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  • Other Sources  (37)
  • Elsevier  (14)
  • Center for Akad. Publ. Japan  (12)
  • Geozon Science Media  (6)
  • American Chemical Society
  • Annual Reviews
  • U.S. Geological Survey
  • 1980-1984  (14)
  • 1975-1979  (23)
  • 1984  (14)
  • 1978  (23)
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Language
Years
  • 1980-1984  (14)
  • 1975-1979  (23)
Year
  • 1
    Publication Date: 2022-08-04
    Description: Das Ca/Mg-Verhältnis wurde auf typischen Kartenausschnitten einer großflächigen geologisch-bodenkundlichen Kartierung auf dem nordfriesischen Festland mit anderen Merkmalen dargestellt und verglichen. Es zeigt keine Beziehungen zu den Sedimentationsbedingungen und damit keine deutbaren Zusammenhänge mit den Kartiereinheiten und den meisten Geländemerkmalen. Dagegen kommt eine deutliche Abhängigkeit von postsedimentären Faktoren heraus, die sich überall anders überlagern und das Ca/Mg-Verhältnis bestimmen. Es ist deshalb als Grundlage für eine Kartierung und Klassifizierung der Marschböden nicht geeignet.
    Description: research
    Keywords: ddc:551.7
    Language: German
    Type: doc-type:article , publishedVersion
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  • 2
    Publication Date: 2022-08-02
    Description: Auf drei kleinen benachbarten Moorflächen des Bruchberg-Moores wurden ein durchlaufendes Pollenprofil hergestellt und weitere Untersuchungen nächst der Torfbasis durchgeführt. Anhand der Untergrundmorphologie und der Basisproben konnte die flächenhafte Moorausbreitung rekonstruiert werden. Die ältesten Vermoorungen setzen demnach im Präboreal ein. Unterbrechungen im Moorwachstum wurden am Ende der Waldzeiten VI (älteres Atlantikum) und in VIII b (Subboreal) gefunden.
    Description: research
    Keywords: ddc:551.7
    Language: German
    Type: doc-type:article , publishedVersion
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  • 3
    Publication Date: 2022-08-02
    Description: Aus einer detaillierten geomorphologischen Probekartierung (nach GMK 25) im Jungmoränengebiet nördlich des Chiemsees werden die genetisch-chronologischen Probleme der Vorlandfächer des Inn- und Achen (= Chiemsee-) Gletschers in ihrem nördlichen Kontakt-und Wirkungsbereich vorgestellt. Die Darstellung eines phasenhaften Nieder- und Rückschmelzens der würmzeitlichen Vorlandeismassen bestätigt oder differenziert teilweise die bisherigen Untersuchungen, teilweise werden sie aufgrund der Geländebefunde abgelehnt. Am Schluß sind die wesentlichen Ergebnisse thesenartig zusammengefaßt.
    Description: research
    Keywords: ddc:551.7
    Language: German
    Type: doc-type:article , publishedVersion
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  • 4
    Publication Date: 2022-08-05
    Description: Nach Vorarbeiten 1977 und 1979 wurden im Bereich der paläolithischen Fundstelle Şehremuz im Jahre 1982 zwei Grabungskampagnen von je zwei Monaten durchgeführt. Es konnten zwei archäologische Komplexe in unterschiedlicher geologischer Lagerung festgestellt werden: a) Silexabschläge und Faustkeile im obersten aufgeschlossenen Schotter des Keluşk-Baches, eines Euphratzuflusses. Dieser Seitentalschotter ist korrelierbar mit einem etwa 60 m über der heutigen Talaue liegenden Euphratschotter. b) „Mittelpaläolithische" Inventare in einem über den Keluşk-Schottern liegenen Glacis, weitgehend nur aus Oberflächenfunden bekannt. Sie sind aufgrund ihrer Einlagerung jünger als der "Faustkeilkomplex". Die Inventare mit Faustkeilen sind einem entwickelten faustkeilführenden Paläolithikum zuzurechnen. Auf sie ist die vorliegende Untersuchung konzentriert. Die durch die Silexartefakte belegten zahlreichen Begehungen des alten Keluşk-Bettes durch den paläolithischen Menschen haben ihre Ursache u.a. in einem hohen natürlichen Anteil von Silex im Schotter. Neben vollständigen Knollen liegt zahlreicher Naturbruch vor, der gegen die Stücke mit anthropogenen Bearbeitungsspuren abgegrenzt werden muß. Dabei kommt der Konfiguration der Einzelmerkmale — Dimensionen; Abbaufläche und Schlagmerkmale — die größte Bedeutung zu. Die Bearbeitung der Steinartefakte unter funktionalen Gesichtspunkten ist ein wichtiger Teil der Untersuchungen: Die Methoden werden beschrieben. Form und Zurichtung der Faustkeile lassen makroskopisch mögliche Funktionsflächen zum tiefen Einschneiden etwa in Fleisch und mögliche Funktionskanten zum Ritzen oder flach Einschneiden erkennen. Im mikroskopischen Bereich werden an Artefakten punktuell Gebrauchsspuren faßbar, die z.B. die Benutzung eines Faustkeils sowohl zum Einschneiden in Fleisch wie auch zum Zertrümmern von Knochen belegen.
