North End Research Articles

Paleolimnological assessment of human impacts on an urban South African lake

North End Lake is a polluted and eutrophic freshwater system located in Port Elizabeth, South Africa. Since the lake is expected to be used for recreational/tourist purposes by 2010, a rehabilitation program will have to be designed. For this reason, we retrieved a sediment core from the central region of the lake to decipher the effect of historical human impacts on the water body. Pre-disturbance paleolimnological inferences indicate that the lake was likely mesotrophic. After ∼1831, when sheep farming activities were undertaken in the catchment, increases in trophic state and changes in sediment composition were observed. After ∼1937, increases in trace metal levels, organic matter, spheroidal carbonaceous particles (SCP) and changes in sediment composition were recorded. The system became eutrophic as indicated by the dominance of the diatom Actinocyclus normanii, a cosmopolitan species often observed in systems where water quality has been dramatically degraded. The conditions worsened after 1986 because of the construction of a storm-water retention system, which intentionally channeled storm-water runoff into the lake. Because of this, extremely high values of fecal coliforms (i.e. 2 × 106 every 100 ml) have been measured in the water column. The paleolimnological information identified the sharp increase in organic content in the uppermost section of the core, and this could be correlated to the operation of the storm-water retention system. Therefore, as an immediate management measure, we suggest that the storm-water retention system should either no longer be utilized, or the storm-water runoff should be treated before disposal into the lake. In addition, an effective sewage system has to be constructed.

Middle Eocene deformation and sedimentation in the Puna-Eastern Cordillera transition (23°-26°S): Control by preexisting heterogeneities on the pattern of initial Andean shortening

The Quebrada de los Colorados Formation, at the north end of Calchaqui Valley in Salta Province, northwest Argentina, preserves evidence of syndepositional deformation since the middle Eocene (ca. 40 Ma) that includes (1) an angular unconformity with the underlying Salta Group (Paleogene), and (2) internal unconformities and changes in vertical facies succession and provenance. Its fossil record [mammalian (notoungulates), middle Eocene] is correlatable to the Casa Grande Formation, which also unconformably overlies the Salta Group; both units record middle Eocene deformation along the eastern border of the Puna Plateau and outline previous fi rst-order mechanical heterogeneities related to the Cretaceous rift basin border. Along the western margin of the Puna, Eocene deformation coincides with thermal (magmatic arc) and mechanical (basin inversion) heterogeneities. Thus, the distribution of Eocene deformation followed an irregular pattern as a consequence of the heritage of preexisting heterogeneities.

Anatomy of an Extreme Event: The July 14–15, 2004 Peterborough Rainstorm

The July 14−15, 2004 rainstorm in Peterborough, Ontario, produced the largest 24 hour total rainfall depth (>220 mm) on record for southern Ontario. The storm was localized over the city for much of this period and rainfall depths and peak rainfall intensities dropped markedly with distance from the city. Peak intensity for 0.5 hour duration at the Trent Weather Station (TWS) in the north end of the city was 93 mm h−1, while peak intensity for one hour duration was 87 mm h−1. Even greater intensities may have occurred in other parts of the city. These intensities exceeded the corresponding 100−year return period values (81 and 53 mm h−1, respectively) estimated from the 1971 to 2002 record at the Peterborough Airport (PA) station, southwest of the city. Another critical characteristic of the July 14−15, 2004 storm was the distinctive shape of its intensity−duration−frequency curve relative to that for the PA. The TWS intensities for the July 14−15, 2004 storm showed a more protracted decline with increasing duration compared to the PA 100−year return period values. The storm produced the largest instantaneous peak flow on record for Jackson Creek, which flows through Peterborough's downtown area. Peak rainfall intensities exceeded the infiltration capacities of artificial surfaces as well as many nominally−pervious surfaces in Peterborough and the ensuing surface runoff contributed to widespread flooding in the city. These results strongly suggest that such storm properties, and their influence on surface runoff generation in urban areas, need to be considered when planning engineering structures such as storm sewer networks and storm water retention ponds in the Peterborough region.

