bluuebunny/crossref_metadata_2025_split huggingface dataset:
Geologic mapping, morphometric characterization, and statistical analyses of six venusian shield fields: Insights into the processes related to their formation
Authors: Nypaver* Cole , Lang† Nicholas P. , Thomson Bradley J. 
Published: October 2019

ABSTRACT
Small shield volcanoes with basal diameters &lt;20 km represent the most abundant type of volcano on Venus. These shield volcanoes number &gt;&gt;106 in population and often occur in clusters known as shield fields, which have been interpreted to be analogous to basaltic volcanic fields on Earth. Despite previous work on shield fields, questions related to edifice morphology and magma viscosity, timing relations of events across an individual field, volume of erupted material, and the role of tectonic structures are still unresolved. Here, we address those questions through geologic mapping, volumetric calculations, and statistical analysis of possible edifice alignments in six venusian shield fields: Asherat Colles, Chernava Colles, Monoshi Tholus, Nordenflycht Patera, Ran Colles, and Urutonga Colles. Our results indicate that all of these shield fields and their associated deposits are younger than the surrounding units within the mapping areas, and each field displays overlapping temporal relations with local extensional and contractional structures. Each field also displays a lack of a consistent pattern in the temporal distribution of volcanism with regards to edifice type. Analyses of possible edifice alignments suggest edifice trends that are consistent with mapped tectonic structures within all studied fields except Asherat Colles. Comparison of these six venusian fields to terrestrial basaltic volcanic fields shows that venusian fields may be up to two to three orders of magnitude larger in their areal expanse and volume of erupted material. Our results are consistent with previous interpretations of venusian shield fields representing low rates (likely &lt;5 × 10−4 km3/yr) of magma supply feeding these magmatic centers and highlight the effects of the resolution limit of the Magellan data set on interpreting fundamental geologic processes on the venusian surface.
Taxonomy of Cretaceous–Paleogene coniferous woods and their distribution in fossil Lagerstätten of the high latitudes
Authors: Dolezych* M. , Reinhardt* L. , Kus* J. , Annacker* V. 
Published: October 2019

ABSTRACT
Anatomical analyses of fossil woods, supplemented by information from coal petrographic investigations, provide data for reconstructing the Cretaceous–Paleogene, mostly swampy woodland vegetation of the high latitudes. This paper is focused on the taxonomic description of conifers that have been recovered from a number of plant fossil Lagerstätten in Nathorstland, Yukon North Slope–western Mackenzie Delta, Ellesmere Island, northern Trolleland, and Kotel’nyi Island. The investigation revealed a relatively low taxonomic diversity. Wood-anatomical identification of Taxodioxylon vanderburghii provides evidence for the genus Metasequoia. The determination of Glyptostroboxylon cf. rudolphii demonstrates the most likely presence of Glyptostrobus, and the genus Cunninghamia is proved by the identification of Glyptostroboxylon tenerum. Moreover, this first evidence of Cunninghamia in the high latitudes establishes this plant as an “Arctic conifer.” Piceoxylon laricinoides (Høeg) comb. nov., a new combination, is proposed for a fossil wood species that represents the genus Larix. Fossils identified as Protopiceoxylon woods, Protopiceoxylon sp., and Protopiceoxylon yukonense represent the extinct gymnospermous Protopinaceae group. A fossil forest from the Split Lake Lagerstätte focusing on the habitus of in situ trunks and stumps was reconstructed. The vegetation encompasses a succession with three stages, an Equisetum reed facies, a Metasequoia swamp forest facies, and a Larix swamp forest facies. The taxonomic investigation suggests a widely distributed zone of vegetation with various conifers in the high latitudes. The lignite samples are characterized by predominantly woody (xylite) tissues with well-preserved, mummified stems and roots and a variable content of liptinite macerals, mostly resinite and suberinite. The intensive yellow fluorescent textinite of characteristic zoned structures and distinct microspores was observed in all investigated lignites.
Subsidence, rapid inversion, and slow erosion of the Central Tertiary Basin of Svalbard: Evidence from the thermal evolution and basin modeling
Authors: Dörr N. , Lisker F. , Jochmann M. , Rainer T. , Schlegel A. , Schubert K. , Spiegel* C. 
Published: October 2019

