scholarly journals Seismological Investigations in the Olduvai Basin and Ngorongoro Volcanic Highlands (Western Flank of the North Tanzanian Divergence)

2020 ◽  
Vol 91 (6) ◽  
pp. 3286-3303 ◽  
Author(s):  
Laura Parisi ◽  
Ian Stanistreet ◽  
Jackson Njau ◽  
Kathy Schick ◽  
Nicholas Toth ◽  
...  
Keyword(s):  
Sedimentary Basins ◽  
Quality Analysis ◽  
Fault System ◽  
Conservation Area ◽  
Data Set ◽  
The North ◽  
Western Flank ◽  
Passive Seismic ◽  
African Rift ◽  
Western Side

Abstract We present data and results of a passive seismic experiment that we operated between June 2016 and May 2018 in the Ngorongoro Conservation Area (northern Tanzania), located on the western side of the eastern branch of the Eastern African Rift (EAR) system. The motivation for this experiment is twofold: (1) investigating the extension of the Olduvai basin, referred to also as the “Cradle of Human Mankind,” as it hosted a variety of paleoenvironments exploited by hominins during their evolution; and (2) studying the link between the fault system in the main EAR and in its western flank. We conduct detailed data-quality analysis of the seismic recordings based upon ambient noise characterization and numerical waveform simulations. Our data set is of good quality, and we observe that local magnitude can be overestimated up to at least 0.23, due to wave-amplifications effects occurring at sites with loose sedimentary material. Based on a new but simple approach using power spectral density measurements, we calculate the thickness of sedimentary basins. This allows us to map the bottom of the Olduvai paleolake confirming that its sedimentary record may be at least 200 m deeper than previously inferred from core drilling. We also map the bottom of the Olbalbal depression for the first time. In addition, we present a seismicity map of the Ngorongoro Conservation Area with unprecedented detail. The seismicity depicts the suture zone between the Tanzanian craton and the Mozambique belt and reveals that the fault system in the western flank of the rift merges at depth into a single detachment that joins the Manyara fault on the western side of the main rift valley.

scholarly journals A review of the Pan-African evolution of the Arabian Shield

GeoArabia ◽  
2002 ◽  
Vol 7 (1) ◽  
pp. 103-124 ◽  
Author(s):  
Pierre Nehlig ◽  
Antonin Genna ◽  
Fawzia Asfirane ◽  
C. Guerrot ◽  
J.M. Eberlé ◽  
...  
Keyword(s):  
Structural Evolution ◽  
Sedimentary Basins ◽  
Fault Zones ◽  
Fault System ◽  
Arabian Shield ◽  
Geologic History ◽  
Lower Paleozoic ◽  
The North ◽  
Pan African ◽  
History Of

ABSTRACT Recent fieldwork and the synthesis and reappraisal of aeromagnetic, geologic, structural, geochemical, and geochronologic data have provided a new perspective on the structural evolution and geologic history of the Arabian Shield. Although Paleoproterozoic rocks are present in the eastern part of the Shield, its geologic evolution was mainly concentrated in the period from 900 to 550 Ma during which the formation, amalgamation, and final Pan-African cratonization of several tectonostratigraphic terranes took place. The terranes are separated by major NW-trending faults and by N-, NW- and NE-oriented suture zones lined by serpentinized ultramafic rocks (ophiolites). Terrane analysis using the lithostratigraphy and geochronology of suture zones, fault zones, overlapping basins, and stitching plutons, has helped to constrain the geologic history of the Arabian Shield. Ophiolites and volcanic-arcs have been dated at between 900 and 680 Ma, with the southern terrane of Asir being older than the Midyan terrane in the north and the Ar Rayn terrane in the east. Final cratonization of the terranes between 680 and 610 Ma induced a network of anastomosing, strike-slip faults consisting of the N-trending Nabitah belt, the major NW-striking left-lateral transpressive faults (early Najd faults), lined by gneiss domes and associated with sedimentary basins, and N- to NE-trending right-lateral transpressive faults. Following the Pan-African cratonization, widespread alkaline granitization was contemporaneous with the deposition of the Jibalah volcanic and sedimentary rocks in transtensional pull-apart basins. Crustal thinning was governed by the Najd fault system of left-lateral transform faults that controlled the formation of the Jibalah basins and was synchronous with the emplacement of major E- to NW-trending dike swarms throughout the Arabian Shield. The extensional episode ended with a marine transgression in which carbonates were deposited in the Jibalah basins. Continuation of the thinning process may explain the subsequent deposition of the marine formations of the lower Paleozoic cover. Our interpretation of the distribution and chronology of orogenic zones does not correspond entirely to those proposed in earlier studies. In particular, the N-trending Nabitah and NW-trending Najd fault zones are shown to be part of the same history of oblique transpressional accretion rather than being two distinct events related to accretion and dispersion of the terranes.

