PERMIAN NON-MARINE BIVALVES FROM THE COLLIO AND GUNCINA FORMATIONS (SOUTHERN ALPS, ITALY): REVISED BIOSTRATIGRAPHY AND PALAEOBIOGEOGRAPHY

Non-marine bivalves are key fossils in Permian continental stratigraphy and palaeogeography. Although known since the end of 19th century, the occurrences from the continental basins of the Southern Alps have never been extensively studied. The non-marine bivalves from the Lower Permian Collio Formation (Brescian pre-Alps) are herein revised, and those from the Guncina Formation (Athesian District) are described for the first time. These two units yielded non-marine bivalves belonging to the genus Palaeomutela sensu lato, which is widespread in the Permian continental successions of eastern Euramerica. Three Palaeomutela morphotypes have been herein described: oval-subtriangular, subtrapezoidal and elongated. The latter includes several specimens herein assigned to Palaeomutela (Palaeanodonta) berrutii sp. nov. and dominates the Collio Formation association. The Guncina Formation yielded also the genus Redikorella, for the first time co-occurring on the same stratigraphic horizon of Palaeomutela, herein assigned to Palaeomutela (Palaeanodonta) guncinaensis sp. nov. To-date, it was generally accepted that the first members of the genera Palaeomutela and Redikorella occurred during the Ufimian (late Kungurian of the global scale) in the non-marine basins of the Cis-Ural Foredeep and of Angara, respectively. Such new finds in the early-middle Kungurian of southwestern Europe, well constrained by radioisotopic dating, suggest new global first appearance (First Appearance Datum) and a possible new center of origin of these genera. This fact raises new questions on biostratigraphy, palaeobiogeography and palaeoecology, which will require further research. If we assume that the genera Palaeomutela and Redikorella had only one center of origin, we need to hypothesise possible migration routes from SW Europe to the continental basins of Eastern Europe and Angara. Apparently, such migration could be better supported by a Pangaea B palaeogeographic configuration.

Brachiopods from the Río del Peñón Formation. Río Blanco Basin, Upper Palaeozoic of Argentina.

This paper reviews the brachiopod fauna from the Ríoo de! Peñón Formation, Río Blanco Basin, Upper Palaeozoic of La Rioja province, Argentina. Traditionally, this unit was referred to the Carboniferous, however the braquiopod fauna here studied suggests a new biostratigraphical interpretation, indicating an age range from the latest Carboniferous to Early Permian. Three different brachiopod assemblages can be identified in the section: Assemblage I, from the lower member, includes Streptorhynchus? sp., Dyschrestia? sp., Costatumulus sp. A, Trigonotreta sp., Spiriferellina sp., Orbiculoidea sp., and unidentifiable productids and strophomenids.Assemblage II, from the middle member, includes Tivertonia jachalensis (Amos), Kochiproductus riojanus (Leanza), Costatumulus sp. B, Trigonotreta riojanensis (Lech and Acefiolaza) and Orbiculoidea sp. Assemblage III, from the highest part of the middle member, includes Neochonetes pegnonensis sp. nov., Costatumulus sp. C, Rhynchopora sp., Septosyringothyris jaguelensis Lech, and Orbiculoidea sp. These brachiopod assemblages demonstrate close affinities with faunas from the lower Permian of Western Australia and India. Affinities with faunas from Peru and Texas are less close.

Sedimentary characteristics and sand body distributions in the Lower Permian He 8 member, Ordos Basin, China

