Pompeii to Stabiae: downcurrent versus substrate-induced variations of the AD 79 Vesuvius pyroclastic current deposits and their impact on human settlements

Santangelo Ileana1, Scarpati Claudio1, Perrotta Annamaria1, Sparice Domenico2, Fedele Lorenzo1, Chiominto Giulia1, Muscolino Francesco2, Rescigno Carlo3, Silani Michele3, Massimo Osanna2

1Department of Earth, Environmental and Resources Sciences, University of Napoli Federico II, Napoli, Italy; 2 Parco Archeologico di Pompei, Pompei, Italy; 3Dipartimento di Lettere e Beni Culturali, Università della Campania Luigi Vanvitelli, Santa Maria Capua Vetere, Italy

The AD 79 Vesuvius eruption buried the Roman towns around the volcano under several metres of pyroclastic materials. The destruction of these Roman towns allows volcanologists to build models that can provide valuable information on the extent and type of damage that a future Plinian eruption could cause in urbanized areas. In order to fully understand these phenomena, volcanologists need to observe the sequence of volcanic layers (stratigraphic reconstruction) that buried the city during the AD 79 eruption and which of these layers are associated with damage and victims. This study reports the results of a collaboration between the Archaeological Park of Pompeii and the University of Naples Federico II to document the stratigraphic sequence and the distribution of damage and victims unearthed by new excavations in the archaeological sites of Pompeii and Stabiae. A systematic survey of all exposed pyroclastic sequences allowed us to study in detail the distribution and lateral facies variations of the different stratigraphic units. The deposit of stratified ash forming the upper part of the pyroclastic succession, was studied in detail to define the downcurrent variations of its sedimentological features and how these were influenced by urban structures. Pronounced lateral variations are observed in the upper part of the sequence at Pompeii, mainly consisting of a pyroclastic density current (PDC), stratified ash deposit, that ranges in thickness from few tens of centimetres to two metres. In this case, thin, massive ash layers can be traced laterally into thick, poorly sorted, ash and lapilli layers, with well-developed sedimentary structures. All PDC layers, except the lowermost, are dispersed across the entire Pompeii area, although some are missing locally as a result of the erosive action of the following PDC. The layer associated with the most destructive impact on the Roman buildings shows a strong lateral variation in thickness (0 to 330 cm) and sedimentary structures. Where it is less than 30 cm thick, the deposit is fine-grained and thinly stratified. Where it thickens, the lower part is rich in coarse pumice lapilli and locally shows well-developed stratifications, while the upper part shows an internal arrangement of alternating layers of fine and coarse ash forming progressive dunes. Upwards, ash deposits show rare pumice lapilli clasts and diffuse accretionary lapilli. This ash sequence is interstratified with four well-sorted, thin lithic-rich layers that exhibit mantling structures of fall deposits. At Stabiae, the ash PDC deposit ranges in thickness from 70 to 160 centimetres. Its internal structure shows the same types of stratification observed at Pompeii. Ash layers thicken and show lateral lithofacies variations where the pumice deposit thins and close to standing walls. It is proposed that the urban structures affect the structure of the deposit much more than the variations induced by the increase in the distance from the eruptive vent.


Biography

“I obtained my bachelor degree and master degree in Geology at University of Federico II, Naples, Italy. With an experimental master thesis in Volcanology I investigated the pyroclastic sequence of the tuff cone of Miliscola, a pre-caldera, monogenetic volcano that partially crops out in the Campi Flegrei volcanic field. As a student, I took part in some summer schools with volcanology theme like the “XI School of Volcanology AIV Bruno Capaccioni” and the “Etna International Training School of Geochemistry 2019 – Science meets practice”.

Dr. Jarrod Hore

Biography:

Dr. Jarrod Hore is an environmental historian of settler colonialism, indigenous knowledge and Australian geology. His work on settler colonial identity, landscape photography, early environmentalism and antipodean Romanticism has been published in Australian Historical Studies, History Australia and the Australian Book Review. Jarrod holds a PhD from Macquarie University (2019) and in 2020 he is the David Scott Mitchell Memorial Fellow at the State Library of New South Wales.

Dr. Heather Handley (Chair)

Biography:

Dr. Heather Handley (Chair) is an Associate Professor of Volcanology and Geochemistry at Macquarie University. She is a Science and Technology Australia 2021-2022 Superstar of STEM. Heather’s current research interests include the integration of Indigenous oral knowledge with volcanological and geochronological knowledge to advance our understanding of prehistoric volcanic eruptions and their impacts in Australasia. Heather is Co-Founder and President of the Women in Earth and Environmental Sciences Australasia Network (WOMEESA). She received an AIPS NSW Young Tall Poppy Award in 2014 and has led more than 40 outreach events and workshops including mentoring in the Waranara Mentoring Program for high achieving Aboriginal and Torres Strait Islander undergraduate students. Heather frequently writes for The Conversation, has given over 60 television, radio and print interviews on volcanoes and she has featured in documentaries for National Geographic and Discovery Channel Science.

