NNW-SSE Striking Faults Research Articles

Present-day incipient fault coalescence at a relay zone (Jiloca extensional basin, Spain): Evidence from instrumental seismicity

The relay zones between NW-SE to NNW-SSE striking faults of the Jiloca graben (Iberian Chain) mostly show distributed along-strike fault and fracture patterns. The latter are chiefly controlled by the Late Pliocene-Quaternary regional stress field, and secondarily respond to local controls from inherited structures. Such fracture patterns contrast with the classical models of transverse connecting faults controlled by relay kinematics. North of the Concud fault trace, at the relay zone with the Sierra Palomera fault, an unusually high seismic activity has been noticed since 2014, with magnitudes up to M = 3.5. Upgrading of the National Seismic Network allowed obtaining such new detailed records, while the installation of a new seismometer by the IGN within the study area has improved the reliability of focal depth data since 2017. A high-precision absolute relocation of seismicity from 01/01/2000 to 30/05/2022 has been carried out. The results show that (i) the epicentres are significantly clustered along a nearly N-S trending band, and (ii) the focal depths range from 0 to 14 km, in good agreement with the thickness of the brittle crust. This 3D spatial distribution of seismicity is interpreted as a consequence of activation of either a single fault or a fault zone, nearly vertical and N-S striking. Such structural setting is consistent with the surficial fracture patterns observed at both map and outcrop scale: NNW-SSE and NNE-SSW oriented faults and fractures, orthogonal to the ENE-WSW to ESE-WNW regional σ3 trajectories, together with NW-SE trending ones controlled by inherited contractive faults. The present-day seismic activity suggests that along-strike, incipient fault propagation at the relay zone between the Concud and Sierra Palomera faults is currently operating under the control of the remote stress field.

Evaluating the Relation of Cave Passage Formation to Stress-Field: Spatio-Temporal Correlation of Speleogenesis with Active Tectonics in Asprorema Cave (Mt. Pinovo, Greece)

Caves serve as time capsules, preserving significant markers of tectonic activity and offering insights into geological history. Fault geometries and past activations found in caves can be correlated with known deformational events in the broader area, temporally delimiting the speleogenesis. More specifically, cave passage formation is suggested to be affected by the regional stress-field. The Asprorema Cave in Northern Greece is a typical example of a fracture guided cave, with passage geometry influenced by relative sidewall movements, revealing these discontinuities as faults. This study constructs the timeframe and conceptual model of speleogenesis in relation to tectonic events, geomorphological evolution and hydrological zones, and verifies its relation to the stress-field. Active tectonics, mineralogy and cave geomorphology are investigated. Results suggest syntectonic speleogenesis under phreatic and epiphreatic conditions. The absence of corrosion on fault slip surfaces implies recent activations post cave’s shift to the vadose zone. Structural analysis identifies three main neotectonic phases: NNW-SSE striking faults (oldest group of structures), NE-SW striking faults with dextral strike-slip movement (post-middle Miocene), and NE-SW striking normal faults indicating extensional stress-regime (Quartenary). The last two phases affect cave passage shape causing wall displacement, highlighting passage formation along discontinuities perpendicular to the horizontal minimum stress axis.

Unravelling the impact of geological heterogeneities in the reservoir management. An integrated study of the deep-water Akpo field (Niger delta)

Geological and seismic data have been integrated to describe the impact of structural and sedimentological heterogeneities on fluid dynamics for one of the reservoirs (Reservoir X) of the Akpo field (deep offshore of Niger Delta). Akpo is a sinuous 4-way anticline formed because of strong deformation occurring within the over pressurized shales of the Akata Formation. Weak deformation may have started since 9 Ma; however, most of the strain associated with shortening was accumulated between ca 7 Ma and ca 3 Ma. The cumulative shortening has been estimated in the order of 4% (ca 400 m). From 3 Ma (during the latest stages of growth of the Akpo anticline) up to Present-day, the residual strain was taken up by oblique (right lateral strike-slip component) extensional faults, between 2 km and ca 15 km in length, organized into two main trends: N-dipping, ENE-WSW to NE-SW striking faults, and NNW-SSE striking faults mainly dipping to the east. These faults are segmented and have a maximum throw in the order of 70 m. Based on the architectural elements identified in this work, the Reservoir X of the Akpo field has been subdivided into three main intervals: a basal lobe (Interval 1a) and a related channel (Interval 1 b); two intermediate generations of meandering channels (Interval 2a and 2 b); and an upper and strongly erosional constructive channel (Interval 3). The 4D signal has been integrated to better understand the complex fluid flow within Reservoir X in time and space. The extensional faults play a role in baffling mainly in the central part of the field, where across-fault flow is likely to occur in correspondence with the spill points. Facies distribution and the nature of the contact between various reservoir intervals are also important because vertical and lateral communication between sand bodies can be complex. Levees or mud barriers can inhibit flow, impacting both efficiency of support between injectors and producers. On the other hand, sand-to-sand communication due to the strong erosional character of the contacts enhances dynamic connectivity between sands belonging to different reservoir intervals. As an example, even if sands belonging to Interval 3 totally erode (i.e. dynamically isolate) those of Interval 2 in the southern part of the field, in the northern sector the two reservoir intervals are in (vertical) communication as suggested by the 4D signal. A key result of this integrated work is that of documenting in detail the modes in which faults and sedimentary features impact fluid flow within and across reservoir intervals in a deep-water environment.

