Paleomagnetic Isochrons, Unsteadiness, and Uniformity of Sedimentation in Miocene Intermontane Basin Sediments at Salla, Eastern Andean Cordillera, Bolivia

McRae, Lee E.

doi:10.1086/629420

Cited by 26 publications

(11 citation statements)

References 24 publications

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“…The burial of the back thrust belt, by its own synorogenic sediments, constrains the cessation of thrusting. The age of these basin sediments range from 24.6 to 33.1 Ma [ GEOBOL , 1997; Gillis et al , 2006; Kay et al , 1998; Lamb and Hoke , 1997; MacFadden et al , 1995; McRae , 1990; Sempere et al , 1990; Suarez and Diaz , 1996]. Growth structures are observed within the Luribay Formation and the lower levels of the Salla Formation (25.5–29.4 Ma), but are not observed in the subhorizontal upper Salla Formation indicating that deformation ceased in this region by ∼28 Ma (Figure 5f) [ Gillis et al , 2006].…”

Section: Discussionmentioning

confidence: 99%

Geometric, kinematic, and erosional history of the central Andean Plateau, Bolivia (15–17°S)

2008

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[1] Latitudinal changes in topography, climate, and thrust belt geometry in the central Andes have led to conflicting hypotheses that climate or tectonics exert a first-order control on orogen evolution. The relative roles of climate and tectonics in the evolution of the Andean orogen are difficult to quantify because of a lack of detailed observations for both the long-term deformation and erosion history of the Andean foldthrust belt. We contribute to the resolution of this problem by presenting a sequentially restored, balanced cross section based on new mapping across the northern Bolivia portion of the thrust belt (15-17°S). The timing and magnitude of exhumation across the cross section are determined by synthesizing 10 new and $70 previously published mineral cooling ages. Once balanced and restored, the section was sequentially forward modeled using stratigraphic and cooling age constraints. Results indicate the Eastern Cordillera (EC) records the highest magnitudes of shortening (123 km or 55%). The Interandean zone (IA) has shortened 48 km or 30%. In both the EC and IA individual thrust sheets are tightly folded and have minor offsets of 1-5 km. The Subandes (SA) has multiple levels of detachments allowing for thrust sheets with relatively large offsets (6-17 km). Total shortening in the SA is 66 km or 40%. Total magnitude of shortening for the entire fold-thrust belt in this region is 276 km (40%). New apatite and zircon fission track cooling ages in conjunction with published ages indicate two phases of rapid exhumation; an earlier phase from $40 to 25 Ma in the EC and one prior to $25 Ma in the IA, followed by distributed exhumation of the entire fold-thrust belt from $15 -0 Ma. Combined exhumation estimates from the balanced cross section and thermochronology suggest $9-11 km of exhumation in the EC, $5-9 km in the IA, and $3-4 km in the SA. Long-term shortening rates are 7 mm/a for the EC and IA and 4-8 mm/a for the SA. The SA shortening rates are based on a $15-0 Ma or 8-0 Ma deformation window. By linking cooling ages to location and magnitude of shortening, we suggest an $10-17 Ma pause or a dramatic deceleration in the rate of deformation and propagation of the fold-thrust belt between 25 and $15 or 8 Ma.

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Section: Discussionmentioning

confidence: 99%

Geometric, kinematic, and erosional history of the central Andean Plateau, Bolivia (15–17°S)

2008

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“…The Salla fauna is assigned to the Deseadan Land Mammal Age based on detailed comparisons of mammal faunas (MacFadden et ., 1985). The results of the calculation of radioisotopic ages suggest a Late Oligocene to Early Miocene date for the Salla deposits, and the absolute age for the Branisella zone is estimated at about 25-26 Ma (MacFadden et al, 1985;Naeser et al, 1987;Hayashida and Danhara, 1985;McRae, 1990). Recently, Kay et al (1998) revised the age of the Salla beds, concluding that the Branisella zone should be placed in the Chron C8 (25.82-27.02 Ma) of the Late Oligocene, and suggested that the geological age of the Salla beds might be slightly younger than that of the Deseadan beds in Patagonia.…”

Section: Geological Setting and The Materialsmentioning

confidence: 98%

New fossil materials of the earliest new world monkey,Branisella boliviana, and the problem of platyrrhine origins

Takai

Anaya

Shigehara

et al. 2000

Am. J. Phys. Anthropol.

