Geochemistry versus grain-size relations of sediments in the light of comminution, chemical alteration, and contrasting source rocks

Around 170 sediment samples from glacial and proximal glacio-fluvial deposits have been analysed for their geochemical composition. Samples derive from two strongly contrasting source areas (granitoids vs. amphibolite) and cover a broad grain-size range from coarse sand to clay. Following descriptive data evaluation, the relation of sediment geochemical composition versus grain size is modelled using linear regression techniques in the Aitchison geometry of the simplex in order to (i) describe the effects of comminution on the composition of individual grain size fractions, (ii) describe the influence of inherited mineral-specific grain-size distributions for contrasting source rocks, and (iii) to test for any potential influence of chemical weathering. Results indicate strong overall grain-size control on sediment composition that is largely reflecting the greater grain-size control on mineralogy. Comminution leads to overall strong enrichment of sheet silicates in the fine-grained fraction at the expense of quartz and, less pronounced, feldspars. Specific elements such as Ca, P, and Ti related to certain minerals do not follow this general trend and clearly indicate source-rock dependent enrichment of certain minerals (e.g. apatite, Ti-minerals) in medium grain-size fractions. Estimates of mineral compositions obtained from a geometric endmember approach support these conclusions. Chemical weathering is shown to be negligible.Peer ReviewedPostprint (published version

Grain-size control on petrographic composition of sediments: compositional regression and rounded zeroes

It is well-known that sediment composition strongly depends on grain size. A number of studies have tried to quantify this relationship focusing on the sand fraction, but only very limited data exists covering wider grain size ranges. Geologists have a clear conceptual model of the relation between grain size and sediment petrograpic composition, typically displayed in evolution diagrams. We chose a classical model covering grain sizes from fine gravel to clay, and distinguishing five types of grains (rock fragments, poly- and mono crystalline quartz, feldspar and mica/clay). A compositional linear process is fitted here to a digitized version of this model, by (i) applying classical regression to the set of all pairwise log-ratios of the 5-part composition against grain size, and (ii) looking for the compositions that best approximate the set of estimated parameters, one acting as slope and one as intercept. The method is useful even in the presence of several missing values. The linear fit suggests that the relative influence of the processes controlling the relationship between grain size and sediment composition is constant along most of the grain size spectrum.Postprint (published version

Messung, Bewertung und Einflussfaktoren der Trübung in der Wassersäule – Schlussfolgerungen für einen die Sedimentakkumulation optimierenden Küstenschutz auf Hallig Langeneß

Online First, geplanter Druck 202

Discrimination of TiO2 polymorphs in sedimentary and metamorphic rocks

Investigation by Raman spectroscopy of samples from different geological settings shows that the occurrence of TiO2 polymorphs other than rutile can hardly be predicted, and furthermore, the occurrence of anatase is more widespread than previously thought. Metamorphic pressure and temperature, together with whole rock chemistry, control the occurrence of anatase, whereas variation of mineral assemblage characteristics and/or fluid occurrence or composition takes influence on anatase trace element characteristics and re-equilibration of relict rutiles. Evaluation of trace element contents obtained by electron microprobe in anatase, brookite, and rutile shows that these vary significantly between the three TiO2 phases. Therefore, on the one hand, an appropriation to source rock type according to Nb and Cr contents, but as well application of thermometry on the basis of Zr contents, would lead to erroneous results if no phase specification is done beforehand. For the elements Cr, V, Fe, and Nb, variation between the polymorphs is systematic and can be used for discrimination on the basis of a linear discriminant analysis. Using phase group means and coefficients of linear discriminants obtained from a compilation of analyses from samples with well-defined phase information together with prior probabilities of groupings from a natural sample compilation, one is able to calculate phase grouping probabilities of any TiO2 analysis containing at least the critical elements Cr, V, Fe, and Nb. An application of this calculation shows that for the appropriation to the phase rutile, a correct-classification rate of 99.5% is obtained. Hence, phase specification by trace elements proves to be a valuable tool besides Raman spectroscopy.Postprint (published version

Origin, timing and paleogeographic implications of Paleogene karst bauxites in the northern Transdanubian range, Hungary