    Description: research
    Keywords: ddc:551.7
    Language: German
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  • 5
    Publication Date: 2022-08-05
    Description: Einige mehrgliedrige Lößprofile im Raum der Tagebaue Treue, Helmstedt und Alversdorf der Braunschweigischen Kohlenbergwerke bei Helmstedt werden beschrieben, interpretiert und datiert. In den vollständigen Jungwürm-Profilen lassen sich bis zu vier Naßböden ausgliedern. Eine Parallelisierung mit der Jungwürm-Gliederung von Rohdenburg & Meyer (1966) ist möglich. Erstmals werden aus dem Gebiet am N-Rand der Lößgrenze 1 —1,2 m mächtige Mittelwürmlösse nachgewiesen, die an zwei Lokalitäten (im Tagebau Alversdorf) vom Lohner Boden abgeschlossen werden. Der Altwürmabschnitt weist in den vollständigen Profilen außerhalb von Dellen bis zu 3 Humuszonen bzw. -reste auf, zwischen die Bleichzonen eingeschaltet sind. Der letztwarmzeitliche Boden ist sowohl auf Löß (als Pseudogley oder im oberen Teil pseudovergleyter Bt-Horizont) als auch auf glazifluviatilen und moränalen Ablagerungen entwickelt. Aus den Diskordanzen innerhalb der Profile werden bis zu vier Dellenbildungsphasen und einige weitere Abtragungsphasen abgeleitet.
    Description: research
    Keywords: ddc:551.7
    Language: German
    Type: doc-type:article , publishedVersion
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  • 6
    Publication Date: 2022-08-05
    Description: Im unteren und mittleren Werratal läßt sich eine 5—8 m ü. Talaue gelegene Terrasse ausgliedern, die an mehreren Lokalitäten eine weite Verbreitung hat und aufgrund ihres Aufbaus und ihrer Deckschichten (z.T. Löß) als hochwürmzeitliche Niederterrasse eingestuft wird. Sie wurde schon im Spätglazial durch 0,5—1,0 m tiefen Rinnen zerschnitten, die von wahrscheinlich umgelagerten Niederterrassenschottern oder feinkörnigeren Sedimenten wieder aufgefüllt wurden. Die spätglaziale und frühholozäne Flußgeschichte läßt sich dank zeitweilig günstiger Aufschlußverhältnisse bei Eschwege recht gut rekonstruieren (Abb. 6 und 7). Dies gelingt hier besser als im Werraabschnitt auf dem Gebiet der DDR, der von Ellenberg (1967 bis 1975) sehr genau untersucht worden ist. „Ried"ablagerungen in ehemaligen Werrarinnen können präallerödzeitlichen und jungtundrenzeitlichen bis borealen Alters sein. Wie im Leinetal finden sich im Werratal zwei verschieden alte Auelehme, von denen der ältere stellenweise eine wahrscheinlich dem postglazialen Klimaoptimum zuzuordnende Auen-Schwarzerde trägt. In den „Ried"ablagerungen konnten 12 Flußmuschel- bzw. -Schneckenarten gefunden und bestimmt werden.
