Pliocene Sedimentary Rocks Research Articles

Spatio-temporal variation of the strain field in the southern Central Andes broken-foreland (27°30′S) during the Late Cenozoic

We present an integrated structural and Anisotropy of Magnetic Susceptibility (AMS) study focused on the characterization of the spatio-temporal variation of the strain field during the main Neogene deformation, of the Argentine Precordillera and the northern Sierras Pampeanas, immediately to the south of the Puna plateau (27°30′S). The AMS from 43 sites and fault-slip data analysis from mesoscale faults (n = 540) were carried out in Lower Miocene to Middle Pliocene sedimentary and volcaniclastic rocks. The AMS results show moderate values of anisotropy degree near to deformation zones, and low and high values of bulk susceptibility. The most predominant magnetic fabric is sedimentary type I and II, with a weak magnetic lineation. In areas where the rocks are deformed, the incipient magnetic lineation are subparallel to the regional structural trend and present a main N–S orientation in the Precordillera and Fiambalá basin, while in the Sierras Pampeanas they are mostly NE-oriented. Combining these results with kinematic analysis from fault-slip data, we identify, in the Precordillera and Fiambalá basin areas, a contractional event with E-W main direction, from ~23 Ma to 5 Ma, mostly active from the onset of deposition of Neogene sequences. During this period, in the NW Sierras Pampeanas, the contraction directions follow a NW orientation. The onset of N–S to NNW contraction, mostly recognized in rocks younger than 5 Ma, exposed in the northern areas of Precordillera and Sierra Pampeanas, documents a change of the strain field during the Early-to-Middle Pliocene, associated with a shift in the contractional direction from E-W to N–S. We relate the change to the rapid uplift of the southern Puna, generating a juxtaposition of an area under N–S extension, affecting the topographically-higher Puna, with the other area under N–S contraction in the adjacent Precordillera and Sierras Pampeanas. We associate these two events as part of the evolution of this segment of the Andes, where the broken foreland setting is active during this time. By combining the AMS and kinematic analysis results, we obtain a timing for the spatio-temporal change of contraction directions, which allows us to compare both the broken-foreland and foreland basins to understand spatio-temporal strain variations.

Application of spectral analysis to determine geothermal anomalies in the Tuzla region, NW Turkey

We used remote sensing data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite to identify the mineral properties and geothermal anomalies related to hot springs in the Tuzla area, including the fault system with NW-SE trend, which is located southwest of Canakkale, NW Turkey. In the study area, the lithological units of the Tuzla geothermal field and the surrounding area consist of Miocene volcanic (trachyandesite, trachyte, and ignimbrites) and Pliocene sedimentary (conglomerate, sandstone, and mudstone) rocks with siliceous, argillaceous, and ferrous alteration linked to the geothermal fluid. ASTER visible/near-infrared (VNIR), short-wave infrared (SWIR), and TIR bands were analyzed by different approaches in order to highlight hot springs in the study area. From these approaches, band ratios were constructed from ASTER VNIR, SWIR, and TIR bands for obtaining geological properties of the region. The geothermal areas were defined by the minimum noise fraction (MNF) and principal component analysis (PCA) methods that was extracted from 5 thermal infrared (TIR) bands as well. Land surface temperatures (LST) support the results from MNF and PCA that were estimated for 5 TIR bands using the inversion of Planck function method. Four days of data including daytime and nighttime satellite images from ASTER were used for the analysis. The used procedure displayed a good match with the ground reality based on field observations in the Tuzla Region.

Organic geochemistry of the Upper Miocene-Lower Pliocene sedimentary rocks in the Hellenic Fold and Thrust Belt, NW Corfu island, Ionian sea, NW Greece

Abstract The northwestern margin of the Hellenic Fold and Thrust Belt situated along the southern edge of the Dinarides – Albanides - Hellenides continental convergent zone, has been studied in terms of its hydrocarbon generating potential. More than a hundred (100) samples of the Upper Miocene-Lower Pliocene sedimentary rocks from several sites in Corfu Island were analyzed using Rock-Eval VI pyrolysis, while a selected representative group was further analyzed using bitumen extraction, open column chromatography and gas chromatography-mass spectrometry. Results of this investigation revealed units with sufficient organic material of good enough quality and quantity to be considered as potential source rocks. A general Type III kerogen was identified, indicating terrestrial origin of the organic matter. Tmax and Production Index values further indicate that the most promising parts of the sediments are immature with respect to oil generation and have not experienced high temperature during burial. n-alkanes distribution for selected samples of the Northern Miocene to Pliocene mudstones present dominance of the long-chain components. Immaturity of the organic matter is also evident by the low Pr/Ph and 20S/(20S + 20R) steranes ratios.

