Slide Sheets Research Articles

Effects of Slide Sheet Use and Bed Position on Muscle Activities in the Low Back and Extremities: A Pilot Experimental Simulation Study.

Low-friction slide sheets (SS) are designed to reduce compression loads on the body during manual handling tasks, such as boosting patients. Using SS has been shown to decrease muscle activity in the lower back and upper extremities. However, it is unclear if this effect varies with different bed positions. To investigate this, we studied the effects of SS use, bed height, and their combination on muscle activity during a simulated patient boost. Thirty-three Japanese undergraduate students (age 21.0 ± 1.1 years; 14 men, 19 women) participated. Participants were asked to boost a dummy figure on the bed three times each using four conditions. During the repositioning task, electromyography of eight muscles of the lower back and upper and lower extremities, hip and knee joint flexion angles, pelvic forward tilt angle, and position of the center of mass based on the posterior superior iliac spine were evaluated. Electrophysiological activities of muscles of lower back and upper extremities were significantly lower with SS than without it in both bed positions (30% and 40% of body height); the reduction in muscle activities with SS use was 20% to 40%. Lowering the bed did not affect the SS effect magnitude on reducing muscle activities, although postural changes, including hip and knee joint flexion, were observed. SS reduced muscle activities in the back, upper, and lower extremities when the bed was in the low position, and this effect persisted at a bed height of ≥30% of the participant's height.

Overcoming Fundamental Restrictions: Novel Multistation Measurement While Drilling Survey Correction

Summary The traditional multistation analysis (MSA) method for drilling string magnetization compensation considers significantly limited information, only consisting of a single measurement while drilling (MWD) six-axis survey run. The limitations of this approach are an excessive scatter in the corrected azimuth values, poor accuracy in attitudes near the horizontal east/west directions, and low robustness of the algorithm, which make it nearly impossible to automate the survey processing. A novel MSA correction, involving further elaboration of the conventional MSA method, is proposed in this study. The proposed algorithm utilizes all available drilling information, including data from geomagnetic reference, error models, multiple six-axis runs, bottomhole assembly (BHA) designs, and slide sheets. This improvement moves the optimization task to find the survey correction vector from multiple independent spaces of total gravity field, total magnetic field, and dip angle (GBD) for each MWD run into a single GBD + north/east/vertical space of the entire well. Unlike the conventional MSA, which processes only a small portion of the available information, each MWD runs independently, the proposed algorithm finds the survey correction vector for all MWD runs simultaneously with additional constraints of trajectory steering and drillstring interference (DSI) modeling. Consequently, the proposed MSA method provides the best borehole positional accuracy for MWD surveys. Depending on the input conditions, the accuracy of the proposed MSA can be improved by an order of magnitude relative to the accuracy performance of the conventional MSA correction. In addition, this approach demonstrates better stability and robustness than the conventional MSA. The proposed method provides high startup performance, especially during the drilling of the tangent section. This is critically important for building automatic drilling systems and avoiding nonproductive time. Under normal conditions, the proposed MSA algorithm does not have a no-go zone and allows the correction of MWD surveys at the horizontal east/west tangent sections.

Community Structure of Periphytic Diatoms in Early-stage Marine Biofilms in a Mariculture-impacted Area

