Evidence for syntectonic crystallization for the mudstone to slate transition at Lehigh gap,Pennsylvania, U.S.A.

Data primarily for phyllosilicates have been obtained for the continuous transitional sequence from mudstone to slate with well-developed slaty cleavage at Lehigh Gap, Pennsylvania, and for slates from quarries in the same area. Samples were studied by optical microscopy, powder X-ray diffraction and electron microprobe analysis, with emphasis on transmission and analytical electron microscopy. Mineral grains are virtually free of deformation-induced strain. Concomitant with the gradual development of cleavage normal to bedding the following changes are observed or confirmed: (1) the orientation of phyllosilicate grains changes discontinuously from being preferentially parallel to bedding to being parallel to cleavage; (2) crystal imperfections as expressed in layer terminations, low angle grain boundary-like features and other defects decrease in density; (3) complex mixed layering is replaced by homogeneous packets of layers of single phases and (4) illite transforms to muscovite, with increase in K + Al and change from a 1M_d to 2M polytype. Slaty cleavage apparently develops due in part to pressure solution of phyllosilicates oriented parallel to bedding, mass transport of components, and crystallization to form new grains parallel to cleavage. It reflects transitions from imperfect, metastable phases toward ordered stable phases in a low temperature (∼225°C) metamorphic environment.     

Sinkhole formation and subsidence along the Dead Sea coast,Israel

More than 4,000 sinkholes have formed since the 1980s within a 60-km-long and 1-km-wide strip along the western coast of the Dead Sea (DS) in Israel. Their formation rate accelerated in recent years to >400 sinkholes per year. They cluster mostly in specific sites up to 1,000 m long and 200 m wide, which align parallel to the general direction of the fault systems associated with the DS Rift. The abrupt appearance of the sinkholes reflects changes to the groundwater regime around the shrinking DS. The eastward retreat of the shoreline and the lake-level drop (1 m/year in recent years) cause an eastward and downward migration of the fresh/saline groundwater interface. Consequently, a subsurface salt layer, which was previously enveloped by saline groundwater, is gradually being invaded and submerged by relatively fresh groundwater, and cavities form due to the rapid dissolution of the salt. Collapse of the overlying sediments into these cavities results in sinkholes at the surface. An association between sinkhole sites and land subsidence is revealed by interferometric synthetic aperture radar (InSAR) measurements. On a broad scale (hundreds of meters), subsidence occurs due to compaction of fine-grained sediments as groundwater levels decline along the retreating DS shoreline. At smaller scales (tens of meters), subsidence appears above subsurface cavities in association with the sinkholes, serving in many cases as sinkhole precursors, a few weeks to more than a year before their actual appearance at the surface. This paper overviews the processes of sinkhole formation and their relation to land subsidence.     

Sinkhole hazards along the eastern Dead Sea shoreline area, Jordan: a geological and geotechnical consideration

For the last four decades, the level of the Dead Sea has been subjected to continual variation which, among other important factors, has led to the occurrence of much subsidence and many sinkholes in the southern Dead Sea area. Sinkhole activities occurred repetitively and were observed in open farms, across roads, near dwellings and near an existing factory, thus causing a serious threat to the locals and farmers of the area and their properties. This paper presents the main results from detailed geological and geotechnical studies of this area. Aerial photo interpretation and borehole drilling aided these studies. Parallel geophysical investigations (vertical electrical sounding and seismic refraction) and hydrological and hydrogeological studies were made by others in the same area to also investigate this phenomenon. It was found that sinkholes are aligned to and follow old water channels and are concentrated parallel to the recent shoreline of the Dead Sea. The development of subsurface cavities is associated mainly with the variation in the level of the Dead Sea over the four past decades, the presence of regional salt intrusion under the surface of salt beds, the fluctuation of the water table and continuous dissolution and the active tectonism of the area. Moreover, this work showed that the area is still under active sinkhole hazards and other parts of the area will be inevitably affected by sinkholes in the future.No practical engineering solution to this problem is feasible. Received: 1 July 1999 / Accepted: 11 October 1999     

The Liquefaction-Collapse Sinkhole Formation and Assessment of Its Danger to Buildings and Structures

Doklady Earth Sciences - A poorly studied genetic type of sinkhole formation, which is typical for areas where karstified rocks are covered by water-saturated or unsaturated cohesionless soils is...     

