High-resolution Magnetic Data Research Articles

Magnetic Exploration of Structurally Controlled Mineralization at Low Latitudes: A Case from the Masara Gold District, Mindanao, Philippines

Abstract Magnetic data transformations are applied to the high-resolution magnetic data from the Masara gold district in the southern Philippines to enhance features related to a porphyry copper prospect and epithermal gold deposit. Using several filtering methods and structural mapping techniques, we were able to highlight the signal coming from a shallow chlorite-sericite alteration zone. Although the epithermal veins are mainly composed of nonmagnetic minerals, calculation of the tilt derivative of the magnetic grid revealed linear features that are coincident with the surface projection of the gold-bearing veins. Furthermore, dip directions of the magnetic sources were determined using Euler deconvolution, and they were found to coincide with the dip directions of the veins as determined by structural measurements at different underground levels. Aside from showing the utility of the magnetic methods in epithermal gold deposit exploration, this study also demonstrates that challenges of processing and interpreting magnetic anomalies in areas near the equator can be overcome. This research outlines a processing workflow that can be adopted for further investigation of other mineralized areas.

Tailored spiral in-out spectral-spatial water suppression pulses for magnetic resonance spectroscopic imaging.

To develop short water suppression sequences for 7 T magnetic resonance spectroscopic imaging, with mitigation of subject-specific transmit RF field ( B1+) inhomogeneity. Patient-tailored spiral in-out spectral-spatial saturation pulses were designed for a three-pulse WET water suppression sequence. The pulses' identical spatial subpulses were designed using patient-specific B1+ maps and a spiral in-out excitation k-space trajectory. The subpulse train was weighted by a spectral envelope that was root-flipped to minimize peak RF demand. The pulses were validated in in vivo experiments that acquired high resolution magnetic resonance spectroscopic imaging data, using a crusher coil for fast lipid suppression. Residual water signals and MR spectra were compared between the proposed tailored sequence and a conventional WET sequence. Replacing conventional spectrally-selective pulses with tailored spiral in-out spectral-spatial pulses reduced mean water residual from 5.88 to 2.52% (57% improvement). Pulse design time was less then 0.4 s. The pulses' specific absorption rate were compatible with magnetic resonance spectroscopic imaging TRs under 300 ms, which enabled spectra of fine in plane spatial resolution (5 mm) with good quality to be measured in 7.5 min. Tailored spiral in-out spectral-spatial water suppression enables efficient high resolution magnetic resonance spectroscopic imaging in the brain. Magn Reson Med 79:31-40, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

High Resolution Magnetic Anomaly Modelling and its Implication for Petroleum Prospectively on Seram Island, Maluku, Indonesia

An airborne magnetic survey was conducted over Seram Island in 2012. The Total Magnetic Intensity ranged from 41,565.7 nT to 41,715.2 nT. High anomaly were observed with a range between 41,665.7 nT and 41,715.2 nT. These anomalies were predominately located in western part of the survey area with some small high frequencies and a long wave length anomalies present in the southeastern part of the island. The high anomalies have been interpreted as Paleozoic rocks of Taunusa Formation. Medium anomaly range from 41,618.9 nT to 41,665.7 nT are present in the east, northeast and west northwest of Seram Island. This magnetic response has been interpreted to reflects the occurence of Mesozoic rocks from Kanikeh Formation. The low magnetic anomalies which range from 41,565.7 nT to 41,618.9 nT are present in the centre and northeast of the island, and reflects the occurence of Jurassic Manusela Formation. Modelling of the high resolution magnetic anomalies, constrained by well data information, confirms the rock stratigraphy while also indicates folds, thrust fault structures and basement fractures being present over the survey area. The occurence of hydrocarbons in the area have been interpreted to be associated with traps in basement fractures. Areas with similar tectonic structure, as interpreted from the high resolution magnetic data, represent a high potential for the presence of further hydrocarbons. The recommended areas are dominated by basement fractures and thrust fault structures. The modelling shows that the source rock, the Jurassic Kanikeh Formation, has thickness of about 2,623.5 metres. The Kanikeh Formation is estimated to have high porosity because it consists of fractured sandstone (Tjokrosaputro et. al., 1993). From the modelling it is also observed that the cap-rock, the Jurassic sedimentary rocks, have thickness reached of about 1,166 metres.

