Sediments cored at DSDP Sites 362 and 532 on the Walvis Ridge provide a Neogene-Quaternary history of the development of the upwelling system on the southwest African margin. Upwelling occurs principally on the landward side of the Benguela Current. The upwelling centres have shifted northward since the Middle Miocene as the current has intensified and has flowed farther to the north. Changes in productivity are recorded in the types, proportions and preservation of foraminifera, radiolaria, diatoms, organic matter, and clay minerals in the sedimentary record. Prior to the Late Miocene (10 Ma), the Benguela Current did not reach the Walvis Ridge, and enhanced productivity is not evident in the sediments at this location. Between 10 to 5.2 Ma, upwelling was recorded in the DSDP sites in glacial periods, indicating that the Benguela Current intensified during glacial periods and transported evidence of upwelling to Sites 362/532 from near-coastal areas. During interglacial periods the current was not as strong and did not reach the Walvis Ridge, turning instead to the west within the Cape Basin. Strengthening of the current continued such that by the Pliocene and Quarternary the upwelling signal is contained in interglacial sediments. Sediments deposited in these more recent glacial times contain a weak or absent upwelling signal because glacial intensification shifts the Benguela Current system northward to reach the Angola Basin before it turns westward away from its coast-parallel direction.

The history of the northward growth and of the fluctuations of the Benguela Current from the middle Miocene (ca. 14 Ma) to the uppermost late Miocene (ca. 5 Ma) has been reconstructed from analyses of the coarse and clay fractions and geochemical analyses of the organic matter in sediments from Deep Sea Drilling Project Sites 362 and 532. In the middle Miocene the Benguela Current had not yet reached the Walvis Ridge, and consequently, no local upwelling occurred. Carbonate preservation was good during this period of low productivity. Rhythmic changes related to Antarctic Copyright 1990 by the American Geophysical Union. Paper number 90PA00559. 0883-8305/90/90PA-00559 $10.00 ice volumes were weak, leading to slightly higher organic matter concentrations and higher montmorillonite/illite (M/I) ratios in sediments deposited during times of greater continental ice. Montmorillonite was carried north from the Orange River by the Benguela Current, whereas illite originated from the nearby Namib Desert. In the early late Miocene the Benguela Current reached the Walvis Ridge in colder periods and led to welldeveloped rhythmic increases in opal, which was transported from near-coastal upwelling areas. Organic matter concentration, carbonate dissolution, and M/I ratios were also enhanced during periods of greater ice volume. During the late Miocene, farther northward migration of the Benguela Current led to a change in the uppermost Miocene sediments: opal contents and M/I ratios were high during times of low ice volume rather than in colder times. During the cold periods, local winds from the Namib desert increased the illite supply to the Walvis Ridge and depressed the M/I ratio. In these periods, the Benguela Current flowed farther to the north, reaching the Angola Basin as it did in Quaternary glacial periods. Throughout these changes, sediment organic carbon content was always enhanced in highice-volume periods from near-bottom downslope transport of organic matter from shelf regions during regressions, and carbonate dissolution in the sediments was increased as a result of oxidation of this organic matter. for the first time at these locations on the Walvis Ridge Terrace at 10 Ma [Siesser, 1980]. The appearance of this system could be detected by means of abundant opal skeletons, which point to nearcoastal upwelling, and the westward turning Benguela Current transported the opal skeletons from shelf areas to the deeper Walvis Ridge depositional sites. Both long-term and short-term changes in the Benguela Current system have been observed [Diester-Haass and Rothe, 1987; Diester-Haass, 1988]. The most important features are the northward migration of the Benguela Current during the late Miocene and a shifting of the current axis with a glacial-interglacial cyclicity. The overall driving force of these changes is the Antarctic ice mass with its growth and fluctuations during the Miocene. Changes in the volume of Miocene Antarctic ice must have been sufficiently large as to have produced changes in sea level comparable t...