Simulation study on evolution of coalbed methane reservoir in Qinshui basin, China

A dynamic equilibrium model has been proposed to describe the coalbed methane concentration–dissipation evolution process in coal, including its generation, storage and migration. The model, developed with a computational program, has been applied to the Qinshui basin, China, which allows to evaluate features of coal seam of the basin including coal quality and burial, palaeo-geothermal field, and coal organic material maturation evolution history. The simulation study was focused on coalbed methane concentration–dissipation evolution history of the upper and lower main coal seams in the basin. The results indicate that the whole evolution process can be divided into three stages. At the first stage, i.e. the primary concentration stage, gas generation quantity and gas content were lower and only weak diffusion took place. The second stage can be called the active concentration–dissipation stage. During this period, coal organic material was matured at a higher rate, generating a large amount of gas because of abnormal high palaeo-geothermal field in the Middle and Late Yanshan Epoch. As a result, gas content in coal reservoir was higher and gas could be lost in different ways including diffusion, cap outburst and permeation. The third stage can be defined as the absolute dissipation stage at which coal organic material no longer generates gas. Meanwhile much gas was lost mainly by diffusion and partly by permeation. Simulation results further show that, although the high gas generation led to active dissipation in the coal reservoir, there still remains comparatively high gas content on the south and north ends of the Qinshui basin due to the preserving geological conditions. This suggests that these regions are favorable for coalbed methane exploitation which has been confirmed by recent geological exploitations in Qinshui basin.

Lectotypification of Jaltomata weberbaueri (Solanaceae)

In the protologue the type locality is given as ‘‘Ocros, dep. Ancachs, prov. Cajatambo . . . 3400 m.’’ On modern maps Ocros is the capital town of the province Ocros, at the south end of the department of Ancash, while province Cajatambo is at the north end of the department of Lima, just south of the department of Ancash. This species has broadly campanulate, violet corollas to 6 cm across and copious red-orange nectar. A berry measured in the field was 14 3 19 mm and contained 350 seeds (T. Mione, S. Levia & L. Yacher 725). The fruit is orange.

A note on the effects of two versus one feeder locations on the feeding behaviour and growth performance of pigs in a deep-litter, large group housing system

The aim of this experiment was to test the hypothesis that reducing the distance that the pig must travel to feed in a deep-litter, large group system will result in shorter, more frequent feeding bouts, thus improving pig growth performance (feed intake, growth rate and feed:gain). The experiment studied pigs from 9 to 22 weeks of age, using 720 crossbred pigs. There were two trials conducted, utilising 360 pigs each time. The two treatments were: (A) maximum distance to travel to the feeder (MAX) – one feeder located on the north end of the pen and (B) minimum distance to travel to feeder (MIN) – two feeders: one located on the north end of the pen and one at the south end. Feeding behaviour was observed at 14 and 22 weeks of age. There was no evidence to support the hypothesis that reducing the distance that the pigs had to travel to feed, by placing a second feeding station in the pen, produced shorter and more frequent feeding events ( P > 0.05) and improved growth performance ( P > 0.05).

Fra underjordiske dysser til synlige trapezformede anlæg – om stenaldergravene ved Harreby i Sønderjylland

Fra underjordiske dysser til synlige trapezformede anlæg – om stenaldergravene ved Harreby i Sønderjylland

Integral‐Rotation Linear‐Strain Model and Intraplate Deformation‐Strain Field of the Philippine Sea Plate

