3D geological models from combined interpretation of airborne-TEM and geological data- Two examples from Sweden

2020 ◽  
Author(s):  
Mehrdad Bastani ◽  
Lena Persson ◽  
Peter Dahlqvist ◽  
Eva Wendelin ◽  
Johan Daniels
Keyword(s):  
Groundwater Resources ◽  
Geophysical Data ◽  
Saline Groundwater ◽  
Middle Cambrian ◽  
3D Geological Modeling ◽  
Rock Types ◽  
Transient Electromagnetic ◽  
Lower Ordovician ◽  
Geological Models ◽  
Resistivity Image

<p><span><span>The geological survey of Sweden (SGU) has carried out several detailed airborne TEM (Transient Electromagnetic) surveys in recent years. The data collected in these surveys were inverted to provide models of the resistivity of the subsurface, down to a few hundred meters depth. </span></span><span>These resistivity models together with the data from existing boreholes and ground observations offer an excellent basis for further 3D geological modeling.  </span></p><p><span>The airborne TEM data presented in this study were collected between 2013 and 2016, covering large areas of the islands of Öland and Gotland, in Sweden. Both islands face problems with water supply due to limited groundwater resources. The aim of the surveys was to identify new groundwater resources, specify the depth to saline groundwater and to improve the understanding of the geology of the islands. On Öland, the Paleozoic sedimentary succession reaches thicknesses of approximately 250 m and is composed of Lower Cambrian sandstone, Middle Cambrian siltstone, and claystone followed by the Alum Shales of Upper Cambrian and Lower Ordovician age. Above this lies an up to 40 m thick Lower Ordovician limestone succession, which forms the bedrock at the surface across much of the island. The entire sedimentary sequence rests on Precambrian crystalline rocks. On the Island of Gotland, Silurian bedrock represents the upper part of a 250-800 m thick Paleozoic sequence overlying the crystalline basement. The Silurian bedrock is dominated by interbedded layers </span><span><span>of limestone and marlstone, where the interface between limestone and marlstone is often the primary hydraulic conductor.</span></span></p><p><span>After acquisition, these data were processed and inverted (1D inversions with lateral constraints), to provide a series of large airborne datasets, providing a resistivity image down to depths of about 250 m in some areas. The considerable resistivity contrast between lithologies, e.g. limestone and marlstone on Gotland, provided an excellent opportunity to resolve boundaries between the different rock types. Borehole information, geological maps, ground geophysical data and the inversion results were incorporated in a 3D geological modelling software. On comparison of the </span><span><span>airborne models, ground geophysical data and borehole information it was clear that the airborne resistivity models correlated well with the other available data. Hence, t</span>he resistivity models were used as the basis for constructing the 3D hydrogeological and geological models over significant parts of the islands. <span>In this study we present the 3D geological models over the islands of Öland and Gotland which were constructed from the integrated interpretation of all the available data. The models are composed of voxels, each representing a certain lithology classified using a statistical approach. The classification is based on the resistivity range, distance to the neighboring wells/boreholes and the geological observations at the surface. The 3D voxel models will be/have been utilized in hydrological modelling, societal planning, and groundwater management.</span></span></p>

Petrology and geochemistry of Cambrian volcanic rocks from the Avalon Zone in New Brunswick

1985 ◽  
Vol 22 (6) ◽  
pp. 881-892 ◽  
Author(s):  
John D. Greenough ◽  
S. R. McCutcheon ◽  
V. S. Papezik
Keyword(s):  
New Brunswick ◽  
Volcanic Rocks ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Middle Cambrian ◽  
Mafic Rocks ◽  
Rock Types ◽  
Petrology And Geochemistry ◽  
Eastern Seaboard ◽  
Highly Evolved

Lower to Middle Cambrian volcanic rocks occur within the Avalon Zone of southern New Brunswick at Beaver Harbour and in the Long Reach area. The Beaver Harbour rocks are intensely altered, but the major- and trace-element geochemistry indicates that they could be highly evolved (basaltic andesites) within-plate basalts. The mafic flows from the Long Reach area form two chemically and petrologically distinct groups: (1) basalts with feldspar phenocrysts that represent evolved continental tholeiites with some oceanic characteristics; and (2) a group of aphyric basalts showing extremely primitive continental tholeiite compositions, also with oceanic affinities and resembling some rift-related Jurassic basalts on the eastern seaboard. Felsic pyroclastic rocks in the Long Reach area make the suite bimodal. This distribution of rock types supports conclusions from the mafic rocks that the area experienced tension throughout the Early to Middle Cambrian.

