bluuebunny/crossref_metadata_2025 huggingface dataset:
Episodic tectonics in the Phanerozoic succession of the Canadian High Arctic and the “10-million-year flood”
Authors: Embry* Ashton , Beauchamp Benoit , Dewing Keith , Dixon James
Published: October 2019

We have identified 57 large-magnitude, sequence boundaries in the Phanerozoic succession of the Canadian High Arctic. The characteristics of the boundaries, which include angular unconformities and significant changes in depositional and tectonic regimes across the boundaries, indicate that they were primarily generated by tectonics rather than by eustasy. Boundary frequency averages 10 million years throughout the Phanerozoic and there is no notable variation in this frequency.

It is interpreted that each boundary was generated during a tectonic episode that lasted two million years or less. Each episode began with uplift of the basin margins and pronounced regression. This was followed by a rapid subsidence and the flooding of the basin margins. Each tectonic episode was terminated by a return to slow, long-term subsidence related to basin forming mechanisms such as thermal decay. The tectonic episodes were separated by longer intervals of tectonic quiescence characterized by slow subsidence and basin filling.

The tectonic episodes are interpreted to be the product of changes in lithospheric stress fields with uplift being related to increased, compressional horizontal stress and the following time of rapid subsidence reflecting a decrease in such stresses or an increase in tensional stresses. Conversely, the longer intervals of tectonic quiescence would reflect relatively stable, horizontal stress fields. The episodic changes in stress fields affecting the Canadian High Arctic throughout the Phanerozoic may be a product of intermittent, plate tectonic reorganizations that involved changes in the speed and directions of plate movements. The longer intervals of tectonic quiescence would occur during times of quasi-equilibrium in the plate tectonic mosaic.

The tectonic episodes that generated the sequence boundaries were governed by nonlinear dynamics and chaotic behavior, and there is a one-in-10-million chance that a tectonic episode will be initiated in the Canadian High Arctic in any given year. Thus, the major transgression associated with each episode can be referred to as a “10-million-year flood.”
Detrital zircon U-Pb and Lu-Hf analysis of Paleozoic sedimentary rocks from the Pearya terrane and Ellesmerian Fold Belt (northern Ellesmere Island): A comparison with Circum-Arctic datasets and their implications on terrane tectonics
Authors: Malone* Shawn J. , McClelland* William C. , Gosen* Werner von , Piepjohn* Karsten
Published: October 2019

Detrital zircon U-Pb and Hf isotopic data from Ordovician to Devonian–Carboniferous sedimentary rocks sampled from the Pearya terrane and adjacent areas, northern Ellesmere Island, record temporal variation in detrital zircon signature on the northeastern Arctic margin of Laurentia. Ordovician to Silurian clastic sediments deposited on the Pearya terrane record a provenance signal from before terrane accretion. This signal is dominated by Ordovician arc material and grains derived from recycling of Proterozoic metasedimentary and metaigneous basement. This pattern is similar to Neoproterozoic detrital zircon spectra from the Svalbard and East Greenland Caledonides, supporting the exotic nature of the Pearya terrane and links between Pearya and the Arctic Caledonides. Sedimentary rock deposited in the late Ordovician and early Silurian deep water basin of the Clements Markham fold belt likewise record a recycled source containing abundant early Neoproterozoic and Mesoproterozoic aged zircon. This contrasts with similarly aged units on Franklinian shelf, which contain much more abundant Paleoproterozoic zircon ages.

The provenance of the late Devonian–Carboniferous(?) Okse Bay Formation is dominated by sediment reworked from the units exposed in Pearya or the East Greenland Caledonides, with new sources derived from Paleoproterozoic domains of the Canadian-Greenland shield and late Devonian igneous rocks documented in Ellesmere and Axel Heiberg Islands, and Arctic Alaska. In contrast, detrital zircon age spectra from Devonian sedimentary rocks in the western Ellesmerian Clastic Wedge and northern Cordilleran clastic wedge of the Mackenzie Mountains contain abundant zircon grains yielding ages characteristic of the Caledonian and Timanian Orogens. This contrast suggests that the northeastern and northwestern sectors of the Paleozoic Laurentian Arctic margin received sediments from different terranes, with the northeast being dominated by reworked Caledonide terrane and Laurentian craton detritus, and the northwest likely receiving sediment from elements of Arctic Alaska–Chukotka. These detrital zircon data indicate that the Pearya terrane was isolated from northern Laurentia until after the late Silurian. The accretion of the Pearya terrane is constrained between the late Silurian and middle Devonian by stratigraphy, detrital zircon provenance shifts indicating a Laurentian cratonic source by the early Carboniferous, metamorphism in the orthogneiss basement observed between ca. 395 and 372 Ma, and the emplacement of the Cape Woods post-tectonic pluton at 390 Ma.
Early Carboniferous syn-rift sedimentation in the Sverdrup Basin (Yelverton Pass area, northern Ellesmere Island, Arctic Canada): A solution to the Okse Bay problem
Authors: Beauchamp B. , Alonso-Torres D. , Piepjohn K. , Thériault P. , Grasby S.E.
Published: October 2019

