Jorge Civis

Late Miocene globorotaliid event-stratigraphy and biogeography in the NE-Atlantic and Mediterranean

Abstract The quantitative study of keeled and unkeeled globorotallids in several Late Miocene sites of the NE Atlantic, the North Betic and South Rifian Gateways and the Western Mediterranean enabled us to recognize a sequence of planktic foraminiferal (PF) events useful for a high resolution correlation of the Mediterranean with the global ocean for the time interval immediately prior to the salinity crisis. PF-Event 1 (6.7 Ma, end of Subchron 7n1) is defined by the sudden disappearance or reduction ofGloborotalia menardii group I (sinistral) in most of the NE Atlantic and Mediterranean. This is probably due to a southward migration of these forms to more subtropical latitudes. PF-Event 2 (6.56 Ma; Subchron 6r2) is defined by the abundant occurrence ofGloborotalia menardii group II (dextral). Between PF-Events 1 and 2, the temperate waters of the NE Atlantic Ocean and Mediterranean Sea were almost completely lacking in keeled globorotaliids. The most prominent change in the assemblages, the replacement of theGloborotalia menardii group II by theGloborotalia miotumida group (PF-Event 3; 6.4 Ma, Subchron 6n) may be correlated with the Tortonian/Messinian boundary and is related to a widespread second southward migration of northern temperate faunas replacing the subtropical ones as the North Atlantic latitudinal thermal gradients increased. This event also coincides with the beginning of the Mediterranean crisis recorded by isotope fluctuations in surface waters and immediately followed by the development of widespread anoxic conditions in the deep and intermediate waters during the deposition of the Tripoli Formation. PF-Event 4 (first abundant occurrence of dextral specimens in theNeogloboquadrina acostaensis group; approximately between 5.6 and 5.5 Ma, Subchron 5r1) and PF-Event 5 (reduction or disappearance of theGloborotalia miotumida group; approximately between 5.6 and 5.5 Ma, Subchron 5r1) pre-date the Lower Evaporites and PF-Event 6 (First abundant occurrence ofGloborotalia margaritae s.s.; Subchron 5n1) is contemporary to their deposition. The coiling direction of unkeeled globorotaliids, highly variable in the first part of the Late Tortonian, became almost 100% dextral (PF-Event A) a short time after PF-Event 2. This group maintained this pattern until the Late Messinian with the exception of a short interval with a peak of sinistral forms just at the Tortonian/Messinian boundary. On comparing these events with the carbon isotope records of different sites of the Atlantic Ocean we recognized similar trends between the events. Maximum δ13C values in planktic and benthic foraminifera coincide with PF-Event 1, they decrease between PF-Events 1 and 2 and increase again immediately after PF-Event 2. PF-Event 3 coincides with the beginning of the global Late Miocene carbon shift.

Tsunami vs. storm surge deposits: a review of the sedimentological and geomorphological records of extreme wave events (EWE) during the Holocene in the Gulf of Cadiz, Spain

The Gulf of Cadiz region of Spain has undergone many studies examining Holocene tsunami and storm deposists. Some of the studies aimed at determining recurrence intervals of events interpreted of tsunamigenic origin. A review of geomorphologic, sedimentary and paleontological features of these deposits suggests that only a few of them can be accurately ascribed to tsunami events; instead, most of them lack conclusive evidence of a tsunamigenci genesis and should be referred to as generated by extreme wave events (EWE)

Vegetation, sea-level, and climate changes during the Messinian salinity crisis

The Messinian salinity crisis (late Miocene) is one of the most fascinating paleoceanographic events in the recent geological history of the Mediterranean Sea, defining a time when it partly or nearly completely dried out. However, the relative roles of tectonic processes and sea-level changes, as triggers for restriction and isolation of the Mediterranean Sea from the open ocean, are still under debate. In this study, we present a detailed pollen, dinoflagellate cyst (dinocyst), and magnetic susceptibility analysis of a sequence of late Neogene (between ca. 7.3 and 5.2 Ma) marine sediments from the Montemayor-1 core (lower Guadalquivir Basin, southwestern Spain), which provides a continuous record of paleoenvironmental variations in the Atlantic side of the Betic corridors during the late Miocene. Our results show that significant paired vegetation and sea-level changes occurred during the Messinian, likely triggered by orbital-scale climate change. Important cooling events and corresponding glacio-eustatic sea-level drops are observed in this study at ca. 5.95 and 5.75 Ma, coinciding with the timing and duration of oxygen isotopic events TG32 and TG22–20 recorded in marine sediments worldwide. It is generally accepted that the onset of the Messinian salinity crisis began at ca. 5.96 ± 0.02 Ma. Therefore, this study suggests that the restriction of the Mediterranean could have been triggered, at least in part, by a strong glacio-eustatic sea-level drop linked to a climate cooling event occurring at the time of initiation of the Messinian salinity crisis.