ABSTRACT
The Central Tertiary Basin (CTB) of Svalbard provides a rare opportunity for studying the sedimentary response to the Cenozoic evolution of the Barents Sea area. Here we present a basin model based on low-temperature thermochronology data, vitrinite reflectance measurements, and clay mineralogy from two drill cores inside the CTB. Our model suggests a tight relationship between the basin history and the regional geodynamic evolution. Enhanced heat flow during the Paleocene implies an extensional or transtensional origin of the basin, prior to Eurekan deformation. The first, compressional stage of the Eurekan orogeny was associated with rapid basin subsidence and high deposition rates, causing the coalification of the CTB hard coals. The second, transpressional stage of the Eurekan triggered rapid basin erosion and was associated with a decreasing heat flow. Onset of erosion is placed at ~45 ± 5 Ma, suggesting cessation of CTB deposition already by the late Early Eocene. Rapid erosion stopped coevally or just prior to the change to an extensional setting at the end of Eurekan deformation. Between ~40 and 10 Ma, the CTB experienced continuous slow erosion. From the Late Miocene onwards, erosion again accelerated, maybe related to lithospheric processes associated with northward propagation of the Knipovich Ridge. Estimates from our best-fit model suggest that nearly ~4 km of overburden was removed from the CTB since the end of Early Eocene.
Geochemical constraints on the provenance of pre-Mississippian sedimentary rocks in the North Slope subterrane of Yukon and Alaska
Authors: Nelson Lyle L. , Strauss Justin V. , Crockford Peter W. , Cox Grant M. , Johnson Benjamin G. , Ward William , Colpron Maurice , McClelland William C. , Macdonald Francis A. 
Published: October 2019

ABSTRACT
The North Slope subterrane of Arctic Alaska extends from the northeastern Brooks Range of Alaska into adjacent Yukon, Canada, and includes a pre-Mississippian deep-water sedimentary succession that has been historically correlated with units exposed in the Selwyn basin of northwestern Laurentia. Sedimentary provenance data, including Sm-Nd isotopes and major and trace element geochemistry, provide detailed geochemical characterization of the regional pre-Mississippian strata of the North Slope subterrane. Combined with paleontological and geochronological age constraints, these new data record a marked shift in provenance in the Ordovician–Devonian(?) Clarence River Group, evidently linked to an influx of juvenile, arc-derived material. The timing and nature of this provenance change are consistent with early Paleozoic tectonic reconstructions of the Arctic margin that restore the North Slope subterrane to northeastern Laurentia (present coordinates), proximal to the Appalachian-Caledonian orogenic belt. Such a restoration requires significant post-Early Devonian sinistral strike-slip displacement to later incorporate the North Slope subterrane into the composite Arctic Alaska terrane.
Age, geochemistry, and significance of Devonian felsic magmatism in the North Slope subterrane, Yukon, Canadian Arctic
Authors: Ward William P. , Strauss Justin V. , Johnson Benjamin G. , McClelland* William C. , Colpron Maurice , von Gosen Werner , Piepjohn Karsten , Coble Matthew A. , Crockford Peter W. , Landis Joshua 
Published: October 2019

