Nazca-South America interactions and the late Eocene-late Oligocene flat-slab episode in the central Andes

Tectonics ◽  
2012 ◽  
Vol 31 (2) ◽  
pp. n/a-n/a ◽  
Author(s):  
Leland J. O'Driscoll ◽  
Mark A. Richards ◽  
Eugene D. Humphreys
Keyword(s):  
South America ◽  
Central Andes ◽  
Late Eocene ◽  
Late Oligocene ◽  
Flat Slab

scholarly journals Basement-involved deformation overprinting thin-skinned deformation in the Pampean flat-slab segment of the southern Central Andes, Argentina

2016 ◽  
Vol 153 (5-6) ◽  
pp. 1042-1065 ◽  
Author(s):  
MARIA SILVIA JAPAS ◽  
GUILLERMO HÉCTOR RÉ ◽  
SEBASTIÁN ORIOLO ◽  
JUAN FRANCISCO VILAS
Keyword(s):  
South America ◽  
Central Andes ◽  
Flat Slab ◽  
Kinematic Data ◽  
Sierras Pampeanas ◽  
Fold And Thrust Belt ◽  
Deformation Features ◽  
Southern Central ◽  
Argentine Precordillera ◽  
Northern Sector

AbstractIn the southern Central Andes, the Andean foreland was deformed due to Neogene shallowing of the Nazca slab beneath the South America plate. In this 27–33ºS Pampean flat-slab segment, the N-trending Argentine Precordillera transpressional fold-and-thrust belt and the Sierras Pampeanas broken foreland developed as a consequence of inward migration of the orogenic front. At 28ºS, a NNE-trending westward-dipping, thick Neogene synorogenic sequence is exposed in the Sierra de los Colorados, which shares deformation features of the Precordillera and the Sierras Pampeanas. Integration of new structural and kinematic data and available structural, kinematic, geophysical and palaeomagnetic information allows consideration of the Sierra de los Colorados area as part of the northern sector of the Precordillera during the middle Neogene. Atc. 9 Ma, basement block exhumation started with the uplift of the Sierra de Umango-Espinal that was triggered by deformation along the NE-trending Tucumán oblique belt. This stage marked the beginning of compartmentalization of the incipiently deformed Vinchina foreland. Sincec. 6.8–6.1 Ma, basement block uplift linked to the Miranda–Chepes and Valle Fértil NNW-trending sinistral transpressional belts, as well as kinking of the Neogene sequence by localized WNW-striking cross-strike structures, resulted in multiple segmentation that produced a complex mosaic of basement-block pieces. The overprint of these regional, basement-involved, oblique, brittle–ductile transpressional and cross-strike megazones could be related to high interplate coupling. Localized mechanical and rheological changes introduced by magmatism favoured this thick-skinned deformation overprint.

Late Paleogene paleotopographic evolution of the northern Cordilleran orogenic front: Implications for demise of the orogen

2021 ◽  
Author(s):  
Majie Fan ◽  
Kurt N. Constenius ◽  
Rachel F. Phillips ◽  
David L. Dettman
Keyword(s):  
Initial Phase ◽  
Middle Eocene ◽  
High Elevation ◽  
Late Eocene ◽  
Crustal Extension ◽  
Late Oligocene ◽  
Slab Rollback ◽  
Basin Floor ◽  
Climate Cooling ◽  
High Range