scholarly journals Measurements of the dissolved inorganic carbon system and associated biogeochemical parameters in the Canadian Arctic, 1974–2009

2014 ◽  
Vol 6 (1) ◽  
pp. 91-104 ◽  
Author(s):  
K. E. Giesbrecht ◽  
L. A. Miller ◽  
M. Davelaar ◽  
S. Zimmermann ◽  
E. Carmack ◽  
...  
Keyword(s):  
Quality Control ◽  
Inorganic Carbon ◽  
Dissolved Inorganic Carbon ◽  
Canadian Arctic ◽  
The Arctic ◽  
Data Set ◽  
The North ◽  
Western Side ◽  
Biogeochemical Parameters ◽  
Carbon System

Abstract. We have assembled and conducted primary quality control on previously publicly unavailable water column measurements of the dissolved inorganic carbon system and associated biogeochemical parameters (oxygen, nutrients, etc.) made on 26 cruises in the subarctic and Arctic regions dating back to 1974. The measurements are primarily from the western side of the Canadian Arctic, but also include data that cover an area ranging from the North Pacific to the Gulf of St. Lawrence. The data were subjected to primary quality control (QC) to identify outliers and obvious errors. This data set incorporates over four thousand individual measurements of total inorganic carbon (TIC), alkalinity, and pH from the Canadian Arctic over a period of more than 30 years and provides an opportunity to increase our understanding of temporal changes in the inorganic carbon system in northern waters and the Arctic Ocean. The data set is available for download on the CDIAC (Carbon Dioxide Information Analysis Center) website: http://cdiac.ornl.gov/ftp/oceans/IOS_Arctic_Database/ (doi:10.3334/CDIAC/OTG.IOS_ARCT_CARBN).

Surface and subsurface fault mapping in the Yorkshire Wolds, UK

2020 ◽  
Author(s):  
Rowan Vernon ◽  
Jon Ford ◽  
Katie Watkinson ◽  
Richard Haslam ◽  
Mark Woods ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Geological Mapping ◽  
Fault System ◽  
British Geological Survey ◽  
Field Mapping ◽  
Northern Margin ◽  
The North ◽  
Passive Seismic ◽  
History Of ◽  
Environment Agency

<p>The Flamborough Head Fault Zone (FHFZ) marks the southern extent of the Cleveland Basin and the northern margin of the Market Weighton Block, England. It is a regionally-significant structural zone which has undergone a complex history of Mesozoic-Cenozoic extension and compression. It is predominantly comprised of east-west trending faults which form a graben that is dissected by north-south trending faults, including the southern extension to the Peak Trough, the Hunmanby Fault. To the west, FHFZ links with the Howardian Fault System and offshore, in the east, it is truncated by the north-south trending Dowsing Fault. The FHFZ is well exposed and described from coastal cliff sections at Flamborough Head but the inland development of the faults have hitherto been poorly explored predominantly due to limited inland-exposure.</p><p>The region around the FHFZ is underlain by the Chalk Group, a 500 m thick limestone succession. The Chalk Group is a principal aquifer that is the main source of water supply in East Yorkshire. The geometry and physical characteristics of the Chalk succession, including the effects of faulting, influence groundwater flow across the region. A range of modern data and recent geological research highlight that considerable changes can be made to the region’s current geological maps and subsurface understanding. Ensuring these features are better-documented is key for up-dating groundwater models to enable more confident decisions about land-use, water management and environmental regulation.</p><p>A multi-faceted approach to geological mapping has been undertaken in the region by the British Geological Survey (BGS), in collaboration with the Environment Agency. Remote sensing and field mapping of the superficial deposits has better characterised the extent and nature of these deposits and identified potential recharge ‘windows’ into the bedrock. Remote sensing, targeted field mapping, palaeontological analysis, passive seismic and 2D onshore seismic interpretation have been integrated to produce a new map of the Chalk succession, which reveals the inland extension of the FHFZ in unprecedented detail. Combining these techniques has enabled us to bridge the gap between the surface geology and deeper subsurface structure, increase our understanding of the geology of the region and produce an improved conceptual model at a range of depths which will be used to better manage water resources.</p>

scholarly journals Integrated geophysical investigations of deeper stratigraphy of the Irish Rockall Basin

