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CURATOR
A pinboard by
Christopher Todd

PhD Student, James Cook University

PINBOARD SUMMARY

This project takes place in Porcupine Gorge of northern Queensland, Australia, which preserves a continuous Permian to Cretaceous sedimentary succession through the Galilee and Eromanga basins of eastern Australia. Through the use of the mineral zircon to date sedimentary rock units in the gorge it is possible to determine the stratigraphic positions of each unit compared to spatially correlatable formations from around Queensland. This project also combines these ages with ancient flow direction markers and rocks compositions to determine possible sources for the sediments that make up these rocks. By completing these analyses certain tectonic trends become apparent, such as uplift of the eastern Australian margin in the Late Triassic period causing the erosion of Triassic volcanics from the rock record, and the flow direction shift in the Cretaceous that can be linked to the Eromanga Sea transgression into continental Australia.

6 ITEMS PINNED

Palaeoenvironment and provenance in the early Cape Basin of southwest Gondwana: sedimentology of the Lower Ordovician Piekenierskloof Formation, Cape Supergroup, South Africa

Abstract: The lowermost unit of the Table Mountain Group (Cape Supergroup), the Ordovician Piekenierskloof Formation is a siliciclastic succession that formed during the initial stages of the Cape Basin development in southwest Gondwana. This contemporary sedimentological re-evaluation of the depositional history and provenance of the Piekenierskloof Formation provides new insights into the palaeoenvironment and tectonic setting of the early Cape Basin. Outcrop-based sedimentary facies analysis revealed distinctive depositional features, dominated by large trough cross-bedding, which suggest a shallow, perennial, sand-bed braided fluvial style with bedload transportation in roughly 1 to 2.5 m deep and relatively wide channels. This fluvial style was possibly influenced by the global absence of substrate stabilizing terrestrial flora in pre-Devonian rivers. Based on an integrated approach of clast count, framework petrography and palaeocurrent studies, the provenance analysis show that the source rocks of the Piekenierskloof Formation were likely situated in source areas characterized by two main rock types: (1) a dominant low metamorphic rank metasedimentary rock suite with parent rocks of variable grain-size, and (2) minor plutonic rocks. The data also suggest that the parent rocks were locally intruded by quartz veins and/or pegmatites. Consistent palaeoflow to the southeast and east further indicates that these source areas were located to the northwest and west of the clastic sediment depocentres in the Cape Basin of southwest Gondwana in the Early Ordovician. Accessible outcrops of the Piekenierskloof Formation are mostly laterally limited and sparsely distributed, which hinder stratigraphic correlations, and therefore inferences of tectonic activity during the sedimentation in the Early Ordovician cannot be convincingly made. For a better understanding of the Early Palaeozoic evolution of the Cape Basin in southwest Gondwana, systematic outcrop studies acquiring high-resolution digital imagery using unmanned aerial vehicles (UAVs) and terrestrial laser scanning, coupled with subsurface facies analysis should be undertaken. The Piekenierskloof Formation and the rest of the Table Mountain Group, with their exceptionally extensive, but rather inaccessible cliff faces, are excellent candidates for such high-resolution digital-based studies.

Pub.: 17 Oct '16, Pinned: 07 Aug '17

Provenance analysis of Jurassic sandstones from the Otlaltepec Basin, southern Mexico: Implications for the reconstruction of Pangea breakup

