Conference Agenda

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Session Overview
1.1-2 Sediment routing systems and provenance analysis
Monday, 20/Sept/2021:
1:30pm - 3:00pm

Session Chair: Laura Stutenbecker, TU Darmstadt
Session Chair: Hilmar von Eynatten, University of Göttingen
Session Chair: Guido Meinhold, Keele University

This session is co-hosted by the 'Fachsektion Sedimentologie' of the DGGV.

Session Abstract

The composition of clastic sediments or sedimentary rocks is a result of source area properties, sediment generation and transport processes as well as post-depositional changes. Deciphering the provenance of clastic deposits can therefore provide valuable insights into tectonic, geomorphic, climatic and anthropogenic factors and processes shaping sedimentary systems over different temporal and spatial scales. This session welcomes contributions that investigate (1) the provenance of clastic deposits by analyzing compositional (e.g. mineralogical, geochemical) properties, (2) the processes that modify detrital signals throughout the sedimentary routing system, and (3) the relationships to internal and external forcing mechanisms.

1:30pm - 2:00pm

Transcontinental retroarc sediment routing controlled by subduction geometry and climate change (Central and Southern Andes, Argentina)

Eduardo Garzanti1, Tomas Capaldi2, Giovanni Vezzoli1, Mara Limonta1, Numa Sosa1,3

1Laboratory for Provenance Studies, Department of Earth and Environmental Sciences, Università di Milano-Bicocca, 20126 Milano, Italy; 2Department of Geosciences, University of Nevada, Las Vegas, NV, 89154, USA.; 3Centro de Investigaciones Geológicas (CONICET), Universidad Nacional de La Plata, Diag.113 # 275, La Plata (B1900TAC), Argentina

Central Argentina from the Pampean flat-slab segment to northern Patagonia (27-41°S) represents a classic example of a broken retroarc basin with strong tectonic and climatic control on fluvial sediment transport. In this provenance study, we combine framework petrography and heavy-mineral data to trace multistep dispersal of volcaniclastic detritus first eastwards across central Argentina for up to ~1500 km and next northwards for nearly another 1000 km along the Atlantic coast. Compositional signatures reflect different tectono-stratigraphic levels of the orogen uplifted along strike in response to varying subduction geometry as well as a different character and crystallization condition of arc magmas through time and space.

In the presently dry climate, fluvial discharge is drastically reduced to the point that even the Desaguadero trunk river has become endorheic and orogenic detritus is dumped in the retroarc basin, reworked by winds, and temporarily accumulated in dune fields. At Pleistocene to early Holocene times, instead, much larger amounts of water were released by melting of the Cordilleran ice sheet or during pluvial events. The sediment-laden waters of the Desaguadero and Colorado rivers then rushed from the tract of the Andes with greatest topographic and structural elevation, fostering alluvial fans inland and flowing in much larger valleys than today toward the Atlantic Ocean. Sand and gravel supply to the coast was high enough not only to promote rapid progradation of large deltaic lobes but also to feed a cell of littoral sediment transport extending as far north as the Río de la Plata estuary.

2:00pm - 2:15pm

Proximal to distal grain-size distribution of basin-floor lobes: A study from the Battfjellet Formation, Central Tertiary Basin, Svalbard

Yvonne T. Spychala1, Thymen A.B. Ramaaker2, Joris T. Eggenhuisen2, Sten-Andreas Grundvåg3, Florian Pohl4, Sara Wroblewska5

1Institut für Geologie, Leibniz Universität Hannover, Germany; 2Department of Earth Science, Utrecht University, 3584 CB, Utrecht, Netherlands; 3Department of Geosciences, UiT – The Arctic University of Norway, PO Box 6050 Langnes, N-9037 Tromsø, Norway; 4Durham University, Department of Earth Sciences, Stockton Road, Durham DH1 3LE, UK; 5Faculty of Geology, University of Warsaw, Żwirki i Wigury 93, 02-089 Warsaw, Poland