Magnetic and Gravity Gradiometry Framework for Mesoproterozoic Iron Oxide-Apatite and Iron Oxide-Copper-Gold Deposits, Southeast Missouri

High-resolution airborne magnetic and gravity gradiometry data provide the geophysical framework for evaluating the exploration potential of hidden iron oxide deposits in Mesoproterozoic basement rocks of southeast Missouri. The data are used to calculate mineral prospectivity for iron oxide-apatite (IOA) ± rare earth element (REE) and iron oxide-copper-gold (IOCG) deposits. Results delineate the geophysical footprints of all known iron oxide deposits and reveal several previously unrecognized prospective areas. The airborne data are also inverted to three-dimensional density and magnetic susceptibility models over four concealed deposits at Pea Ridge (IOA ± REE), Boss (IOCG), Kratz Spring (IOA), and Bourbon (IOCG). The Pea Ridge susceptibility model shows a magnetic source that is vertically extensive and traceable to a depth of greater than 2 km. A smaller density source, located within the shallow Precambrian basement, is partly coincident with the magnetic source at Pea Ridge. In contrast, the Boss models show a large (625-m-wide), vertically extensive, and coincident dense and magnetic stock with shallower adjacent lobes that extend more than 2,600 m across the shallow Precambrian paleosurface. The Kratz Spring deposit appears to be a smaller volume of iron oxides and is characterized by lower density and less magnetic rock compared to the other iron deposits. A prospective area identified south of the Kratz Spring deposit shows the largest volume of coincident dense and nonmagnetic rock in the subsurface, and is interpreted as prospective for a hematite-dominant lithology that extends from the top of the Precambrian to depths exceeding 2 km. The Bourbon deposit displays a large bowl-shaped volume of coincident high density and high-magnetic susceptibility rock, and a geometry that suggests the iron mineralization is vertically restricted to the upper parts of the Precambrian basement. In order to underpin the evaluation of the prospectivity and three-dimensional models, an extensive statistical summary of density and apparent magnetic susceptibility measurements is presented that includes data on several hundred samples taken from the deposits, altered wall rocks, and unaltered country rocks.

The Dynamic Basis for Signal Propagation in Human Pin1-WW

Allostery is the structural manifestation of information transduction in biomolecules. Its hallmark is conformational change induced by perturbations at a distal site. An increasing body of evidence demonstrates the presence of allostery in very flexible and even disordered proteins, encouraging a thermodynamic description of this phenomenon. Still, resolving such processes at atomic resolution is difficult. Here we establish a protocol to determine atomistic thermodynamic models of such systems using high-resolution solution state nuclear magnetic resonance data and extensive molecular simulations. Using this methodology, we study information transduction in the WW domain of a key cell-cycle regulator Pin1. Pin1 binds promiscuously to phospho-Ser/Thr-Pro motifs, however, disparate structural and dynamic responses have been reported upon binding different ligands. Our model consists of two topologically distinct states whose relative population may be specifically skewed by an incoming ligand. This model provides a canonical basis for the understanding of multi-functionality in Pin1.

A new tectonic model for the Palaeoproterozoic Kautokeino Greenstone Belt, northern Norway, based on high-resolution airborne magnetic data and field structural analysis and implications for mineral potential

A new tectonic model for the Palaeoproterozoic Kautokeino Greenstone Belt, northern Norway, based on high-resolution airborne magnetic data and field structural analysis and implications for mineral potential

The Paleoproterozoic Singo granite in south-central Uganda revealed as a nested igneous ring complex using geophysical data

