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USGS2012

Chemistry of rock-forming minerals of the Cretaceous-Paleocene batholith in southwestern Japan and implications for magma genesis

Petrographic descriptions and electron microprobe analyses of minerals are presented for 35 specimens from seven suites chosen to examine the transition from magnetite series to ilmenite series granitoids along two transects across the Cretaceous-Paleocene Inner Zone batholith of southwestern Japan. Regularities in chemical compositions of amphiboles, biotites, and feldspars suggest that fundamentally similar processes produced the magmas that formed the two series. Constant or decreasing Fe/(Fe+Mg) for biotites and amphiboles with increasing host rock silica content, coupled with the absence of early formed magnetite and sphene, suggest that magnetite series rocks may have become oxidized during crystallization near the level of intrusion, through the processes of second boiling and differential loss of hydrogen. For the Daito-Yokota, magnetite series suite, Fe/(Fe+Mg) for biotites decreased from 0.48 to 0.37 as SiO 2 content of the host rock increased from 55.3 to 75.5 wt %; for an ilmenite series suite from the Takanawa Peninsula, Fe/(Fe+Mg) for biotites increased from 0.51 to 0.77 with an increase in host rock SiO 2 from 53.4 to 75.5. Detailed consideration of amphibole chemistry shows predominance of edenitic and tschermakitic substitution schemes as well as coupling between substitutions of Ti in octahedral sites and Al IV . Interrelations between amphibole and biotite chemistry show that Fe/(Fe+Mg) and Mn contents can be interpreted in terms of equilibration, whereas Ti content cannot. The chemistry of chlorites correlates well with that of biotites; primary and secondary muscovites are distinct in composition. Plagioclase in all studied suites shows igneous zoning appropriate to host rock composition; perthitic alkali feldspars in all samples have lost albite component, and temperatures based on the two-feldspar geothermometer are low. The biotite-apatite geothermometer is also inoperative for this group of samples because fully fluorinated apatites typically occur in biotites of modest F content. Whereas magnetites have reequilibrated, analyses of ilmenites for the representative Daito-Yokota and Takanawa suites corroborate biotite compositional data and suggest that f O2 probably differed by 2 to 3 orders of magnitude during crystallization of silica-rich magnetite and ilmenite series granites. Whole-rock chemistry supports mineral chemistry in suggesting that the studied granitoids have crystallized from magmas generated in a lower crustal environment in which mantle-derived magmas partially melted source materials with igneous characteristics.

Journal of Geophysical Research Solid Earth↗

USGS1989

Sensitive strata in Bootlegger Cove Formation

Sensitivity magnitudes are interpreted from remolded strength values in recent subsurface geologic, geotechnical, and geochemical data from the Bootlegger Cove Formation adjacent to the Turnagain Heights Landslide. The results show that strata composed of highly sensitive clays occur in both the middle and lower zones of the formation, and that between these strata the clays are generally of low-to-medium sensitivity. The most sensitive stratum is in the middle zone between two sand layers, and its sensitivity increases from both clay-sand interfaces to a maximum at the center of the stratum. The pore fluid chemistry of the highly sensitive materials differs from that in the materials of low to medium sensitivity only in their concentrations of organic carbon, chloride, bicarbonate, and sulfate. The total dissolved solids concentration is low, and the ratio of monovalent to divalent cations is very high throughout the middle and lower zones of the formation. Of the known causes of high and extremely high sensitivities, only organic and/or anionic dispersants are consistent with these findings.

Journal of Geotechnical Engineering↗

USGS1997

Acidic deposition, cation mobilization, and biochemical indicators of stress in healthy red spruce