scholarly journals Quantifying aquifer properties and freshwater resource in coastal barriers: a hydrogeophysical approach applied at Sasihithlu (Karnataka state, India)

2012 ◽  
Vol 16 (11) ◽  
pp. 4387-4400 ◽  
Author(s):  
J.-M. Vouillamoz ◽  
J. Hoareau ◽  
M. Grammare ◽  
D. Caron ◽  
L. Nandagiri ◽  
...  
Keyword(s):  
Sea Level ◽  
Groundwater Resources ◽  
Time Lapse ◽  
Unconfined Aquifer ◽  
Spatial Knowledge ◽  
Western India ◽  
Transient Electromagnetic ◽  
Freshwater Resource ◽  
Aquifer Properties ◽  
Rainfall Patterns

Abstract. Many human communities living in coastal areas in Africa and Asia rely on thin freshwater lenses for their domestic supply. Population growth together with change in rainfall patterns and sea level will probably impact these vulnerable groundwater resources. Spatial knowledge of the aquifer properties and creation of a groundwater model are required for achieving a sustainable management of the resource. This paper presents a ready-to-use methodology for estimating the key aquifer properties and the freshwater resource based on the joint use of two non-invasive geophysical tools together with common hydrological measurements. We applied the proposed methodology in an unconfined aquifer of a coastal sandy barrier in South-Western India. We jointly used magnetic resonance and transient electromagnetic soundings and we monitored rainfall, groundwater level and groundwater electrical conductivity. The combined interpretation of geophysical and hydrological results allowed estimating the aquifer properties and mapping the freshwater lens. Depending on the location and season, we estimate the freshwater reserve to range between 400 and 700 L m−2 of surface area (± 50%). We also estimate the recharge using time lapse geophysical measurements with hydrological monitoring. After a rainy event close to 100% of the rain is reaching the water table, but the net recharge at the end of the monsoon is less than 10% of the rain. Thus, we conclude that a change in rainfall patterns will probably not impact the groundwater resource since most of the rain water recharging the aquifer is flowing towards the sea and the river. However, a change in sea level will impact both the groundwater reserve and net recharge.

scholarly journals Multi-geophysical data integration using cluster analysis: Assisting geological mapping in Trøndelag, Mid-Norway

2020 ◽  
Author(s):  
Ying Wang ◽  
Anna K Ksienzyk ◽  
Ming Liu ◽  
Marco Brönner
Keyword(s):  
Cluster Analysis ◽  
Data Integration ◽  
Geological Mapping ◽  
Geophysical Data ◽  
Supervised Machine Learning ◽  
Spatial Density ◽  
Depth Information ◽  
Rock Types ◽  
Gravity Measurements ◽  
Single Attribute

Summary Modern geophysical data acquisition technology makes it possible to measure multiple geophysical properties with high spatial density over large areas with great efficiency. Instead of presenting these co-located multi-geophysical datasets in separate maps, we take advantage of cluster analysis and its pattern exploration power to generate a cluster map with objectively integrated information. Each cluster in the resulting cluster map is characterised by multi-geophysical properties and can be associated with certain geological attributes or rock types based on existing geological maps, field data and rock sample analysis. Such a cluster map is usually high in resolution and proven to be more helpful than single-attribute maps in terms of assisting geological mapping and interpretation. In this paper, we present the workflow and technical details of applying cluster analysis to multi-geophysical data of a study area in the Trøndelag region in Mid-Norway. We address the importance of carefully designed pre-processing procedures regarding the input datasets to ensure an unbiased data integration using cluster analysis. Random Forest as a supervised machine learning method for classification/regression is strategically employed post-clustering for quality evaluation of the results. The multi-geophysical data used for this study include airborne magnetic, frequency electromagnetic and radiometric measurements, together with ground gravity measurements. Due to the nature of these input data, the resulting cluster map carries multi-depth information. When associated with available geological information, the cluster map can help interpret not only bedrock outcrops, but also rocks underneath the sediment cover.