Paleogene karst bauxites in the northeastern Transdanubian Range and their cover sequences provide valuable sedimentary archives, despite their weathered nature and vague paleontological records. U–Pb detrital zircon geochronology combined with heavy mineral analysis indicates ‘local’ Alpine aeolian and fluvial sources and ‘distant’ aeolian sources connected to the Bohemian Massif. Records of episodic Paleogene volcanic eruptions related to igneous complexes of the Adamello and probably also the Bergell, Recsk and Balkan Peninsula, are reflected by euhedral zircon crystals. Their U–Pb geochronology supplies age constraints for the phases of subaerial exposure of the karstic surface and the accumulation of bauxitic protoliths and helps to improve the existing stratigraphic records and to define stages of denudation in the northeastern Transdanubian Range. Distinct phases of subaerial exposure and accumulation of the bauxite's protoliths are identified as ca. 42, 35 and 31 Ma; alternating with episodes of subsidence, represented by siliciclastic and carbonatic sequences at ca. 38, 32 and 31 Ma. Besides Paleogene volcanism, zircon dating also revealed contributions from the Middle Triassic tuffs of the Transdanubian Range. Garnet, epidote, kyanite, staurolite, and xenotime/monazite crystals suggest fluvial drainage of diverse metamorphic units of the Austroalpine basement from the Eastern- and Southern Alps, which also supplied most of the pre-Mesozoic zircons. However, the unexpectedly high proportion of Variscan ages in the bauxites most likely relate to igneous rocks of the Bohemian Massif, thus suggesting additional long-distance aeolian sources. The new data allow for detailed reconstructions of the Paleogene evolution and palaeogeography of the northeastern Transdanubian range

La procedencia sedimentaria como herramienta para exploración de hidrocarburos: caso del antearco del sur peruano

Los sedimentos son los registros accesibles más tangibles del desarrollo litosférico en las cuencas sedimentarias, los cuales ocurren en un determinado área y en un determinado tiempo (McCann & Saintot, 2003). En los últimos años se han incrementado el número de estudios que ayudaron a desenmarañar los vínculos entre la geodinámica y sus respuestas sedimentarias. El estudio de la procedencia de sedimentos inicia con la definición de la geometría estratigráfica y facies sedimentarias, los cuales nos dirigen a estudios puntuales, tales como estudios de litogeoquímica, geoquímica, petrofísica, y geocronología (von Eynatten & Dunkl, 2012), incluyendo estratigrafía secuencial. Los beneficios en términos socio-económicos se reflejan en la determinación de la calidad de potenciales reservorios de hidrocarburos y/o recursos hídricos, en la definición de afinidades en correlaciones estratigráficas y en caracterizar y/o predecir los impactos diagenéticos en la mineralogía de los depósitos, los cuales influyen directamente en la calidad del reservorio (cf. Smyth et al., 2014). En este resumen se muestra como ejemplo-caso el análisis de la cuenca sedimentaria Camaná (Cenozoico) del antearco del sur de Perú (Figura 1), en la cual se definió los procesos geodinámicos que dieron origen a los distintos procesos sedimentarios, y se presentó una caracterización analítica de facies sedimentarias con el objetivo de proveer aportes en la calidad de los reservorios y predicciones en la extensión de las facies

Arquitectura estratigráfica onshore-offshore de la cuenca cenozoica Camaná-Mollendo (antearco externo del sur de Perú): Implicancias en la exploración de hidrocarburos

