Great circle analysis of South American VGP-distributions suggests widespread Cretaceous remagnetizations: case study of the Itararé Group Rocks from Brazil

<p>South American Jurassic/Cretaceous rocks has been troubled by elongated virtual geomagnetic pole (VGP) distributions, while many discordant poles from the Carboniferous to the Triassic have also been recognized, rendering the South American apparent polar wonder path (APWP) problematic. </p><p>We have conducted a paleomagnetic study of the sedimentary Permo-Carboniferous Itararé Group rocks within the state of São Paulo, Brazil, including three intruding mafic sills that are attributed to Early Cretaceus magmatic activity. The site-mean VGP distributions obtained from the sedimentary rocks define elongations that include the VGPs of the mafic intrusions, and are interpreted as remagnetization paths toward the directions characteristic of the sills. These interpretations are supported by extensive rock-magnetic data that provide a viable mechanism for the secondary magnetizations. Careful analysis of the paleomagnetic data of the sedimentary rocks enables isolation of a primary VGP distribution that is consistent with the reference Carboniferous pole position.</p><p>Analysis of other Carboniferous to Triassic South American paleomagnetic VGPs reveals that the majority of these data are also elongated: regardless of the age of the rocks, the elongations dominantly intersect at the location of the Late Cretaceous reference pole, and a second location similar to the intersection of the VGP elongations of some Jurassic/Cretaceous rock formations, and also coincides with the cusp of the debated loop in the Carboniferous-Triassic APWP. Based on multiple lines of evidence, we interpret the elongations and their intersections to reflect remagnetizations that occurred as a result of the widespread magmatism associated with the opening of the South Atlantic. We suggest that the extent of the remagnetizations is formation-specific, and that other rock-formations should be carefully re-evaluated.</p>

Aesthetic-remarkable localities of Kharkiv region as geotourism objects

Formulation of the problem. The aim of work is to prove the expedience of using the beautiful localities with valuable geosites of the Kharkiv region as geotourism objects. Presentation of the main material. The most interesting objects of geotourism in the Kharkiv region are Izyum district, Gorodishhenska and Kozacha mountains, locality Kruchi in Zmijov district, Bajdaki cretaceous rock near Protopopivka village in Balakliya district, cretaceous mountains in Oskil and the Volcha river valleys in Dvorichna and Volchansk districts, locality Krutyj Log near Ruski Tyshki village in Kharkiv district. The objects of Izyum district are described in details. They are located in the south-east of the Kharkiv region near Izyum town, at the distance of 130 km from Kharkiv. Apart from picturesque landscapes, there are 3 remarkable geosites in this locality: Kremenec mountain, Protopivska ravine and lower part of the Grekivka river valley, which is also called the Big Kamenka outcrops. Kremenec mountain is situated on the territory of the Izyum town. The outcrops are located on the crest and western slope of this upland and are composed of Jurassic and Cretaceous deposits. The Big Kamenka outcrops and Protopivska ravine are located on the territory of the Kamenka village. The Big Kamenka outcrops are composed of Jurassic gritstones, sandstones, aleurolites, clay deposits and limestones. The Protopivska ravine is located in the core of Kamenka anticline and is composed of Triassic deposits. In the Izyum district different types of valuable geological objects have been discovered, namely: paleontological – Triassic flora, Jurassic fauna; stratigraphical – the stratotypes of regional suites of Triassic, Jurassic, Cretaceous sediments – Protopivska, Izyumska, Kremenecka, Priizyumska suites; mineralogical – quartz, chalcedony, calcite, limonite; petrographical – non-ordinary rocks as coral limestones etc.; tectonic – are visible folds and faults – for example, Kamenska anticline; paleogeographical – consists of geological evidences of different conditions of sedimentation – for example, the Oxfordian bioherms, Kimmeridgian lagoonal deposits; geomorphological – remarkable forms of surface, such as limestone rocky outcrops of Iziumska Suites; hydrogeological – the Jurassic springs (Big Kamenka outcrops); raw materials – Turonian chalk, phosphorite concretions in the Cenomanian sediments, which have practical value; mining history – remainders of chalk quarry on the summit of the Kremenec hill; memorial – prominent geologists' work-places and spots of findings of valuable geological materials, such as Cenomanian plesiosaur Cimoliosaurus bernardi Owen in Kremenec and others. Conclusion. The Izyum area contains numerous remarkable geological objects, beautiful landscapes and can be successfully used for geotourism.