We used high-resolution airborne magnetic and radiometric data and satellite gravity data to investigate the form of occurrence of the Paleoproterozoic Singo granite in west-central Uganda. This granitic body covers an area of ∼700 km2, intrudes Paleoproterozoic crystalline rocks and overlain by Paleoproterozoic-Mesoproterozoic sedimentary rocks, both of which belong to the Rwenzori terrane, and it is host to hydrothermally-formed economic minerals such as gold and tungsten. Our analysis provided unprecedented geometrical details of the granitic body and revealed the following: (1) the margins of the Singo granite are characterized by a higher magnetic signature compared to the interior of the granitic body as well as the surroundings. These anomalies are apparent in both the total magnetic field and horizontal derivative images and define eight overlapping ring features. (2) the depth continuation of these magnetic anomalies define outward but steeply-dipping features as indicated by the tilt images extracted from the airborne magnetic data. This is further supported by forward modeling of the magnetic and gravity data. (3) the Singo granite is characterized by relatively high and evenly-distributed equivalent concentration of Uranium (eU) and Thorium (eTh) compared to the surroundings and this is apparent in the Potassium (K)-eTh-eU radiometric ternary image. (4) the granitic body is defined by a gravity low anomaly that persisted to a depth of three km as shown by the Bouguer anomaly image and its five km upward continuation. We used these observations to identify this granitic body as a nested igneous ring complex and we refer to it as the Singo Igneous Ring Complex (SIRC). We further interpreted the eight ring structures as individual igneous ring complexes aligned in an E–W and NE–SW direction and these were developed due to repeated calderas collapse. Additionally, we interpreted the ring-shaped magnetic anomalies as due to hydrothermally-altered margins of the granite resulting from hot fluid circulation facilitated by the presence of concentric fracture zones that developed in association with the collapse of the calderas. We propose that the nested pattern of the SIRC was developed due to dominantly east and southwest migration of magma plumbing systems. Identifying the SIRC as a nested igneous ring complex has its importance in guiding future mineral exploration activities. Our study highlights the importance of high resolution geophysical data in mapping near surface igneous ring complexes, hence allowing for further examination of their magma plumbing systems.

High resolution δ13CTOC and magnetic susceptibility data from the late Early Pleistocene southern margins of the Chinese Loess Plateau

On the Chinese Loess Plateau, stable carbon isotope values for total organic matter (δ13CTOC) from more than 10 loess/paleosol sequences since the last glacial/interglacial show generally consistent variations, with enriched values normally occurring in paleosol layers. The only exceptions are records from the westernmost and northwestern Chinese Loess Plateau. However, both Asian summer monsoon intensity and temperature have been suggested as the principal factor affecting these consistently similar δ13CTOC variations. Until now, δ13CTOC records covering the whole Quaternary have been relatively rare, with problems including low resolution and conflicts in both the C4 expansion history and with related climatic interpretations. In this paper, we report on high resolution, late Early Pleistocene low-frequency magnetic susceptibility (χlf) and δ13CTOC data from Yushan section on the southern margins of the Chinese Loess Plateau. Our δ13CTOC data present an abstruse relation with the glacial/interglacial cycles represented by loess/paleosol sequences, with δ13C-enriched excursions in some paleosol layers and δ13C-depleted excursions in others. Furthermore, our δ13CTOC data shows negative and positive correlations with χlf data, using a threshold χlf value of 70×10−8m3/kg. If the χlf data are taken as an indicator of pedogenetic intensity, and therefore an indicator of Asian summer monsoon intensity, there are two possible relations between Chinese loess δ13CTOC and Asian summer monsoon intensity, i.e. the Chinese loess δ13CTOC cannot simply be adopted as the sole indicator of Asian summer monsoon intensity, at least during the late Early Pleistocene on the southern margins of the Chinese Loess Plateau. Our results demonstrate that C4 plants became a significant proportion of local vegetation cover only when Asian summer monsoon intensity exceeded a certain degree, for example, in the surface vegetation for the S15 and S16 paleosol layers of the Yushan section. The relation between climate and Chinese loess δ13CTOC requires further, detailed study.

Geophysical mapping of Vercelli Seamount: Implications for Miocene evolution of the Tyrrhenian back arc basin

