Seismic-Scale Evidence of Thrust-Perpendicular Normal Faulting in the Western Outer Carpathians, Poland

Based on the interpretation of 2D seismic profiles integrated with surface geological investigations, a mechanism responsible for the formation of a large scale normal fault zone has been proposed. The fault, here referred to as the Rycerka Fault, has a predominantly normal dip-slip component with the detachment surface located at the base of Carpathian units. The fault developed due to the formation of an anticlinal stack within the Dukla Unit overlain by the Magura Units. Stacking of a relatively narrow duplex led to the growth of a dome-like culmination in the lower unit, i.e., the Dukla Unit, and, as a consequence of differential uplift of the unit above and outside the duplex, the upper unit (the Magura Unit) was subjected to stretching. This process invoked normal faulting along the lateral culmination wall and was facilitated by the regional, syn-thrusting arc–parallel extension. Horizontal movement along the fault plane is a result of tear faulting accommodating a varied rate of advancement of Carpathian units. The time of the fault formation is not well constrained; however, based on superposition criterion, the syn -thrusting origin is anticipated.

Influence of mass transport deposit (MTD) surface topography on deep-water deposition: an example from a predominantly fine-grained continental margin, New Zealand

Three-dimensional (3D) seismic data reveal the complex interplay between the surface topography of a c. 4405 km3 mass transport deposit (MTD) and overlying sedimentary packages over approximately the last two million years. The data image part of the Pleistocene to recent shelf to slope to basin-floor Giant Foresets Formation in offshore western New Zealand. The MTD created substantive topographic relief and rugosity at the contemporaneous seabed, formed by the presence of a shallow basal detachment surface, and very large (up to 200 m high) intact slide blocks, respectively. Sediments were initially deflected away from high-relief MTD topography and confined in low areas. With time, the MTD was progressively healed by a series of broadly offset-stacked and increasingly unconfined packages comprised of many channel bodies and their distributary complexes. Positive topography formed by the channels and their distributary complexes further modified the seafloor and influenced the location of subsequent sediment deposition. Channel sinuosity increased over time, interpreted as the result of topographic healing and reduced seafloor gradients. The rate of sediment supply is likely to have been non-uniform, reflecting tectonic pulses across the region. Sediments were routed into deep water via slope-confined channels that originated shortly before emplacement of the MTD.

Open-slope, translational submarine landslide in a tectonically active volcanic continental margin (Licosa submarine landslide, southern Tyrrhenian Sea)

The southern Tyrrhenian continental margin is the product of Pliocene–Recent back-arc extension. An area of approximately 30 km2 of gentle (about 1.5°) lower slope of the last glacial outer shelf sedimentary wedge in water depths of between 200 and 300 m failed between 14 and 11 ka BP. We approached the landslide by multibeam and sub-bottom profiler surveying, high-resolution multichannel seismics, and coring for stratigraphic and geotechnical purposes. With regard to a slope-stability analysis, we carried out an assessment of the stratigraphic and structural setting of the area of the Licosa landslide. This analysis revealed that the landslide detached along a marker bed that was composed of the tephra layer Y-5 (c. 39 ka). Several previously unknown geological characteristics of the area are likely to have affected the slope stability. These are the basal erosion of the slope in the Licosa Channel, a high sedimentation rate in the sedimentary wedge, earthquake shaking, the volcanic ash nature of the detachment surface, subsurface gas/fluid migration, and lateral porewater flow from the depocentre of wedge to the base of the slope along the high-permeability ash layers. A newly discovered prominent structural discontinuity is identified as the fault whose activity may have triggered the landslide.

