Making geological sense of 'Big Data' in sedimentary provenance

Sedimentary provenance studies increasingly apply multiple chemical, mineralogical and isotopic proxies to many samples. The resulting datasets are often so large (containing thousands of numerical values) and complex (comprising multiple dimensions) that it is warranted to use the Internet-era term ‘Big Data’ to describe them. This paper introduces Multidimensional Scaling (MDS), Generalised Procrustes Analysis (GPA) and Individual Differences Scaling (INDSCAL, a type of ‘3-way MDS’ algorithm) as simple yet powerful tools to extract geological insights from ‘Big Data’ in a provenance context. Using a dataset from the Namib Sand Sea as a test case, we show how MDS can be used to visualise the similarities and differences between 16 fluvial and aeolian sand samples for five different provenance proxies, resulting in five different ‘configurations’. These configurations can be fed into a GPA algorithm, which translates, rotates, scales and reflects them to extract a ‘consensus view’ for all the data considered together. Alternatively, the five proxies can be jointly analysed by INDSCAL, which fits the data with not one but two sets of coordinates: the ‘group configuration’, which strongly resembles the graphical output produced by GPA, and the ‘source weights’, which can be used to attach geological meaning to the group configuration. For the Namib study, the three methods paint a detailed and self-consistent picture of a sediment routing system in which sand composition is determined by the combination of provenance and hydraulic sorting effects

An R package for statistical provenance analysis

© 2016 Elsevier B.V. This paper introduces provenance, a software package within the statistical programming environment R, which aims to facilitate the visualisation and interpretation of large amounts of sedimentary provenance data, including mineralogical, petrographic, chemical and isotopic provenance proxies, or any combination of these. provenance comprises functions to: (a) calculate the sample size required to achieve a given detection limit; (b) plot distributional data such as detrital zircon U-Pb age spectra as Cumulative Age Distributions (CADs) or adaptive Kernel Density Estimates (KDEs); (c) plot compositional data as pie charts or ternary diagrams; (d) correct the effects of hydraulic sorting on sandstone petrography and heavy mineral composition; (e) assess the settling equivalence of detrital minerals and grain-size dependence of sediment composition; (f) quantify the dissimilarity between distributional data using the Kolmogorov-Smirnov and Sircombe-Hazelton distances, or between compositional data using the Aitchison and Bray-Curtis distances; (e) interpret multi-sample datasets by means of (classical and nonmetric) Multidimensional Scaling (MDS) and Principal Component Analysis (PCA); and (f) simplify the interpretation of multi-method datasets by means of Generalised Procrustes Analysis (GPA) and 3-way MDS. All these tools can be accessed through an intuitive query-based user interface, which does not require knowledge of the R programming language. provenance is free software released under the GPL-2 licence and will be further expanded based on user feedback

Discussion on the article “Remarks on the Permian-Triassic transition in Central and Eastern Lombardy (Southern Alps, Italy)” by G. Cassinis, M. Durand and A. Ronchi

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Climate-driven hydrological change and carbonate platform demise induced by the Paleocene–Eocene Thermal Maximum (southern Pyrenees)

The Campo section in the Spanish Pyrenees is classical for shallow-water Paleocene-Eocene Thermal Maximum (PETM) studies. Despite extensive work in the last decades, the stratigraphic location of the onset of the negative carbon isotope excursion (CIE), and hence the Paleocene/Eocene (P/E) boundary, remains a matter of considerable debate in the Campo section. Here we present new biostratigraphic, sedimentological and carbon-isotopic data across the late Paleocene to Eocene strata to constrain the precise stratigraphic position of the P/E boundary and investigate environmental changes across the PETM. Foraminiferal assemblages of biozone SBZ4 found below the Claret Formation are replaced by SBZ6 assemblages above. Detailed microfacies analysis indicated that the pre-PETM upper Navarri Formation represents transgressive inner-ramp deposits, overlain unconformably by mixed carbonate-siliciclastic deposits of the syn-PETM Claret Formation, overlain unconformably in turn by renewed carbonate-ramp deposition in the post-PETM lower Serraduy Formation. The temporary demise of the carbonate ramp during the PETM is ascribed to increased siliciclastic supply associated with a significant change in regional hydrology driven by an increase in magnitude and frequency of extreme rainfall and runoff events

Shallow-water carbonate responses to the Paleocene–Eocene thermal maximum in the Tethyan Himalaya (southern Tibet): Tectonic and climatic implications

