), Gulf of Saint Lawrence (Canada), Chesapeake Bay (North America), and the Amazon Estuary (Brazil).

Determining Geoheritage Values, Figure 1

The six steps in the use of the geoheritage tool kit to identify geological features across various regions leading to designation of types of geoconservation. The boxed text and illustrations labeled A, B, C, from Brocx (2008), summarize the scope of geoheritage in terms of its categories, scales of application, and potential levels of significance that can be assigned to geosites.

Determining Geoheritage Values, Figure 2

Simplified map of the main regions of estuaries in Australia based on geological setting, oceanography and tidal regime, and climate.

In regard to cultural or historical significance, estuaries may function as highly significant systems or may carry historical significance. The Camargue in the estuary of the Rhone (France) is an example of the former, and Port Hacking (Australia) and the Thames (the United Kingdom) are examples of the latter. Estuaries also can function as geohistorical sites showing ancient sequences where earth history can be determined. In regard to their stratigraphy and stranded geomorphology, they retain records over the past 7,000 years when sea level stabilized to its present position of coastal history and valley-fill history (Roy et al., 1980). Estuarine sequences that record estuarine evolution in Australia and North America (Fisher, 1969; Roy et al., 1980; Semeniuk, 2000) provide examples of the geohistorical importance of estuaries and illustrate the variety of pathways an estuary may take in its development. Estuaries also retain records of previous estuarine history in their stratigraphy and older estuarine geomorphology.

Estuaries illustrate modern landscapes and settings where earth processes are still active. They represent an environment where fluvial sedimentation interacts with basin processes to mobilize and deposit sediments into shoals, platforms, and basin-fill sheets. Flood and ebb tides form flood and ebb tidal deltas, and a plethora of biological, geochemical, hydrochemical, and physical processes at the finest scale result in various sedimentary deposits, biogenic deposits, sedimentary bedforms and structures, and mineral precipitates.

Some estuaries may belong to more than one geoheritage category. For instance, as a World Heritage area, the estuary of the Ganges-Brahmaputra river system serves as a reference site and as a location of modern landscapes and settings where estuarine and deltaic earth processes are still active in the largest tidal-dominated system in the world.

• Step 4 allocates the geologic features to a scale, so that comparative assessments of levels of significance can be undertaken within a similar scale. The various scales used in dealing with sites of geoheritage significance are regional, large, medium, small, fine, and very fine scales (Figure 3). Scale is important to consider in geoheritage/geoconservation since features of significance can range from crystals, bedding planes, and outcrops to that of landscapes and mountains. In many locations, sites are important because of crystal-sized phenomena and crystal fabrics (e.g., dolomite or permineralization in estuarine shorelines) or because of outcrops and bedding scale features (such as elevated estuarine fossil deposits). In the case of estuaries, the largest scale involves the size of the estuarine embayment, which may be tens of kilometers in size, and can involve the lower reaches of the drainage basin.

• Step 5 assesses the level of geoheritage significance of the geological features regardless of their scale (Figure 4). The level of importance attributed to a given feature of geoheritage significance is related to how frequent or common is the feature within a scale of reference and/or how important is the feature to a given culture. Levels of significance are (Brocx and Semeniuk, 2007) (1) international, (2) national, (3) statewide to regional, and (4) local. Levels of significance of geoheritage features of (and within) estuaries are illustrated in Figure 4.

  Determining Geoheritage Values, Figure 3

  

  Scales of features of geoheritage significance in estuaries.

  Determining Geoheritage Values, Figure 4

  

  Assessment of the level of geoheritage significance (based on the approach described by Brocx and Semeniuk 2007 but modified to focus on estuaries and deltas). The examples used to illustrate nationally significant geoheritage features are ria coasts of Tasmania, New South Wales, and Northern Territory (from Australia) and shown in their global context. The examples used to illustrate statewide/regional significance are barred estuaries (>5 km in size), drawn from Australia and shown in a comparative global and national context. The examples used to illustrate local significance are flood-tidal deltas from barred estuaries of southeastern Australia shown in a context of barred estuaries in Australia (See also “ Geoheritage ”).

After an assessment of the range, categories, interrelationships, and level(s) of significance of the geological features, the final step is Step 6 which will determine what type and what level of geoconservation are assigned to the estuary whether in toto or in part.

Large estuaries, or sites within estuaries that are of geoheritage significance, or an amalgamation of numerous smaller sites of geoheritage significance can be assigned to geopark status. The Global Geoparks initiative supported by UNESCO sees geoparks as a territory encompassing one or more sites of scientific importance, not only for geological reasons but also by virtue of its archaeological, ecological, or cultural value. An estuary thus can qualify for this designation. The European Geoparks Network, established in 2000 (Zouros, 2000), defines a geopark as an area to conserve and valorize geological heritage through the integrated and sustainable development of their territories. Similarly, an estuary can qualify also for this designation. The Asia Pacific Geoparks Network, founded in 2007, defines geoparks as nationally protected areas containing a number of geological heritage sites of particular importance, rarity or aesthetic appeal. These earth heritage sites are part of an integrated concept of protection, education, and sustainable development. An estuary can qualify also for this designation. All these initiatives aim to protect geodiversity, promote geological heritage, and support local sustainable economic development, thus involving community and commercial interests.

