Stacked megafans of the Kalahari Basin as archives of paleogeography, river capture, and Cenozoic paleoclimate of southwestern Africa

2020 ◽  
Vol 90 (9) ◽  
pp. 980-1010
Author(s):  
Georg J. Houben ◽  
Stephan Kaufhold ◽  
Roy McG Miller ◽  
Christoph Lohe ◽  
Matthias Hinderer ◽  
...  
Keyword(s):  
Source Rock ◽  
Southern Africa ◽  
Intrusive Complex ◽  
The Core ◽  
Semiarid Climate ◽  
The North ◽  
River Capture ◽  
Granitoid Rocks ◽  
Freshwater Aquifers ◽  
Sedimentation History

ABSTRACT The Cenozoic Kalahari Basin covers large parts of southern Africa. A continuous 400 m core was obtained in northern Namibia and analyzed in detail. Here, we present sedimentological, geochemical, mineralogical, granulometric, and hydraulic data, which were used to derive the sedimentation history and the Cenozoic paleoclimate and paleogeography of SW Africa. The first absolute ages for the Kalahari Basin were obtained by dating of calcretes, which showed that the core covers almost the entire Cenozoic. Two megafans could be distinguished. The older, buried Olukonda Megafan stems from a mafic source rock, potentially the Kunene Intrusive Complex, and was deposited by a paleo–Kunene River towards the southeast and east, under a semiarid climate. The younger Cubango Megafan (Andoni Formation) has a completely different provenance, namely felsic metamorphic and granitoid rocks, transported from the north by the Cubango River. The capture of the Kunene towards the Atlantic during the Eocene resulted in this change in provenance. Despite the distinct differences between the formations, the temporal hiatus between them must have been short. The results are a showcase of the potential of megafans for hosting major deep freshwater aquifers.

The Archaean Atâ intrusive complex (Atâ tonalite), north-east Disko Bugt, West Greenland

1999 ◽  
pp. 103-112
Author(s):  
Feiko Kalsbeek ◽  
Lilian Skjernaa
Keyword(s):  
Intrusive Complex ◽  
The South ◽  
Original Series ◽  
Early Proterozoic ◽  
West Greenland ◽  
North East ◽  
The North ◽  
Southern Border ◽  
Area North ◽  
Igneous Layering

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Kalsbeek, F., & Skjernaa, L. (1999). The Archaean Atâ intrusive complex (Atâ tonalite), north-east Disko Bugt, West Greenland. Geology of Greenland Survey Bulletin, 181, 103-112. https://doi.org/10.34194/ggub.v181.5118 _______________ The 2800 Ma Atâ intrusive complex (elsewhere referred to as ‘Atâ granite’ or ‘Atâ tonalite’), which occupies an area of c. 400 km2 in the area north-east of Disko Bugt, was emplaced into grey migmatitic gneisses and supracrustal rocks. At its southern border the Atâ complex is cut by younger granites. The complex is divided by a belt of supracrustal rocks into a western, mainly tonalitic part, and an eastern part consisting mainly of granodiorite and trondhjemite. The ‘eastern complex’ is a classical pluton. It is little deformed in its central part, displaying well-preserved igneous layering and local orbicular textures. Near its intrusive contact with the overlying supracrustal rocks the rocks become foliated, with foliation parallel to the contact. The Atâ intrusive complex has escaped much of the later Archaean and early Proterozoic deformation and metamorphism that characterises the gneisses to the north and to the south; it belongs to the best-preserved Archaean tonalite-trondhjemite-granodiorite intrusions in Greenland.

scholarly journals North Atlantic warming over six decades drives decreases in krill abundance with no associated range shift

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Martin Edwards ◽  
Pierre Hélaouët ◽  
Eric Goberville ◽  
Alistair Lindley ◽  
Geraint A. Tarling ◽  
...  
Keyword(s):  
North Atlantic ◽  
Range Shift ◽  
The Core ◽  
Krill Abundance ◽  
The North ◽  
Living Space ◽  
Warming Climate ◽  
Two Temperatures ◽  
The North Atlantic