This study presents a detailed stratigraphic record of the Paleocene–Eocene Thermal Maximum (PETM) in the Gamba area of the Tethyan Himalaya, a carbonate-platform succession originally deposited along the southern margin of the eastern Tethys Ocean. The Paleocene-Eocene boundary interval is marked by a negative carbon isotope excursion at the boundary between members 3 and 4 of the Zongpu Formation. The succession is erosionally truncated at this surface, which is overlain by an intraformational carbonate conglomerate, and only the upper part of the PETM interval is preserved. Foraminiferal assemblages of Shallow Benthic Zone 4 are present below the conglomerate bed, but are replaced by assemblages of Shallow Benthic Zone 6 above the conglomerate. Depositional facies also change across this surface; below the disconformity, floatstones and packstones containing nummulitid forams record progressive transgression in an open-marine environment, whereas restricted or lagoonal inner-ramp deposits containing Alveolina and Orbitolites are typical above the disconformity. The prominent negative excursion observed in the δ13C of whole-rock carbonate (− 1.0‰ at Zongpu, − 2.4‰ at Zengbudong) and organic matter (− 24.7‰, at Zengbudong) is correlated to the characteristic PETM carbon isotope excursion. This major negative excursion in shallow-marine carbonates may have partly resulted from syndepositional alteration of organic matter. The erosional unconformity can be constrained to the lower PETM interval (between 56 and 55.5 Ma), and is identifiable throughout the Tethyan Himalaya. This widespread disconformity is attributable to tectonic uplift associated with the southward migration of an orogenic wave, originated 3 ± 1 Ma earlier in the middle Paleocene at the first site of India-Asia continent-continent collision. A possible eustatic component of the pre-PETM sea-level fall, which resulted in the excavation of incised valleys filled during the subsequent sea-level rise when the conglomerate bed was deposited, remains to be assessed

Sandstone provenance analysis in Longyan supports the existence of a Late Paleozoic continental arc in South China

Because of the limited magmatic and metamorphic record, the Late Paleozoic tectonic setting in South China remains controversial. This paper presents sedimentologic data and provenance analysis of Upper Paleozoic sandstones in Longyan, which are rich in quartz (73–90%) and poor in lithic fragments (2–12%) and feldspar (3–25%). Devonian sandstones contain mostly metamorphic lithic fragments (e.g., quartzite), whereas Carboniferous-Permian sandstones contain mostly felsic volcanic and subvolcanic lithic fragments indicating provenance from felsic volcanic rocks. Detrital zircon U-Pb age spectra of Devonian-Carboniferous sandstones display modes at ~440 Ma and 420–380 Ma, with subordinate Mesoproterozoic age components, pointing at the Nanling terrane and the western-middle part of the Wuyi terrane as most likely ultimate sediment sources. Permian sandstones inherited the age components mentioned above, but also include peaks at ~290 Ma and ~1850 Ma. The ~290 Ma component corresponds to the age of Late Paleozoic magmatism in southeastern China and southwest Japan. Numerous detrital zircons aged at 350–250 Ma also occur in Permo-Triassic strata exposed across South China and southwest Japan. Based on regional data and on the ages and Hf isotope signatures of detrital zircon, we infer that a Late Paleozoic continental arc existed in the coastal area of southeastern China and contributed detritus to the adjacent sedimentary basins. The Permo-Triassic igneous rocks locally exposed in the area may represent the remnant of that continental arc. Arc growth may have been responsible for the westward retreat of a broad Upper Paleozoic carbonate platform

Weathering indices as climate proxies. A step forward based on Congo and SW African river muds

Despite the influence of other geological and geomorphological factors, chemical weathering at the Earth's surface is strongly controlled by climate. Thus, a measure of weathering intensity determined from soils or sediments should provide information about the climatic conditions associated with their formation. Available geochemical and mineralogical data on modern fluvial and marine muds from different regions of southern Africa and its Atlantic continental margin are used to review the links between sediment composition and climatic properties together with the possible causes of variance. Although river muds may not be generated exclusively in a single sedimentary cycle and erosion and weathering processes do not necessarily take place in a spatially homogeneous way, significant relationships between mineralogical and geochemical signatures of river mud and rainfall in the corresponding catchment area were recognised. Our study shows that the composition of clay is strongly influenced by climatically-driven weathering, whilst coarser mud fractions tend to be more affected by provenance, grain size, hydraulic sorting, and recycling. In the marine environment the climatic signal may be lost even in clay, because of hydraulic fractionation, authigenic mineral growth and mixing with foreign particles. Given the ubiquitous character of fluvial muds, and the easy and non-expensive methods available for separating and analysing clay fractions, their geochemical fingerprints represent a most precious source of information concerning climate. Any geochemical parameter used as a regional proxy of climate, however, still requires that the diversity of geological, geomorphological, and biological factors that affect its value are cautiously considered