2021 ◽  
Author(s):  
Gaurav Tomar ◽  
Srikumar Roy ◽  
Christopher J. Bean ◽  
Satish C. Singh ◽  
Brian O'Reilly ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
Sedimentary Basins ◽  
Moho Depth ◽  
The South ◽  
Data Set ◽  
Late Mesozoic ◽  
The North ◽  
Stretching Factor ◽  
The Uk ◽  
Early Cenozoic

<p>The Rockall Trough is an elongate bathymetric depression trending NNE-SSW. It is approximately 1200 km long and up to 300 km wide, extending over the UK and Irish continental margins. The trough is underlain by the Rockall Basin, which forms part of a chain of late Paleozoic-Cenozoic sedimentary basins. The Irish Rockall Basin is vastly unexplored as compared to the UK sector, where extensive flood basalt lava flows, sill complexes and volcanic centers of Late Cretaceous-to-Early Eocene age have been described, which belong to the North Atlantic Igneous Province (NAIP) (Archer et al., 2005). An integrated study of seismic, gravity and magnetic methods elucidates the deeper stratigraphy of the Irish Rockall Basin. More than 10 km of sediments is present in the central part of the basin. We perform first arrival travel time tomography on a downward continued data set of three seismic profiles to model the velocity of the sedimentary structures down to 6 km depth. To better understand the deep structure of the basin we need to estimate the Moho depth from constrained gravity modelling. The modelling results indicate that the Moho depth varies from 12 km to 20 km depth beneath ~10 km thick sediments in the basin. This allows us to measure the crustal stretching factor β. The minimum stretching factor in the basin varies between ~7 in the north to ~6.5 in the south. These values are within the range needed for mantle serpentinisation (O'Reilly et al., 1996; Perez-Gussinye and Reston, 2001). Furthermore, we observe four volcanic ridges in the south part of the basin, which are ~20 km wide and ~ 3 km thick, possibly comprising the Barra Volcanic Ridge System (BVRS) (Scrutton and Bentley, 1988). Results indicate several failed rifting attempts times in late Mesozoic/early Cenozoic times, generating significant basic volcanism, associated with the NAIP. We resolve new volcanic ridges (of late Mesozoic/early Cenozoic age) in the southern part of the Rockall Basin, like many other volcanic ridges/centres observed in other parts of the basin, with correlatable magnetic and gravity anomalies. These may be of late Cretaceous age similar to those found on the conjugate Canadian margin.</p>

Illegal rattan extraction trends in the Ankasa Conservation Area in Ghana

2018 ◽  
Vol 2 (3) ◽  
pp. 84-92
Author(s):  
R. Obour, D. Amankwaa, A. Asare
Keyword(s):  
Protected Areas ◽  
Biological Diversity ◽  
Forest Products ◽  
Simple Random Sampling ◽  
Sampling Techniques ◽  
Snowball Sampling ◽  
Conservation Area ◽  
Forest Reserve ◽  
The North ◽  
Non Timber Forest Products

Protected Areas (PAs) are created for the protection and maintenance of biological diversity, but many of Ghana’s PAs are subjectto severe pressures and threats, the main pressures being the illegal extraction of natural resources. Rattans are indisputablyone of the most important Non-Timber Forest Products (NTFPs) in Ghana’s Protected Areas that is without doubt one of thereasons for which it has drawn the attention of researchers. In this study the illegal rattan extraction patterns in the AnkasaConservation Area (ACA) in Ghana was inspected. Simple random sampling and Snowball sampling techniques were used. Datacollection employed the use of semi-structured questionnaires, interviews and field enumeration of rattans as well as an analysisof Effective Patrol Man-days (EPMDS) from 2004 to 2012. The results showed a significant positive correlation (r = 0.75, p<0.05, r2 = 0.557) between patrol effort and rattan extraction encounters. In addition, there was a general reduction in illegalrattan extraction encounters from 2004 to 2012 at a rate of 4.3 per year. The highest illegal rattan extraction incidences wererecorded in 2006 (76 encounters), 2005 (35 encounters), 2008 (22 encounters), 2004 (18 encounters) and the least incidencewere recorded in both 2010 (3 encounters) and 2011 (3 encounters).The research also revealed that Eremospatha macrocarpawas the most extracted rattan species followed by Laccosperma secundiflorum. The major rattan extraction and trade routesoriginate in the northern parts and in the area east of the reserve and also south of Draw River Forest Reserve. Generally, rattanpoaching in Ankasa Conservation Area has declined, but there are still human incursions in the northern part of the reserve. Thestudy recommended an intensification of patrols in the north of the reserve. Also, enrichment planting and Agroforestry practicesof inter-cropping rattans with seasonal crops should be pursued vigorously for the local communities.

