SPONGE SPICULE ASSEMBLAGES FROM THE MIDDLE ORDOVICIAN OF PONÓN TREHUÉ, SOUTHERN MENDOZA, ARGENTINA

Sponge spicule assemblages are described fom residues of conodont samples from Ordovician strata in the Sierra Pintada, southern Mendoza Province, Argentina. Spicules have been recovered from the Arenigian allochthonous megaconglomerates and from autochthonous limestones and carbonates sandstones of the Ponón Trehue Formation. This formation is a elastic-carbonate sequence representing olistostromic and turbidite facies. Conodonts in this formation are Llandeillan in age. The spicules are calcified and moderately preserved. The material shows a low diversity. Poriferan taxa found in this formation include heteractinid spicules as well as hexactinellid hexactines and non-lithistid demospongiid triaene and oxeas with some doubt. Associations of exclusively heteractinid spicules are restricted to allochthonous blocks of the shallow carbonate platform of the San Juan Formation (Arenig). In the outer platform and slope, autochthonous calcarenites and dark limestones contain hexactine spicules. These spicules evidence the existence of sponges in the Ordovician of the Ponón Trehue area, as a part of the Precordillera terrane.

Resources of quartz raw materials, Gargan block, East Sayan quartzite-bearing area

The evaluation (according to structural and geochemical rock properties ) of the quartzites from the East Sayan quartzite-bearing area as a potential source of quartz raw material for crystalline silicon and optical glass manufacturing can significantly expand the forecast resources of this type of raw materials. The geological structure of the Irkut Formation, productive of high-purity quartzites is specified within the Oka-Urik, Urengenur and Urdagargan quartz-bearing areas; geological, mineralogical-petrographic and geochemical characteristics of the main quartzite types are given, the main morphological features of productive high-purity quartzite bodies are specified to predict their occurrence at depth. The major factors in the formation of high-purity quartzite bodies include: 1) quartzites are accumulated in the siliceous-carbonate sequence of the Middle Riphean Irkut Formation within a broad but isolated basin; 2) high-purity quartzite bodies are produced as a result of dynamic recrystallization due to the deformation of primary microquartzites resulting from the collision of the Dunzhugar island arc with the Gargan microcontinent margin. Within the western part of the East-Sayan quartz-bearing area, quartzite reserves as a potential source for silicon metallurgy and production of optical glass were estimated as 134 mln tons.

Sedimentological And Stratigraphical Analysis Of Kaki Bukit Formation (Lower Setul Member) At Teluk Ewa, Pulau Langkawi

The identification of new units on the carbonate sequence of Teluk Ewa (from Tg. Mendidih to Teluk Ewa) has given an idea for the review of stratigraphic succession of Kaki Bukit Formation (Lower Setul Member). The analysis is related to a sedimentology study, where the sedimentary sequences formed as a mixed siliciclastic–carbonate shallow marine system that combines the carbonate and silisiclastic deposits. Eight facies have been recognised such as (1) argillite facies, (2) interlayer of mudstone and limestone facies, (3) wavy stromatolites limestone facies, (4) linear stromatolites limestone facies, (5) heterolithic of mudstone-limestone facies, (6) shale facies, (7) massive limestone facies and (8) thrombolites limestone facies. Each facies are divided into four litostratigraphic units based on the evaluation from Malaysian Stratigraphic Nomenclature Committee (1997) and North American Stratigraphic Code 2005. (1) The clastic unit referring to the uppertmost part of Machinchang Formation maintains it's name. Meanwhile, the suggested nomenclature for the new units such as (2) The Sabung Member is referring to the basal carbonate unit comprising microbial facies and mixed silisiclastic-carbonate sediment. (3) The Pesak Seluar Member in the middle is a silisiclastic unit that consists of shale facies and (4) The Ewa Member at the top representing the upper limestone unit. All units show a similar litostratigraphic characteristics that are found in Tarutao Group, Pante Malaka Formation, Rung Nok Formation and Lae Tong Formation in Thailand as described by Wongwanich et al. (1990; 2002) and Imsamut & Abdul Rahman (2017).