ABSTRACT
New zircon U-Pb dates from the Mount Fitton, Mount Sedgwick, Mount Schaeffer, Old Crow, and Dave Lord plutons indicate that granitoids of the Old Crow plutonic suite in northern Yukon were emplaced in the North Slope subterrane of the Arctic Alaska composite terrane between 375 ± 2 Ma and 368 ± 3 Ma. Whole-rock major and trace element and Nd-Sr isotope geochemistry, combined with zircon trace element and Hf isotope geochemistry, indicate magma genesis involved significant contribution from older continental crust. Samples from the five plutons yield whole-rock εNd(t) values from -3.9 to -11.6 and 87Sr/86Sr(i) ratios of 0.7085–0.7444 and 0.8055. Zircon εHf(t) values range from -6.2 to -13.3. These North Slope subterrane granitoids are generally younger and isotopically more evolved than felsic rocks in the Coldfoot and Hammond subterranes of the southern Brooks Range (Arctic Alaska terrane), but in part are coeval with felsic rocks on the Seward and Chukotka peninsulas. The North Slope granitoids are also coeval and geochemically similar to arc magmatism in the Yukon-Tanana terrane in Yukon and on Axel Heiberg and northern Ellesmere islands, Nunavut. The Old Crow plutonic suite is interpreted as part of a Late Devonian arc system developed along the Arctic and Cordilleran margins. Late Devonian plutons were most likely emplaced after initial translation of the North Slope subterrane along the northern Laurentian margin. The plutons lie within or north of the Porcupine shear zone and thus do not limit post-Late Devonian displacement on the boundary between the North Slope subterrane and northwestern Laurentia.
Evidence for subtropical warmth in the Canadian Arctic (Beaufort-Mackenzie, Northwest Territories, Canada) during the early Eocene
Authors: Salpin Marie , Schnyder Johann , Baudin François , Suan Guillaume , Suc Jean-Pierre , Popescu Speranta-Maria , Fauquette Séverine , Reinhardt Lutz , Schmitz Mark D. , Labrousse Loïc 
Published: October 2019

ABSTRACT
During the Paleocene–Eocene, the Earth experienced the warmest conditions of the Cenozoic and reduced equator-to-pole temperature gradients. Compared to low- and mid-latitude sites, Paleogene environmental changes are less documented in Arctic regions, although such high latitude areas constitute a critical domain to constrain global climate changes. Floral and faunal assemblages indicative of exceptionally warm and humid conditions during the late Paleocene–early Eocene have been reported in several localities around the Arctic Ocean. Additional studies are required to ascertain the effects of Paleocene–Eocene global environmental changes on western Arctic regions. Here we present multiproxy data from early Eocene deltaic plain sediments of the Mackenzie Delta (Canada). This environment is characterized by littoral forest, including swamp, showing that the mangrove Avicennia grew in Arctic Canada near 75°N under air temperatures averaging 21–22 °C annually and 10–14 °C in winter and with precipitation of 1200–1400 mm/yr. Kaolinite contents are high (up to 75% of clay assemblages), as under a modern subtropical climate. The Avicennia pollens recently found in the New Siberian Islands and in Arctic Canada imply that warm and wet conditions were widespread along the Arctic coast during the early Eocene. It also suggests a marine connection between the Arctic Basin and the mid-latitude oceans. We propose that an oceanic current must have connected the Arctic Basin to the Atlantic and/or Pacific and that an internal current developed in the Arctic Basin since the early Eocene.
Latest Cretaceous–early Eocene Pacific-Arctic?-Atlantic connection: Co-evolution of strike-slip fault systems, oroclines, and transverse fold-and-thrust belts in the northwestern North American Cordillera
Authors: Murphy* Donald C. 
Published: October 2019

ABSTRACT
Comprehensive understanding of the pre-Paleogene kinematic evolution of the North American Cordillera in the context of evolving global plate interactions must begin with an understanding of the complex Late Cretaceous–early Eocene structural geometry and evolution of the northwestern Cordillera of Alaska, United States, and Yukon, Canada. Here, I present a kinematic model of the region that shows how regional strike-slip fault systems, including plate-boundary transform faults, interacted with each other, and with north-striking oroclinal folds and fold-and-thrust belts, which formed progressively during coeval shortening between Eurasia and North America. These Late Cretaceous–early Eocene interactions are manifestations of the plate reorganizations in the Pacific and Atlantic-Arctic regions that took place at that time, and that led to rifting and seafloor spreading within the globe-encircling Eurasian–North American plate and to the formation of transform-dominant North American–Pacific (sensu lato) and possibly North American–Arctic plate boundaries.
Genesis of the Edwards (Balcones Fault Zone) Aquifer
Authors: Schindel Geary M. 
Published: October 2019

