The Agulhas Basin is an oceanic basin located south of South Africa where the South Atlantic Ocean and south-western Indian Ocean meet. Part of the African plate , it is bounded by the Agulhas Ridge (part of the Agulhas–Falkland fracture zone ) to the north and the Southwest Indian Ridge to the south; by the Meteor Rise to the west and the Agulhas Plateau to the east. Numerous bathymetric anomalies hint at the basin's dynamic tectonic history.
27-874: In a Late Paleocene (59–56 Ma) reconstruction of the opening of the South Atlantic Ocean (i.e. the separation of South America and Africa during the Gondwana break-up ) the Meteor Rise lies conjugate to the Islas Orcadas Rise (east of the Falkland Plateau ). The separation of the Meteor Rise and the Islas Orcadas Rise marks the beginning of the formation of the Agulhas Basin. The Agulhas Ridge extends from
54-741: A similar structure on the American side, but there is a Zapiola Seamount Complex south of the eastern end of the Rio Grande Rise. The formation of this mirrored structure is the result of the opening of the South Atlantic some 120 Mya and the Paraná and Etendeka continental flood basalts , the lateral-most parts of the structure, formed at the beginning of this process in areas that are now located in Brazil and Namibia . The Walvis Ridge
81-648: Is divided into three main sections: Cretaceous kimberlites in the central Democratic Republic of Congo and Angola align with the Walvis Ridge. The Tristan-Gough hotspot track first formed over the mantle plume that formed the Etendeka-Paraná continental flood basalts some 135 to 132 Ma . The eastern section of the ridge is thought to have been created in the Middle Cretaceous period, between 120 to 80 Ma . While
108-635: Is part of the ridge. The Eocene Layer of Mysterious Origin (Elmo) is a period of global warming that occurred 53.7 Ma , about two million years after the Paleocene–Eocene Thermal Maximum . This period manifests as a carbonate-poor red clay layer unique to the Walvis Ridge and is similar to the PETM, but of smaller magnitude. The Walvis Ridge is a natural obstacle for the Agulhas rings , mesoscale warm core rings that are shed from
135-620: Is responsible for this drop, since the rings' speed drops to 4.3±2.2 km/day between the Walvis Ridge and the Mid-Atlantic Ridge. The rings can cross the South Atlantic in 2.5–3 years but only two thirds make it farther than the Walvis Ridge. When the rings pass over the Cap Basin south of the Walvis Ridge they are frequently disturbed by the Benguela Current , interaction between rings, and bottom topography such as
162-459: Is still poorly understood. In the Agulhas basin, half of these rings are subdivided one or several times. A majority of the subdivided rings split at or near the bathymetric obstacles on the western side of the Agulhas Basin but almost a quarter of them also merge there either because of the obstacles or because of intense interaction with other rings. Antarctic Bottom Water (AABW) originated in
189-646: Is the abandoned Malvinas-Africa ridge crest. 97 Ma the plate boundary in the Agulhas Basin was reorganised when the Mid-Atlantic Ridge made an eastward jump. This brought the boundary towards the Agulhas Plateau where excessive volcanism was building a large igneous province . The inception of the Malvinas plate accompanied this shortening of the Agulas fracture zone. 61 Ma, the Malvinas plate
216-527: The Agulhas Current south of the Agulhas Bank . In average, five such rings are shed each year, a number that varies considerably between years. The rings tend cross the Walvis Ridge at its deepest part, but they still lose transitional speed and many rings decay rapidly. Their transitional speed drops from 5.2±3.6 km/day to 4.6±3.1 km/day, but it is not clear how much the Walvis Ridge
243-537: The Itaboraian South American land mammal ages and the upper Nongshanian and Gashatan Asian land mammal ages . The Thanetian is contemporary with the middle Wangerripian regional stage of Australia and the upper Ynezian regional stage of California . It overlaps the obsolete regional stages Landenian and Heersian of Belgium . The Sézanne flora is a fossil assemblage preserved in freshwater limestone deposits at Sézanne , laid down during
270-534: The Tristan Hotspot is one of few primary or deep mantle hotspots. Apart from the Mid-Atlantic Ridge, the Walvis Ridge and the Rio Grande Rise are the most distinctive feature of the South Atlantic sea floor. They originated from hotspot volcanism and together they form a mirrored symmetry across the Mid-Atlantic Ridge, with the Tristan Hotspot at its centre. Two of the distinct sections in
297-721: The Vema Seamount , but there are fewer obstacles and disturbances west of the Walvis Ridge were the rings tend stabilise. The Agulhas rings transport an estimated 1-5 Sv (millions m /s) of water from the Indian Ocean to the South Atlantic. Originating around Antarctica, Antarctic Bottom Water (AABW) enters the Cape Basin between the Agulhas Bank and the Agulhas Ridge after which it flows west north of
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#1732772431981324-760: The Ypresian Age (part of the Eocene ). The Thanetian is sometimes referred to as the Late Paleocene . The Thanetian was established by Swiss geologist Eugène Renevier in 1873. The Thanetian is named after the Thanet Formation , the oldest Cenozoic deposit of the London Basin , which was first identified in the area of Kent (southern England ) known as the Isle of Thanet . The base of
351-879: The Oligocene with the opening of the Drake Passage and the Tasmanian Seaway and resulted in the thermal insulation of Antarctica. AABW mixes with other masses in the Antarctic Circumpolar Current (ACC) to form the Circumpolar Deep Water (CDW). In the Agulhas Basin CDW flows northward and is deflect mostly westward by the Agulhas Ridge. A branch of CDW, however, enters the Cape Basin west of