The paleotopographic history of the North American Cordilleran orogen holds the key to understanding mechanisms of orogenesis and subsequent orogenic collapse. It has been suggested that the orogenic front in western Montana (USA) and Alberta (Canada) was more than 4 km high during Late Cretaceous−early Eocene contractional deformation and during the initial phase of extension in the middle Eocene; however, the late Eocene−Oligocene topographic evolution during continued extensional collapse remains poorly constrained. Here we extend the paleotopographic record in the Kishenehn Basin in northwestern Montana and southeastern British Columbia (Canada) to the late Oligocene by studying δ18O values of fossil mollusks and cement and paleosol carbonates. The molluscan taxa changed from three sympatric groups with preferred habitats ranging from tropical wet, semi-arid subtropical, and temperate during the middle and late Eocene, to mainly a single group associated with temperate environment during the Oligocene, reflecting a decline in molluscan biodiversity induced by climate cooling across the Eocene−Oligocene transition. Reconstructed δ18O values of alpine snowmelt and basinal precipitation decreased by 1.4‰ and 3.8‰, respectively, from the middle to late Eocene, reflecting climate cooling and ∼1 km surface uplift of the basin floor. The reconstructed alpine snowmelt δ18O values then increased by 2.9‰ in the Oligocene suggesting a ∼0.5 km drop in elevation of the orogenic front. Collectively, the results of our new and previously published δ18O data chronicle the paleotopographic response to the change from flat-slab subduction to slab rollback over a 45 m.y. period. These data suggest that the orogenic front was characterized by high elevation (>4 km) in the ancestral Lewis-Clark-Livingston ranges during latest Cretaceous−early Eocene (ca. 75−52 Ma) contraction. The initial phase of extension related to the Kishenehn Basin created a lowland basin with a surface elevation of only ∼1.5 km during the early middle Eocene (ca. 46−44 Ma) whereas the ranges remained >4 km high. The high range elevations were sustained for at least 12 m.y. in the middle to late Eocene concurrent with extension, while the basin floor elevation was uplifted to ∼2.5 km by the latest Eocene (ca. 36−34 Ma). Basin aggradation can explain at most half of the 1 km basin floor uplift. The remaining amount (at least 0.5 km) and sustained high range elevation suggest that range denudation and crustal extension was compensated by the isostatic and thermal effects of slab rollback and/or passage of a slab window and infusion of hot asthenosphere beneath the continent. The range elevation in the orogenic front decreased ∼0.5 km by the late Oligocene (ca. 28 Ma), associated with a decrease in rock uplift rate associated with extension. A post-Oligocene elevation drop of ∼1 km resulted in both the ranges and basin floor reaching modern topography in the Kishenehn Basin drainage, likely due to the regional effect of Neogene Basin and Range extension. This study, along with the previous investigation of the Kishenehn Basin by Fan et al. (2017), are the first studies that systematically investigate paleorelief of the orogenic belt by reconstructing paleoelevations of the mountains and the basin at the same time. The results highlight that the Cordilleran orogenic front of northern Montana and southern British Columbia sustained its high elevation edifice for at least 12 m.y. after the start of extension. We suggest that initial crustal extension did not result in orogenic demise because of concurrent thermal and isostatic uplift.

scholarly journals A second peirosaurid crocodyliform from the Mid-Cretaceous Kem Kem Group of Morocco and the diversity of Gondwanan notosuchians outside South America

2021 ◽  
Vol 8 (10) ◽  
Author(s):  
Cecily S. C. Nicholl ◽  
Eloise S. E. Hunt ◽  
Driss Ouarhache ◽  
Philip D. Mannion
Keyword(s):  
South America ◽  
Late Cretaceous ◽  
North Africa ◽  
Lateral Surface ◽  
Middle Jurassic ◽  
Tooth Enamel ◽  
Phylogenetic Analyses ◽  
Late Eocene ◽  
South American ◽  
Early Late

