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Well-log based rock physics template of the Vienna Basin and the underlying Calcereous Alps

Tucovic N., Gegenhuber N.

Acta Geophysica

2017

Vol. 65, no. 3

441--451

In this study, the ratio of compressional and shear wave velocity versus acoustic impedance as rock physics template for northern part of the Vienna Basin has been derived for siliciclastic rocks based on formation evaluation of well-log data. The results have been verified through wells in different areas drilled in various depths. Additionally, depositional sequences like prograding deltas and braided rivers have been plotted onto the rock physics template to illustrate the effect of changing shale volume. Carbonates below the basin have been included into the study and results from previous projects, based on laboratory data and petrophysical models on certain lithologies in the Vienna Basin, have been used to compare the outcome. The result is a rock physics template which includes important properties such as porosity, true vertical depth and fluid type from log data and which is considered useable throughout different areas and various lithologies of the Vienna Basin.

Śródmenilitowe piaskowce magdaleńskie jako przykład płytkowodnej sedymentacji deltowej w Karpatach

Dziadzio P. S.

Nafta-Gaz

2015

R. 71, nr 9

624--631

W pracy przedstawiono wyniki badań śródmenilitowych piaskowców magdaleńskich, które występują w jednostce śląskiej w obrębie tzw. fałdu Gorlic w Karpatach Zewnętrznych. Były one dotychczas interpretowane jako utwory prądów zawiesinowych (turbidytów) powstałych w głębokowodnym, batialnym zbiorniku sedymentacyjnym. Szereg zinterpretowanych struktur sedymentacyjnych oraz rekonstrukcja systemu depozycyjnego wskazuje jednak na ich płytkowodną, deltową, zdominowaną procesami falowymi i pływowymi genezę. Utwory te powstały w strefie aktywnego, kontrolowanego procesami tektonicznymi szelfu. Pełna sukcesja warstw menilitowych i piaskowców magdaleńskich jest interpretowana, jako sekwencja depozycyjna z rozwiniętymi w jej obrębie traktami: niskiego stanu, transgresywnym i wysokiego stanu względnego poziomu morza.

Recent sedimentological studies of the Menilite Beds in the Gorlice area suggest a shallow-marine origin of this succession, including the Magdalena Sandstone. The occurrence of features interpreted as wave-ripple cross-lamination and hummocky stratification implies deposition above the storm wave base, which means a water depth, of perhaps less than 50 m on the account of the landlocked nature of the narrow Carpathian Paratethys seaway. The Menilite Beds with Magdalena Sandstone deposits form a 180-m thick succession comprising three coarsening-upwards regressive parasequences. The basal shales of the succession contain sandstone bodies interpreted to be shelf-margin channels or gullies filled by debris flows and high-density turbidity currents, and considered to be a signal of an impending forced regression driven by tectonic uplift. Each of the overlying parasequences commences with heterolithic deposits dominated by black to grey shales and showing lenticular, wavy or flaser bedding as well as graded beds with plane-parallel or hummocky stratification and wave-ripple cross-lamination, interpreted to be outer-shelf tidalites and distal tempestites. The thicker sandstone beds in parasequence middle part, with parallel and apparent hummocky stratification as well as wave-ripple cross-lamination, are considered to be sublittoral prodelta tempestites. The upper part of each parasequence is dominated by coarse-grained quartz-glauconite sandstones and quartz-rich pebble conglomerates, which form broadly convex-upwards packages stacked in an offset ‘compensational’ manner, interpreted to be shingled distal to proximal mouth bars of an advancing shoal-water deltaic system. Sedimentation is thought to have occurred on a tectonically-steepened perched narrow shelf, where the accommodation-driven deltaic system was readily reaching the shelf margin. Marine flooding events are attributed to the shelf episodic foundering. The ultimate collapse of the shelf then brought turbiditic sedimentation represented by the overlying succession of late Oligocene–Miocene Krosno Beds. The Menilite Beds with Magdalena Sandstone are interpreted as a depositional sequence with lowstand (first parasequence), transgressive (second and third parasequences) and highstand systems tracts.