Abstract: The structural evolution that accompanied the breakup of Pangea during Jurassic time has been constrained in Mexico only at the regional scale on the basis of global plate tectonics and geometric considerations. According to available regional-scale reconstructions, the Jurassic tectonic evolution of Mexico was characterized by: (1) anticlockwise rotation of the Yucatán block along NNW-trending dextral faults and (2) sinistral block motions along W- to WNW-trending faults, which are geometrically needed to restore southern and central Mexico to the northwest of its present position during early Mesozoic time and avoid the overlap between North and South America in the reconstruction of Pangea. Reports of W- to WNW-trending sinistral faults that were active in Mexico during Jurassic time are presently few, and the existence, extension, and age of some of these structures have been questioned by many authors. In this work, we present the provenance analysis from a Jurassic clastic succession deposited within the Otlaltepec Basin in southern Mexico. Whole-rock sandstone petrography integrated with chemical analysis of detrital-garnet and U-Pb detrital-zircon geochronology documents that the analyzed stratigraphic record was deposited during rapid exhumation of the Totoltepec pluton along the Matanza fault, which is a W-trending sinistral normal fault that extends along the southern boundary of the Otlaltepec Basin. U-Pb zircon ages and biostratigraphic data bracket the age of the Matanza fault between 163.5 ± 1 and 167.5 ± 4 Ma. This indicates that the Matanza fault was involved in the crustal attenuation that accompanied the breakup of Pangea and that sinistral motion of continental blocks along W-trending structures was taking place in southern Mexico as predicted by global plate tectonic reconstructions.

Pub.: 30 Nov '16, Pinned: 07 Aug '17

Detrital zircon and provenance analysis of Eocene-Oligocene strata in the South Sistan suture zone, southeast Iran: Implications for the tectonic setting

Abstract: The north-south–trending Sistan suture zone in east Iran results from the Paleogene collision of the Central Iran block to the west with the Afghan block to the east. We aim to document the tectonic context of the Sistan sedimentary basin and provide critical constraints on the closure time of this part of the Tethys Ocean. We determine the provenance of Eocene–Oligocene deep-marine turbiditic sandstones, describe the sandstone framework, and report on a geochemical and provenance study including laser ablation–inductively coupled plasma–mass spectrometry U-Pb zircon ages and 415 Hf isotopic analyses of 3015 in situ detrital zircons. Sandstone framework compositions reveal a magmatic arc provenance as the main source of detritus. Heavy mineral assemblages and Cr-spinel indicate ultramafic rocks, likely ophiolites, as a subsidiary source. The two main detrital zircon U-Pb age groups are dominated by (1) Late Cretaceous grains with Hf isotopic compositions typical of oceanic crust and depleted mantle, suggesting an intraoceanic island arc provenance, and (2) Eocene grains with Hf isotopic compositions typical of continental crust and nondepleted mantle, suggesting a transitional continental magmatic arc provenance. This change in provenance is attributed to the Paleocene (65–55 Ma) collision between the Afghan plate and an intraoceanic island arc not considered in previous tectonic reconstructions of the Sistan segment of the Alpine-Himalayan orogenic system.

Pub.: 28 Nov '16, Pinned: 07 Aug '17

Provenance analysis of the Late Paleozoic sedimentary rocks in the Xilinhot Terrane, NE China, and their tectonic implications

Abstract: Publication date: Available online 19 December 2016 Source:Journal of Asian Earth Sciences Author(s): Jie Han, Jian-Bo Zhou, Simon A. Wilde, Min-Chun Song The Xilinhot Terrane is located in the eastern segment of the Central Asian Orogenic Belt in NE China, and is a key to a hotly debated issue on the Paleozoic tectonic evolution of this giant progenic belt. To constrain the tectonic evolution of the Xilinhot Terrane in the Late Paleozoic, we undertook zircon U–Pb dating and geochemical analyses of the Zhesi and Benbatu formations in the Suolun and Xi Ujimqin areas in the Xilinhot Terrane. Samples of the Benbatu Formation yield detrital zircon U–Pb ages ranging from 2659 Ma to 316 Ma, with four age populations at: 2659–1826 Ma, 1719–963 Ma, 590–402 Ma, and 396–316 Ma, whereas samples from the Zhesi Formation yield detrital zircon U–Pb ages ranging from 1967 Ma to 250 Ma, with four age populations at: 1967–1278 Ma, 971–693 Ma, 561–403 Ma, and 399–250 Ma. The age groups of both the Benbatu and Zhesi formations in the Xilinhot Terrane are similar to those in other parts of the Central Asian Orogenic Belt (CAOB). This evidence indicates that the Xilinhot Terrane is a microcontinent, and not an accretionary complex as previously thought. Furthermore, the youngest zircon grains in the Benbatu and Zhesi formations yield weighted mean 206Pb/238U ages of 322 ± 12 Ma (MSDW=0.12, n=4) and 257 ± 2.8 Ma (MSDW=1.6, n=8), respectively. Combined with fossil data, our new data suggest that the Benbatu and Zhesi formations in the Xilinhot Terrane were possibly deposited at ∼322 Ma and ∼257 Ma, repsectively. Based on the provenance of the Carboniferous–Permian sandstones came from the blocks of NE China, we speculate that the Xilinhot Terrane is the western part of the Songliao block.

