Influencing factors on petrography interpretations in provenance research – a case-study review

The use of framework petrography is a common initial step in provenance research of sand and sandstone. The data tend to be interpreted based on the three main components quartz, feldspar, and lithic fragments. Surprisingly often, this is done without taking other influencing factors than the tectonic setting of the catchment and/or the surroundings of the depositional basin into account. Based on a database of 14 studies with approximately 900 petrographic data points from sand and sandstone, this study demonstrates quantitative effects on the apparent composition resulting from both geological and non-geological biases. The study illustrates sandstone-classification differences based on different specifications of the three end-members quartz, feldspar, and lithic or rock fragments, how the point-counting method can affect the apparent petrographic composition of sandstone, how sorting and facies bias may be differentiated from a climate or provenance signal, and how bias due to diagenetic effects can be minimised. In conclusion, both geological and non-geological biases should be considered for provenance studies that include petrographic data.publishedVersio

Provenance of late Palaeozoic sediments in the southern Patagonian Andes

U-Pb-Datierungen von detritischen Zirkonen des sedimentären Grundgebirges der Anden (47-51°S) zeigen maximale Ablagerungsalter von Devon - Frühkarbon bis Spätkarbon - Frühperm an. Die hauptsächlichen Liefergesteine waren felsisch, metasedimentär und metamorph, und das Material wurde in der Kruste vor der Ablagerung recycelt wie angedeutet von KL von Quarz, Turmalin-Chemismus, Gesamtgesteinselement- und Sr-Nd-isotop-Chemie, und U-Pb Alter detritischer Zirkone. U-Pb-Alter und Hf-Isotopie von Einzelzirkonen zeigen, dass die ursprünglichen Hauptquellen das argentinsche Patagonien und die Sierra de la Ventana, das südliche Afrika, die Ostantarktis und das Falklandplateau waren. Die ?permischen Sedimente hatten felsische, magmatische Hauptquellen mit kontinentalem Ursprung und die Sedimente hatten kurze Transportwege. Mit Hilfe der obengenannten Daten stützt diese Studie einen Beginn von Subduktion am pazifischen Kontinentalrand Gondwanas im Spätkarbon

Provenance, depositional setting and diagenesis as keys to reservoir quality of the Lower Cretaceous in the SW Barents Sea

This study examines the role of the depositional environment for the final reservoir quality in four Lower Cretaceous sandstone reservoirs in the southwestern Barents Sea by linking facies to the distribution of primary textures, composition, and diagenetic alteration. Facies analysis reveals slope-to-basin-floor, distal shallow-marine, and deltaic depositional environments. The slope-to-basin-floor sandstone has the highest porosity of 3–19% (avg. 13%). It is attributed to good sorting, non-pervasive carbonate cementation that inhibited compaction and allowed for secondary porosity through later dissolution, and moderate clay infiltration that resulted in clay cutanes on grain rims and the precipitation of chlorite (which inhibited quartz growth). For the deltaic sandstone, moderate to fluctuating energy and sediment supply provided good conditions for mechanical clay infiltration and varying porosity of 2–18% (avg. 8%). The distal shallow-marine sandstone reservoir has the lowest porosity of 1–12% (avg. 7%). Based on its fine-grained and bioturbated character, deposition in a low-energy environment with low sediment supply seems likely. The combination of fine-grained lamina, interstitial matrix and bioturbation led to porosity reduction. Abundant mica and feldspar grains in the shallow-marine sandstone, partly a result of the provenance, and deep burial also resulted in extensive illitization. High mineralogical maturity, much monocrystalline quartz in the quartz-grain populations, and similar felsic chemical rock compositions for all facies associations and wells indicate similar source rocks with some variations. Abundant mechanically unstable mica makes the nearby Loppa High a plausible catchment, which is supported by the seismic geometries. This study demonstrates that the porosity evolution of the studied Lower Cretaceous sandstone reservoirs is determined mainly by the depositional environment despite minor provenance and major diagenetic variationspublishedVersio

etrological, geochemical (major, trace, and rare earth elements), and U–Pb zircon data of the Tamatán Group, NE Mexico

From samples of the Paleozoic Tamatán Group (Huizachal–Peregrina Anticlinorium, Tamaulipas, Mexico), petrographic (qualitative and modal) and geochemical analyses (major, trace, and rare earth elements) were conducted. The first U–Pb geochronological data on detrital zircons of the Tamatán Group were generated using four samples. The data presented here contains a broad overview of photomicrography, recalculated modal point-count data, raw geochemical data, and simple statistics of selected geochemical parameters. The data presented in this article are interpreted and discussed in the research article titled “Provenance and tectonic setting of the Tamatán Paleozoic sequence, NE Mexico: Implications for the closure of the Rheic Ocean at the northwestern part of Gondwana”publishedVersio

Petrology and geochemistry of meta-ultramafic rocks in the Paleozoic Granjeno Schist, northeastern Mexico: Remnants of Pangaea ocean floor