Thermodynamic Simulation of Essentuki Type Mineral Water Formation

Thermodynamic models of Essentuki and Nagutsky fields of Caucasian Mineral Waters deposits (KMW) are developed. The models are based on laboratory studies of core samples of aptian-albian lower Cretaceous rock dissolution. The rock samples were disintegrated up to 0.25 mm grains. The rock grains were mixed with distilled or mineral waters and the mixtures were kept at 20-25°С and 65-70°С, carbon dioxide pressure of 4.04 MPa. The results of experimental and thermodynamic modeling are showed that aqueous solution composition formed, in particular, microcomponent concentrations, depends on the rock cement composition (clayey, calcic, siliceous, ferriferous, chloritic, zeolitic phosfatic, sulfatic or mixed) and on the percentage of the microelement mineral-bearing in the water-bearing rock. Also the aqueous solution composition depends on temperature and CO2 partial pressure in the silt - rain water CO2 system. Thermodynamic modeling of the system confirmed gypsum dominant role in sulfate type water formation against pyrite role.

Study on Water Disaster Prevention and Control Technology under Condition of Extra-thick Coal Seam with Slicing Fullmechanized Caving Mining

Some coal seams belong to cretaceous strata in the east of Inner Mongolia, China. There are obvious differences of rock characteristics and mechanical properties between Cretaceous and Carboniferous- Permian strata. The overburden failure characteristics of extra-thick coal seam with slicing full-mechanized caving mining are studied through rock mechanics experiment, field observation and theoretical analysis and so on. Water disaster prevention and control method of roof and goaf is put forward under the condition of extra-thick coal seam with slicing full-mechanized caving mining. The final research results include: (1) The rock of cretaceous strata has low strength and soft characteristic, its stability is very poor, cretaceous rock belongs to weak type; (2) Under the condition of extra-thick coal seam with slicing full-mechanized caving mining, the ratio between caving zone and mining height of field observation result is 4.58～4.74, the observation results of two boreholes are close; (3) It is significantly effective to prevent and control water disaster from goaf through roof hole drainage method, coal and rock safety pillar remain method is used to limit mining height under the Tertiary gravel aquifer, which makes the working face exploit safely.

Grasping the shape of belemnoid arm hooks—a quantitative approach

Chitinous arm hooks (onychites) of belemnoid coleoid cephalopods are widely distributed in Mesozoic sediments. Due to their relative abundance and variable morphology compared with the single, bullet-shaped, belemnite rostrum, arm hooks came into the focus of micropaleontologists as a promising index fossil group for the Jurassic–Cretaceous rock record and have been the target of functional, ecological, and phylogenetic interpretations in the past. Based on three well-preserved arm crowns of the Toarcian diplobelid Chondroteuthis wunnenbergi, we analyzed the shape of a total of 87 micro-hooks. The arm crown of Chondroteuthis is unique in having uniserial rather than biserial hooks. The first application of elliptic Fourier shape analysis to the arm weapons of belemnoid coleoids allows for the distinction of four micro-hook morphotypes and the quantification of shape variation within these morphotypes. Based on the best-preserved arm crown, we reconstructed the distribution of morphotypes within the arm crown and along a single arm. Our quantitative data support former observations that smaller hooks were found close to the mouth and at the most distal arm parts, while the largest hooks were found in the central part of the arm crown. Furthermore, we found a distinct arm differentiation, as not every arm was equipped with the same hook morphotype. Here, we report the functional specialization of the belemnoid arm crown for the first time and speculate about the potential function of the four morphotypes based on comparisons with modern cephalopods. Our analyses suggest a highly adapted functional morphology and intra-individual distribution of belemnoid hooks serving distinct purposes mainly during prey capture.

Critical porosity and elastic properties of microporous mixed carbonate-siliciclastic rocks

By integrating elastic-property measurements and quantitative mineralogic and petrographic analyses of 45 mixed carbonate-siliciclastic samples from two wells drilled in Late Cretaceous rock of the South Provence Basin (southeast France), we can (1) identify and quantify the parameters controlling elastic properties; (2) demonstrate that micrite can be considered as a porous medium with a low critical porosity, averaging 18%; and (3) relate diagenetic transformations, pore-structure modifications, and elastic-property changes. Microporous carbonates with compact anhedral and euhedral microrhombic micrites display a steeper decrease in compressional and shear velocities with increasing porosity than do carbonate rocks with moldic, intergranular, or intercrystalline macroporosity. The low value of critical porosity estimated in micrites (18%), as well as the steep slopes of velocity-porosity relationships at low porosity, is believed to result from a pore-network geometry characterized by very flat, thin pores bounded by planar faces of micrite crystals. Cementation of microrhombic micrite steeply increases elastic moduli, whereas dissolution processes significantly increase porosity with low variations of elastic moduli. Thus, critical-porosity concepts can help describe and model elastic properties of micritic microporous carbonate.