New stratigraphic constraints on the late Miocene–early Pliocene tectonic development of the Aorangi Range, Wairarapa

ABSTRACTA revised stratigraphy is presented for the late Miocene–early Pliocene sedimentary rocks of the northern Aorangi Range, Wairarapa. Despite major differences in lithology, the Clay Creek Limestone and Bells Creek Mudstone are shown to be partially coeval, while the overlying Makara Greensand is shown to be a diachronous unit that ranges from late Miocene (Kapitean) to early Pliocene (Opoitian) age. This revised stratigraphy raises questions about the current classification of the Palliser and Onoke groups, and provides new insights into regional geological history. Previous seismic imaging studies have identified an episode of accelerated crustal shortening and deformation in the Wairarapa region near the Miocene–Pliocene boundary. The Clay Creek Limestone has proven to be a useful marker horizon for constraining the timing and style of this deformational episode, which is interpreted to have occurred prior to 7.2 Ma.

Fault zone architecture within Miocene–Pliocene syn-rift sediments, Northwestern Red Sea, Egypt

The present study focusses on field description of small normal fault zones in Upper Miocene–Pliocene sedimentary rocks on the northwestern side of the Red Sea, Egypt. The trend of these fault zones is mainly NW–SE. Paleostress analysis of 17 fault planes and slickenlines indicate that the tension direction is NE–SW. The minimum (σ3) and intermediate (σ2) paleostress axes are generally sub-horizontal and the maximum paleostress axis (σ1) is sub-vertical. The fault zones are composed of damage zones and fault core. The damage zone is characterized by subsidiary faults and fractures that are asymmetrically developed on the hanging wall and footwall of the main fault. The width of the damage zone varies for each fault depending on the lithology, amount of displacement and irregularity of the fault trace. The average ratio between the hanging wall and the footwall damage zones width is about 3:1. The fault core consists of fault gouge and breccia. It is generally concentrated in a narrow zone of ∼0.5 to ∼8 cm width. The overall pattern of the fault core indicates that the width increases with increasing displacement. The faults with displacement < 1 m have fault cores ranging from 0.5 to 4.0 cm, while the faults with displacements of > 2 m have fault cores ranging from 4.0 to 8.0 cm. The fault zones are associated with sliver fault blocks, clay smear, segmented faults and fault lenses’ structural features. These features are mechanically related to the growth and linkage of the fault arrays. The structural features may represent a neotectonic and indicate that the architecture of the fault zones is developed as several tectonic phases.

Age and provenance of Late Miocene-Early Pliocene sedimentary rocks from the Patao high hydrocarbon reservoir offshore NE Venezuela – U-Pb detrital zircon age, Sm-Nd isotope, and biostratigraphic data

Since discovery of hydrocarbon reservoirs in Late Miocene-Early Pliocene sedimentary rocks of the Patao High offshore northeastern Venezuela back in the 1980's the provenance of these rocks has been uncertain. In this contribution U-Pb LA-ICPMS detrital zircon ages of sandstone samples from offshore wells in the Patao High are presented together with Sm-Nd isotopes and biostratigraphy data. A total of 566 zircon grain analyses from six samples taken from six wells show a sediment mix with ages ranging from Archean to latest Miocene time. About half of the detrital zircon grains have Late Mesoproterozoic-Early Neoproterozoic (∼1.3–0.9 Ga), Paleozoic, and Jurassic ages, indicating Andean crystalline basement sources that travelled from west to east across the South American continent probably in the paleo-Orinoco River system. Cratonic sources like the Guayana Shield (>1.35 Ga) are relatively underrepresented (∼20%) compared to modern sediment from the Orinoco River and Miocene-Pliocene sedimentary rocks from Trinidad. The youngest zircon grains suggest syn-sedimentary Late Miocene (5.6 ± 0.3 Ma) volcanic activity. Such igneous activity has been reported from the eastern Paria Peninsula. Late Miocene-Early Pliocene sedimentation is further constrained by biostratigraphic data reported here. Mixing of continental South American sediment sources with juvenile sources of the Caribbean realm is indicated by Cretaceous and Cenozoic zircon (∼17%) and Sm-Nd isotope data (εNd = −10.6 to −8.0). Stratigraphic and sedimentological data together with a significant number of Late Neoproterozoic zircon, favor a model in which detritus from the paleo-Orinoco River was mixed with detritus from the paleo-Amazon River prodelta that traveled along the continental shelf northwestward by long-shore drift.