Sinkhole distribution in a rapidly developing urban environment: Hillsborough County, Tampa Bay area, Florida

Sinkhole formation in Florida is a common event. The Florida karst plain is significantly altered by human development and sinkholes cause considerable property damage throughout much of the state. We present in this paper a morphometric analysis of karst depressions in the Tampa Bay area, and the relation with the known distribution of sinkholes. We selected the Tampa Bay area because it is particularly susceptible to the evolution of karst depressions in relation with development of the built-up environment. Karst depressions were mapped from the 1:24,000 USGS topographic maps and a morphometric analysis was performed by using parameters such as shape, circularity index, perimeter, area, length, width, and orientation. Maps showing the distribution of depression density, and the sectors with greatest areas of karst depression were produced using a GIS. These results were compared with data compiled from the database of sinkhole occurrences in Florida maintained by the Florida Geological Survey. Our analysis demonstrates that the distribution of new sinkhole occurrences differs from the distribution of existing sinkholes, indicating that there are processes acting today that are influencing karst landscape formation that are different from those acting in the past.     

Structure and late quaternary activity of the northern Owens valley fault zone, Owens valley, California

The Fish Springs fault is a primary strand in the northern end of the Owens Valley fault zone (OVFZ). The Fish Springs fault is the northwest strand in a 3-km-wide left echelon step of the OVFZ which bounds the Poverty Hills bedrock high. The Fish Springs fault strikes approximately north-south, dips steeply to the east, and is marked by a prominent east-facing scarp. No other faults in the OVFZ have prominent east-facing scarps at the latitude of Fish Springs, which indicates that the Fish Springs fault has accommodated virtually all of the local late Quaternary vertical displacement on the OVFZ.

The Fish Springs fault exhibits normal dip slip with no measurable lateral slip. Vertical displacements of a Late Pleistocene (0.314 ± 0.036 Ma, 2σ) cinder cone and of an overlying Tahoe-age (0.065–0.195 m.y.) alluvial fan are 76±8 m and 31±3 m, respectively. The maximum vertical 3.3. m. Two nearly equal vertical displacements of the active stream channel in the Tioga-age fan total 2.2. m. Vertical displacement of a stream terrace incised into the cinder cone is 1.2 ± 0.3 m. The minute amount of incision into that terrace indicates that uplift of the terrace probably occurred during the 1872 Owens Valley earthquake.

Three displacements of 1.1 ± 0.2 m each apparently have occurred at the Tioga-age fan since the midpoint of the Tioga interval, allowing an average recurrence interval of 3500 to 9000 years. Based on the age and displacement of the cinder cone, the average late Quaternary vertical displacement rate is 0.24 ± 0.04 mm/yr (2σ). At this rate, and assuming an average vertical displacement of 1.1 ± 0.2 m per event, the average recurrence interval would be 4600 ± 1100 years (2σ). The recurrence interval for the Fish Springs fault is similar to that for a strand in the southern part of the OVFZ which also ruptured in 1872.

Right-lateral, normal oblique slip characterizes the OVFZ. The location of the Poverty Hills bedrock high at a left step in the north-northwest-striking fault zone is consistent with the style of slip of the zone. The pure normal slip on the north-striking Fish Springs fault and the alignment of local cinder cones along north-striking normal faults indicate that the late Quaternary maximum horizontal compression has been oriented north-south at the north end of the OVFZ. Data from southern Owens Valley indicate a similar stress regime there. Late Quaternary slip on the OVFZ is consistent with north-south maximum horizontal compression.     

The incised valley of Baffin Bay,Texas: a tale of two climates

Baffin Bay, Texas is the flooded Last Glacial Maximum incised valley of the Los Olmos, San Fernando and Petronila Creeks along the north‐western Gulf of Mexico. Cores up to 17 m in length and high‐resolution seismic profiles were used to study the history of Baffin Bay over the last 10 kyr and to document the unusual depositional environments within the valley fill. The deposits of the Baffin Bay incised valley record two major and two minor events. Around 8·0 ka, the estuarine environments backstepped more than 15 km in response to an increase in the rate of sea‐level rise. Around 5·5 ka, these estuarine environments changed from environments similar to other estuaries of the northern Gulf of Mexico to the unusual suite of environments found today. Another minor flooding event occurred around 4·8 ka in which several internal spits were flooded. Some time after 4·0 ka, the upper‐bay mud‐flats experienced a progradational event. Because of its semi‐arid climate and isolation from the Gulf of Mexico, five depositional environments not found in the other incised‐valley fills of the northern Gulf of Mexico are found today within Baffin Bay. These deposits include well‐laminated carbonate and siliciclastic open‐bay muds, ooid beaches, shelly internal spits and barrier islands, serpulid worm‐tube reefs and prograding upper‐bay mud‐flats. Based on these unusual deposits, and other characteristics of Baffin Bay, five criteria are suggested to help identify incised valleys that filled in arid and semi‐arid climates. These criteria include the presence of: (i) hypersaline‐tolerant fauna; (ii) aeolian deposits; and (iii) carbonate and/or evaporite deposits; and the absence of: (iv) peat or other organic‐rich deposits in the upper bay and bay‐margin areas; and (v) well‐developed fluvially dominated bayhead deltas.     

