Abstract Very large rock avalanches, involving more than about 10 6 m 3 of rock debris, exhibit anomalously low coefficients of friction. Consequently they travel much farther than conventional slope-stability criteria predict. Such long-runout landslides ( sturz-strom ) include the catastrophic Elm (1881), Frank (1903), and Sherman Glacier (1964) events. Attempts to explain this behavior have considered water or air lubrication, local steam generation, or even the formation of melt layers within the rock debris. Discovery of deposits of such landslides on Mars and the moon, however, appears to rule out the fundamental involvement of volatiles or atmospheric gases in the flow mechanism. It appears that large, high-frequency pressure fluctuations due to irregularities in the flow of the debris may locally relieve overburden stresses in the rock mass and allow rapid pseudoviscous flow of even dry rock debris. If the avalanche volume is large enough, the rate of production of this vibrational (acoustic) energy exceeds its loss rate, and sustained motion is possible. Small-scale laboratory experiments have verified theoretical predictions of the rheology of such acoustically fluidized debris. This rheology is consistent with the rate and pattern of observed large rock avalanches. Although much work remains to be done, acoustic fluidization is the most plausible explanation of the fluidity of large, dry debris avalanches.

Abstract Although the Rheic Ocean was the widest to be closed during the assembly of Pangaea, its suture zone is dominated by a younger (Rhenohercynian) Wilson Cycle. The present paper briefly summarizes the Rhenohercynian and reviews the relicts of the Rheic. The absence of a Rheic orogen is mainly due to bipolar subduction of the Rheic Ocean, which created two magmatic arcs and largely destroyed the passive margin prisms, thus depriving the collision zone of building material. Also, displacement of Variscan zones in England, France and Germany along a curvature of the dextral Bristol/Bray/Bohemia shear zone has effected their anticlockwise rotation. Younger, ENE-trending reverse faults have truncated the NE-trending structural boundaries and excised pre-Devonian, Rheic-related rocks west of the River Rhine, while the northern Rheic Arc and Cambrian–Silurian deposits of the Rheic Ocean have been preserved further east. Opening of the Rhenohercynian successor ocean to the Rheic put a brake on plate convergence and hindered formation of a large collisional belt. Scarce relicts of the southern Rheic Arc and rocks with Silurian deformation exist in the (largely eroded) upper plate of the Rhenohercynian collisional belt, mostly in the form of clasts and detrital zircons in Upper Devonian/lower Carboniferous flysch and in tectonic mélange at the base of the allochthon.

We transliterate these alphabets (Bulgarian, Russian, Serbian, Ukrainian and White Russian) according to the Library of Congress rules of 1931 with a few minor changes such as using i for H, rather than ̄i. Various other commonly encountered transliterations are added in parentheses in the table below. Traditional spellings of some well-known names are retained (e.g., Salensky for Zalenskiǐ).

Abstract On the basis of a brief survey of the subdivision and evolution of the Variscides, this paper addresses controversial issues relating to the plate kinematic assembly and the ‘collapse’ of the orogen. A widespread phase of Devonian extension and basaltic magmatism is at variance with overall convergence. This episode either reflects subduction of the Rheic mid-ocean ridge, or else relates to a set of mantle plumes that also produced the Dniepr-Donets aulacogen. Another controversy regards the position of Gondwana in Devonian and Early Carboniferous time. Contrary to recent proposals of a wide Palaeotethys ocean, biogeographical and palaeomagnetic data suggest, until the Late Carboniferous, a Pangaea B model with Gondwana juxtaposed against Southern Europe. Contrary to the concept of Late Carboniferous-Permian ‘collapse’ of a central Variscan high plateau, major crustal thickening occurred only in relatively narrow belts, and parts of the central Variscides were close to sea level from the Late Devonian onwards. Collision occurred in a high-temperature regime from c . 340–350 Ma onwards. Heating by several independent mechanisms effected the reduction of orogenic roots by buoyant rise and lateral spreading of thermally softened crust. However, major flysch wedges reflect the importance of erosion and uplift. Late Carboniferous-Permian magmatism and extension associated with strike-slip zones affected a largely equilibrated crust. These events probably relate to the westward displacement of Gondwana and the opening of the Palaeotethys embayment (Pangaea B to Pangaea A).

Abstract The structures and chemistry of the oxide and oxysalt minerals are impressive in both their complexity and diversity, and it can be reasonably asserted that our understanding of these aspects lags far behind our experimental capabilities for their characterization. Nevertheless, there are some empirical rules that (sometimes weakly) govern the constitution of these minerals, rules that date back to early work on the modern electronic theory of valence (Lewis, 1923) and the structure of crystals. The most rigorous rule is that of electroneutrality: the sum of the formal charges of all the ions in a crystal is zero. Other rules grew out of observations on a few mineral and inorganic structures, and various ideas emerged during the 1920s: that atoms have a specific size, tables of atomic and ionic radii, the idea of coordination number, considering structures as polymerizations of coordination polyhedra. These ideas were refined by Pauling (1929, 1960) who synthesized them into his well-known rules for the behaviour of ‘complex ionic crystals.’ Some aspects of these ideas have been extensively developed up to the present time. There are now available tables of accurate empirical ‘ionic’ radii (Shannon, 1976) whereby mean interatomic distances for specific coordinations can be predicted typically to within ∼0.01 Å. Individual bond lengths can be predicted via various developments of Pauling’s second rule ( e.g ., Baur, 1970, 1971), and the relative strengths of bonds can be calculated (Brown & Shannon, 1973) given the observed bond lengths in a structure. Thus we can currently predict various geometrical