Hydrothermal activity in the Upper Permian Ravnefjeld Formation of central East Greenland – a study of sulphide morphotypes

1998 ◽  
pp. 81-87
Author(s):  
Jesper Kresten Nielsen ◽  
Mikael Pedersen
Keyword(s):  
Base Metal ◽  
Early Period ◽  
Sedimentary Basins ◽  
Hydrothermal Activity ◽  
Source Rocks ◽  
Upper Permian ◽  
Thermal Activity ◽  
East Greenland ◽  
The North ◽  
Alum Shale

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Kresten Nielsen, J., & Pedersen, M. (1998). Hydrothermal activity in the Upper Permian Ravnefjeld Formation of central East Greenland – a study of sulphide morphotypes. Geology of Greenland Survey Bulletin, 180, 81-87. https://doi.org/10.34194/ggub.v180.5090 _______________ Bituminous shales of the Ravnefjeld Formation were deposited in the subsiding East Greenland basin during the Upper Permian. The shales are exposed from Jameson Land in the south (71°N; Fig. 1) to Clavering Ø in the north (74°20′N) and have attracted considerable attention due to their high potential as hydrocarbon source rocks (Piasecki & Stemmerik 1991; Scholle et al. 1991; Christiansen et al. 1992, 1993a, b). Furthermore, enrichment of lead, zinc and copper has been known in the Ravnefjeld Formation on Wegener Halvø since 1968 (Lehnert-Thiel 1968; Fig. 1). This mineralisation was assumed to be of primary or early diagenetic origin due to similarities with the central European Kupferschiefer (Harpøth et al. 1986). Later studies, however, suggested base metal mineralisation in the immediately underlying carbonate reefs to be Tertiary in age (Stemmerik 1991). Due to geographical coincidence between the two types of mineralisation, a common history is a likely assumption, but a timing paradox exists. A part of the TUPOLAR project on the ‘Resources of the sedimentary basins of North and East Greenland’ has been dedicated to re-investigation of the mineralisation in the Ravnefjeld Formation in order to determine the genesis of the mineralisation and whether or not primary or early diagenetic base metal enrichment has taken place on Wegener Halvø, possibly in relation to an early period of hydrothermal activity. One approach to this is to study the various sulphides in the Ravnefjeld Formation; this is carried out in close co-operation with a current Ph.D. project at the University of Copenhagen, Denmark. Diagenetically formed pyrite is a common constituent of marine shales and the study of pyrite morphotypes has previously been successful from thermalli immature parts of elucidating depositional environment and thermal effects in the Alum Shale Formation of Scandinavia (Nielsen 1996; Nielsen et al. 1998). The present paper describes the preliminary results of a similar study on pyrite from thermally immature parts of the Ravnefjeld Formation which, combined with the study of textures of base metal sulphides in the Wegener Halvø area (Fig. 1), may provide an important step in the evaluation of the presence or absence of early thermal activity on (or below) the Upper Permian sea floor.

scholarly journals Local radon flux maxima in the quaternary sediments of Schleswig–Holstein (Germany)

2021 ◽  
Author(s):  
Johannes Albert ◽  
Maximilian Schärf ◽  
Frieder Enzmann ◽  
Martin Waltl ◽  
Frank Sirocko
Keyword(s):  
Water Content ◽  
Pore Space ◽  
Mineralogical Composition ◽  
Fault System ◽  
Near Surface ◽  
Salt Diapirism ◽  
The North ◽  
Radon Flux ◽  
Published Evidence ◽  
Tectonically Active