Source parameters of the 8 February 2016, Mw=4.2 Los Humeros earthquake by the inversion of InSAR-based ground deformation

We investigate ground movements induced by the 8 February 2016, Mw=4.2 earthquake at the Los Humeros Geothermal Field (Mexico) using Sentinel-1 radar interferometry. Previous estimated focal mechanism solution based on seismic data with a hypocentral depth of 1900 m could not resolve the measured coseismic surface deformation pattern. In this study, we applied inverse elastic dislocation models to estimate the source parameters of the seismic event. Our models suggest the reverse reactivation of the Los Humeros normal fault at a shallower depth (<1000 m), with a more significant left lateral component below ~400 m depth. The occurrence of such shallow events at Los Humeros pose increased risks for the neighboring communities and infrastructure. Therefore, continuous monitoring of seismicity and cautious planning of field operations are crucial.A NNW-SSE striking fault swarm, including the Los Humeros fault, acts as a major boundary of the subsiding area observed by InSAR time-series between February 2016 and May 2019. A potential explanation of the reverse reactivation of the Los Humeros fault and following downward movement of the eastern fault block is the depressurization of the whole hydrothermal system. Such depressurization can occur due to the exploitation of the geothermal field and/or due to natural pressure/temperature changes related to magmatic activity.

Fault relay zones evolving through distributed longitudinal fractures: The case of the Teruel graben system (Iberian Chain, Spain)

A new type of fault relay zone in extensional contexts, dominated by distributed along-strike or longitudinal fractures, is defined. It contrasts with the classical models reported in the literature, in which transverse connecting faults controlled by the own relay kinematics prevail. The new model is based on structural features of the Teruel graben system, as well as on analogue modelling. Relay zones between the NW-SE to NNW-SSE striking faults that delimit the eastern boundary of the Jiloca Graben (Calamocha, Sierra Palomera and Concud faults), together with the Teruel Fault, have been studied. All of these relay faults show recent (Neogene-Quaternary) ruptures at different scales, mostly parallel to the macrostructural trend and to the maximum horizontal stress (SHmax) trajectories (i.e., orthogonal to the ENE-WSW regional extension direction that characterises the nearly biaxial or radial stress regime active during Upper Pliocene-Quaternary times). Transverse ruptures are almost absent, with the exception of the northern relay zone (Calamocha-Sierra Palomera), where an incipient NE-SW striking connecting fault does exist. Analogue models have been run under a biaxial extension regime similar to the regional one. They allowed analysing the main factors controlling fracture propagation, depending on the ratio of extension velocities and the orientation of the master faults relative to extension directions. Laboratory fracture patterns, as in the natural studied examples, are mostly controlled by the inherited anisotropies and, in a greater extent, by the imposed extension trajectories, which results in a clear prevalence of longitudinal fractures. Such external controls, usually disregarded in numerical and analogue modelling, tend to induce fault coalescence through along-strike (parallel or at very-low-angle) propagation resulting in a final braided fault pattern.

