10:00am - 10:15amTopics: 3.06 Present and past sediment routing systems
Partitioning of organic carbon across submarine slope environments
1Leibniz University Hannover, Germany; 2Universitat Autònoma de Barcelona, Spain; 3Federal Institute for Geosciences and Natural Resources (BGR), Hannover, Germany
Although the burial of organic carbon in submarine fans and its importance for the carbon cycle have recently received growing attention, our understanding of the mechanisms at play is still lacking compared to other organic carbon storing environments.
Here, we present insights on the distribution of organic carbon throughout marine slope environments from the Arro System, Aínsa Basin (Spain). Evaluation of TOC content by C/S analysis from 82 samples show that there are distinct partitioning patterns of organic carbon between different depositional slope environments and mass transport complexes (MTC). Channel axes are relatively poor in organic carbon (average 0.1% TOC), while overbank deposits are relative enriched (average 0.49% TOC). Intraslope lobes show high variability between their sub-environments. Lobe axis deposits have an average TOC content of 0.13%, lobe fringe deposits 1.21% and the lobe distal fringe deposits 0.55%. Mass transport complexes have an average TOC content of 0.53 %. Integration of Hydrogen Indeces (HI) and Tmax, established by RockEval analyses, points towards our samples falling within the range between Type III and Type II kerogen (terrestrial and marine matter), while δC13 show a range between 24.5 and 26.5‰, indicating a predominantly terrestrial source.
Our study shows the partitioning of organic carbon across slope environments that are dominated by different depositional processes. The understanding of this variability is important as wrong assumptions about carbon content can be made from studies that ignore spatial differences and potentially lead to false interpretations of climatic/tectonic changes and estimations on carbon budgets.
10:15am - 10:30amTopics: 3.06 Present and past sediment routing systems
Ambiguity of provenance studies in complex source-to-sink settings – sediment recycling, basement exhumation and signal mixing in the Schilfsandstein (Central European Basin)
1Geowissenschaftliches Zentrum der Georg-August-Universität Göttingen, Germany; 2Geologischer Dienst, LUNG M-V; 3Institute of Geography and Geology, University of Greifswald; 4Karlsruhe Institute of Technology, Institute for Applied Geosciences,
Provenance studies in the Central European Basin are challenged by the complex geology of source areas. The Variscan orogen represents a puzzle of Cadomian terranes, Variscan-aged domains and Palaeozoic sediments with Baltica-/Gondwana-derived detritus. The Caledonian-Fennoscandian source area comprises the Caledonian Belt, Archean to Neoproterozoic domains (Baltica), Variscan molasse sediments and Permo-Carboniferous igneous rocks.
The low-maturity Schilfsandstein (Stuttgart Formation), composed of first- and second-cycle sands, is an ideal candidate to evaluate provenance tools in a complex setting. Within a basin-scale study, subsurface facies maps, heavy minerals, and U-Pb zircon ages were applied to samples from Germany and onshore UK. Results show that the Schilfsandstein represents variable mixtures of recycled sediments and eroded basement. Heavy minerals are dominated by the Gt-Zr assemblage in North Germany (Fennoscandia), by the Ap-Zr-Ep assemblage in southern NW Germany (Rhenish Massif), and by Gt-Zr, Ap-Zr or Ap-Gt-Zr assemblages in Central and South Germany (Bohemian Massif, Vindelician Land). The clear discrimination of Variscan and Fennoscandian sources based on heavy minerals and subsurface facies maps is less constrained by zircon age spectra. Samples from North Germany either show a mix of Fennoscandian and Variscan spectra or typical Variscan spectra comparable to spectra of samples from Central and South Germany. The statistically identical age spectra of samples from North and South Germany (except UK) suggests mixing of source signals in Schilfsandstein rivers or recycling of Variscan molasse sediments in Fennoscandian catchment areas. The results show that complex source-to-sink settings need integrated approaches, individual provenance tools may lead to ambitious results.
10:30am - 10:45amTopics: 3.06 Present and past sediment routing systems
Variscides everywhere? Multi-stage sedimentary recycling in Central Europe
Senckenberg Naturhistorische Sammlungen Dresden, Germany
We used original detrital zircon morphology, trace element, and U-Pb age data obtained from Upper Rotliegend II strata (Upper Permian) to reveal sedimentary fluxes within the Central German Basin. Understanding the evolution of such a system is crucial for further studies, given that the North German Basin is storage to vast natural gas resources and may also serve as an intermediary sedimentary repository for younger strata.
The detrital zircon dating results revealed the presence of main age clusters from the Permian, Carboniferous, and Cambrian periods. Additionally, several minor clusters from the Neo-, Meso-, and Palaeoproterozoic eras were also identified. These ages are remnants of the Cadomian and Variscan orogenies and the opening and closure of the Rheic Ocean. Zircon grain morphologies varied from completely unrounded to completely rounded grains across the age range. The heterogeneity of the data obtained from the studied mineral grains is vital to understanding the sedimentary history of the Central German Basin. It suggests that the basin fill is most likely a mixture of repeatedly recycled material and directly derived material from bedrock sources.
The detrital zircon trace element data support these findings, showing a wide range of values indicating different magma sources. These results underline the complexity of detrital zircon, and shed further light on the sedimentary history of the Central German Basin. We also found that the North German Basin is an integral part of a sedimentary recycling system spanning Central Europe, which is active since the Neoproterozoic.
11:00am - 11:15amTopics: 3.06 Present and past sediment routing systems
Rapid downdip textural and compositional maturation of Moodies Group siliciclastics, Barberton Greenstone Belt, South Africa and Eswatini
The Paleoarchean Moodies Group (ca. 3.22 Ga) of the Barberton Greenstone Belt (BGB) is the oldest known well-preserved, shallow-water siliciclastic sequence on Earth. Proximal-to-distal textural and petrographic examination of selected units across adjacent terrestrial, coastal, and shallow-marine depositional facies of this strongly deformed unit provides the opportunity to constrain Archean weathering conditions by source-to-sink analysis, complementing previous bulk analyses. We examined conglomerate, sandstone, and shale composition by detailed geologic mapping and facies analysis along progressive downdip sediment routing systems, after excluding regions of syndepositional hydrothermal alteration. The majority of quartz and feldspar grains in the central BGB was sourced from intermediate to felsic intrusives and (sub-)volcanics of the Hooggenoeg Formation of the Onverwacht Anticline (OA). Downdip textural and mineralogical maturation from immature, F-, L- and matrix-rich, coarse-grained debris-flow-style units to texturally and compositionally supermature fine-grained sandstone occurs within a few km; facies belts fringe the OA. Chemical weathering and mechanical disaggregation of latite-dominated clast populations in proximal facies accompanied decomposition of F to clay (now partially preserved as sericite grains) and of intermediate volcanic grains to quartz-sericite-mosaic grains within a few km from their source. Energetic reworking in wide coastal-facies belts winnowed the abundant clay from the sediment and generated supermature sand, possibly aided by high tides. We deduce that Moodies Group sediment generation appears to have occurred in an aggressive weathering environment; in the coastal zone, only sediment which was silicified surficially and pre-compaction escaped transformation to a sedimentary “restite”.