Dendrochemical and biochemical markers link stress in apparently healthy red spruce trees ( Picea rubens ) to acidic deposition. Acidic deposition to spruce forests of the northeastern USA increased sharply during the 1960s. Previous reports related visible damage of trees at high elevations to root and soil processes. In this report, dendrochemical and foliar biochemical markers indicate perturbations in biological processes in healthy red spruce trees across the northeastern USA. Previous research on the dendrochemistry of red spruce stemwood indicated that under uniform environmental conditions, stemwood concentrations of Ca and Mg decreased with increasing radial distance from the pith. For nine forest locations, frequency analysis shows that 28 and 52% of samples of red spruce stemwood formed in the 1960s are enriched in Ca and Mg, respectively, relative to wood formed prior to and after the 1960s. This enrichment in trees throughout the northeastern USA may be interpretable as a signal of increased availability of essential cations in forest soils. Such a temporary increase in the availability of Ca and Mg could be caused by cation mobilization, a consequence of increased acidic deposition. During cation mobilization, essential Ca and Mg as well as potentially harmful Al become more available for interaction with binding sites in the soil and absorbing roots. As conditions which favor cation mobilization continue, Ca and Mg can be leached or displaced from the soil. A measure of the interaction between Ca and Al is the Al/Ca binding ratio (molar charge ratio of exchangeable Al to exchangeable Ca). As the Al/Ca binding ratio in the root zone increased from 0.3 to 1.9, the foliar concentration of the biochemical stress marker putrescine also increased from 45 to 145 nm g −1 . The correlation of the putrescine concentration to the Al/Ca binding ratio (adj. r 2 = 0.68, P < 0.027) suggests that foliar stress may be linked to soil chemistry.

Journal of Environmental Quality↗

USGS1996

40Ar/39Ar whole-rock data constraints on Acadian diagenesis and Alleghanian cleavage in the Martinsburg formation, eastern Pennsylvania

A comparison of 40 Ar/ 39 Ar age spectra of whole-rock mudstone and slate samples from the Ordovician Martinsburg Formation at Lehigh Gap, Pennsylvania and stratigraphic and thermal constraints support Alleghanian age for regional slaty cleavage and a late Acadian age for diagenesis in these rocks. Age spectra from mud-stones have a sigmodal shape, with slopes that climb steeply from apparent Mesozoic ages to intermediate saddle regions with Devonian apparent ages, and then climb steeply again to Late Proterozoic apparent ages. The steps with these oldest apparent ages are interpreted to be dominated by late Proterzoic detrial muscovite. The saddle region of the mudstone samples gives very Late Silurian to earliest Devonian ages, which are maximum ages of diagenetic micas and which eliminate a Taconic age for the cleavage. The ages of saddle regions of the slate samples constraining cleavage-forming muscovite is <~375. This is the maximum age of this mica and requires an Alleghanian age for the cleavage. These age constraints are supported by ages of individual mica components calculated with knowledge of the total gas ages and mass fractions of the micas and by predictions from thermal modeling. We conclude that the Taconic orogeny in the Martinsburg Formation in eastern Pennsylvania was a very mild event. Not only is the cleavage in these rocks not Taconic in age, but even the mild (~100C) diagenetic growth of illite was Silurian of younger. Thus the Taconic event in these rocks in limited to loading of lass than about 3 km.

Connecticut, Delaware, Maryland, Pennsylvania, New↗

USGS1993

Population trends of Alaskan seabirds

Ornithology in Alaska formally began with the observations of Georg Wilhelm Steller during Vitus Bering's voyage of discovery in 1741. Steller's journal makes brief mention of various seabird species he encountered during his travels in the Gulf of Alaska and Aleutian Islands (Frost and Engel 1988). For more than 100 years following Steller, the Russian-American Company was active in commercial fur harvesting throughout southern coastal Alaska, but this period saw little contribution to a scientific understanding of the region's avifauna. With the purchase of Alaska by the United States in 1867, a period of American exploration began that included significant work by pioneering naturalists such as Dall (1873, 1874), Elliot (1881), Nelson (1883), and Turner (1885, 1886). While this activity established a comprehensive list and general knowledge of the distribution of seabird species occurring in Alaska, early observers provided no quantitative estimates of abundance for any colony or region. The observations of Heath (1915) and Willett (1912, 1915, 1917) at two locations in southeastern Alaska are notable for including the first numerical estimates of any seabird populations for comparison with recent data. Willett's (1912, 1915) estimates of 13 species are given in Table 1 with results from a 1976 Survey at Forrester Island (DeGange et al. 1977) and a 1981 survey at St. Lazaria Island (Nelson et al 1982). In the aggregate, seabird numbers appeared to increase dramatically at both sites, but the differences may be largely artificial. Because Willett (1915) did not employ rigorous sampling methods, DeGange et al. (1977) surmised that he grossly underestimated the populations of burrowing species such as storm-petrels, Cassin's Auklets. and Rhinoceros Aulkets. Nelson et al. (1982) offered a similar interpretation of total storm-petrel numbers at St. Lazaria, but felt that a shift in the species ratio of Leach's and Fork-tailed Storm-Petrels had likely occurred. It seems reasonably certain that real changes in some of the open-nesters like Common Murres (down at Forrester Island, up at St. Lazaria) and Glaucous-winged and Herring Gulls (absent or down at both sites) have occurred since Willet's time.