Since the Tortonian, the geodynamic evolution of the Tyrrhenian Sea has been driven by an eastward roll-back of the entire Apennine subduction system, triggering distinct episodes of back-arc basin formation with spots of oceanic crust. Major structural differences are observed between northern and southern portions of the Tyrrhenian Sea, reflecting two distinct evolution stages of the Ionian slab retreat. In the central portion of the Tyrrhenian Sea, the seafloor morphology is characterized by a set of magmatic intrusions and structural highs associated to an E–W magnetic lineament along the 41st geographical parallel. The Vercelli seamount represents one example of structural highs correlated to Miocene magmatic episodes along the 41st parallel zone. In this study, we discuss the results of new high resolution magnetic data and morphological mapping of the Vercelli seamount acquired during the VER2010 cruise. The seamount represents the relict part of a granitic intrusion emplaced during the Tortonian phase of Tyrrhenian rifting. Tectonic and deep-sea erosive processes have jointly modified the seamount structure that can be observed nowadays. Cumulative gradient analysis highlights an asymmetric morphology of the flanks as a result of erosive action of opposite water mass gyres which modelled the southern portion of the seamount. The joint interpretation of magnetic and bathymetric datasets identifies a high magnetized source laying close to the base of the seamount and located in correspondence to a small basin. This structure has been modelled as a post-Tortonian lava sequence emplaced between structural highs in correspondence of N–S elongated flat sedimentary basin. Modelling of new geophysical data highlights the relationship between crustal setting and magnetic evidences of the central Tyrrhenian Sea, providing a new interpretation of the 41st magnetic lineament.

Regional 3D geophysical investigation of the Sudbury Structure

The 3D geologic and structural setting of the Sudbury Structure was predicted by an integration of surface and subsurface geologic data with 2.5D modeling of high-resolution airborne magnetic and gravity data using 3D GeoModeller software. Unlike other CAD-based 3D software, GeoModeller uses the field interpolator method, whereby contacts of rock units are assumed to be equipotential surfaces, whereas orientation data determine the gradient and direction of the surfaces. Contacts and orientation variables are cokriged to generate 3D continuous surfaces for each geologic unit. Our 3D geologic model was qualitatively evaluated by forward computing the predicted gravity response at 1 m above topography and by comparing this response to the measured gravity field. Large-scale structures within the Onaping Formation and Archean basement, which overlie and underlie the Sudbury Igneous Complex (SIC), respectively, were not the cause of the linear gravity high in the center of the Sudbury Structure. We suggested that the deformation of the initial circular SIC may have commenced under the Sudbury Basin due to the reversal of the normal faults related to the Huronian rift system during the Penokean orogeny, therefore resulting into a north verging fold at the base of the SIC in the south range. This new interpretation was consistent with the magnetic and gravity data and honoured most of the significant seismic reflectors in the Lithoprobe seismic sections.

Extent, kinematics and tectonic origin of the Precambrian Aswa Shear Zone in eastern Africa

The Aswa Shear Zone (ASZ) is a fundamental Precambrian lithospheric structure that has been shaped by many tectonic events in eastern Africa. It separates the Saharan Metacraton in the northeast from the Northern Uganda terrane (which represents part of the Northeastern Congo block of the Congo craton) to the southwest. Nonetheless, its tectonic evolution is not fully understood. We used high-resolution airborne magnetic and radiometric data over Uganda integrated with Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) in South Sudan to assess the extent, kinematics and contribute to the understanding of the tectonic origin of the ASZ. (1) Our results showed that the ASZ extends in a NW–SE direction for ~550km in Uganda and South Sudan. (2) The airborne magnetic and radiometric data revealed a much wider (~50km) deformation belt than the 5-10km of the exposed surface expression of the ASZ. The deformation belt is defined by three NW-trending sinistral strike-slip shear zones bounding structural domains with magnetic fabric showing splays of secondary shear zones and shear-related folds. These folds are tighter close to the discrete shear zones with their axial traces becoming sub-parallel to the shear zones. A similar fold pattern is observed in South Sudan from the SRTM DEM. We interpreted these folds as due to ENE–WSW contraction associated with the sinistral strike-slip movement. (3) To the northeast, the magnetic patterns and radiometric signatures suggest the presence of a series of W-verging nappes indicative of strong E–W to NE–SW contraction deformation. (4) We relate the evolution of the ASZ to E–W to NE–SW Neoproterozoic oblique collision between East and West Gondwana. The deformation related to this collision was partitioned into E–W to NE–SW contraction resulting in W-verging thrusts in the east and a sinistral strike-slip movement along the NW-trending ASZ with the strain localized at the boundary between the Saharan Metacraton and the Northern Uganda terrane.

Correlating carbon and oxygen isotope events in early to middle Miocene shallow marine carbonates in the Mediterranean region using orbitally tuned chemostratigraphy and lithostratigraphy.