Pub.: 20 Dec '16, Pinned: 07 Aug '17

Provenance of the Lunz Formation (Carnian) in the Western Carpathians, Slovakia: Heavy mineral study and in situ LA–ICP–MS U–Pb detrital zircon dating

Abstract: The Middle Carnian (Julian) detritic sediments of the Lunz Formation were deposited during of the so-called Carnian Pluvial Event. They are the only siliciclastic sediments embedded in purely carbonatic formations. The paper brings the first provenance analysis of this formation from the Western Carpathians (Slovakia), where it occurs in the Hronic, Fatric and Veporic zones. Sandstones of the Lunz Formation belong to feldspatic greywackes and less to lithic greywackes. Modal analyses indicate that the sand material was derived from dissected arc and less from a recycled orogen. The heavy mineral assemblage is dominated by zircon and by apatite, slightly lesser amount of garnet, Cr-spinels and tourmaline. Analysis of tourmalines (schorl and dravite) shows their primary provenance mainly from the metapelites and metapsammites coexisting, or not coexisting with an Al-saturating phase; some were also derived from Fe3 +-rich quartz–tourmaline rocks, calc-silicate rocks and metapelites, and a slightly smaller group of grains was derived from Li-poor granitoid rocks and their associated pegmatites and aplites. Most of the garnet grains belong to almandine, less to spessartine. All of them have a wide spectrum of potential primary source rocks from low- to medium-grade metamorphic rocks and magmatites. The analysed spinel grains (Cr-rich spinel, chromite and magnesiochromite) match mostly the podiform chromitites, harzburgite and cumulate fields or supra-subduction zone peridotites field, whereas Al-depleted spinel best match the arc volcanic field. Some spinels were affected by alteration or metamorphism. The in-situ LA–ICP–MS isotopic U–Pb dating shows a wide age interval of detrital zircon crystals in the Lunz Formation. Concordant zircon data show a wide interval of Late Triassic (Carnian) to Early Proterozoic ages (~ 230–2500 Ma). Majority of zircons shows Paleozoic (pre-Variscan and Variscan) ages, whereas Neoproterozoic to Paleoproterozoic age populations are relatively scarce. Age populations and chemical composition of zircon reveal their dominant primary provenance from various suites of magmatic rocks, including Variscan granitic rocks and pre-Variscan metaigneous lithologies. Characteristic is big scatter in zircon ages and the dominance of ultrastable minerals, as zircon, tourmaline, rutile and Cr-spinels, and quite a good correlation between zircons and Cr-spinels. This indicates that most of the heavy minerals were not directly derived from some distinct primary magmatic or metamorphic sources, but as recycled particles from older sediments, or metasediments. In the context with the previously published palaeogeographic reconstructions, the provenance analysis indicates that the source area was most likely situated outside the Alpine-Carpathian shelf. They are most likely related to the coeval, mostly fluvial Stuttgart Formation in the Central European Basin (Germanic Triassic Basin).

Pub.: 07 Feb '17, Pinned: 07 Aug '17