    Description: research
    Keywords: ddc:551.7
    Language: German
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  • 7
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 14 B, pp. 225, (ISBN 3-7643-7011-4)
    Publication Date: 1984
    Keywords: Applied geophysics ; seismic Migration ; Seismics (controlled source seismology) ; Acoustics
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  • 8
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    Elsevier
    In:  Amsterdam, Elsevier, vol. Developments in Petroleum Science vol. 15A, no. Publ. No. 12, pp. 9, (ISBN: 0-12-636380-3)
    Publication Date: 1984
    Keywords: Borehole geophys. ; Textbook of geophysics ; GFZ ; RUB ; GMG ; 3.45.8 ; UniL ; IfGuG ; in ; Französisch
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  • 9
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    Center for Akad. Publ. Japan
    In:  Bull., Polar Proj. OP-O3A4, Earthquake Precursors, Tokyo, Center for Akad. Publ. Japan, vol. 37, no. 16, pp. 105-113, (ISBN: 3-540-23712-7)
    Publication Date: 1978
    Keywords: Earthquake precursor: prediction research ; Earthquake precursor: Vp/Vs anomalies ; Seismics (controlled source seismology)
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  • 10
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    Elsevier
    In:  Amsterdam, Elsevier, vol. 81A and 81B, no. 22, pp. 65-70, (1405101733, 336 p.)
    Publication Date: 1984
    Keywords: Textbook of geophysics ; Earth model, also for more shallow analyses !
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  • 11
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    Center for Akad. Publ. Japan
    In:  Bull., Polar Proj. OP-O3A4, Earthquake Precursors, Tokyo, Center for Akad. Publ. Japan, vol. 65, no. Subvol. b, pp. 43-49, (ISBN 0080419208)
    Publication Date: 1978
    Keywords: Earthquake precursor: prediction research ; Fault zone ; Project report/description
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  • 12
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    Center for Akad. Publ. Japan
    In:  Bull., Polar Proj. OP-O3A4, Earthquake Precursors, Tokyo, Center for Akad. Publ. Japan, vol. 65, no. Subvol. b, pp. 203-217, (ISBN 0080419208)
    Publication Date: 1978
    Keywords: Earthquake precursor: prediction research ; Dual Induction Latero logAT ; Laboratory measurements ; Earthquake precursor: simulated in laboratory tests
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  • 13
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    U.S. Geological Survey
    In:  Bull., Open-File Report, Proc. Symposium on The New Madrid Seismic Zone, Luxembourg, U.S. Geological Survey, vol. 14, no. 84-770, pp. 330-352, (ISBN 0080419208)
    Publication Date: 1984
    Keywords: Seismology ; Source parameters ; Strong motions ; Source
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  • 14
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    Center for Akad. Publ. Japan
    In:  Bull., Open-File Rept., Earthquake Precursors, Tokyo, Center for Akad. Publ. Japan, vol. 5, no. 16, pp. 85-93, (ISBN 1-86239-165-3, vi + 330 pp.)
    Publication Date: 1978
    Keywords: Earthquake precursor: prediction research ; Earthquake precursor: statistical anal. of seismicity ; Seismicity
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  • 15
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    Center for Akad. Publ. Japan
    In:  Bull., Open-File Rept., Earthquake Precursors, Tokyo, Center for Akad. Publ. Japan, vol. 231, no. 16, pp. 115-121, (ISBN 1-86239-165-3, vi + 330 pp.)
