Why Do Bio-Carbonates Exist?

Calcium carbonate precipitation associated with biotic activity is first recorded in Archaean rocks. The oldest putative fossils related to hydrothermal vents have been dated at ~3.77 Ga (possibly 4.29 Ga). Stromatolites, the oldest dated at 3.70 Ga, have since occurred through Earth history, despite dramatic changes in physical and chemical conditions in aquatic environments. A key question is: what advantages do photosynthesizing aquatic prokaryotes and algae gain by precipitating carbonates? We propose the Phosphate Extraction Mechanism (PEM) to explain the benefits of biomineralization in warm, oligotrophic, alkaline, euphotic environments. Carbonate precipitation enhances access to otherwise limited carbon dioxide and phosphate in such environments. This mechanism also provides an explanation for prolific production of carbonates during times of elevated atmospheric carbon dioxide at intervals in the Phanerozoic.JIB acknowledges funding from the Basque Government to the Research Group IT1602-22. L.P., P.H. and G.M.-V. participation did not involved external funding aside from their academic institutions

Estratigrafía y sedimentología del Mioceno de la Plana Negra-Sancho Abarca (sector central-occidental de la Cuenca del Ebro)

Este trabajo abarca el estudio sedimentológico y estratigráfico de los depósitos del Burdigaliense (Mioceno inferior) y Langhiense (Mioceno medio) de la Plana Negra y la Plana de Sancho Abarca, sector central-occidental de la Cuenca del Ebro (NE de la Península Ibérica). Se han identificado un total de 5 litofacies (unidades cartografiables) constituidas por areniscas, lutitas, margas y calizas en variables proporciones, equiparables a miembros (informales) de la Formación Tudela. Se han realizado dos perfiles estratigráficos que abarcan las unidades tectosedimentarias T5 y T6 definidas para la Cuenca del Ebro; dicho límite es una conformidad que se reconoce como el paso de lutitas con intercalaciones de areniscas y calizas a predominio de calizas, y constituye un nivel excelente de correlación. Los depósitos de T5 tienen 130 m de espesor y los de T6 tienen 63 m. Las paleocorrientes medidas en la unidad T5 señalan procedencia del margen pirenaico. Se han caracterizado 17 facies sedimentarias (detríticas, mixtas y carbonatadas) que muestran gran variedad biótica (ostrácodos, carófitos y gasterópodos) y rasgos pedogenéticos. Se agrupan verticalmente en 5 asociaciones de facies que caracterizan los ambientes fluvial-aluvial distal, palustre y lacustre somero. El modelo de sedimentación propuesto se basa en la distribución espacial de esas asociaciones y expresa la relación entre dichos ambientes. La correlación de las secciones estudiadas con otras tres de áreas adyacentes que disponen de datación magneto-bioestratigráfica ha permitido datar con precisión la sucesión estudiada y el límite T5/T6 (C5Cn.1n, entre 16,062 y 16,099 Ma). La integración de las cinco secciones permite distinguir cuatro estadios evolutivos, definidos por la progradación-retrogradación del medio aluvial o retracción-expansión de los ambientes palustres y lacustres. Se relacionan con la tectónica y el clima, que controlaron la evolución de los sistemas sedimentarios a través de variaciones de los aportes y del nivel lacustre en el área estudiada.<br /

Multi-aged social behaviour based on artiodactyl tracks in an early Miocene palustrine wetland (Ebro Basin, Spain)

We present a new locality with at least 880 vertebrate tracks found at the top of a limestone bed from the lower Miocene Tudela Formation (Spain). The trampled surface was formed by artiodactyls that crossed a muddy carbonate accumulated under the influence of water level variations in a palustrine environment. The tracks reflect different types of morphological preservation. The well-preserved tracks have tetradactyl digit impressions caused by both manus and pes, and are the type series of a new artiodactyl ichnotaxon, Fustinianapodus arriazui ichnogen. nov. and ichnosp. nov. The rest of the tracks, which are not as well preserved, are didactyl and were classified as undetermined artiodactyl tracks. According to their preservation, morphology, size, arrangement and orientation, we propose that this tracksite is the product of a social behaviour, particularly gregariousness, of a multi-age group of artiodactyls ~19Ma ago. The morphologic and palaeoecologic data presented here suggest that the trackmakers were a group of anthracotheres with a livelihood similar to current hippos. They crossed, periodically, a fresh water palustrine area along some preferential pathways (trails)