Breakdown of Earthquake Self‐Similar Scaling and Source Rupture Directivity in the 2016–2017 Central Italy Seismic Sequence

AbstractTo analyze the source characteristics of the 2016–2017 central Italy seismic sequence, source spectra of 78 earthquakes of ML = 3.5–6.1 were separated from the S wave Fourier spectra using the two‐step nonparametric generalized inversion technique. Source parameters (e.g., stress drop) were estimated from the source spectra following the ω‐square model. Stress drops were found mainly in the range 0.113–12.190 MPa. The significant dependence of stress drop on magnitude indicates the breakdown of earthquake self‐similar scaling in this sequence. The low stress drops for small events following the release of high stress by the mainshock might have led to stress accumulation on the unruptured fault, which could explain the subsequent occurrence of multiple major events. We investigated the source rupture directivity for 36 events through the azimuthal variation of apparent source spectra. Significant variation was observed at specific frequency bands (generally, over corner frequencies) in 10 events caused by rupture directivity, which was verified by the stable estimation of rupture plane. The rupture parameters confirmed unilateral ruptures predominantly on the NNW–SSE striking fault with fast rupture velocity (2.52–2.84 km/s) for the 10 events. Rupture parameters for an additional four events with stable estimated rupture plane were also analyzed. These were characterized by slow rupture velocity causing weak directivity effects. According to the rupture parameters for the 14 events, prevailing SSE or SEE (NNW or NNE) rupture directivity was a common feature for events to the north (south) of the mainshock in this earthquake sequence.

The development of a regional-scale intraplate strike-slip fault system; Alpine deformation in the north of Ireland

A paucity of displacement markers can make constraining the kinematics and interaction of regional-scale strike-slip faults difficult. In this study, a high-resolution aeromagnetic survey allows quantitative analysis of kilometre-scale Paleogene faulting in the north of Ireland. Mapping offset dykes and igneous centres reveals the presence of two orientations of Cenozoic strike-slip faults attributed to broadly N-S Alpine shortening arising from the convergence of Africa and Europe. Reactivated NE-SW striking faults accommodated up to 2.3 km of sinistral displacement mainly during the Paleocene. Following tectonic quiescence, up to 2.5 km of Oligocene-aged dextral movement was accommodated on newly-formed NNW-SSE striking faults. Displacement analysis suggests that the faults were kinematically linked and experienced a switch in polarity of the predominantly active fault orientation during the Paleogene, forming an apparent conjugate system with asymmetric displacement distributions. The switch in fault polarity is attributed to a rotation in the regional maximum horizontal stress orientation and the locus of deformation moving from pre-existing reactivated structures to newly formed faults. The analysis also illustrates that, despite low strain rates, the interaction of the principal components of the fault system controlled the formation of sedimentary basins and defined the present-day geography of the region, far from an active plate boundary.

Kilometer-scale fault-related thermal anomalies in tight gas sandstones

Upper Carboniferous sandstones make one of the most important tight gas reservoirs in Central Europe. This study integrates a variety of geothermometers (chlorite thermometry, fluid inclusion microthermometry and vitrinite reflection measurements) to characterize a thermal anomaly in a reservoir outcrop analog (Piesberg quarry, Lower Saxony Basin), which is assumed responsible for high temperatures of circa 300 °C, deteriorating reservoir quality entirely. The tight gas siliciclastics were overprinted with temperatures approximately 90–120 °C higher compared to outcropping rocks of a similar stratigraphic position some 15 km to the west. The local temperature increase can be explained by circulating hydrothermal fluids along the fault damage zone of a large NNW-SSE striking fault with a displacement of up to 600 m in the east of the quarry, laterally heating up the entire exposed tight gas sandstones. The km-scale lateral extent of this fault-bound thermal anomaly is evidenced by vitrinite reflectance measurements of meta-anthracite coals (VRrot ∼ 4.66) and the temperature-related diagenetic overprint. Data suggest that this thermal event and the associated highest coalification was reached prior to peak subsidence during Late Jurassic rifting (162 Ma) based on K-Ar dating of the <2 μm fraction of the tight gas sandstones. Associated stable isotope data from fluid inclusions, hosted in a first fracture filling quartz generation (T ∼ 250 °C) close to lithostatic fluid pressure (P ∼ 1000 bars), together with authigenic chlorite growth in mineralized extension fractures, demonstrate that coalification was not subject to significant changes during ongoing burial. This is further evidenced by the biaxial reflectance anisotropy of meta-anthracite coals. A second event of quartz vein formation occurred at lower temperatures (T ∼ 180 °C) and lower (hydrostatic) pressure conditions (P ∼ 400 bars) and can be related to basin inversion. This second quartz generation might be associated with a second event of illite growth and K-Ar ages of 96.5–106.7 Ma derived from the <0.2 μm fraction of the tight gas sandstones.This study demonstrates the exploration risk of fault-bound thermal anomalies by deteriorating entirely the reservoir quality of tight gas sandstones with respect to porosity and permeability due to the cementation with temperature-related authigenic cements. It documents that peak temperatures are not necessarily associated with peak subsidence. Consequently, these phenomena need to be considered in petroleum system models to avoid, for example, overestimates of burial depth and reservoir quality.

