Unraveling the influence of throw and stratigraphy in controlling subseismic fault architecture of fold-thrust belts: An example from the Qaidam Basin, northeast Tibetan Plateau

Understanding the detailed fault architecture of reverse faulting is critical for understanding the processes involved in fold-thrust belts as well as predicting the degree of fault compartmentalization, the relationship between folds and faults, the distribution of strain, and subseismic faulting deformation. The Lenghu5 fold-thrust belt provides an exceptionally well-exposed outcrop example of a reverse fault-related fold. Detailed stratigraphic logging coupled with high-resolution cross sections provides a unique insight into the three-dimensional geometry of a thrust fault at both basin and outcrop scale. In this study, we observe that 85%–90% of the estimated throw is accommodated on the main fault zone, which has sufficient throw to be imaged on a seismic profile, whereas 15%–20% of the throw is accommodated on smaller-scale folds and faults that are beyond seismic resolution. The plan-view mapping of the structure reveals that there is significant variation in how strain is accommodated along the structure, which is associated with the throw variations in the main fault. In addition, by coupling the structural observations within a stratigraphic context, we can demonstrate that although the main fault controls the overall strain in the system, the local stratigraphy plays a critical role in how the strain is accommodated and whether it is partitioned into single faults, multiple-fault splays, or folding. By demonstrating the remarkable geometric similarity between the outcrop observations with a comparable structure in the subsurface (Niger Delta), the study provides an insight into the potential subseismic fault-zone geometry present in poorly imaged fold-thrust systems

The use of phylogeny to interpret cross-cultural patterns in plant use and guide medicinal plant discovery: an example from Pterocarpus (Leguminosae)

The study of traditional knowledge of medicinal plants has led to discoveries that have helped combat diseases and improve healthcare. However, the development of quantitative measures that can assist our quest for new medicinal plants has not greatly advanced in recent years. Phylogenetic tools have entered many scientific fields in the last two decades to provide explanatory power, but have been overlooked in ethnomedicinal studies. Several studies show that medicinal properties are not randomly distributed in plant phylogenies, suggesting that phylogeny shapes ethnobotanical use. Nevertheless, empirical studies that explicitly combine ethnobotanical and phylogenetic information are scarce.In this study, we borrowed tools from community ecology phylogenetics to quantify significance of phylogenetic signal in medicinal properties in plants and identify nodes on phylogenies with high bioscreening potential. To do this, we produced an ethnomedicinal review from extensive literature research and a multi-locus phylogenetic hypothesis for the pantropical genus Pterocarpus (Leguminosae: Papilionoideae). We demonstrate that species used to treat a certain conditions, such as malaria, are significantly phylogenetically clumped and we highlight nodes in the phylogeny that are significantly overabundant in species used to treat certain conditions. These cross-cultural patterns in ethnomedicinal usage in Pterocarpus are interpreted in the light of phylogenetic relationships.This study provides techniques that enable the application of phylogenies in bioscreening, but also sheds light on the processes that shape cross-cultural ethnomedicinal patterns. This community phylogenetic approach demonstrates that similar ethnobotanical uses can arise in parallel in different areas where related plants are available. With a vast amount of ethnomedicinal and phylogenetic information available, we predict that this field, after further refinement of the techniques, will expand into similar research areas, such as pest management or the search for bioactive plant-based compounds

Origins of stereoselectivity in the trans Diels-Alder paradigm.

The regioselectivity and stereoselectivity aspects of the Diels-Alder/radical hydrodenitration reaction sequence leading to trans-fused ring systems have been investigated with density functional calculations. A continuum of transition structures representing Diels-Alder and hetero-Diels-Alder cycloadditions as well as a sigmatropic rearrangement have been located, and they all lie very close in energy on the potential energy surface. All three pathways are found to be important in the formation of the Diels-Alder adduct. Reported regioselectivities are reproduced by the calculations. The stereoselectivity of radical hydrodenitration of the cis-Diels-Alder adduct is found to be related to the relative conformational stabilities of bicyclic radical intermediates. Overall, the computations provide understanding of the regioselectivities and stereoselectivities of the trans-Diels-Alder paradigm

Field-based investigation on fault architecture: a case study from the Lenghu fold-and-thrust belt, Qaidam basin, NE Tibetan Plateau

The fault zone architecture of a thrust fault zone is critical for understanding the strain accommodation and structural evolution in contractional systems. The fault architecture is also important for understanding fluid-flow behavior both along and/or across thrust fault zones and for evaluating potential fault-related compartmentalization. Because mesoscale (1−100 m) structural features are normally beyond seismic resolution, high-resolution outcrop in situ mapping (5−10 cm resolution) was employed to study the deformation features of a thrust fault zone located in the Qaidam Basin, northeastern Tibetan Plateau. The excellent exposure of outcrops enables the detailed investigation of the Lenghu thrust fault zone and its architecture. The Lenghu thrust fault, a seismically resolvable fault with up to ∼800 m of throw, exhibits a large variation of fault architecture and strain distribution along the fault zone. Multiple structural domains with different levels of strain were observed and are associated with the fault throw distribution across the fault. Based on previously proposed models and high-resolution outcrop mapping, an updated fault zone model was constructed to characterize the structural features and evolution of the Lenghu thrust. The possible parameters that impact fault architecture and strain distribution, including fault throw, bed thickness, lithology, and mechanical heterogeneity, were evaluated. Fault throw distributions and linkages control the strain distribution across a thrust fault zone, with local folding processes contributing important elements in Lenghu, especially where more incompetent beds dominate the stratigraphy. Mechanical heterogeneity, induced by different layer stacking patterns, controls the details of the fault architecture in the thrust zone. The variations in bed thicknesses and mechanical property contrasts are likely to control the initial fault dips and fault/fracture density. Large fault throws are associated with wide strain accommodation and damage zones, although the relationship between the development and width of the fault zone and the throw accumulation remains to be assessed. By presenting the high-resolution mapping of fault architecture, this study provides an insight into the subseismic fault zone geometry and strain distributions possible in thrust faults and reviews their application to assessments of fault zone behavior