Sag Structures Research Articles

A Novel Hydrophobic Polyimide Film with Sag Structure Derived from Multi-Hybrid Strategy.

Polyimide (PI) film with hydrophilic greatly limits their application in the field of microelectronic device packaging. A novel hydrophobic PI film with sag structure and improved mechanical properties is prepared relying on the reaction between anhydride-terminated isocyanate-based polyimide (PIY) containing a seven-membered ring structure and the amino-terminated polyamide acid (PAA) via multi-hybrid strategy, this work named it as hybrid PI film and marked it as PI-PIY-X. PI-PIY-30 showed excellent hydrophobic properties, and the water contact angle could reach to 102°, which is 20% and 55% higher than simply PI film and PIY film, respectively. The water absorption is only 1.02%, with a decrease of 49% and 53% compared with PI and PIY. Due to that the degradation of seven-membered ring and generation of carbon dioxide led to the formation of sag structure, the size of sag structures is ≈16.84 and 534.55nm for in-plane and out-plane direction, which are observed on surface of PI-PIY-30. Meanwhile, PI-PIY-30 possessed improved mechanical properties, and the tensile strength is 109.08MPa, with 5% and more than 56% higher than that of pure PI and PIY film, showing greatly application prospects in the field of integrated circuit.

Tectonostratigraphic analysis of the syn-rift infill in the Drava Basin, southwestern Pannonian Basin System

The Drava Basin in the SW Pannonian Basin System (PBS) was initially formed by passive rifting with accompanying sedimentary infill. Although this has been the subject of much previous work, an account of tectonic control has been lacking. Based on cores, wire logging, and seismic data, the tectonostratigraphic interpretation, depositional systems, and control on depositional systems of the syn-rift infill of the eastern part of the Drava Basin were studied. The rifting phase is characterised by the formation of half-grabens, grabens, a sag, and supradetachment basin structures with structural ramp and structural highs. The syn-rift infill can be divided into second-order tectonostratigraphic sequences corresponding to the early and late rift stages. The second-order sequences are further subdivided into third-order tectonostratigraphic sequences formed in response to higher-order tectonic events associated with local rift migration. In contrast to the early-stage structures, the late-stage rift structures are primarily controlled by extensional detachments that represent parts of the Drava Rift Fault System (DRFS). The early syn-rift is characterised by continental deposition through alluvial fans, fan deltas, and lacustrine environments. The late syn-rift stage is characterised by marine deposition in shallow water, fan deltas, and submarine slope-aprons, with deep marine sedimentation and intense volcanic activity. The ramp, basin slopes, and fault scarp slopes represent the major sediment transport pathways involved in the formation of alluvial fans, fan deltas, or submarine slope-aprons. Basinal sedimentation and major depocenters are located within synforms formed by structural lows in the geometry of extensional detachments. This study gives an example of syn-rift tectonic control for the SW part of the PBS and the influence of detachment geometry on basin fill. We have presented an approach based on 3D seismostratigraphic interpretation of tectonostratigraphic sequences, and the correlation of seismic facies with depositional environments developed in a back-arc setting.

Wave Transformation on a Fringing Reef System With Spur and Groove Structures

AbstractSpurs and Grooves (SAG) are coral forereef structures with their main axis normal to the reef crest. The dimensions of SAG vary considerably on a global scale. Despite being common, there are relatively few studies that relate SAG morphology with wave transformation processes. Measurements of wave transformation are presented from Xahuayxol, Quintana Roo, Mexico, across a SAG zone with larger spurs than in previous studies. An array of pressure sensors and current meters sampling at high frequencies were deployed over 8 days. Our results show that SAG structures are more important for wave transformation than previously reported since a high rate of wave energy flux dissipation (up to 0.077 kW/m2) was found and the corresponding wave dissipation friction factor, fw (1.01), was four times higher as compared to other reefs. We also found that the wave dissipation rate over the spurs can be up to three times higher than the adjacent grooves (0.098 vs. 0.028 kW/m2). This study demonstrates that SAG plays a very important role in wave dissipation over coral reefs.