Prof. Patrick Nunn

Biography:

Prof. Patrick Nunn is a Professor of Geography & Co-Director of the Sustainability Research Centre. He has worked extensively on Indigenous insights into Holocene volcanism in Australia and the Pacific Islands, as well as on Indigenous memories of island collapse (mega-landsliding) and associated extreme wave impacts. He has also done a lot of work on Indigenous recollections of postglacial sea-level rise in Australia and elsewhere. Firmly believing in the importance of community awareness, Patrick has ensured that the results of his research have been returned to the people of the land in ways that they can understand its nature and importance, something helped in the case of Fiji by his fluency in the Fijian language and his familiarity with cultural protocols.

Prof. Greg Lehman

Biography:

The University’s (UTAS) Pro Vice Chancellor, Professor Greg Lehman, leads a team dedicated to consolidating a whole of University respect and embedding of Indigenous perspectives, knowledges and culture across research, teaching and community partnership. We want to ensure that engaging with the University of Tasmania, whether as a student, staff member or community member, provides the experience of a University that celebrates Aboriginal Tasmania’s deep history, its diversity of cultures and values, and continually builds its Aboriginal connections.

Dr. Duane Hamacher

Biography:

Dr. Duane Hamacher is an Associate Professor of Cultural Astronomy in the ARC Centre of Excellence in All-Sky Astrophysics in 3-Dimensions (ASTRO 3D) within School of Physics at the University of Melbourne. Duane researches cultural astronomy, Dark Sky studies, astronomical heritage, and the history and philosophy of science. He developed a subject on Indigenous Astronomy at the University of Melbourne (PHYC10010) which kicks off in Semester 1 of 2021, which features Indigenous guest lecturers from around the world. Duane’s service includes working as a heritage expert for UNESCO, an expert panellist for the National Aboriginal and Torres Strait Islander Curricula Project.

Rebe Taylor

Biography:

Senior Research Fellow, College of Arts, Law and Education UTAS: Rebe Taylor took on the role as Senior Research Fellow at the College of Arts, Law and Education in April 2018. She is an award-winning historian with more than twenty years of experience researching and writing the histories of southeast Australian indigenous peoples and European settlement for academic and literary publications, web resources and museum spaces. Until early 2018, Rebe held the inaugural Coral Thomas Fellow at State Library NSW. She has also held numerous Fellowships at The University of Melbourne and Kings College London. Rebe’s most recent book, Into the Heart of Tasmania, published by Melbourne University Press, won the 2018 Tasmanian Book Prize, the 2018 Queensland Premier’s Award for history, and the inaugural Joan and Dick Family Green Award for Tasmanian History.

Geochemical and mineralogical characterization of tailings: Evaluating the potential for reprocessing the Bobadil tailings, Rosebery

1Jackson, Laura, 2K ng, Lexi, 1Parbhakar-Fox, Anita, 3Meffre, Sebastien

1The W.H. Bryan Mining & Geology Research Centre, Sustainable Minerals Institute, The University of Queensland, Brisbane, Australia; 2RGS Environmental, Brisbane, Australia; 3 The school of Natural Sciences, The University of Tasmania, Hobart, Tasmania

The Rosebery Pb-Zn-Cu-Ag mine, 3 km north west of Rosebery, Tasmania, Australia has been in operation since 1936. During this time >17 Mt of tailings were deposited in Bobadil Tailings Storage Facility, which opened in 1974 and reached capacity in 2018. Historically the materials contained in the Bobadil tailings are known to be endowed in ecotoxic metals including Pb, Zn, Cu, As and Mn, as would be expected based on the ore mineralogy (i.e., sphalerite, galena, pyrite). To assess the risks posed, samples were collected from 10 trenches (52 samples) and 4 cores the upper 2 m across the accessible parts of the TSF and detailed geochemical and mineralogical studies (e.g., acid base accounting (ABA), X-ray diffractometry, sulphide alteration index (SAI), mineral liberation analysis (MLA), scanning electron microscopy, laser ablation ICPMS) undertaken to assess the viability of reprocessing as a means to reducing environmental risks associated with the facility, and extend the mine life.

