Control of Precambrian-to-Paleozoic orogenic trends on along-strike variations in Early Cretaceous continental rifts of the South Atlantic Ocean

2019 ◽  
Vol 7 (4) ◽  
pp. SH45-SH69 ◽  
Author(s):  
Kyle Reuber ◽  
Paul Mann
Keyword(s):  
Early Cretaceous ◽  
South Atlantic ◽  
Orogenic Belt ◽  
Deep Penetration ◽  
The South ◽  
The North ◽  
Continental Rifts ◽  
Rift Zones ◽  
Seismic Reflection Profiles ◽  
Orogenic Belts

The Early Cretaceous (135–130 Ma) continental rupture of Western Gondwana to form the South American and African plates closely paralleled the elongate trends of Precambrian and Paleozoic orogenic belts. These orogenic belts were produced as a result of the Neoproterozoic convergent and strike-slip assembly of Gondwana that redeformed during later, Paleozoic orogenic events. Continued continental rifting led to the formation of conjugate, South Atlantic volcanic passive margins whose widths vary from 55 to 180 km. Along-strike variations in crustal stretching, as measured from deep-penetration seismic reflection profiles, correlate with parallel and oblique orientations of rifts relative to the trend of the orogenic, basement fabric. Where orogenic fabric trends parallel to the north–south South Atlantic rift direction such as in the Dom Feliciano orogenic belt of Uruguay and Brazil and the Kaoko Uruguay/Brazil and Kaoko orogenic belt of Namibia, we observe narrow (55–90 km) rift zones with modest continental beta factors of 2.5–3.5 because smaller amounts of rifting were needed to stretch the weaker and parallel, orogenic, basement fabric. Where the basement fabric trends near-orthogonally to the north–south South Atlantic rift direction such as in the Salado suture of Southern Uruguay and the Damara Belt of Namibia, we observe wider (185–220 km) rift zones with higher beta factors of 4.3–5 because greater amounts of stretching were needed to rupture the orthogonal, orogenic, basement fabric. The rift-oblique Gariep Belt intersects the South Atlantic continental rupture at an intermediate angle (30°) and exhibits a predicted intermediate beta factor of 4.0. A compilation of published beta factors from 36 other rifted margins worldwide supports the same basement-trend-degree of stretching relationship that we have developed — with rift-parallel margins having lower beta factors in a range of 1.3–3.5 and rift-orthogonal or oblique margins having higher beta factors in a range of 4–8.

scholarly journals Sedimentary and Source-to-Sink Evolution of Intracontinental Basins: Implications for tectonic and Climate Evolution in the Late Mesozoic (Southern Junggar Basin, NW China)

2022 ◽  
Vol 9 ◽  
Author(s):  
Xutong Guan ◽  
Chaodong Wu ◽  
Xuecai Zhang ◽  
Weiwei Jia ◽  
Wei Zhang
Keyword(s):  
Early Cretaceous ◽  
Late Jurassic ◽  
Junggar Basin ◽  
Orogenic Belt ◽  
Alluvial Fan ◽  
Late Mesozoic ◽  
The North ◽  
Source To Sink ◽  
Tianshan Orogenic Belt ◽  
Orogenic Belts

Sedimentary investigations, petrography, heavy mineral and conglomerate component analyses, and detrital zircon U-Pb geochronology were conducted to reconstruct the sedimentary and source-to-sink evolution of the Southern Junggar Basin, an intracontinental basin in the late Mesozoic. A paludal deltaic environment evolved into a fluvial environment, and abruptly prograded into alluvial fan and aeolian environments in the Late Jurassic, which was replaced by fan deltaic and lacustrine environments in the Early Cretaceous. Three source-to-sink systems were identified, according to different source-to-sink system features. In the northern piedmont of the Tianshan Orogenic Belt, the North Tianshan Orogenic Belt mainly provided sediments in the Late Jurassic. The North Tianshan and Central Tianshan Orogenic Belt both supplied sediments in the Early Cretaceous. In the northern piedmont of the Bogda Orogenic Belt, the Bogda Orogenic Belt was constantly the primary provenance, and the Tianshan Orogenic Belt also provided sediments. Sediment recycling occurred in the basin margin in the Late Jurassic and more metamorphic rocks were denudated in the Early Cretaceous. The source-to-sink system shrank in the Late Jurassic and expanded in the Early Cretaceous. This source-to-sink evolution and the conglomerates in the Kalazha Formation with seismite structures responded to the aridification in the Late Jurassic, the uplift of the Bogda and Tianshan Orogenic Belts in the Late Jurassic, and the exhumation of the Bogda and Tianshan Orogenic Belts in the Early Cretaceous.

