Arden R. Bashforth

Bio: Arden R. Bashforth is an academic researcher from University of Copenhagen. The author has contributed to research in topics: Pennsylvanian & Cordaites. The author has an hindex of 20, co-authored 32 publications receiving 1023 citations. Previous affiliations of Arden R. Bashforth include Smithsonian Institution & Dalhousie University.

Pennsylvanian uplands were forested by giant cordaitalean trees

Abstract: The precise timing of when upland terrains first became forested is highly controversial. Pennsylvanian palynoflora and megaflora transported into marine highstand deposits imply that emergent topographic highs may have supported cordaitalean forests. The discovery of a new Pennsylvanian (Bolsovian) plant assemblage in southwest Newfoundland confirms this hypothesis and allows the architecture of these upland trees to be reconstructed in detail. The assemblage includes several hundred calcareously permineralized stumps, trunks, and branches, and represents the remains of shallowly rooted cordaitalean trees that were ≤48.5 m high when mature. The fossils occur in alluvial conglomerates that constitute a 10-km-diameter outlier on the margins of the paleoequatorial Variscan foreland. The paleogeographic setting together with plant taphonomic inferences strongly indicate that these giant trees were transported from nearby upland alluvial plains and deposited in an elevated intermontane basin. This interpretation is supported by analysis of rootstock morphology, which implies tree growth in thin soils consistent with an alluvial gravel substrate. This improved understanding of Pennsylvanian upland forests has important implications for geochemical modeling of the global carbon cycle.

Palaeozoic co-evolution of rivers and vegetation: a synthesis of current knowledge

Abstract: As vegetation evolved during the Palaeozoic Era, terrestrial landscapes were substantially transformed, especially during the ∼120 million year interval from the Devonian through the Carboniferous Early Palaeozoic river systems were of sheet-braided style – broad, shallow, sandbed rivers with non-cohesive and readily eroded banks Under the influence of evolving roots and trees that stabilised banks and added large woody debris to channels, a range of new fluvial planform and architectural styles came to prominence, including channelled- and island-braided systems, meandering and anabranching systems, and stable muddy floodplains River systems co-evolved with plants and animals, generating new ecospace that we infer would have promoted biological evolution By the end of the Carboniferous, most landforms characteristic of modern fluvial systems were in existence

The Theory of Island Biogeography

Abstract: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

Maximum leaf conductance driven by CO2 effects on stomatal size and density over geologic time

Abstract: Stomatal pores are microscopic structures on the epidermis of leaves formed by 2 specialized guard cells that control the exchange of water vapor and CO2 between plants and the atmosphere. Stomatal size (S) and density (D) determine maximum leaf diffusive (stomatal) conductance of CO2 (gcmax) to sites of assimilation. Although large variations in D observed in the fossil record have been correlated with atmospheric CO2, the crucial significance of similarly large variations in S has been overlooked. Here, we use physical diffusion theory to explain why large changes in S necessarily accompanied the changes in D and atmospheric CO2 over the last 400 million years. In particular, we show that high densities of small stomata are the only way to attain the highest gcmax values required to counter CO2“starvation” at low atmospheric CO2 concentrations. This explains cycles of increasing D and decreasing S evident in the fossil history of stomata under the CO2 impoverished atmospheres of the Permo-Carboniferous and Cenozoic glaciations. The pattern was reversed under rising atmospheric CO2 regimes. Selection for small S was crucial for attaining high gcmax under falling atmospheric CO2 and, therefore, may represent a mechanism linking CO2 and the increasing gas-exchange capacity of land plants over geologic time.

State of science: mental workload in ergonomics

Abstract: Mental workload (MWL) is one of the most widely used concepts in ergonomics and human factors and represents a topic of increasing importance. Since modern technology in many working environments imposes ever more cognitive demands upon operators while physical demands diminish, understanding how MWL impinges on performance is increasingly critical. Yet, MWL is also one of the most nebulous concepts, with numerous definitions and dimensions associated with it. Moreover, MWL research has had a tendency to focus on complex, often safety-critical systems (e.g. transport, process control). Here we provide a general overview of the current state of affairs regarding the understanding, measurement and application of MWL in the design of complex systems over the last three decades. We conclude by discussing contemporary challenges for applied research, such as the interaction between cognitive workload and physical workload, and the quantification of workload ‘redlines’ which specify when operators are approachi...

Pre-Carboniferous, episodic accretion-related, orogenesis along the Laurentian margin of the northern Appalachians

Abstract: Abstract During the Early to Middle Palaeozoic, prior to formation of Pangaea, the Canadian and adjacent New England Appalachians evolved as an accretionary orogen. Episodic orogenesis mainly resulted from accretion of four microcontinents or crustal ribbons: Dashwoods, Ganderia, Avalonia and Meguma. Dashwoods is peri-Laurentian, whereas Ganderia, Avalonia and Meguma have Gondwanan provenance. Accretion led to a progressive eastwards (present co-ordinates) migration of the onset of collision-related deformation, metamorphism and magmatism. Voluminous, syn-collisional felsic granitoid-dominated pulses are explained as products of slab-breakoff rather than contemporaneous slab subduction. The four phases of orogenesis associated with accretion of these microcontinents are known as the Taconic, Salinic, Acadian and Neoacadian orogenies, respectively. The Ordovician Taconic orogeny was a composite event comprising three different phases, due to involvement of three peri-Laurentian oceanic and continental terranes. The Taconic orogeny was terminated with an arc–arc collision due to the docking of the active leading edge of Ganderia, the Popelogan–Victoria arc, to an active Laurentian margin (Red Indian Lake arc) during the Late Ordovician (460–450 Ma). The Salinic orogeny was due to Late Ordovician–Early Silurian (450–423 Ma) closure of the Tetagouche–Exploits backarc basin, which separated the active leading edge of Ganderia from its trailing passive edge, the Gander margin. Salinic closure was initiated following accretion of the active leading edge of Ganderia to Laurentia and stepping back of the west-directed subduction zone behind the accreted Popelogan–Victoria arc. The Salinic orogeny was immediately followed by Late Silurian–Early Devonian accretion of Avalonia (421–400 Ma) and Middle Devonian–Early Carboniferous accretion of Meguma (395–350 Ma), which led to the Acadian and Neoacadian orogenies, respectively. Each accretion took place after stepping-back of the west-dipping subduction zone behind an earlier accreted crustal ribbon, which led to progressive outboard growth of Laurentia. The Acadian orogeny was characterized by a flat-slab setting after the onset of collision, which coincided with rapid southerly palaeolatitudinal motion of Laurentia. Acadian orogenesis preferentially started in the hot and hence, weak backarc region. Subsequently it was characterized by a time-transgressive, hinterland migrating fold-and-thrust belt antithetic to the west-dipping A–subduction zone. The Acadian deformation front appears to have been closely tracked in space by migration of the Acadian magmatic front. Syn-orogenic, Acadian magmatism is interpreted to mainly represent partial melting of subducted fore-arc material and pockets of fluid-fluxed asthenosphere above the flat-slab, in areas where Ganderian's lithosphere was thinned by extension during Silurian subduction of the Acadian oceanic slab. Final Acadian magmatism from 395–c. 375 Ma is tentatively attributed to slab-breakoff. Neoacadian accretion of Meguma was accommodated by wedging of the leading edge of Laurentia, which at this time was represented by Avalonia. The Neoacadian was devoid of any accompanying arc magmatism, probably because it was characterized by a flat-slab setting throughout its history.