ABSTRACT
The San Antonio segment of the Edwards (Balcones Fault Zone) Aquifer of south-central Texas is one of the most important and prolific karst aquifers in the United States. Extending from Kinney County (west) to Hays County (northeast), it is the primary source of water for the municipal and agricultural communities surrounding the greater San Antonio area. Deposited in Early Cretaceous time, rocks of the Edwards Group vary from 150 to 300 m thick and include eight members with highly variable hydraulic attributes and solubility. Its complex tectonic, weathering, and geologic history has allowed dissolution of the highly soluble members to form a highly transmissive karst aquifer. Regionally, the Balcones fault zone provides pathways that allow captured streams to flow into the aquifer in the contributing and recharge zones.
Karstification of the aquifer has occurred by multiple processes, both epigenic and hypogenic, with visual documentation obvious in numerous caves of the area. Currently, overprinting of hypogenic systems by epigenic systems is common. The en echelon down-to-the-south faulting of the Balcones fault zone has resulted in deep burial of the aquifer in the artesian zone, with dissolution at depth driven by numerous processes, including infiltration of chemically aggressive surface water, hydraulic head, mixing corrosion, and biogenic acids. Well production in the artesian zone is commonly limited only by the discharge rate of the pump. The Edwards Aquifer is also noted for its diverse and widespread aquifer-adapted fauna, implying that the aquifer has a well-integrated karst conduit system.
Devils River watershed: Southern Edwards-Trinity Aquifer
Authors: Green R.T. , Fratesi B. , Toll N. , Bertetti F.P. , Nunu R. 
Published: October 2019

ABSTRACT
The Devils River in south-central Texas is recognized as one of the remaining pristine rivers in the state. Adding to its importance, the Devils River is a key tributary to the Rio Grande, providing essential freshwater flows to south Texas and the Rio Grande Valley. An efficient conveyance system for groundwater is shown to have formed in the karst carbonate watershed, located in a semiarid environment with modest distributed recharge, oftentimes less than 1–2 cm/yr. This conveyance system comprises preferential flow pathways that developed coincident with river channels. A strong correlation between wells with high well yield and proximity to higher-order river channels (i.e., within 2.5 km) was used as evidence of the presence of preferential flow pathways. An important observation is that groundwater flow in the Devils River watershed appears to be controlled by the morphology of the area more than the bulk hydraulic properties of the rocks. Flow measurements in the Devils River measured under relatively high- and low-flow conditions support the hypothesis that the river is gaining in downstream reaches. This characteristic leads to perennial river flow being restricted to only the lower reach of the river. Last, essentially all of the recharge to Amistad Reservoir that is derived from the Devils River watershed is contributed as surface flow from the river, and there is minimal underflow or cross-formational flow from the watershed at the point where the watershed abuts Amistad Reservoir.
Water quality and the bad-water (saline-water) zone of the Edwards (Balcones Fault Zone) Aquifer
Authors: Sharp John M. , Smith Brian A. 
Published: October 2019

ABSTRACT
The Edwards aquifers are typically faulted, karstified, and transmissive. Water quality is generally excellent; the hydrochemical facies is mostly a calcium bicarbonate water with total dissolved solids (TDS) &lt;500–1000 mg/L. Exceptions to this result from both natural and anthropogenic factors. In the Edwards Plateau, mixing of the formation water with underlying water from the Trinity aquifers or Permian rocks increases salinity to the west. Along the Balcones fault zone, the southern and eastern borders of the Edwards (Balcones Fault Zone) Aquifer are demarcated by a bad-water line where salinity rises to over 1000 mg/L. Detailed studies show that this line is a band, because salinities in the aquifer are not uniform with depth. The bad-water (or saline-water) zone is relatively stable over time, and six hydrochemical facies were identified, which are created by different combinations of dissolution of evaporite and other minerals, mixing with basinal brines, dedolomitization, and cross-formational flow from underlying formations. Flow in this zone is restricted, the waters are reducing, and recent studies suggest that microbes play important chemical and physical roles. The bad-water zone has sufficient water in storage and sufficient permeability so that desalination could be a future water-source option.
Aquifer storage and recovery in the Edwards Aquifers, Texas
Authors: Deeds Neil E. , Blumberg Fred 
Published: October 2019

