Uplift and erosion of the San Bernardino Mountains associated with transpression along the San Andreas fault, California, as constrained by radiogenic helium thermochronometry

Apatite helium thermochronometry provides new constraints on the tectonic history of a recently uplifted crystalline mass adjacent to the San Andreas fault. By documenting aspects of the low-temperature (40°–100°C) thermal history of the tectonic blocks of the San Bernardino Mountains in southern California, we have placed new constraints on the magnitude and timing of uplift. Old helium ages (64–21 Ma) from the large Big Bear plateau predate the recent uplift of the range and show that only several kilometers of exhumation has taken place since the Late Cretaceous period. These ages imply that the surface of the plateau may have been exposed in the late Miocene and was uplifted only ∼1 km above the Mojave Desert in the last few Myr by thrusting on the north and south. A similar range in helium ages (56–14 Ma) from the higher San Gorgonio block to the south suggests that its crest was once contiguous with that of the Big Bear block and that its greater elevation represents a localized uplift that the Big Bear plateau did not experience. The structure of the San Gorgonio block appears to be a gentle antiform, based on the geometry of helium isochrons and geologic constraints. Young ages (0.7–1.6 Ma) from crustal slices within the San Andreas fault zone indicate uplift of a greater magnitude than blocks to the north. These smaller blocks probably experienced ≥3–4 km of uplift at rates ≥1.5 mm/yr in the past few Myr and would stand ≥2.5 km higher than the Big Bear plateau if erosion had not occurred. The greater uplift of tectonic blocks adjacent to and within the San Andreas fault zone is more likely the result of oblique displacement along high-angle faults than motion along the thrust fault that bounds the north side of the range. We speculate that this uplift is the result of convergence and slip partitioning associated with local geometric complexities along this strike-slip system. Transpression thus appears to have been accommodated by both vertical displacement within the San Andreas fault zone and thrusting on adjacent structures

Spatially Heterogeneous Post-Caledonian Burial and Exhumation Across the Scottish Highlands

The postassembly, postrift evolution of passive margins is an essential element of global continental tectonics. Thermal and exhumational histories of passive margins are commonly attributed to a number of drivers, including uplift and erosional retreat of a rift-flank escarpment, intraplate fault reactivation, mantle-driven uplift, and erosional disequilibrium, yet in many cases, a specific factor may appear to dominate the history of a given passive margin. Here, we investigate the complex evolution of passive margins by quantifying exhumation patterns in western Scotland. We build upon the well-studied thermal evolution of the Scottish North Atlantic passive margin to test the importance of spatially heterogeneous factors in driving postorogenic burial and exhumation. Independent investigations of the cooling history from seven different field sites across the western Scottish Highlands using radiogenic apatite helium thermochronometry ([U-Th]/He; n = 14; ca. 31–363 Ma) and thermal modeling confirm that post-Caledonian heating and burial, as well as cooling and exhumation, must have been variable across relatively short distances (i.e., tens of kilometers). Heating associated with Paleogene hotspot activity and rifting locally explains some of this spatial variation, but additional drivers, including margin tilting during rifting, vertical separation along reactivated faults, and nonuniform glacial erosion in the late Cenozoic, are also likely required to produce the observed heterogeneity. These results indicate that passive margins may experience variable burial, uplift, and erosion patterns and histories, without exhibiting a single, dominant driver for behavior before, during, and after rifting

Interspecies physiological variation as a tool for cross-species assessments of global warming-induced endangerment: validation of an intrinsic determinant of macroecological and phylogeographic structure

Global warming is now recognized as the dominant threat to biodiversity because even protected populations and habitats are susceptible. Nonetheless, current criteria for evaluating species' relative endangerment remain purely ecological, and the accepted conservation strategies of habitat preservation and population management assume that species can mount ecological responses if afforded protection. The insidious threat from climate change is that it will attenuate or preclude ecological responses by species that are physiologically constrained; yet, quantitative, objective criteria for assessing relative susceptibility of diverse taxa to warming-induced stress are wanting. We explored the utility of using interspecies physiological variation for this purpose by relating species' physiological phenotypes to landscape patterns of ecological and genetic exchange. Using a salamander model system in which ecological, genetic and physiological diversity are well characterized, we found strong quantitative relationships of basal metabolic rates (BMRs) to both macroecological and phylogeographic patterns, with decreasing BMR leading to dispersal limitation (small contemporary ranges with marked phylogeographic structure). Measures of intrinsic physiological tolerance, which vary systematically with macroecological and phylogeographic patterns, afford objective criteria for assessing endangerment across a wide range of species and should be incorporated into conservation assessment criteria that currently rely exclusively upon ecological predictors