Alaska↗

USGS2008

Surface processes recorded by rocks and soils on Meridiani Planum, Mars: Microscopic Imager observations during Opportunity's first three extended missions

The Microscopic Imager (MI) on the Mars Exploration Rover Opportunity has returned images of Mars with higher resolution than any previous camera system, allowing detailed petrographic and sedimentological studies of the rocks and soils at the Meridiani Planum landing site. Designed to simulate a geologist's hand lens, the MI is mounted on Opportunity's instrument arm and can resolve objects 0.1 mm across or larger. This paper provides an overview of MI operations, data calibration, and analysis of MI data returned during the first 900 sols (Mars days) of the Opportunity landed mission. Analyses of Opportunity MI data have helped to resolve major questions about the origin of observed textures and features. These studies support eolian sediment transport, rather than impact surge processes, as the dominant depositional mechanism for Burns formation strata. MI stereo observations of a rock outcrop near the rim of Erebus Crater support the previous interpretation of similar sedimentary structures in Eagle Crater as being formed by surficial flow of liquid water. Well‐sorted spherules dominate ripple surfaces on the Meridiani plains, and the size of spherules between ripples decreases by about 1 mm from north to south along Opportunity's traverse between Endurance and Erebus craters.

Journal of Geophysical Research E: Planets↗

USGS2012

Three-dimensional P velocity structure of the crust below Newberry Volcano, Oregon

Utilizing teleseismic P residuals, we have detected a column of high P velocity material extending from within 10 km of the surface below the summit of Newberry Volcano, Oregon, to midcrustal depths near 25 km. We interpret this column to be the expression of a swarm of predominantly subsolidus gabbroic sills and dikes which were intruded as the volcano was built. The high P velocities observed below the volcano severely limit the size of magma chambers which could presently exist in the crust below Newberry Volcano. Those possible include a few percent of partial melt distributed through large volumes of a mafic intrusion zone in the midcrust; a few, smaller, higher melt fraction zones in the midcrust with dimensions less than 6 km and whose aggregate volume is only a few percent of enclosing volumes of 200 km 3 ; small magma bodies with dimensions of a few kilometers located within the upper 10 km of the crust; or a mafic, crystal-rich magma of arbitrary dimensions located in the upper few km. The low P velocities detected in the upper 4 km beneath the center of the summit caldera may be partially caused by a magma chamber in the second of these catagories.

Journal of Geophysical Research Solid Earth↗

USGS2010

Algal blooms and "Marine snow": Mechanisms that enhance preservation of organic carbon in ancient fine-grained sediments

Combined petrographic and geochemical methods are used to investigate the microfabrics present in thin sections prepared from representative organic carbon-rich mudstones collected from three successions (the Kimmeridge Clay Formation, the Jet Rock Member of the Whitby Mudstone Formation, and the pebble shale and Hue Shale). This study was initiated to determine how organic carbon-rich materials were being delivered to the sediment–water interface, and what happened to them after deposition, prior to deep burial. Analyses of the fabrics present shows that they exhibit many common attributes. In particular they are all: (1) highly heterogeneous on the scale of a thin section, (2) organized into thin beds (< 10 mm thick) composed mainly of mineral mixtures of fine-grained siliciclastic detritus and carbonate materials, and (3) contain significant concentrations of organic carbon, much of which is organized into laminasets that contain abundant organomineralic aggregates and pellets. In addition, framboidal pyrite (range of sizes from < 20 μm to < 1 μm) and abundant agglutinated foraminifers are present in some units. The individual beds are commonly sharp-based and overlain by thin, silt lags. The tops of many of the beds have been homogenized and some regions of the pelleted laminasets contain small horizontal burrows. The organomineralic aggregates present in these mudstones are interpreted to be ancient examples of marine snow. This marine snow likely formed in the water column, particularly during phytoplankton blooms, and was then transported rapidly to the seafloor. The existence of the thin beds with homogenized tops and an in-situ infauna indicates that between blooms there was sufficient oxygen and time for a mixed layer to develop as a result of sediment colonization by diminutive organisms using either aerobic or dysaerobic metabolic pathways. These textures suggest that the constituents of these mudstones were delivered neither as a continuous rain of sediment nor were the bottom waters persistently anoxic. In addition, the presence of thin lags and sharp-based beds suggests that the seafloor was being episodically reworked during deposition. These fabrics indicate that conditions in the water columns and at the seafloors while these rocks were being deposited were very dynamic, and episodic fluxes of high concentrations of organic carbon to the seafloor, during phytoplankton blooms, likely enhanced preservation of organic carbon.