Soft-sediment deformation structures (SSDS) in the Ediacaran and lower Cambrian succession of the Aksu area, NW Tarim Basin, and their implications

The Tarim Basin, the largest continental and marine superimposed basin in the northwestern part of China, is typically viewed as a stable and uninterrupted sequence during the Ediacaran-Cambrian transition. Undeformed strata, thick shallow marine sediments and thin deep marine sediments characterize the basin. In this study, we identify various types of soft-sediment deformation structures (SSDS) and an unconformity at four localities in the Aksu area, NW Tarim Basin. SSDSs include large-scale load structures, plastic intrusions and extrusions, load casts and pillow structures, liquefied breccias, ground fissures and lateral liquefaction, boudinage-like SSDSs, mound and sag structures, slumps, and small syn-sedimentary faults. The deformed layers are sandwiched between undeformed sedimentary rocks. Deformation features are found in the (a) lower Cambrian Yuertusi Formation consisting of interbedded thin black shale and phosphorite chert layers, thick-bedded shallow gray dolomite and silicate layers; (b) upper Ediacaran Qigebulak Formation composed of dark gray to gray dolomite and grayish green mudstone layers; (c) in the brown sandstone layers of the lower Ediacaran Sugaitebulak Formation. These units contain fluvial-lacustrine, nearshore, carbonate platform, shelf, and bathyal sedimentary environments. The SSDSs and more detailed stratigraphy indicate a dynamic setting that includes the heretofore unrecognized unconformities, a sub-stratigraphic sequence interface and high magnitude seismic events. The SSDS were produced during rifting, short sub-aerial exposure and frequent seismic disturbances. Combined on the carbon and oxygen isotope records, gamma radiations and the concentrations of main and trace elements, the differences between the SSDS layers and the undeformed layers are preliminary analyzed. We propose that this sequence not reflect a stable tectonic-sedimentary environment during the Ediacaran-Cambrian transition. Therefore, these units provide a unique glimpse into paleo-tectonic activity and paleo-ecological-environmental variation in the Tarim Basin during the late period of Rodinia breakup and the assembly of Gondwana.

Volcanic reconstruction of the Paleoproterozoic Stroud Breccia: Understanding the transition from a primitive to mature arc and its impact on VMS ore-formation, Snow Lake, Manitoba, Canada

The Stroud Breccia is a ≤400 m thick package of dominantly felsic volcaniclastic rocks within the Paleoproterozoic Snow Lake arc assemblage. It stratigraphically overlies the ore-interval for the Anderson, Stall and Rod volcanogenic massive sulfide (VMS) deposits at Snow Lake, Manitoba, Canada and occupies the stratigraphic interval between the underlying primitive arc Anderson sequence and the overlying mature arc Chisel sequence.The Stroud Breccia is interpreted to be a product of subaqueous pyroclastic and effusive, dominantly rhyolitic, volcanism, and concomitant subsidence. It consists of felsic tuff to lapilli-tuff, crystal-rich felsic tuff, felsic lapillistone, felsic tuff breccia, mafic tuff to lapilli-tuff, heterolithic tuff breccia to breccia and rhyolite. The finer felsic volcaniclastic units are characterised by angular or broken quartz crystals, angular lithic rhyolite lapilli, and pumice. Fine ash, broken crystals and pumice suggest they were deposited by eruption-fed density currents associated with a phreatomagmatic eruption. The coarser felsic volcaniclastic units are characterized by blocks of strongly quartz-feldspar porphyritic rhyolite and pumice and are interpreted to have been deposited during the reworking of pyroclastic debris flow deposits on the seafloor during mass wasting events at fault scarps. Planar and cross laminations, graded beds and bomb sag structures suggest the mafic tuff to lapilli-tuff unit was deposited by a combination of subaqueous eruption-fed density currents and eruption driven ballistically emplaced ejecta, likely through subaqueous tephra jetting.Lithofacies analyses, and geochemistry has allowed comparison between the felsic volcanic rocks of the Stroud Breccia and those that host the Anderson, Stall and Rod VMS deposits. Detailed mapping has led to the identification of synvolcanic faults, defining basins and volcanic vents, that indicate that the process of incipient rifting of the Anderson sequence primitive arc continued during emplacement of the Stroud Breccia. These structures also define magma and fluid pathways critical in controlling the formation of the Anderson VMS deposits, meaning they represent deep-seated and long-lived structures that can be used as vectors to mineralization at depth.

Stratigraphy and reservoir quality of the turbidite deposits, western sag, Bohai bay, China P.R.