Notosuchians are an extinct clade of terrestrial crocodyliforms with a particularly rich record in the late Early to Late Cretaceous (approx. 130–66 Ma) of Gondwana. Although much of this diversity comes from South America, Africa and Indo-Madagascar have also yielded numerous notosuchian remains. Three notosuchian species are currently recognized from the early Late Cretaceous (approx. 100 Ma) Kem Kem Group of Morocco, including the peirosaurid Hamadasuchus rebouli . Here, we describe two new specimens that demonstrate the presence of at least a fourth notosuchian species in this fauna. Antaeusuchus taouzensis n. gen. n. sp. is incorporated into one of the largest notosuchian-focused character-taxon matrices yet to be compiled, comprising 443 characters scored for 63 notosuchian species, with an increased sampling of African and peirosaurid species. Parsimony analyses run under equal and extended implied weighting consistently recover Antaeusuchus as a peirosaurid notosuchian, supported by the presence of two distinct waves on the dorsal dentary surface, a surangular which laterally overlaps the dentary above the mandibular fenestra, and a relatively broad mandibular symphysis. Within Peirosauridae, Antaeusuchus is recovered as the sister taxon of Hamadasuchus . However, it differs from Hamadasuchus with respect to several features, including the ornamentation of the lateral surface of the mandible, the angle of divergence of the mandibular rami, the texture of tooth enamel and the shape of the teeth, supporting their generic distinction. We present a critical reappraisal of the non-South American Gondwanan notosuchian record, which spans the Middle Jurassic–late Eocene. This review, as well as our phylogenetic analyses, indicate the existence of at least three approximately contemporaneous peirosaurid lineages within the Kem Kem Group, alongside other notosuchians, and support the peirosaurid affinities of the ‘trematochampsid’ Miadanasuchus oblita from the Maastrichtian of Madagascar. Furthermore, the Cretaceous record demonstrates the presence of multiple lineages of approximately contemporaneous notosuchians in several African and Madagascan faunas, and supports previous suggestions regarding an undocumented pre-Aptian radiation of Notosuchia. By contrast, the post-Cretaceous record is depauperate, comprising rare occurrences of sebecosuchians in north Africa prior to their extirpation.

scholarly journals Reticulate Nummulites (N. fabianii Linage) and Age of the Pellatispira-Beds of the Drazinda Formation, Sulaiman Range, Pakistan

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Ozcan E
Keyword(s):  
Mediterranean Region ◽  
Late Eocene ◽  
Test Surface ◽  
Time Interval ◽  
Late Oligocene ◽  
Shallow Marine ◽  
Western Tethys ◽  
Two Samples ◽  
Evolutionary Scheme ◽  
Weak Surface

The Eocene shallow marine Pellatispira-beds in the upper part of the Drazinda Formation represent the latest phase of Cenozoic Tethyan marine deposition in the Sulaiman Range, West Pakistan. The unit consists of stratigraphically important taxa as Heterostegina,Silvestriella, Pellatispira, a new Baculogypsina (possibly ancestral to modern Baculogypsina) and reticulate Nummulites implying a latest middle to late Eocene (late Bartonian-Priabonian) age. A more precise age of the unit requires the biometric study of reticulate Nummulites, the evolutionary scheme of which is better known from the peri-Mediterranean region in the Tethys. This group, which was subdivided into a series of successive chrono-species based on the biometry of inner cross-diameter of proloculus and changes in the types of granulation/reticulation on the test surface in the late Eocene-late Oligocene interval, appears to have a significant biostratigraphic potential for a high-resolution biostratigraphy in the peri-Mediterranean region (Western Tethys). The reticulate Nummulites in two samples from Rakhi Nala and Zinda Pir, ZP22 and RNB10, were studied and compared with those from the peri-Mediterranean region. The isolated specimens have a weak surface granulation externally, a distinct small umbonal granule (pile) and typical reticulation. The samples ZP22 and RNB10 from Zinda Pir and and Rakhi Nala sections have an average inner cross diameter of proloculus of 152.0 and 153.0 μm respectively. The reticulate Nummulites in both samples are assigned to N. hormoensis, a chrono-species characteristic for the shallow benthic zone (SBZ 18), referable to latest Bartonian-early Priabonian time interval. Since Heterostegina in peri-Mediterranean region and in Pakistan belongs to different lineages, a correlation of N. hormoensis in the studied samples with the wellestablished evolutionary scheme of Heterostegina reticulata and H.armenica lineages from the Western Tethys was not possible.

scholarly journals A new species of pitviper of the genus Bothrops (Serpentes: Viperidae: Crotalinae) from the Central Andes of South America