The grain-size distribution of sediment particles is an important aspect of the architecture of submarine fans and lobes. It governs depositional sand quality, and reflects distribution of particulate organic carbon and pollutants. Documenting the grain-size distribution of these deep-marine sedimentary bodies can also offer us an insight in the flows that deposited them. Submarine lobes are commonly assumed to linearly fine from an apex, meaning there should be a proportional relation between grain size and distance from the lobe apex. However, not much detailed quantitative work has been done to test this hypothesis. Exposure of a 5 km long dip-section of basin-floor lobes in Clinoform 12, Battfjellet Formation, Spitsbergen, enable the study of basinward grain-size evolution in lobe deposits. Furthermore, the dataset allows testing if there are any documentable grain-size differences between lobe sub-environments.

The results show that fining of lobe deposits occurs predominantly in the most proximal and most distal parts of the lobe, while the intermediate lobe, which is dominated by lobe off-axis deposits, is characterized by a relatively consistent grain-size range. Lobe sub-environments show statistically distinct grain-size distributions from lobe axis to lobe fringe. An explanation for these trends is the interplay of capacity and competence-driven deposition with the grain-size stratification of the flows.

The outcomes of this study help to better understand the proximal to distal evolution of turbidity currents and their depositional patterns. They also provide important insights in reservoir potential of basin-floor fans at lobe scale.

2:15pm - 2:30pm

Automated heavy mineral analysis of silt-sized sediment by artificial-intelligence guided Raman Spectroscopy

Nils Keno Lünsdorf1, Jan Ontje Lünsdorf3, Gábor Újvári2, Hilmar von Eynatten1

1Georg-August-Universität Göttingen, Department of Sedimentology and Environmental Geology, Göttingen, Germany; 2Institute for Geological and Geochemical Research, Research Centre for Astronomy and Earth Sciences, Budapest, Hungary; 3Insterburger Straße 2, 26127, Oldenburg

Compositional data on heavy minerals is fundamental in sedimentary provenance analysis. Typically, this data is gathered by optical microscopy and more recently, by mineral chemical analysis (MLA, QEMSCAN) or Raman micro-spectroscopy. In silt-sized sediments optical microscopy is unfeasible. We introduce a systematic and highly efficient approach to assess the heavy mineral composition in fine grain-size fractions (10-30 µm and 30-62 µm) by Raman micro-spectroscopy.

The approach starts with a web-application that creates and visualizes large mosaic images from which arbitrary objects can be selected for training and inference of a region-based convolutional neural network (R-CNN). Here, mineral grains are automatically selected by passing the tiles of a mosaic image of the sample slide into the R-CNN. For each detected grain a polygon is computed from which positional and optical parameters are derived. Using this polygon data, the measurement parameters at the Raman spectrometer are individually set to account for varying Raman scattering intensities and irradiation resistivity. After the compositional data is obtained, Raman spectra are evaluated and further single-grain geochemical methods (ICPMS, EMPA) can be applied to the identified and referenced grains (e.g. U-Pb dating of zircon).

The method was tested on 13 samples from three loess profiles from Germany and Hungary. About 100.000 minerals were analyzed and provenance signals demonstrate clear contrasts between the sections. Being automated, this approach allows for analyzing large sample numbers with higher precision (i.e. counting statistics) on silt-sized materials, thus opening new avenues in sedimentary provenance analysis.

2:30pm - 2:45pm

The Segmented Zambezi Sedimentary System from Source to Sink 1. Sand Petrology and Heavy Minerals

Eduardo Garzanti1, Guido Pastore1, Alberto Resentini1, Giovanni Vezzoli1, Pieter Vermeesch2, Lindani Ncube3, Helena Johanna Van Niekerk3, Gwenael Jouet4, Massimo Dall'Asta5