Stratigraphic and subtle reservoirs such as pinchouts, sand lenses and unconformities have been discovered in Bohai basin. These reservoirs occur in sub-basins and sag structures called depressions. A prolific depression is the Liaohe depression that has been filled with rapidly changing mixed alluvial fan deposit of the Cenozoic age. Attempts made at recovering residual hydrocarbon from the subtle reservoir have necessitated the re-evaluation of available data to characterize and model the prolific Shahejie Formation turbidite deposit occurring as pinchouts and sand lenses for hydrocarbon assessment, reservoir quality and possible recovery through enhanced methods. Methods employed covered well logs analysis, clustering analysis for electrofacies and fuzzy logic analysis to predict missing log sections. Stratigraphic and structural analysis was done on SEGY 3D seismic volume after seismic to well tie. Stochastic simulation was done on both discrete and continuous upscaled data. This made it possible to correctly locate and laterally track identified reservoir formation on seismic data. Petrophysical parameters such as porosity and permeability were modeled with result of clustering analysis. Result shows that electrofacies converged on 2 rock classes. The area is characterized by the presence of interbeded sand-shale blanket formations serving as reservoir and seal bodies. The reservoir quality of the formations as seen on the petrophysical analysis done is replicated in simulation volume results. Reservoir rocks have porosity between 0.1 and 0.25, permeability between 1 and 2mD and hydrocarbon saturation as high as 89%. Lithofacies are observed to be laterally inconsistent, sub-parallel to dipping and occurring as porous and permeable continuous beds or pinchouts hosting hydrocarbon. The stochastic stratigraphic model depicts rock units in associations that are synsedimentary. The prevalent configuration gotten from the model gave an insight into exploring and developing the field for enhanced oil recovery of the heavy hydrocarbon of this area.

Sedimentological evidence of Pleistocene earthquakes in NW Poland induced by glacio-isostatic rebound

Soft-sediment deformation structures are abundantly present in two levels within Warthanian/Eemian lacustrine sediments at Siekierki, near the Polish/German border. The two ‘event horizons’ show intense folding, collapse, sag and load structures, indicative of liquidization and fluidization. The structures must have been caused by sudden shocks, most probably resulting from earthquakes that were induced by glacio-isostatic rebound, probably after the Warthanian deglaciation. Such seismites have not been previously recognized in Polish Quaternary sediments. They provide supporting evidence for glacio-isostatic movements that were interpreted up till now based on drilling, lithostratigraphic, geophysical and geodetic data. The recognition of seismites in NW Poland may help recognize other deformed ‘event horizons’ in Pleistocene sediments as glacio-isostatic or neotectonic seismites.

Reservoir systems of the Pennsylvanian lower Atoka Group (Bend Conglomerate), northern Fort Worth Basin, Texas: High-resolution facies distribution, structural controls on sedimentation, and production trends

This study defines the depositional systems of mature lower Atoka Group reservoirs, structural influence on their sedimentation, and sand-transport patterns at a higher degree of resolution and over a significantly larger part of the play area than previously conducted. The reservoir systems are characterized by pronounced variations in depositional style, even between stratigraphically adjacent systems. They represent a variety of on-shelf siliciclastic depositional facies, including gravelly braided river, fluvial-dominated delta, and low-sinuosity incised river deposits. Penecontemporaneous, high-angle, basement-rooted reverse faults and genetically associated folds of the Mineral Wells–Newark East fault system exerted direct control on the orientation of complex fluvial-channel and delta-distributary sand-transport pathways and the geometry of deltaic depocenters. Multiple contemporaneous source areas, including the Ouachita fold belt to the southeast, the Muenster arch to the northeast, and the south flank of the Red River arch, also contributed to the complexity of sandstone trends in the lower Atoka play area. Bubble maps of normalized per-well first-year production and total cumulative production allow qualitative conclusions regarding geologic controls on production distribution. Most wells with optimal gas production occur within two northwest-trending production fairways that coincide with primary sandstone trends of one or more reservoir systems. Highest per-well oil production exists where lower Atoka reservoir facies occur above oil-prone Barnett Shale source rocks (vitrinite reflectance 1.1% Ro) in the western and northwestern parts of the study area. Widespread fault-bounded, karst-produced sag structures that extend vertically from the source rocks through the lower Atoka Group most likely served as hydrocarbon-migration conduits and formed traps for both oil and gas.