Volcano-structural analysis of La Garrotxa Volcanic Field (NE Iberia): Implications for the plumbing system

The Garrotxa Volcanic Field is related to the Neogene–Quaternary European Rift system and is the youngest representation of monogenetic volcanism in the Iberian Peninsula. It encompasses over 50 eruptive vents, most of them well-preserved cones, in an area of about 600km2 lying between the cities of Olot and Girona (NE Spain). In this paper we investigate the relationship between the Neogene extensional tectonics and the spatial distribution of the volcanoes in the area. The analysis includes the distribution of faults, fissures and vents, as well as morphostructural lineaments, and the morphometrical analysis of volcanic cones and craters. In addition, we use the location of the regional seismicity recorded since 1978 and the sites of freshwater springs and mantle-derived gases as indicators of active faults and open fractures. Finally, we consider the location of ultramafic xenoliths within volcanic deposits as a way of identifying the deepest fractures in the zone and estimating magma ascent velocities. The results obtained show that this volcanic area consists of an extensional basin delimited by two principal NW–SE faults that favoured the ascent of magma from either the source region or from shallower reservoirs located at the base of the crust. Towards the upper part of the crust, magma transport was captured by shallow secondary extensional NNW–SSE striking faults whose formation is linked to the slight transtensional movement of the main bounding faults. Our study provides evidence of how the local stress field and contrasts in substrate stratigraphy could have controlled magma migration, which suggests that precise knowledge of the stress configuration, substrate geology and structural discontinuities in such regions is crucial in the forecasting of monogenetic volcanism.

The use of speleothem damage and in situ fault displacement monitoring to characterise active tectonic structures: an example from Západní Cave, Czech Republic

The EU-TecNet fault displacement monitoring network records three-dimensional displacements across specifically selected tectonic structures within the crystalline basement of central Europe. This paper presents a study of recent and active tectonic fault displacement recorded at Západní Cave in northern Bohemia (Czech Republic). It extends previous geological research by measuring speleothem damage within the cave and monitoring displacements across two fault structures within the Lusatian Thrust Zone. The measured speleothem damage, which are characterised by strike-slip movements, show dextral strike-slip displacement along the WSW-ENE striking fault and sinistral strike-slip displacement along the NNW-SSE striking fault. It is found that the compressive stress σ1 is located in the NW or SE quadrant while the tensile stress σ3 is oriented perpendicular to σ1, i.e. in the NE or SW quadrant. The results of fault displacement monitoring show a long-term dextral strike-slip trend along the WSW-ENE striking fault while the NNW-SSE striking fault presents evidence for uplift of the eastern block. There are notable periods of increased geodynamic activity, referred to as pressure pulses, in 2008, 2010-2011, and 2012. The significant correspondence between the measured speleothem damage and the results of fault displacement monitoring confirm the supposition that, at this site, the compressive stress σ1 persists in the NW or SE quadrant. The presented results offer an insight into the periodicity of pressure pulses, demonstrate the necessity for protracted monitoring periods as a means for better understanding geodynamic processes, and show that it is possible to characterise the displacements that occur across individual faults in a way that cannot be accomplished from geodetic measurements made using Global Navigation Satellite Systems.

Terrain characterization and structural control of the Auca Mahuida volcanism (Neuquén Basin, Argentina)

Geomorphometric parameters (slope, aspect, valley depth, and areal density of cones) derived from a moderate resolution digital elevation model with a grid spacing of 100 m are used in an attempt to interpret the tectonic/structural features related to surface deformation in the Auca Mahuida volcanic terrain (Neuquén Basin, Argentina). The Auca Mahuida (2.03–0.88 Ma) is the southernmost volcanic field of the Payenia volcanic province, in the Andean foreland. The foreland is subjected to an E–W compression related to the eastward migration of the N–S striking thrust front of the Andes. The geomorphometric analysis indicates that the Auca Mahuida consists of a basal, E–W elongated lava field with monogenic vents and a summit, polygenic, also E–W elongated, cone. A N100°E striking fault controls the southern flank of the field, which is also affected by scarps related to erosional and gravity-controlled processes. The drainage network shows a pseudo-radial pattern around the summit cone, and the Auca Mahuida's deepest valley is structurally controlled by a NNW–SSE striking fault affecting the sedimentary basement. The volcanic field lies on a NE to E dipping substratum. The areal distribution of the monogenic cones is consistent with ascent of magmas along E–W striking fractures, and with elastic models of a pressurized hole (magma chamber) subjected to an E–W compression. At Auca Mahuida, the ascent of melts from the mantle is controlled, in the overriding crust, by tectonic structures formed in response to the E–W compression of the Andes.

