Basement-controlled deformation of sedimentary sequences,Anadarko Shelf,Oklahoma

Structures rooted in the crystalline basement frequently control the deformation of the host bedrock and the overlying sedimentary sequences. Here, we elucidate the structure of the c. 2-km deep Precambrian granitic basement in the Anadarko Shelf, Oklahoma, and how the propagation of basement faults deformed the sedimentary cover. Although the basin is foreland in origin, the gently dipping shelf sequences experienced transpressional deformation in the Late Palaeozoic. We analyse a 3-D seismic reflection data set and basement penetrating well data in an area of 824 km². We observe: (a) pervasive deformation of the basement by basement-bounded interconnected mafic sills, and a system of subvertical discontinuity planes (interpreted as faults) of which some penetrate the overlying sedimentary cover; (b) three large (>10 km-long) through-going faults, with relatively small (<100 m) vertical separation (Vsep) of the deformed stratigraphic surfaces; (c) upward propagation of the large faults characterized by faulted-blocks near the basement, and faulted-monoclines in the deeper sedimentary units that transition into open monoclinal flexures up-section; (d) cumulative along-fault deformation of the stratigraphy exhibits systematic trends that varies with offset accrual; (e) two styles of Vsep—Depth distribution which include a unidirectional decrease of Vsep from the basement through the cover rocks (Style-1) and a bidirectional decrease of Vsep from a deep sedimentary unit towards the basement and shallower sequences (Style-2). We find that the basement-driven propagation (Style-1) shows greater efficiency of driving the fault deformation to shallower depths compared to the intrasedimentary-driven fault nucleation and propagation (Style-2). Our study demonstrates an evolution of cumulative Vsep trends with offset accrual on the faults, and the partial inheritance of the heterogeneous intra-basement deformation by the sedimentary cover. This contribution provides important insight into the upward propagation of basement-driven faulting associated with structural inheritance in contractional sedimentary basins.     

Measured oxygen fugacities of the Angra dos Reis achondrite as a function of temperature

Measurements of the oxygen fugacity (?O₂) as a function of temperature (T) were made on an interior bulk sample of the cumulate achondrite, Angra dos Reis. Data clustered between the?O₂-T relationship of the iron-wüstite assemblage and 1.2 log atm units above iron-wüstite. Interpretation of the data indicates that, throughout most of the cooling history of the meteorite, ?O₂ values were defined by equilibria involving iron-bearing species at values close to the ?O₂ of the assemblage iron-wüstite. Measured ?O₂ data are compatible with crystallization and cooling at pressures greater than 50 bars.     

Bioenergetics modeling to investigate habitat use by the nonindigenous crab,Carcinus maenas, in Willapa Bay, Washington

A bioenergetics model was developed and applied to questions of habitat use and migration behavior of nonindigenous European green crab (Carcinus maenas) in Willapa Bay, Washington, USA. The model was parameterized using existing data from published studies on the ecology and physiology ofC. maenas and allied brachyuran crabs., Simulations of the model were run describing four scenarios of habitat use and behavior during a 214-d simulation period (April–October) including crabs occupying mid littoral habitat, high littoral habitat, sublittoral habitat, and sublittoral habitat but undertaking intertidal migrations. Monthly trapping was done along an intertidal gradient in Willapa Bay to determine the actual distribution of crabs for the same time interval as the simulation period, and model results were compared to the observed pattern. Model estimates suggest no intrinsic energetic incentive for crabs to occupy littoral habitats since metabolic costs were c. 6% higher for these individuals than their sublittoral counterparts. Crabs in the littoral simulations were also less efficient than sublittoral crabs at converting consumed energy into growth. Monthly trapping revealed thatC. maenas are found predominantly in mid littoral habitats of Willapa Bay and there is no evidence of resident sublittoral populations. The discrepancy intimates the significance of other factors, including interspecific interactions, that are not incorporated into the model but nonetheless increase metabolic demand. Agonistic encounters with native Dungeness crabs (Cancer magister) may be chief among these additional costs, andC. maenas may largely avoid interactions by remaining in littoral habitats neglected by native crabs, such as meadows of nonindigenous smooth cordgrass (Spartina alterniflora). AdultC. maenas in Willapa Bay may occupy tidal elevations that minimize such encounters, and metabolic costs, while simultaneously maximizing submersion time and foraging opportunities.     

Physical constraints on impact melt properties from Lunar Reconnaissance Orbiter Camera images

Impact melt flows exterior to Copernican-age craters are observed in high spatial resolution (0.5 m/pixel) images acquired by the Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC). Impact melt is mapped in detail around 15 craters ranging in diameter from 2.4 to 32.5 km. This survey supports previous observations suggesting melt flows often occur at craters whose shape is influenced by topographic variation at the pre-impact site. Impact melt flows are observed around craters as small as 2.4 km in diameter, and preliminary estimates of melt volume suggest melt production at small craters can significantly exceed model predictions. Digital terrain models produced from targeted NAC stereo images are used to examine the three-dimensional properties of flow features and emplacement setting, enabling physical modeling of flow parameters. Qualitative and quantitative observations are consistent with low-viscosity melts heated above their liquidii (superheated) with limited amounts of entrained solids.     

Is the Collapse of Mud Shrimp (<Emphasis Type="Italic">Upogebia pugettensis</Emphasis>) Populations Along the Pacific Coast of North America Caused by Outbreaks of a Previously Unknown Bopyrid Isopod Parasite (<Emphasis Type="Italic">Orthione griffenis</Emphasis>)?

A dramatic increase in prevalence of the recently discovered bopyrid isopod parasite, Orthione griffenis, likely introduced in the 1980s from Asia to the Pacific coast of North America, coincided with the 2002 collapse of a population of its burrowing mud shrimp host, Upogebia pugettensis, in Willapa Bay, Washington that had been stable since monitoring began in 1988. An examination of whether O. griffenis infections were sufficient to cause this decline and other recently noted U. pugettensis population collapses in Pacific Coast estuaries was conducted. O. griffenis prevalence was the highest in large reproductive-sized female shrimp and caused an estimated average 68% loss of U. pugettensis reproduction in Yaquina Bay, Oregon over a 5-year period. O. griffenis prevalence fluctuated from year to year, but trends were similar in all estuaries sampled. Uninfected shrimp transplanted back into locations from which they had disappeared acquired the parasite, suggesting that O. griffenis is extremely effective at finding its host even in estuaries with very low host density. Since both U. pugettensis and O. griffenis have pelagic larval stages, their population dynamics are also influenced by coastal nearshore oceanography and estuarine recruitment success. Coastwide lack of estuarine recruitment appears to coincide with declines in density of a co-occurring thalassinid shrimp, Neotrypaea californiensis, but cannot alone explain U. pugettensis population collapses. Although patterns observed to date could be explained by the presence of either a native or introduced parasitic castrator, assumptions of a resilient co-evolved host–parasite relationship do not apply for introduced species, so continued efforts to follow the spatial extent and consequences of the O. griffenis–U. pugettensis host–parasite relationship are warranted.