THE INTERPLAY OF EUSTASY AND LITHOSPHERIC FLEXURE IN FORMING STRATIGRAPHIC SEQUENCES IN FORELAND SETTINGS: AN EXAMPLE FROM THE ANTLER FORELAND, NEVADA AND UTAH

Power-law viscous flow describes well the first-order features of long-term lithosphere deformation. Due to the ellipticity of the Earth, the lithosphere is mechanically analogous to a shell, characterized by a double curvature. The mechanical characteristics of a shell are fundamentally different to the characteristics of plates, having no curvature in their undeformed state. The systematic quantification of the magnitude and the spatiotemporal distribution of strain, strain-rate and stress inside a deforming lithospheric shell is thus of major importance: stress is for example a key physical quantity that controls geodynamic processes such as metamorphic reactions, decompression melting, lithospheric flexure, subduction initiation or earthquakes.Stress calculations in a geometrically and mechanically heterogeneous 3-D lithospheric shell require high-resolution and high-performance computing. The pseudo-transient finite difference (PTFD) method recently enabled efficient simulations of high-resolution 3-D deformation processes, implementing an iterative implicit solution strategy of the governing equations for power-law viscous flow. Main challenges for the PTFD method is to guarantee convergence, minimize the required iteration count and speed-up the iterations.Here, we present PTFD simulations for simple mechanically heterogeneous (weak circular inclusion) incompressible 2-D power-law viscous flow in cartesian and cylindrical coordinates. The flow laws employ a pseudo-viscoelastic behavior to optimize the iterative solution by exploiting the fundamental characteristics of viscoelastic wave propagation.The developed PTFD algorithm executes in parallel on CPUs and GPUs. The development was done in Matlab (mathworks.com), then translated into the Julia language (julialang.org), and finally made compatible for parallel GPU architectures using the ParallelStencil.jl package (https://github.com/omlins/ParallelStencil.jl). We may unveil preliminary results for 3-D spherical configurations including gravity-controlled lithospheric stress distributions around continental plateaus.

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Ecological succession as an aspect of structure in fossil communities

Paleobiology ◽

10.1017/s0094837300002505 ◽

1975 ◽

Vol 1 (3) ◽

pp. 238-257 ◽

Cited By ~ 139

Author(s):

Kenneth R. Walker ◽

Leonard P. Alberstadt

Keyword(s):

Environmental Changes ◽

Food Chains ◽

Short Term ◽

Niche Specialization ◽

Pattern Diversity ◽

Physical Environments ◽

Autogenic Succession ◽

Succession Stage ◽

Stratigraphic Sequences

Succession involves changes in a community through time, whether internally or externally controlled. As succession progresses, niche specialization, species diversity (variety and equitability), complexity of food chains, and pattern diversity increase; net production and species growth rate decrease. We apply the succession concept to three types of ancient community sequences: 1) fossil reefs (Ordovician—Cretaceous in age), 2) short-term successions occurring through thin stratigraphic intervals, and 3) long-term successions occurring through thicker stratigraphic intervals. Ancient reefs show four vertical zones: (1) a basal stabilization zone (autogenic), 2) the overlying colonization zone (autogenic, pioneer stage), 3) the diversification zone, the bulk of most reefs (diversification culminating in climax), and 4) the uppermost domination zone. The first three zones represent autogenic succession but the final stage may involve allogenic succession. Short-term succession usually occurs where periodic allogenic catastrophes wipe out the community which is rebuilt through autogenic succession. Opportunistic pioneer species are important and in our examples (Ordovician, Silurian, and Cretaceous) are species which pave soft substrata. Paleozoic strophomenid brachiopods filled this role, and inoceramid pelecypods served the function in the Mesozoic. The succession which begins with opportunists progresses to a climax community of equilibrists. Repetition of catastrophe-succession couplets produces a cyclic stratigraphic record. Long-term successions are recorded in thicker stratigraphic sequences, and are of two types: 1) autogenic succession in unchanging physical environments and 2) allogenic succession in changing physical environments. Our examples of these are from the Devonian Haragan-Bois D'Arc formations of Oklahoma and the Lime Creek Formation of Iowa. This type of succession represents a temporal-spatial mosaic. The Haragan data (unchanging environments) indicate characteristic, intergrading, and ubiquitous species in the brachiopod communities. Most ubiquitous species in the pioneer community were eurytopic opportunists. The Lime Creek data allows testing of the prediction that environmental changes cause regression to an earlier succession stage. The brachiopod communities after environmental changes have more ubiquitous and intergrading eurytopic species. These represent an earlier stage in the succession.

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