Rodent palaeoecology of the Continental Upper Miocene of Crevillente (Alicante, SE Spain)

Abstract The Upper Miocene succession of Crevillente presents an alternation of continental and marine beds. The marine fossils have been studied in order to obtain a reliable correlation with other marine sections. On the basis of these data, the entire section can be dated as Upper Tortonian/Messinian. The alternation of continental and marine beds fits the known eustatic sea-level and climatic curves. These correlations are used to assign ecological preferences to the components of the micromammal faunas at species level; it becomes clear that working at the genus level does not provide valid results. With the assignments, it is possible to demonstrate consistent climatic differences between the coastal plain of Crevillente and the area of Teruel on the Meseta of Central Spain.

Virtual 3D tour of the Neogene palaeontological heritage of Huelva (Guadalquivir Basin, Spain)

Virtual fieldtrips in palaeontology and geology offer an expanded environment to make field sites more accessible for a broader audience. Based on extensive experience working in upper Neogene deposits in the province of Huelva, on the western edge of the Guadalquivir Basin, we have selected 10 sites for their regional palaeontological-geological interest (geosites). By applying geoinformatic tools, we have produced a virtual 3D tour of the georeferenced geosites, integrating multiple thematic digital layers (including geological maps, topographical maps, a digital terrain model and orthophotos). Each stop in the tour contains descriptive and graphic elements that can be viewed in free virtual globes (e.g., Google Earth), combined with diagrams, photographs and information sheets that quantitatively assess the cultural tourism, scientific and educational value of the geosite. From this digital 3D geodatabase, we propose a virtual flight itinerary that can be displayed in compatible video formats and using new technologies, such as smartphones, tablets or iPads.

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.

Augmented Reality in a Hiking Tour of the Miocene Geoheritage of the Central Algarve Cliffs (Portugal)

Eight sites with geological (including palaeontological and geomorphological) interest (geosites) representative of the Lower and Middle Miocene carbonate deposits near Albufeira in central Algarve (southern Portugal) have been selected based on our extended working experience. The sites can be visited by hiking in a 1-day field trip. A virtual 3D tour of the georeferenced sites was produced using augmented reality technique and geoinformatic tools which integrate thematic digital layers such as geological maps and orthophotos. Every stop in the tour includes descriptive and graphic elements that can be viewed in free virtual globes (e.g. Google Earth) combined with diagrams, photographs and information sheets that quantitatively assess the cultural-touristic, educational and scientific value of the geosites. A virtual flight itinerary compatible with video formats in the new free technologies (smartphones, tablets and iPads) is also presented.

Messinian productivity changes in the northeastern Atlantic and their relationship to the closure of the Atlantic–Mediterranean gateway: implications for Neogene palaeoclimate and palaeoceanography

The stable isotope composition of planktic and benthic foraminifera and the distribution of selected benthic foraminiferal species from a Messinian record of the lower Guadalquivir Basin, northeastern Atlantic Ocean, show that regional productivity changes were linked to glacioeustatic fluctuations. Glacial periods were characterized by poorly ventilated bottom waters as a result of weak Atlantic Meridional Overturning Circulation (AMOC), and by phases of high productivity related to intensified upwelling. In contrast, well-ventilated bottom waters owing to strong AMOC, the presence of degraded organic matter in the upper slope, and high input of degraded terrestrial organic matter derived from fluvial discharge to the outer shelf were recorded during interglacial periods. Before closure of the adjacent Guadalhorce Corridor at 6.18 Ma, which was the final active Betic Atlantic–Mediterranean gateway, the study area was alternately influenced by well-ventilated Mediterranean Outflow Water (MOW) and poorly ventilated Atlantic Upwelled Water (AUW). Following closure of the corridor, cessation of the MOW reduced the AMOC and promoted glacial conditions in the northern hemisphere, resulting in the establishment of local upwelling cells.

Evolution of the pollution in the Piedras River Natural Site (Gulf of Cadiz, southern Spain) during the Holocene

The Piedras River marshland and El Rompido spit bar is a Natural Site in close proximity to two of the most polluted rivers in the world: the Tinto and Odiel Rivers. The aim of this study is to determine the degree of contamination of this Natural Site using a variety of pollution indices. At this site the Holocene infilling sequence is recorded and applied to a study of the pollution history and the possible impacts of human activity. The depositional history of the Piedras River estuary during the Holocene recorded open marine conditions at ca. 6500 calBP when sea-level was at its Holocene maximum. To study the pollution of the estuary during the Holocene, catchment background geochemistry was established using samples that pre-date human activity (agriculture and mining). Additionally, the sedimentary environment was reconstructed throughout the Holocene; comparison of pollution levels is interpreted to be more reliable if the sedimentary environment has remained similar throughout the depositional record. Results show that, despite being located nearby very polluted estuaries, the Piedras River marshland contains unpolluted sediments mainly because of the small catchment area relative to that of neighbouring more polluted rivers, and thus has not been affected by human activity such as mining.

The chronostratigraphic position of the Camping Francas section(Neogene of Tarragona, Spain)

Abstract The presence of Cirsotrema (s.s.) pumiceum (BROCCHI) and Chlamys (Manupecten) pesfelis (LINNE) in the section of Camping Francas (Province of Tarragona, Spain) suggests that the age of the deposits be changed from the upper Miocene (Tortonian) to the Pliocene. The change is of particular significance as the site is one of the classic localities of Pectinidae of the Neogene in North East Spain, and is type locality of Pecten (Flabellipecten) constisulcatus ALMERA & BOFILL.