During the Miocene prominent oxygen isotope events (Mi‐events) reflect major changes in glaciation, while carbonate isotope maxima (CM‐events) reflect changes in organic carbon burial, particularly during the Monterey carbon isotope excursion. However, despite their importance to the global climate history they have never been recorded in shallow marine carbonate successions. The Decontra section on the Maiella Platform (central Apennines, Italy), however, allows to resolve them for the first time in such a setting during the early to middle Miocene. The present study improves the stratigraphic resolution of parts of the Decontra section via orbital tuning of high‐resolution gamma ray (GR) and magnetic susceptibility data to the 405 kyr eccentricity metronome. The tuning allows, within the established biostratigraphic, sequence stratigraphic, and isotope stratigraphic frameworks, a precise correlation of the Decontra section with pelagic records of the Mediterranean region, as well as the global paleoclimatic record and the global sea level curve. Spectral series analyses of GR data further indicate that the 405 kyr orbital cycle is particularly well preserved during the Monterey Event. Since GR is a direct proxy for authigenic uranium precipitation during increased burial of organic carbon in the Decontra section, it follows the same long‐term orbital pacing as observed in the carbon isotope records. The 405 kyr GR beat is thus correlated with the carbon isotope maxima observed during the Monterey Event. Finally, the Mi‐events can now be recognized in the δ18O record and coincide with plankton‐rich, siliceous, or phosphatic horizons in the lithology of the section.

Timing of the Matuyama–Brunhes geomagnetic reversal: Decoupled thermal maximum and sea-level highstand during Marine Isotope Stage 19

Recent high-resolution magnetic and microfossil data from a long core penetrating the Osaka Group, Japan are astronomically tuned and reassessed to reveal detailed stratigraphic features across the Matuyama–Brunhes (MB) polarity transition during Marine Isotope Stage (MIS) 19. The sediments have a uniform and high average accumulation rate of 63 cm/ky. Astronomical tuning based on six calibration points, including a clear MIS 19.2 sea-level lowstand, dates the main MB boundary (MBB) to 777.6 ka, the sea-level peak of the MIS 19.3 highstand to 780.7 ka, and the climatic thermal maximum (TM) to 776.4 ka. The MB transition began with a short-lived normal polarity episode that occurred before the highstand at MIS 19.3, and terminated with multiple rapid reversals that occurred between highstand MIS 19.3 and lowstand 19.2. The TM just postdates the termination of the MB transition, and occurs about 4000 years after the sea-level peak. The delayed TM is also observed at Gesher Benot Ya'aqov, Israel and on the Mediterranean coast, and possibly at Lake Baikal. In high-resolution records from Chinese loess–paleosols and deep-sea sediments, the rapid reversal zone of the MBB has a very similar climatostratigraphic character. These magneto-climatostratigraphic features in MIS 19 are useful for correlating between terrestrial and marine sediments. The delay in warming relative to the sea-level highstand seems to have been due to a cloud-albedo effect induced by an increase in galactic cosmic ray flux during an extremely low magnetic field intensity interval.

Mapping horizons and fracture patterns in coal measures using magnetics for coalbed methane exploration in Queensland

High resolution magnetic data has successfully been used to map the top and base of coal measures, related faults and fracture patterns across the Red Hill area in the northern Bowen Basin, eastern Australia. A horizon mapping technique, based on energy spectral analysis (ESA), was used to detect magnetic susceptibility contrasts that were laterally merged to form two magnetic interfaces, corresponding to the top of the Fair Hill Formation and base of the Goonyella Middle Seam in the Permian Moranbah coal measures. The depth estimates were made at stations on a regular mesh of 400 m x 400 m and at nine wells. The final detailed mapping of both horizons was constructed from spectral depth estimates on a regular mesh of 100 m x 100 m. Major faults, associated structures and fractures were mapped in 3D from the magnetic data by using automatic curve matching (ACM). This technique was applied to detect single magnetic anomalies produced by inter-sedimentary sources. These results were used to interpret magnetic lineaments in, above and below the coal measures to produce a rock fabric model. The results obtained from the interpretation of the magnetic data are consistent with structures mapped from existing seismic and well data. The mapped rock fabric was also confirmed by well results to be a fair representation of the open fracture set, which has an orientation that is consistent with the existing stress regime.