Journal of Sedimentary Research↗

USGS2015

Comment on Spracklandus Hoser, 2009 (Reptilia, Serpentes, ELAPIDAE): request for confirmation of availability of the generic name and for the nomenclatural validation of the journal in which it was published (Case 3601; BZN 70:234–237; 71:30–38; 133-135,181-182 ,252-253)

In Case 3601 Raymond Hoser has asked the Commission to validate for the purposes of nomenclature the name Spracklandus Hoser, 2009, and ‘the journal in which it was published,’ issue 7 of the Australasian Journal of Herpetology (AJH). We note that the entire run of AJH has been written, edited, and published solely by Hoser. Although his requests to the Commission were presented as narrow and, in his words, ‘routine matters,’ we are convinced that they represent an important tipping-point with broad implications of major concern for zoological taxonomy and nomenclature as a whole and, by extension, the greater scientific community. Since Hoser’s actions and works have failed to follow scientific best practices (e.g. Turtle Taxonomy Working Group, 2007, 2014; Kaiser et al., 2013; Kaiser, 2014) and both the Commission’s general Recommendations and Code of Ethics in Appendix A, the global herpetological community has widely rejected his taxonomic decisions and resultant nomenclature. This has unfortunately caused a confusing dual nomenclature to develop in the herpetological community, with most boycotting or ignoring Hoser’s 700+ new names coined in the AJH, while he and a few personal followers actively promote their usage. We believe that suppression of the name Spracklandus , and all issues of AJH, is the only effective way to bring this contentious and confusing issue to resolution. The plenary power available under Article 81.1 of the Code exist specifically to allow the Commission to make rulings in individual cases that disturb stability and cause confusion, whether the works are Code-compliant or not. We maintain that it is in the interest of nomenclatural stability, not only for herpetology, but for all of zoological taxonomy, that the plenary power be invoked to declare the works in AJH unavailable, regardless of any narrow interpretation of their technical Code-compliance. We present our arguments for rejection of the validity of AJH in the following commentary. In view of the wide-reaching implications of this case for all of zoology, and reflecting the deep and broad-based community concern over these issues, our contributing authors include 70 global scientific leaders and accomplished amateurs from a wide variety of zoological disciplines.

Bulletin of Zoological Nomenclature↗

USGS2013

Field measurement of basal forces generated by erosive debris flows

It has been proposed that debris flows cut bedrock valleys in steeplands worldwide, but field measurements needed to constrain mechanistic models of this process remain sparse due to the difficulty of instrumenting natural flows. Here we present and analyze measurements made using an automated sensor network, erosion bolts, and a 15.24 cm by 15.24 cm force plate installed in the bedrock channel floor of a steep catchment. These measurements allow us to quantify the distribution of basal forces from natural debris‒flow events that incised bedrock. Over the 4 year monitoring period, 11 debris‒flow events scoured the bedrock channel floor. No clear water flows were observed. Measurements of erosion bolts at the beginning and end of the study indicated that the bedrock channel floor was lowered by 36 to 64 mm. The basal force during these erosive debris‒flow events had a large‒magnitude (up to 21 kN, which was approximately 50 times larger than the concurrent time‒averaged mean force), high‒frequency (greater than 1 Hz) fluctuating component. We interpret these fluctuations as flow particles impacting the bed. The resulting variability in force magnitude increased linearly with the time‒averaged mean basal force. Probability density functions of basal normal forces were consistent with a generalized Pareto distribution, rather than the exponential distribution that is commonly found in experimental and simulated monodispersed granular flows and which has a lower probability of large forces. When the bed sediment thickness covering the force plate was greater than ~ 20 times the median bed sediment grain size, no significant fluctuations about the time‒averaged mean force were measured, indicating that a thin layer of sediment (~ 5 cm in the monitored cases) can effectively shield the subjacent bed from erosive impacts. Coarse‒grained granular surges and water‒rich, intersurge flow had very similar basal force distributions despite differences in appearance and bulk‒flow density. These results demonstrate that debris flows can have strong control on rates of steepland evolution and contribute to a foundation needed for modeling debris‒flow incision stochastically.