The unit previously mapped as the lower Upper Devonian Okse Bay Formation in the Yelverton Pass area of northern Ellesmere Island, considered indicative of syn-orogenic foreland (Devonian clastic wedge) basin deposition along the apex of the Ellesmerian Orogen, is in fact Early Carboniferous (Serpukhovian) in age and belongs to the Borup Fiord Formation of the successor Sverdrup Basin. The principal lines of evidence in favor of the original Okse Bay formational assignment were: (1) the presence of late Middle (Givetian) or early Late (Frasnian) Devonian palynomorphs; (2) a set of lithofacies presumably different from that of the Borup Fiord Formation; and (3) an angular unconformity between the so-called Okse Bay strata and overlying Pennsylvanian carbonates of the Nansen Formation. Here we demonstrate that the Devonian palynomorphs were eroded from the Devonian clastic wedge, transported for some distance, and deposited into the Sverdrup Basin in the Early Carboniferous. We also show that the units mapped as Okse Bay and Borup Fiord formations share the same clastic lithofacies assemblages, albeit in different proportions. We report the presence of Early Carboniferous palynomorphs in the uppermost part of a section assigned to the Okse Bay Formation, and show that detrital zircons contained in the middle part of the Okse Bay Formation yield dates as young as 358 Ma, thus demonstrating that the rocks that contain them are considerably younger than the assumed youngest age (Frasnian) based on palynology. We conclude that the Okse Bay Formation is the same unit as the Borup Fiord Formation and should be remapped as such. Both units are part of the same unconformity-bounded syn-rift Serpukhovian sequence that was rotated and differentially eroded prior to the widespread Pennsylvanian transgression.

The Serpukhovian sequence comprises three lithofacies assemblages: meandering stream clastic, braided stream/alluvial fan clastic, and shallow marine carbonate. These lithofacies assemblages were deposited as part of a differentially subsiding rift system likely bounded to the south by one or more master listric faults and associated footwall uplift, and to the north by hanging wall ramp uplift. The Serpukhovian sequence comprises three fourth-order sequences, each interpreted as corresponding to a rift pulse. Relatively coarse terrigenous sediments derived from the erosion of the Franklinian basement (Laurentia margin) and the Devonian clastic wedge entered the rift basin at a high angle through broad alluvial fans and braided river systems. These streams fed into a NE-flowing basin-axial meandering system, which met a shallow sea to the northeast. An additional source of sediments is Crockerland to the north, including syn- to post-Ellesmerian intrusions that shed detrital zircons of latest Devonian age once sufficient unroofing of these had occurred during the Serpukhovian.
Triassic history of the Tanquary High in NE Sverdrup Basin, Canadian Arctic Archipelago
Authors: Embry* Ashton
Published: October 2019

The Tanquary High is a positive tectonic feature that was identified on the southern margin of the far northeastern portion of Sverdrup Basin. A sequence stratigraphic analysis of the Triassic succession of northern Ellesmere Island, involving 27 measured sections and one well section, has allowed the geometry and evolution of the high in the Triassic to be elucidated. The Triassic succession occurs within five second-order sequences, and each sequence boundary reflects the occurrence of a tectonic episode that included basin margin uplift and basinward movement of the shoreline.

The Tanquary High was uplifted during these tectonic episodes, which occurred in the latest Permian, latest Early Triassic, latest Middle Triassic, latest Carnian, and latest Norian. Each sequence is truncated toward the crest of the high where Rhaetian strata now overlie Cambrian strata. Isopach and facies data for each sequence reveal that, at the times of maximum uplift of the Tanquary High, the subaerially exposed part of the high extended 100–150 km down its northwest-trending axis and up to 150–200 km down each flank. Rapid subsidence completed each tectonic episode and initiated the development of a new sequence. The Tanquary High was completely drowned at these times. It is hypothesized that the tectonic episodes were generated by changes in horizontal stress fields driven by plate tectonic reorganizations.

