Paleomagnetic and paleoenvironmental implications of magnetofossil occurrences in late Miocene marine sediments from the Guadalquivir Basin, SW Spain

Although recent studies have revealed more widespread occurrences of magnetofossils in pre-Quaternary sediments than have been previously reported, their significance for paleomagnetic and paleoenvironmental studies is not fully understood. We present a paleo- and rock-magnetic study of late Miocene marine sediments recovered from the Guadalquivir Basin (SW Spain). Well-defined paleomagnetic directions provide a robust magnetostratigraphic chronology for the two studied sediment cores. Rock magnetic results indicate the dominance of intact magnetosome chains throughout the studied sediments. These results provide a link between the highest-quality paleomagnetic directions and higher magnetofossil abundances. We interpret that bacterial magnetite formed in the surface sediment mixed layer and that these magnetic particles gave rise to a paleomagnetic signal in the same way as detrital grains. They, therefore, carry a magnetization that is essentially identical to a post-depositional remanent magnetization, which we term a bio-depositional remanent magnetization. Some studied polarity reversals record paleomagnetic directions with an apparent 60-70 kyr recording delay. Magnetofossils in these cases are interpreted to carry a biogeochemical remanent magnetization that is locked in at greater depth in the sediment column. A sharp decrease in magnetofossil abundance toward the middle of the studied boreholes coincides broadly with a major rise in sediment accumulation rates near the onset of the Messinian salinity crisis (MSC), an event caused by interruption of the connection between the Mediterranean Sea and the Atlantic Ocean. This correlation appears to have resulted from dilution of magnetofossils by enhanced terrigenous inputs that were driven, in turn, by sedimentary changes triggered in the basin at the onset of the MSC. Our results highlight the importance of magnetofossils as carriers of high-quality paleomagnetic and paleoenvironmental signals even in dominantly terrigenous sediments.This study was funded by the Guadaltyc project (MINECO, CGL2012–30875), ARC grant DP120103952, and NSFC grant 41374073

Stratigraphy and petrology af the miocene Montjuïc delta (Barcelona, Spain)

The Neogene rift in the Catalan Coastal Ranges, which is located in the NE part of the Eastern Iberian Margin, corresponds to a system of grabens formed at the north-western edge of the Valencia Trough. In the central part of the Catalan Coastal Ranges are the Vallès - Penedès half-graben in the onshore and the Barcelona half-graben in the offshore, which are separated by the Garraf and the Collserola-Montnegre horsts. Montjuïc hill is a tilted block, which is located to the S of the Barcelona city, between the Collserola-Montnegre horst and the Barcelona half-graben . The Middle Miocene section of Montjuïc is constituted by an alternation of conglomerate, sandstone, mudstone and marlstone beds. The Montjuïc section was divided into four lithostratigraphic units from base to top: (1) The Morrot conglomerate and sandstone Unit, interpreted as delta plain deposits; (2) the Castell conglomerate, sandstone and mudstone Unit considered as proximal delta front deposits; (3) the Miramar marlstone Unit attributed to prodelta deposits; and (4) the Mirador conglomerate, sandstone and mudstone Unit interpreted as delta front deposits. As regards the foraminifera association, the Miocene of Montjuïc may be attributed to the N9-N10 zones of Blow, indicating a Serravallian age. The palaeobotanical record suggests that the climate during the deposition of the Miocene of Montjuïc was temperate-warm and humid. The sandstones and conglomerates are litharenites and lithorudites; they show variable amounts of matrix and are well cemented. The main framework components are quartz, rock fragments and K-feldspar. The Collserola mountain, where Palaeozoic materials crop out is the deduced source area. Montjuïc sandstones are characterized by an early silicic cementation consisting of K-feldspar overgrowths, quartz overgrowths, mesoquartz intergranular cement and a microquartz transformation of a former detrital matrix. A surface cementation is considered for these cements in the absence of compaction and the geological setting.Peer ReviewedPostprint (published version

Preliminar paleontologic study from upper Tortonian deposits of «Las Pajanosas» (Sevilla, Guadalquivir Basin)