AbstractIn this paper, we create an integral‐rotation linear‐strain model (IRLSM) for the Philippine Sea plate (PHIL) on the basis of the ITRF2000 velocities of 7 sites on the PHIL. Our study indicates that the current‐day tectonic motion of PHIL is a clockwise rotation, which is consistent with the rotational direction estimated by NNR‐NUVEL‐1A, but largely different from the rotational pole position and angle velocity of NNR‐NUVEL‐1A. Our model can uniformly and accurately describe the current tectonic movement and interior deformation of PHIL as compared with Sella's rigid motion model (RMM). There is an intensive deformation‐strain field within the PHIL and there is consistent eastward deformation on the plate. The deformation rate is small near the central tectonic line and large near the eastern and western boundaries, small at the southern and northern ends and large in the central part. The eastward deformation rate on the Mariana Arc is as large as 48.4mm/a. The NS‐trending deformation on the plate differs evidently in the eastern and western parts with a very small rate in the eastern part and a larger rate near the Manila Trench in the western part. The northward deformation rate at the north end is 11.3mm/a and the southward deformation rate at the south end is 29.3mm/a. The principal strain field is divided into the eastern and western areas from the central tectonic line. In the eastern area, the tensile strain is very intensive, while the compressive strain is very weak. The principal tensile strain is in near‐EW direction, the principal tensile and compressive strain rates increase gradually from the central tectonic line to the east, and the principal tensile strain rate reaches the highest value of 8.58×10−8/a near the southeast boundary (148°E, 15°N). In the western area, the principal compressive strain is very strong in a direction of NW‐SE, while the principal tensile strain is rather weak. From the central tectonic line to the west, the principal compressive and tensile strain rates increase gradually and the principal compressive strain rate reaches the maximum value of 5.71×10−8/a near the northwest boundary (122°E, 23°N). Closely related to the intraplate and surrounding tectonic settings, the spatial variation of deformation‐strain field of PHIL can be considered as a reflection of tectonic stress field.

Nest Fate and Productivity of American Oystercatchers, Cumberland Island National Seashore, Georgia

Abstract The American Oystercatcher (Haematopus palliatus) is listed as a species of high priority by the U.S. Shorebird Conservation Plan and is state-listed as rare in Georgia; however, biologists have not focused on identifying the causes of egg and hatchling losses. In 2003 and 2004, continuous video monitoring was used to document reproductive success of American Oystercatchers and identify causes of nest failure at Cumberland Island National Seashore, Georgia. The modified Mayfield method and program CONTRAST were used to determine and compare survival of eggs and nestlings. Eleven pairs made 32 nest attempts during two seasons. Nine attempts were successful, fledging 15 chicks. Daily survival of clutches was 0.973 (95% CI = 0.960-0.987) for 2003, 0.985 (95% CI = 0.974-0.995) for 2004, and 0.979 (95% CI = 0.970-0.987) for combined years. Daily survival was greater on the North End, than on the South End of the island (χ21 = 7.211, P = 0.007). Eighteen of 20 nest failures during the egg stage and one...

Chinatown Mud

Chinatown Mud Gregory Rossi (bio) Click for larger view View full resolution Figure 1. [End Page 30] Snow fell on New Year's this year, in Chinatown, where it matters. It snowed all over Chicago, but in early February it was only New Year's in Chinatown. And when the next thaw happened in March, it left gobs of soggy firecracker wrappings all over the streets and sidewalks—spitballs forming a wet cushion of Chinatown mud. I bet some Chinese guy was happy with the New Year's snow, saw it as a sign of luck. They always see something as either a sign of luck or a curse. I know about Chinatown mud because my ma uses the post office on Wentworth instead of the one over by the Stock Yards. We're from Bridgeport. You have to tell people [End Page 31] that as soon as possible, Chicago's just that way. Anyway, my ma doesn't drive, so every Tuesday I take a couple hours away from my house-painting business and take her over to Chinatown because she's always mailing a package or needing to buy a book of stamps for letters. The post office is at the south end of Wentworth, a couple of blocks before it passes over the Stevenson Expressway and turns into Bridgeport. From the post office we can see the north end of Wentworth, with those archways and Chinese roofs. So in March, right after Chicago's big thaw, I stand on the sidewalk in front, waiting for my ma, who's inside. And this woman, she's beautiful, comes up and asks me to help her lift a box from the trunk of her car. She wants me to bring it inside the post office, so I walk over to her car. Then, just as the trunk lid opens, there her hand is, waving a Handi-Wipe in my face. She wants me to clean myself first. I stare her down for a second, thinking, "What the—" Then I smile, getting it, and wipe the back of my hand with two fingers. "It's paint, dried, won't come off until later." "Oh," she apologizes. She drives a Jetta, not a Jap car. And she dresses cool, too. Before I lift the box, I fish a card from my pocket and give it to her to show that I'm not some grunt. Kean & Clean, it reads, J. D. Kean owner, Interior and Exterior Decorating, phone 312-555-KEAN. "That's me. J. D.," I say; then I pick up the box and carry it in. When I get inside I hear, "There's your boy," from Imogene behind the counter. She's the clerk my ma will wait an extra turn in line to get. "Hey, Genie." I smile and set the box on the counter. "This is for this woman." Imogene nods at me with her eyes wide open and the ends of her mouth tugging down hard in a smirk. "You're all set, ma'am," I say smiling, knowing I never say "ma'am." "Thank you," she says, with a tiny accent, and hands me her card. Realty USA, hers reads, Elizabeth Chiu, and it has some markings on it, in Chinese. "What's this?" I ask. "The same information in Chinese." "Is your name Elizabeth in Chinese?" [End Page 32] "No, it is not," she says. So I just nod my head and say, "Nice to meet you, Elizabeth." She sticks out her hand. I look at mine, with the paint on it. She smiles. After we shake hands I am careful not to put her card with mine in my wallet and into my back pocket, because once I heard that it's an insult to Oriental businessmen to do so. It's as if you are putting them next to your ass and sitting on them and crushing them. I avoid any potential insult and let the card dangle from my fingers as my mom finishes up and we say good-bye to Genie. * * * After dropping my mom off, I stop back at the job site briefly and find Tommy, my foreman...

