Search

Holocene variations of tropical moisture balance have been ascribed to orbitally forced changes in solar insolation. If this model is correct, millennial-scale climate evolution should be antiphased between the northern and southern hemispheres, producing humid intervals in one hemisphere matched to aridity in the other. Here we show that Holocene climate trends were largely synchronous and in the same direction in the northern and southern hemisphere outer-tropical Andes, providing little support for the dominant role of insolation forcing in these regions. Today, sea-surface temperatures in the equatorial Pacific Ocean modulate rainfall variability in the outer tropical Andes of both hemispheres, and we suggest that this mechanism was pervasive throughout the Holocene. Our findings imply that oceanic forcing plays a larger role in regional South American climate than previously suspected, and that Pacific sea-surface temperatures have the capacity to induce abrupt and sustained shifts in Andean climate.

An ash-rich volcaniclastic sandstone immediately underlying dinosaur-rich material from the Danek Bonebed in the Horseshoe Canyon Formation (HCF), Edmonton, Alberta, Canada, contains accessory zircon, which have been dated employing U-Pb geochronology. Both laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and chemical abrasion isotope dilution thermal ionization mass spectrometry (ID-TIMS) U-Pb analyses have been conducted. The zircon age distributions are complex with U-Pb dates ranging from Precambrian to Cretaceous. We consider the youngest ID-TIMS 206Pb/238U date of 71.923 ± 0.068 Ma as the maximum deposition age of the ash-rich sandstone, placing the overlying Danek bonebed in the early Maastrichtian. This age is compatible with the paleontological assemblage from the Danek Bonebed and the regional stratigraphy. The zircon age distribution also implies that the HCF had a complex provenance of the detritus with some Archean and Proterozoic zircons, a group of Mesozoic, and alarge compliment of Cretaceous grains. The results highlight the importance of high precision geochronology in constraining the age of important fossil deposits such as the Danek Bonebed. Un gres volcano-clastique riche en cendres, situe immediatement sous le materiau riche en dinosaures du Danek Bonebed (<< lit d'os Danek >>) dans la Formation de Horseshoe Canyon, a Edmonton, Alberta, Canada, contient des zircons accessoires qui ont ete dates par geochronologie U-Pb. Des analyses U-Pb par spectrometrie de masse a plasma induit couplee a l'ablation laser (LA-ICP-MS) et par abrasion chimique, dilution isotopique et spectrometrie de masse a thermoionisation (ID-TIMS) ont ete effectuees. Les distributions des ages du zircon sont complexes avec des dates U-Pb dans une plage du Precambrien au Cretace. Nous considerons la plus recente date de 71,923 ± 0,068 Ma, determinee par ID-TIMS 206Pb/238U, comme etant l'age maximum de deposition du gres riche en cendres, ce qui place le lit d'os Danek sus-jacent au Maastrichtien precoce. Cet age est compatible avec l'assemblage paleontologique du lit d'os Danek et la stratigraphie regionale. La distribution des ages du zircon signifie aussi que la provenance des detritus de la Formation de Horseshoe Canyon est complexe; en effet, quelques zircons datent de l'Archeen et du Proterozoique et la formation contient ainsi un groupe de grains du Mesozoique et de nombreux grains du Cretace. Les resultats soulignent l'importance d'une geochronologie de grande precision pour bien encadrer l'age des importants depots de fossiles tels que le lit d'os Danek. [Traduit par le Redaction], Introduction The Danek Bonebed (hereafter DBB) in Edmonton, Alberta, is a Late Cretaceous paleontological locality that yielded important information on dinosaur behavior, evolution, and ecology. However, until now an explicit [...]

During the course of excavating the Maastrichtian Danek Bonebed in the city of Edmonton, a range of well-preserved organic materials was recovered alongside vertebrate remains, including amber, coal, and unpermineralized plant fragments. Herein, we report carbon and hydrogen stable isotopic characterizations of these materials to provide ancillary insights into genesis of the fossil deposit. These analyses permit isotopic comparisons between the various organic fractions at the Danek locality, as well as with other Late Cretaceous localities in Alberta. The investigation of amber proves particularly informative, with carbon stable isotope ratios that are regionally consistent and furthermore conform to the larger, global-scale isotopic trend for this material, and hydrogen results that inform paleoclimatic conditions at the time of amber formation. When coupled with chemotaxonomic information from amber Fourier-transform infrared spectroscopy, the isotopic results indicate a consistent taxodioid forest composition and relatively stable environmental conditions across the three horizons that encapsulate the Danek bonebed. Au cours de l'excavation du Danek Bonebed (Maastrichtien) dans la ville d'Edmonton, une gamme de materiaux organiques bien conserves a ete recuperee tout pres de restes de vertebres; ces materiaux comprennent de l'ambre, du charbon et des fragments de plantes non permineralises. Dans cet article, nous presentons les caracterisations des isotopes stables carbone et hydrogene de ces materiaux afin de fournir des points de vue supplementaires sur la genese du depot fossilifere. Ces analyses permettent de comparer les isotopes des diverses fractions organiques a l'emplacement Danek et a d'autres localites du Cretace tardif en Alberta. L'etude de l'ambre s'est averee particulierement informative. En effet, les rapports stables des isotopes du carbone sont constants a travers la region et, de plus, ils concordent avec la tendance isotopique a plus grande echelle pour ce materiau et avec les resultats pour l'hydrogene qui donnent des indices quant aux conditions paleoclimatiques au moment de la formation de l'ambre. Lorsque jumeles a l'information chimiotaxonomique d'une spectroscopie infrarouge a transformation de Fourier de l'ambre, les resultats isotopiques indiquent une composition de foret taxodioide et des conditions environnementales relativement stables a travers les trois horizons qui contiennent le <> de Danek. [Traduit par le Redaction], Introduction An array of information can be extracted from dinosaur bonebed material to recreate both the populations of organisms preserved within the deposit and the environment in which they lived. [...]