The Lower Permian He 8 Member (P1h8) in the Ordos Basin is a typical producing zone of tight lithologic gas reservoirs. Analyses of sedimentary characteristics, electrofacies, and sand-body distributions of P1h8, conducted on modern fluvial deposits, outcrops, cores, and well logs, revealed that braided rivers that developed in the Lower P1h8 and Upper P1h8 are characterized by meandering river. Within these fluvial deposits, the procedure consists of analyzing high-resolution sequence stratigraphy and sedimentary dynamics defined from calibrated logging curve signatures and depositional studies. According to modern and ancient fluvial deposits, we have developed a process-based sedimentary conceptual model for interpreting and predicting the distribution and geometries of sand bodies in braided and meandering deposits. The main sand body of the braided river system was bars and channel fill deposits. The braided river sand bodies are distributed over multiple vertical superimpositions and overlapping horizontal connections. The meandering river sand bodies are mainly point-bar deposits, which are bead-shaped and exhibit scattered development in the vertical direction. This comparison indicates that there were significant differences between braided and meandering deposystems. The sand bodies in the Lower P1h8 were multidirectionally connected and primarily distributed in a stacked pattern. In contrast, the sand bodies in the Upper P1h8 were distributed in an isolated manner, and fine grains (mud and silt) were deposited between the sand bodies with poor connectivity. We interpreted the fluvial deposits that control the distributions of the sand body of the He8 Member in the eastern Sulige gas field and constructed a corresponding prediction model of a braided-meandering reservoir. This model will promote understanding of the extent of fluvial deposits and sand-body distribution of P1h8, thus elucidating hydrocarbon-bearing sand units of the Ordos Basin for future exploration.

Permian Ages of “Younger Granites” from Mounio Province (Gouré area, Southeastern Niger)

African formations intruded by the “Younger Granites” ring complex. In the study area, the “Younger Granites” are represented by volcanic to acid plutonic rocks with hyperalkaline trends (pyroclastic rocks, rhyolites, microgranites, granites, syenites), forming in the North, a circular structure called Gouré ring complex. Preliminary geochronological datings of the Mounio granites have yielded Carboniferous ages. However, recent investigations carried out in this province have identified structures similar to Pan-African deformation structures, such as folds and several generations of schistosity/foliation. Analysis of the relationship between deformation and magmatism has removed any ambiguity regarding the relative age of the deformation. This study focuses on the radiometric dating of the “Younger Granites” of Gouré area, in order to update the geochronological data. Thus, three samples (pyroclastitic rock, rhyolite, microgranite) were dated by the K-Ar method on total rock using a mass spectrometertype MI 1201 IG. Radiometric dating results assign a Lower Permian age (293-287 Ma) to the “Younger Granites” Ring Complex of the Mounio Province in Niger, classically considered to be Carboniferous in age.

Reservoir Characteristics of the Lower Permian Marine-Continental Transitional Shales: Example from the Shanxi Formation and Taiyuan Formation in the Ordos Basin

The pore types and pore structure parameters of the heterogenetic shale will affect the percolation and reservoir properties of shale; therefore, the research on these parameters is very important for shale reservoir evaluation. We used X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), low-pressure CO2 adsorption analysis, mercury injection capillary pressure (MICP), and high-pressure methane adsorption analysis to analyze the characteristics of different pore types and their parameters of the Lower Permian Shanxi Formation and Taiyuan Formation in the Ordos Basin. The influence of different mineral contents on the porosity and pore size is also investigated. The Shanxi Formation (SF) is composed of quartz (average of 38.4%), plagioclase, siderite, Fe-dolomite, calcite, pyrite, and clay minerals (average of 50.1%), while the Taiyuan Formation (TF) is composed of calcite (average of 37%), siderite, Fe-dolomite, quartz, pyrite, and clay minerals (average of 32.3%). The most common types of pores observed in this formation are interparticle pores (InterP pores), intraparticle pores (IntraP pores), interclay pores, intercrystalline pores (InterC pores), organic matter pores (OM pores), and microfractures. CO2 adsorption analysis demonstrates the type I physisorption isotherms, showing microporous solids having comparatively small external surfaces. The similar types of isothermal shapes of the Shanxi Formation (SF) and Taiyuan Formation (TF) suggest that both types have similar pore size distribution (PSD) within the measured pore range by the low-pressure CO2 adsorption experiment. The micropore pore size of the TF is larger than that of the SF. MICP shows the larger pores (>50 nm), and most of the volume was adsorbed by macropores. Methane gas sorption capacity increases with increasing pressure. Clay minerals and quartz played an important role in providing adsorption sites for methane gas. The overall analysis of both formations shows that TF has good reservoir properties than SF.