Stratigraphy and sedimentology of distal-alluvial and lacustrine deposits of the western-central Ebro Basin (NE Iberia) reflecting the onset of the middle Miocene Climatic Optimum

The stratigraphic and sedimentologic study of Miocene deposits in the Plana Negra-Sancho Abarca area fills a gap in the Ebro Basin knowledge. Five main lithofacies were characterized and mapped. The boundary between regional tectosedimentary units T5 and T6 is recognized as a conformity at a major facies change. Unit T5, up to 130m thick, consists of mudstones with interbedded sandstones and limestones. Unit T6, with 30 to 62m of preserved thickness, is made of limestones, marls and minor mudstones. Correlation of the studied outcrops with nearby sections that already had detailed magnetoestratigraphic and biostratigraphic data allows dating the studied succession as Burdigalian (early Miocene)-Langhian (middle Miocene), from C5Dr to C5Cn, and the boundary between units T5 and T6 to be located at 16.062-16.099 Ma. Seventeen sedimentary facies associated in seven vertical facies sequences document deposition in fluvial-distal alluvial, palustrine and lacustrine environments. A shallow (2-4m deep) lake body was locus for charophytes, ostracods, bivalves and gastropods to thrive. Occasional bottom currents reworked and transported allochems and fine-siliciclastic sediment offshore, forming laminated limestones. Bioturbation and desiccation features are abundant, indicating wide palustrine areas and episodic exposure. Low-sinuosity channels associated to the Pyrenean-derived Luna fluvial system run across the alluvial-plain. Four evolutionary stages of alluvial progradation-retrogradation and retraction-expansion of the palustrine-lacustrine system, likely related to Pyrenean tectonic activity, are distinguished. Maximum lacustrine expansion took place at the beginning of unit T6 deposition. This is consistent with initial conditions of increasing humidity of the Middle Miocene Climatic Optimum (MMCO)

K/T muga euskokantauriar arroan

Kretazeo eta Tertziarioaren arteko mugan gertatu zen suntsipen masiboak Lurreko espezieen hiru laurden baino gehiago desagertarazi zuen eta gaur egun zientzia-eremu ezberdinetako zientzialarien interesa suspertzen du; haien artean paleontologoak, geokimikoak, astrofisikoak eta abarrak. Ikertzaileok, Biziaren historiaz gain Lur planetaren eboluzioaz arduratzen dira. Euskokantauriar Arroan K/T muga ebaki anitzetan gorde da, Kretazeoaren amaierako krisiari buruzko ikerketak garatzeko leku aparta izanik

Haizeolak eta burdin hobiak Euskal Herrian

Urteetan zehar Baskonian eta inguruetan, Zientzia eta Teknologia Fakultateko jakintza alor anitzeko irakasle talde batek, egindako lanei esker, frogatu du haizeola kopuru handia gelditzen dela, orain arte esan denaren aurka; hala ere hainbat eta hainbat haizeola deseginda daude. Haizeola hauen labeak tamaina handiko egitura edo kubetak dira, kono-enbor eiteduna edo udare formadunak. Egitura hauek aspalditik karabiekin nahasiak, hauetatik bereizten dira, batez ere, beheko aldean duten kanal baten bidez kanpoko aldearekin loturik daudelako. Halaber, labearen barnea tarteka burdin zepak dituen buztinezko geruza batez estalia agertzen da. Zepak dentsoak dira eta Fe, Si eta Al eduki handia dute (fayalita, wustita eta herzinita mineral gisan). Honek adierazten du baxua zela metala ateratzeko prozesuaren errendimendua. Mendi lepoetan eta erreka batetik gertu kokatzen ohi dira, Behe Kretazeoko arrokez osaturiko zonaldeetan eta, hein txikiagoan Paleozoikoko arrokez osaturiko zonaldeetan ere. Aipagarria litzateke era berean haizeola hauen eta -ola aurrizki edo atzizkia duten toponimoen arteko harremana ere