Extensional strain and displacement distribution due to mesoscale normal faults in Late Miocene-Pliocene sedimentary rocks along the northwestern side of the Red Sea, Egypt

Field observations are presented on the NW-SE mesoscale, dip-slip, normal faults in the Late Miocene–Pliocene sedimentary rocks, along the northwestern part of the SW side of the Red Sea, Egypt. These faults were initiated parallel to the Red Sea, and were originated by the NE-SW extension associated with the Red Sea opening in the Late Oligocene-Early Miocene time. About 100 mesoscale normal faults were measured in the Late Miocene-Pliocene sedimentary rocks along seven scan-lines. The extensional strain determined in five scan-lines ranges from 2.6393 to 5.12% with an average of 3.53145%. The other two scan-lines have anomalous values of 6.2988 and 15.53%. The represented data demonstrate that the extensional strain varies significantly from profile to profile and even along the fault because of several surficial factors. The first factor is a difference in lithology. The second and third factors are the local stress and the difference between perpendicular to the direction of maximum lateral extension of area and strike of faults. The L-D (Length-Displacement) diagrams along twelve selected faults reveal three patterns. These patterns include a cone-shaped (C-type), meso-shaped (M-type), and a zigzag-shaped (Z-type). The remarkable variation of displacement (D) along the fault plane (L) is a result of the difference in lithology, and/or the overlapping fault segments, as well as the local stress along the faults.

Initiation, movement, and run-out of the giant Tsaoling landslide — What can we learn from a simple rigid block model and a velocity–displacement dependent friction law?

Tsaoling landslide is the largest and best documented landslide among several large landslides induced by the 1999 Taiwan Chi-Chi earthquake. Pliocene sedimentary rocks of about 125Mm3 in volume slid along very flat bedding planes dipping by 14° with an average speed of 35–40m/s for about 1650m, before hitting the bank of the Chinshui River during the landslide. Detailed analysis of DTMs before and after the earthquake using a GIS software leads to an accurate determination of the locations of the centroids of landslide mass, revealing the horizontal and vertical displacements of the 2524m and 524m, respectively. Those displacements and landslide mass give an apparent friction coefficient of 0.21 and the release of the potential energy of 1.6×1015J. We conducted rotary-shear high-velocity friction experiments on fault gouge from bedding-parallel faults under semi-wet conditions and at 3MPa normal stress corresponding to the overburden pressure of the landslide mass. We also compiled reported data on the frictional properties on shale powders and fault gouge from the landslide site under both dry and wet conditions, and proposed a velocity–displacement dependent friction law that can describe most experimental data. Newmark analysis of landslide motion with six scenarios for different landslide materials and conditions, assuming a simple rigid block sliding and using measured frictional parameters, revealed that the landslide did not occur with dry frictional properties, and that the landslide occurred at 38–39s with accumulated displacements of 0.62m–1.09m and reached at the river bank at 82–87s after the generation of Chi-Chi earthquake at its epicenter. Those timings are consistent with high-frequency signals at 32–40s and at 76s recorded at a nearby seismic station and with a survivor's witness that the landslide initiated 10s after he felt strong ground motion, possible S wave arrival at 25.2s. Slip-weakening is essential in initiating the landslide and low friction coefficient (0.08–0.1) allowed high-speed of the landslide possible. The landslide was caused by a few peaks of northeast-oriented strong accelerations of the ground motion. Frictional work during the sliding of the landslide mass was estimated to be of about 23% of potential energy, and the rest of the released energy is likely to have been consumed during the stopping phase of the landslide after hitting the river bank in complex processes such as fragmentation, heat dissipation, and spreading of the landslide deposits.

