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SUMMARYThis paper explains a novel 'back-analysis' scheme to determine rock mass behaviour modes from an array of deformational measurements. The input will be the locations of data points and the set of measured displacements, as well as description of the locations and orientations of planes of discontinuity, and the blocks they determine. The output, drawn by the computer, will be the set of block displacements, rotations, and strains that determine the behavioural mode of the mass.

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SUMMARYThis paper provides the theoretical basis for a forward numerical model of rock block systems. This method was developed to compute stress, strain, sliding and opening of rock blocks; rigid body movement and deformation occur simultaneously. Input data consist of block geometry, loading forces, the deformability constants E and v, and the restraint or boundary conditions of the block system. Output data give the movements, deformations, stresses and strains of each block, and the sliding and detachment or rejoining of blocks.The forces acting on each block, from external loading or contact with other blocks, satisfy the equilibrium equations. Equilibrium is also achieved between external forces and the block stresses. Furthermore, this analysis fulfills constraints of no tension between blocks and no penetration of one block into another. To achieve equilibrium and satisfy these constraints, simultaneous equations are solved repeatedly with partial changes of the coefficients each time the contact constraints are chosen.

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The study aims to provide a comprehensive systematic account of Lower Permian brachiopods and molluscs (excluding gastropods) from the upper Jungle Creek Formation in northern Yukon Territory, western Canada, and to assess their biostratigraphic and paleoecological significance. Sixty-nine brachiopod species belonging to 53 genera, six bivalve species belonging to five genera, and one ammonoid species are described and illustrated. New taxa include Arctitreta peelensis n. sp., Orthotetes canadensis n. sp., Liosotella compacta n. sp., Anemonaria auriculata n. sp., Costispinifera paucispinosa n. sp., Rugivestis arctica n. sp., Thamnosia spinosa n. sp., Globiella costellata n. sp., Protoanidanthus umbonatus n. sp., Rhynoleichus dorsoconvexa n. sp., Septacamera triangulata n. sp., Composita bamberi n. sp., Ogilviecoelia inflata n. gen. et sp., Tumarinia yukonica n. sp., Yukonella plana n. gen. et sp., Timaniella convexa n. sp., Yukonospirifer yukonensis n. gen. n. sp., Larispirifer ettrainensis n. sp., Domokhotia junglensis n. sp., Tiramnia canadica n. sp., and Retimarginiferinae n. subfam. The three brachiopod biozones previously recognized within the upper Jungle Creek Formation are revised and substantiated. These are the (in ascending stratigraphic order) Yakovlevia transversa Assemblage Zone, Ogilviecoelia inflata Assemblage Zone, and Jakutoproductus verchoyanicus Assemblage Zone. The distribution of these zones in the study area and their correlation with other major Lower Permian marine sequences in North America and the Arctic are discussed. Close correlation of the Yukon brachiopod faunas with those from the Urals, northeast Russia, and the Canadian Arctic, reinforced by some data from fusulinids and ammonoids, suggests that the Yakovlevia transversa Zone is probably Early Sakmarian (Tastubian) in age, the Ogilviecoelia inflata Zone is Late Sakmarian (Sterlitamakian), and Jakutoproductus verchoyanicus Zone is Early Artinskian (Aktastinian). A computerized ordination technique (principal components analysis) is used to delineate recurrent paleocommunities. Four fossil communities are recognized: Rhynchopora magna, Fimbrinia-Tubersulculus-Kutorginella, Ogilviecoelia inflata, and Tityrophoria nelsoni- Septacamera triangulata. These paleocommunities are analyzed in terms of faunal composition and possible depositional environments. They seem to record positions in an onshore to offshore sequence across a shallow marine shelf, with the Rhynchopora magna paleocommunity possibly representing a shallow subtidal restricted zone; the Fimbrinia-Tubersulculus-Kutorginella paleocommunity representing probably an open shelf, above wave base zone; the Ogilviecoelia inflata paleocommunity possibly an open shelf, near or at wave base zone; and the Tityrophoria nelsoni-Septacamera triangulata paleocommunity a low energy position, farther offshore, below wave base.