scholarly journals Bayesian geological and geophysical data fusion for the construction and uncertainty quantification of 3D geological models

2021 ◽  
Vol 12 (1) ◽  
pp. 479-493 ◽  
Author(s):  
Hugo K.H. Olierook ◽  
Richard Scalzo ◽  
David Kohn ◽  
Rohitash Chandra ◽  
Ehsan Farahbakhsh ◽  
...  
Keyword(s):  
Data Fusion ◽  
Uncertainty Quantification ◽  
Geophysical Data ◽  
Geological Models

scholarly journals Lithostratigraphic and allostratigraphic framework of the Cambrian–Ordovician Potsdam Group and correlations across Early Paleozoic southern Laurentia

2017 ◽  
Vol 54 (5) ◽  
pp. 550-585 ◽  
Author(s):  
David G. Lowe ◽  
R.W.C. Arnott ◽  
Godfrey S. Nowlan ◽  
A.D. McCracken
Keyword(s):  
Climate Change ◽  
Early Paleozoic ◽  
Middle Cambrian ◽  
Shallow Marine ◽  
Upper Cambrian ◽  
Subaerial Exposure ◽  
Marine Sedimentation ◽  
Lower Ordovician ◽  
Fluvial Sedimentation ◽  
Mixed Carbonate

The Potsdam Group is a Cambrian to Lower Ordovician siliciclastic unit that crops out along the southeastern margins of the Ottawa graben. From its base upward, the Potsdam consists of the Ausable, Hannawa Falls, and Keeseville formations. In addition, the Potsdam is subdivided into three allounits: allounit 1 comprises the Ausable and Hannawa Falls, and allounits 2 and 3, respectively, the lower and upper parts of the Keeseville. Allounit 1 records Early to Middle Cambrian syn-rift arkosic fluvial sedimentation (Ausable Formation) with interfingering mudstone, arkose, and dolostone of the marine Altona Member recording transgression of the easternmost part of the Ottawa graben. Rift sedimentation was followed by a Middle Cambrian climate change resulting in local quartzose aeolian sedimentation (Hannawa Falls Formation). Allounit 1 sedimentation termination coincided with latest(?) Middle Cambrian tectonic reactivation of parts of the Ottawa graben. Allounit 2 (lower Keeseville) records mainly Upper Cambrian quartzose fluvial sedimentation, with transgression of the northern Ottawa graben resulting in deposition of mixed carbonate–siliciclastic strata of the marine Rivière Aux Outardes Member. Sedimentation was then terminated by an earliest Ordovician regression and unconformity development. Allounit 3 (upper Keeseville) records diachronous transgression across the Ottawa graben that by the Arenigian culminated in mixed carbonate–siliciclastic, shallow marine sedimentation (Theresa Formation). The contact separating the Potsdam Group and Theresa Formation is conformable, except locally in parts of the northern Ottawa graben where the presence of localized islands and (or) coastal salients resulted in subaerial exposure and erosion of the uppermost Potsdam strata, and accordingly unconformity development.

Semiautomated geologic mapping using self-organizing maps and airborne geophysics in the Brazilian Amazon

Geophysics ◽  
2012 ◽  
Vol 77 (4) ◽  
pp. K17-K24 ◽  
Author(s):  
Cleyton de Carvalho Carneiro ◽  
Stephen James Fraser ◽  
Alvaro Penteado Crósta ◽  
Adalene Moreira Silva ◽  
Carlos Eduardo de Mesquita Barros
Keyword(s):  
Gamma Ray ◽  
Gold Mineralization ◽  
Brazilian Amazon ◽  
Geophysical Data ◽  
Self Organizing Map ◽  
Self Organizing Maps ◽  
Spectrometric Data ◽  
Rock Types ◽  
Geologic Map ◽  
Self Organizing