KurzfassungEine bis zu 1000 m mächtige Schichtenfolge von karbonatischen Gesteinen des norischen und rätischen Alters ist in dem südwestlichen Teil Sloweniens als Hauptdolomit, nur in den Gebieten von Trnovski gozd und Banjska planota sind die oberen 200m überwiegend als Dachsteinkalk entwickelt.Der Hauptdolomit zeigt Markmale der loferitischen Entwicklung. Bis zum Meter mächtige Schichten von biomikritischem und körnigem Dolomit wechseln sich mit dünneren Stromatolith-und Laminit-Schichten rhytmisch ab. Das Abla gerungsmilieu von Hauptdolomit war ein sehr flacher abgeschlossener Schelf, häufig der intertidale Bereich innerhalb der Dinarischen Karbonat-Plattform. Der Dolomit ist in der frühen Diagenese (Stromatolith-Schichten) sowie während der spätdiagenetischen Prozesse (körniger Dolomit) entstanden.Der Kratka vsebinaDo tisoč metrov debela skladovnica karbonatnih kamnin norijske in retijske starosti je v jugozahodnem delu Slovenije razvita kot glavni dolomit, le na Trnovskem gozdu in na Banjski planoti je v vrhnjih dvesto metrih zaporedja pretežno dachsteinski apnenec.Glavni dolomit kaže značilnosti loferskega razvoja. Ritmično se menjavajo do meter debele plasti biomikritnega in zrnatega dolomita ter tanjše stromatolitne in laminitne plasti. Sedimentacijsko okolje glavnega dolomita je bilo zelo plitev zaprt self, pogosto medplimski pas znotraj Dinarske karbonatne platforme. Dolo mit je nastal v zgodnji diagenezi (stromatolitne plasti) in med kasnodiagenetskimi procesi (zrnati dolomit).Dachsteinski apnenec predstavlja lateralni facies glavnega dolomita. Odlagal se je na odprtem plitvem šelfu. Sedimentne teksture, značilne za medplimsko okolje, so zelo redke. Korozijske votline in intraformacijske breče v apnencu kažejo na občasne lokalne okopnitve med njegovim nastajanjem.Na geokemično sestavo slednih prvin v apnencih in dolomitih so najbolj vplivali diagenetski procesi, predvsem dolomitizacija, manj pa okolje nastanka karbonatnih sedimentov. Apnenci vsebujejo v primerjavi z dolomiti v splošnem dvakrat več Sr, medtem ko imajo dolomitni vzorci več Fe, Mn in Na. Zgodnjediagenetski dolomit je obogaten s težkimi izotopi бО'^ in бС^, medtem ko vsebujejo kasnodiagenetski dolomiti več lahkega bO^^. Apnenec se je odlagal pri temperatu rah okrog 24°C. EINLEITUNG Bisherige UntersuchungenDer Hauptdolomit und der Dachsteinkalk des Alpenraums waren Gegenstand zahlreicher, sowohl regionalgeologischer als auch sedimentologischer Untersuchun gen. Die Arbeiten von Stur (1858) aus der Gebiet von Postojna und von Lipoid (1858), die in der Gegend von Cerknica (Abb. 1) durchgeführt wurde, stellten mit die früheste geologische Bearbeitungen dar.In den sehr wichtigen Arbeiten von Ko s s ma t (1898,1905, 1906 und 1920)

ZusammenfassungAus dem Basalkomplex der Kanareninsel Fuerteventura werden pr~ivulka-nische Sedimentserien besebrieben, die aus insgesamt fiber 1000 m miichtigen Kalk-, Ton-, Mergel-, Sand-und Siltsteinen bestehen; die jiingsten haben nach Foraminiferen Oberkreide-Alter. Die gesamte Schichtserie umfal3t naeh einem Vergleich mit Profilen aus dem gegenfiberliegenden afrikanisehen Gebiet wahrseheinlieh aul3erdem noeh Jura und Unterkreide. Die Sehichten sind zu einem ESE-streichenden Cebirge mit wenigstens teilweise iiberkippter Lagerung strukturiert.Danach sind die Ostkanaren keine ,,ozeanischen" Inseln; sie geh/Sren geologisch zum afrikanischen Kontinent oder zum Kontinentalsehelf. Die Sedimentserie wird von den autometamorphen basahisehen G~ingen des ~iltesten Vulkanismus der Insel durehtrfimert. Der Beginn des kanarischen Vulkanismus lag dana& frfihestens in der Oberkreide. Aufgrund entspreehender geologischer Verh~iltnisse auf der Kapverdeninsel Maio wird ein 5hnlicher Bau des afrikanischen Kontinentalrandes im Bereich beider Archipele angenommen. AbstractThe western part of the chiefly volcanic island of Fuerteventura (Canary Islands) is underlain by a series of more than 1000 m of limestones, shales, marls, siltstones, and sandstones. The sedimentary rocks strike ESE, are partly overturned, and are at least as old as Upper Cretaceous, based on foraminifera. The entire sequence may also comprise Jurassic and Lower Cretaceous rocks as is shown by comparison with similar series on the neighbouring African continent.Thus Fuerteventura is part of the African continent or of the continental shelf and is no true "oceanic" island. The sedimentary rocks show striking similarities with the island of Maio (Capverde Islands) supporting similarities in the structure of the continental margin in both areas.

No abstract