[ESP] La Cuenca Camaná-Mollendo es una depresión elongada ~NO-SE formada en un margen activo, el cual se extiende desde la Cordillera de la Costa del sur de Perú hasta la fosa Perú-Chile. Esta cuenca contiene la Formación Camaná del Cenozoico. Una integración de datos recopilados de columnas estratigráficas, análisis de proveniencia sedimentaria, geocronología U-Pb en zircones y nuevas interpretaciones sísmicas 2D (offshore) permitió elaborar un esquema tectonoestratigráfico de toda la Cuenca Camaná-Mollendo hasta el offshore de Arequipa y Tacna. Los resultados permiten afirmar que la Fm. Camaná consiste en deltas de grano grueso (Unidad CamA, Oligoceno-Mioceno medio) sobreyacidas por conglomerados fluviales (Unidad CamB, Mioceno superior-Plioceno). Estas unidades han sido identificadas en las secciones sísmicas del offshore, donde los deltas de grano grueso se hacen más potentes hacia el interior de la cuenca y las facies de conglomerados sobreyacentes empiezan a tener también geometría deltaica. Se ha logrado identificar al menos 4 depocentros en el offshore de Arequipa, considerados como reservorios potenciales y atractivos para la exploración de hidrocarburos. El modelo estructural corresponde a un sistema de grábenes orientados ~NO-SE, el cual ayudó a generar los respectivos espacios de acomodación para la acumulación de los depocentros de la Fm. Camaná.[ENG] The Camaná-Mollendo Basin is a depression ~NW-SE elongated, formed in an active margin, which extends from the Coastal Cordillera of southern Peru up to the Peru-Chile Trench. This basin contains the Cenozoic Camaná Formation. An integration of compiled onshore stratigraphic logs, sediment provenance data, zircon U-Pb geochronology and new 2D seismic interpretations (offshore) supports a refined tectonochrono- stratigraphic framework for the entire Camaná-Mollendo Basin fill until the offshore of Arequipa and Tacna. The results allow stating that the Camaná Fm. consists on coarse-grained deltas (CamA Unit, Oligocene-Middle Miocene) underlying fluvial conglomerates (CamB Unit, Late Miocene-Pliocene). These units are also identified in the 2D seismic data of the offshore, where coarse-grained deltas become thicker basinwards and overlying conglomerate deposits start to get deltaic geometry too. We identified at least 4 depocenters in the offshore of Arequipa that correspond to potential and attractive reservoirs for hydrocarbon exploration. The structural framework consists of a graben system ~NW-SE oriented, which supported the creation of respective accommodation space for depocenters of the Camaná Fm

Evolución geológica de las cuencas de antearco del sur de Perú (Moquegua y Camaná-Mollendo): Proveniencia sedimentaria y análisis de facies en rocas cenozoicas