AbstractIn the North Atlantic, euphausiids (krill) form a major link between primary production and predators including commercially exploited fish. This basin is warming very rapidly, with species expected to shift northwards following their thermal tolerances. Here we show, however, that there has been a 50% decline in surface krill abundance over the last 60 years that occurred in situ, with no associated range shift. While we relate these changes to the warming climate, our study is the first to document an in situ squeeze on living space within this system. The warmer isotherms are shifting measurably northwards but cooler isotherms have remained relatively static, stalled by the subpolar fronts in the NW Atlantic. Consequently the two temperatures defining the core of krill distribution (7–13 °C) were 8° of latitude apart 60 years ago but are presently only 4° apart. Over the 60 year period the core latitudinal distribution of euphausiids has remained relatively stable so a ‘habitat squeeze’, with loss of 4° of latitude in living space, could explain the decline in krill. This highlights that, as the temperature warms, not all species can track isotherms and shift northward at the same rate with both losers and winners emerging under the ‘Atlantification’ of the sub-Arctic.

scholarly journals Geomagnetic secular variation

1989 ◽  
Vol 329 (1606) ◽  
pp. 415-502 ◽  
Keyword(s):  
Steady Flow ◽  
Southern Africa ◽  
Secular Variation ◽  
Static Field ◽  
Time Interval ◽  
The Core ◽  
Flow Maps ◽  
The Pacific ◽  
Construct Maps ◽  
Eighteenth And Nineteenth Centuries

We analyse over 175000 magnetic observations from an interval spanning 1695-1980 to produce a sequence of maps of the magnetic field at the core-mantle boundary; we find that even the earlier data enable us to determine reliable maps. We produce these maps at approximately 60-year intervals through the eighteenth and nineteenth centuries, and at 10-year intervals in the twentieth century. This span of maps is long enough to render straightforward the distinction between static and drifting features in the field: we observe that some features show no sign whatsoever of drift over the entire 285-year time interval, although others drift westwards. In particular, we observe that the secular variation is very low beneath the Pacific ocean, but beneath southern Africa and the South Atlantic ocean we observe rapid secular variation. We interpret the morphology of the static field in terms of a simple model of the dynamo, and conjecture that interactions between the core and the mantle are an important element of the process. As part of the static field we identify four main concentrations of flux, two in each hemisphere, at high latitudes: these features largely account for the Earth’s axial dipole moment. We find unequivocal evidence that magnetic flux has not remained frozen over the time span of our models; much of the diffusive behaviour that we identify is associated with the formation of a pair of flux spots (a ‘core spot’) beneath southern Africa, early in this century. Nevertheless, we are able to construct maps that satisfy a set of necessary conditions for frozen-flux, and use these maps to construct maps of the core surface fluid flow, based on the steady flow hypothesis. Although we find no strong evidence against the steady flow hypothesis, we do find some grounds on which to doubt the validity of the flow maps.

scholarly journals The distribution and synonyms of Breutelia microdonta (Mitt.) Broth. with additional notes on certain taxa of Breutelia

1992 ◽  
Vol 5 (1) ◽  
pp. 55-59
Author(s):  
Dana Griffin
Keyword(s):  
Southern Africa ◽  
The Philippines ◽  
Tropical Species ◽  
Spore Ornamentation ◽  
The North ◽  
Pacific Species

Breutelia microdonta (Mitt.) Broth., described originally from Brazil, is the oldest name for a disjunct widespread tropical species that includes as synonyms B. angustifolia Rehm. ex Sim of Southern Africa and B. merrillii Broth. of the Philippines. Breutelia kilaueae (C. Muell.) Broth. of Hawaii is considered a synonym of the austral Pacific species B. affinis (Hook.) Mitt., and B. brachyphylla Broth. of Ecuador is reduced to synonymy under the North Andean B. squarrosa Jaeg. Breutelia anacolioides Herz. of Bolivia is removed to Philonotis as a synonym of the North Andean P. incana (Tayl.) H. Robins. Differences in spore ornamentation offer an additional character distinguishing Breutelia from Philonotis.

Radiogenic Isotope Signatures of Holocene Sediments from Kane Basin: Linkage with the Re-opening and Evolution of Nares Strait

2021 ◽  
Author(s):  
Lina Madaj ◽  
Friedrich Lucassen ◽  
Claude Hillaire-Marcel ◽  
Simone A. Kasemann
Keyword(s):  
Ellesmere Island ◽  
The Arctic ◽  
Baffin Bay ◽  
Low Salinity ◽  
The Core ◽  
The Past ◽  
Nares Strait ◽  
The North ◽  
Sediment Input ◽  
Detrital Sediment