La erupción estromboliana violenta y freatomagmática de 1723 en el volcán Irazú, Costa Rica

The largest of the recorded historic eruptions at Irazu volcano began on February 16, 1723 and lasted until at least December 11. We here critically examine deposits of this eruption exposed on the summit of Irazu. Our reconstruction of the eruption is based on the unique chronicle of the Spanish governor Diego de la Haya. The eruption began with a < 10 cm thick surge deposit of phreatic origin showing block sag structures. The deposit is overlain by 6 m-thick coarse-grained basaltic andesitic non-graded juvenile fallout tephra consisting of highly vesicular (22-59 vol.%) bombs and lapilli with minor hydrothermally altered lapilli (1-7 vol.%) and rare light colored andesitic vesicular lapilli (< 1%). These fallout deposits are interpreted as strombolian, possible generated during a short-lived scoria cone at the end of February 1723, dominate volumetrically in the proximal facies. Overlying <1.2 m thick phreatomagmatic deposits of finely laminated lapilli-bearing gray ash (fallout and surge deposits) some with contorted bedding and sag structures, are in turn overlain by a 1.2 m thick bed of ash matrix-rich bomb/block deposit. The 1723 eruption was accompanied by shallow volcano-tectonic earthquakes (Modified Mercalli scale Intensity MMI VI-VII, magnitude ML ~5.5) that possibly facilitated magma/water interaction. Phenocrysts in the basaltic andesite (~53-55 wt.% SiO2) bombs comprise plagioclase (6.1-21.6 vol.%, An52-35), clinopyroxene (2.5-10 vol.%), orthopyroxene (0.7-2 vol.%), olivine (0.1-2.2 vol.%; Fo76-88) and Fe/Ti-oxides (0.1-1%), in a groundmass (66.5-90.3 vol. %), dominated by plagioclase (An69-54), clinopyroxene and opaques in brown and black glass with the same range of chemical composition (SiO2= 57-64 wt.%). Rare white pumiceous lapilli in the scoria deposits are high-K, hornblende andesite (SiO2: 58-60 wt.%), geochemically unrelated to the scoria deposits. Thus, two different magmas co-existing in the magma chamber were mingled shortly before, and during, the eruption, suggesting that the eruption was triggered by magma mingling between hornblende andesite and basaltic andesite magma.

Quantifying the origin and geometry of circular sag structures in northern Fort Worth Basin, Texas: Paleocave collapse, pull-apart fault systems, or hydrothermal alteration?

Three-dimensional seismic data reveal numerous subcircular sag structures in the northern Fort Worth Basin. The structures are defined by concentric faults that extend vertically upward 760–1060 m (2500–3500 ft) from the Lower Ordovician Ellenburger Group. The largest structures remained active into the lower Desmoinesian Strawn Group. Criteria are outlined for defining seismically resolvable sag structures, and a detailed quantitative analysis of the geometries of these circular features was undertaken. Results are compared and contrasted, with reviews of subsurface collapse mechanisms and strike-slip processes that are known to produce subsurface circular to subcircular sag geometries in plan view. In this manner, we develop several constraints for differentiating collapse-related sag structures from strike-slip–related sag structures. Qualitative analyses indicate that the geometries observed are strongly analogous to subsurface collapse features where material is removed at depth to create a void, into which the overburden subsequently sags and collapses. Quantitative analyses support the formation of these features by incremental collapse and suprastratal deformation above a linked system of coalesced, collapsed paleocaves within the Ellenburger Group. Observations and criteria presented herein provide valuable information in defining seismically resolvable collapse features worldwide and help distinguish sag features of collapse affinity from those of other origins.

A Review of Coalesced, Collapsed-Paleocave Systems and Associated Suprastratal Deformation

Coalesced, collapsed-paleocave systems and associated suprastratal deformation appear to be prominent diagenetic/structural features in carbonate sections at/near composite unconformities. The basic architecture of the system can be divided into two sections. The lower karsted section, where high-density cave formation took place, is preserved as massive breccias commonly displaying a rectilinear pattern in map view. The overlying suprastratal deformation section is characterized by large, circular to linear sag structures containing faults and fractures. Regional distribution of coalesced, collapsed-cave systems commonly appears as large-scale (hundreds to thousands of square kilometers in area), rectilinear patterns with areas of concentrated, coalesced breccias separated by relatively undisturbed host rock. This pattern may reflect development of the paleocave system along fracture swarms. Collapsed-paleocave systems are large, complex features that show broad-scale organization. The complete paleocave system may need seismic data or large, mountain-scale outcrops to define their architecture and distribution.

