Abstract
The crystalline fraction of enamel, dentin and metapodial bone of modern and fossil mammals were studied by X-ray diffraction analysis. The powdered samples were collected from several equids, giraffids, rhinocerotids and proboscideans of Spanish Neogene deposits. Changes in the crystallinity index (CI) of apatite are particularly useful to estimate later diagenetic changes in the fossil material. The enamel displays larger CI than dentine and metapodial bone since they have a more dense structure; furthermore there is not a clear relationship between the CI enlargement and the geological age of samples. In addition, the fluorine content increases during the fossilization process and accordingly the parameter CI increases in fossil samples. The carbonate enrichment is not linked to the age of the deposits; however this carbonate increase in enamel, dentine and metapodial bone reduces the CI parameter. The host sediments play an essential role in the crystallinity changes observed in fossil bones; e.g., in the silica sands case, samples display a high CI while in the claystone and chalks case, they display a lower crystallinity index.
Highlights
fossil mammals were studied by X-ray diffraction analysis
The powdered samples were collected from several equids
the fluorine content increases during the fossilization process
Summary
Se han analizado un total de 65 muestras actuales y fósiles pertenecientes a esmaltes, dentinas y metápodos de équidos, jiráfidos, rinocerótidos y proboscídeos. Del rinoceronte actual no se ha podido analizar el metápodo por no disponer de material. El material procede en su mayor parte de las colecciones de vertebrados fósiles y actuales del Museo Nacional de Ciencias Naturales. Para identificar las distintas fases minerales de los componentes de las muestras y calcular su índice de cristalinidad (IC) se han utilizado técnicas de difracción de rayos X (DRX), con un difractómetro Philips modelo PW 1710 del Laboratorio de DRX del Museo Nacional de Ciencias Naturales, equipado con monocromador de grafito y utilizando la radiación Cu Kα. Las características microtexturales y mineralógicas de las muestras se han estudiado mediante Microscopía Electrónica de Barrido (MEB) y análisis EDX del Servicio de Microscopía Electrónica del Museo Nacional de Ciencias Naturales. Las observaciones se efectuaron sobre superficies de fractura fresca de pequeñas muestras de material óseo, cubiertas de una película de oro
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