ABSTRACT
Aquifer storage and recovery (ASR) is a proven water-supply strategy that uses an aquifer to store surplus water that will be available for later use when that stored water is needed. Although only three ASR systems are currently operating in Texas, recent incentives from the state, along with changes in regulatory framework, have helped to encourage consideration of ASR as a viable water-supply strategy. The changes in Texas law primarily reduced the power of groundwater conservation districts to regulate ASR, and they put the majority of the role of project authorization in the hands of the Texas Commission on Environmental Quality.
Two Edwards-named aquifers in Texas were considered in this work: the Edwards-Trinity (Plateau) and the Edwards (Balcones Fault Zone) Aquifers. Both of the aquifers have areas that appear to be suitable, from a hydrogeologic standpoint, for ASR. The Edwards hydrostratigraphic unit of the Edwards-Trinity (Plateau) Aquifer has generally good productivity and water quality. However, in some locations, the high natural gradient combined with low porosity may increase the design challenge due to bubble drift. These same characteristics exist in many areas of the freshwater portion of the Edwards (Balcones Fault Zones) Aquifer, although its high productivity makes for very attractive per-well recharge and recover rates. The lower natural gradient (and thus smaller potential for bubble drift) in the brackish portion of the Edwards Aquifer may make it a good candidate in areas where productivity is sufficient.
Tracer testing in the Edwards Aquifer
Authors: Johnson Steven , Schindel Geary M. , Van Brahana John 
Published: October 2019

ABSTRACT
Tracer testing is established as one of the best techniques for determining groundwater velocities and identifying groundwater flow directions in karstic systems. It has been employed in the Edwards (Balcones Fault Zone) Aquifer since the mid-1980s. Nontoxic, fluorescent organic dyes are most commonly used because they are comparatively inexpensive, relatively easily accessible, detectable at low concentrations, and not harmful to organisms that use or dwell in the aquifer or its springs. Tracer tests provide empirical evidence that is difficult to obtain any other way. Tracer tests have shown rapid groundwater velocities in the contributing, recharge, and artesian zones. Groundwater velocities were found to range from 915 to 9150 m/d in the Barton Springs segment of the aquifer; 1–3600 m/d in the San Marcos Springs area; 300–640 m/d near Comal Springs; 13 to &gt;5300 m/d in San Antonio/northern Bexar County; and 1–1367 m/d in Kinney County, Texas. Tracer testing has shown: (1) preferential flow paths are conduit-dominated; (2) in places, there is a hydraulic connection with the underlying Glen Rose Formation; (3) large offsets on faults are not barriers to flow; and (4) portions of the aquifer act as separate pools.
Multilevel monitoring of the Edwards and Trinity Aquifers
Authors: Smith Brian A. , Hunt Brian B. 
Published: October 2019

ABSTRACT
Multiport monitor wells have been used by the Barton Springs/Edwards Aquifer Conservation District (BSEACD) to study complex, multilayer, and stacked aquifers in central Texas. Much of the data from water wells that are used for hydrogeological studies are of limited use owing to the thickness of the aquifers, vertical variation in hydraulic properties, and the often-uncertain completion of the wells. To address these concerns, hydrogeologists and engineers have employed various methods, such as installation of nested wells, multilevel completions in a single borehole, and multiport wells. The BSEACD has used multiport wells to determine vertical variations in an aquifer and the hydraulic relationships between stacked aquifers. With multiport wells, properties such as hydraulic head, temperature, hydraulic conductivity, and water quality of discrete units within an aquifer can be determined. The use of multiport wells has shown how portions of the Upper Trinity lithologic units are hydraulically connected to the overlying Edwards lithologic units, and how the Edwards Aquifer is hydraulically isolated from the Middle and Lower Trinity Aquifers.