Foraminiferal biotopes in a shallow continental shelf environment: Esperance Bay (southwestern Australia)

The Great Australian Bight is a large carbonate cold water environment located on the central and western portions of the southern Australia. Seagrasses (Posidonia sp.) and macroalgae benthic habitats are widely distributed in the shallow water environment of southern Australia, contributing to the carbonate factory. This study investigated the distribution of modern benthic foraminiferal assemblages in the microtidal wave-dominated inner-shelf of Esperance Bay (southwestern Australia), that lies on the western margin of the Great Australian Bight. Benthic foraminifera were taxonomically identified and biotic parameters (species richness, density, Fisher-α index, Shannon–Weaver index, dominance) were calculated. Multivariate analyses (Hierarchical Cluster Analysis, Principal Component Analysis) were performed to understand foraminiferal distribution in the context of environmental conditions. Four main Foraminiferal assemblages have been recognized: (I) a nearshore assemblage of dense seagrass meadow, dominated by Lamellodiscorbis dimidiatus, Elphidium craticulatum, Elphidium crispum, Cibicidoides lobatulus, II) a second assemblage associated with unvegetated seabed (approximately 30 m depth) with Lamellodiscorbis dimidiatus, Elphidium crispum, Quinqueloculina disparilis, III) a third assemblage in the central sector of the bay, characterized by a discontinuous and mixed seagrass-algae coverage with Lamellodiscorbis dimidiatus, Elphidium crispum, Elphidium macellum, Cibicides refulgens, and Quinqueloculina poeyana, and IV) an epiphytic assemblage of transitional zone from the coastline to the upper limit of a mixed seagrass-algae meadow, dominated by Elphidium crispum, Chrysalidinella dimorpha, Planulinoides biconcava, Planoglabratella opercularis, Rugobolivinella elegans. The spatial distribution of the four assemblages appears closely related to sediment texture, seagrass cover and depth, but it is also influenced by the shoreface morphology and the hydrodynamic energy. The understanding of the ecological parameters that influence benthic foraminiferal distribution, composition and assemblage structure within seagrass meadows is useful for paleoecological and paleoenvironmental interpretations

Geomorphology and sedimentology of Porto Pino, SW Sardinia, Western Mediterranean

This paper presents a detailed (1:4000) geomorphological, sedimentological and ecological map of a Mediterranean microtidal wave-dominated beach system and adjacent inner shelf. This map is an innovative cartographic product that integrates a range of processes of present and past timeframes. It is part of a larger cartography on the coastal geomorphology of Sardinia (Italy) aiming to facilitate coastal management practices and future scientific research. The study area is located in SW Sardinia (Italy), and focuses on Porto Pino beach, an important tourist destination of semi-pristine nature, facing environmental pressures common to many coastal Mediterranean settings. In this context, the main human impact on coastal dune habitats is described and a full environmental characterization of the beach system is presented

The influence of geomorphology and sedimentary processes on benthic habitat distribution and littoral sediment dynamics: Geraldton, Western Australia

Understanding of the processes regulating sediment transport, accumulation and erosion requires an appropriate mapping of coastal geomorphology, seabed sediments and benthic habitat distribution to allow management issues to be identified, understood and addressed. In this study multibeam echo-sounder data were used to map shallow water geomorphological features and the spatial distribution of benthic habitats, with the support of underwater imagery for ground truthing the acoustic data. At Geraldton, sediment analyses have revealed a dominant biogenic nature, with modern carbonate sedimentation linked to the seagrass and macroalgal carbonate factories colonising these shallow (<30 m) coastal embayments. Whilst seagrasses are common on sheltered hardgrounds blanketed by fine sand, macroalgae were found on high energy limestone reefs. The distribution of sand bar and sheet systems is regulated by wave induced sediment transport with the influence of pre-existing seabed topography. Exposure to wave energy, seabed geomorphology and sediment characteristics is closely related to the distribution of benthic habitats and sand substrates, highlighting the value of an integrated analysis of these parameters. The capability of multibeam echo-sounder backscatter data to discriminate between seagrass meadows, macroalgal communities and sandy substrates was also evaluated and the acoustic response from the seabed was better explained by considering together seafloor geomorphology and biota type, as both these parameters influence backscatter strengt

Geomorphology of marine and transitional terraces and raised shorelines between punta paulo and porvenir, tierra del fuego, straits of magellan – Chile