Eleven facies (A to K) were visually defined in these sampled tailings, ranging from oxidised hardpan (i.e., Facies K) to fresher sulphide dominated tailings (Facies A). Despite this visual heterogeneity, ABA results classified all samples as potentially acid forming (PAF) with total sulphur ranging from 3.8 to 13.8 %. The inherent acid neutralising potential (ANC) was low across all facies (0.5 to 1.9 % carbon) and is complimentary to the measured tailings mineralogy which reported a low abundance of carbonates (<2 % calcite). Sulphide alteration index (SAI) values confirm most tailings as un-oxidised to partially armoured. When SAI values are screened against paste pH values, these materials classified as PAF with a lag time to AMD generation anticipated. MLA results reported >89 % of pyrite as liberated and where locked, mineral associations were dominantly with muscovite and quartz. To determine the tenor and deportment of precious, base and critical metals in the pyrite and sphalerite LA-ICP-MS analysis reported trace metals (e.g., Co, Ni, Cd and Bi) in pyrite were considered low, whist in sphalerite bivalent metals including Cd and Mn were notably high. Only two Au inclusions were identified in MLA-SEM images.  Due to the homogenous, trace element free and highly liberated pyrite particles these tailings could be amenable to reprocessing and desulphurisation. The remaining gangue tailings have the potential to be reused into products such as ceramics, road base and industrial building materials. With additional analysis of tailings at depth, a robust retreatment framework could be redeveloped to help remove the requirement to maintain and manage a large tailings facility in perpetuity.


Biography

Lexi is a geochemist at RGS Environmental. She has completed an Honours degree in Environmental Geochemistry at the University of Tasmania. Her Honours study involved the characterisation of mineralogy and geoenvironmental behaviour of mine waste (tailings) as part of the rehabilitation plan for a tailings storage facility in Western Tasmania.

A new approach to integrate passive seismic HVSR depth models in magnetotelluric (MT) 1D inversion to characterize the cover-basement interface.

Suriyaarachchi, Nuwan1,2 , Giraud, Jeremie1,2, Seille, Hoel3 , Jessell, Mark1,2, Lindsay, Mark1,2, Hennessy, Lachlan4, Ogarko, Vitaliy5

 1Centre of Exploration Targeting, School of Earth Sciences, University of Western Australia, 35 Stirling Highway, Perth  6009 WA, Australia; 2Mineral Exploration Cooperative Research Centre (MinEx CRC), School of Earth Sciences, University of Western Australia, 35 Stirling Highway, Perth 6009 WA, Australia; 3CSIRO Deep Earth Imaging FSP, Australian Resources Research Centre, 26 Dick Perry Avenue, Kensington 6151 WA, Australia; 4Anglo American, Group Discovery and Geosciences, 201 Charlotte Street, Brisbane 4000 QLD, Australia; 5International Centre for Radio Astronomy Research, University of Western Australia, 35 Stirling Highway, Perth 6009 WA, Australia

Electromagnetic methods are useful tools to understand cover-basement interface in many aspects. They could provide valuable information to exploration targeting, mineral prospectivity mapping and in some cases. They can also provide volume constraints for groundwater and energy resource estimates with a fraction of the cost of drilling. In this study, we use passive seismic Horizontal to Vertical Spectral Ratios (HSVR) to reduce the uncertainties of detecting cover-basement contact in Magnetotelluric (MT) depth-resistivity models. 

We invert MT apparent resistivity and phase using Occam’s inversion algorithm to obtain resistivity-depth model. Generally, Occam’s inversion produces the smoothest model that fits the observations (data) with a certain target misfit. But the smoothest model may not fully describe a realistic resistivity structure, such as thin resistivity layers and sharp resistivity contrasts (eg. impermeable basement), which is critical to identify the cover-basement transition and thus interface. For this study, we expect to control the MT depth-resistivity model smoothness (or roughness) without producing unrealistic models. For that, we brought forward the importance of detection of cover-basement interface prior to 1D MT inversion. Our approach is to use a prior interface-depth model to support interface prediction by adjusting the model roughness values in Occam’s 1D inversion. This prior interface-depth model is generated from co-located or reasonably placed passive seismic-HVSR models, which give robust results to detect possible interfaces up to 1500m depths.

To test our approach, we created a synthetic homogenous two-layer cover-basement case with 20 Ω m cover resistivity, 1000 Ω m basement resistivity and a cover-basement interface at 1000m depth. The 1D forward response (from 104 to 10-3 Hz) was calculated and 5% random noise was added to the synthetic data. Firstly, a cover-basement interface depth interval is estimated using synthetic HVSR model data. Then we performed 1D MT inversions. The inversions are regularized using a series of roughness penalty values ranging from 0 (no penalty) to 1.00 (maximum penalty) within this hypothetical cover-basement transition depth interval.  Thinner MT depth mesh was used at the HVSR derived cover-basement interface region to identify accurate resistivity variations.