    Publication Date: 1978
    Keywords: Earthquake precursor: prediction research
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  • 16
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    Center for Akad. Publ. Japan
    In:  Bull., Polar Proj. OP-O3A4, Earthquake Precursors, Tokyo, Center for Akad. Publ. Japan, vol. 186, no. XVI:, pp. 79-83, (ISBN: 3-540-23712-7)
    Publication Date: 1978
    Keywords: Earthquake precursor: prediction research ; Earthquake precursor: deformation or strain ; Crustal deformation (cf. Earthquake precursor: deformation or strain)
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  • 17
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    Center for Akad. Publ. Japan
    In:  Bull., Open-File Rept., Earthquake Precursors, Tokyo, Center for Akad. Publ. Japan, vol. 14, no. 86-425, pp. 31-41, (ISBN 0080419208)
    Publication Date: 1978
    Keywords: Earthquake precursor: prediction research ; Seismicity ; Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Earthquake precursor: deformation or strain
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  • 18
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    Center for Akad. Publ. Japan
    In:  Tokyo, 296 pp., Center for Akad. Publ. Japan, vol. 12, no. XVI:, pp. 9-66, (ISBN 0-7923-5587-3)
    Publication Date: 1978
    Keywords: Earthquake precursor: prediction research ; Handbook of geophysics
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  • 19
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    Center for Akad. Publ. Japan
    In:  Professional Paper, Earthquake Precursors, Tokyo, Center for Akad. Publ. Japan, vol. 16, no. 16, pp. 185-202, (ISBN 0080419208)
    Publication Date: 1978
    Keywords: Earthquake precursor: prediction research ; Laboratory measurements ; Earthquake precursor: simulated in laboratory tests ; Rock mechanics
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  • 20
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    Elsevier
    In:  Professional Paper, Computer-aided seismic analysis and discrimination, Washington, D. C., Elsevier, vol. 16, no. 16, pp. 133-146, (ISBN 1-86239-165-3, vi + 330 pp.)
    Publication Date: 1978
    Keywords: Data analysis / ~ processing ; Discrimination ; Seismics (controlled source seismology) ; Pattern recognition ; Detectors
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  • 21
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    Center for Akad. Publ. Japan
    In:  Professional Paper, Earthquake Precursors, Tokyo, Center for Akad. Publ. Japan, vol. 4, no. 231, pp. 243-250, (ISBN 1-4020-1729-4)
    Publication Date: 1978
    Keywords: Earthquake precursor: prediction research ; Earthquake precursor: statistical anal. of seismicity ; Seismology ; Earthquake ; Seismicity
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  • 22
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    Elsevier
    In:  Bull., Polar Proj. OP-O3A4, Computer-Aided Seismic Analysis and Discrimination, London, Elsevier, vol. 16, no. 4, pp. 97-109, (ISBN 0080419208)
    Publication Date: 1978
    Keywords: Earthquake ; Seismics (controlled source seismology) ; Discrimination ; Velocity analysis
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  • 23
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    Center for Akad. Publ. Japan
    In:  Professional Paper, Open-File Rept., Earthquake Precursors, Tokyo, Center for Akad. Publ. Japan, vol. 8, no. 16, pp. 51-68, (ISBN 0080419208)
    Publication Date: 1978
    Keywords: Earthquake precursor: prediction research ; Earthquake precursor: deformation or strain ; Crustal deformation (cf. Earthquake precursor: deformation or strain)
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  • 24
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    U.S. Geological Survey
    In:  Open-File Report, Kiel, U.S. Geological Survey, vol. C 560, 183 pp., no. 84-770, pp. 267-278, (ISBN 3-933346-037)
    Publication Date: 1984
    Keywords: Seismology ; Seismicity
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  • 25
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    U.S. Geological Survey
    In:  Open-File Report, Stavanger, U.S. Geological Survey, vol. 339-350, no. 84-770, pp. 33-62, (ISBN 3-933346-037)
    Publication Date: 1984
    Keywords: Earthquake ; Source parameters ; Seismology
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  • 26
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    Center for Akad. Publ. Japan
    In:  Professional Paper, Open-File Rept., Earthquake Precursors, Tokyo, Center for Akad. Publ. Japan, vol. 22, no. 16, pp. 231-241, (ISBN 0080419208)
    Publication Date: 1978
    Keywords: Earthquake precursor: prediction research ; Dual Induction Latero logAT ; Earthquake precursor: Vp/Vs anomalies ; Hypocentral depth
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  • 27
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    Annual Reviews
    In:  Annual Review of Earth and Planetary Sciences, 6 (1). pp. 353-375.