Shallow-water, eruption-fed, mafic pyroclastic deposits along a Paleoproterozoic coastline: Kangerluluk volcano-sedimentary sequence, southeast Greenland

The 200–300 m thick, volcano-sedimentary sequence at Kangerluluk is part of the psammite zone, one of four major zones, which constitute the 1.8 Ga Ketilidian orogen in south Greenland. Three lithofacies are emphasized in the study: (1) the conglomerate-sandstone; (2) the volcanic; and (3) the pyroclastic lithofacies. The 2–40 m thick conglomerate-sandstone lithofacies represents a subaerial to subaqueous fan-delta deposit. Matrix- and clast-supported conglomerates are interpreted as debris flow and longitudinal gravel bar deposits. Erosive-based conglomerate channel fills attest to stream incision. Trough crossbedded sandstone, interpreted as lunate megaripples, planar-bedded sandstone indicative of upper flow regime bar-top sands, and small-scale trough crossbeds reflecting ripples follow up-section, form collectively with the conglomerate, 0.40–2.50 m thick fining-upward sequences. The sandstone-dominated unit, up-section from the conglomerates and composed of planar and low-angle crossbeds, minor ripples and graded beds as well as mudstone is indicative of a lower shoreface deposit below normal wave base. The clastic sedimentary rocks are suggestive of a fan-delta setting. The 100–200 m thick volcanic lithofacies, composed of pillowed and pillow brecciated lava flows, is consistent with shallow-water deposition. Interstratification of lava flows with both conglomerate-sandstone and pyroclastic lithofacies, intrusion of dykes into volcaniclastic rocks, and peperite formation accentuate contemporaneity between volcanism and sedimentation and is a common feature of island arcs. The 1–50 m thick, pyroclastic lithofacies with sharp depositional contacts to the overlying volcanic and underlying conglomerate-sandstone lithofacies, was emplaced in a subaqueous setting. The lithofacies is divided into a planar- to crossbedded tuff-lapilli tuff and a bedded lapilli tuff breccia, whereby both deposits are inferred to result from shallow-water surtseyan-type eruptions. The 5–15 m thick, bedded lapilli tuff breccia with abundant bomb sag structures and graded beds is considered a result of subaqueous eruptions strong enough to form an insulating steam cupola characterized by ballistically emplaced bombs that rapidly collapsed allowing for transport via mass flow processes. The deposits are considered proximal to the vent. The 2–50 cm thick, planar- to crossbedded tuff-lapilli tuff featuring abundant euhedral and broken crystals of feldspar (≤2cm) and minor pyroxene (≤1 cm), are massive, graded, crossbedded and stratified. The planar but laterally discontinuous beds, characterized by abundant low-angle scours, are interpreted as low- to high-concentration sediment gravity flows produced directly from subaqueous tephra jets that collapsed due to massive water ingestion. Local breccia-size pyroclasts disrupting beds are interpreted as bomb sags. The mafic, eruption-fed, Surtseyan-type deposits, postulated to be a subaqueous counterpart of cold, subaerial base surges, originate from subaqueous tuff cones formed along a rugged volcanic-dominated shoreline featuring high-energy fan-deltas.

Geology and geochemistry of Gannet (Karewa) Island, Tasman Sea: A rift‐related nephelinitic tuff ring