Connecting onshore-offshore Campos Basin structures: Interpretation of high-resolution airborne magnetic data

We interpreted northwest-trending transfer faults whose extensions are not entirely mapped in the Precambrian basement of the onshore and offshore Campos Basin. To enhance the subtle northwest–southeast lineaments not clearly seen in the total-field data, we reprocessed and merged two airborne magnetic data sets aiming at producing a single merged magnetic data set. Next, we applied a directional filter to these integrated magnetic data. Finally, we applied a multiscale edge detection method to these filtered data. This combination allowed the detection of edges and ridges that are used to produce several northwest–southeast lineations. We interpreted these northwest-trending lineations as magnetic expressions of transfer faults that cut across the onshore adjacent basement of the Campos Basin to the shallow and deep Campos Basin waters. These interpreted northwest-trending faults suggested the continuity of the known northwest-striking transfer faults in the deep Campos Basin waters toward the shallow Campos Basin waters and the adjacent continent. Moreover, our interpreted northwest-trending faults revealed the control of several known oilfields in the Campos Basin. This result supported the hypothesis of the influence of the northwest–southeast-trending transfer faults on the petroleum system of Campos Basin, which were reactivated in the Tertiary providing a pathway for the turbidite sedimentation, reworking, and redistribution of several deepwater reservoirs. In addition, it was hypothesized that this faulting system controlled the hydrocarbon migration paths from the presalt source rocks through salt windows into basal suprasalt layers.

Regional Brain Morphometric Characteristics of Nonsyndromic Cleft Lip and Palate

Nonsyndromic cleft lip and palate (NSCLP) encompasses a group of orofacial abnormalities. Emerging evidence has revealed the presence of structural brain abnormalities in affected individuals. Previous studies have performed structure-based volumetric analysis of the brain assessing gross lobular subdivisions of the cerebral cortex and white matter which may have only vague relationships to the functional subregions implicated in behavioral and cognitive deficits observed in NSCLP patients. High-resolution magnetic resonance imaging structural data were acquired to provide a detailed characterization of the brain with respect to both regional cortical volume and thickness in 26 children with NSCLP and 26 age- and demographically matched typically developing children. Children with NSCLP exhibited abnormally large cerebral cortex grey matter volumes with decreased volumes of subcortical grey matter and cerebral white matter structures. Hemisphere-specific patterns of cortical volume and thickness abnormalities were identified. This study is the first to examine cortical thickness abnormalities in NSCLP. Overall, these findings suggest that the brains of children with NSCLP are less mature than those of their age-matched peers. Gender-specific comparisons reveal that NSCLP females were more immature compared to their typically developing peers compared to NSCLP males.

Application of high resolution airborne geophysical data in geological modelling of Mohar Cauldron Complex, Bundelkhand Massif, central India: implications for uranium exploration

The Mohar cauldron, located near Mohar village, Shivpuri District, Madhya Pradesh, India, represents an explosive felsic volcanic event. The Mohar Cauldron Complex (MCC) is an important target area for uranium exploration as collapse breccias associated with extensional tectonics are traditionally important for multi-metal deposits, including uranium. Advanced processing and interpretation of the high resolution airborne electromagnetic (AEM), magnetic and radiometric data acquired over the Mohar cauldron and the surrounding environs by Fugro Airborne surveys, successfully mapped the major geological domains in the area based on their distinct geophysical characteristics. Interpretation of the data indicated the presence of three felsic intrusive bodies, only one of which, the MCC, reached the surface and collapsed. Variation in the geophysical characteristics of the three bodies is attributed to variations in hydrothermal alteration. Magnetic signature and radiometric response of the MCC and surrounding area also show signs of intense alteration. AEM data has allowed the boundary of the sediments within the MCC to be mapped accurately, along with the surrounding brecciated zone. Conductivity depth imaging calculated to a depth of 500 m clearly indicated the geometry and disposition of different layers of MCC. 3D voxel modelling of the MCC also allowed for the identification of the different lithologies that constitute the cauldron structure. 3D conductivity isosurfaces provided a thorough understanding of the subsurface distribution of conductivities.