The precambrian magmatic rocks of timna valley,southern israel

In the Timna Valley in southern Israel a small ‘layered’ serpentinized-chloritized gabbroic rock occupies the core of Har Timna and an alkali-potassium syenite to granite composes most of the area. Intermediary rock types between the basic and acid rocks are common. This magmatic sequence is in agreement with the latest model suggested for the last phase of Precambrian activity in the Arabo-Nubian massif.Mantle-derived basaltic magma intruded the crust from a shallow, layered magmatic chamber. This magma was the heat source that caused a partial melting of the crust and the formation of A-type, alkali, potassium rich, granitic magma. This acid magma was the source of the alkali rhyolitic dykes and the Biqat Hayareah volcanic rock types. This whole process took place in a cyclic manner under a tensional tectonic regime. Creation or reactivation of deepseated faults caused a new pulse of intrusion of basic magma and a remelting of the crust.Serpentinization was the last phase - hydrothermal activity at temperatures of less than 400°C. This hydrothermal activity could have been caused by radioactive heating of the alkali granite after its final stage of crystallization or by recent Dead Sea Rift hydrothermal waters.     

The relationship between methane migration and shale-gas well operations near Dimock,Pennsylvania, USA

Migration of stray methane gas near the town of Dimock, Pennsylvania, has been at the center of the debate on the safety of shale gas drilling and hydraulic fracturing in the United States. The presented study relates temporal variations in molecular concentrations and stable isotope compositions of methane and ethane to shale-gas well activity (i.e., vertical/horizontal drilling, hydraulic fracturing and remedial actions). This was accomplished by analyzing data collected, between 2008 and 2012, by state and federal agencies and the gas well operator. In some cases, methane migration started prior to hydraulic fracturing. Methane levels of contaminated water wells sampled were one to several orders of magnitude greater than the concentrations due to natural variation in water wells of the local area. Isotope analyses indicate that all samples had a thermogenic origin at varying maturity levels, but from formations above the hydraulically fractured Marcellus Shale. The results from the initial water well samples were similar to annular gas values, but not those of production gases. This indicates that leakage by casing cement seals most likely caused the impacts, not breaks in the production casing walls. Remediation by squeeze cementing was partially effective in mitigating impacts of gas migration. In several cases where remediation caused a substantial reduction in methane levels, there were also substantial changes in the isotope values, providing evidence of two sources, one natural and the other man-induced. Sampling water wells while venting gas wells appears to be a cost-effective method for determining if methane migration has occurred.

     

The Late Devensian and Flandrian history of the Teith valley, Scotland

Two episodes of glaciation are identified in the Teith valley, central Scotland. During the earlier episode, the valley was wholly occupied by an ice sheet, but during the later episode, correlated with the Loch Lomond Readvance, ice only occupied the upper part of the valley. The deglaciation which followed each episode was marked in particular by sequences of kame and outwash terraces. A terrace related to the second episode grades into a large fan buried beneath a sequence of marine deposits in the nearby Forth valley. The latest of these, the carse clays, are related to Flandrian terraces in the Teith valley.     

The palaeo‐valley infilling glaciogenic Sarah Formation,an example from Rahal Dhab palaeo‐valley,Saudi Arabia