Triggering and runaway processes of catastrophic Tsaoling landslide induced by the 1999 Taiwan Chi-Chi earthquake, as revealed by high-velocity friction experiments

Pliocene sedimentary rocks of about 130 Mm3 in volume slid along bedding planes dipping by 14°, with an average speed of about 35 m/s, during the Tsaoling landslide. We conducted friction experiments to reproduce the initiation processes of this landslide, by idealizing landslide movements during the earthquake as accelerating/decelerating motion. Experiments were done on shale from the field, at 3 MPa normal stress corresponding to the overburden pressure. Results indicate that the accelerating/decelerating motion causes weakening and strengthening at each oscillation cycle and results in overall slip weakening which can be approximated as an exponential slip weakening. Behaviors during oscillatory slip are fairly similar to those during sliding at constant slip rates. Newmark analysis with measured frictional properties reveals that the landslide can be triggered with wet gouge properties, but the landslide motion stops with parameters for dry shale gouge. Delayed initiation of the landslide is consistent with a survivor's witness.

Geotechnical Behavior of Pliocene Sedimentary Rocks Exposed along Qena-Safaga Road at Qena region, Egypt

Geotechnical properties of Pliocene sedimentary rocks (Durri Formation) exposed along Qena-Safaga road were investigated to evaluate their geotechnical behaviour. The purpose of this research was to interpret a real reason of cracks occurring in the asphalt layer and in the area around the road and to suggest the suitable treatment of theses cracks. Durri Formation lies under the asphalt layer as sub-grade and exposed along the road at the study area. Mineralogical analysis of the studied samples showed that the Pliocene sedimentary rocks were mainly composed of calcite and clay minerals. Petrographical investigation showed that the studied Pliocene sedimentary rocks of Durri Formation at the studied area were mainly composed of five sedimentary microfacieses including mudstone, marlstone, marly, dolomitic and detrital limestone. Unconfined compressive strength of the studied sedimentary microfacieses was ranging from 155.92 to 291.92kg/cm<SUP>2</SUP>. Mudstone and detrital limestone microfacieses had the lowest values (155.92 to 197.50kg/cm<SUP>2</SUP>); in contrast, marlstone, marly limestone and dolomitic limestone microfacieses had the highest values (218.29 to 291.92kg/cm<SUP>2</SUP>). Swelling pressure value of the mudstone microfacies was 6.50kg/cm<SUP>2</SUP> and the swelling pressure of the marly limestone microfacieses was ranging from 0.44 to 2.10kg/cm<SUP>2</SUP>. Marlstone microfacies had the highest swelling pressure value (16.00kg/cm<SUP>2</SUP>). In contrast, dolomitic and detrital limestone microfacieses had not swelling pressure. Retained percent of the slaking durability test of the studied sedimentary microfacieses was ranging from 88.70 to 94.60% having medium to high durability according to slake durability classification of Gamble, except one high expansive marlstone microfacies had low retained percent (58.00%) and was described as low durability microfacies. Expansive sedimentary rock microfacieses of Durri Formation including mudstone, marlstone and marly limestone microfacieses which represent the sub-grade of the road were swollen due to water coming from the damaged old water pipe that runs parallel to the road and that led to a heave of both the road and the damaged old water pipe. The heave of the old water pipe led to an increase of the damage and the amount of the water coming from this pipe. In addition, drying the saturated Pliocene sedimentary microfacieses due to solar radiation led to a formation of large scale mud cracks having triple junction, polygonal and randomly oriented forms. These cracks occurs on the asphalt layer and in the area around the road at the study area. Grouting of the cracks using cement and chemical stabilization of the expansive sub-grade sedimentary microfacies utilizing lime were suggested to treat these cracks and to reduce the swelling pressure respectively. In addition, monitoring system of the cracks using total station was suggested to evaluate the displacement of these cracks and to determine the relationship between cracks origin and recent tectonic movement at the study area.