Periphytic diatoms constitute a major part of complex unicellular aggregations called marine biofilm or periphyton, of which little is known about in tropical marine environments. The early-stage community structure of periphytic diatom genera on two artificial substrates – glass slide and polycarbonate sheets – was characterized. These artificial substrates were placed underwater for 6 d and examined on Days 1, 3, and 6 in four sites around Santiago Island, Bolinao, Pangasinan, Philippines, with different relative distances from the intensive milkfish mariculture area. Correlations of diatom community structures in these sites with physico-chemical factors were investigated. The five most abundant diatom genera – namely, Cylindrotheca, Nitzschia, Navicula, Amphora, and Pleurosigma – exhibited a weak correlation with nutrients. Less abundant genera Pseudonitzschia, Haslea, Bacillaria, Thalassionema, Rhizosolenia, Eucampia, Diploneis, Asterionellopsis, Chaetoceros, Bacteriastrum, Licmophora, Skeletonema, Lioloma, Thalassiosira, and Thalassiothrix showed a positive correlation with nutrients. Among sites, the highest benthic diatom cell densities (4.6 × 105 cells cm−2) after 6 d was found in Lucero. Generic richness and diversity varied among sites, with the highest diversity (H’ = 1.58) on Day 1 in Tomasa, the site nearest to the mariculture area, whereas the highest richness (D = 2.17–3.26) for all days and diversity (H’ = 1.38–1.52) for Days 3 and 6 were recorded in Silaqui, the most distal site. Generally, the highest diversity and richness were found on Day 1, which then decreased on succeeding days in all sites. The lack of a clear pattern in community structure among sites relative to the proximity of these sites to the mariculture area may in part be attributed to the presence of other nutrient sources. Results of the study provide baseline information on the variability of periphytic diatom community structure in a mariculture-impacted area, and insights on how benthic diatoms may be used in monitoring the impacts of nutrient pollution.

When Slick Is Not Smooth: Bottomhole Assembly Selection and Its Impact on Wellbore Quality

Summary Appropriate selection of a bottomhole assembly (BHA) is critical to the success of a drilling operation. In US land drilling, these assemblies are often selected using local heuristics rather than rigorous analysis. These heuristics are frequently derived from the incentives of the directional contractor as opposed to incentives for the operator. Large motor bends enable more rotation through the curve and reduce the possibility of tripping for build rates. Unstabilized motors are believed to aid sliding and tool face control. Both of these practices lead to drilling a more tortuous wellbore and may cause problems later in the well’s life. This study quantifies the impact of these practices and proposes alternatives that can balance the needs of directional companies with the desire of operators for high-quality wellbores. More than 60 conventional motor assemblies used to drill curves in the Eagle Ford and Permian basins were analyzed for directional performance using commercial drillstring analysis software. The sliding and rotary tendencies were modeled through the curve across a range of potential drilling conditions. Expected build-rate models were validated by comparison to the maximum achieved doglegs in the directional surveys. When available, additional validation was performed using motor yields calculated from slide sheets. The validated models were compared to the dogleg severity (DLS) requirements for each assembly’s respective well plan. Comparisons of slide ratios and slide/rotate tendencies of the BHAs were used to estimate the impact on wellbore quality using the tortuosity metric proposed by Jamieson (2019). Typical well plans for both basins had curves of 10° per 100 ft with no well plan greater than 12° per 100 ft. Typical BHAs were capable of >15° per 100 ft under normal sliding conditions, with some assemblies capable of >20° per 100 ft of build. Predicted build rates were validated by slide sheets and observed DLSs. Common characteristics among assemblies with excess capacity were high-bend angles (≥2°) and minimal stabilization. These understabilized assemblies exhibited unstable rotary tendencies across a range of drilling parameters. The combination of high-build rates with rotary drop masks the true level of tortuosity in a wellbore, leading to an underestimation of unwanted curvature. A minority of the assemblies used a lower motor bend angle (<2°) combined with multiple stabilizers. These assemblies had a more consistent directional capability throughout the curve and exhibited stable behavior in rotation. The success of these assemblies confirms that there is potential for tailoring BHA designs to improve wellbore quality without compromising the technical objectives of the well. As increasing attention is afforded to the topic of wellbore quality, it is important to have methods available to technically achieve high-quality wellbores. In addition to the management of drilling practices, it is also important to have an appropriate BHA design that can enable those practices