Journal of Geophysical Research F: Earth Surface↗

USGS2017

Ascaulocardium armatum (Morton 1833), new genus (Late Cretaceous): the ultimate variation on the bivalve paradigm

Cretaceous clavagellid pelecypods are a poorly known group, and have previously received little study. Ascaulocardium armatum is conchologically the most complex burrowing pelecypod known. From the study of living clavagellids, it is possible to interpret the various tubes extending outward from the adventitious crypt of A. armatum as devices for hydraulic burrowing and deposit feeding. The conchologically complex A. armatum occurs near the beginning of the history of the Clavagellidae, and does not seem to have given rise to any younger species. Ascaulocardium armatum is known only from the Upper Cretaceous rocks (Santonian–Maastrichtian) of the east Gulf and Atlantic Coastal Plains of the United States of America, as is probably the genus Ascaulocardium . All known Cretaceous clavagellids are burrowing species having a free right valve, and this is the ancestral mode of life of the Clavagellidae. Clavagellids that have a boring habit are a more recent evolutionary development, as are burrowing species having both juvenile valves cemented to the crypt. Clavagellids probably evolved from Jurassic–Early Cretaceous pholadomyids. Almost all Cretaceous clavagellids occur outside the Tethyan Zoogeographic Realm; this distribution is in marked contrast to the modern distribution of the family. Living species mostly inhabit clear, shallow seas in subtropical to tropical shelf areas.

Journal of Paleontology↗

USGS2007

Paleoecology of the Late Pennsylvanian-age Calhoun coal bed and implications for long-term dynamics of wetland ecosystems

Quantitative plant assemblage data from coal balls, miospores, megaspores, and compression floras from the Calhoun coal bed (Missourian) of the Illinois Basin (USA) are used to interpret spatial and temporal changes in plant communities in the paleo-peat swamp. Coal-ball and miospore floras from the Calhoun coal bed are dominated strongly by tree ferns, and pteridosperms and sigillarian lycopsids are subdominant, depending on geographic location within the coal bed. Although the overall composition of Calhoun peat-swamp assemblages is consistent both temporally and spatially, site-to-site differences and short-term shifts in species dominance indicate local topographic and hydrologic control on species composition within the broader context of the swamp. Statistical comparison of the Calhoun miospore assemblages with those from other Late Pennsylvanian coal beds suggests that the same basic species pool was represented in each peat-swamp landscape and that the relative patterns of dominance and diversity were persistent from site to site. Therefore, it appears that the relative patterns of proportional dominance stayed roughly the same from one coal bed to the next during Late Pennsylvanian glacially-driven climatic oscillations.

International Journal of Coal Geology↗

USGS2008

Seismicity and deformation induced by magma accumulation at three basaltic volcanoes

We analyzed the evolution of volcano‐tectonic (VT) seismicity and deformation at three basaltic volcanoes (Kilauea, Mauna Loa, Piton de la Fournaise) during phases of magma accumulation. We observed that the VT earthquake activity displays an accelerating evolution at the three studied volcanoes during the time of magma accumulation. At the same times, deformation rates recorded at the summit of Kilauea and Mauna Loa volcanoes were not accelerating but rather tend to decay. To interpret these observations, we propose a physical model describing the evolution of pressure produced by the accumulation of magma into a reservoir. This variation of pressure is then used to force a simple model of damage, where damage episodes are equivalent to earthquakes. This model leads to an exponential increase of the VT activity and to an exponential decay of the deformation rate during accumulation phases. Seismicity and deformation data are well fitted by such an exponential model. The time constant, deduced from the exponential increase of the seismicity, is in agreement with the time constant predicted by the model of magma accumulation. This VT activity can thus be a direct indication of the accumulation of magma at depth, and therefore can be seen as a long‐term precursory phenomenon, at least for the three studied basaltic volcanoes. Unfortunately, it does not allow the prediction of the onset of future eruptions, as no diverging point (i.e., critical time) is present in the model.

