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The distribution pattern and genetic structure of plant species have been profoundly influenced by climate oscillations. Phylogeographic analyses have been numerously conducted in biodiversity hotspot regions and some general conclusions have been documented. However, other regions have received less attentions and these places may serve as potential glacial refugia for plant species to survive the Quaternary glaciation. Here, we used six nuclear and three cpDNA markers to estimate the phylogeographic pattern of Populus davidiana, a widespread species distributed in southwest China. As a widely distributed species in southwest China, the nucleotide diversity of P. davidiana was relatively high (Na = 6.28, HO = 0.534, and HE = 0.658). Genetic differentiation (FST) between the two main distribution regions, Yunnan and Guizhou provinces, was 0.21221. According to the composition of chloroplast haplotypes and the result of structure in these populations, we clearly distinguished two distantly sublineages corresponding to two distribution regions. Results of the Mantel test showed that there was a significant correlation between genetic distance and geographical distance (R2 = 0.8252, p<.05). The topographically heterogeneous regions and the low dispersal ability of seed and pollen may lead to high genetic differentiation between these two regions. A potential glacial refugia for P. davidiana located in adjacent regions to the Hengduan range was revealed and allopatric divergence in separated glacial refugia may directly lead to the present phylogeographic pattern of this species. [ABSTRACT FROM AUTHOR]

In order to characterize the petrophysical properties of shale using NMR technique, eight shale samples from the Lower Cambrian Qiongzhusi Formation in the eastern Yunnan province were measured by porosity and permeability tests, field emission scanning electron microscopy (FE-SEM) and NMR experiment. Pore types were obtained from the shape and distribution of transverse relaxation time (T 2 ) spectrum. Residual porosity and movable porosity could be well estimated based on T 2 spectrum area fraction. On the basis of Coates model, we proposed a regional Coates model to calculate the NMR permeability of shale. A method for determining T 2cutoff of shale samples was also expounded. Moreover, the specific surface area distributions and pore size distributions could be obtained based on the mathematical equation of T 2 . Results show that T 2 spectrums of shale samples at water-saturated condition can be divided into unimodal and bimodal T 2 spectrums. Continuous bimodal T 2 spectrums reflect the samples with good connectivity between small pores and large pores, whereas discontinuous bimodal T 2 spectrums reflect that the connectivity between small pores and large pores is poor. Shale samples with higher bound water content have a greater T 2cutoff . The NMR permeability is close to gas log permeability, which proves the applicability of regional Coates model. In eight shale samples, transition pores account for the largest proportion, followed by mesopores, indicating that transition pores and mesopores are the major sites for the accumulation of shale gas. [ABSTRACT FROM AUTHOR]

In order to study pore structure and fractal characteristics of the organic-rich marine shale, fourteen shale samples from Lower Cambrian Qiongzhusi formation in Malong block of eastern Yunnan province were investigated by organic geochemical analysis (total organic carbon content analysis and thermal maturity analysis), X-ray diffraction (XRD) analysis, porosity and permeability tests, field emission scanning electron microscopy (FE-SEM), low-pressure nitrogen adsorption and methane adsorption experiments. Fractal dimensions D 1 and D 2 (at relative pressure of 0–0.5 and 0.5–1, respectively) were obtained from the nitrogen adsorption data using the fractal Frenkel–Halsey–Hill (FHH) method. Not only have the relationships among pore structure parameters of shale, the relationships between TOC content, mineral compositions, pore structure parameters and fractal dimensions been discussed, but also the significance of two fractal dimensions D 1 and D 2 and the impact of fractal dimensions on adsorption capacity have been investigated. The results showed that fourteen shale samples have TOC content ranging from 1.25% to 7.72%, two fractal dimensions both increase with the increasing TOC content, and gradually come to a standstill—the curves present the shape of “parabola”. The major mineralogical compositions of shales are quartz and clay minerals, the quartz contents are between 25.5% and 42.7%, the clay contents are between 26.6% and 44.2%. Fractal dimension D 1 has a negative correlation with quartz contents and a positive correlation with clay minerals contents, but fractal dimension D 2 has no apparent relationship with quartz and clay minerals contents. The specific surface area is in the range of 4.98 m 2 /g–19.66 m 2 /g, the total pore volume is between 0.00479 cm 3 /g and 0.01765 cm 3 /g, and the average pore diameter is between 3.37 nm and 6.02 nm. Two fractal dimensions increase with the increasing surface area and pore volume, and also increase with the decreasing average pore diameter because of the complicated pore surface and structure of small pores. Further investigation indicates that D 1 represents fractal characteristics from the irregular pore surface, while D 2 represents fractal characteristics related to the complicated pore structure, and shale samples with larger fractal dimensions have higher methane adsorption capacity. Therefore fractal analysis is helpful to have a better understanding of pore structure and adsorption capacity of marine shale. [ABSTRACT FROM AUTHOR]