Slide-Drilling Guidance System Optimizes Directional Drilling Path

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 194096, “Slide-Drilling Guidance System for Directional-Drilling Path Optimization,” by Can Pehlivanturk and John D’Angelo, The University of Texas at Austin, and Dingzhou Cao, Anadarko, et al., prepared for the 2019 SPE/IADC International Drilling Conference and Exhibition, The Hague, 5–7 March. The paper has not been peer approved. The amount of uncertainty related to directional drilling makes accurate drilling challenging, leaving much to human know-how and interpretation. Additionally, few path-planning methods in the literature consider the directional steering tool being used. The formulation of the problem of optimization varies greatly between rotary steerable systems (RSS) and mud-motor configurations. Additional cost functions and constraints exist for mud-motor use, which significantly increases the complexity of the problem. A slide-drilling-guidance system is proposed to combat this issue and to help automate directional drilling. Introduction Despite the numerous technological advancements that made directional drilling a reality, directional drilling is still viewed more as an art than as a science. The drillstring and penetrated rock formations are complex systems whose interaction makes prediction and planning highly uncertain. Analytical, geometric approaches have sought to formulate the curvature of the well path in a way that eases the planning process and ensures smooth trajectories. The literature on directional drilling is rich in well-path-optimization methodologies based on operating constraints and well-path geometry. However, few of these methods seem to consider the tool used to generate the well path, and those that do typically use RSS because these yield better results from a technical perspective. Mud motors, however, are still used extensively because of cost effectiveness. The complete paper proposes a directional-drilling guidance system targeted at downhole motors and slide drilling to generate optimal well paths and associated slide-drilling instructions. Instead of a simplistic shortest-path approach, various cost functions aimed at maximizing the value of the well are considered. For wellbore-propagation prediction, a computationally efficient and accurate model is used. The proposed methodology is built into a software package and is being developed and implemented currently for use in the real-time drilling (RTD) system of an operator. The three main modules of the software are discussed in detail in the complete paper. The wellbore-propagation model predicts the evolution of the borehole and returns the predicted 3D path given the initial condition and a slide sheet. The fitness-evaluation module calculates the fitness of the 3D path using a cost function and returns a scalar value representing the overall value of the path. The genetic-algorithm solver generates candidate slide sheets and approaches an optimal slide sheet by iterating over generations. Software Implementation Graphical User Interface (GUI). The GUI serves as a tool to visualize the well under consideration and to study the optimization results and the effectiveness of the approach. The GUI is written in MATLAB and uses the Runtime environment. Here, the data for the planned path and the actual survey data are loaded. The planned path and the surveyed path (up to the time for which such data are available) are displayed.

Cytology smears for DNA extraction: Practical approach for selecting the best slide.

Next generation sequencing (NGS) to detect actionable genetic abnormalities is standard of care in advanced stage lung adenocarcinoma. Many studies have shown that the molecular results obtained from fine needle aspiration cytology material are comparable to those obtained from formalin-fixed tissue samples. We undertook this study to validate DNA extraction from cytology material for molecular studies and to find any correlation between DNA yield, pattern of tumour cells and tumour fraction. DNA was extracted from 34 cytology slides of pulmonary adenocarcinoma cases with predetermined EGFR mutation status. Cytology slides were reviewed for pattern of tumour distribution and tumour fraction. NGS was performed on five slides with variable DNA and compared with original results. There were 14 alcohol-fixed and 20 air-dried smears. The mean DNA yield was 1.74μg and median of 0.4μg (range, 0.02-21μg). Tumour fractions varied from 10% to 90%. No correlation was found between tumour fraction and DNA yield (P=0.14). The mean DNA yield was high in slides with tumour throughout the slide (sheets or scattered clusters) as compared to rare scattered clusters and/or single cells. EGFR mutation was found in four of the five cases sent for NGS lung panel while one case revealed BRAF mutation. DNA with good quantity and quality can be extracted from the cytology slides for NGS irrespective of type of fixation. DNA yield has better correlation with distribution pattern of tumour cells on the slides rather than tumour fraction.

Forces involved when sliding a patient up in bed.

This study investigated the effects of 3 different types of slide sheets upon hand forces while sliding a patient up in bed. The sheets used included the reusable Arjo Maxislide, the McAuley disposable sheet, and a standard cotton sheet. Hand forces were measured from 38 male and female participants as they slid a 'patient' up in bed. A repeated measures ANOVA with 5 levels to the repeated factor (number of sheets and sheet type) was used, along with post-hoc repeated measures contrasts to compare differences between each condition. A significant reduction in required force occurred when using the friction reducing sheets as compared to the cotton sheets when used according to manufacturer recommendations, as well as a reduction in one of the single friction reducing sheet categories compared to the cotton. However, it is important to note that there was still substantial force being placed on the participants. This study illustrates the importance of using friction reducing slide sheets while engaging in manual patient handling. Future research should investigate the forces involved with other friction reducing materials and methods as well as the possibility of combining said materials and methods.