Constraints on the history and topography of the Northeastern Sierra Nevada from a Neogene sedimentary basin in the Reno-Verdi area, Western Nevada

Neogene (Miocene–Pliocene) sedimentary rocks of the northeastern Sierra Nevada were deposited in small basins that formed in response to volcanic and tectonic activity along the eastern margin of the Sierra. These strata record an early phase (ca. 11–10 Ma) of extension and rapid sedimentation of boulder conglomerates and debrites deposited on alluvial fans, followed by fluvio-lacustrine sedimentation and nearby volcanic arc activity but tectonic quiescence, until ∼ 2.6 Ma. The fossil record in these rocks documents a warmer, wetter climate featuring large mammals and lacking the Sierran orographic rain shadow that dominates climate today on the eastern edge of the Sierra. This record of a general lack of paleo-relief across the eastern margin of the Sierra Nevada is consistent with evidence presented elsewhere that there was not a significant topographic barrier between the Pacific Ocean and the interior of the continent east of the Sierra before ∼ 2.6 Ma. However, these sediments do not record an integrated drainage system either to the east into the Great Basin like the modern Truckee River, or to the west across the Sierra like the ancestral Feather and Yuba rivers. The Neogene Reno-Verdi basin was one of several, scattered endorheic (i.e., internally drained) basins occupying this part of the Cascade intra-arc and back-arc area.

Structural control on present-day topography of a basement massif: the Central and Eastern Anti-Atlas (Morocco)

The Anti-Atlas basement massif extends South of the High Atlas, and, despite a very mild Cenozoic deformation, its altitude exceeds 1500m in large areas, reaching 3305m in Jbel Sirwa. Structural contours of the present elevation of a polygenic planation surface (the High Erosional surface) and of the base of Cretaceous and Neogene inliers have been performed to characterize the major tectonic structures. Gentle Cenozoic WSW-ENE- and N-Strending folds, of 60 to100km wavelength, reactivate Variscan structures, being the major contributors to the local topography of the Anti-Atlas. Reactivated thrusts of decakilometric to kilometric-scale and E-W trend involving the Neogene rocks exhibit a steep attitude and a small displacement, but they also produce a marked topographic expression. The resulting Cenozoic horizontal shortening along N-S sections across the Anti-Atlas is about 1%. The position of the major anticlinal hinges determines the location of the fluvial divides of the Warzazat basin and the Anti-Atlas, and a structural depression on one of these hinges (Jbel Saghro anticline) allowed the formerly endorheic Warzazat basin to drain southwards. The first Cenozoic structures generating local topography are of pre-mid Miocene age (postdated by 6.7Ma volcanic rocks at the Jbel Saghro), whereas the youngest thrust movements postdate the Pliocene sedimentary and volcanic rocks (involving 2.1Ma volcanic rocks at Jbel Sirwa). In addition to these features, the mean elevation of the Anti-Atlas at the regional scale is also the result of a mantle thermal anomaly reported in previous works for the entire Atlas system.

Catastrophic landslide induced by Typhoon Morakot, Shiaolin, Taiwan

Typhoon Morakot induced the catastrophic and deadly Shiaolin landslide in southern Taiwan on 9 August 2009, resulting in more than 400 casualties. We undertook a geological and geomorphological investigation with the aim of reconstructing the events leading up to this landslide and to clarify factors that contributed to its development. Cumulative rainfall reached up to 1676.5 mm in about three days under the influence of the typhoon, and the Shiaolin landslide, with a volume of 25 × 10 6 m 3, occurred one day after the peak in rainfall intensity. The landslide occurred on a dip slope overlying late Miocene to early Pliocene sedimentary rocks consisting of silty shale, massive mudstone, and sandstone. It started as a rockslide in the upper third of the landslide area and transformed into a rock avalanche that crossed a series of terraces and displaced or buried the village below. It buried the riverbed of the Chishan River and ran up the opposite slope, creating a landslide dam 60 m high, which was breached about 1 h and 24 min later, flooding the village. The velocity of the landslide is estimated to have been 20.4 to 33.7 m s − 1 and its apparent friction angle was 14°, which indicates its high mobility. The detachments in the source area consist of combinations of bedding planes and joints or faults. The landslide was preceded by gravitational deformation, which appeared as hummocky landforms before the landslide and as buckle folds exposed after the event. The landslide deposits consist of fragments of mudstone, shale, and sandstone, as well as clayey material at its base. This clayey material, consisting of illite, chlorite, quartz, feldspar, and calcite, is assumed to have strongly influenced the long, rapid runout.