Spatio-temporal evolution of intraplate strike-slip faulting: the Neogene-Quaternary Kuh-e-Faghan Fault, Central Iran

Central Iran provides an ideal region to study the long-term morphotectonic response to the nucleation and propagation of intraplate faulting. In this study, a multidisciplinary approach that integrates structural and stratigraphic field investigations with apatite (U+Th)/He (AHe) thermochronometry is used to reconstruct the spatio-temporal evolution of the Kuh-e-Faghan Fault (KFF) in northeastern Central Iran. The KFF is a narrow, ca. 80 km long, deformation zone that consists of three main broadly left stepping, E-W trending, dextral fault strands that cut through the Mesozoic-Paleozoic substratum and the Neogene-Quaternary sedimentary cover. The AHe thermochronometry results indicate that the intra-fault blocks along the KFF experienced two major episodes of fault-related exhumation at ~18 Ma and ~4 Ma. The ~18 Ma faulting/exhumation episode is chiefly recorded by the structure and depositional architecture of the Neogene deposits along the KFF. A source-to-sink scenario can be reconstructed for this time frame, where topographic growth caused the synchronous erosion/exhumation of the pre-Neogene units and deposition of the eroded material in the surrounding fault-bounded continental depocenters. Successively, the KFF gradually entered a period of relative tectonic quiescence and, probably, of regional subsidence during which a thick pile of fine-grained onlapping sediments were deposited. This may have caused resetting of the He ages of apatite in the pre-Neogene and the basal Neogene successions. The ~4 Ma faulting episode caused the final exhumation of the fault system, resulting in the current fault zone and topography. The two fault-related exhumation episodes fit with the regional early Miocene collision-enhanced uplift/exhumation, and the late Miocene–early Pliocene widespread tectonic reorganization of the Iranian plateau. The reconstructed long term, spatially and temporally punctuated fault system evolution in intraplate Central Iran during Neogene-Quaternary times may reflect states of far-field stress changes at the collisional boundaries

Population assessment of the American crocodile Crocodylus acutus (Crocodilia: Crocodylidae) on the Pacific coast of Costa Rica

The American crocodile, Crocodylus acutus, is widely distributed in the American neotropics. It is endangered throughout most of its range and is listed as vulnerable by the International Union for the Conservation of Natural Fauna and Flora (IUCN) and on Appendix I of the Convention for the International Trade in Endangered Species of Wild Flora and Fauna (CITES). Despite this listing, there are few published reports on population status throughout most of its range. We investigated the status of the C. acutus, at several locations along the Pacific coast of Costa Rica. We carried out spotlight and nesting surveys from 2007-2009 along the Costa Rican Pacific coast in four distinct areas, coastal areas of Las Baulas (N=40) and Santa Rosa (N=9) National Parks and the Osa Conservation Area (N=13), and upriver in Palo Verde National Park (N=11). We recorded crocodile locations and standard environmental data at each observation. Encounter rates, population structure, distribution within each area and data on successful nesting (presence of hatchlings, nests, etc) were determined. We attempted to capture all crocodiles to record standard morphometrics. A total of 586 crocodiles were observed along 185.8km of survey route. The majority of animals encountered (54.9%) were either hatchlings (<0.5m) or juveniles (0.5-1.25m). The average non-hatchling encounter rate per survey for the Pacific coast was 3.1 crocodiles/km, with individual encounter rates ranging from 1.2 crocodiles/km to 4.3 crocodiles/km in Las Baulas National Park and the Osa Conservation Area respectively. Distribution of size classes within the individual locations did not differ with the exception of Santa Rosa and Las Baulas National Parks, where hatchlings were found in water with lower salinities. These were the first systematic surveys in several of the areas studied and additional work is needed to further characterize the American crocodile population in Costa Rica.Rev. Biol. Trop. 60 (4): 1889-1901. Epub 2012 December 01

Mojave desert tortoise (Gopherus agassizii) thermal ecology and reproductive success along a rainfall cline

