A chemical investigation of microstructural changes in oyster (Magallana gigas) shells

<p>The shells of oysters (Family Ostreidae) are predominantly composed of two different calcite microstructures: A dense foliated structure consisting of sheet-like folia (“foliated” microstructure) and a more porous microstructure consisting of less well organized leaf-shaped crystals (“chalky” microstructure). These unique characteristics of oyster shells have been subject to a number of studies, with some authors hypothesizing that the chalky structures are mineralized by bacteria living in the shell (Vermeij, 2014). The formation of these microstructures is of great interest, because the phenomenon is unique in the mollusk phylum and because the shells of oysters are popular archives for paleoclimate and paleoenvironment reconstructions (e.g. Bougeois et al., 2018; de Winter et al., 2018). Previous authors have challenged the bacterially mediated mineralization hypothesis through microstructural observations of different parts of the oyster shell (Checa et al., 2018).</p><p>Here, we expand on this structural evidence by adding detailed observations of differences in chemical composition between the foliated and chalky microstructures. We combine information on trace element concentrations with stable carbon, oxygen, nitrogen and sulfur isotope ratios as well as carbonate clumped isotope analyses of samples from foliated and chalky structures in multiple modern specimens of Magallana gigas, the Pacific oyster. These analyses shed light on the chemical variability within the oyster shell and how it relates to the occurrence of various calcite microstructures. Given the unique isotopic signature of bacterially mediated calcite, our isotopic analysis results allow us to definitively conclude whether the chalky shell structure in modern oysters was precipitated via symbiotic microbes. Furthermore, the degree of intra-shell chemical variability has implications for paleoclimate and paleoenvirionmental reconstructions from fossil oyster shells, for which the applied trace element and isotope systems function as important proxies. The results of this study therefore yield important recommendations for sampling fossil oyster shells for reconstructions, and provide a baseline for the investigation of chemical variability between shell microstructures throughout the Ostreidae family and the mollusk phylum.</p><p> </p><p><strong>References</strong></p><p>Bougeois, L., Dupont-Nivet, G., De Rafélis, M., Tindall, J. C., Proust, J.-N., Reichart, G.-J., de Nooijer, L. J., Guo, Z. and Ormukov, C.: Asian monsoons and aridification response to Paleogene sea retreat and Neogene westerly shielding indicated by seasonality in Paratethys oysters, Earth and Planetary Science Letters, 485, 99–110, 2018.</p><p>Checa, A. G., Harper, E. M. and González-Segura, A.: Structure and crystallography of foliated and chalk shell microstructures of the oyster Magallana: the same materials grown under different conditions, Scientific reports, 8(1), 7507, 2018.</p><p>Vermeij, G. J.: The oyster enigma variations: a hypothesis of microbial calcification, Paleobiology, 40(1), 1–13, 2014.</p><p>de Winter, N., Vellekoop, J., Vorsselmans, R., Golreihan, A., Soete, J., Petersen, S., Meyer, K., Casadio, S., Speijer, R. and Claeys, P.: An assessment of latest Cretaceous Pycnodonte vesicularis (Lamarck, 1806) shells as records for palaeoseasonality: a multi-proxy investigation, Climate of the Past, 14(6), 725–749, 2018.</p>

Rekomendasi Pemanfaatan Marmer Daerah Besole, Kecamatan Besuki, Kabupaten Tulungagung, Provinsi Jawa Timur Berdasarkan Karakteristiknya