The facies and isopach maps of the latest Triassic to early Early Jurassic (Rhaetian-Sinemurian) second-order sequence demonstrate that the Tanquary High ceased to exist following the first order, latest Norian sequence boundary. A complete reversal of source areas and the initiation of the Amerasia rift basin coincided with the demise of the Tanquary High.
Early Cretaceous magmatism and post-Early Cretaceous deformation on Ellef Ringnes Island, Canadian High Arctic, related to the formation of the Arctic Ocean
Authors: Estrada Solveig , Piepjohn Karsten
Published: October 2019

Ellef Ringnes Island in the western Queen Elizabeth Islands near the Canadian Polar margin is characterized by intrusions of Cretaceous mafic sills and dikes related to the Canadian portion of the High Arctic Large Igneous Province (HALIP) and the presence of a unique network of NNE–SSW and WSW–ENE striking steep faults. The exposed dikes on northern Ellef Ringnes Island are mostly oriented parallel to the NNE–SSW faults according to the radiating dike swarm of the HALIP. The studied sills and dikes are geochemically very homogeneous and probably related to the same intrusion event at ca. 121 Ma. They share geochemical similarities with other tholeiitic basaltic rocks related to the first stage of the HALIP (ca. 130–120 Ma) that are exposed on Axel Heiberg and northern Ellesmere islands. All these suites were probably generated from a common large magmatic center related to a mantle plume. The NNE–SSW striking faults are characterized by dextral strike-slip kinematics active after ca. 100 Ma (after the intrusion of the Early Cretaceous sills and dykes and the deposition of the Christopher Formation) and before the deposition of the Neogene Arctic continental terrace wedge. However, they cannot be related to the dextral strike-slip regime parallel to the continental margin during stage 2 of the Eurekan deformation in the Late Eocene. Instead, the NNE–SSW dextral faults may represent dextral antithetic Riedel faults of a wide, NE–SW striking, anastomosing strike-slip fault zone along the northern continental margin of North America, which was possibly active during Eurekan stage 1 in the Early Eocene.
Aeromagnetic high-resolution survey over the Vendom Fiord region, Ellesmere Island, Canadian High Arctic
Authors: Ruppel Antonia , Damaske Detlef , Piepjohn Karsten
Published: October 2019

Within the Canadian High Arctic, Ellesmere Island represents a key region for improving our understanding of the plate tectonic configuration during the Paleogene times when Arctic Canada and Greenland represented two independently moving plates. Here, we present 4050 line kilometers of new high-resolution aeromagnetic data gathered across an area of 7000 km2 in the Vendom Fiord region on southern Ellesmere Island. The survey was flown with a two-kilometer line spacing and covered sedimentary rocks of the Franklinian Basin and the partly ice-covered basement rocks of the Inglefield Uplift. Magnetic domains, major lineaments, and depths of magnetic sources as well as magnetic trend lines are detected from total field data. These data and additional ground-based magnetic susceptibility measurements are integrated with exposure information and structural data in order to distinguish whether or not the ca. NNE–SSW trending Vendom Fiord Fault Zone can be related to the Wegener Fault. In addition, high-resolution aeromagnetic data and digital enhancement provide support for early Eocene deformation in the Vendom Fiord region during “Eurekan stage 1,” which seems to be decoupled from Paleocene to early Eocene deformation along the Wegener Fault.

A distinct NNE–SSW trending magnetic anomaly characterized by long wavelength is bordered by the Eurekan Fold-and-Thrust Belt in the western survey area. On a regional scale, this anomaly can be traced toward the NE where it represents the boundary between the deep water and shelf sequences of the Franklinian Basin along the Archer Fiord Fault Zone. Based on aeromagnetic anomaly data, the ice-covered boundary between sediments of the Franklinian Basin and the Precambrian basement is identified. High frequency anomalies east of this boundary characterize the basement rocks and show strong similarities to the Kane Basin region in the NE. The similarity of magnetic anomaly patterns in both regions indicates that the NNE–SSW trend of the fault zones in the study area west of the Inglefield Uplift turns continuously into an E–W trend north of the uplift in the Kane Basin region.
Structural evidence for sinistral displacement on the Wegener Fault in southern Nares Strait, Arctic Canada
Authors: von Gosen* W. , Piepjohn* K. , Gilotti* J.A. , McClelland* W.C. , Reinhardt* L.
Published: October 2019

The sinistral Wegener Fault in the Nares Strait between northwest Greenland and eastern Ellesmere Island (Canadian Arctic) represents a tectonic element in the Arctic whose existence and significance have been controversial for more than 50 years. Some workers interpret the Wegener Fault as an important early Tertiary transform related to movement of the Greenland plate relative to the North American plate. Others view it as insignificant or reject its existence. While onshore studies in the Canadian portion of the northern Nares Strait region have proven the existence of important sinistral strike-slip faults related to the offshore Wegener Fault, the southern continuation of the Wegener Fault in the southern Kane Basin and Smith Sound is unclear. In particular, Smith Sound has been interpreted as a location of an undisturbed continuation of the Proterozoic basement from Greenland to Ellesmere Island, with only one possible location of the Wegener Fault near the east coast of Ellesmere Island.

