Search

Collected samples of bentonite and associated facies from the Justina deposit of Cretaceous age (Anacleto Formation) have been studied. Facies analysis, mineralogical, and geochemical studies have been carried out using several techniques, including: XRD, FTIR, DTA-TGA, microscopy (OM, SEM-EDX), and chemical analysis. The deposit occurs in a shallow, saline lacustrine environment developed over a fluvial floodplain, with a thickness between 0.21 and 0.8 m intercalated between fine-grained siliciclastic facies. Three mineral assemblages were found. In assemblage 1, the bentonite has low content of detrital minerals and the smectite is sodic. In assemblage 2, the bentonite shows the occurrence of minor analcime and mica, slightly higher detrital mineral content and the smectite is sodic to sodic-calcic. The associated detrital facies (assemblage 3) is dominated by illite and a mixed layer of illite and calcic smectite (R0), subordinately kaolinite + chlorite, and locally low-ordered smectite. As inherited minerals are found: quartz, potassium feldspar, plagioclase, illite-mica, heavy minerals (monazite, zircon, apatite, titanomagnetite) and volcanic rock fragments (andesite, glass). Authigenic minerals are: sodium smectite, analcime, barite, celestine, gypsum, and hematite. A model for the formation of authigenic minerals is proposed, highlighting the formation of sodic smectite from the alteration of volcanic glass of trachyandesitic composition. [ABSTRACT FROM AUTHOR]

The effect of dietary inclusion of a mixture of microalgae meal (Schizochytrium limacinum and Nannochloropsis oceanica) (1:1 ratio) on growth performance, gene expression, histology and muscle fatty acid composition of rainbow trout (Oncorhynchus mykiss) reared in saltwater was investigated. Three experimental extruded diets containing 0%, 9% and 17% of a mixture of microalgae meal were evaluated in triplicate groups during 10‐week bioassay. The results showed that growth performance and feed conversion ratio were significantly reduced by increasing the dietary inclusion of a mixture of microalgae meal. No significant trends were observed with respect to feed intake and relative gene expression of hsp70, scarb1, IL‐12 and myod. Conversely, increasing dietary levels of a mixture of microalgae meal led to a decrease in vacuolar degeneration of hepatocytes. A reduction of 23% on the amount of 20:5n−3 fatty acid in the muscle was found between the fish fed control and the highest level of the microalgae meal blend diets. Nevertheless, 22:6n−3 fatty acid content did not vary among dietary treatments. These results demonstrate that a mixture of microalgae meal has a potential to be included up to 90 g kg−1 within diets for rainbow trout as a sustainable replacement for fish oil. [ABSTRACT FROM AUTHOR]

It is widely accepted that the polymodal fault patterns accommodate triaxial deformation. Multiphase extension and inherited structural fabrics have been counted as common features for the development of polymodal faults in extensional systems. This research documents the development of a polymodal normal fault system in the Mesa Central of Mexico, focusing on the evolution of the deformation field. The fault system comprises NW and NE grabens and N‐S and E‐W faults. These faults affected silicic volcanic rocks in two Oligocene extensional phases. In the Rupelian (~31 Ma), a NW trending domino fault system was formed, associated with fault domain boundaries (transfer or accommodation zones) oriented NW, NE, N‐S, and E‐W. The domino faults tilted the early Rupelian rocks, and the deformation was biaxial with the principal extension NE‐SW. Subsequently, the Rupelian structures were buried by the middle and late Rupelian volcanism. The second extensional phase occurred in the Chattian (after 28 Ma). In this phase, the Rupelian fault domain boundaries acted as faulting zones forming a polymodal fault system in the volcanic cover. The resulting deformation was triaxial with ENE and NNW horizontal principal extensions. From revision of cases in the literature and the deformation documented in the Mesa Central, we propose a general way to form a brittle triaxial deformation zone, requiring (1) the presence of planes of weakness in the upper crust, (2) the deposition of a cover, and (3) a subsequent faulting event reactivating the underlying anisotropies and producing new faults in the cover. Key Points: A brittle triaxial deformation area can be formed under a single stress state owing to kinematic interaction among preexisting faultsThe Oligocene extensional system in the Mexican Mesa Central evolved from biaxial domino style to triaxial polymodal faultingThe rupture of the cover in the Mexican Mesa Central produced the triaxial deformation in response to underlying anisotropies' reactivation [ABSTRACT FROM AUTHOR]

