The ability to trace sediments from their sources to sedimentary basins is a prerequisite for quantitative analysis of Earth-surface dynamics. The comparatively recent revival of sedimentary provenance analysis goes hand-in-hand with the ever expanding range of analytical tools available for quantifying sediment properties (isotopic, mineral, chemical, and petrographic composition, grain-size and shape distributions, age spectra, etc.), and for interpreting such data in paleo-geographic, -tectonic and -climatic terms. The breakdown of sediment budgets into source-specific contributions - one of the most important tasks of provenance analysis - permits quantification of rates of surface processes in the geological past ("deep time"), even in cases where the source areas themselves have been destroyed by global tectonics. Quantitative sedimentary provenance analysis is therefore crucial to the reconstruction of ancient sediment-routing systems, the fundamental units of mass transfer at the Earth's surface.
This special issue of Sedimentary Geology results from the 2nd meeting of the Working Group on Sediment Generation (WGSG), held in June 2014 at the Georg-August University of Göttingen, Germany. The meeting hosted scientists from a broad range of disciplines and included, besides diverse topics related to provenance analysis and data treatment, contributions focused on detrital geochronology, sediment budgets and applied geomorphology. The meeting recorded the growth of the WGSG group with new participants from academic institutions including Trinity College Dublin, Darmstadt Technical University, Bern University, University College London, University of Münster and industrial partners such as Chemostrat Ltd. During the meeting, objectives for future research were defined, including the understanding and quantification of (i) the effects of sediment recycling in the geological record, (ii) mechanical weathering, i.e. the selective breakdown of particles, and (iii) chemical weathering.
The special issue presents a selection of contributions to the 2nd WGSG meeting. It opens with a critical review of models currently used in provenance analysis of sands and sandstones by Eduardo Garzanti, who shows that the relationship between sediment composition and geodynamic setting is far from univocal. He proposes a new descriptive classification scheme to be used as a starting point for an upgraded dynamic approach to sedimentary petrology focusing on the nature and tectono-stratigraphic level of source terranes. The fundamental information obtained by petrographic investigation of rock fragments is emphasized.
The second section concentrates on analytical methods and tests of provenance approaches. Pieter Veermesch and co-authors present provenance, a software package within the well-known open-source statistical programming environment “R” that aims to facilitate the visualisation and interpretation of large amounts of sedimentary provenance data, including mineralogical, petrographic, chemical and isotopic proxies. The package provides a number of functions tools and will be regularly expanded based on user feedback.
Abijit Basu and co-authors test the applicability of chemical composition of siliciclastic rocks to infer their provenance and tectonic setting. The authors validate some of the indications given by traditional diagrams, but more importantly, they discuss the factors that may complicate interpretation.
Christiane Scholonek and Carita Augustsson focus on the use of cathodoluminescence for extracting provenance information from feldspar grains. Their results, obtained from the measurement of a great number of feldspar crystals contained in both igneous and metamorphic rocks, support the usefulness of this technique in provenance studies.
The third section includes case studies on modern sediments. Fabio Scarciglia and co-authors integrate macro- and micromorphological observations with physico-mechanical field tests and petrographic, mineralogical and geochemical analyses to constrain the first step of sediment generation and quantify soil production and erosion rates of weathering profiles on granitoid rocks of the Sila Massif in southern Italy.
Hilmar von Eynatten and co-authors investigate sediments generated from plutonic bedrocks exposed to humid-temperate Mediterranean climate. Geochemical data of several grain size fractions from coarse sand to clay are coupled to mineralogical data obtained by X-ray diffraction and Mineral Liberation Analysis (MLA). By means of linear regression modeling of geochemistry vs. grain-size variability the authors relate compositional changes to sediment formation processes.
Eduardo Garzanti and Alberto Resentini question the use of classical chemical indices (e.g., CIA, WIP, α values) to infer weathering and paleo-weathering conditions in source areas. In their modern case study of sediments generated in Taiwan, where even in wet-tropical climate physical erosion prevails because of extreme tectonic-uplift rates, chemical parameters are documented to depend chiefly on provenance rather than on weathering.
Sandra Schneider and co-authors investigate the effects of chemical weathering on sands and muds generated in equatorial Africa, the factors controlling weathering rates, and the extent and conditions under which original provenance signatures are preserved. In the extreme case of the rift-related Rwenzori basement uplift, they document how daughter sediments may faithfully reflect parent lithologies even in wet equatorial climate.
Anne Krippner and co-authors use heavy-mineral analysis and geochemistry of garnets in bedrocks and stream sediments derived from the Almklovdalen peridotite massif in SW Norway to test the representativeness of provenance signals provided by these methods. The results underline the high potential of both methods in reconstructing sediment provenance if (i) sampling sites in the drainage system are carefully selected and (ii) a relatively wide grain-size spectrum is considered to avoid misleading interpretations.
The fourth section includes contributions on volcaniclastic sedimentation and dispersal mechanisms. Luca Caracciolo and co-authors focus on chemical fingerprints of detrital amphibole and pyroxene to reconstruct the dispersal mechanisms of volcanic material recorded in the Tertiary volcaniclastic sediments of the northwestern Thrace basin. Single-grain compositional signatures are used to discriminate provenance from the numerous volcanic centres active at the time of deposition.
Kathleen Marsaglia and co-authors study proximal arc-derived Cretaceous sediments deposited in a volcano-bounded shallow-marine basin and in a fault-bounded deep-marine basin to evaluate the role of depositional processes on sediment detrital modes. They demonstrate that both differences in basin type and mechanisms of deposition have limited effects on sediment composition when sedimentation is controlled by a single major subaerial volcanic edifice.
Andrea Di Capua and co-authors integrate sedimentological analysis with conglomerate clast counting and petrographic analyses to determine the influence of climate, tectonic activity and volcanism on sediment supply in the Oligocene foredeep of the northern Appenines. Their results indicate strong control by the activation of deformational fronts during syn- and post-eruptive periods.
The 5th and last section present a series of assorted provenance case studies. Heinrich Bahlburg and Jasper Berndt analyse detrital zircons from the Devonian and Upper Paleozic siliciclastic rocks of northern Chile. Their results would point to provenance from the Faja Eruptiva, a Ordovician calc-alkaline intrusive belt in NW Argentina, which is in clear disagreement with mass-balance calculation and paleocurrent data. The authors show how the misleading provenance indications provided by detrital-zircon geochronology can be ascribed to the effects of assimilation of and contamination of magma by crustal igneous, metamorphic and sedimentary rocks during its evolution and ascent.
Pedro Dinis and Álvaro Oliveira use X-ray diffraction and bulk-rock geochemistry to reconstruct the provenance of recycled Pliocene clays in western Iberia (Portugal) and evaluate the mineralogical transformation occurred during the last depositional cycle. They also consider different grain-size windows and conclude that REE still preserve the original provenance signal, whereas major elements reflect different degrees of chemical weathering in different parent lithologies.
Udo Zimmermann and co-authors adopt a comprehensive analytical approach to characterise the composition and provenance of 5th-6th century pottery material from southwestern Norway. The combination of bulk-rock geochemistry EDS, XRD and Raman spectroscopy reveals the provenance of the material studied, pointing to the Karmøy region as the place of origin. The final contribution to this special issue represents one of the many potential applications of provenance analysis outside of the field of sedimentary geology.