AbstractThis paper presents radon flux profiles from four regions in Schleswig–Holstein (Northern Germany). Three of these regions are located over deep-rooted tectonic faults or salt diapirs and one is in an area without any tectonic or halokinetic activity, but with steep topography. Contrary to recently published studies on spatial patterns of soil radon gas concentration we measured flux of radon from soil into the atmosphere. All radon devices of each profile were deployed simultaneously to avoid inconsistencies due to strong diurnal variations of radon exhalation. To compare data from different seasons, values had to be normalized. Observed radon flux patterns are apparently related to the mineralogical composition of the Quaternary strata (particularly to the abundance of reddish granite and porphyry), and its grain size (with a flux maximum in well-sorted sand/silt). Minimum radon flux occurs above non-permeable, clay-rich soil layers. Small amounts of water content in the pore space increase radon flux, whereas excessive water content lessens it. Peak flux values, however, are observed over a deep-rooted fault system on the eastern side of Lake Plön, i.e., at the boundary of the Eastholstein Platform and the Eastholstein Trough. Furthermore, high radon flux values are observed in two regions associated with salt diapirism and near-surface halokinetic faults. These regions show frequent local radon flux maxima, which indicate that the uppermost strata above salt diapirs are very inhomogeneous. Deep-rooted increased permeability (effective radon flux depth) or just the boundaries between permeable and impermeable strata appear to concentrate radon flux. In summary, our radon flux profiles are in accordance with the published evidence of low radon concentrations in the “normal” soils of Schleswig–Holstein. However, very high values of radon flux are likely to occur at distinct locations near salt diapirism at depth, boundaries between permeable and impermeable strata, and finally at the tectonically active flanks of the North German Basin.

scholarly journals Volcanism and Volcanogenic Submarine Sedimentation in the Paleogene Foreland Basins of the Alps: Reassessing the Source-to-Sink Systems with an Actualist View

Geosciences ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 23
Author(s):  
Andrea Di Capua ◽  
Federica Barilaro ◽  
Gianluca Groppelli
Keyword(s):  
Foreland Basin ◽  
Fault System ◽  
Foreland Basins ◽  
The North ◽  
Source To Sink ◽  
The Alps ◽  
Alpine Foreland ◽  
Alpine Foreland Basin ◽  
Tectonic Lineament ◽  
First Time

This work critically reviews the Eocene–Oligocene source-to-sink systems accumulating volcanogenic sequences in the basins around the Alps. Through the years, these volcanogenic sequences have been correlated to the plutonic bodies along the Periadriatic Fault System, the main tectonic lineament running from West to East within the axis of the belt. Starting from the large amounts of data present in literature, for the first time we present an integrated 4D model on the evolution of the sediment pathways that once connected the magmatic sources to the basins. The magmatic systems started to develop during the Eocene in the Alps, supplying detritus to the Adriatic Foredeep. The progradation of volcanogenic sequences in the Northern Alpine Foreland Basin is subsequent and probably was favoured by the migration of the magmatic systems to the North and to the West. At around 30 Ma, the Northern Apennine Foredeep also was fed by large volcanogenic inputs, but the palinspastic reconstruction of the Adriatic Foredeep, together with stratigraphic and petrographic data, allows us to safely exclude the Alps as volcanogenic sources. Beyond the regional case, this review underlines the importance of a solid stratigraphic approach in the reconstruction of the source-to-sink system evolution of any basin.

scholarly journals Regional differences in the evolution of the merger of /ʃ/ and /ç/ in Luxembourgish

2021 ◽  
pp. 1-18
Author(s):  
François Conrad
Keyword(s):  
Language Contact ◽  
Sound Change ◽  
Young Generation ◽  
The South ◽  
Data Set ◽  
West Germanic ◽  
The North ◽  
Minimal Pairs ◽  
Old Men ◽  
Middle Generation

The merger of post-alveolar /ʃ/ and palatal /ç/ into alveolopalatal /ɕ/ has recently gained growing interest in sociophonetic research, especially in the Middle German dialect area. In Luxembourgish, a Continental West Germanic language, the sound change has been linked to age differences, while its origins remain unclear. Two studies with a regional focus are presented in this paper. The first study examines the merger in the Centre and the South of Luxembourg. The acoustic examination of both the spectral peak and the centre of gravity of a spoken data set of five minimal pairs embedded in read and orally translated sentences from 48 speakers (three generations (old generation, 65–91 years; middle generation, 40–64 years; young generation, 20–39 years; each generation, n = 16), men and women) reveals interesting results related to their regional background. In the old generation, the merger is further advanced in the speech of old men from the former mining region in the South compared to their peers in the Centre, the former leading this sound change. On the other hand, young speakers in both regions produce only alveolopalatal /ɕ/, the merger being complete in this generation. The second study presents exploratory data from the East and the North of the country. The analysis of this smaller sample (n = 6 speakers) reveals patterns similar to the central region. Pointing to language contact with Romance in the South as cradle and/or catalyser of the merger, these results not only give further clues as to the development in Luxembourg, but also add to a deeper understanding of sound changes in process in complex sibilant systems.

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