<p>The re-opening of the Arctic Ocean-Baffin Bay gateway through Nares Strait, following the Last Glacial Maximum, has been partly documented, discussed and revised in the past decades. The Nares Strait opening has led to the inception of the modern fast circulation pattern carrying low-salinity Arctic water towards Baffin Bay and further towards the Labrador Sea. This low-salinity water impacts thermohaline conditions in the North Atlantic, thus the Atlantic Meridional Overturning Circulation. Available land-based and marine records set the complete opening between 9 and 7.5 ka BP [1-2], although the precise timing and intensification of the southward flowing currents is still open to debate. A recent study of a marine deglacial sedimentary record from Kane Basin, central Nares Strait, adds information about subsequent paleoceanographic conditions in this widened sector of the strait and proposed the complete opening at ~8.3 ka BP [3].</p><p>We present complementary radiogenic strontium, neodymium and lead isotope data of the siliciclastic detrital sediment fraction of this very record [3] further documenting the timing and pattern of Nares Strait opening from a sediment provenance approach. The data permit to distinguish detrital material from northern Greenland and Ellesmere Island, transported to the core location from both sides of Nares Strait. Throughout the Holocene, the evolution of contributions of these two sources hint to the timing of the ice break-up in Kennedy Channel, north of Kane Basin, which led to the complete opening of Nares Strait [3]. The newly established gateway of material transported to the core location from the north via Kennedy Channel is recorded by increased contribution of northern Ellesmere Island detrital sediment input. This shift from a Greenland (Inglefield Land) dominated sediment input to a northern Ellesmere Island dominated sediment input supports the hypothesis of the newly proposed timing of the complete opening of Nares Strait at 8.3 ka BP [3] and highlights a progressive trend towards modern-like conditions, reached at about 4 ka BP.</p><p>References:</p><p>[1] England (1999) Quaternary Science Reviews, 18(3), 421–456. [2] Jennings et al. (2011) Oceanography, 24(3), 26-41. [3] Georgiadis et al. (2018) Climate of the Past, 14 (12), 1991-2010.</p>

The Westwood Deposit, Southern Abitibi Greenstone Belt, Canada: An Archean Au-Rich Polymetallic Magmatic-Hydrothermal System—Part II. Hydrothermal Alteration, Mineralization, and Geologic Model

2021 ◽  
Author(s):  
D. Yergeau ◽  
P. Mercier-Langevin ◽  
B. Dubé ◽  
V. McNicoll ◽  
S. E. Jackson ◽  
...  
Keyword(s):  
Hydrothermal System ◽  
Greenstone Belt ◽  
Massive Sulfide ◽  
Alteration Zone ◽  
Intrusive Complex ◽  
Calc Alkaline ◽  
Abitibi Greenstone Belt ◽  
The North ◽  
Vms Deposits ◽  
Ore Zones

Abstract The Westwood deposit, located in the Archean Doyon-Bousquet-LaRonde mining camp in the southern Archean Abitibi greenstone belt, contains 4.5 Moz (140 metric t) of gold. The deposit is hosted in the 2699–2695 Ma submarine, tholeiitic to calc-alkaline volcanic, volcaniclastic, and intrusive rocks of the Bousquet Formation. The deposit is located near the synvolcanic (ca. 2699–2696 Ma) Mooshla Intrusive Complex that hosts the Doyon epizonal intrusion-related Au ± Cu deposit, whereas several Au-rich volcanogenic massive sulfide (VMS) deposits are present east of the Westwood deposit. The Westwood deposit consists of stratigraphically stacked, contrasting, and overprinting mineralization styles that share analogies with both the intrusion-related and VMS deposits of the camp. The ore zones form three distinct, slightly discordant to stratabound corridors that are, from north (base) to south (top), the Zone 2 Extension, the North Corridor, and the Westwood Corridor. Syn- to late-main regional deformation and upper greenschist to lower amphibolite facies regional metamorphism affect the ore zones, alteration assemblages, and host rocks. The Zone 2 Extension consists of Au ± Cu sulfide (pyrite-chalcopyrite)-quartz veins and zones of disseminated to semimassive sulfides. The ore zones are spatially associated with a series of calc-alkaline felsic sills and dikes that crosscut the mafic to intermediate, tholeiitic to transitional, lower Bousquet Formation volcanic rocks. The metamorphosed proximal alteration consists of muscovite-quartz-pyrite ± gypsum-andalusite-kyanite-pyrophyllite argillic to advanced argillic-style tabular envelope that is up to a few tens of meters thick. The North Corridor consists of auriferous semimassive to massive sulfide veins, zones of sulfide stringers, and disseminated sulfides that are hosted in intermediate volcaniclastic rocks at the base of the upper Bousquet Formation. The Westwood Corridor consists of semimassive to massive sulfide lenses, veins, zones of sulfide stringers, and disseminated sulfides that are located higher in the stratigraphic sequence, at or near the contact between calc-alkaline dacite domes and overlying calc-alkaline rhyodacite of the upper Bousquet Formation. A large, semiconformable distal alteration zone that encompasses the North Corridor is present in the footwall and vicinity of the Westwood Corridor. This metamorphosed alteration zone consists of an assemblage of biotite-Mn garnet-chlorite-carbonate ± muscovite-albite. A proximal muscovite-quartz-chlorite-pyrite argillic-style alteration assemblage is associated with both corridors. The Zone 2 Extension ore zones and associated alteration are considered synvolcanic based on crosscutting relationships and U-Pb geochronology and are interpreted as being the distal expression of an epizonal magmatic-hydrothermal system that is centered on the upper part of the synvolcanic Mooshla Intrusive Complex. The North and Westwood corridors consist of bimodal-felsic Au-rich VMS-type mineralization and alteration produced by the convective circulation of modified seawater that included a magmatic contribution from the coeval epizonal Zone 2 Extension magmatic-hydrothermal system. The Westwood Au deposit represents one of the very few documented examples of an Archean magmatic-hydrothermal system—or at least of such systems formed in a subaqueous environment. The study of the Westwood deposit resulted in a better understanding of the critical role of magmatic fluid input toward the formation of Archean epizonal intrusion-related Au ± Cu and seafloor/subseafloor Au-rich VMS-type mineralization.

