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Textural and geochemical characteristics of late Pleistocene to Holocene fine-grained deep-sea sediment cores(GM6 and GM7),recovered from southwestern Gulf of Mexico

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Journal of Palaeogeography 2018年第3期7卷 253-271页

作者： Abigail Anaya-Gregorio John S.Armstrong-Altrin Marfa Luisa Machain-Castillo Patricia C.Montiel-Garcia Mayla A.Ramos-Vazquez licenciatura en ingenieria en geologia ambiental Area Academica de Ciencias de la Tierra y MaterialesUniversidad Autonoma del Estado de HidalgoMineral de la ReformaHidalgoMexico. Instituto de Ciencias del Mary Limnologia Universidad Nacional Autenoma de MexicoUnidad de Procesos Oceanicos y CosterosCiudad Universitaria04510 Ciudad de MexicoMexico. Area Academica de Ciencias de la Tierra y Materiales Universidad Autonoma del Estado de HidalgoCiudad UniversitariaCarretera Pachuca-Tulancingo Km 4.5Col.CarbonerasC.P.42184 Mineral de la ReformaHidalgoMexico. Posgrado en Ciencias del Mary Limnologia Universidad Nacional Autonoma de MexicoCiudad Universitaria3000CoyoacanC.P.04510 Ciudad de MexicoMexico.

Texture, mineralogy, geochemistry, and 14C ages of two deep-sea sediment cores （GM6 and GM7） recovered in the southwestern Gulf of Mexico were investigated to infer their provenance and depositional condition. The sediments are enriched in fine-grained silt and clay and poor in sand content. Mineralogically, the sediments consist of quartz, calcite, smectite, and kaolinite. Based on the ]4C data, the age of the GM6 and GM7 sediment cores were calculated as 23,615 cal yrs. BP and 19,007 cal yrs. BP, respectively. The weathering indices such as chemical index of alteration （CIA）, chemical index of weathering （CIW）, and plagioclase index of alteration （PIA） in GM6 （56-69, 60-74, and 6]-73, respectively） and GM7 （54-69, 57-76, and 55-74, respectively） cores revealed a moderate-to-high intensity of weathering. The rare earth element （REE） patterns suggested that the sediments were derived mostly by the weathering of intermediate rocks, exposed along the coastal regions of the Gulf of Mexico. The trace elemental ratios like V/Cr （〈2）, Ni/Co （〈2）, and Cu/Zn （〈1）, authigenic uranium content （〈1）, and Ce anomaly （Ce/Ce＊ ≤1） suggested that the sediments were deposited under an oxic condition, which was also revealed by the benthic foraminiferal assemblages throughout the GM6 and GM7 sediment cores.

关键词： Radiocarbon age Manganosite Weathering Palaeoredox condition Provenance Holocene Gulf of Mexico

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Mid and late Holocene forest fires and deforestation in the subalpine belt of the Iberian range,northern Spain

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Journal of Mountain Science 2016年第10期13卷 1760-1772页

作者： Jose M.GARCIA-RUIZ Yasmina SANJUAN Graciela GIL-ROMERA Penelope GONZALEZ-SAMPERIZ Santiago BEGUERIA Jose ARNAEZ Paz COBA-PEREZ Amelia GOMEZ-VILLAR Javier ALVAREZ-MARTINEZ Noemi LANA-RenAULT Estela PEREZ-CARDIEL Carlos LOPEZ DE CALLE Instituto Pirenaico de Ecologfa Consejo Superior de Investigaciones Cientificas(IPE-CSIC)Campus de Aula DeiP.O.Box 13.03450.080-ZaragozaSpain Estacion Experimental de Aula Dei Consejo Superior de Investigaciones Cientificas(EEAD-CSIC)Campus de Aula DeiP.O.Box 13.03450.080-ZaragozaSpain Area of Physical Geography University ofLa Rioja26.004-LogronoSpain Centro de Investigaciones en Geografia ambiental Universidad Nacional Autonoma de MexicoUnidad MoreliaAntigua Carretera a Patzcuaro 870158190-MoreliaMichoacanMexico Departamento de Geografia y geologia Faeultad de Filosofia y LetrasUniversidad de LeonCampus de Vegazana24.071-LeonSpain Departamento de ingenieria Agricola y Forestal Universidad de ValladolidCampus La Yutera34.071-PalenciaSpain Department of Geography and Land Management University of Zaragoza50.009-ZaragozaSpain Freelance archaeologist Auda.Colon426003-LogronoSpain

The conversion of subalpine forests into grasslands for pastoral use is a well-knownphenomenon, although for most mountain areas the timing of deforestation has not been determined. The presence of charcoal fragments in soil profiles affected by shallow landsliding enabled us to date the occurrence of fires and the periods of conversion ofsubalpine forest into grasslands in the Urbión Mountains, Iberian Range, Spain. We found that the treeline in the highest parts of the northwestern massifs of the Iberian Range(the Urbión, Demanda, Neila, and Cebollera massifs) is currently between 1500 and 1600 m a.s.l., probably because of pastoral use of the subalpine belt, whereas in the past it would have reached almost the highest divides(at approximately 2100–2200 m a.s.l.). The radiocarbon dates obtained indicate that the transformation of the subalpine belt occurred during the Late Neolithic, Chalcolithic, Bronze Age, Iron Age, and Middle Ages. Forest clearing was probably moderate during fires prior to the Middle Ages, as the small size of the sheep herds and the local character of the markets only required small clearings, and therefore more limited fires. Thus, it is likely that the forest recovered burnt areas in a few decades; this suggests the management of the forest and grasslands following a slash-andburn system. During the Middle and Modern Ages deforestation and grassland expansion affected most of the subalpine belt and coincided with the increasing prevalence of transhumance, as occurred in other mountains in the Iberian Peninsula(particularly the Pyrenees). Although the occurrence of shallow landslides following deforestation between the Neolithic and the Roman Period cannot be ruled out, the most extensive shallow landsliding processes would have occurred from the Middle Ages until recent times.

关键词： Forest fires Holocene Subalpinegrasslands Shallow landslides Landscape changes Iberian Range

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