A self-organizing map (SOM) approach has been used to provide an integrated spatial analysis and classification of airborne geophysical data collected over the Brazilian Amazon. Magnetic and gamma ray spectrometric data were used to extract geophysical signatures related to the spatial distribution of rock types and to produce a geologic map over the prospective Anapu-Tuerê region. Particular emphasis was given to discriminating and identifying rock types, and the processes related to gold mineralization, which are known to occur in the Anapu-Tuerê region. SOM was able to identify and map distinctive geophysical signatures related to the various geologic units identified on the published geologic map. Furthermore, SOM was able to identify and enhance very subtle signatures derived jointly from the magnetic and gamma ray spectrometric data that could be related to geologic processes present in the area. These results demonstrate the effectiveness of using SOM as a tool for geophysical data analysis and for semiautomated mapping in regions such as the Amazon.

scholarly journals Quantifying freshwater resource in coastal barriers: the joint use of transient electromagnetic and magnetic resonance soundings

2012 ◽  
Vol 9 (4) ◽  
pp. 5261-5294
Author(s):  
J.-M. Vouillamoz ◽  
J. Hoareau ◽  
M. Grammare ◽  
D. Caron ◽  
L. Nandagiri ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Sea Level ◽  
Fresh Water ◽  
Groundwater Resources ◽  
Spatial Knowledge ◽  
Western India ◽  
Transient Electromagnetic ◽  
Freshwater Resource ◽  
Aquifer Properties ◽  
Rainfall Patterns

Abstract. Many human communities living in coastal areas in Africa and Asia rely on thin fresh water lenses for their domestic supply. Population growth together with change in rainfall patterns and sea level will probably impact these vulnerable groundwater resources. A spatial knowledge of the aquifer properties and the use of groundwater model are required for the sustainable management of the resource. This paper presents a ready-to-use methodology for estimating the key aquifer properties based on the joint use of two non-invasive geophysical tools together with common hydrological measurements. We applied the proposed methodology on a coastal sandy barrier in South-Western India. We found that the joint use of magnetic resonance and transient electromagnetic soundings allows to map the fresh water lens and to estimate the specific yield, the hydraulic conductivity, the water salinity and the water table recharge. From the geophysical results, we estimate the fresh water reserve to range between 400 and 700 l m−2 of surface area according to the location and to the season. Using time lapse geophysical measurements and common groundwater monitoring, we also estimate the recharge of a rainy event to be about 100% of the rain, and the net recharge at the end of the monsoon to be less than 10% of the rain. Thus, we conclude that a change in rainfall patterns will probably not impact the groundwater resource since most of the rain water recharging the aquifer is flowing towards the sea and the river. However, a change in sea level will impact both the groundwater reserve and net recharge.

scholarly journals Mapping Saltwater Intrusion using Transient ElectroMagnetic Data in Maopa, Central Province, Papua New Guinea

2021 ◽  
Author(s):  
◽  
Ronald Verave
Keyword(s):  
Papua New Guinea ◽  
Saltwater Intrusion ◽  
Groundwater Resources ◽  
Cost Effective ◽  
New Guinea ◽  
Small Island ◽  
Mixing Zone ◽  
Low Resistivity ◽  
Transient Electromagnetic ◽  
Tem Method

<p>Saltwater intrusion studies in coastal Papua New Guinea (PNG) are a rarity despite recognized vulnerabilities to salination of coastal groundwater resources. For many seaside communities such as Maopa the threat of salination is exacerbated by high extraction rates by a growing population and the likelihood of the effects of climate change. Saltwater intrusion can be addressed using various methods, including direct water sampling from wells and electrical resistivity measurements. This study advances knowledge of a previous assessment of saltwater intrusion and groundwater in this region that used DC Schlumberger resistivity soundings, through an extensive and cost-effective Transient ElectroMagnetic (TEM) survey. The study aims to map the lateral and vertical extent of salination and the characterization of groundwater in the landward direction over seven lines of TEM soundings along Keakalo Bay. The TEM method proved successful in identifying four main geoelectric layers. The top layer has a highly variable resistivity (range of 5 to 355 Ωm) inferred as the vadose zone. Beneath this layer is a layer of intermediate resistivity (100 Ωm > p ≥ 20 Ωm) characterizing a perched freshwater aquifer with a thickness range of 3.2 to 15 m. An intermediate layer of low resistivity (20 Ωm > p ≥ 3 Ωm) was detected at the boundary separating the freshwater aquifer from the inferred saltwater intrusion. This layer is typically thicker than the freshwater aquifer and is referred to as the mixing zone. The deepest layer constituting the salination zone has a very low resistivity (3 Ωm > p ≥ 0.4 Ωm), occurring at depths of up to 42 m. The depth to the salination zone varied from deep in the middle of the survey area to shallow in the fringes of the survey. This pattern is reflective of surface seawater infiltration marked by mangrove forest in the interior and subsurface infiltration from the coast. Similar depth trends but at shallower depths were also observed for the mixing zone, and the freshwater region. In some cases the mixing area overwhelms the freshwater regions. Layering confirmed groundwater resource and salination patterns as those of basic models reflective of small island hydrology, except that salination and the freshwater boundary were less distinctive due to the relatively high thickness of the dispersion zone. The use of different sounding parameters in line 7 provided useful information about the nature of the deep basement unit and thickness of the overlying unconsolidated quaternary sediment.</p>