Property concepts in Tabaq: More than one road can lead to Rome

2020 ◽  
Vol 51 (1) ◽  
pp. 63-78
Author(s):  
Gertrud Schneider-Blum ◽  
Birgit Hellwig
Keyword(s):  
Small Class ◽  
North West ◽  
The Core ◽  
The North ◽  
Limited Role ◽  
Core Function ◽  
Word Classes ◽  
Semantic Types ◽  
Property Concepts

Abstract In this paper, we investigate the interplay between the morphosyntactic class of adjectives, the semantics of property concepts, and the function of noun modification in Tabaq, a Kordofan Nubian language (Nilo-Saharan phylum) spoken in the north-west of the Nuba Mountains in Sudan. Tabaq has a small class of adjectives containing few semantic types, and playing only a limited role with respect to the core function of adjectives: the modification of nouns. By contrast, a large number of descriptive modifiers is derived from two other word classes, verbs and nouns, and this paper describes the different ways of coding property concepts in Tabaq.

Catawba

Fit for War ◽  
2017 ◽  
Author(s):  
Mary Elizabeth Fitts
Keyword(s):  
North Carolina ◽  
Eighteenth Century ◽  
Seventeenth Century ◽  
American Indian ◽  
Slave Trade ◽  
Daily Life ◽  
Territorial Expansion ◽  
Charles Town ◽  
The Core ◽  
The North

Chapter 3 documents the emergence, composition, and political interactions of the Catawba Nation through the mid-eighteenth century. Between the Spanish incursions of the 1560s and the establishment of Charles Town in 1670, a group of Catawba Valley Mississippians known as Yssa rose to become the powerful Nation of Esaws that formed the core of the eighteenth-century Catawba Nation. In the late seventeenth century this polity was a destination for European traders as well as American Indian refugees fleeing hostilities associated with the Indian Slave trade and settler territorial expansion. While many of these refugees were from the Catawba River Valley, others—most notably the Charraw—were Piedmont Siouans who fled southward from the North Carolina-Virginia border. The incorporation of refugees had significant implications for Catawba politics and daily life, which are explored in subsequent chapters.

What Is Decolonial Love?

2018 ◽  
pp. 1-14
Author(s):  
Joseph Drexler-Dreis
Keyword(s):  
North Atlantic ◽  
Atlantic World ◽  
Critical Reflection ◽  
Positive Response ◽  
The Core ◽  
The North ◽  
European Experience ◽  
Core Concepts ◽  
The North Atlantic

The introduction establishes the decolonial perspective that prompts the questions to which the book responds. In light of the modern/colonial context of the North Atlantic world, the introduction raises two basic questions. First, can theology, as a mode of critical reflection that employs core concepts and images within lineages grounded in the European experience, contribute to the task of decolonization? Second, if a positive response to this question were offered, what would the content of that response look like? The introduction then proceeds to map out how the core image of decolonial love is developed through the book as a basis for responding to these questions.

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