1Laboratory for Provenance Studies, Department of Earth and Environmental Sciences, University of Milano-Bicocca, 20126 Milano, Italy; 2London Geochronology Centre, Department of Earth Sciences, University College London, London, WC1E 6BT, UK; 3Department of Environmental Sciences, University of South Africa, Florida, South Africa; 4Unité de Recherche Geosciences Marines, Ifremer, CS 10070, 29280 Plouzané, France; 5TOTAL E&P, CSTJF, Avenue Larribau - 64018 Pau Cedex Pau, France

The Zambezi River rises at the center of southern Africa, flows across the low-relief Kalahari Plateau, meets Karoo basalt, plunges into Victoria Falls, follows along Karoo rifts, and pierces through Precambrian basement to eventually deliver its load onto the Mozambican passive margin. The river is subdivided into segments with different geological and geomorphological character, a subdivision fixed by man’s construction of large reservoirs and testified by sharp changes in sediment composition. Pure quartzose sand recycled from Kalahari desert dunes in the uppermost tract is next progressively enriched in basaltic rock fragments and clinopyroxene. Sediment load is renewed first downstream Lake Kariba and next downstream Lake Cahora Bassa, documenting a stepwise decrease in quartz and durable heavy minerals. Composition becomes quartzo-feldspathic in the lower tract, where most sediment is supplied by high-grade basements rejuvenated by the southward propagation of the East African rift. Feldspar abundance in Lower Zambezi sand has no equivalent among big rivers on Earth and far exceeds that in sediments of the northern delta, shelf, and slope, revealing that provenance signals from the upper reaches have ceased to be transmitted across the routing system after closure of the big dams. This high-resolution petrologic study of Zambezi sand allows us to critically reconsider several dogmas, such as the supposed increase of mineralogical “maturity” during long-distance fluvial transport, and forges a key to unlock the rich information stored in sedimentary archives, with the ultimate goal to reconstruct the evolution of African landscapes since the late Mesozoic.

2:45pm - 3:00pm

Tectonic and environmental perturbations at the Permian-Triassic boundary: insights from the Blue Nile River Basin in central Ethiopia

Maryam Mansouri1, Matthias Hinderer1, Laura Stutenbecker1, Guido Meinhold2, Enkurie L. Dawit3, Jasper Berndt4, Robert Bussert5

1Institute of Applied Geosciences, Technische Universität Darmstadt, Darmstadt, Germany; 2School of Geography, Geology and the Environment, Keele University, Keele, UK; 3Department of Geology, University of Gondar, Gondar, Ethiopia; 4Institut für Mineralogie, Westfälische Wilhelms-Universität, Münster, Germany; 5Institut für Angewandte Geowissenschaften, Technische Universität Berlin, Berlin, Germany

The Blue Nile River Basin contains a thick fluvio-lacustrine sediment succession of Permian to Jurassic age. Its evolution is linked to extensional tectonics during break-up of Pangea in the aftermath of the Carboniferous-Permian glaciation. We collected sandstone samples from several sections in order to study the tectonic evolution and possible impacts of environmental perturbation around the Permian-Triassic boundary. Based on thin-section petrography, bulk-rock geochemistry, heavy mineral spectra, and detrital zircon U-Pb ages we are able to establish a provenance model for the Permian-Triassic basin-fill evolution. The results reveal distinct differences between Lower Permian and Upper Permian to Upper Triassic sediments. The Lower Permian sandstones are rich in feldspar, carbonate cement, and relatively unstable heavy minerals like apatite and garnet. The chemical index of alteration and trace elements suggest little chemical weathering and proximity to the source area. Upper Permian to Upper Triassic sandstones, however, contain a large amount of ultra-stable heavy minerals, and geochemical data point to intense chemical weathering, reworking and/or recycling. In the Lower Permian, detrital zircon U-Pb age spectra are dominated by Pan-African and Tonian ages, whereas Upper Permian and Upper Triassic samples show a higher proportion of old zircons and young zircons (c. 1 Ga and c. <541 Ma) probably from intraplate magmatic rocks. The results show that during the Upper Permian and Triassic, uplift and unroofing was happening accompanied by climate change.