The Sarah Formation is a glaciogenic sedimentary unit deposited along the Gondwana margin during the latest Ordovician ice age and represents a major hydrocarbon reservoir in northern Saudi Arabia. Large‐scale glacial palaeo‐valleys cut into the Qasim Formation and were infilled by the Sarah Formation. Post‐glacial transgression in the earliest Silurian resulted in the deposition of the Qusaiba Shale Member and associated organic‐rich basal source rocks, which cap the Sarah Formation infilled palaeo‐valleys. This unique setting makes the Sarah Formation an important emerging exploration target in Saudi Arabia. This study focuses on the facies and depositional architecture in seismic‐scale outcrops of the Sarah Formation in north‐western Saudi Arabia. The Rahal Dhab palaeo‐valley provides a 100 km long dip‐oriented cross‐section which has been covered by 24 vertical sections, sedimentary architectural analyses at metre to kilometre scale and by three cored shallow boreholes. In the Rahal Dhab palaeo‐valley, the Sarah Formation was deposited in a proglacial setting that ranged from marginal marine to offshore prodelta and is made up of three units: (i) the Sarah Sandstone; (ii) the Sarah Shale; and (iii) the Uqlah Member. This study shows the relationships between these three units and architectural controls on reservoir quality in this system. This paper contributes to the regional understanding of the Sarah Formation, and the new depositional model of the Rahal Dhab palaeo‐valley provides an outcrop‐reservoir analogue for hydrocarbon exploration in adjacent areas.     

The Middle Pleistocene terraces of the central Waveney valley,Earsham, south Norfolk,UK

Although substantial work has been done on the pre-glacial terraces of East Anglia, very little systematic work has been done to understand the origin of river terraces in East Anglia that have formed since ice last covered the region. This paper records the results of studies of exposures and borehole records in ‘classical’ Quaternary terrace landforms that are considered to have formed since the Anglian (MIS 12) Glaciation, in the middle Waveney Valley. These features have been examined in terms of their morphological and sedimentological properties, in order to provide a detailed record of their form and composition, understand their processes of formation, and identify their stratigraphical status. The results show that the main body of the highest terrace (Homersfield Terrace, Terrace 3) is not composed of river sediments, but of shallow marine sediments, and is a remnant of early Middle Pleistocene Wroxham Crag. River sediments, in the form of Anglian age (MIS 12) glaciofluvial Aldeby Sands and Gravels also exist in the area as a channel fill, cut through the Wroxham Crag, and reflect outwash erosion and sedimentation from a relatively proximal ice margin to the west. The results mean that the interpretations previously presented for the terrace landforms of the middle Waveney valley are not applicable. The issue of why the terrace stratigraphy, hitherto identified in East Anglia cannot be related to that for the River Thames to the south and the rivers of Midland England to the west, still requires further research.     

Fracture controls on valley persistence: the Cairngorm Granite pluton,Scotland

International Journal of Earth Sciences - Valleys are remarkably persistent features in many different tectonic settings, but the reasons for this persistence are rarely explored. Here, we examine...     

The relationship between spring discharge,drainage, and periglacial geomorphology of the Frome valley,central Cotswolds,UK

The Frome near Stroud is an unusual example of a Cotswold stream that flows west, against regional topographic and geological dips. As a result, a deeply incised and irregularly indented valley has been carved through a succession of Jurassic strata of varying competencies and permeabilities. The landscape has been modified by intense, locally variable periglacial erosion during Devensian times, resulting in a number of characteristic landforms including landslip, valley bulging, and limestone cambering. This study assesses the importance of spring and river discharge upon the sculpting of such a unique landscape. An extensive discharge survey of 67 hillside springs has revealed two well defined springlines that form at stratigraphical interfaces. Groundwater issues in greater abundance from the lower, Inferior Oolite, aquifer; discharge here is more regular throughout the year. Groundwater flow is a function of the regional SE strata dip, and of the heavily fissured character of the limestone, which provides rapid preferential flow pathways. Discharge of the River Frome was measured at four localities and cannot be explained by a simple model using upstream drainage area, as the channel can run completely dry over limestone in summer. The position of the springs has influenced the development of a line of settlements along the valley sides, as well as the proliferation of industry in the valley floor, with mills sited at points of high stream power. Geology affects valley shape, width, and orientation; the structure of the jointed limestone aquifer guides spring discharge and the orientation of many dry valleys.     