    Publication Date: 2020-06-09
    Type: Article , PeerReviewed
    Format: text
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  • 28
    Publication Date: 2016-04-12
    Description: Thick sediments (maximum of at least 4900 m) infill the Natal Valley, which lies between the coast of South Africa/Mozambique and the Mozambique Ridge. Eight physiographic provinces are recognised in the valley, and their boundaries can be related to well-defined sediment thickness or facies discontinuities within the basin infill. The acoustic stratigraphy of the area is established by reference to two regionally developed reflecting horizons, which, on the basis of previously published borehole and seismic data, are tentatively identified as mid-Cretaceous (McDuff) and mid-Cainozoic (Angus) hiatuses or important facies boundaries. Sedimentation began in the Natal Valley before mid-Cretaceous times and since then sediment dispersion has been strongly influenced by the disposition of large basement (? volcanic) highs: the approximately NE—SW Almirante Leite and Naudé ridges, and the larger N—S Mozambique Ridge. There is abundant evidence that sedimentation in the vicinity of these ridges has been current-controlled since at least mid-Cainozoic (Angus) times. The two main terrigenous sediment input points have been the Tugela and Limpopo rivers, which have large sediment cones adjacent to their mouths.
    Type: Article , PeerReviewed
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  • 29
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    Elsevier
    In:  Journal of Experimental Marine Biology and Ecology, 75 (2). pp. 171-190.
    Publication Date: 2016-04-25
    Description: The exchange of inorganic nutrients; ammonium, nitrate and reactive phosphate between burrows of the infaunal polychaete Nereis virens Sars and the overlying water was assessed using V-shaped sediment cores. Exchange was determined by monitoring ventilation current and nutrient concentration of in- and excurrent water. Ammonium supply appeared independent of overlying water concentrations, showing a constant release of 0.5 μmol·h−1 (for a 2-g individual + burrow system) at concentrations from 2 to 87 μM. Of this release ≈40% originated from worm excretion, and the rest from microbial mineralization. Nitrate and phosphate exchange appeared very sensitive to overlying water concentrations, having equilibrium (zero flux) at 10–15 and 3 μM, respectively. Below these concentrations nitrate showed a slight release (due to nitrification), whereas phosphate was released at a rate of 3.2 × 10−2 μmol·h−1 at 1 μM (mineralization and desorption). Above equilibrium they both were removed during water passage through worm burrows, reaching 0.4 μmol·h−1 for nitrate at 107 μM (nitrate reduction) and 3.7 × 10−2 μmol·h−1 for phosphate at 5.6 μM (adsorption processes). The burrow system apparently acted as a buffer for phosphate and, to some degree, nitrate in the overlying water. At the study site (Norsminde Fjord estuary) nereid burrows were estimated to increase the sediment-water interface 150%. About 17% of the water column was cycled through the sediment by Nereis each day. The worm + burrow system was estimated to release 95 μmol· m−2·h−1 ammonium to the overlying water, which was ≈76–90% of the total release of ammonium from the sediment (30–36% was worm excretion).
    Type: Article , PeerReviewed
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  • 30
    Publication Date: 2016-04-08
    Description: Isopach asymmetry, and sediment component changes in DSDP cores from the SE Atlantic (Orange Basin) support the hypothesis of major drainage system changes in SW Africa during late Cretaceous—Cenozoic time. This involved alternations in the use of the 28°S (modern Orange River) and 31°S (modern Olifants River) exit points across the western escarpment by rivers carrying run-off from the Upper Orange/Vaal catchment areas, as well as radical re-organizations of internal drainage geometry. It is postulated that during late Cretaceous times the 28°S exit was used, with the Middle Orange River following a course in the interior well to the south (up to 150 km) of its modern channel. Sediment discharge rates from this river were relatively high (at least 10 × 106 m3 yr−1), and resulted in rapid advancement of the continental margin sediment prism west of the mouth by large-scale slumping. The Palaeogene Orange/Vaal river exit was via the 31°S escarpment crossing, and during the later part of this period, the Cape Canyon was cut across the continental shelf and slope. A significant reduction in sediment discharge (to 2.0 × 106 m3 yr−1) suggests that the Lower Tertiary climate for SW Africa was drier than that of late Cretaceous times. However, aridity did not commence until late Miocene times, when the Orange/Vaal discharge had switched back to the 28°S exit. Modern sediment discharge rates (6.5 × 106 m3 yr−1) are relatively high and reflect soil erosion caused by agricultural activity. The two major alterations in exit point of the Orange/Vaal (late Cretaceous—early Tertiary, and late Oligocene—early Miocene) are related to periods of low sea level, which promoted river capture adjacent to the western escarpment. An additional factor in the first course change may have been the disruption of the Middle Orange channel by late Cretaceous igneous intrusions. Less important internal reorganizations of the drainage system are postulated in late Miocene—Pleistocene times. Economic implications for offshore diamond distribution are briefly mentioned.