The syn- and post-collisional evolution of the Romanian Carpathian foredeep: New constraints from anisotropy of magnetic susceptibility and paleostress analyses

The first results of anisotropy of the magnetic susceptibility (AMS) data from the Romanian Carpathian foredeep reveal compression directions generally perpendicular to the highly bended Carpathian orogenic arc. The distribution of the present-day stress field in the Pannonian–Carpathian region reflects pre-imposed plate boundaries that were established during late Miocene collision. Analysis of the AMS along the eastern and southern Carpathian foredeep, at the contacts of the orogenic nappe pile, the lower plate, and the overlying sedimentary rocks, indicates that two factors are critical for the distribution of the stress field during and after collision, i.e. 1) the inherited highly bended plate geometry and 2) the Quaternary deformation that lead to differential vertical and horizontal movements in the SE Carpathians. The AMS analysis was successfully used in the (weakly) deformed Mio–Pliocene sedimentary rocks from the Carpathian foredeep, revealing information about the deformation history of the soft, non-competent rocks where the poor preservation of traditional kinematic indicators (e.g., faults and folds) is difficult.

Tectonic deformation buildup in folded mountain terrains in the October 23, 2004, Mid-Niigata earthquake

The October 23, 2004, Mid-Niigata Earthquake jolted central Japan, causing serious damage in a mountainous region of Pliocene sedimentary rocks. Though aftershocks distribution showed a diffused pattern, it indicated that a blind-thrust fault having a NE–SW strike and inclined towards NW was the most causative. Tectonic deformation caused by this faulting was considered to be one of the causes of flooding that occurred about 8 months after the earthquake. Precise digital elevation models (DEMs) before and after the earthquake were obtained with stereoscopy for aerial photographs and laser imaging detection and ranging technology (LIDAR), respectively, and then compared to detect elevation changes and translations. Lastly, the changes of landforms due to landslides are excluded from the estimated deformations to obtain only the components of tectonic deformations of the ground surface.

Geology, ore deposits and hydrothermal venting in Bahía Concepción, Baja California Sur, Mexico

Abstract Bahía Concepción is located in the eastern coast of the Baja California peninsula and it is shaped by northwestern–southeastern normal faults. These are associated with a 12–6 Ma rifting episode, although some have been reactivated since the Pliocene. The most abundant rocks correspond to the arc related Comondú Group, Oligocene to Miocene, which forms a mainly calc‐alkaline volcanic and volcaniclastic sequence. There are less extensive outcrops of sedimentary rocks, lava flows, domes and pyroclastic rocks of Pliocene to Quaternary ages. The Neogene volcanism in the area indicates a shift from a subduction regime to an intraplate volcanism related to continental extension and the opening of an oceanic basin. The Bahía Concepción area contains numerous Mn ore deposits, being the biggest at El Gavilán and Guadalupe. The Mn deposits occur as veins, breccias and stockworks, and are composed by Mn oxides (pyrolusite, coronadite, romanechite), dolomite, quartz and barite. The deposits are hosted in volcanic rocks of the Comondú Group and, locally, in Pliocene sedimentary rocks. Thus, the Mn deposits formed between the Middle Miocene and the Pliocene. The mineralized structures are associated with Miocene northwestern–southeastern fault systems, which are analogous to those associated with the Cu‐Co‐Zn‐Mn deposits of El Boleo. The Bahía Concepción area also bears subaerial and submarine hot springs, which are associated with the same fault systems and host rocks. The submarine and subaerial geothermal manifestations south of the bay are possibly related with recent volcanism. The geothermal manifestations within the bay are intertidal hot springs and shallow submarine diffuse venting areas. Around the submarine vents (5–15 m deep, 87°C), Fe‐oxyhydroxide crusts with pyrite and cinnabar precipitate. In the intertidal vents (62°C), aggregates of opal, calcite, barite and Ba‐rich Mn oxides occur covered by silica‐carbonate stromatolitic sinters. Some 10–30 cm thick crustiform veins formed by chalcedony, calcite and barite are also found close to the vents. The hydrothermal fluids exhibit mixed isotopic compositions between δ18O‐enriched meteoric and local marine water. The precipitation of Ba‐rich Mn oxides around the vent sites could be an active analog for the processes that produced Miocene to Pliocene hydrothermal Mn‐deposits.

