Person: Pérez Garrido, Carlos
Loading...
First Name
Carlos
Last Name
Pérez Garrido
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Geológicas
Department
Mineralogía y Petrología
Area
Cristalografía y Mineralogía
Identifiers
2 results
Search Results
Now showing 1 - 2 of 2
Item Diagenetic albitization in the Tera Group, Cameros Basin (NE Spain) recorded by trace elements and spectral cathodoluminescence(Chemical geology, 2012) González Acebrón, Laura; Götze, Jens; Barca, Donatella; Arribas Mocoroa, José; Más Mayoral, Ramón; Pérez Garrido, CarlosThis paper deals with the diagenetic albitization of both plagioclases and K-feldspars in the Tithonian fluvial sandstones of a rift basin (Cameros Basin). The sandstones in the lower part of the rift record have not suffered this albitization process. A clear relationship is observed between sodium contents, as the main element of some feldspars and their cathodoluminescence (CL) color (the higher the sodium content, the lower is their CL intensity). In conclusion, albitization processes are detectable by decreased CL intensities and changes in the CL spectra. In addition, very different trace element compositions are obtained by laser ablation when comparing trace elements of non-albitized feldspars in sandstones of the lower part of the rift record with those of albitized feldspars in sandstones of the infill top. Non-albitized K-feldspars show Rb, Sr, Ba and Pb contents of up to 1000 ppm. In contrast, very flat profiles of trace element contents (< 250 ppm) are recorded in albitized feldspars (both K-feldspars and plagioclases). Thus, albitization implies feldspars impoverished in trace elements, including REE, which suggests that albitization is a dissolution and reprecipitation process. Further, albitized plagioclases show higher REE contents than albitized K-feldspars. We report here that REE patterns partly depend on the initial composition of the feldspar (K-feldspar or plagioclase) as a useful geochemical criterion for distinguishing albitized detrital plagioclases from albitized detrital K-feldspars. CL spectra from non-albitized and albitized K-feldspars and plagioclases revealed marked differences. Non-albitized K-feldspars present blue (main emission band at 460 nm) and brownish CL colors (590 nm), sometimes in the same grain. Brownish colors are related to weathering processes. The primary blue emission is related to Al–O−–Al centers, enhanced probably by Al incorporation due to the coupled substitution of Ba2+ + Al3+ ↔ M+ + Si4+. Weathered K-feldspars present 4.8 times lower Ba content than fresh blue luminescent ones. The brownish colors are related to the external border or fractured grain zones, altered by weathering processes. Therefore, the observed 590 nm emission is assumed to be caused by structural defects resulting from weathering and alteration. Albitized K-feldspars are usually weak luminescent with a typical CL emission band at 620 nm. Sometimes, relicts of the original blue luminescence (460 nm band) are still present. The leaching of probably both Al and Ba can be responsible for the decrease in the blue band. The characteristic 620 nm band is also dominant in albitized weak luminescent plagioclases. Two additional emission bands at 440 nm (Al–O−–Al center) and 565 nm (Mn2+) occur, when albitized plagioclases preserved their original CL characteristics (green CL color). Another spectral peak at ca. 720 nm can be explained by Fe3+ activation due to Fe3+–Al3+ substitution. The spectral CL measurements indicate that changes in luminescence due to albitization (620 nm emission) seem to be more related to structural defects than to trace element activation or quenching.Item Very coarse-grained beaches as a response to generalized sea level drops in a complex active tectonic setting: Pleistocene marine terraces at the Cadiz coast, SW Spain(Marine Geology, 2016) González Acebrón, Laura; Más Mayoral, Ramón; Arribas Mocoroa, José; Gutiérrez Mas, José Manuel; Pérez Garrido, CarlosThe studied Pleistocene deposits at the Cadiz coast are located on the current intertidal zone or at cliffs parallel to the actual coast (6.50 m a.s.l.) from the localities of El Puerto de Santa María to Chiclana. Five sequences of very coarse-grained beaches have been recognized and dated. They unconformably overlie Pliocene units and are formed by clast-supported conglomerate and coarse-grained sandstone. Chronological ages (⁸⁷Sr/⁸⁶Sr and AMS ¹⁴C analysis) and stratigraphic correlation stand that the oldest marine terrace is the one placed topographically higher and towards the SE of Cadiz city, dated as Early Pleistocene (1.3 Ma). After it, the sea retreatment produces subaerial exposure of Sequence 1 and the development of several calcrete profiles and a paleokarst. Subsequent sea-level rises allow the sedimentation of Sequences 2, 3 and 4 during Early-Middle Pleistocene (1 to 0.8 Ma) in areas close to Cadiz city, with subaerial exposure recorded at the top of Sequences 3 and 4. During the very Upper Pleistocene, sedimentation of Sequence 5 occurs towards the SE of Cadiz city. Based on the spatial position of Sequence 5 we can conclude that this area constituted a downthrown block during the Latest Pleistocene, in relation to neotectonic processes and diapirism