Raman spectroscopy in thrust-stacked carbonates: an investigation of spectral parameters with implications for temperature calculations in strained samples

Raman spectroscopy is commonly used to estimate peak temperatures in rocks containing organic carbon. In geological settings such as fold-thrust belts, temperature constraints are particularly important as complex burial and exhumation histories cannot easily be modelled. Many authors have developed equations to determine peak tempertaures from Raman spectral parameters, most recently to temperatures as low as 75 °C. However, recent work has shown that Raman spectra can be affected by strain as well as temperature. Fold-thrust systems are often highly deformed on multiple scales, with deformation characterised by faults and shear zones, and therefore temperatures derived from Raman spectra in these settings may be erroneous. In this study, we investigate how the four most common Raman spectral parameters and ratios change through a thrust-stacked carbonate sequence. By comparing samples from relatively low-strain localities to those on thrust planes and in shear zones, we show maximum differences of 0.16 for I[d]/I[g] and 0.11 for R2, while FWHM[d] and Raman Band Separation show no significant change between low and high strained samples. Plausible frictional heating temperatures of faulted samples suggest that the observed changes in Raman spectra are not the result of frictional heating. We apply three equations used to derive the peak temperatures from Raman spectra to our data to investigate the implications on predicted temperatures between strained and unstrained samples. All three equations produce different temperature gradients with depth in unstrained samples. We observe that individual equations exhibit apparently varying sensitivities to strain, but calculated temperatures can be up to 140 °C different for adjacent strained and unstrained samples using the same temperature equation. These results have implications for how temperatures are determined in strained rock samples from Raman spectra.

Stable isotope and chemical stratigraphy of the Eocene Tambaba Formation: correlations with the Palaeocene-Eocene Thermal Maximum event

The Paraíba Basin has a well-defined carbonate depositional sequence from the Upper Cretaceous (Campanian) to the Eocene. The carbonate sequence consists of Itamaracá, Gramame, Maria Farinha and Tambaba formations, which mainly contain calcareous sandstones and carbonates with siliciclastics, limestone-marl alternations, limestones and marls, and limestones, respectively. The Tambaba Formation is composed of reef limestones, ranging from fossil- and ichnofossil-rich calcilutite to calcarenite. We investigated the rocks of this unit located on a representative geological section in the Tambaba Beach, Northeastern Brazil, in order to elucidated the environmental responses recorded in geochemical proxies (C and O isotopic composition, and distribution of major and trace elements). The δ13C and δ18O values ranged from 1.0 to 2.7‰ VPDB and from -1.3 to 1.1‰ VPDB, respectively. The interpretation of this response suggests environmental changes, such as an increase or decrease in bioproductivity from the organisms that build these reef limestones. These changes are also recorded in the behavior of the major and trace elements, for example, the relationship among SiO2, Al2O3, MgO and CaO, characterizing two different cycles during the deposition of these limestones: the first one characterized by a predominantly carbonate deposition, and the second one presenting a pulse of siliciclastic content. In addition, the palaeotemperature values (9 to 15°C, obtained by δ18O data) found together with chemostratigraphic profiles of previous studies (e.g. δ13C, CaO, MgO, SiO2, Al2O3) indicate that the reef limestones of the Tambaba Formation were probably deposited about 5 Ma after the Palaeocene-Eocene Thermal Maximum event.

Mineralization constraints on the origin of polymetallic (Pb, Ag, Zn, Cu, Au) deposits hosted in the metasedimentary Lajeado Group, Southern Ribeira Belt, Brazil

The sediment-hosted polymetallic (Pb, Zn, Ag, Au-Cu) mineralization of the Vale do Ribeira Mineral District has been known since the beginning of the 20th century, but exploration was interrupted just before the turn of the century. The Vale do Ribeira Mineral District is part of the Southern Ribeira Belt, developed during the Brasiliano-Pan African orogeny. Polymetallic mineralization is mainly hosted in metalimestones of the Lajeado Group, a typical platform carbonate sequence of a passive margin, which has been deformed during the Gondwana assembly. The region has a gap of research since the mines were closed, which justifies new projects on their mineral economic potential. Fieldwork, petrographic and geochemical analyses were developed in five currently inactive mines (Panelas, Barrinha, Rocha, Lajeado, and Furnas) and their surroundings, along with the description of a drill core executed in the 1980s. The main type of ore consists of polymetallic fault-fill veins of massive sulfide, which are composed essentially by argentiferous galena, sphalerite, pyrrhotite, arsenopyrite, and chalcopyrite. The highest ore grades were obtained from samples in the Panelas Mine, with contents of up to 35% lead, 5% zinc, > 1% copper and 564 ppm silver, as well as 23% iron. New ore occurrences were described in a secondary gallery of the Barrinha Mine, whose gold grades reached up to 5,630 ppb. The main controls of the mineralization are lithological - since the ore occurs exclusively in carbonate rocks, irrespective of the geological unit - and structural, related to NE high-angle strike-slip fault zones, including evidence of fault-valve behavior. Fault zones as the main control of the polymetallic veins is an innovative interpretation, increasing the perspectives for mineral exploration in the area. Although they are small deposits, the presented data indicate that the region has potential for new discoveries and that the mined deposits are probably not exhausted.