Our structural studies along the west coast of Smith Sound and adjacent areas of eastern Ellesmere Island suggest a three-phase tectonic evolution. Phase 1 is a brittle deformation (strike-slip faults, partly as conjugate sets) that took place under ~NW–SE shortening. It also occurs at the Smith Sound coast and did not affect the Paleogene deposits. Structures of this phase are assigned to the Paleocene and can be related to the Wegener Fault in the offshore area of Smith Sound just east of the eastern coast of Ellesmere Island. Deposition of thick conglomerates of the Paleocene Cape Lawrence Formation and relatively younger clastic sediments of the Eureka Sound Group (Paleocene–?Eocene) is interpreted to be related to local depocenters associated with the sinistral Wegener Fault.

Following uplift and subsidence during normal faulting associated with Phase 2 deformation, younger contractional deformation under ~NE–SW shortening (strike-slip faults, partly as conjugate sets) of Phase 3 deformation also affected the Paleogene deposits. Phases 2 and 3 can both be assigned to the Eocene.

Our interpretation points to a polyphase deformational history in the early Paleogene, which partly interfered with deposition of Paleogene clastic sediments. The first deformational phase in the Paleocene is related to the sinistral Wegener Fault, which, in the offshore areas, is not interpreted as a distinct through-going plane but as displaced by ~W–E striking faults. Therefore, our observation and interpretation support the existence of this fault in the southern Nares Strait region, east of the Ellesmere Island coast in Smith Sound.
Detrital zircon U-Pb geochronological and Hf isotopic constraints on the geological evolution of North Yukon
Authors: Colpron* Maurice , McClelland* William C. , Strauss* Justin V.
Published: October 2019

North Yukon lies at the intersection of two major tectonic domains that define the western and northern edges of the North American continent—the northern Cordilleran mountain belt and the Arctic Ocean. The pre-Carboniferous geology in North Yukon includes the Neoproterozoic−lower Paleozoic North Slope subterrane of the Arctic Alaska terrane and, south of the Porcupine shear zone, Mesoproterozoic−Paleozoic rocks of the Yukon stable block. The North Slope subterrane was deformed prior to deposition of Carboniferous and younger strata, and its paleogeographic origins are debated. North Yukon was deformed again during Cretaceous−Cenozoic development of the northern Cordilleran−Brookian orogen.

To help refine understanding of the geological evolution of the region, we present detrital zircon U-Pb and Hf isotopic data for 21 sandstone and conglomerate samples from Neoproterozoic to Cenozoic strata collected across North Yukon, between ~69°15′N and 67°11′N. Neoproterozoic−Cambrian strata in the British Mountains are characterized by a dominance of Paleoproterozoic zircons (peak at 1.7–1.8 Ga), whereas samples from the Barn Mountains to the south have abundant Mesoproterozoic grains (1.0–1.5 Ga), suggesting these rocks may have been deposited along different segments of the northern Laurentian margin. Regional geophysics suggest these domains could be separated by a fault. Northeastern Laurentian origins are indicated by distinct early Neoproterozoic and Ordovician−Silurian zircons in Upper Silurian−Lower Devonian immature sandstone and conglomerate of the Clarence River Group and provide the most compelling evidence for large-scale translation along northern Laurentia.

Precambrian detrital zircons in Carboniferous and younger strata reflect mostly recycling of local older strata. Carboniferous conglomerates all show Late Devonian peaks (365–378 Ma) consistent with erosion of nearby granitoid plutons. Triassic to Paleocene samples yielded a range of Neoproterozoic−Paleozoic zircons recycled from nearby Devonian flysch. Most significantly, these samples also yielded juvenile zircons that are close to depositional age, but for which arc sources are only known in southern Yukon and Alaska, more than 700 km away. These source regions are distinct from NE Russian sources inferred for early Brookian (Early Cretaceous) foreland deposits in Alaska.
Pre-Mississippian stratigraphy and provenance of the North Slope subterrane of Arctic Alaska I: Platformal carbonate rocks of the northeastern Brooks Range and their signifi cance in circum-Arctic evolution
Authors: Strauss Justin V. , Macdonald Francis A. , McClelland William C.
Published: October 2019