Biomechanical evaluation and perceived exertion of a lateral patient-handling task

BACKGROUND: Slide sheets (SS) are friction-reducing devices used during patient-handling tasks. A modified SS position (modSS), with the slider placed beneath the regular bedsheet, may decrease a caregiver’s workload and reduce low back injuries, as the SS could remain in place for longer periods of time, thus reducing patient re-positioning frequency. OBJECTIVE: To investigate the efficacy of modSS use on back muscle activity, pulling force, and perceived effort during lateral patient-handling tasks, and determine whether lumbar electromyography (EMG) correlates with perceived effort (RPE) during such tasks. METHODS: Ten females completed 9 lateral patient-handling tasks with 3 simulated patients (45 kg, 68 kg and 91 kg) and 3 SS conditions (absent, normal, modSS). Outcomes included peak pulling force, back muscle EMG, RPE and subjective reports of low-back discomfort and preference. RESULTS: ModSS use was as effective as or better than normal SS use at reducing back muscle EMG, pulling force, RPE and perceived discomfort in all 9 conditions, when compared to no SS ( p< 0.05). The relationship between RPE and EMG was moderately strong (r = 0.75). CONCLUSION: ModSS use may reduce caregiver injury rates, as it reduces biomechanical and perceived demands associated with lateral patient-handling tasks at least as well as normal SS use, if not better.

Comparison of Caregiver Forces Required for Sliding a Patient up in Bed Using an Array of Slide Sheets

This study investigated the forces required while performing the common patient handling task of moving a patient up in bed using traditional cotton sheets or friction-reducing slide sheets. Twenty-nine healthy adult participants 18 to 36 years of age were recruited as "patients." Hand forces and lumbar compression and shear forces were calculated on the "caregiver" when performing the repositioning task. Significant differences in lumbar compression and lumbar sagittal shear forces at L4-L5 and at L5-S1 were found among the three sheet types. No difference in peak sum hand force was found between the slide sheets; however, the traditional cotton sheet created the greatest force at the hands and every sheet exceeded the recommended summative hand force of 35 pounds. As such, sliding patients up in bed may contribute to increased risk of musculoskeletal injuries in caregivers.

Comparison of Caregiver Forces Required for Sliding a Patient Up in Bed Using an Array of Slide Sheets

Comparison of Caregiver Forces Required for Sliding a Patient Up in Bed Using an Array of Slide Sheets

Microcirculation System with a Dialysis Part for Bioassays Evaluating Anticancer Activity and Retention

Medicines are distributed to the whole body and excreted over time. A micromodel of the circulation-excretion system was developed to mimic these processes. This system comprised a dialysis part, a microperistaltic pump, and a target tissue. This microcirculation system was created on a microchip composed of a glass slide and polydimethylsiloxane sheets with microchannels fabricated by photolithography. A dialysis membrane was settled between two channels to form the dialysis part, and a pneumatic peristaltic pump was used to make the solution flow. The excretion and half-life of solute substances absorbed to albumin were changed according to their affinity to the protein. MCF-7 human breast cancer cells were cultured as target cells for drug samples, and the activities of anticancer agents were assayed using our system. Our data demonstrated that the anticancer activity of docetaxel or thio-TEPA could be assayed on the microcirculation-excretion chip. This system may allow for reduced consumption of cells and reagents compared to those required for conventional in vitro bioassay systems.

The utilization of seismic interpretation to identify and describe the shallow subsurface structures in the southeastern Mediterranean Sea