© 2017 The Author(s). This paper presents a coastal geomorphology map of some of the Chilean region of the Straits of Magellan, and is based on a combined geomorphological and sedimentological approach applicable to a larger section of the coast. The mapped area is located in Tierra del Fuego between the Segunda Angostura of the Straits of Magellan and Bahía Inútil. A detailed geomorphological map was compiled at a scale of 1:50,000, describing a sequence of 4 marine and transitional (glacio-lacustrine to marine) terrace orders and raised marine shorelines found between 0 and + 20 m. These features are mainly linked to glacio-eustasy and secondarily to Holocene neo-tectonics. This research derives from the interpretation of aerial photographs and remote sensing imagery along with geomorphological-stratigraphic field surveys and geochemical data. The Main Map illustrates an area with dominant palaeo-glacial and glacio-lacustrine morphology with extensive lacustrine deposits and well-developed lake systems characterising the Porvenir region

Crystallization and partial melting of rhyolite and felsite rocks at Krafla volcano: A comparative approach based on mineral and glass chemistry of natural and experimental products

Rhyolite and felsite cuttings were collected at Krafla volcano during the perforation of the Iceland Deep Drilling Project Well 1 (IDDP-1). The perforation was stopped at a depth of 2100 m due to intersection with a rhyolite magma that intruded the felsite host rock. Rhyolite cuttings are vitrophiric (glass ~95%, RHL) and exhibit a mineral assemblage made of plagioclase + augite + pigeonite + titanomagnetite. Felsite cuttings display evidences of partial melting, responding to variable degrees of quartz + plagioclase + alkali feldspar + augite + titanomagnetite dissolution. The interstitial glass analyzed close to (i.e., FLS1) and far from (i.e., FLS2) the reaction surface of pyroxene from felsite cuttings shows continuous changes between the two end-members. FLS1 is compositionally similar to RHL, showing Na2O + K2O + REE depletions, counterbalanced by MgO + CaO enrichments. Conversely, FLS2 exhibits opposite chemical features. REE-exchange thermobarometric calculations reveal that plagioclase and augite cores from rhyolite and felsite formed under identical conditions, along a thermal path of 940â\u80\u93960 °C. However, in terms of major and trace element concentrations, plagioclase and augite crystal cores are not in equilibrium with the rhyolite magma, suggesting the incorporation of these minerals directly from the host felsite. To better understand the petrogenetic relationship between rhyolite and felsite, two sets of crystallization and partial melting experiments have been carried out at P = 150 MPa and T = 700â\u80\u93950 °C. Rhyolite crystallization experiments (RCE) reproduce the two-pyroxene assemblage of IDDP-1 rhyolite cuttings only at T â\u89¤ 800 °C, when the crystal content (â\u89¥19%) is higher than that observed in the natural rhyolite (~5%). Under such conditions, the RCE glass is much more differentiated (i.e., marked CaO depletion and Eu anomaly) than RHL. On the other hand, felsite partial melting (FPM) experiments show interstitial glass with a bimodal composition (i.e., FPM1 and FPM2) comparable to FLS1 (â\u89\u88RHL) and to FLS2, only at T = 950 °C. This effect has been quantified by fractional crystallization and batch melting modeling, denoting that FLS1 (â\u89\u88RHL) and FLS2 reflect high (â\u89¥70%) and low (â\u89¤8%) degrees of felsite partial melting, respectively. In contrast, modeling RHL by crystal fractionation requires the removal of an amount (~22%) of solid material that is inconsistent with the low crystal content of the natural IDDP-1 rhyolite. It is therefore concluded that natural rhyolite and felsite represent, respectively, the near-liquidus and sub-solidus states of a virtually identical silicic magma, either feeding aphyric to subaphiric rhyolitic eruptions, or solidifying at depth as phaneritic quartzofeldspathic rocks. Felsite lenses from the Krafla substrate may explore variable degrees of remelting and remobilization processes. The intrusion into felsite of a fresh silicic magma from depth may lead to low degrees of partial melting, whereas the persistent heat release from intense basaltic intrusive events at Krafla may be the source of high degrees of felsite partial melting and consequent rejuvenation of the previously solidified silicic magma

Geomorphology, Sedimentology, Benthic Habitat as Tools for Supporting Coastal Management: Comparison between Australian and Mediterranean Beach Systems

© Coastal Education and Research Foundation, Inc. 2018. The characterization of a nearshore system using geomorphological, sedimentological and ecological data is regarded as baseline knowledge to effectively manage the coast and warrant coastal conservation. Particularly in areas where sediment nourishment is a regular practice, the differentiation between in-situ sediment production and artificial placement, revealed by detailed sediment analyses, is often an important task. In Esperance Bay (Western Australia) sediment nourishment and dumping are ongoing since the 1950s. The comparison with a Mediterranean site (Porto Pino, Sardinia, Italy) has improved the understanding of processes that regulate sediment distribution in the urbanized beach system of Esperance Bay. Porto Pino is a Mediterranean microtidal wave dominated embayment, characterized by environmental conditions similar to those of Esperance (i.e. climate, sediments, geology and benthic habitats), where sediment nourishment was not undertaken previously and the sediment facies can be considered as a natural analogue of the Esperance sediments. The results presented in this paper are useful for Esperance coastal managers as their provide further insights on the distribution of sediment derived from artificial placement