Rapid changes in the level of Kluane Lake in Yukon Territory over the last millennium

The level of Kluane Lake, the largest lake in Yukon Territory, was lower than at present during most of the Holocene. The lake rose rapidly in the late seventeenth century to a level 12 m above present, drowning forest and stranding driftwood on a conspicuous high-stand beach, remnants of which are preserved at the south end of the lake. Kluane Lake fell back to near its present level by the end of the eighteenth century and has fluctuated within a range of about 3 m over the last 50 yr. The primary control on historic fluctuations in lake level is the discharge of Slims River, the largest source of water to the lake. We use tree ring and radiocarbon ages, stratigraphy and sub-bottom acoustic data to evaluate two explanations for the dramatic changes in the level of Kluane Lake. Our data support the hypothesis of Hugh Bostock, who suggested in 1969 that the maximum Little Ice Age advance of Kaskawulsh Glacier deposited large amounts of sediment in the Slims River valley and established the present course of Slims River into Kluane Lake. Bostock argued that these events caused the lake to rise and eventually overflow to the north. The overflowing waters incised the Duke River fan at the north end of Kluane Lake and lowered the lake to its present level. This study highlights the potentially dramatic impacts of climate change on regional hydrology during the Little Ice Age in glacierised mountains.

Taiwan's High-Tech Hubbub

This paper looks at the controversy surrounding the construction of a bullet train that would go from the north end of Taiwan to the south. Aside from conflicting with plans for a new semiconductor manufacturing park in Tainan, the transportation project has also been plagued by allegations of irregularities, particularly in the manner by which the vibration mitigation contract was manipulated to favor certain individuals and how construction expenses appear to have been inflated. The high-speed railway is set to begin commercial operation in October 2006 - more than three years behind schedule

PAH-concentrations and compositions in the top 2 cm of forest soils along a 120 km long transect through agricultural areas, forests and the city of Oslo, Norway

The top 2 cm of forest soils were collected along a 120 km long south–north transect running through Norway's largest city Oslo. Forty samples were analysed for their polycyclic aromatic hydrocarbon (PAH 16 as defined by the U.S. Environmental Protection Agency) concentrations and compositions. Local variations in the PAH values are high and the reported concentrations are in general low (maximum sumPAH 16: 2.6 mg/kg). The transect shows distinct differences of sumPAH 16 values from south to north. PAH concentrations are substantially lower in the less populated areas at the north end of the transect than at the urbanised and much more populated south end. Several high values occur in a forested area to the north of Oslo, used for recreation purposes. The PAH distribution patterns point towards a predominantly pyrogenic origin. Local Cambrian carbon-rich black shales can be excluded as sources for PAHs in the forest soils.