Abstract Tectonic zones and palaeogeographic units (terranes) in the German segment of the Variscides correlate with equivalents in the Sudetes at the NE margin of the Bohemian Massif. This correlation defines an arcuate structure with an opening angle of about 90°. The structure is truncated to the SE by a crustal scale. NE-trending fault zone with dextral transpression, the Moldanubian Thrust (MT). The arc cannot have been formed by northeastward indentation of the Bohemian Massif, since there is no evidence of a fault zone on the NW flank of the notional indenter, and little evidence for northeastward tectonic transport. Kinematic and age constraints on the main fault zones instead suggest that the structural array was formed by a complex sequence of events. Northwestward displacement along the margin of the East European Platform (EEP) with clockwise rotation was followed by large southwestward movements along the Moldanubian Thrust, and renewed northwestward displacement along the SW margin of the East European Platform.

Abstract Paleodrainage mapping of the Mississippian-Pennsylvanian unconformity in northwestern West Virginia verifies the existence of an incised, sub-Pennsylvanian paleovalley system there that extends for over 130 km. The paleovalleys are filled mostly with quartzose sandstones of the New River Formation. This paleovalley system was carved by a southwest-draining network of rivers that was rejuvenated during the mid-Carboniferous. Bedload-dominated streams that occupied the paleovalleys deposited most of the valley-fill sediment. Regional paleodrainage data indicate that the sub-Pennsylvanian paleovalleys in northwestern West Virginia form the middle reach of a major paleoriver system which includes the Middlesboro paleovalley in eastern Kentucky, the Sharon paleovalley in eastern Ohio, and the Perry paleovalley in southeastern Ohio. This regional paleodrainage network (herein named the Middlesboro-Sharon-Perry paleovalley system) transported sediment from the craton north of the central Appalachian basin to the mid-Carboniferous depocenter in southwestern Virginia. Although it has been previously suggested that maximum erosional development of the Mississippian-Pennsylvanian unconformity occurred during the Early Pennsylvanian, paleoslope considerations rule against an Early Pennsylvanian age for carving of the Middlesboro-Sharon-Perry paleovalley system. Existing biostratigraphic data from the mid-Carboniferous depocenter in southern West Virginia support the existence of an Upper Mississippian (Chokierian-Alportian stages of the Namurian Series) hiatus there, suggesting that incision of the Middlesboro-Sharon-Perry paleovalley system was dominantly a Late Mississippian (Chokierian-Alportian) event. Uplift of the craton north of the central Appalachian basin combined with subsidence within the basin that increased in rate toward the mid-Carboniferous depocenter in southern West Virginia created the generally south-dipping paleoslope which the Middlesboro-Sharon-Perry paleoriver system drained. The regional paleodrainage picture rules against tectonic uplift of the Cincinnati arch as a key factor in driving the incision of the Middlesboro-Sharon-Perry paleovalley system. Carving of this paleovalley system apparently was driven by a previously documented, Late Mississippian (Chokierian-Alportian) eustatic sea-level drop. Regional tectonic uplift during the Early Pennsylvanian may have influenced erosional development of the Mississippian-Pennsylvanian after the Late Mississippian incision of the Middlesboro-Sharon-Perry paleodrainage system.

Abstract Thick nonmarine coals and large epigenetic uranium deposits occur within the Wasatch (Eocene) and Upper Fort Union (late Paleocene) Formations in the Powder River Basin, Wyoming. The regional depositional framework of these formations as determined from published data is characterized by a northward-flowing intermountain basinal fluvial system. This system has three major components: a trunk stream along the basinal axis, a tributary subsystem along the basin margin and a paludal subsystem between the trunk stream and the tributary subsystems.Data from eighteen continuous cores in the lower Wasatch and upper Fort Union Formations from a four square mile area in southeastern Campbell County provide information for determining the depositional and stratigraphic characteristics of the tributary subsystem. The sedimentary rocks above and below the thick Anderson coal bed within the study area consist of fine-grained sandstones, siltstones, mudstones and claystones interbedded with thin discon-tinuous coal beds. The physical, lithological and biological characteristics of these sediments are similar to floodbasin sequences in the Holocene Atchafalaya Basin of Louisiana. Specific environments recognized include point bars, crevasse splays, lacustrine deltas, natural levees, lakes, abandoned channel fills, and well- to poorly-drained swamps. With the exception of the laterally continuous Anderson coal bed, lateral and vertical variability in lithologies is the rule rather than the exception within the study area.Thick, low ash, coal beds such as the Anderson probably originated as extensive peat swamps in the paludal subsystem. How the even thicker peats that formed these coals segregated themselves from adjacent alluvial sedimentation is still a matter of debate. Thin discontinuous coals with clay interbeds probably originated as small interchannel peat swamps that developed on slightly better drained crevasse splay platforms in the tributary subsystem.