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Branisella boliviana, from the Late Oligocene of Salla, Bolivia, is the oldest fossil platyrrhine monkey discovered. To date, several fossil specimens of Branisella have been obtained, but most of them are fragmentary dentitions, so the animals craniodental morphology is still obscure. During the 1996 field season a pair of upper and lower jaw fragments and another nearly complete mandible were recovered. These new fossil materials reveal the following morphological features in Branisella: 1) P(2) is much smaller than P(3,4), whereas P(2) is relatively small but probably sexually dimorphic; 2) the zygomatic arch protrudes smoothly posterolaterally from the maxillary bone, as in extant Callicebus; 3) the mandibular arcade is nearly V-shaped and the symphysial angle, which is formed by the horizontal plane and the anterior face of mandibular symphysis, is about 40 degrees, i.e., it neither leans as far anteriorly as in callitrichines nor does it stand as vertically as Cebus; 4) upper and lower molars wore down rapidly in life, suggesting a herbivorous diet and the possibility of terrestriality; and 5) dental eruptive sequence is the same as in extant Aotus. As a whole, the dentition of Branisella is very similar to that of Proteopithecus from the Late Eocene of Fayum, Egypt, except in the lower canine morphology, suggesting a close phyletic relationship between them. The origin and early diversification of platyrrhine monkeys might have occurred on the African continent before crossing the Atlantic Ocean.

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“…1.9, as well as 24.0 t 1.5 Ma by the zircon fission-track method (Hayashida and Danhara, 1985). Among these absolute ages, it is very significant that there is concordance between two K-Ar dates (26.4 +-1.0 and 25.1 +-0.7 Ma), which were acquired independently from the same level just below the Branisella zone (MacFadden et al, 1985;Naeser et al, 1987; see also McRae, 1990). The results of these studies suggest a late Oligocene to early Miocene date for the Salla deposits, and an age of about 25-26 Ma for the Branisella zone.…”

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confidence: 93%

New specimens of the oldest fossil platyrrhine, Branisella boliviana, from Salla, Bolivia

Takai¹,

Anaya²

1996

Am. J. Phys. Anthropol.

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During the 1992 and 1993 field seasons, several new specimens of Branisella boliviana, the oldest fossil platyrrhine, were discovered in the late Oligocene deposits at Salla, northwestern Bolivia. The new materials are two maxillary fragments and seven mandibular fragments, including P3 and P2, neither of which have previously been recovered. All new and previously reported materials, including the holotype and referred specimens, were apparently recovered from the same horizon, called the Branisella zone (MacFadden et al. [1985] J. Geol. 93:223-250; MacFadden [1990] J. Hum. Evol. 19:7-21. The crown morphology of the newly discovered upper and lower premolars suggests that Branisella has a close affinity with callitrichines. A detailed examination of all molar specimens suggests that "Szalatavus attricuspis," which was recovered at Salla in 1981 and described as a new genus by Rosenberger et al. (1991), is a junior synonym of Branisella. The Branisella-like upper molar, in which a small hypocone is preserved on the poorly developed distolingual cingulum, is a shared-derived character with callitrichines and does not correspond to the primitive state for platyrrhine phylogeny. The ancestral upper molar morphotype for platyrrhines should have a moderate to large hypocone and a well developed talon area.

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Paleomagnetic Isochrons, Unsteadiness, and Uniformity of Sedimentation in Miocene Intermontane Basin Sediments at Salla, Eastern Andean Cordillera, Bolivia

Cited by 26 publications

References 24 publications

Geometric, kinematic, and erosional history of the central Andean Plateau, Bolivia (15–17°S)

Geometric, kinematic, and erosional history of the central Andean Plateau, Bolivia (15–17°S)

New fossil materials of the earliest new world monkey,Branisella boliviana, and the problem of platyrrhine origins

New specimens of the oldest fossil platyrrhine, Branisella boliviana, from Salla, Bolivia

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