Paleoseismology of the southeastern Reelfoot Rift in western Tennessee and implications for intraplate fault zone evolution

The southeastern Reelfoot Rift margin is expressed as a series of collinear scarps across western Tennessee, and shallow S wave reflection profiles, coring, and trenches show late Quaternary faulting along this lineament. At the north end, our seismic profile and coring suggest ≥1.5 m of Wisconsin down‐to‐the‐NW faulting. Coring and trenches across the central lineament show ≥3 m of up‐to‐the‐NW and 8–15 m of right‐lateral Late Wisconsin/Holocene faulting. Averaged late Quaternary right‐lateral slip has been 0.85–0.37 mm/yr on one fault plane at this locality, suggesting that total slip across all southeast rift margin fault planes may accommodate much of the regional strain. Our seismic profile at this site shows up‐to‐the‐west faulting of Eocene strata folded down‐to‐the‐west, indicating structural inversion. Seismic profiles, electrical surveys, coring, and a trench across the southern lineament segment show Holocene faulting. Trenching exposed a vertical fault with ∼0.5 m of late Holocene down‐to‐the‐NW displacement. Nearby, coring and electrical surveys show ∼0.5 m of late Holocene up‐to‐the‐NW faulting. We conclude the southeastern Reelfoot Rift margin is a right‐lateral system with high‐angle faults showing both up‐to‐the‐NW and down‐to‐the‐NW separations. Age constraints permit an earthquake circa 2500 to 2000 years B.P. on the southwestern/central segment of this fault system that ruptured ≥80 km. We suggest the northeastern segment of the southeastern rift margin turned off in Holocene when the Reelfoot step over thrust turned on.

Smong: How an Oral History Saved Thousands on Indonesia's Simeulue Island during the December 2004 and March 2005 Tsunamis

The tsunamis on 26 December 2004 and 28 March 2005 killed only 7 people on Simeulue Island in Indonesia's Aceh province. At Langi, on the north end of Simeulue, which is 40 km south of the December earthquake's epicenter, maximum wave heights exceeded 10 m less than 10 minutes after the shaking ceased. In the more populous south, wave heights averaged 3 m and caused significant structural damage, destroying entire villages. Oral histories recount a massive 1907 tsunami and advise running to the hills after “significant” shaking (∼1 minute). All the interviewed Simeulue survivors knew of this event and of the necessary action. However, Jantang, on the Aceh mainland, suffered far more casualties. Simeulue's oral history provided an extraordinarily powerful mitigation tool that saved countless lives where even a high-tech warning system with a 15-minute response time would have been of no help.

Comprehensive analysis of earthquake source spectra in southern California

We compute and analyze P wave spectra from earthquakes in southern California between 1989 and 2001 using a method that isolates source‐, receiver‐, and path‐dependent terms. We correct observed source spectra for attenuation using both fixed and spatially varying empirical Green's function methods. Estimated Brune‐type stress drops for over 60,000 ML = 1.5 to 3.1 earthquakes range from 0.2 to 20 MPa with no dependence on moment or local b value. Median computed stress drop increases with depth in the upper crust, from about 0.6 MPa at the surface to about 2.2 MPa at 8 km, where it levels off and remains nearly constant in the midcrust down to about 20 km. However, the results at shallow depths could also be explained as reduced rupture velocities near the surface rather than a change in stress drop. Spatially coherent variations in median stress drop are observed, with generally low values for the Imperial Valley and Northridge aftershocks and higher values for the eastern Transverse ranges and the north end of the San Jacinto fault. We find no correlation between observed stress drop and distance from the San Andreas and other major faults. Significant along‐strike variations in stress drop exist for aftershocks of the 1992 Landers earthquake, which may correlate with differences in main shock slip.