378-533: The Thanetian Age, when Europe enjoyed a tropical climate. In the lagerstätte , leaves, entire flowers and seeds are minutely preserved. Also, the first representatives of Proboscidea appeared, Eritherium . This period was characterized by temperatures warmer than those of today. Walvis Ridge The Walvis Ridge ( walvis means whale in Dutch and Afrikaans ) is an aseismic ocean ridge in
405-733: The Thanetian Stage (the base of the Ypresian) is defined at a strong negative anomaly in δ C values at the global thermal maximum at the Paleocene-Eocene boundary . The Thanetian Stage is coeval the lower Neustrian European land mammal age (it spans the Mammal Paleogene zone 6 and part of zones 1 through 5. ), the upper Tiffanian and Clarkforkian North American land mammal ages , the Riochican and part of
432-570: The Thanetian Stage is laid at the base of magnetic chronozone C26n. The references profile ( Global Boundary Stratotype Section and Point ) is in the Zumaia section (43° 18'N, 2° 16'W) at the beach of Itzurun, Pais Vasco , northern Spain . Fossils of the unicellular planktonic marine coccolithophore Areoligeria gippingensis make their first appearance at the base of the Thanetian, and help define its lowest stratigraphic boundary. The top of
459-518: The Walvis Ridge have similar mirrored regions in the Rio Grande Rise; for example, the eastern section of the Walvis Ridge evolved in conjunction with the Torres Arch (the western end of the Rio Grande Rise, off the Brazilian coast) and, as the South Atlantic gradually opened, these structures became separated. The complex of seamounts in the western end of the Walvis Ridge, however, does not have
486-590: The cyclonic path followed by CDW.) 45°S 20°E / 45°S 20°E / -45; 20 Late Paleocene The Thanetian is, in the ICS Geologic timescale , the latest age or uppermost stratigraphic stage of the Paleocene Epoch or Series . It spans the time between 59.2 and 56 Ma . The Thanetian is preceded by the Selandian Age and followed by
513-482: The mantle plume remained large and stable, the eastern Walvis Ridge formed along with the Rio Grande Rise over the Mid-Atlantic Ridge. During the Maastrichtian 60 million years ago , the orientation of spreading changed, which is still visible in the orientation of the various sections of the Walvis Ridge. The mantle plume then gradually became unstable and bifurcated 60 to 70 Ma to produce
540-552: The northern tip of the Meteor Rise towards the Agulhas Bank south of South Africa . The ridge, however, ends abruptly in a small plateau at 40°S 15°E / 40°S 15°E / -40; 15 where it intersects a northeastward-trending spreading centre (the Agulhas Rift) that was abandoned during the Early Paleocene (61 Ma). The presence of a short-lived tectonic plate between these structures
567-588: The ridge from where it flows west along the northern side of the ridge before being deflected north-east (along the Walvis Ridge ) at the eastern end of the ridge. This long detour in the Cape Basin and mixing with North Atlantic Deep Water (NADW) results in warmer water than other CDW masses. Antarctic Intermediate Water (AAIW) flows above the CDW in the Agulhas Basin in an anti-cyclonic path (in contrast to
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#1732772431981594-542: The southern Atlantic Ocean . More than 3,000 km (1,900 mi) in length, it extends from the Mid-Atlantic Ridge , near Tristan da Cunha and the Gough Islands , to the African coast (at 18°S in northern Namibia ). The Walvis Ridge is one of few examples of a hotspot seamount chain that links a flood basalt province to an active hotspot. It is also considered one of the most important hotspot tracks because
621-455: The southern tip of Africa, it retroflects back into the Indian Ocean. At this retroflection it leaks warm core eddies known as Agulhas rings into the South Atlantic. This mesoscale anti-cyclonic rings feed the Atlantic meridional overturning circulation (AMOC) and are therefore believed to affect the global climate, although the connection between the leakage, AMOC, and climate change
648-525: The spreading of South America and Africa. Furthermore, magnetic anomalies on the Malvinas plate do not align with their conjugates on the African plate if the spreading rates and directions of South America and Africa are used as a guide. They also noted that the Agulhas fracture zone do not lay perpendicular to traces of the South America-Africa spreading north of it and cannot, therefore, have been generate by this spreading. The Agulhas Rift
675-476: The two separate Tristan and Gough hotspot tracks. It finally disintegrated 35 to 45 Ma and formed the guyot province in the western end of the ridge. Hundreds of volcanic explosions were recorded on the Walvis Ridge in 2001 and 2002. These explosions seemed to come from an unnamed seamount on the northern side of the ridge and are thought to be unrelated to the Tristan hotspot. The Ewing Seamount
702-607: Was finally incorporated into the African plate when the Malvinas-Africa ridge was abandoned as the result of a westward ridge jump along the Agulhas–Falkland fracture zone. This second ridge jump reduced one of the most spectacular fracture zones in Earth's history — 1,200 km (750 mi) in length — to 180 km (110 mi). The Agulhas Current flows south along the African east coast. When it reaches
729-519: Was first proposed by LaBrecque & Hayes 1979 . They named it the Malvinas plate and proposed that it was active from 90 Ma until the spreading ceased in the Agulhas Basin at 65 Ma. The plate is located at a proto- Bouvet triple junction . Marks & Stock 2001 found that Late Cretaceous (100–66 Ma) fracture zones generated on the Agulhas Rift do not align with those north of the Agulhas fracture zone and cannot therefore have been formed by
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