[ESP] Este estudio integra datos sobre proveniencia sedimentaria (dataciones U-Pb y análisis de minerales pesados), análisis de facies sedimentarias y estratigrafía secuencial con el objetivo de establecer patrones de deformación tectónica en términos de levantamiento y exhumación. Este estudio fue realizado en rocas sedimentarias de dos cuencas cenozoicas del antearco del sur de Perú (entre 15° y 18°S). Estas cuencas tienen forma elongada con orientación general ~NO-SE, habiendo una cuenca ubicada en la parte interna del antearco (Cuenca Moquegua), y la otra cuenca posicionada en la parte externa (Cuenca Camaná-Mollendo) encarando al Océano Pacífico. Ambas están separadas por la Cordillera de la Costa y sus sedimentos fluyeron al suroeste. El Grupo Moquegua y la Formación Camaná constituyen el relleno sedimentario de cada cuenca, respectivamente, y ambas unidades litoestratigráficas son equivalentes en cronología (Oligoceno a Plioceno). Aunque la Cordillera de la Costa separa al Grupo Moquegua de la Formación Camaná, estas unidades comparten ciertas similitudes en sus facies y en la proveniencia de sus sedimentos, y son clave para definir sus procesos sedimentarios. Por ejemplo, la Unidad Moquegua C del Grupo Moquegua consiste en depósitos fluviales y lacustres y representa un “Relleno balanceado de cuenca fluviolacustre”. Este concepto sugiere que el ingreso de agua y sedimentos iguala al espacio de acomodación de la Cuenca Moquegua. Sugiere además que proporciones menores de sedimentos drenaron periódicamente a través de la Cordillera de la Costa hacia la Cuenca Camaná-Mollendo, formando parte de la parte inferior de la Fm. Camaná (Unidad Camaná A), tal como lo evidencian sus espectros de minerales pesados. En contraste, la depositación de la Unidad Moquegua D del Grupo Moquegua representó un “Sobre-relleno de cuenca fluvio-lacustre”, el cual excedió el espacio de acomodación de la Cuenca Moquegua y se propagó en grandes volúmenes hasta la Cuenca Camaná-Mollendo, sobrepasando la Cordillera de la Costa y prolongándose como la parte superior de la Fm. Camaná, manteniendo los mismos espectros minerales. Considerando que la Cordillera Occidental y la Cordillera de la Costa ejercieron significante influencia en la sedimentación del antearco, presentamos precisiones sobre sus proporciones de levantamiento. Utilizando termocronología previa, se dedujo que la Cordillera de la Costa se levantó <2.5 km entre el Oligoceno y Mioceno medio, y provocó la depositación de la parte inferior de la Fm. Camaná (Unidad Camaná A). Simultáneamente, la depositación de la Unidad Moquegua C ocurrió debido al levantamiento de la Cordillera Occidental. En el Mioceno superior, la Cordillera Occidental se levantó aún más drásticamente y produjo depositaciones más prolongadas (Unidad Moquegua D y Unidad Camaná B), mientras que la Cordillera de la Costa experimentó menor levantamiento (±0.5 km). Estas declaraciones son consistentes con los conceptos genéticos de un “relleno balanceado” en la Cuenca Moquegua entre el Oligoceno y Mioceno medio y un posterior “sobrerelleno” en la misma cuenca desde el Mioceno superior, afectando a la Cuenca Camaná-Mollendo. Los levantamientos de la Cordillera Occidental y la Cordillera de la Costa ejercieron un control casi exclusivo en la generación de los sedimentos en las cuencas Moquegua y Camaná-Mollendo, mientras que su espacio de acomodación se debió a una evidenciada inestabilidad en el interior del antearco del sur Peruano.[ENG] This study integrates data on sediment provenance (U-Pb dating and heavy mineral analysis), facies analysis and sequence stratigraphy to establish patterns of geodynamic deformation in terms of uplift and exhumation. This study is accomplished on sedimentary rocks deposited in two Cenozoic sedimentary basins within southern Peruvian forearc (15°-18°S). These are ~NW-SE elongated basins; being one located in an internal position called the Moquegua Basin, and the other located in an external position termed Camaná Basin. Both basins are separated by the Coastal Cordillera and their sediments flowed southwestward. Moquegua Group and Camaná Formation form the sedimentary filling of each basin, respectively, and both lithostratigraphic units are equivalent in chronology (Oligocene to Pliocene). Although Coastal Cordillera separates the Moquegua Group and Camaná Fm., both units share some similarities in their facies and sediment provenance, and they are key elements to define sedimentary processes. For instance, Moquegua C Unit of Moquegua Group consists of fluvial and lacustrine deposits which represent a “balanced-fill fluvio-lacustrine basin”. This concept indicates that influx of sediments and water closely equaled accommodation space of the Moquegua Basin. It also suggests that minor proportions of such sediments periodically overflowed Moquegua Basin and drained onto the Camaná-Mollendo Basin through the Coastal Cordillera, and join sediments of lower Camaná Formation, as heavy mineral spectra proves. In contrast, deposits of Moquegua D Unit represent an “over-filled fluvio-lacustrine basin”, which exceeded accommodation space in Moquegua Basin and have prograded onto the Camaná Basin as upper Camaná Formation, keeping the same heavy mineral spectra. Considering that Cordillera Occidental and Coastal Cordillera exerted significant influence on sedimentation, we present precisions on their uplift proportions. By constraining previous thermochronology and sedimentary proxies, Coastal Cordillera uplifted <2.5 km between Oligocene and Middle Miocene. Simultaneously, deposition of Moquegua C Unit occurred due to uplift of Western Cordillera. Around Late Miocene, Western Cordillera has uplifted again, however drastically, and triggered protracted deposition of Moquegua D Unit (and Camaná B Unit), while Coastal Cordillera experimented minor uplift (±0.5 km). These statements are consistent with concepts on genetics of a “balanced basin-fill” of Moquegua Basin between Oligocene and Middle Miocene, and a later “overfilled basin-fill” on the same basin since Late Miocene, affecting Camaná-Mollendo Basin. Uplifts of Western Cordillera and Coastal Cordillera exerted an almost exclusive control on sediment generation on Moquegua and Camaná-Mollendo Basins, while their respective accommodation spaces for sedimentation were given due to instability within forearc of Southern Peru