    Type: Article , PeerReviewed
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  • 31
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    Annual Reviews
    In:  Annual Review of Earth and Planetary Sciences, 6 (1). pp. 205-228.
    Publication Date: 2020-06-09
    Description: The causes of the growth and collapse of the large Pleistocene ice sheets is a topic of intense scientific debate. The amount of new data and ideas has been prodigious during the last ten years. This review concentrates on the shifting patterns of glacial advance and shrinkage during the last Glaciation. We also examine reconstructions of conditions during the maximum of this Glaciation about 18,000 BP, and the mechanisms that might have caused the rapid collapse of many of the world's ice sheets between 18,000 and 8000 BP. Our paper focuses on the North Atlantic sector because it is there that the major Pleistocene ice sheets grew, developed, and retreated.
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  • 32
    Publication Date: 2016-05-30
    Description: A geochemical rock- and soil-sampling program was carried out in the vicinity of eight concealed “Cyprus type” deposits, occurring in marginal mafic to intermediate metapillow lavas of the Troodos Ophiolite Complex. The mineralization of massive and stockwork sulfide ore is characterized by the predominance of pyrite, intergrown with less chalcopyrite and minor amounts of sphalerite. Background values of Hg are in the range of 8–12 ppb for soils and 3–6 ppb for surface rocks. Anomaly/background ratios of 10:1 (soils) and 5:1 (rocks) have been found only, where Hg migrated along channels formed by faults cutting shallow-seated mineralization. Here, Hg sometimes shows significant correlations with Cu, Zn, Ba and exceptionally with Co. However in one case an Hg anomaly in soils and surface rocks was detected directly over a deposit. The use of Hg as indicator element for these types of deposits is therefore limited. Buried mineralization may be delineated more distinctly by Cu, Zn and Ba.
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  • 33
    Publication Date: 2016-07-08
    Description: The cause of the climatically controlled fluctuations in the carbonate content of deep-sea sediments remains the subject of uncertainty and debate. Three variables are involved: supply of biogenic carbonate, loss by dissolution, and dilution by non-carbonate phases. It is suggested that 230Th, which is produced in the ocean at a constant rate provides a reliable reference for measuring variations in rate of sedimentation on a regional scale. Results of a preliminary analysis based on published data indicate that, for depths at and above the lysocline, the carbonate fluctuations observed in cores from the North Atlantic Ocean are due primarily to variations in the terrigenous clay input, which was 2–5 times higher during glacials than during interglacials. Carbonate deposition appears to have been somewhat reduced during glacials, but probably not by more than a factor of 2. From published 230Th232Th profiles it appears that the South Atlantic Ocean also received increased inputs of terrigenous clay during glacial periods.
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  • 34
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    Elsevier
    In:  Marine Geology, 54 (3-4). pp. 237-247.
    Publication Date: 2016-09-05
    Description: DSDP cores from areas of low (Site 505) and high heat flow (Site 504 B) near the Costa Rica Rift, together with seismic profiles from the Panama Basin, have been studied to determine the relationship between: (1) carbonate content and physical and acoustic properties; and (2) carbonate content, carbonate diagenesis and acoustic stratigraphy. Except for ash and chert layers, bulk density correlates strongly and linearly with carbonate content. Velocity is uniform downcore and only small variations at a small scale are measured. Thus an abrupt change in carbonate content will cause abrupt changes in acoustic impedance and should cause reflectors that can be detected acoustically. A comparison of seismic profiler reflection records with physical properties, carbonate content and reflection coefficients indicates that the main reflectors can be identified with ash layers, diagenetic boundaries, and carbonate content variations. Diagenesis of carbonate sediments is present at Site 504 B in a 260 m-thick ooze—chalk—limestone/chert sequence. These diagenetic sequences occur in areas of higher heat flow (200 mW m−2). Seismic profiler records can be used to map the extent and depth of these diagenetic boundaries.
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  • 35
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    Elsevier
    In:  Earth and Planetary Science Letters, 37 (3). pp. 409-420.