Observed seasonal regimes of North-South Atlantic Ocean interbasin exchange

2019 ◽  
Author(s):  
Hamed D. Ibrahim
Keyword(s):  
North Atlantic ◽  
Climate Models ◽  
South Atlantic ◽  
Meridional Overturning Circulation ◽  
Volume Flux ◽  
The South ◽  
The North ◽  
Basin Scale ◽  
Interbasin Exchange ◽  
North And South

North and South Atlantic lateral volume exchange is a key component of the Atlantic Meridional Overturning Circulation (AMOC) embedded in Earth’s climate. Northward AMOC heat transport within this exchange mitigates the large heat loss to the atmosphere in the northern North Atlantic. Because of inadequate climate data, observational basin-scale studies of net interbasin exchange between the North and South Atlantic have been limited. Here ten independent climate datasets, five satellite-derived and five analyses, are synthesized to show that North and South Atlantic climatological net lateral volume exchange is partitioned into two seasonal regimes. From late-May to late-November, net lateral volume flux is from the North to the South Atlantic; whereas from late-November to late-May, net lateral volume flux is from the South to the North Atlantic. This climatological characterization offers a framework for assessing seasonal variations in these basins and provides a constraint for climate models that simulate AMOC dynamics.

Taxonomy of Nystiellidae (Caenogastropoda, Epitonioidea) from Brazil, with description of three new species from the South-western Atlantic

2017 ◽  
Vol 98 (7) ◽  
pp. 1619-1644 ◽  
Author(s):  
Alexandre Dias Pimenta ◽  
Bruno Garcia Andrade ◽  
Ricardo Silva Absalão
Keyword(s):  
Rio Grande ◽  
Taxonomic Revision ◽  
South Atlantic ◽  
Shell Morphology ◽  
The South ◽  
Western Atlantic ◽  
North East ◽  
The North ◽  
Eastern Brazil ◽  
North Eastern

A taxonomic revision of the Nystiellidae from Brazil, including samples from the Rio Grande Rise, South Atlantic, was performed based on shell morphology. Five genera and 17 species were recognized. For the richest genus,Eccliseogyra, the three species previously recorded from Brazil were revised:E. brasiliensisandE. maracatu, previously known only from their respective type series, were re-examined. Newly available material ofE. maracatuexpanded the known geographic range of this species to off south-east Brazil.Eccliseogyra nitidais now recorded from north-eastern to south-eastern Brazil, as well as from the Rio Grande Rise. Three species ofEccliseogyraare newly recorded from the South Atlantic:E. monnioti, previously known from the north-eastern Atlantic, occurs off eastern Brazil and on the Rio Grande Rise; its protoconch is described for the first time, confirming its family allocation.Eccliseogyra pyrrhiasoccurs off eastern Brazil and on the Rio Grande Rise, andE. folinioff eastern Brazil. The genusIphitusis newly recorded from the South Atlantic.Iphitus robertsiwas found off northern Brazil, although the shells show some differences from the type material, with less-pronounced spiral keels. Additional new finds showed thatIphitus cancellatusranges from eastern Brazil to the Rio Grande Rise, and Iphitusnotiossp. nov. is restricted to the Rio Grande Rise.Narrimania, previously recorded from Brazil based on dubious records, is confirmed, including the only two living species described for the genus:N. azelotes, previously only known from the type locality in Florida, andN. concinna, previously known from the Mediterranean. A third species,Narrimania raquelaesp. nov. is described from eastern Brazil, diagnosed by its numerous and thinner cancellate sculpture. To the three species ofOpaliopsispreviously known from Brazil, a fourth species,O. arnaldoisp. nov., is added from eastern Brazil, and diagnosed by its very thin spiral sculpture, absence of a varix, and thinner microscopic parallel axial striae.Papuliscala nordestina, originally described from north-east Brazil, is recorded off eastern Brazil and synonymized withP. elongata, a species previously known only from the North Atlantic.

scholarly journals New insights on the early Mesozoic evolution of multiple tectonic regimes in the northeastern North China Craton from the detrital zircon provenance of sedimentary strata

Solid Earth ◽  
2018 ◽  
Vol 9 (6) ◽  
pp. 1375-1397 ◽  
Author(s):  
Yi Ni Wang ◽  
Wen Liang Xu ◽  
Feng Wang ◽  
Xiao Bo Li
Keyword(s):  
North China Craton ◽  
North China ◽  
Early Jurassic ◽  
Orogenic Belt ◽  
Detrital Zircons ◽  
Late Triassic ◽  
Early Triassic ◽  
The South ◽  
The North ◽  
Early Mesozoic