Zootaxa ◽  
2019 ◽  
Vol 4656 (1) ◽  
pp. 99-120 ◽  
Author(s):  
JUAN TIMMS ◽  
JUAN C. CHAPARRO ◽  
PABLO J. VENEGAS ◽  
DAVID SALAZAR-VALENZUELA ◽  
GUSTAVO SCROCCHI ◽  
...  
Keyword(s):  
New Species ◽  
South America ◽  
Central Andes ◽  
Color Pattern ◽  
Body Color ◽  
Montane Forests ◽  
Southern Peru ◽  
Large Trees ◽  
A New Species

We describe a new species of montane pitviper of the genus Bothrops from the Cordillera Oriental of the Central Andes, distributed from southern Peru to central Bolivia. The new species can be distinguished from its congeners by the characteristic combination of a dorsal body color pattern consisting of triangular or subtriangular dark brown dorsal blotches, paired dark brown parallel occipital stripes, a conspicuous dark brown postocular stripe, the presence of canthorostrals in some specimens, prelacunal fused or partially fused with second supralabial, one scale usually separating internasals, rostral trapezoidal, two canthals oval to rounded, similar size or slightly larger than internasals, three or four medial intercanthals, eight to twelve intersupraoculars, intercanthals and intersupraoculars keeled and frequently slightly keeled, supraoculars oval, one to three suboculars, two to three postoculars, loreal subtriangular, two to six prefoveals, subfoveals absent, two or none postfoveals, one or two scales between suboculars and fourth supralabial, seven or eight supralabials, nine or eleven infralabials, 23–25 middorsal scales, 189–195 ventrals in females and 182–190 in males, 48–58 subcaudals in females and 54–63 in males, exceptionally undivided. The new species is apparently restricted to areas within Andean montane forests that are less humid and devoid of large trees. 

Peonza: new gastropod genus from the middle Tertiary of Patagonia and Chile

1994 ◽  
Vol 68 (2) ◽  
pp. 279-286 ◽  
Author(s):  
Amalia M. Olivera ◽  
William J. Zinsmeister ◽  
S. Graciela Parma
Keyword(s):  
New Species ◽  
Temporal Distribution ◽  
Late Eocene ◽  
Tierra Del Fuego ◽  
Early Miocene ◽  
Late Oligocene ◽  
Southern Chile ◽  
Santa Cruz ◽  
Two New Species

A new Tertiary gastropod genus, Peonza n. gen., is described, along with two new species, P. torquata from southern Argentina and P. benjamina from southern Chile. These muricacean gastropods, of uncertain familial status, occur in the late Eocene San Julián Formation and in the late Oligocene to early Miocene? Monte León Formation, Santa Cruz Province, Argentina. They also were recorded in the (probably) Oligocene Magellanian beds in Tierra del Fuego, Argentina, and in early Miocene deposits of the Tres Montes region in the Chilean Canals. In spite of the small number of specimens, Peonza n. gen. seems to have had a wide geographic and temporal distribution.

Apatite fission-track thermochronology of the Western Pontides (NW Turkey)

2011 ◽  
Vol 149 (1) ◽  
pp. 133-140 ◽  
Author(s):  
WILLIAM CAVAZZA ◽  
ILARIA FEDERICI ◽  
ARAL I. OKAY ◽  
MASSIMILIANO ZATTIN
Keyword(s):  
Fission Track ◽  
Late Eocene ◽  
Tectonic Activity ◽  
Late Oligocene ◽  
Apatite Fission Track ◽  
Tectonic Events ◽  
Fission Track Thermochronology ◽  
Nw Turkey ◽  
Tectonic Contact ◽  
North And South

AbstractThe results of apatite fission-track analyses of the Western Pontides of NW Turkey point to three discrete episodes of Cenozoic exhumation correlatable with major supraregional tectonic events. (1) Paleocene–early Eocene exhumation reflected the closure of the İzmir–Ankara ocean. (2) Late Eocene–earliest Oligocene exhumation was the result of renewed tectonic activity along the İzmir–Ankara suture. (3) Late Oligocene–early Miocene exhumation recorded the onset of northern Aegean extension. Samples collected north and south of the tectonic contact between the two terranes forming the Western Pontides (i.e. İstanbul and Sakarya terranes) record the same cooling events, suggesting that such terranes were amalgamated in pre-Cenozoic times.

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