Estuaries lend themselves to designation as geoparks because they inherently have multiple uses (fishing, boating, shoreline nature walks, areas of conservation for waterbirds) and often illustrate interrelated features of landscape, geology, estuarine geomorphology, and sedimentology that can be utilized for science and education and tourism. Brocx and Semeniuk (2009) identified the Walpole-Nornalup Inlet Estuary in Western Australia as an integrated geopark, wherein the various Cenozoic and Holocene geological and estuarine features could be used as features for nature tours. Thus, estuaries can be viewed as potential geoparks, i.e., conservation, and promotional entities focused on geological and geomorphological attributes for local sustainable development.

The leschenault inlet estuary and walpole-nornalup inlet estuary: case studies

The Leschenault Inlet Estuary and Walpole-Nornalup Inlet Estuary provide examples of the application of the geoheritage tool kit to identify and assess features of geoheritage significance in the estuaries. Both present two extremes of types in Western Australia. The Leschenault Inlet Estuary, a barrier dune barred estuarine lagoon, with two contributing rivers at its southern end, is located in a subhumid part of Western Australia, facing the swell-dominated Indian Ocean (Brocx and Semeniuk, 2011). Brocx and Semeniuk (2011) identify 10 features of geoheritage significance in the estuary. Of these, one feature is assessed as internationally significant, two as nationally significant, and seven as being of statewide or regionally significant (Figure 5). Brocx and Semeniuk (2011) proffer that the estuarine system, with its geological framework, complex shores, estuarine geomorphology and stratigraphy, and multitude of important small-scale features, also could function as geopark for geotours, research, and education.

Determining Geoheritage Values, Figure 5

Application of the geoheritage tool kit to the Leschenault Inlet Estuary (Modified from Brocx and Semeniuk 2011). Inset A – the categories of geoheritage applicable to this area are highlighted in gray. Inset B – selected features of geoheritage significance are illustrated, graded in decreasing scale from left to right (a map of the barrier and lagoon, a map of estuarine habitats, cross section of barrier-to-lagoon stratigraphy, a chenier perched on a tidal flat, map of the Collie Delta, calcitized sea rush roots, and an estuarine foraminifer). Inset C – geoheritage features are allocated to a level of significance.

The Walpole-Nornalup Inlet Estuary, a twin ria estuary with a dune barrier and three contributing rivers, is located in the most humid part of Western Australia, facing the high-energy Southern Ocean (Semeniuk et al., 2011). Semeniuk et al. (2011) identify 22 features of geoheritage significance that include its intra-estuarine delta and peat-floored peripheral wetlands. Of these, one feature is assessed as internationally significant, two as nationally significant, and 19 as statewide or regionally significant (Figure 6). Semeniuk et al. (2011) proffer that the estuarine system of Walpole-Nornalup Inlet, with its geological framework, estuarine geomorphology and stratigraphy, and multitude of important small-scale features, could function as geopark for geotours, research, and education.

Determining Geoheritage Values, Figure 6

Application of the geoheritage tool kit to the Walpole-Nornalup Inlet area (Modified from Semeniuk et al. 2011). Most of the estuarine geoheritage features rank as regional to statewide significance, while some are national significance, and one feature of international significance.

Summary

In estuaries, to date, there has been emphasis on their biological significance, e.g., their vegetation complexes, productivity, invertebrate fauna, and fisheries, and hence their conservation and management from a biological perspective, and less on the importance of their geology, geomorphology, sedimentology, hydrology, and geohistorical evolution. However, there are two components to estuaries, i.e., the biotic and the abiotic (that underpins biodiversity). Geoheritage and geoconservation are concerned with the recognition and preservation of the abiotic world and in this context can be directed to the recognition and preservation of the geodiversity of estuaries. For instance, based on a world map of estuary types and their uniqueness or representativeness, it can involve the recognition and geoconservation of end-member types of estuaries as global “type examples” of the variety forms expressed around the world in response to climate, hydrodynamic setting, sediment types, and framework geology. At this scale, geoheritage recognizes the range of estuarine systems that are manifest around the world and attempts to address the significance of the variety of these estuaries that have formed in different geological, hydrological, sedimentological, and climatic settings within a variable biogeographic context. At the next level, geoheritage and geoconservation can involve the geoconservation of geological processes and products operating and occurring within estuaries, e.g., deltaic sedimentation and its variety of landforms, sand platforms and their surface bedforms, evolution of estuarine stratigraphy, stratigraphic/hydrologic interactions, and styles of hydrochemical mixing. At the finest scale, geoheritage and geoconservation can involve the recognition and geoconservation of microscale processes and products, often specific to an environmental setting and climate, e.g., diagenetic features such as calcitization of shoreline rush rhizomes, occurrence of dolomite, formation of pyrite nodules, the permineralization of skeletons, and the effects of freshwater seepage.

It should be noted that just as biologic systems are diverse, geological systems are also diverse (geodiversity), and in the case of estuaries, estuarine systems are also diverse and there are a large range of estuarine types, as exemplified by variation in their setting, shape, size, estuarine landforms, hydrology, and internal functioning. The classification of estuary types, using the geoheritage tool kit, has attempted to address this. Similar to the objective of nature conservation, to conserve the vast diversity of life forms, an objective of the conservation of sites of geoheritage significance in estuaries would be the conservation of the variety of their forms on the earth. In this context, the conservation of a single “estuary” as an example of an estuarine system as representative of the full variety of estuarine types globally is insufficient. If estuaries, for instance, exhibit a large diversity of geometric and hydrologic types, stratigraphic fills, and origins, then at the least their conservation should encompass an example of each of the types.

Cross-references

• Geoheritage