Abstract. To investigate the timing of deposition and provenance of early Mesozoic strata in the northeastern North China Craton (NCC) and to understand the early Mesozoic paleotectonic evolution of the region, we combine stratigraphy, U–Pb zircon geochronology, and Hf isotopic analyses. Early Mesozoic strata include the Early Triassic Heisonggou, Late Triassic Changbai and Xiaoyingzi, and Early Jurassic Yihe formations. Detrital zircons in the Heisonggou Formation yield  ∼ 58 % Neoarchean to Paleoproterozoic ages and  ∼ 42 % Phanerozoic ages and were sourced from areas to the south and north of the basins within the NCC, respectively. This indicates that Early Triassic deposition was controlled primarily by the southward subduction of the Paleo-Asian oceanic plate beneath the NCC and collision between the NCC and the Yangtze Craton (YC). Approximately 88 % of the sediments within the Late Triassic Xiaoyingzi Formation were sourced from the NCC to the south, with the remaining  ∼ 12 % from the Xing'an–Mongolia Orogenic Belt (XMOB) to the north. This implies that Late Triassic deposition was related to the final closure of the Paleo-Asian Ocean during the Middle Triassic and the rapid exhumation of the Su–Lu Orogenic Belt between the NCC and YC. In contrast,  ∼ 88 % of sediments within the Early Jurassic Yihe Formation were sourced from the XMOB to the north, with the remaining  ∼ 12 % from the NCC to the south. We therefore infer that rapid uplift of the XMOB and the onset of the subduction of the Paleo-Pacific Plate beneath Eurasia occurred in the Early Jurassic.

scholarly journals Agulhas ring injection into the South Atlantic during glacials and interglacials

Ocean Science ◽  
2008 ◽  
Vol 4 (3) ◽  
pp. 223-237 ◽  
Author(s):  
V. Zharkov ◽  
D. Nof
Keyword(s):  
Critical Angle ◽  
South Atlantic ◽  
African Continent ◽  
The South ◽  
Wind Stress Curl ◽  
Agulhas Current ◽  
The North ◽  
Meridional Overturning ◽  
The Indian Ocean ◽  
The Last Glacial

Abstract. Recent proxies suggest that, at the end of the last glacial, there was a significant increase in the injection of Agulhas rings into the South Atlantic (SA). This brought about a dramatic increase in the salt-influx (from the Indian Ocean) into the SA helping re-start the then-collapsed meridional overturning cell (MOC), leading to the termination of the Younger Dryas (YD). Here, we propose a mechanism through which large variations in ring production take place. Using nonlinear analytical solutions for eddy shedding, we show that there are restricted possibilities for ring detachment when the coast is oriented in the north-south direction. We define a critical coastline angle below which there is rings shedding and above which there is almost no shedding. In the case of the Agulhas region, the particular shape of the African continent implies that rings can be produced only when the retroflection occurs beyond a specific latitude where the angle is critical. During glaciation, the wind stress curl (WSC) vanished at a latitude lower than that of the critical angle, which prohibited the retroflection from producing rings. When the latitude at which the WSC vanishes migrated poleward towards its present day position, the corresponding coastline angle decreased below the critical angle and allowed for a vigorous production of rings. Simple process-oriented numerical simulations (using the Bleck and Boudra model) are in satisfactory agreement with our results and enable us to affirm that, during the glacials, the behavior of the Agulhas Current (AC) was similar to that of the modern East Australian Current (EAC), for which the coastline slant is supercritical.

scholarly journals Stalked crinoids (Echinodermata) collected by the R/V Polarstern and Meteor in the south Atlantic and in Antarctica

Zootaxa ◽  
2012 ◽  
Vol 3425 (1) ◽  
pp. 1 ◽  
Author(s):  
MARC ELÉAUME ◽  
JENS-MICHAEL BOHN ◽  
MICHEL ROUX ◽  
NADIA AMÉZIANE
Keyword(s):  
North Atlantic ◽  
Deep Sea ◽  
South Atlantic ◽  
The South ◽  
The West ◽  
Walvis Ridge ◽  
The North ◽  
West Antarctic ◽  
Stalked Crinoids ◽  
Hard Substrates

During the last decades, R/V Meteor and R/V Polarstern deep-sea investigations in the south Atlantic and neighbouringSouthern Ocean collected new samples of stalked crinoids belonging to the families Bathycrinidae, Phrynocrinidae andHyocrinidae which are herein described. The species found are Bathycrinus australis A.H. Clark, 1907b (the most abun-dant), Dumetocrinus aff. antarcticus (Bather, 1908), Hyocrinus bethellianus Thomson, 1876, Feracrinus heinzelleri newspecies, and Porphyrocrinus cf. incrassatus (Gislén, 1933). As only stalk fragments of bathycrinids were frequently col-lected, a distinction between the two Atlantic species B. australis and B. aldrichianus is proposed using characters of co-lumnal articulations. A few specimens attributed to Porphyrocrinus cf. incrassatus, Hyocrinus bethellianus and Hyocrinussp. collected by the N/O Jean Charcot on the Walvis Ridge are also described, plus a new specimen of Porphyrocrinusincrassatus collected in the central mid-Atlantic. Biogeography and close affinities between species in the genera Bathy-crinus and Porphyrocrinus suggest an Antarctic origin of some stalked crinoids among the north Atlantic deep-sea fauna.The presence of B. australis in both the Angola and Cape basins suggests that the Walvis Ridge is not a bio-geographicalbarrier for this relatively eurybathic species, which can attach to hard substrates as well as anchor in sediment. The genusDumetocrinus seems to be an example of colonization of the west Antarctic platform from deeper environment where its ancestor lived.

