Greedy parabolics: Wind flow direction within the deflation basin of parabolic dunes is governed by deflation basin width and depth

Parabolic dunes are ‘U’ or ‘V’-shaped aeolian landforms that form on pre-existing sand deposits. Their morphology consists of an upwind deflation basin, bordered by often vegetated trailing arms and a downwind depositional lobe. The orientation of parabolic dunes is commonly attributed to the prevailing or resultant wind direction. Consequently, the orientation of parabolic dunes stabilised by vegetation growth has been used as a proxy for wind direction during past climates in several studies. However, the ability or extent of parabolic dune morphology to steer incident wind flow parallel to the orientation of the landform, and thus migrate in the direction of the current landform orientation rather than prevailing wind direction, is unknown. By numerically modelling wind flow within the deflation basin of eight parabolic dunes, we demonstrate for the first time that wind flow direction within the deflation basin of a parabolic dune is highly controlled by the depth and width of the deflation basin. The greater the depth–width ratio of the landform (i.e. the deeper and narrower the deflation basin), the greater the degree of flow steering relative to the axis orientation of the landform. These results demonstrate that future studies must exercise caution when using parabolic dune orientation as a direct proxy for prevailing wind direction, especially where parabolic dunes have a relatively high deflation basin depth–width ratio, as the deflation basin of these landforms may continue to migrate in an antecedent wind direction.

Turbidite sedimentology, biostratigraphy and paleoecology: A case study from the Oligocene Zuberec Fm. (Liptov Basin, Central Western Carpathians)

Outcrops of a thick turbiditic succession are exposed on the northern bank of the Liptovská Mara reservoir near Liptovská Ondrašová and Ráztoky. The section consists of rhythmic, predominantly thin- to medium-bedded turbidites of the Rupelian age. Their biostratigraphy is based on the calcareous nannofossils. Facies associations of these deposits represent different components of depositional lobe deposits in the turbidity fan system, including mainly the lobe fringe and lobe distal fringe/inter-lobe facies associations and locally the medium bedded deposits of the lobe off-axis facies association. This interpretation is supported by statistical analysis. The deep-sea turbiditic deposits contain trace fossil associations, which include deep-tier fodinichnia and domichnia up to shallow-tier graphoglyptids. Paleocurrent measurements indicate that the majority of sedimentary material was transported from SW and W.

Depositional architecture of marginal multiple-source ramp of the Magura Basin (Eocene Flysch formation, Outer Western Carpathians)

The Zembrzyce Beds were studied to interpret the environments and facies in the western part of the Siary Subunit. New sedimentological data were obtained for the reconstruction of the depositional architecture of the Zembrzyce Beds. Based on detailed facies analysis, 9 facies and 4 facies associations were recognized. The facies associations represent different architectural elements of a submarine fan, such as: termination of distributary channel with transition to depositional lobe (distal part of mid-fan/outer fan sub-deposystem), lobes and distal lobes (outer fan sub-deposystem). According to the classification of Reading & Richards (1994) the fan deposystem can be classified as mud/sand-rich ramp. This system consists of several elongated lobes that formed synchronously, migrated laterally, and then retreated or decayed. The depositional system was supplied from the north and north-east. The inner-fan sub-deposystem was not detected. The sediments were deposited by high- and low-density turbidity currents and hyper-concentrated density flows sensu Mulder & Alexander (2001) with participation of the depositional background processes (pelagic settling). The sedimentary conditions of the Zembrzyce Beds during the Late Eocene were controlled by tectonic movements, the progress of the subduction and the global sea level changes.