scholarly journals Stratigraphy and geochemical composition of the Cambrian Alum Shale Formation in the Porsgrunn core, Skien–Langesund district, southern Norway.

2018 ◽  
Vol 66 ◽  
pp. 1-20
Author(s):  
Niels Hemmingsen Schovsbo ◽  
Arne Thorshøj Nielsen ◽  
Andreas Olaus Harstad ◽  
David L. Bruton
Keyword(s):  
Gamma Ray ◽  
Geochemical Composition ◽  
Middle Cambrian ◽  
Alum Shale ◽  
Carbon Isotope Excursion ◽  
Lower Ordovician ◽  
Shale Formation ◽  
Sedimentary Succession ◽  
Southern Norway ◽  
Spice Event

The fully cored BHD-03-99 borehole (hereafter referred to as the Porsgrunn borehole and core) penetrated Ordovician and Cambrian strata in the Skien–Langesund district, southern part of the Oslo region in Norway. Hand-held X-ray fluorescence (HH-XRF) measurements combined with spectral gamma ray and density core scanning of the Middle Cambrian – Furongian Alum Shale Formation have been made and compared with similar measurements obtained on Alum Shale cores from Scania (southernmost Sweden) and Bornholm (Denmark). The Porsgrunn drill site is located in an area that was only mildly overprinted by Caledonian tectonics and represents one of the few sites in the Oslo area where a nearly untectonised sedimentary succession can be studied in terms of thickness and geochemistry. The Alum Shale Formation is 28.8 m thick in the Porsgrunn core, excluding the thickness of five 0.9–5.5 m thick dolerite sills of assumed Permian age. In the Alum Shale Formation the bulk densities are around 2.7 g/cm3 with a slightly decreasing trend up through the formation. The shale has total organic carbon (TOC) values up to 14 wt%, which is comparable to the TOC levels for the Alum Shale elsewhere in the Oslo area and for dry gas matured Alum Shale in Scania and Bornholm. The basal Furongian is characterised by a gamma ray low and an increase in Mo interpreted to reflect the Steptoean Positive Carbon Isotope Excursion (SPICE) event. The Porsgrunn core data suggest that the Mo concentration remained high also after the SPICE event. Characteristic, readily identified features in the gamma log motif are named the Andrarum gamma low (AGL), base Furongian gamma low (BFGL), Olenus triple gamma spike (OTGS) and the Peltura gamma spike (PGS). No Lower Ordovician Alum Shale is present. The 14.8 m thick Furongian part of the Alum Shale represents the Olenus, Parabolina, Leptoplastus, Protopeltura and Peltura trilobite superzones judging from log-stratigraphic correlations to Scania and Bornholm. The Middle Cambrian interval is 14.0 m thick and includes the Exsulans Limestone Bed and 1.4 m of quartz sandstone. A 0.3 m thick primary limestone bed may be an equivalent to the Andrarum Limestone Bed. The succession represents the Paradoxides paradoxissimus and P. forchhammeri superzones. The Alum Shale Formation rests atop the 13.0 m thick Lower Cambrian Stokkevannet sandstone (new informal name) that in turn directly overlies the basement. Overall, the stratigraphic development of the comparatively thin Alum Shale Formation resembles the condensed sequence seen on Bornholm.

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