The shallow subsurface structures of the offshore Nile Delta particularly in the southeastern Mediterranean were dealt through the interpretation of 40 two-dimensional seismic reflection lines. The interpretations of seismic reflection data indicated that the principle sedimentary processes affecting the study area include three main structural groups according to their origin and development. The first group of structures comprises of gravity-driven structures, which include slides, slumps, turbidities, and debris flow. Slides are present in three different forms on seismic sections: slide sheets, slides with scar, and wedges of slide materials. Slumps have many geometrical shapes: lenses, spoon-shaped slumps, and slumped blocks bound by growth faults. Debris flows are present as transparent unit (due to the dispersion of seismic waves at debris boundaries), whereas turbidities appear on the seismic profiles, which are formed of closely spaced parallel thin reflectors analogous to their thin stratified bedded layers. The second group of structures is syn-depositional structures, which include growth faults, and tilted and rotated fault blocks. Growth faults are listric in shape and usually dip seaward; displacements along the fault plane increase with depth. Some of these faults are incipient, and some are complicated and intersected by secondary antithetic faults. Most of the growth faults soles out basin wards and in the evaporites layer. Fault blocks are formed due to the Messinian evaporite movement vertically and horizontally due to its mobility as a consequence to the pressure resulted from the overloading of Pliocene sediment. The third group of structures comprises evaporite flow structures such as diapiric structures and graben collapse structures. The surface of the Messinian evaporites was folded during its flow as a consequence to the lateral compression acted on the mobile strata of the Messinian evaporites to form diapiric triangular structures and creates a stress zone faulting and fractures system. These conditions led to the formation of collapse structures or graben collapse structures.

Intervening to improve quality and safety of care for the obese in an orthopaedic unit: A collaborative action-oriented quality improvement project in a Magnet recognised facility

Our study aimed to identify and address impediments to nursing staff providing safe and quality care for obese patients on the orthopaedic unit of a medium sized medical/surgical acute care Magnet Recognised hospital using a participatory action oriented quality improvement methodology. Both registered nurses and assistants-in-nursing indicated that placing a blue 'B' Magnet on the patients' room door as a way of identifying the patient as an obese patient ('B' for bariatric) was the most helpful and practical intervention. This was followed by the intervention of using at least three staff to roll a patient and use of two slide sheets for the larger patients with a BMI greater than 30 or weight greater than 100 kg. Collaborative participatory action-oriented quality improvement methods can engage staff at all levels in positive change to health service delivery in order to enhance the quality and safety of care for both patients and staff. Our project demonstrated that simple but effective interventions in the care of obese patients are readily adopted by staff who have had the opportunity to be involved in their development, implementation and evaluation.

Tips for Protecting Critically Ill Patients From Pressure Ulcers

Animportant focus in critical care units is maintaining circulatory, respiratory, and renal function. Care of critically ill patients also requires interventions that are designed to prevent pressure ulcers, an all-too-common complication of immobility, inadequate nutrition, and illnesses or medications that affect blood flow and perfusion. Pressure injuries may be avoidable when consistent attention is given to assessment, nutrition, and appropriate positioning within appropriate time frames. At least 10 published guidelines for the prevention and treatment of pressure ulcers can be found on the National Guidelines Clearinghouse Web site (www.guideline.gov). A planned repositioning schedule tailored to each individual patient is recommended in all pressure ulcer prevention guidelines. Recently, the National Pressure Ulcer Advisory Panel, in collaboration with the European Pressure Ulcer Advisory Panel, announced updated guidelines for prevention and treatment of pressure ulcers. Each guideline recommendation is supported by a rigorous review of the literature and a strength-of-evidence rating. The goals in progressive mobility programs, specifically prevention of complications associated with immobility, are aligned with recommended interventions for pressure ulcer prevention. Techniques for progressive mobility can be combined with repositioning techniques recommended for prevention of pressure ulcers.

Late Neoproterozoic carbonate productivity in a rifting context: the Adoudou Formation and its associated bimodal volcanism onlapping the western Saghro inlier, Morocco