Emplacement and Differentiation of the York Haven Diabase Sheet, Pennsylvania

Many of the high-Ti quartz-normative tholeiitic intrusive sheetsin the early Mesozoic rift basins of the Eastern USA exhibitlateral differentiation from mafic cumulate units, through diabase,to relatively evolved iron-rich rock types. We have investigateda representative example in detail, the York Haven sheet inthe Gettysburg basin of south–central Pennsylvania. Itranges in thickness from 330 m to 675 m, and we have sampledit from base to top along four separate stratigraphic sectionsevenly spaced over the extent of the intrusion. The easternmostsection (York Haven) is entirely basaltic bronzite cumulate(average 15 vol. % bronzite), whereas the westernmost (ReesersSummit) consists of diabase and low-MgO diabase with a middleto upper ‘sandwich zone’ of ferrogabbro. The interveningsections feature rock types transitional between the two end-membersequences. Chemically, the rock series shows a gradual eastto west depletion of compatible elements (Mg, Ca, Ni, and Cr),and enrichment of incompatible elements [Ti, Fe, Na, K, P, Cu,Zr, Th, Ta, Hf, Sb, Cs, As, platinum group elements (PGEs),and rare earth elements (REEs)]. We suggest two main processes for the trends observed in theYork Haven sheet. First, flow differentiation during ascentand lateral injection of the parental magma produced a tongueof basaltic bronzite cumulate that thins from southeast to northwestand passes laterally into diabase, and, at the distal end ofthe intrusion, into low-MgO diabase. Then, in the latter stagesof crystallization, densitydriven hydrothermal fluids transportedincompatible elements westward, into structurally higher partsof the intrusion. Reaction of this residual aqueous fluid withpartly crystallized low-MgO diabase produced a zone of ferrogabbrorich in hydrothermal replacement products (e.g., Cl-amphibole,biotite, ferrohypersthene, and skeletal ilmenite) and precipitates(e.g., quartz, fayalite, Cl-apatite, sulfides, and PGE minerals). ^* Present address: US Geological Survey, Hawaiian Volcano Observatory, Hawaii National Park, Hawaii 96718     

The geochemistry of mercury in sedimentary rocks and soils in Pennsylvania

The mercury contents of 11 sandstone, 11 shale and 6 limestone samples from Pennsylvania average 7, 23 and 9 ppb Hg, respectively, which is lower than the values for sedimentary rocks reported in the literature. The differences may arise because many of the reported high values are from regions characterized by more mineralization and volcanism than is present in central Pennsylvania. The lowest values found for shale and sandstone in Pennsylvania (0.4 and 0.5 ppb Hg, respectively) are lower by an order of magnitude than the lowest previously reported values. The mercury content of sedimentary rocks varies markedly due to the effects of volcanism, organic material and sulfur in reducing environments, iron and manganese oxides in oxidizing environments, diagenesis, hydrothermal processes, and the thermal history of the rock.Soils in Pennsylvania have much greater amounts of mercury than their parent rocks even after taking into account possible residual concentration, suggesting that mercury is added to the soils from an outside source. Rain is the major source of mercury absorbed by the soil. A portion of the absorbed mercury returns to the atmosphere, establishing a rain-soil-atmosphere mercury cycle. The general enrichment of mercury in soils and sediments compared to rocks is supported by the observation that the mercury content of rain is greater than freshwater. The much higher values of mercury in unconsolidated sediments compared to sedimentary rocks suggest that mercury is lost during diagenesis.Man's contribution of mercury to the surface environment is nearly equal to the natural contribution. Industrial loss contributes more than 65 per cent of man's total, and the contribution of fossil fuel consumption is small, although it may be locally important. The implications of mercury loss and absorption by soils may be an important factor in concentrating mercury in crops and other living matter, especially near industrialized areas.     

Geomorphology and palaeoecology of the Mark valley (southern Netherlands): geomorphological valley development during the Weichselian and Holocene

Vandenberghe, Jef, Bohncke, Sjoerd, Lammers, Wim & Zilverberg, Liesbeth 1987 03 01: Geomorphology and palaeoecology of the Mark valley (southern Netherlands): geomorphological valley development during the Weichselian and Holocene. Boreas , Vol. 16, pp. 55–67. Oslo. ISSN 0300–9483.
The actual area of the Mark valley is limited by the borders of an Early Weichselian erosion phase. The subsequent accumulation has resulted in the formation of a Weichselian Pleniglacial terrace which has been deeply dissected by Late Glacial erosion. The present alluvial plain is formed by Late Glacial and Holocene infilling. The maximum incision of the Late Glacial fluvial phase was reached slightly before 11,780 B.P. and involved locally dry conditions which have given rise to aeolian activity during this period (Older Dryas). On the deepest parts of the Pleniglacial terrace, a backswamp environment was established until the end of the Alleröd. At the beginning of the Younger Dryas the river invaded the terrace but shortly afterwards aeolian activity progressively increased. At the climax of the Younger Dryas, deep seasonal frost or local permafrost characterized the Mark valley.