Geological structure of the eastern side of the lower Jordan valley/Dead Sea rift: Reflection seismic evidence

Interpretation of recently released seismic reflection lines from the Shuna (Eastern Jericho) Basin combined with re-analysis of the lithologic logs of the deep JV-1 and JV-2 boreholes provide new insights into the structure of the sedimentary basin that formed along the Dead Sea Transform fault north of the Dead Sea in Jordan. We identified four major seismic boundaries in the reflection profiles. The upper two were correlated with borehole stratigraphy. These reflection boundaries include the top of the pan-African basement (R4), the base of the Mesozoic (R3), the base of the Cretaceous (R2), and the base of the post-Eocene section (R1). The latter records sedimentation during the Dead Sea Transform tectonic regime. The total thickness attained by the older sedimentary units (Late Cretaceous through Cambrian) is apparently less than 2 km. We identified a subsurface structure, a faulted monocline, with a N-S trend, sub-parallel to the strike of the Dead Sea Transform, that is named here Al Kharrar monocline. The Al Kharrar structural ensemble is buried by syntectonic lacustrine and fluviatile sediments of the Jordan Valley Group. The structure formed as part of the Dead Sea Transform deformation overprinting the Late Cretaceous Syrian arc folds. Continued tectonic deformation is evident from the prominent unconformity at the base of post-Eocene syntectonic deposits that dip NW, W and S away from the structural high. Along the NW-flank of the Al Kharrar monocline syntectonic sediment thickness is generally less than 0.5 km while along the SW-flank it thickens rapidly to nearly 1 km at the southern end of the interpreted seismic lines. This rapid southern subsidence probably continues into the north end of the Dead Sea Basin the lake's shoreline being located less than 3 km to the south. Young bifurcating faults with reverse slip components cutting the eastern part of the Al-Kharrar monocline are attributed to a positive flower structure. This pattern suggests strike slip with localized active compression northeast of the Dead Sea. It may result from local transpression between fault strands that appear to be a northward continuation of the eastern boundary fault of the Dead Sea Basin.

Wave energy and clast transport in eastern Tasman Bay, New Zealand

AbstractCoarse‐gravel beaches are common features along the eastern margin of Tasman Bay, at the north end of South Island, New Zealand. Although these features have traditionally been interpreted as spits, contemporary incident wave energy appears too small to transport boulders and cobbles persistently along the beaches and platforms by longshore drift. An alternative explanation suggests that boulder beaches are essentially derived in situ from resistant bedrock, which lies seaward and was buried by gravel during the Holocene sea level rise. Wind, wave and clast size data from Cable Bay and the Nelson Boulder Bank were used to resolve this problem. Wave and wind data indicate that waves reaching these areas are derived locally in Tasman Bay, and are limited in size and energy. Hindcasting predicts a 4·7 m wave could propagate from Tasman Bay. However, during Cyclone Yalli, the most intense storm in nearly 40 years of wind records, the largest wave measured in the nearby area of Cable Bay was only 2·7 m high. Maximum orbital velocity on the seabed beneath a 4·7 m is calculated to be 2·9 m s−1, which cannot initiate transport of clasts greater than 0·15 m in diameter. Clasts on the gravel platforms have average diameters greater than this, but some clasts may be as large as 1·0 m in diameter. By comparison, a swash run‐up method predicts that a wave 4·7 m high can transport clasts no larger than 0·3 m in diameter. These data and approximate calculations strongly suggest that the present wave environment in eastern Tasman Bay is not capable of consistently transporting clasts on the boulder platforms by longshore drift. Reduced sea levels in the pre‐Holocene period would further reduce wave energies available in Tasman Bay. Copyright © 2006 John Wiley & Sons, Ltd.

Hybrid Life-Cycle Assessment of Natural Gas Based Fuel Chains for Transportation

This research compares the use of natural gas, methanol, and hydrogen as transportation fuels. These three fuel chains start with the extraction and processing of natural gas in the Norwegian North Sea and end with final use in Central Europe. The end use is passenger transportation with a sub-compact car that has an internal combustion engine for the natural gas case and a fuel cell for the methanol and hydrogen cases. The life cycle assessment is performed by combining a process based life-cycle inventory with economic input-output data. The analysis shows that the potential climate impacts are lowest for the hydrogen fuel scenario with CO2 deposition. The hydrogen fuel chain scenario has no significant environmental disadvantage compared to the other fuel chains. Detailed analysis shows that the construction of the car contributes significantly to most impact categories. Finally, it is shown how the application of a hybrid inventory model ensures a more complete inventory description compared to standard process-based life-cycle assessment. This is particularly significant for car construction which would have been significantly underestimated in this study using standard process life-cycle assessment alone.

