Rodriguez-Lopez J.P.,Complutense University of Madrid |
Melendez N.,Complutense University of Madrid |
Melendez N.,Institute Geociencias |
de Boer P.L.,University Utrecht |
And 2 more authors.
Aeolian Research | Year: 2013
During the Albian Iberia was under the influence of the Northern-Hemisphere Hot Arid Belt favouring the development of an extensive sandy desert system with a marine-erg margin where prograding aeolian dunes interacted with Tethyan waters. The interplay of different controls, such as synsedimentary tectonics, compaction of the underlying coal-bearing unit, eustatic sea-level variations, climate modulation, and the autodynamics of the different sedimentary subenvironments determined the character of bounding surfaces, which separate four erg sequences. These bounding surfaces, or supersurfaces, may display a different sedimentary expression in adjacent areas. Bounding surface 1 is a sand-drift surface (SDS) in the central-erg and a transgressive surface (TS) in the marine erg margin. Bounding surface 2 is associated with a basin re-configuration associated to active extension tectonics, followed by deflation. Bounding surface 3 marks the end of erg expansion, the start of its partial destruction and redeposition and reworking in restricted marine environments. Bounding surface 4 marks the return to more arid conditions and draa progradation into Tethyan waters. These bounding surfaces separate four erg sequences. On the basis of the relative role of allocyclic processes, two megasequences are defined. The first comprises erg sequences 1-3, and the second megasequence comprises erg sequence 4. Erg megasequence 1 developed while synsedimentary tectonic activity and substrate (peat) compaction were active. Erg megasequence 2 was mainly modulated by climate (change). A nomenclature for supersurfaces is proposed based on the types of external control. © 2013 Elsevier B.V.
Perez-Zarate D.,National Autonomous University of Mexico |
Santoyo E.,National Autonomous University of Mexico |
Guevara M.,National Autonomous University of Mexico |
Torres-Alvarado I.S.,National Autonomous University of Mexico |
And 2 more authors.
Applied Thermal Engineering | Year: 2015
Water/Rock Interaction (WRI) experiments, Na-K geothermometry and geochemometrics modeling have been used for the study of the kinetic behavior of the volcanic rock dissolution under geothermal conditions. Ionic exchange reactions between Na-K and alkaline-feldspar minerals were monitored at 90°C and 150°C for a period of nearly 24 and 3 months, respectively. Na/K ratios (inferred from WRI experiments and Na-K geothermometers) and reaction times were used for estimating the most probable quasi-steady state conditions. A geochemometrics modeling was also performed to predict the reaction times required to achieve quasi-steady state conditions in the WRI experiments. This modeling was validated with WRI experimental data reported in the literature for which quasi-steady state conditions were known with accuracy. New WRI experiments were additionally carried out using batch reactors under controlled pressure and temperature conditions. Volcanic rock (basalt and dacites) crushed samples (500-1000 mm grain size) were reacted with distilled water at 90°C and 150°C using a W/R mass ratio of 5. Rock and fluid samples were collected and analyzed for major composition, before and after each experiment. The experimental results were subsequently used to calculate log(Na/K) values for describing the kinetic behavior of the alkaline-feldspar mineral dissolution. Values of log(Na/K) and reaction time at quasi-steady state conditions were reproduced with good accuracy by using the rational polynomial and logarithmic transformation regression models. These results were compared with those values inferred from the Na-K geothermometry, which theoretically assume deep geothermal equilibrium conditions. © 2014 Elsevier Ltd. All rights reserved.
Dominguez-Castro F.,University of Extremadura |
Dominguez-Castro F.,National Polytechnic School of Ecuador |
de Miguel J.C.,Archivo del Ministerio de Asuntos Exteriores y de Cooperacion |
Vaquero J.M.,University of Extremadura |
And 3 more authors.
