Modern Analogues of Sedimentation of Lower Permian Reservoirs in the Dnieper-Donets Depression

The paper considers the problematics of identifying proper analogues for understanding carbonate and clastic reservoir distribution and prediction in the Lower Permian and Upper and Lower Carboniferous within the Dnieper-Donets basin. The focus of the exploration team was finding meandering rivers. This choice was proven good in mapping reservoirs and finding traps deeper in the Upper and Middle Carboniferous, although for Permian clastic section the approach was not helpful. The second option was desert dunes, but poor sorting of reservoirs suggests a more complex picture. Analogues such as desert environment is quite logical for describing Lower Permian as aridic climate, with red and brown shales and sands. Lower Permian reservoirs have a moon-like shape in the vertical sections that could be easily mistaken for river channels, but in such a dry climate, it is very likely water flow channels with sporadic hurricane-related activities. Core and logs shows chaotic grain sizes, but more with fine grains with almost no coarse grains. The source of sedimentary material could be mountains of Ukrainian Rock Shield from the South and Voronezh massif from the North. This conceptual model is proposing not to look for meandering channels, but more for braided channels with poorly sorted material. The current time analogue could be the Oman desert between the mountains and peninsula. From satellite images, braided channels are clearly visible in the direction towards the Indian Ocean. The channels’ internal structure is quite heterogeneous. This method suggests exploration targets with possible widths of the channels as big as hundreds of meters and their lengths under 10 and between 10-20 kilometres maximum.

Robotic modelling of snake traversing large, smooth obstacles reveals stability benefits of body compliance

Snakes can move through almost any terrain. Although their locomotion on flat surfaces using planar gaits is inherently stable, when snakes deform their body out of plane to traverse complex terrain, maintaining stability becomes a challenge. On trees and desert dunes, snakes grip branches or brace against depressed sand for stability. However, how they stably surmount obstacles like boulders too large and smooth to gain such ‘anchor points’ is less understood. Similarly, snake robots are challenged to stably traverse large, smooth obstacles for search and rescue and building inspection. Our recent study discovered that snakes combine body lateral undulation and cantilevering to stably traverse large steps. Here, we developed a snake robot with this gait and snake-like anisotropic friction and used it as a physical model to understand stability principles. The robot traversed steps as high as a third of its body length rapidly and stably. However, on higher steps, it was more likely to fail due to more frequent rolling and flipping over, which was absent in the snake with a compliant body. Adding body compliance reduced the robot's roll instability by statistically improving surface contact, without reducing speed. Besides advancing understanding of snake locomotion, our robot achieved high traversal speed surpassing most previous snake robots and approaching snakes, while maintaining high traversal probability.

Hexagonal Fracture Patterns On Navajo Sandstone Crossbeds At Yellow Knolls, Washington County

At this geosite, the main features of interest—remarkably uniform and beautiful fracture patterns dominantly composed of linked hexagons—are present on outcrops of the Jurassic Navajo Sandstone. The Navajo was deposited by large, southward-migrating desert dunes about 200 million years ago, but the fractures that define the hexagons here are just a surficial veneer less than 20 inches (half a meter) deep. The fractures are a weathering phenomenon that developed under climate conditions similar to today’s. Steep thermal gradients develop in the sandstone because it is exposed to solar radiation and changing air temperature. Polygonal fracturing is present in other Navajo exposures in southern Utah, but only in non-bedded (homogeneous) rock. The beautiful, bedding-parallel fracture pattern developed here is very rare; it developed because the bedding planes in the rock at Yellow Knolls are unusually wide-spaced.