Isotopic disequilibrium in migmatitic hornfels of the Gennargentu Igneous Complex (Sardinia, Italy) records the formation of low ⁸⁷Sr/⁸⁶Sr melts from a mica-rich source

Isotopic disequilibrium is increasingly recognized as a common feature of magmatic systems, but the details of the mechanism(s) underpinning the development of isotopic disequilibrium during partial melting processes are not fully understood. Partial melting of mica-rich lithologies may be predicted to generate melts enriched in radiogenic Sr compared to the bulk protolith compositions due to the typically high Rb/Sr ratio coupled with low melting temperature of mica in crustal rocks. Here we report a puzzling case study where the Sr-isotope composition of the melt fraction (leucosome) of partially molten metapelites (migmatites) is less radiogenic than the restitic component (melanosome). The examined migmatites fringe (50m wide zone) a low-pressure (≤200 MPa), high-temperature (1050°C) quartz-dioritic intrusion, which was emplaced in the Gennargentu Igneous Complex (Sardinia, Italy) at 306626Ma (bulk-rock Rb/Sr dating). The migmatites derive from anatexis of the muscovite-rich metapelitic wall-rocks. They include a quartzo-feldspathic leucosome and a melanosome containing cordierite, K-feldspar, plagioclase, biotite, Fe-Ti oxide minerals and both corundum and hercynite. The leucosome has a less radiogenic Sr and more radiogenic Nd isotope composition than the melanosome (87Sr/86Sr(306 Ma)= 0·71068 and 0·71536; εNd(306Ma) = -6·4 and -9·2, respectively), with bulk migmatite samples having intermediate compositions. The significantly lower content of mica in the migmatites compared to the protolith indicates that muscovite and, to a lesser extent, biotite largely contributed to melt formation. However, the leucosome volume (50%) estimated through mass balance calculations is considerably higher than the amount of melt (≤10 vol. %) generally produced by mica-dehydration melting in the crust, suggesting that partial melting was enhanced by an external hydrous fluid. The O-isotope composition of the migmatites is lower than the typical metapelite values (>10‰) but overlaps with the δ18O range of the quartz-diorites (8·8-9·9‰), suggesting that such a hydrous fluid was released from the quartz-dioritic intrusion. We put forward a model whereby the anatexis temperature conditions (T < 800°C) favored the preservation of isotopic disequilibrium of micas and plagioclase in the protolith. In this context, the leucosome formed by the preferential melting of less radiogenic plagioclase rather than more radiogenic micas. The melt was then efficiently separated from the melanosome containing restitic biotite and 'peritectic K-feldspar and magnetite' derived from mica breakdown. During the anatectic process the quartz-diorite provided not only the heat budget, but also the fluid amount responsible for (i) the hydration of the pelitic country rock, (ii) the increase of melt fraction, and (iii) the higher mobility of anatectic magma

Geomorphological and sedimentological surrogates for the understanding of seagrass distribution within a temperate nearshore setting (Esperance Western Australia)

© 2019, Springer-Verlag GmbH Germany, part of Springer Nature. Seagrass meadows are important benthic habitats contributing to many aspects of ecological community health, beach stability and sediment supply. Relationships between morpho-sedimentary features and distribution of seagrass meadows were investigated through an integrated analysis of geomorphology, sediments and benthic habitat structure in a temperate nearshore setting (Esperance Bay, Western Australia). The results demonstrate that seagrass distribution is related to gradients in sediment texture and composition, hydrodynamics and human impact. Dense seagrass meadows occurred in more sheltered regions of the bay, whereas sparser vegetation was found in areas of higher wave energy and artificial activities (like ship anchoring and dredging activities). A preferential retention of heavier siliciclastic sediments was recorded in the seagrass meadows especially in areas with high sediment supply resulting in elevated beds and formation of intermates. Sediment characteristics suggest that carbonate sediment is transported onshore from the seagrass meadow supplying the beach system. The combined analyses of geomorphological features and sediment characteristics at Esperance have allowed identification of a prevalent eastward oriented sediment transport current. Seagrass beds are confirmed to be a sediment source in terms of sediment budget contributing to beach stability. Integrated geomorphological data, sediment analyses and benthic habitat mapping provide useful information for the management of coastal environments characterized by the presence of seagrass meadows by providing new insights on coastal processes