Preliminary results on the synthetic test show that the depth roughness penalty values between 0.05-0.25 reveal sharp resistivity contrasts consistent with the true depth to cover basement interface. We tested a spectrum of cover-basement depths and cover basement resistivity scenarios. We expect to test the procedure further for multi-layer synthetic cases and analysed the results statistically to validate our approach. Additional priori information, such as borehole data and stratigraphy data will be used to improve the HVSR-based constrain for the 1D MT (real data) inversion.

We acknowledge the support of the MinEx CRC and the Loop: Enabling Stochastic 3D Geological Modelling (LP170100985) consortia. The work has been supported by the Mineral Exploration Cooperative Research Centre whose activities are funded by the Australian Government’s Cooperative Research Centre Programme. This is MinEx CRC Document 2020/xxx.


Biography

Nuwan is a PhD candidate working with Mark Jessell, Jeremie Giraud, Mark Lindsay, Hoel Seille, Lachlan Hennessy and Vitaliy Ogarko. He is working to Integrate magnetotelluric data and Passive seismic data to characterize the cover-basement interface. This project is a collaboration between MInexCRC and Loop consortium

The urban geochemical baseline of Canberra: Does it provide dirt on criminals?

Aberle, Michael1, de Caritat, Patrice2,1, McQueen, Ken1, Hoogewerff, Jurian1

1National Centre for Forensic Studies, Faculty of Science and Technology, University of Canberra, Canberra, Australia; 2Geoscience Australia, GPO Box 378, Canberra, Australia

Topsoil is a common material that may be transferred to people and objects prior to, during, or after perpetrating a criminal activity. Traditionally the use of soil material in law enforcement operations involves one-to-one comparison of recovered soil evidence with reference samples collected from known areas of interest. In casework and intelligence applications where this contextual information is not available, properties of the recovered evidence may be used to triage geographical regions as areas of low and high interest. If sufficient relevant spatial information is available, this approach may provide forensic intelligence to better focus operational resources on areas of interest. Here, spatial variability is both a strength and a weakness, with research required to determine 1) which parameters are sufficiently discriminatory at the chosen spatial scale, and 2) the effect of contributing anthropogenic and geogenic sources on forensic soil provenancing applications.

 To investigate these issues, a high-density (1 site/km2) geochemical survey has been conducted to map the compositional variation of ~700 urban topsoil (0-5 cm depth) samples across Canberra, Australian Capital Territory. As a study location, Canberra represents a large city (population > 450k) with a system of urban open green spaces and bushland reserves, as well as minimal heavy industrial activity. Thus, in addition to law enforcement applications, the effect of urbanisation on the environment can be studied without significant masking by industrial pollutant sources. Using standard protocols for urban geochemical surveys, including extensive quality control measures, the samples have been prepared in a fusion flux matrix and characterised for bulk elemental geochemistry using X-Ray Fluorescence and Inductively Coupled Plasma – Mass Spectrometry analysis of total acid digests. Bulk mineralogy has been determined on a subset of samples using powder X-Ray Diffraction.

The results demonstrate that the geochemistry of the topsoils is strongly influenced by the dominant lithological units of the underlying bedrock. While the concentrations of known anthropogenic elements are mainly below thresholds for health-based investigation (with 1 or 2 sites marginally at threshold), there is evidence of diffuse anthropogenic contributions, particularly in older suburbs and light industrial areas.

For provenancing applications, a number of different approaches have been suggested to ‘match’ a recovered sample to a map. Typically, these involve comparing the properties of the recovered sample to those in each ‘target’ survey grid cell and attributing statistical significance to some measure of ‘overlap’ at an arbitrary inclusion/exclusion threshold (e.g. 95%). By instead comparing each grid cell to a series of questioned samples from within and outside the survey boundary, and weighing each probability by the probability of observing the grid cell value in the total dataset in a likelihood ratio approach, we have demonstrated that regions of interest may be reduced in a more conservative manner better suited to forensic provenancing than previous approaches.

Further merits and challenges of provenancing topsoil from urban environments will be presented, notably the significance and impact of displacement and introduction of topsoil material from other areas on developing forensic soil surveys, as well as determining the source of questioned samples.


Biography

Michael Aberle is currently a PhD candidate at the National Centre for Forensic Studies, University of Canberra. Together with industry partners, his research primarily focuses on evaluating the forensic utility of a fit-for-purpose, high-density soil geochemical survey of the Australian Capital Territory for forensic provenancing of bulk and trace soils.

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