The Mesa Central (MC) of Mexico presents a noticeable feature as is the three-dimensional (3D) deformation of Cenozoic volcanic rocks. To figure out when this unusual deformation began, we constructed a geological map at 1:100,000 scale, with detailed stratigraphy, and thirteen new U-Pb ages in the southern MC. The mapped area is dominated by silicic volcanic rocks with ages from ca. 34.4 Ma to ca. 23.5 Ma affected by coeval normal faulting. An angular unconformity evidences a shift in the deformation style that occurred around 30 Ma, from an NW-trending fault system in domino-style to a polymodal fault system, which also temporally coincided with the emplacement of lava dome complexes. The structural and stratigraphic data give new insight for understanding how the polymodal fault system developed in the southern MC, suggesting that the change in the deformation and volcanism regime played an important role. [ABSTRACT FROM AUTHOR]

The Mesa Central of Mexico (MC) is an elevated plateau located 2000 m above sea level in central Mexico, where intrusions outcrop that register the history of exhumation-erosion occurring during the Late Cretaceous-Paleogene. The tectonic history of the region records formation of the Late Cretaceous-Paleogene 'Mexican orogen'; this was followed by extension of the entire region and several plutons were then exhumed. The age and magnitude of the crustal uplift and erosion occurring during exhumation has not been addressed to date. Therefore, this study reports the crystallization and cooling ages of two plutons, the Tesorera Granodiorite and the Comanja Granite, and estimates their emplacement depths. Based on these data, the exhumation age of the Tesorera Granodiorite is estimated to be between ~73 Ma and ~63 Ma at an exhumation rate of ~528 m/m. y. and that of the Comanja Granite is 52 Ma and 48 Ma at an exhumation rate of ~2500 m/m. y. Exhumation-erosion event of the Tesorera Granodiorite was located on the trace of the San Luis-Tepehuanes Fault System and that of the Comanja Granite on the a trace of the El Bajío Fault System. Furthermore, the high exhumation rate in the Comanja Granite suggests that gravitational collapse played an important role during exhumation. [ABSTRACT FROM AUTHOR]

Piscirickettsia salmonisis the causative bacterial pathogen of piscirickettsiosis, a salmonid disease that causes notable mortalities in the worldwide aquaculture industry. Published research describes the phenotypic traits, virulence factors, pathogenicity and antibiotic‐resistance potential for various P. salmonisstrains. However, evolutionary and genetic information is scarce for P. salmonis. The present study used multilocus sequence typing (MLST) to gain insight into the population structure and evolution of P. salmonis. Forty‐two Chilean P. salmonisisolates, as well as the type strain LF‐89T, were recovered from diseased Salmo salar, Oncorhynchus kisutchand Oncorhynchus mykissfrom two Chilean Regions. MLST assessed the loci sequences of dnaK, efp, fumC, glyA, murG, rpoD and trpB. Bioinformatics analyses established the genetic diversity among P. salmonis isolates (H = 0.5810). A total of 23 sequence types (ST) were identified, 53.48% of which were represented by ST1, ST5 and ST2. Population structure analysis through polymorphism patterns showed few polymorphic sites (218 nucleotides from 4,010 bp), while dN/dS ratio analysis indicated purifying selection for dnaK, epf, fumC, murG, and rpoD but neutral selection for the trpB loci. The standardized index of association indicated strong linkage disequilibrium, suggesting clonal population structure. However, recombination events were detected in a group of seven isolates. Findings included genogroups homologous to the LF‐89T and EM‐90 strains, as well as a seven‐isolate hybrid genogroup recovered from both assessed regions (three O. mykiss and four S. salar isolates). The presented MLST scheme has comparative potential, with promising applications in studying distinct P. salmonis isolates (e.g., from different hosts, farms, geographical areas) and in understanding the epidemiology of this pathogen. [ABSTRACT FROM AUTHOR]