    Publication Date: 2016-09-09
    Description: Five separate exposures of oceanic basalts were dredged in the vicinity of the Peru-Chile Trench between 9° and 27°S latitude. Each dredge is dominated by abundant pillow basalts. Approximately ten of the most unaltered, glassy and fine-grained samples were selected for detailed chemical and petrographic analyses from each dredge area. All basalts recovered in the Peru-Chile Trench are olivine and quartz-normative tholeiites that are believed to have formed at the now extinct Galapagos Rise 30–50 m.y. ago. Detailed chemical analyses of the basalts, including major and selected trace and rare earth elements, indicate that considerable compositional variability exists both within each of the dredged areas as well as between areas. Most of the inherent chemical variability observed within particular basement sections appears consistent with the concept of temporal evolution of magma bodies at a former spreading center by shallow-level fractional crystallization involving primarily plagioclase and olivine. In contrast, important chemical differences between the dredged areas suggest compositional heterogeneities in the mantle source regions. Our results indicate that although shallow-level fractionation has brought about large changes in composition of basalts in each area, compositional trends are distinct and appear to reflect original mantle-derived compositional differences.
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  • 36
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    Elsevier
    In:  Journal of Volcanology and Geothermal Research, 4 (1-2). pp. 99-116.
    Publication Date: 2016-09-09
    Description: Thirty-four ash layers of Pleistocene and Pliocene age from DSDP Site 192, northwestern Pacific Ocean, have been subjected to detailed chemical and optical study to evaluate: (1) the chemical and optical variability in glass shards from deep-sea ash layers, and (2) secondary changes brought about by prolonged exposure to seawater. Glass shards from approximately half of the ash layers studied were found to have uniform compositions which approach the precision of the microprobe chemical analyses, whereas the remainder are compositionally diverse (e.g., SiO2, variations of 5–15% among shards from the same ash layer) and appear to be the eruptive products of compositionally zoned magma chambers. Optical studies of glass shards confirm the absence of devitrification or the formation of pervasive secondary alteration products. By contrast, chemical studies suggest that the glass shards have experienced progressive hydration with possible minor ion exchange of K, Mg, Ca and Si. The hydration occurs rapidly and leads to a rather uniform water content of 4.5–5% after several hundred thousands of years exposure to seawater. Step-wise heating dehydration experiments, optical effects, and published'oxygen isotope studies indicate that the water of hydration is incorporated uniformly within the glass. Systematic chemical differences between electron microprobe analyses of glass shard interiors and corresponding bulk chemical study by atomic absorption lead us to postulate that glass shard margins have undergone a minor chemical exchange with major cations in seawater. They have gained 0.10–0.20 wt. % K20, MgO, and CaO while losing a corresponding amount of Si2O. Although the glass shards from DSDP Site 192 are hydrated and may have experienced subtle, surficial ion exchange, we stress that they are the most chemically representative samples available of magmas that were explosively erupted from volcanic arcs.
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  • 37
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    Elsevier
    In:  Marine Geology, 60 (1-4). pp. 165-198.
    Publication Date: 2020-04-27
    Description: Wave-formed sedimentary structures can be powerful interpretive tools because they reflect not only the velocity and direction of the oscillatory currents, but also the length of the horizontal component of orbital motion and the presence of velocity asymmetry within the flow. Several of these aspects can be related through standard wave theories to combinations of wave dimensions and water depth that have definable natural limits. For a particular grain size, threshold of particle movement and that of conversion from a rippled to flat bed indicate flow-velocity limits. The ratio of ripple spacing to grain size provides an estimate of the length of the near-bottom orbital motion. The degree of velocity asymmetry is related to the asymmetry of the bedforms, though it presently cannot be estimated with confidence. A plot of water depth versus wave height (h—H diagram) provides a convenient approach for showing the combination of wave parameters and water depths capable of generating any particular structure in sand of a given grain size. Natural limits on wave height and inferences or assumptions regarding either water depth or wave period based on geologic evidence allow refinement of the paleoenvironmental reconstruction. The assumptions and the degree of approximation involved in the different techniques impose significant constraints. Inferences based on wave-formed structures are most reliable when they are drawn in the context of other evidence such as the association of sedimentary features or progradational sequences.
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