Abstract An interval of episodic carbonate productivity, lithostratigraphically recognized as the ‘Calcaires inférieurs’ (upper member of the Adoudou Formation), took place across the Neoproterozoic–Cambrian transition onlapping the western Saghro inlier, Morocco. Sedimentation of the ‘Calcaires inférieurs’ was highly variable: in relatively stable substrates, a peritidal-dominated mixed platform is recorded where deposition was primarily controlled by autocyclic processes and accommodation space availability, whereas, in unstable substrates, the tectonic activity associated with the inherited block-faulting basement led to deposition of complex slide sheets composed of penecontemporaneous isoclinal folds and disrupted strata. The uppermost part of the ‘Calcaires inférieurs’ displays a negative δ 13 C shift reaching values of −6.5‰. This shift may represent the δ 13 C excursion to −6‰ that marks the Neoproterozoic–Cambrian boundary in the western Anti-Atlas. Two volcanic episodes bracketed the carbonate productivity. They consist of lower basaltic flows and an upper rhyolitic ignimbrite, with a SiO 2 gap between 52 and 74 wt%. The basic rocks resemble those of tholeiitic magmas in continental rifts. The felsic rocks show high light to heavy rare earth element abundances and negative Nb, Ta, P and Ti anomalies, and were probably generated as a result of either fractional crystallization coupled with relative crustal contamination, or from a different magmatic source. The lower basic flows of tholeiitic affinity predated and geochemically differ from the alkaline magmatism of the Alougoum volcanic complex (Boho jbel) that surrounds the neighbouring Bou-Azzer inlier.

Stratigraphic reconstruction of the Ediacaran Yangtze platform margin (Hunan province, China) using a large olistolith

The southeast-facing slope of the Yangtze platform during deposition of the Ediacaran Doushantuo Formation included several submarine slides and olistostromes of regional extent. These platform margin-derived slides provide windows into the contemporaneous platform margin. This manuscript proposes a paleoenvironmental reconstruction and evolution of the Ediacaran Yangtze platform margin using facies analysis of one of these large-scale slide sheets, which transported shallow-marine platform facies. The base of the slide sheet shows dolomite, chert, evaporites, and phosphorites, lithological association with “tepee” structures and storm-induced microbreccia. Dolomitised limestones with current-related sedimentary structures overlie these facies. Thus, the Ediacaran Yangtze platform may have evolved from a shallow, rimmed platform with shallow, restricted, back-rim, basins developed on the margin to a wave-dominated, shallow subtidal platform. Sequence analysis applied to the slide sheet sediments allows relative dating of the sliding.

Large-scale slope instability at the southern margin of the Ediacaran Yangtze platform (Hunan province, central China)

Thirteen stratigraphical sections from the Doushantuo Formation, Hunan province, central China, indicate large-scale mass wasting of the Yangtze platform margin between the late Neoproterozoic glaciation and the earliest Cambrian. Numerous sedimentary discontinuities, due to regional slides, olistostromes, and slumps have modified the stratigraphy between the shallow-water carbonate platform margin and the siliciclastic slope. Slide blocks are predominantly gently deformed and are largely composed of shallow water dolomitized limestones. Slide sheets may reach a regional extent of up to ∼5000 km 2 and are embedded in anoxic shales at an unknown water depth.

Detachment folding–related Miocene submarine slope instability in the Romagna Apennines (Italy)

The relationships between slope failure and growing thrust‐related structures have been explored in the Miocene Marnoso‐Arenacea foredeep basin (Romagna Apennines). Impressive fossil slump layers are distributed along the footwall of the regional Mount Nero thrust, which evolved from detachment fold to breakthrough thrust. During the detachment fold stage, development of growth strata on the rotating forelimb was preceded by the emplacement of slump layers that are currently part of the Mount Nero thrust footwall. In this process, sliding is assumed to nucleate along the contacts between different lithologies in the semiconsolidated rock mass. The conditions of sliding, specifically the critical angle of sliding αcrit, are quantified by adding the influence of cohesion of sediments to the equilibrium analysis reported in Hubbert and Rubey's (1959) classical work. The resulting angles αcrit are discussed with respect to the depth of the basal surface of sliding and pore fluid pressure states. On the basis of such an analysis and field work results, an evolutionary model is proposed in which slide sheets come from the crest and upper forelimb of growing detachment folds and attain a deeper detachment depth as the forelimb rotates and steepens. Pore fluid pressure is found to play a major role by radically decreasing the critical angle of sliding. Likewise, localization of overpressures may also control the depth of sliding during progressive forelimb rotation. To allow sliding along gently dipping bedding surfaces, slope failure is interpreted as being related to the reactivation of anisotropies represented by lithological discontinuities.