scholarly journals A Climatology of Subtropical Cyclones in the South Atlantic

2012 ◽  
Vol 25 (21) ◽  
pp. 7328-7340 ◽  
Author(s):  
Jenni L. Evans ◽  
Aviva Braun
Keyword(s):  
North Atlantic ◽  
Warm Season ◽  
Hybrid Structure ◽  
South Atlantic ◽  
The South ◽  
Rossby Wave Breaking ◽  
The North ◽  
Brazil Current ◽  
Eastern Australia ◽  
Upper Level

A 50-yr climatology (1957–2007) of subtropical cyclones (STs) in the South Atlantic is developed and analyzed. A subtropical cyclone is a hybrid structure (upper-level cold core and lower-level warm core) with associated surface gale-force winds. The tendency for warm season development of North Atlantic STs has resulted in these systems being confused as tropical cyclones (TCs). In fact, North Atlantic STs are a regular source of the incipient vortices leading to North Atlantic TC genesis. In 2004, Hurricane Catarina developed in the South Atlantic and made landfall in Brazil. A TC system had been previously unobserved in the South Atlantic, so the incidence of Catarina highlighted the lack of an ST climatology for the region to provide a context for the likelihood of future systems. Sixty-three South Atlantic STs are documented over the 50-yr period analyzed in this climatology. In contrast to the North Atlantic, South Atlantic STs occur relatively uniformly throughout the year; however, their preferred location of genesis and mechanisms for this genesis do exhibit some seasonal variability. Rossby wave breaking was identified as the mechanism for the ST vortex initiation for North Atlantic STs. A subset of South Atlantic STs forms via this mechanism, however, an additional mechanism for ST genesis is identified here: lee cyclogenesis downstream of the Andes in the Brazil Current region—an area favorable for convection. This formation mechanism is similar to development of type-2 east coast lows in the Tasman Sea off eastern Australia.

scholarly journals Interannual Variability of Northwest Australian Tropical Cyclones

2010 ◽  
Vol 23 (17) ◽  
pp. 4538-4555 ◽  
Author(s):  
Kevin H. Goebbert ◽  
Lance M. Leslie
Keyword(s):  
Standard Deviation ◽  
North America ◽  
Atlantic Ocean ◽  
Southern Oscillation ◽  
South Atlantic ◽  
Conclusive Evidence ◽  
South Atlantic Ocean ◽  
Northwest Pacific ◽  
The South ◽  
The North

Abstract Tropical cyclone (TC) activity over the southeast Indian Ocean has been studied far less than other TC basins, such as the North Atlantic and northwest Pacific. The authors examine the interannual TC variability of the northwest Australian (NWAUS) subbasin (0°–35°S, 105°–135°E), using an Australian TC dataset for the 39-yr period of 1970–2008. Thirteen TC metrics are assessed, with emphasis on annual TC frequencies and total TC days. Major findings are that for the NWAUS subbasin, there are annual means of 5.6 TCs and 42.4 TC days, with corresponding small standard deviations of 2.3 storms and 20.0 days. For intense TCs (WMO category 3 and higher), the annual mean TC frequency is 3.0, with a standard deviation of 1.6, and the annual average intense TC days is 7.6 days, with a standard deviation of 4.5 days. There are no significant linear trends in either mean annual TC frequencies or TC days. Notably, all 13 variability metrics show no trends over the 39-yr period and are less dependent upon standard El Niño–Southern Oscillation (ENSO) variables than many other TC basins, including the rest of the Australian region basin. The largest correlations with TC frequency were geopotential heights for June–August at 925 hPa over the South Atlantic Ocean (r = −0.65) and for April–June at 700 hPa over North America (−0.64). For TC days the largest correlations are geopotential heights for July–September at 1000 hPa over the South Atlantic Ocean (−0.7) and for April–June at 850 hPa over North America (−0.58). Last, wavelet analyses of annual TC frequencies and TC days reveal periodicities at ENSO and decadal time scales. However, the TC dataset is too short for conclusive evidence of multidecadal periodicities. Given the large correlations revealed by this study, developing and testing of a multivariate seasonal TC prediction scheme has commenced, with lead times up to 6 months.

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