Geology of Los Angeles, California, United States of America

Geology of Los Angeles, California, United States of America

Landform evolution in the Marine Plain region, Vestfold Hills, East Antarctica

Landforms of Marine Plain in the Vestfold Hills contrast with those of most in the Vestfold Hills. They include consistent land surfaces at 40+ m and 25 m, characteristics controlled by orientation of rock features, and imprints of phases of glaciation, deglaciation and marine and freshwater inundation. The 40+ m surface is widespread in the Vestfold Hills and has been noted previously. The 25 m level was an earlier coastline, is more localized and marked by water rounded boulders; it serves to differentiate clearly between two terrains of different relief and erratic distribution. The Pliocene sedimentary rocks below the 25 m level have been dislocated, probably during an interval of glaciotectonism caused by northward movement of sediments under an ice load due to northern extension of the Sørsdal Glacier or expansion of the East Antarctic Ice Sheet some time after the mid-Pliocene. Soil development is active. These features are accompanied by the normal aspects of a glaciated landscape such as glacial striations, sand wedges, erratics, and patterned ground. Wind has been important in transporting sand and developing honeycomb weathering on exposed rock faces.

Geochemistry of the Pliocene basalts erupted along the Malatya-Ovacik fault zone (MOFZ), eastern Anatolia, Turkey: Implications for source characteristics and partial melting processes

The study area is located on the middle sector of the Malatya-Ovacık Fault Zone (MOFZ) in the eastern Anatolia. Four basaltic flows from bottom to top, which are tholeiitic in character and intercalated with Pliocene sedimentary rocks, were erupted along this fault zone. Chemical compositions of these flows reveal some differences between the first flow and others in terms of high-field strength elements (HFSEs) (e.g. Ti, Zr, Nb). Limited variations in compositions within the first flow and upper flows suggest a limited fractionation range. Trace-element patterns exhibit that all the flows have similar and OIB-like patterns without positive peak at Pb and a trough at Nb—Ta, indicating minimal or no crustal contribution. Rare-earth element (REE) patterns indicate that the first flow has flat patterns with negative Eu anomaly, whereas the upper flows have variable enrichments in LREE and depletions in HREE. La/Sm N, Dy/Yb N and Zr/Y ratios exhibit that the degree of partial melting decreases from the first flow to upper flows. Higher values of La/Yb N ratio for the upper flows and depletions at Y and Yb on the trace-element patterns suggest the presence of garnet as a residual phase, which imply that the depth of partial melting took place solely in the garnet-stability field. OIB-like trace-element patterns and trace-element ratios (e.g. La/Nb, Ce/Y and Zr/Nb) emphasize that the melts forming the Arguvan basalt were originated from the asthenospheric mantle rather than the lithospheric mantle.

Paleomagnetic evidence for large en-bloc rotations in the Eastern Alps during Neogene orogeny

We present new paleomagnetic data from the Northern Calcareous Alps and the Central Alps of Austria. All new data are overprint magnetizations and can be subdivided into two groups: In rocks older than earliest Rupelian, two remagnetizations reflecting both clockwise and counter-clockwise rotation were detected. In rocks of late Rupelian and younger ages, only a counter-clockwise rotated remagnetization was found. Our results together with results from previous paleomagnetic studies from the Eastern and Southern Alps suggest two main phases of vertical axis rotation. The first, clockwise rotation affecting the Northern Calcareous Alps was active between earliest to Late Rupelian. We propose a model where the Northern Calcareous Alps are segmented into individual blocks. Within a dextral shear corridor these blocks rotated clockwise due to the counter-clockwise rotation of the Southern Alps and Central Alps. The second, counter-clockwise rotation occurred in the Late Oligocene to Middle Miocene, affecting Eastern and Southern Alps. In this stage of orogeny, the internal massifs of the Western Alps were already accreted to the upper plate and therefore included in counter-clockwise rotation. This rotation is contemporaneous with counter-clockwise rotation in the Apennines and opening of the Balearic basin, and a genetic relationship is suggested. A second step of counter-clockwise rotation, reconstructed from published data, is observed in the sedimentary basins at the southeastern margin of the Eastern Alps, where counter-clockwise rotated Miocene and Pliocene sedimentary rocks are present. This rotation is seen in connection to a young counter-clockwise rotation of the Adriatic plate.