Desert resource environments (e.g. microclimates, food) are tied to limited, highly localized rainfall regimes which generate microgeographic variation in the life histories of inhabitants. Typically, enhanced growth rates, reproduction and survivorship are observed in response to increased resource availability in a variety of desert plants and short‐lived animals. We examined the thermal ecology and reproduction of US federally threatened Mojave desert tortoises (Gopherus agassizii), long‐lived and large‐bodied ectotherms, at opposite ends of a 250‐m elevation‐related rainfall cline within Ivanpah Valley in the eastern Mojave Desert, California, USA. Biophysical operative environments in both the upper‐elevation, “Cima,” and the lower‐elevation, “Pumphouse,” plots corresponded with daily and seasonal patterns of incident solar radiation. Cima received 22% more rainfall and contained greater perennial vegetative cover, which conferred 5°C‐cooler daytime shaded temperatures. In a monitored average rainfall year, Cima tortoises had longer potential activity periods by up to several hours and greater ephemeral forage. Enhanced resource availability in Cima was associated with larger‐bodied females producing larger eggs, while still producing the same number of eggs as Pumphouse females. However, reproductive success was lower in Cima because 90% of eggs were depredated versus 11% in Pumphouse, indicating that predatory interactions produced counter‐gradient variation in reproductive success across the rainfall cline. Land‐use impacts on deserts (e.g. solar energy generation) are increasing rapidly, and conservation strategies designed to protect and recover threatened desert inhabitants, such as desert tortoises, should incorporate these strong ecosystem‐level responses to regional resource variation in assessments of habitat for prospective development and mitigation efforts.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111753/1/inz212132.pd

Utilization of passive sonic telemetry as indicators of movement and nesting of the Northern Diamondback Terrapin (Malaclemys terrapin terrapin)

Numerous anthropogenic factors pose serious threats to estuarine ecosystems and the organisms inhabiting them. Bulkheading (i.e., construction of shoreline walls), dredging, boating, shoreline development, over-harvesting, and pollution are some of the major human impacts to estuaries in North America. The diamondback terrapin (Malaclemys terrapin) is an ideal species for determining the effects of human impacts to estuarine wildlife, because their habitat use and behavior uniquely utilize both land and aquatic habitats that comprise estuaries. The objective of this study is to determine the home range and nest site selection of diamondback terrapins in relation to anthropogenic impacts in Barnegat Bay Estuary, New Jersey. We will use passive sonic telemetry technology and multiple Submersible Underwater Receivers (SURs) to remotely track free-ranging terrapins throughout the Bay. We will position SURs in arrays throughout areas of the Bay where we have marked terrapins over the last three years to monitor the movements of individual terrapins. Fifteen terrapins will be outfitted with sonic transmitters per site, which will send signals to the SUR when terrapins are within range. Frequency, date, and time of signal reception will be logged remotely by each SUR. From these data we will determine the individual terrapin whose signal was received, and movements of individuals throughout the monitored areas. Gravid (i.e., egg-bearing) females will be closely monitored to determine the nest site(s) used. Reproductive success of nests will be determined for each monitored female. Wherever possible we will determine the cause(s) of nest failure. Our study will be critical in determining the direct and indirect effects of anthropogenic impacts to terrapins in areas of known high terrapin densities. These findings will aid in management decisions regarding both aquatic (e.g., boat) and land (e.g., beach) uses in relation to ensuring the viability of wildlife resources within the Barnegat Bay Estuary

Crustal-scale structural architecture, shortening, and exhumation of an active, eroding orogenic wedge (Chugach/St Elias Range, southern Alaska)

Active mountain building associated with the accretion of the Yakutat microplate (YT) in southern Alaska is characterized through the combination of a new balanced cross section and new low-temperature cooling ages. This analysis constrains the amount and timing of shortening, the spatial and temporal trends of exhumation, and the interplay between structural development and exhumation. A fold-and-thrust belt comprising three principal thrust sheets (the Hope Creek, Sullivan, and an offshore thrust sheet from north to south) characterizes the YT internal structure, which has absorbed a minimum of ~82 km shortening. Assuming shortening and foreland basin development occurred contemporaneously, the shortening rate across the YT is ~13–14 mm/a after 5.6 Ma. Detrital apatite fission track ages, from south to north, are unreset along the southern edge of the Sullivan thrust sheet at the coast, are reset and have ages younger than 6.3 Ma within the thrust belt, and have reset cooling ages of ~13 Ma in the North American upper plate. Only the zircon samples from the northern, internal YT are potentially reset. Exhumation rates within the thrust belt vary from 0.3 ± 0.1 mm/a to 4 ± 1.8 mm/a. Combining the thermochronometric and structural data indicate that wedge exhumation since ~6 Ma is 500 km² and that particle trajectories have larger horizontal than vertical components. Whereas exhumation and shortening have been focused on the windward side of the Chugach/St. Elias Range since ~6 Ma, the cooling ages do not uniquely distinguish between orographically versus tectonically controlled erosion.Keywords: exhumation, microplate, fold-and-thrust beltKeywords: exhumation, microplate, fold-and-thrust bel