Provenance and recycling of Sahara Desert sand

We here present the first comprehensive provenance study of the Sahara Desert using a combination of multiple provenance proxies and state-of-the-art statistical analysis. Our dataset comprises 44 aeolian-dune samples, collected across the region from 12°N (Nigeria) to 34°N (Tunisia) and from 33°E (Egypt) to 16°W (Mauritania) and characterized by bulk-petrography, heavy-mineral, and detrital-zircon Usingle bondPb geochronology analyses. A set of statistical tools including Multidimensional Scaling, Correspondence Analysis, Individual Difference Scaling, and General Procrustes Analysis was applied to discriminate among sample groups with the purpose to reveal meaningful compositional patterns and infer sediment transport pathways on a geological scale. The overall homogenity across sand samples, however, precluded a detailed narrative. Saharan dune fields are, with a few local exceptions, composed of pure quartzose sand with very poor heavy-mineral suites dominated by durable zircon, tourmaline, and rutile. Some feldspars, amphibole, epidote, garnet, or staurolite occur closer to basement exposures, and carbonate grains, clinopyroxene and olivine near a basaltic field in Libya. Relatively varied compositions also characterize sand along the Nile Valley and the southern front of the Anti-Atlas fold belt in Morocco. Otherwise, from the Sahel to the Mediterranean Sea and from the Nile River to the Atlantic Ocean, sand consists nearly exclusively of quartz and durable minerals. These have been concentrated through multiple cycles of erosion, deposition, and diagenesis of Phanerozoic siliciclastic rocks during the long period of relative tectonic quiescence that followed the Neoproterozoic Pan-African orogeny, the last episode of major crustal growth in the region. The principal ultimate source of recycled sand is held to be represented by the thick blanket of quartz-rich sandstones that were deposited in the Cambro-Ordovician from the newly formed Arabian-Nubian Shield in the east to Mauritania in the west. Durability of zircon grains and their likelihood to be recycled from older sedimentary rocks argues against the assumption, too often implicitly taken for granted in provenance studies based on detrital-zircon ages, that their age distribution reflects transport pathways existing at the time of deposition rather than inheritance from multiple and remote landscapes of the past

Transition from forearc basin to syn-collisional basin in Southern Tibet (Paleocene Cuojiangding Group): Implication to timing of the India-Asia initial collision and of Yarlung Zangbo ophiolite emplacement

In this study, we combine detailed stratigraphic, sedimentological and micropaleontological data on the Upper Cretaceous to Eocene succession of the Cuojiangding area, with sandstone petrography, detrital zircon U–Pb, and detrital Cr-spinel geochemistry data to reconstruct the paleotectonic evolution of the southern margin of Asia during the earliest stages of the India-Asia collision. Our data show that the Upper Cretaceous Padana and Qubeiya formations, deposited in deltaic to inner shelf environments, represent the final filling stage of the Xigaze forearc basin. The discomformably overlying Cuojiangding Group (Quxia and Jialazi formations), deposited in fan-delta environments during the Thanetian of Late Paleocene, represents the earliest syn-collisional stage. Petrographic data document progressive unroofing of the Gangdese arc, which was the main source of detritus during the Late Cretaceous to Paleogene. Detrital Cr-spinels in the Cuojiangding Group are geochemically similar to those of Xigaze forearc strata rather than to those of the Yarlung Zangbo ophiolites. The timing of the India-Asia initial collision should be older than the deposition of the Cuojiangding Group (>56 Ma), while the emplacement of the Yarlung Zangbo ophiolites is mostly post-middle Eocene

Discovery of the Paleocene-Eocene Thermal Maximum in shallow-marine sediments of the Xigaze forearc basin, Tibet: A record of enhanced extreme precipitation and siliciclastic sediment flux

The Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) was one of the major global deep-time hyperthermal events of the past. Studies of shallow-marine PETM records are crucial to understand the continental hydrological response to current global warming. This study presents the first detailed documentation of the PETM in the Xigaze forearc basin located along the northern active continental margin of the eastern Tethys Ocean, and illustrates the associated environmental and hydrological changes. Based on carbon-isotope stratigraphy, foraminiferal biostratigraphy, and zircon Usingle bondPb chronostratigraphy, the PETM event was identified within a siliciclastic unit in the largely calcareous Jialazi Formation. Foraminiferal assemblages of Shallow Benthic Zone 4 are present below the siliciclastic unit, but are replaced by Shallow Benthic Zone 6 assemblages above the siliciclastic unit. High-resolution microfacies analysis indicates that the pre-PETM deposits consist of carbonate-ramp sediments followed by a sudden change to syn-PETM siliciclastic rocks, followed in turn by renewed post-PETM carbonate-ramp deposition. The siliciclastic supply increased notably during the PETM, as indicated by the thickness of both sandstone and shale intervals, resulting in a temporary demise of the carbonate ramp. Provenance analysis does not indicate any major change in the source areas of terrigenous detritus through the early Paleogene. Increasing siliciclastic supply is thus chiefly ascribed to the intensification of seasonal precipitation and consequently increased hydrological circulation in the Gangdese arc during the PETM event