Gannet (Karewa) Island is a small (0.06 km2) island situated in the Tasman Sea, northwest of Kawhia Harbour, western North Island, New Zealand. It consists of well indurated, palagonitic tuff and lapilli tuff with subordinate scoriaceous basalt bombs and blocks (Karewa Volcanic Formation) which are considered to represent the eroded remnants of a tuff ring. Evidence for this includes such features as cross‐bedded coarse ash units, lensoidal beds, U‐channels, and impact sag structures. Juvenile bombs and blocks consist of fine‐grained olivine nephelinite, comprising microphenocrysts of olivine and acicular clinopyroxene, set in a devitrified glassy groundmass. Accidental lithic fragments are abundant and include ultramafic xenoliths (up to 5 cm), sedimentary rock fragments (15 cm), and hornblende andesite crystal tuff (20 cm). The island has previously been mapped as part of the Alexandra Volcanics, but the major and trace element abundances and isotopic composition indicate that it has lower SiO2 (40–42%) and higher TiO2 (3.2–3.5%), MgO (14–16%),Nb(110–125 ppm), Zr(307–343 ppm)andLREE abundances, and lower 87Sr/86Sr (0.7030) and relatively higher SNd (+6.8) compared with the alkaline intraplate basaltic fields of Okete, Ngatutura, or South Auckland, or the convergent margin basalts of the Alexandra Volcanics and Egmont. Juvenile olivine nephelinite bombs have been dated by K‐Ar determination at 0.51 ± 0.05 Ma, much younger in age than the nearby Alexandra Volcanics (2.74–1.60 Ma) or offshore middle‐late Miocene volcanics. Gannet Island is located approximately above the Taranaki Fault, which is shown on offshore seismic profiles as extending northwards, parallel to the coast off western North Island. Movement on the Taranaki Fault, which forms the eastern boundary of the North Taranaki Graben, ceased in the late Miocene. Since the Pliocene, this region of western North Island has been in extension, and hence Gannet Island is interpreted on geochemical constraints and tectonic position to be an isolated rift‐related volcano. This supports the interpretation that the North Taranaki Graben formed as a back‐arc rift rather than an actively spreading back‐arc basin. The nephelinites of Gannet Island, and also those in the South Auckland volcanic field, which have similar ages, lie just to the northwest of the limit of seismic activity on the subducting Pacific plate, and are probably close to the most distal expression of the contemporary plate boundary.

Regional Structure of Michigan Basin from Reprocessed Ancient Gravity Surveys Constrained by Well Data: ABSTRACT

Modern reprocessed gravity and magnetic data acquired from the 1920s to the 1960s in the Michigan basin can now be constrained by voluminous drilling outcomes and detailed subsurface geologic information. Therefore, potential field techniques have lost much of their traditional ambiguity of interpretation. A complex network of northwest-trending listric faults and associated horsts and grabens extends across the southern and central parts of the Michigan basin. Several major faults deduced from gravity surveys have been the epicenters of recent earthquakes. Sags in the rock pile of up to 150 m have been delineated over basement grabens. These sags in the layered rocks are narrow at depth, but laterally widen high in the rock pile. Hydrocarbon accumulation is closely linked to these sag structures. Several case studies will be presented demonstrating interpretational techniques that are centered on shaded-relief images, computer-generated perspective height fields, and homomorphic functions of gravity fields over extensively drilled fault-bounded complexes. Both local and regional aspects of the problems and success of interpreting the relationships between the gravity fields and the Michigan basin structures will be presented.

52. Ballistic trajectories of volcanic blocks analyzed by the impact sag structures(Abstracts of Papers Presented at the Spring Meeting of the Society)

52. Ballistic trajectories of volcanic blocks analyzed by the impact sag structures(Abstracts of Papers Presented at the Spring Meeting of the Society)

67P. Mechanism and processes of steam explosion analyzed by impact sag structures(Abstracts of Papers Presented at the Spring Meeting of the Society)

67P. Mechanism and processes of steam explosion analyzed by impact sag structures(Abstracts of Papers Presented at the Spring Meeting of the Society)

Sediment-ore-structure relations in barite and associated ores and sediments in the Upper Mississippi valley zinc-lead district near Shullsburg, Wisconsin

The deposits which have been studied include the Blackstone, Temperley, and Teasdale mines. Most of the observations were made on sediment-ore-structure relationships. The ores lie in layers and breccia near, and in sag or basin structures at the base of the Quimbys Mill Member of the Platteville formation. The structure and bedding relationships of the contorted calcite and sphalerite bearing limestone layers show that the ores were present in the sediment during deformation. Geopetal and compaction features such as sphalerite nodules in carbonaceous limestones and the bulged ore layers further indicate a sedimentary and diagenetic formation for the ores.

On Certain Slump Structures in the Torridonian Sandstones of Applecross

AbstractTwo types of slumps are described; small sag and drop-shaped structures in the fine sandstones which develop out of iron-ore rich laminae, and the much larger slump folds in the coarse sandstones which have wavelengths of 25 to 200 cm. and are characterized by open “synclines” linked by pointed “anticlines”. Complex structures are common. It is suggested that liquifaction of the lower parts of the slumped beds has resulted in collapse of the upper parts. Kuenen's pseudo-nodule experiments reproduce many of the observed structures.