The paleontological record of a set of upper Tortonian outcrops nearby Las Pajanosas, north of Seville, has been studied. The most complete series of 15 metres of thickness, unconformed over upper Devonian metamorphic rocks, is divided in two sedimentary parts. 60 macrofaunal species have been identified. Bivalves group is the most abundant with 37 species, specially pectinids with 14 species. This outcrop presents the most diversity of pectinids in the Tortonian sections of the Guadalquivir Basin. The fossil content, distribution, taphonomy signature and sedimentological context, suggest a transgressive process over the paleorelief, with progressive deepening of the paleoenvironments in a global eustatic rising settin

Los Rajiformes (Chondrichthyes, Batomorphii) del Plioceno inferior de la Formación Arenas de Huelva, suroeste de España

EL Neógeno marino del suroeste de España ha sido objeto de numerosos estudios, su contenido fosilífero ha sido objeto de numerosos trabajos, abordando diferentes grupos como malacofauna (Andrés, 1982; González-Delgado, 1983), foraminíferos (Sierro, 1984; González-Regalado, 1986), nanoplancton calcáreo (Flores, 1985), ostrácodos (González-Regalado y Ruiz, 1990, 1991; Ruiz y González-Regalado, 1996), polen (Valle y Peñalba, 1987), así como aspectos generales de tafonomía y paleoecología (Mayoral, 1986) y vertebrados (Ruiz et al., 1997). Algunos de estos trabajos indicaban la presencia de restos ictiológicos, como dientes de seláceos y otolitos. En este trabajo se presentan los registros inéditos de los Rajiformes de Formación Arenas de Huelva, Provincia de Huelva, España (Fig. 1) de la tesis doctoral de García (2008)

Unidades litológicas del Neógeno en el extremo oeste de la Cuenca del Guadalquivir y su correlación con el sondeo Huelva-1 (Huelva - España)

A detailed surveying and a new geological map of the sheet at 1:50.000 number 999/1016 (Huelva - Los Caños), located at the west end of the Guadalquivir Basin, has been carried out. This data allows us to propose a new organization of the lithological units present at the west side of the Odiel River. These units include all the sedimentary record in this sector of the Guadalquivir Basin, ranging from Tortonian to Pliocene, but with shallower and coarser facies that are only present in this part of the basin. This fact is due to the location of the area, probably less subsiding due to a longer distance from Betic-Rif orogen. The lithological units are described concisely and a correlation with the core of the Huelva-1 borehole and with the outcrops of Huelva – Palos de la Frontera area is also proposed. The units are organized in a stack of sequences with a progradational pattern, typical of a basin margin, and highlighting a gradual reduction of the accommodation space in the late Messinian and during the Pliocene.Se ha realizado un reconocimiento detallado y un nuevo mapa geológico de la hoja a 1: 50.000 número 999/1016 (Huelva - Los Caños), situada en el extremo oeste de la Cuenca del Guadalquivir. Estos datos nos han permitido proponer una nueva organización de las unidades litológicas presentes en el lado oeste del río Odiel. Estas unidades incluyen el registro sedimentario completo de este sector de la Cuenca del Guadalquivir, que va desde Tortoniense al Plioceno, pero mostrando unas facies más someras y gruesas que solo están presentes en esta parte de la cuenca. Este hecho se debe a la ubicación de la zona, probablemente menos subsidente debido a su mayor distancia con respecto al orógeno Bético-Rifeño. Las unidades litológicas se describen de forma concisa y se propone también su correlación con el testigo del sondeo Huelva-1 y los afloramientos de la zona de Huelva - Palos de la Frontera. Las unidades litológicas se organizan formando un apilamiento de secuencias con un patrón progradacional, típico de un borde de cuenca, y ponen de manifiesto una reducción gradual del espacio de acomodación a finales del Messiniense y durante el Plioceno.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEMinisterio de Economía y Competitividad (MINECO)Plan de Edición de Cartografía Geológica y Geomorfológica del IGME 2013-2016pu

Quantitative taphonomy of the Cacela site (late Tortonian; Algarve, S Portugal)

A quantitative taphonomic analysis were performed in the fossil assemblages of the late Tortonian of the lower-mid part of the Cacela Formation (Cacela, Algarve, S Portugal). Taphonomic results, together with sedimentological analysis and the faunal assemblages, allow to inferring palaeoenvironmental changes. The upper Tortonian sedimentation started with fan-delta conglomerates that quickly changed to outerplatform silty marls deposited in a setting with a relatively low sedimentation rate as indicated by the concentration of glauconite. Higher up into the section, a progressive shallowing trend is inferred, and sediments of inner platform settings were forme