Large-scale gravity sliding in the Miocene Shadow Valley Supradetachment Basin, Eastern Mojave Desert, California

The Miocene Shadow Valley basin in the eastern Mojave Desert of California developed above the active west-dipping Kingston Range-Halloran Hills extensional detachment fault system between 13.5 and ca. 7 mybp. Although mass-wasting processes are common phenomena in supradetachment basins, the Shadow Valley basin is an exceptional locale for the study of such processes, especially rock-avalanches and gravity sliding. A score of megabreccias, interpreted as rock-avalanche deposits, and half that number of very large (> 1 km 2, up to 200 m thick), internally intact gravity-driven slide sheets are interbedded with various sedimentary facies. The slide sheets, variably composed of Proterozoic crystalline rocks and Proterozoic, Paleozoic, and Tertiary sedimentary strata, moved across both depositional and erosional surfaces in the basin. Although the majority consist of Paleozoic carbonate rocks, the largest slide sheet, the Eastern Star crystalline allochthon, contains Proterozoic gneisses and their sedimentary cover and is now preserved as klippen atop Miocene lacustrine and alluvial fan deposits over an area > 40 km 2. Estimates of slide sheet runouts into the basin from higher eastern and northern source terranes range from approximately a few km to > 10 km; in most cases the exact provenances of the slide blocks are not known. The basal contacts of Shadow Valley slide sheets are characteristically knife sharp, show few signs of lithologic mixing of upper- and lower-plate rocks, and locally exhibit slickensided and striated, planar fault-like bases. Pronounced folding of overridden Miocene lacustrine and fan deposits beneath the Eastern Star allochthon extends to depths up to 40 m at widely scattered localities. We conclude that this slow moving slide sheet encountered isolated topographic asperities (hills) and that stress transfer across the basal slide surface produced folding of footwall strata. Synkinematic gypsum veins in footwall playa sediments, with fibers up to 12 cm long, have trends and shear senses compatible with the direction and sense of displacement of the overriding crystalline allochthon. The undisturbed veins, which closely parallel the base of the slide sheet, attest to high fluid presence and pressure in the playa sediments—factors facilitating allochthon movement across them. The long length of the fibers, indicative of a protracted dilational process, is incompatible with a catastrophic rate of emplacement. We believe that the only explanation for slow displacement of this allochthon and other gravity driven slide sheets across the landscape is that they formed as slumps on high, steep bedrock slopes and that their elevated heads drove their toes across lower fan and playa deposits. Initial detachments from bedrock sources were facilitated by pre-existing structural and stratigraphic anisotropies. Detachment of the Eastern Star allochthon from the bedrock of Shadow Mountain likely occurred by inversion along the playa-ward dip of a preexisting Mesozoic thrust fault within Proterozoic rock units.

The influence of tectonic regime on chalk deposition: examples of the sedimentary development and 3D‐seismic stratigraphy of the Chalk Group in the Netherlands offshore area

AbstractThe sediments of the Upper Cretaceous to lower Palaeogene Chalk Group were deposited through a wide range of depositional processes. Chalk was originally formed by settlement of coccolithophorid skeletal remains from suspension in the water column, with bottom currents redistributing the sediment shortly after deposition. Locally, tilting of the sea‐floor resulted in mass‐movement of chalk at scales varying from decimetre‐thick turbidites to slumps and slide sheets that were up to hundreds of metres thick. Syn‐depositional tectonic activity, therefore, constituted an important control on chalk facies. To study this relation in more detail, a three‐dimensional (3D)‐seismic stratigraphical analysis was carried out, comparing two study areas that experienced contrasting syn‐depositional tectonic evolutions. The Vlieland offshore area, which underwent gradual subsidence and westward tilting during deposition of the Chalk Group, is characterised by parallel and continuous reflections thought to represent pelagic chalk deposits. In the Dutch Central Graben, which was tectonically inverted during the Late Cretaceous to early Palaeogene, discontinuous and irregular seismic reflections that indicate large‐scale reworking of sediment are found. The improved image quality of 3D‐ vs. 2D‐seismic data allowed us to study the detailed geometry of allochthonous chalk bodies and aided the identification and tracing of the often subtle intra‐Chalk Group unconformities, resulting in a subdivision of the Chalk Group into seven seismic sequences.