Holocene | Year: 2014
From ad 711 to 1492, several regions in Iberia were under Muslim ruling. This Al-Andalus civilization generated a large amount of documentation during those centuries. Unfortunately, most of the documents are lost. The surviving Arabic documentary sources have never been studied from a climate perspective. In this paper, we present the first attempt to retrieve climate evidence from them. We studied all the Islamic chronicles (documents written by Islamic historians that narrate the social, political and religious history) available for the period ad 711-1010. It is shown that these sources recorded extreme events with a high temporal and spatial resolution. We identified three severe droughts, ad 748-754, ad 812-823 and ad 867-879, affecting Al-Andalus. We also noticed that the weather in Cordoba during the period ad 971-975 showed a higher frequency of snow and hail than current climate. The possibility of obtaining long continuous series from this type of source seems highly difficult. © The Author(s) 2014.
Leao-Santos M.,Colorado School of Mines |
Leao-Santos M.,Institute Geociencias |
Li Y.,Colorado School of Mines |
Moraes R.,University of Brasilia
Geophysics | Year: 2015
Strong hydrothermal alteration modifies rock physical properties in iron oxide-copper-gold deposits (IOCGs) and may result in characteristic signatures detectable in geophysical surveys. Magnetic data are commonly used in characterizing orebodies, and 3D inversions are often used to assist in interpretations. In areas with strong remanence and self-demagnetization, the total magnetization can have directions different from the inducing field direction. This deviation precludes the use of traditional inversion methods. Magnetic amplitude inversion offers one solution to this challenge because the amplitude data are weakly dependent on the magnetization direction. In addition, the low magnetic latitude also imposes difficulty in amplitude data calculation due to the instability in the component conversion in the wavenumber domain. To formulate a practical approach, we present a case study on applying the magnetic amplitude inversion to the Furnas southeast IOCG deposit at the low magnetic latitude in Carajás Mineral Province, Brazil, and demonstrate that the approach can reliably recover an interpretable distribution of effective magnetic susceptibility and identify massive magnetite from hydrothermal alterations associated with the high-grade ore. © 2015 Society of Exploration Geophysicists.
Abella J.,CSIC - National Museum of Natural Sciences |
Alba D.M.,Institute Catala Of Paleontologia Miquel Crusafont |
Robles J.M.,Institute Catala Of Paleontologia Miquel Crusafont |
Robles J.M.,FOSSILIA Serveis Paleontologics I Geologics S.L |
And 7 more authors.
PLoS ONE | Year: 2012
The phylogenetic position of the giant panda, Ailuropoda melanoleuca (Carnivora: Ursidae: Ailuropodinae), has been one of the most hotly debated topics by mammalian biologists and paleontologists during the last century. Based on molecular data, it is currently recognized as a true ursid, sister-taxon of the remaining extant bears, from which it would have diverged by the Early Miocene. However, from a paleobiogeographic and chronological perspective, the origin of the giant panda lineage has remained elusive due to the scarcity of the available Miocene fossil record. Until recently, the genus Ailurarctos from the Late Miocene of China (ca. 8-7 mya) was recognized as the oldest undoubted member of the Ailuropodinae, suggesting that the panda lineage might have originated from an Ursavus ancestor. The role of the purported ailuropodine Agriarctos, from the Miocene of Europe, in the origins of this clade has been generally dismissed due to the paucity of the available material. Here, we describe a new ailuropodine genus, Kretzoiarctos gen. nov., based on remains from two Middle Miocene (ca. 12-11 Ma) Spanish localities. A cladistic analysis of fossil and extant members of the Ursoidea confirms the inclusion of the new genus into the Ailuropodinae. Moreover, Kretzoiarctos precedes in time the previously-known, Late Miocene members of the giant panda clade from Eurasia (Agriarctos and Ailurarctos). The former can be therefore considered the oldest recorded member of the giant panda lineage, which has significant implications for understanding the origins of this clade from a paleobiogeographic viewpoint. © 2012 Abella et al.