The role of material anisotropy in the neotectonic extension of the western Idaho shear zone, McCall, Idaho

Research Article| March 01, 2006 The role of material anisotropy in the neotectonic extension of the western Idaho shear zone, McCall, Idaho Scott Giorgis; Scott Giorgis 1Department of Geology and Geophysics, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53703, USA Search for other works by this author on: GSW Google Scholar Basil Tikoff; Basil Tikoff 1Department of Geology and Geophysics, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53703, USA Search for other works by this author on: GSW Google Scholar Paul Kelso; Paul Kelso 2Department of Geology and Physics, Lake Superior State University, 650 West Easterday Avenue, Sault Ste., Marie, Michigan 59783, USA Search for other works by this author on: GSW Google Scholar Michelle Markley Michelle Markley 3Department of Earth and Environment, Mount Holyoke College, Clapp 320, South Hadley, Massachusetts 01075-6419, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Scott Giorgis 1Department of Geology and Geophysics, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53703, USA Basil Tikoff 1Department of Geology and Geophysics, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53703, USA Paul Kelso 2Department of Geology and Physics, Lake Superior State University, 650 West Easterday Avenue, Sault Ste., Marie, Michigan 59783, USA Michelle Markley 3Department of Earth and Environment, Mount Holyoke College, Clapp 320, South Hadley, Massachusetts 01075-6419, USA Publisher: Geological Society of America Received: 09 Apr 2003 Revision Received: 08 May 2004 Accepted: 25 Jun 2004 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2006) 118 (3-4): 259–273. https://doi.org/10.1130/B25382.1 Article history Received: 09 Apr 2003 Revision Received: 08 May 2004 Accepted: 25 Jun 2004 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Scott Giorgis, Basil Tikoff, Paul Kelso, Michelle Markley; The role of material anisotropy in the neotectonic extension of the western Idaho shear zone, McCall, Idaho. GSA Bulletin 2006;; 118 (3-4): 259–273. doi: https://doi.org/10.1130/B25382.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Basin and Range normal faulting in west-central Idaho reactivates preexisting Cretaceous structures, resulting in a series of normal fault–bound basins. The most intense extensional deformation is concentrated in the Late Cretaceous western Idaho shear zone, resulting in the development of the Long Valley basin. The area affected by the western Idaho shear zone displays two orientations of steep faults: one set of normal faults strikes north-south and is parallel to fabrics within the western Idaho shear zone; the other set strikes east-west and accommodates components of both normal and strike-slip movement. Areas within the Idaho Batholith that do not have strong Cretaceous fabrics (i.e., outside of the western Idaho shear zone) are characterized by a strong preferred north-northeast orientation of faults. From this preferred orientation we infer that the maximum infinitesimal stretch is oriented at 110/290° in this part of the Idaho Batholith. Gravity inversion indicates that the north end of Long Valley is an asymmetric basin about one kilometer deep, with the largest basin-bounding normal fault on the west side of the Long Valley. Paleomagnetic analysis of the Columbia River basalts indicates that the north-south elongate fault blocks within the western Idaho shear zone have not rotated. One block, located just to the west of the western Idaho shear zone, may have rotated counterclockwise. The lack of rotation of north-south oriented fault blocks, in combination with the fault orientations of the Idaho Batholith, indicate that the regional neotectonic deformation within and east of the western Idaho shear zone is characterized by dextral transtension with a divergence vector oriented 130/310°.The extensional reactivation of the western Idaho shear zone demonstrates the effect of material anisotropy at local and regional scales. On a local scale, the mylonitic foliation of the western Idaho shear zone is reactivated as normal faults, even though the regional flow field is oblique to the foliation. On a regional scale, the possible counterclockwise fault block rotation recorded west of the western Idaho shear zone is inconsistent with dextral transtension, suggesting that extensional deformation has reactivated the western edge of the arc-craton boundary as a kinematic domain boundary. We conclude that the preservation of initial features in vertical shear zones and/or plate boundaries is unlikely, due the tendency for well-developed, subvertical fabrics to reactivate, particularly in extension. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.