No abstract

Modern, tide‐dominated and tide‐influenced coastlines are characterized by a range of environments, including deltas, estuaries and lagoons. However, some tide‐dominated basins and related sedimentary units in the rock record, such as the semi‐enclosed, shallow, Utah–Idaho Trough foreland basin of the Jurassic Curtis Sea, do not correspond to any of these modern systems. Persistent aridity caused the characteristic severe starvation of perennial fluvial input throughout this basin, in which the informal lower, middle and upper Curtis, as well as the underlying Entrada Sandstone, and the overlying Summerville Formation were deposited. Wave energy was efficiently dissipated by the shallow basin's elongated morphology (approximately 800 × 150 km), as its semi‐enclosed morphology further protected the system from significant wave impact. Consequently, the semi‐enclosed, shallow‐marine system was dominated by amplified tidal forces, resulting in a complex distribution of heterolithic deposits. Allocyclic forcing strongly impacted upon the system's intrinsic autocyclic processes as the lower Curtis was deposited. Short‐lived relative sea‐level variations, along with uplift and deformation episodes, resulted in the accumulation of three parasequences, each separated by traceable flooding and ravinement surfaces. The subsequent transgression, which defines the base of the middle Curtis, allowed for the shallow‐marine part of the system to enter into tidal resonance as a consequence of the flooded basin reaching the optimal configuration of approximately 800 km in length, corresponding to an odd multiple of the quarter of the tidal wavelength given an average minimum water depth of 20–25 m. This resonant system overprinted the effects of allocyclic forcing and related traceable stratigraphic surfaces. However, the contemporaneous and neighbouring coastal dune field sedimentary rocks of the Moab Member of the Curtis Formation, characterized by five stacked aeolian sequences, as well as the supratidal deposits of the Summerville Formation, lingered to record allocyclic signals, as the Curtis Sea regressed. This study shows that a tide‐dominated basin can enter into tidal resonance as it reaches its optimal morphological configuration, leading to the overprinting of otherwise dominant allocyclic processes by autocyclic behaviour. It is only by considering the sedimentological relationships of neighbouring and contemporaneous depositional systems that a full understanding of the dynamic stratigraphic history of a basin alternatively dominated by autocyclic and allocyclic processes can be achieved.

No abstract

Interpretation of seismic data has played a major role for recent advances in the studies of igneous sill complexes. Seismic modelling studies based on field analogues represent a promising tool to close the scale gap between observations from outcrops and seismic data and support seismic interpretation. Virtual outcrop models are commonly used to include high-resolution geological structures Grande Valley (Fig. 1), where oil is produced from andesitic sills in several fields (e.g., Los Cavaos, Los Volcanes), which intruded in the Vaca Muerta and Agrio formations (Witte et al. 2012). These sills are likely associated with the Upper Miocene Huincán Eruptive Cycle with reported radiometric ages (Ar/Ar) close to the study area between 10.5 Ma and 7 Ma (Nullo et al. 2002; Witte et al. 2012). Many of the sills are heavily fractured, but show generally low porosity except for a few strongly altered "cavity zones" (Witte et al. 2012). Approximately 10 km west of the Los Cavaos oil field, the Sierra Azul basement thrust brought to outcrop, among others, the Vaca Muerta and Agrio formations intruded by numerous andesitic sills (Fig.1). In this study, we focused on a 4km long continuous section, where both the sills and the host rock are accessible in a very high quality outcrop. This exceptional outcrop is a direct field analogue of the nearby Los Cavaos field.

No abstract