Redefinition of the Ilerdian Stage (early Eocene)

The Ilerdian Stage was created by Hottinger and Schaub in 1960 to accommodate a significant phase in the evolution of larger foraminifera not recorded in the northern European basins, and has since been adopted by most researchers working on shallow marine early Paleogene deposits of the Tethys domain. One of the defining criteria of the stage is a major turnover of larger foraminifera, marked by the FO's of Alveolina vredenburgi (formerly A. cucumiformis) and Nummulites fraasi. There is now conclusive evidence that this turnover was coeval with the onset of the Carbon Isotope Excursion (CIE) and, consequently, with the Paleocene-Eocene (P-E) boundary, a temporal correspondence that reinforces the usefulness of the Ilerdian as a chronostratigraphic subdivision of the early Eocene in a regional context. However, in addition to the paleontological criteria, the definition of the Ilerdian was also based on the designation of two reference sections in the southern Pyrenees: Tremp (stratotype) and Campo (parastratotype). In both sections, the base of the stage was placed at the lowest marine bed containing A. vredenburgi specimens. Using the CIE as a correlation tool we demonstrate that these two marine beds occur at different chronological levels, being older in Campo than in Tremp. Further, we show that both beds are in turn younger than the lowest strata with Ilerdian larger foraminifera at the deep-water Ermua section in the Basque Basin (western Pyrenees). Since the age of stage boundaries must be the same everywhere, the choice of these stratotype sections was misleading, since in practice it resulted in the Ilerdian being used as a facies term rather than as a chronostratigraphic unit. To eliminate that conflict, and yet be respectful with established tradition, we propose to redefine the Ilerdian Stage following a procedure similar to the one used by the International Commission on Stratigraphy to establish global chronostratigraphic standards, namely: by using a "silver spike" to be placed in the Tremp section at the base of the Claret Conglomerate, a widespread lithological unit that in the Tremp Graus Basin coincides with the onset of the CIE. The redefined regional Ilerdian Stage becomes thus directly correlatable to the lower part of the global Ypresian Stage, as currently defined by the International Commission on Stratigraphy

The Global Stratotype Sections and Points for the bases of the Selandian (Middle Paleocene) and Thanetian (Upper Paleocene) stages at Zumaia, Spain

The global stratotype sections and points for the bases of the Selandian (Middle Paleocene) and Thanetian (Upper Paleocene) stages have been defined in the coastal cliff along the Itzurun Beach at the town of Zumaia in the Basque Country, northern Spain. In the hemipelagic section exposed at Zumaia the base of the Selandian Stage has been placed at the base of the Itzurun Formation, ca. 49 m above the Cretaceous/ Paleogene boundary. At the base of the Selandian, marls replace the succession of Danian red limestone and limestone-marl couplets. The best marine, global correlation criterion for the basal Selandian is the second radiation of the important calcareous nannofossil group, the fasciculiths. Species such as Fasciculithus ulii, F. billii, F. janii, F. involutus, F.pileatus and F. tympaniformis have their first appearance in the interval from a few decimetres below up to 1.1 m above the base of the Selandian. The marker species for nannofossil Zone NP5, F. tympaniformis, first occurs 1.1 m above the base. Excellent cyclostratigraphy and magnetostratigraphy in the section creates further correlation potential, with the base of the Selandian occuring 30 precession cycles (630 kyr) above the top of magnetochron C27n. Profound changes in sedimentology related to a major sea-level fall characterize the Danian-Selandian transition in sections along the margins of the North Atlantic. The base of the Thanetian Stage is placed in the same section ca. 78 m above the Cretaceous/Paleogene boundary. It is defined at a level 2.8 m or eight precession cycles above the base of the core of the distinct clay-rich interval associated with the Mid-Paleocene Biotic Event, and it corresponds to the base of magnetochron C26n in the section. The base of the Thanetian is not associated with any significant change in marine micro-fauna or flora. The calcareous nannofossil Zone NP6, marked by the first occurrence of Heliolithus kleinpelli starts ca. 6.5 m below the base of the Thanetian. The definitions of the global stratotype points for the bases of the Selandian and Thanetian stages are in good agreements with the definitions in the historical stratotype sections in Denmark and England, respectively