EGS hydraulic stimulation monitoring by surface arrays - location accuracy and completeness magnitude: the Basel Deep Heat Mining Project case study

The potential and limits of monitoring induced seismicity by surface-based mini arrays was evaluated for the hydraulic stimulation of the Basel Deep Heat Mining Project. This project aimed at the exploitation of geothermal heat from a depth of about 4,630 m. As reference for our results, a network of borehole stations by Geothermal Explorers Ltd. provided ground truth information. We utilized array processing, sonogram event detection and outlier-resistant, graphical jackknife location procedures to compensate for the decrease in signal-to-noise ratio at the surface. We could correctly resolve the NNW–SSE striking fault plane by relative master event locations. Statistical analysis of our catalog data resulted in ML 0.36 as completeness magnitude, but with significant day-to-night dependency. To compare to the performance of borehole data with MW 0.9 as completeness magnitude, we applied two methods for converting ML to MW which raised our MC to MW in the range of 0.99–1.13. Further, the b value for the duration of our measurement was calculated to 1.14 (related to ML), respectively 1.66 (related to MW), but changes over time could not be resolved from the error bars.

Fault propagation in a seismic gap area (northern Calabria, Italy): Implications for seismic hazard

The Crati basin is a tectonic depression developed between the Coastal Range and the Sila Massif and is characterised by a sedimentary succession ranging between Late Miocene to Holocene age. Basin cover can be subdivided into a series of stratigraphic intervals bounded by angular unconformities. The general basin architecture is mainly controlled by N–S striking normal faults (the Crati Fault System) cropping out along both basin margins. These faults formed since the Middle Pliocene in the southern part of the basin and propagated northwards, where they developed during Middle–Late Pleistocene. The occurrence of several earthquakes along N–S striking faults, suggest their still ongoing activity. The northernmost part of the Crati basin, bordered by the 30 km long Pollino fault, is thought to be characterised by an important seismic gap; this contrasts with the geological evidences of Quaternary fault activation of both the central part of the Pollino fault and some NNW–SSE striking normal faults. We propose that the NNW–SSE striking faults represent the northernmost prolongation of the Crati Fault System, a large scale active crustal rift related to the Tyrrhenian spreading. These faults mechanically interacted with the Neogene Pollino fault and determined the almost contemporary activation of the central part of this structure, because of stress triggering phenomena, as suggested by the Coulomb failure stress changes.

Paleogene-early miocene deformations of Bukulja-Vencac crystalline (Vardar zone, Serbia)

Low-grade metamorphic rocks of the crystalline of Mts. Bukulja and Vencac, which are integral parts of the Vardar Zone, are of Late Cretaceous age. From the Middle Paleogene to the beginning of the Miocene, they were subjected to three phases of intensive deformations. In the first phase, during the Middle Paleogene, these rocks were subjected to intense shortening (approximately in the E-W direction), regional metamorphism and deformations in the ductile and brittle domains, when first-generation folds with NNE-SSW striking fold hinges were formed. In the second phase, during the Late Oligocene and up to the Early Miocene, extensional unroofing and exhumation of the crystalline occurred, which was followed by intrusion of the granitoid of Bukulja and refolding of the previously formed folds in a simple brachial form of Bukulja and Vencac with an ESE-WNW striking B-axis. The third phase was expressed in the Early lowermost Miocene (before the Ottnanghian), under conditions of NE-SW compression and NW-SE tension. It was characterized by wrench-tectonic activity, particularly by dextral movements along NNW-SSE striking faults.