Besole area, Tulungagung regency, East Java province is an area with measured marble resource potential of 15 million tons. This study aims to determine marble recommendations based on their characteristics. Marble characteristic has brownish white-brown description of megascopis, non-foliated structure, based on fracture density measurement using inventory method, marble has medium density, based on petrographic analysis, marble has crystal size ≤ 0.5 - 2 mm, having texture of metamorphism process resistance ie crystalloblastic and relict, texture of mineral form that is granoblastic, texture of metamorphic rock is decussate and saccharoidal. The composition of marble consists of calcite, dolomite and hematite. Based on analysis of geochemical test using method of ICP-AES (Inductively Coupled Plasma - Atomic Emission Spectroscopy), marble has the main oxide content dominated by CaO 54.6% - 56%, based on the analysis of engineering test yields the average value of compressive strength test of 781,713 kg / cm², wear resistance value 0.0399 mm / min and water absorption value 0.704%. The recommended use of marble based on solid density is utilized as a residential floor with a size of ≤10-40 cm, based on its geochemistry used as paper industry, textile dye, pesticide production, sugar screening and cement production, and based on its technique is used as floor with live load> 250 kg / cm², inner and outer construction stone, and light - medium construction foundation

Degeneration at E2 of certain spectral sequences

We propose a Hodge theory for the spaces [Formula: see text] featuring at the second step either in the Frölicher spectral sequence of an arbitrary compact complex manifold [Formula: see text] or in the spectral sequence associated with a pair [Formula: see text] of complementary regular holomorphic foliations on such a manifold. The main idea is to introduce a Laplace-type operator associated with a given Hermitian metric on [Formula: see text] whose kernel in every bidegree [Formula: see text] is isomorphic to [Formula: see text] in either of the two situations discussed. The surprising aspect is that this operator is not a differential operator since it involves a harmonic projection, although it depends on certain differential operators. We then use this Hodge isomorphism for [Formula: see text] to give sufficient conditions for the degeneration at [Formula: see text] of the spectral sequence considered in each of the two cases in terms of the existence of certain metrics on [Formula: see text]. For example, in the Frölicher case, we prove degeneration at [Formula: see text] if there exists an SKT metric [Formula: see text] (i.e. such that [Formula: see text]) whose torsion is small compared to the spectral gap of the elliptic operator [Formula: see text] defined by [Formula: see text]. In the foliated case, we obtain degeneration at [Formula: see text] under a hypothesis involving the Laplacians [Formula: see text] and [Formula: see text] associated with the splitting [Formula: see text] induced by the foliated structure.

Templates of Two Foliated Attractors — Lorenz and Chen Systems

A chaotic attractor solution of the Lorenz system [Lorenz, 1963] with foliated structure is topologically characterized. Its template permits to both summarize the organization of its periodic orbits and detail the topology of the solution as a branched manifold. A template of an attractor solution of the Chen system [Chen & Ueta, 1999] with a similar foliated structure is also established.

Nacre in an early gryphaeid bivalve (Mollusca)

McRoberts (1992, figs. 4.13, 4.14, 6.8) illustrated the shell microstructure of late Triassic Gryphaea (Gryphaea) arcuataeformis Kiparisova, 1936, and Gryphaea (Gryphaea) nevadensis McRoberts, 1992. McRoberts (1992, p. 33) described the left valve of G. arcuataeformis as showing “neomorphosed calcite with multiple laminae of ?prismatic structure perpendicular to [the] outer shell surface ….” He described the left valve of G. nevadensis as consisting of two distinct layers of neomorphosed calcite:“…an outer layer with ?prismatic structure occasionally with bands of dark material (?micritic matrix), and a much thinner inner layer with ?cross-foliated structure ….” Subsequent study has shown these microstructural diagnoses to be inaccurate. They are revised as follows.

IV.—A Contribution to the Petrology of North-Western Angola

This remarkable rock occurs as a marginal phase of the granulitic albite granites which are found between Noqui and kilometre 16 on the road to San Salvador. In the hand-specimen it shows a finegrained slightly foliated structure with a characteristic pepper and salt appearance, due to the sprinkling of lustrous black plates of riebeckite among iron-stained granular crystals of quartz and felspar. A few small porphyritic crystals of orthoclase are embedded in the main mass of the rock, making up approximately 15 per cent of the whole.