Journal of Geophysical Research B: Solid Earth↗

USGS2012

Electrical structure of Newberry Volcano, Oregon

From the interpretation of magnetotelluric, transient electromagnetic, and Schlumberger resistivity soundings, the electrical structure of Newberry Volcano in central Oregon is found to consist of four units. From the surface downward, the geoelectrical units are (1) very resistive, young, unaltered volcanic rock, (2) a conductive layer of older volcanic material composed of altered tuffs, (3) a thick resistive layer thought to be in part intrusive rocks, and (4) a lower-crustal conductor. This model is similar to the regional geoelectrical structure found throughout the Cascade Range. Inside the caldera, the conductive second layer corresponds to the steep temperature gradient and alteration minerals observed in the USGS Newberry 2 test hole. Drill hole information on the south and north flanks of the volcano (test holes GEO N-1 and GEO N-3, respectively) indicates that outside the caldera the conductor is due to alteration minerals (primarily smectite) and not high-temperature pore fluids. On the flanks of Newberry the conductor is generally deeper than inside the caldera, and it deepens with distance from the summit. A notable exception to this pattern is seen just west of the caldera rim, where the conductive zone is shallower than at other flank locations. The volcano sits atop a rise in the resistive layer, interpreted to be due to intrusive rocks. The intrusive material has served as a heat source to produce enhanced hydrothermal alteration and, perhaps in the case of the west-flank anomaly, elevated fluid temperatures. While no public drill hole information is available to confirm this hypothesis, the west-flank anomaly appears to be a good geothermal target. In addition to the possibility that a region on the west side of the volcano could be favorable for prospecting, part of the resistive structure under the center of the volcano could be due to a vapor-dominated environment with temperatures above 300°C. In other parts of the Cascades, pervasive alteration has produced mixed layer clays and zeolites, resulting in low-resistivity anomalies. Low resistivities cannot be assumed to indicate high-temperature pore fluids. The use of electrical methods that measure resistivity as a function of excitation frequency, such as spectral induced polarization, may provide a way of obtaining information about the type and extent of alteration.

Journal of Geophysical Research Solid Earth↗

USGS2007

Geochemical interpretations of groundwater flow systems

Interest in the geochemistry of groundwater is increasing owing to the great number of current projects involving underground liquid waste storage, artificial recharge of potable water, accidental contamination of groundwater bodies, sanitary landfills, and pollution monitoring. Geochemical techniques used to facilitate the understanding of a groundwater system range from extremely simple to those requiring sophisticated theories, equipment, and procedures. An interpretation of the simple trilinear diagram for samples collected from the Yucatan Peninsula of Mexico provided evidence that the fresh-water body was only a few tens of meters thick and was underlain everywhere by an extensive body of salt water. A geochemical technique that has been used effectively to identify the source of salt water in coastal aquifers is measurement of the carbon-14 concentrations. Carbon-14 has been used in a regional carbonate aquifer to determine the velocity of groundwater movement, rates of chemical reactions, and distribution of hydraulic conductivity. The application of principles of irreversible thermodynamics to groundwater systems provides a basis for constructing models which permit prediction, over both time and space, of changes in head distribution and chemical character of the water resulting from imposed stresses on the system. In essence, proper application of irreversible thermodynamics combines the potential theory of Hubbert with principles of reversible chemical thermodynamics, such as solution of carbonate minerals, to describe and explain controlling chemical reactions and processes of groundwater systems.