Abstract: The Granjeno Schist is a meta-volcanosedimentary upper Paleozoic complex in northeastern Mexico. We suggest different tectonic settings for metamorphism of its serpentinite and talc-bearing rocks based on petrographic and geochemical compositions. According to the REE ratios (LaN/YbN = 0.51–20.0 and LaN/SmN = 0.72–9.1) and the enrichment in the highly incompatible elements Cs (0.1 ppm), U (2.8 ppm), and Zr (60 ppm) as well as depletion in Ba (1 – 15 ppm), Sr (1–184ppm),Pb(0.1–14ppm),andCe(0.1–1.9ppm)the rocks have mid-ocean ridge and subduction zones characteristics.TheserpentinitecontainsAl-chromite,ferrian chromiteandmagnetite.TheAl-chromiteischaracterized byCr#of0.48to0.55suggestingaMORBorigin,andCr#of 0.93 to 1.00 for the ferrian chromite indicates a prograde metamorphism.Weproposeatleasttwoserpentinization stagesoflithosphericmantlefortheultramaficrockofthe GranjenoSchist,(1)afirstinanocean-floorenvironment atsub-greenschisttogreenschistfaciesconditionsand(2) later a serpentinization phase related to the progressive replacement of spinel by ferrian chromite and magnetite atgreenschisttolowamphibolitefaciesconditionsduring regional metamorphism. The second serpentinization phase took place in an active continental margin during the Pennsylvanian. We propose that the origin of the ultramaficrocksisrelated toanobductionandaccretional eventatthewesternmarginofPangea. Keywords: ultramafic rocks; serpentinite; Granjeno Schist;northeasternMexico,Gondwana,Pange

Grafito en el complejo metamórfico paleozoico esquisto granjeno

El Complejo Metamórfico Paleozoico Esquisto Granjeno se compone por rocas con eductos sedimentarios e ígneos. El énfasis de este trabajo radica en la una unidad grafítica, de la cual no se ha entendido completamente su origen y evolución. Durante el metamorfismo las condiciones de grafitización corresponden a un proceso irreversible. Por lo cual el proceso de grafitización se considera un indicador confiable para estimar las condiciones térmicas máximas durante el metamorfismo. Se realizaron análisis geoquímicos en roca total y mineral con la finalidad de estimar las condiciones de grafitización y la mineralogía formada durante este proceso. Se estima que el proceso de grafitización ocurrió en dos rangos de temperatura de 318–339°C y 426–432°C. Por lo tanto, los sedimentos ricos en materia orgánica depositados en una cuenca oceánica localizada en la periferia del NW Gondwana fueron afectados por alto grado de metamorfismo regional durante el cierre de Pangea

Influencing Factors on Petrography Interpretations in Provenance Research—A Case-Study Review

The use of framework petrography is a common initial step in provenance research of sand and sandstone. The data tend to be interpreted based on the three main components quartz, feldspar, and lithic fragments. Surprisingly often, this is done without taking other influencing factors than the tectonic setting of the catchment and/or the surroundings of the depositional basin into account. Based on a database of 14 studies with approximately 900 petrographic data points from sand and sandstone, this study demonstrates quantitative effects on the apparent composition resulting from both geological and non-geological biases. The study illustrates sandstone-classification differences based on different specifications of the three end-members quartz, feldspar, and lithic or rock fragments, how the point-counting method can affect the apparent petrographic composition of sandstone, how sorting and facies bias may be differentiated from a climate or provenance signal, and how bias due to diagenetic effects can be minimised. In conclusion, both geological and non-geological biases should be considered for provenance studies that include petrographic data

Lapillituff som bevis för underjurassisk vulkanism av strombolikaraktär i Skåne

Central Scania, southern Sweden, is penetrated by more than one hundred basaltic volcanic necks of Jurassic age. Pyroclastics, related to the volcanic necks, has been investigated to reveal the volcanic environment, and the eruptive character required to produce the pyroclastics. In this study a strombolian volcanic character is suggested, due to textural and petrographical evidence. Magnetic data support this interpretation, with indications of some reworking of the pyroclastics. The sediment, a lapilli tuff, is clay altered due to early diagenetic processes, but traces of palagonite reveal the former basaltic composition of the lapilli tuff. The volcanoes were part of a monogenetic volcanic field and deposition of the pyroclastic sediment took place on land, close to oceanic water.Populärvetenskaplig sammanfattning: I centrala Skåne finns det rester av fler än ett hundra vulkaner. De var aktiva för mer än 170 miljoner år sedan, under första delen av tidsperioden jura. På några ställen finns det kvar lite av det material som vulkanerna spottade ut. Det är inte lava, utan millimeter- till centimeterstora fragment av pimpsten, så kallade lapilli, som har kastats upp en bit i luften, ungefär 1200°C varma. Under luftfärden hann de svalna något. Efter avsättningen har materialet bildat bergarten lapillituff. Det har skett genom att varma vattenlösningar har cirkulerat i sedimentet och avsatt bland annat mineralet kalcit, som ett cement. Lapillituffen har undersökts, för att ta reda på den vulkaniska karaktär som rådde under jura, och för att få en inblick i hur landskapet kan ha sett ut. Olika metoder har använts. Bland annat har jag mikroskoperat, för att se vilka mineral som finns i lapillituffen och för att titta på bergartens strukturer. Dessa studier har kompletterats med att undersöka bergartens magnetiska egenskaper, med så kallad paleomagnetism. Alla bergarter innehåller små mängder magnetiska mineral. Den magnetiska riktning som mineralen får vid avsvalning under 580°C, kan mätas i en känslig detektor. Genom att stegvis upphetta bergartsprov och mäta riktningen efter varje upphettning, kan man få reda på vid vilken temperatur materialet föll ner på marken efter sin luftfärd. Undersökningarna visar att materialet kastades ut från vulkanerna med en mild explosivitet, som gjorde att materialet slungades upp några hundra meter i luften, för att därefter landa nära vulkanerna. Denna typ av vulkanism kallas för stromboli-vulkanism, namngivet efter den italienska vulkanen Stromboli. De vulkaner som bildas av strombolivulkanism (så kallade scoriakoner), blir sällan högre än ett par hundra meter. De förekommer ofta många tillsammans, med bara någon kilometers mellanrum och dominerar ofta hela landskap, tillsammans med materialet de har kastat ut. Under tidig jura var Skåne delvis ett grunt hav, med långa havsarmar, som flikade sig in i landskapet. De flesta av vulkanerna har troligen stått på land, men nära ett hav