Famennian glaciation in the eastern side of Parnaíba Basin, Brazil: evidence of advance and retreat of glacier in Cabeças Formation

ABSTRACTGlaciotectonic features studied in the siliciclastic deposits of Cabeças Formation, Upper Devonian, represent the first evidence of Famennian glaciation in Southeastern Parnaíba Basin, Brazil. Outcrop-based stratigraphic and facies analyses combined with geometric-structural studies of these deposits allowed defining three facies association (FA). They represent the advance-retreat cycle of a glacier. There are: delta front facies association (FA1) composed of massive mudstone, sigmoidal, medium-grained sandstone with cross-bedding and massive conglomerate organized in coarsening- and thickening-upward cycles; subglacial facies association (FA2) with massive, pebbly diamictite (sandstone, mudstone and volcanic pebbles) and deformational features, such as intraformational breccia, clastic dikes and sills of diamictite, folds, thrust and normal faults, sandstone pods and detachment surface; and melt-out delta front facies associations (FA3), which include massive or bedded (sigmoidal cross-bedding or parallel bedding) sandstones. Three depositional phases can be indicated to Cabeças Formation: installation of a delta system (FA1) supplied by uplifted areas in the Southeastern border of the basin; coastal glacier advance causing tangential substrate shearing and erosion (FA1) in the subglacial zone (FA2), thus developing detachment surface, disruption and rotation of sand beds or pods immersed in a diamicton; and retreat of glaciers accompanied by relative sea level-rise, installation of a high-energy melt-out delta (FA3) and unloading due to ice retreat that generates normal faults, mass landslide, folding and injection dykes and sills. The continuous sea-level rise led to the deposition of fine-grained strata of Longá Formation in the offshore/shoreface transition in the Early Carboniferous.

Seismotectonic Mechanisms of Lushan (Ms7.0) Earthquake in the Frontal Propagation Belt of the Longmen Shan, Sichuan, China

In recent years, the apparent seismic activity around Longmen Shan and its front has included the Wenchuan (Ms8.0) Earthquake and the Lushan (Ms7.0) Earthquake, occurring in 2008 and 2013, respectively. Based on the focal mechanism solution, rupture processes, seismic intensity, surface deformation, and aftershocks of the Lushan Earthquake and the active fault on Longmen Shan, we divided the Longmen Shan and its front into two tectonic deformation belts, the Longmen Shan thrust belt and the frontal propagation belt. By comparing the differences in the tectonic deformation styles, active faults, and earthquake histories of the two belts, we propose two kinds of seismotectonic models: one is a thrusting belt characterized by napping and detachment, and the other is a frontal propagation belt characterized by thrusting and detachment folding. By analyzing the seismogenic mechanisms of thrusting and detachment folding in the frontal propagation belt during the Lushan Earthquake, we have inferred that the Lushan Earthquake was formed by thrusting and detachment folding in the frontal propagation belt. The seismogenic fault of the Lushan Earthquake was the Dayi Fault, which dips NW with a listric surface, and converges on the detachment surface. The detachment surface is the seismic source layer of the Lushan Earthquake.

Structural Deformation of Southern Tien Shan Fold-Thrust Belt — Take the North Margin of Kashi for Example

The Structural and deformational features of fold-thrust belt in the north margin of Kashi，southern Tian Shan were disclosed based on various data such as two dimensional seismic profile and field geologic survey. The results show that the fold-thrustbelt can be divided into several rows of anticlines, includingKalaboketuoer-Wenguer, Tuopa-Kangxiweier, Atushi and Kashi on plane,and the development of Atushi anticlines and its north side was controlled by the activity of the thrust system originated along the middle Cambrian Awatage Group from north to south. The fold-thrust belt can be divided into two different spatial levels: the shallow tectonic is a large scale imbricate thrust system, the detachment surface is uplifted from Cambrian system to Neogene system; the deep structure is a buried duplex structure system, the fault in floor and fault in roof are located at gypsic horizon in Cambrian and Neogene systemrespectively. Based on structural deformation analyzing and balanced section technology, the distribution of each anticlinal belt and the structure style of the low and deep thrust systems are confirmed. In this area the distance is shortened by 32.64～49.1km from north to south since Pliocene with the scalage of 40.5%～50.51%，and its average crustal shortening rate is 9.11～13.71mm/a.