Florida, South Carolina↗

USGS2012

The 1170 and 1202 CE Dead Sea Rift earthquakes and long-term magnitude distribution of the Dead Sea Fault zone

In combination with the historical record, paleoseismic investigations have provided a record of large earthquakes in the Dead Sea Rift that extends back over 1500 years. Analysis of macroseismic effects can help refine magnitude estimates for large historical events. In this study we consider the detailed intensity distributions for two large events, in 1170 CE and 1202 CE, as determined from careful reinterpretation of available historical accounts, using the 1927 Jericho earthquake as a guide in their interpretation. In the absence of an intensity attenuation relationship for the Dead Sea region, we use the 1927 Jericho earthquake to develop a preliminary relationship based on a modification of the relationships developed in other regions. Using this relation, we estimate M7.6 for the 1202 earthquake and M6.6 for the 1170 earthquake. The uncertainties for both estimates are large and difficult to quantify with precision. The large uncertainties illustrate the critical need to develop a regional intensity attenuation relation. We further consider the distribution of magnitudes in the historic record and show that it is consistent with a b-value distribution with a b-value of 1. Considering the entire Dead Sea Rift zone, we show that the seismic moment release rate over the past 1500 years is sufficient, within the uncertainties of the data, to account for the plate tectonic strain rate along the plate boundary. The results reveal that an earthquake of M7.8 is expected within the zone on average every 1000 years. ?? 2011 Science From Israel/LPPLtd.

Israel Journal of Earth Sciences↗

USGS2014

Organic petrology of the Aptian-age section in the downdip Mississippi Interior Salt Basin, Mississippi, USA: Observations and preliminary implications for thermal maturation history

This study identifies a thermal maturity anomaly within the downdip Mississippi Interior Salt Basin (MISB) of southern Mississippi, USA, through examination of bitumen reflectance data from Aptian-age strata (Sligo Formation, Pine Island Shale, James Limestone, and Rodessa Formation). U.S. Geological Survey (USGS) reconnaissance investigations conducted in 2011–2012 examined Aptian-age thermal maturity trends across the onshore northern Gulf of Mexico region and indicated that the section in the downdip MISB is approaching the wet gas/condensate window (R o ~1.2%). A focused study in 2012–2013 used 6 whole core, one sidewall core, and 49 high-graded cutting samples (depth range of 13,000–16,500 ft [3962.4–5029.2 m] below surface) collected from 15 downdip MISB wells for mineralogy, fluid inclusion, organic geochemistry, and organic petrographic analysis. Based on native solid bitumen reflectance (R o generally > 0.8%; interpreted to be post-oil indigenous bitumens matured in situ), R o values increase regionally across the MISB from the southeast to the northwest. Thermal maturity in the eastern half of the basin (R o range 1.0 to 1.25%) appears to be related to present-day burial depth and shows a gradual increase with respect to depth. To the west, thermal maturity continues to increase even as the Aptian section shallows structurally on the Adams County High (R o range 1.4 to > 1.8%). After evaluating the possible thermal agents responsible for increasing maturity at shallower depths (i.e., igneous activity, proximity to salt, variations in regional heat flux, and uplift), we tentatively propose that either greater paleoheat flow or deeper burial coupled with uplift in the western part of the MISB could be responsible for the thermal maturity anomaly. Further research and additional data are needed to determine the cause(s) of the thermal anomaly.

International Journal of Coal Geology↗

USGS1997

An integrated model for the tectonic development of the frontal Brooks Range and Colville Basin 250 km west of the Trans-Alaska Crustal Transect

We present a kinematic model for the sequence of deformation and sedimentation in the frontal Brooks Range and adjacent Colville Basin in the Etivluk River region, 250 km west of the Trans-Alaska Crustal Transect (TACT). The model is based on a tectonic subsidence analysis of the foreland basin, combined with structural, stratigraphic, and thermal studies of the northern edge of the Brooks Range thrust belt. We interpret six discrete tectonic events that led to the present-day configuration of the thrust belt in this area: (1) emplacement of ophiolitic allochthons over the distal continental margin rocks in Valanginian time, hundreds of kilometers south of this study, (2) Hauterivian uplift of the Barrow Arch rift margin, affecting the northern part of the Colville Basin, (3) Barremian contraction involving emplacement of distal continental margin and ophiolitic allochthons onto the Endicott Mountains allochthon and creation of a southward dipping flexural basin on the North Slope autochthon, (4) mid-Cretaceous exhumation of imbricated rocks in the Brooks Range during northward propagation of the thrust front into the foreland, (5) minor thrusting in Late Cretaceous-Paleocene in the northern foreland to the northern limit of contractional structures, and (6) regional exhumation of the orogen and the foreland in Paleocene-Eocene time. This sequence of deformation agrees well with a simple model of a forward propagating thrust system.

Journal of Geophysical Research B: Solid Earth↗