Relay ramp evolution and mass flow deposition (Upper Kimmeridgian–Lower Volgian) in the Tail End Graben, Danish North Sea

ABSTRACTThe Central Graben in the Danish North Sea sector consists of a series of N–S to NW–SE trending, eastward‐tilted half‐grabens, bound to the east by the Coffee Soil Fault zone. This fault zone has a complex Jurassic history that encompasses at least two fault populations; N–S to NNW–SSE striking faults active in the Late Aalenian–Early Oxfordian, and NNW–SSE to WNW–ESE striking faults forming in Late Kimmeridgian time (sensu gallico), following a short period of tectonic quiescence. Sediment transport across the Coffee Soil Fault zone was controlled by fault array evolution, and in particular the development of relay ramps that formed potential entry points for antecedent drainage systems from the Ringkøbing–Fyn High east of the rift. Fault and isochore trends of the Upper Kimmeridgian–Lower Volgian succession in the northeast Danish Central Graben show that accommodation space was initially generated close to several minor, isolated or overlapping faults. Subsidence became focused along a few master faults in the Early Volgian through progressive linkage of selected faults. Seismic time isochore geometries, seismic facies, amplitude trends and well ties indicate the presence of coarse clastic lithologies locally along the fault zone. The deposits probably represent submarine mass flow deposits supplied from footwall degradation and possibly also from the graben hinterland via a relay ramp. The latter source appears to have been cut off as the relay ramp was breached and the footwall block are uplifted. Fault growth and linkage processes thus controlled the spatial and temporal trends of accommodation space generation and sediment supply to the rift basin.

Integrated seismic interpretation of the Carlsberg Fault zone, Copenhagen, Denmark

We locate the concealed Carlsberg Fault zone along a 12-km-long trace in the Copenhagen city centre by seismic refraction, reflection and fan profiling. The Carlsberg Fault is located in a NNW-SSE striking fault system in the border zone between the Danish Basin and the Baltic Shield. Recent earthquakes indicate that this area is tectonically active. A seismic refraction study across the Carlsberg Fault shows that the fault zone is a low-velocity zone and marks a change in seismic velocity structure. A normal incidence reflection seismic section shows a coincident flower-like structure. We have recorded seismic signals in a fan geometry from shots detonated both inside the low-velocity fault zone and up to ∼500 m away from the fault zone. The seismic energy was recorded on three receiver arrays (1.5- to 2.4-km-long arcs) across the expected location of the ∼400- to 700-m-wide fault zone at distances of up to ∼7 km from the shots. Shots detonated inside the fault zone result in (1) weak and delayed first arrivals on the receivers located inside the fault zone compared to earlier and stronger first arrivals outside the fault zone; (2) strong guided P and S waves as well as surface waves inside the fault zone. The fault zone is a shadow zone to shots detonated outside the fault zone. Finite-difference wavefield modelling supports the interpretations of the fan recordings. Our fan recording approach facilitates cost-efficient mapping of fault zones in densely urbanized areas where seismic normal incidence and refraction profiling are not feasible.

Depositional environment and sedimentary of the basinal sediments in the Eibiswalder Bucht (Radl Formation and Lower Eibiswald Beds), Miocene Western Styrian Basin, Austria

The Eibiswald Bucht is a small subbasin of the Western Styrian Basin exposing sediments of Lower Miocene age. In the past the entire sequence exposed in the Eibiswalder Bucht has been interpreted as being of fluvial/lacustrine origin; here, results are presented of detailed sedimentological investigations that lead to a revision of this concept. The lowermost siliciclastic sedimentary unit of the Eibiswalder Bucht sequence is the Radl Formation. It is overlain by the Eibiswald Beds, which are subdivided into the Lower, Middle and Upper Eibiswald Beds. The Radl Formation and the Lower Eibiswald Beds are interpreted as a fan delta complex deposited along NNW-SSE striking faults. Based on the sedimentary facies this fan delta can be subdivided into a subaerial alluvial fan facies group, a proximal delta facies group and a distal delta/prodelta facies group. The Radl Formation comprises the alluvial fan and proximal delta facies groups, the Lower Eibiswald Beds the distal delta/prodelta facies group. The alluvial fan and the proximal delta consist of diverse deposits of gravelly flows. The distal delta/prodelta consists of wave-reworked, bioturbated, low density turbidites intercalated with minor gravelly mass flows. The prodelta can be regarded as as the basin facies of the small and shallow Eibiswalder Bucht, where marine conditions prevailed. The basin was probably in part connected with the Eastern Styrian Basin, the contemporary depositional environment of the Styrian Schlier (mainly turbiditic marine offshore sediments in the Eastern Styrian Basin). Analysis of the clast composition, in conjunction with the paleotransport direction of the coarse delta mass flows of the Radl Formation, shows that the source rocks were exclusively crystalline rocks ranging from greenschists to eclogites.