Regional vegetation patterns at lake Son Kul reveal Holocene climatic variability in central Tien Shan (Kyrgyzstan, Central Asia)

A multiproxy study was conducted on Holocene sediments from the alpine lake Son Kul (3010 m a.s.l, 41°48′33N/75°07′38E) in central Tien Shan (Kyrgyzstan). The combination of high-resolution pollen, palynofacies and magnetic susceptibility data allowed reconstruction of changes in sedimentary and vegetation dynamics regionally at Son Kul between 8350 and ca 2000 cal. BP. Using pollen data to quantify climatic parameters, a quantitative reconstruction of climatic conditions was performed using the “Modern Analogue Vegetation types” (MAV) method and a ranged index of seasonality. The most temperate (e.g. moister) climate conditions occurred between 8350 and 5000–4500 cal. BP when alpine meadow vegetation was enriched in plants requiring moister conditions and trees developed regionally. Conversely, more continental and arid conditions prevailed after 4500 cal. BP with the decline of arboreal vegetation (especially Juniperus) and the extension of an alpine steppe-meadow along with a regional decrease in Poaceae. This climate transition was associated with a change in seasonality as the continentality greatly intensified after 5000–4500 cal. BP. Our results are consistent with other records from the Tien Shan range and the Chinese Province Xinjiang showing that relatively wet conditions prevailed regionally before 5000 cal. BP, whereas reduced moisture conditions were established after that time. From a more global perspective, we highlight that regional rainfall in central Tien Shan and western Central Asia is likely to be predominantly controlled by the Eastern Mediterranean cyclonic system and North Atlantic climate, as based on the close correspondence between climatic archives from western Central Asia, the Levant, the Eastern Mediterranean and Caspian Sea regions. However, the effect of monsoonal dynamics on the regional climatic system in central Tien Shan still remains dubious, since recent modelling studies have shown that no dynamic link exists between humidity in Central Asia and the Indian Summer Monsoon. This study pinpoints the need to explore the effect of remote Eurasian atmospheric circulation patterns on past climate variability in Central Asia.

Improved salt imaging in a basin context by high resolution potential field data: Nordkapp Basin, Barents Sea

ABSTRACTThe seismic imaging of salt diapirs in the Nordkapp Basin gave rise to considerable problems in defining their shape and volume. Independent information was added by integrating the interpretation with high resolution gravity and magnetic data. We developed a novel, iterative workflow, separated into sub‐categories: sediments, salt structures, basement and Moho. Distinctions between the sources of the anomalies from different depths was achieved by utilizing the different decay characteristics of gravity, gravity gradiometry and high resolution magnetic anomalies. The workflow was applied to the southern part of the Nordkapp Basin. It started with the sedimentary model derived from seismics, populated with measured densities and magnetic susceptibilities and a starting model for the base salt. The residual after the removal of this model was interpreted in terms of a crustal model, including flexural isostatic calculations for the Moho with the sedimentary load. The residual after the removal of crustal and early sedimentary model was used to tune the salt model. As these major and minor modelling steps depend on each other, an iterative process was applied to stepwise improve the density and magnetic susceptibility model. The first vertical gradient of gravity and the magnetic field were found to give most information about the cap rock of the diapirs. The improvement in salt imaging, integrated with results from controlled‐source electromagnetic and magneto‐telluric modelling is shown for the salt diapir Uranus, where a well, terminated in the salt, constrains the minimum of the depth to base salt.

The St Lawrence Platform and Appalachian deformation front in the St Lawrence Estuary and adjacent areas (Quebec, Canada): structural complexity revealed by magnetic and seismic imaging

AbstractNew magnetic and seismic datasets offer a unique opportunity to document the geometry of the Appalachian front in a poorly studied segment of the orogen. Interpretation of high-resolution magnetic data allows, for the first time, the documentation of the contact between the autochthonous St Lawrence Platform and the Appalachians and highlights the regional significance of previously poorly documented ENE faults that experienced post-Ordovician strike-slip motion. Seismic data reveal tectonic slices in the foreland domain underlying the Appalachians and show that the depth of the décollement at the base of the Appalachian tectonic wedge varies significantly. Taken together, geological, magnetic and seismic data suggest that the geometry of the Appalachian front exhibits significant variations in map and cross-section views and recorded a polyphased structural history.