The Neoproterozoic–Early Devonian platformal succession of the North Slope subterrane, northeastern Brooks Range, Alaska, represents a carbonate-dominated peri-Laurentian continental fragment within the composite Arctic Alaska–Chukotka microplate. The basal ca. 760–720 Ma Mount Weller Group consists of an ~400 m thick mixed siliciclastic and carbonate succession that records the onset of regional extensional tectonism associated with the separation of southeastern Siberia from northern Laurentia during the break-up of Rodinia. These strata are overlain by ca. 720 Ma continental flood basalts of the Kikiktat volcanic rocks, which provide a link between the northeast Brooks Range platformal succession and the ca. 723–717 Ma Franklin large igneous province (LIP) of northern Laurentia. The overlying Sturtian Hula Hula diamictite and Cryogenian–Ediacaran Katakturuk Dolomite record abbreviated thermal subsidence of the northeast Brooks Range platformal succession prior to renewed Ediacaran–early Cambrian extensional tectonism and deposition of the overlying lower Paleozoic Nanook Group (new name). Equivalent strata of the deep-water Cryogenian–lower Cambrian(?) Ikiakpuk Group (new name) are identified herein with new δ13Ccarb and 87Sr/86Sr isotopic data from the Fourth Range of the northeastern Brooks Range. The Nanook Group is formally divided herein into the Black Dog and Sunset Pass formations, which record isolated peri-Laurentian platformal carbonate sedimentation along the northern margin of Laurentia, in an analogous tectonic position to the modern Bahama Banks. A profound Late Ordovician(?)-Early Devonian unconformity within the platformal succession is marked by subaerial exposure, paleokarst development, and tilting of the northeast Brooks Range peri-Laurentian platformal fragment prior to deposition of the overlying Lower Devonian Mount Copleston Limestone.
Unravelling the thermal evolution of the Neruokpuk Formation in the British Mountains, North Yukon, Canada: Tectonic and orogenic implications
Authors: Bigot-Buschendorf Maelianna , Mouthereau Frédéric , Labrousse Loïc , Fillon* Charlotte , Stübner Konstanze , Bernet Matthias
Published: October 2019

Defining temporal and spatial distribution of shortening is critical to reconstruct past plate motions and to examine mechanical coupling processes at convergent plate boundaries. Understanding the collisional evolution of the British Mountains and Beaufort-MacKenzie basin in the northern Alaska–Yukon region is key for the geodynamics of the Arctic region. With the aim to resolve the exhumation history of this region, we present the first zircon fission-track and (U-Th)/He analyses on apatite and zircon from the Neruokpuk Formation (ca. 720–485 Ma), which forms the orogenic basement of the British Mountains. Zircon fission-track ages show partial resetting, indicating the Proterozoic basement did not reside at temperatures above 240 °C. Thermal modeling of zircon and apatite (U-Th)/He data indicates that our samples reached this maximum temperature at ca. 100 Ma. The onset of the Brookian collision is indicated by exhumation from ca. 80 Ma. A total exhumation of 7–8.5 km since the Late Cretaceous is inferred. Apatite (U-Th)/He ages of ca. 50 Ma show that exhumation was less than 2.5 km since the early Eocene. We infer from a comparison with the temporal evolution of exhumation from adjacent orogenic domains that shortening progressively shifted northward from the British Mountains to the Barn Mountains and offshore in the Beaufort Sea during the Paleocene. Along-strike variations in the architecture of the rifted margin of Arctic Alaska is suggested to have exerted a strong control on the structural styles and observed exhumation patterns.
Numerical groundwater models for Edwards Aquifer systems
Authors: Green R.T. , Winterle J. , Fratesi B.
Published: October 2019

Numerical models have been an integral component in management of the Edwards Aquifer for over four decades. The scale and complexity of the models have varied considerably during this time, with the changes attributed to improvements in both numerical software and the conceptual models on which the models are predicated. Resolution of early models was coarse, which rendered them useful only in large-scale, groundwater-resource assessments. Increased resolution and improved refinement in the conceptualization of the complex hydrostratigraphic framework of the Edwards Aquifer have led to expanded applicability of the ensuing models in terms of accommodating local-scale hydraulic features such as pumping scenarios and changes in recharge/discharge mechanisms (i.e., urbanization and climate change). As part of these improvements and advancements, regional-scale groundwater availability models augmented by local-scale models based upon improved conceptualization provide the ability to: (1) replicate more extreme conditions, such as the drought-of-record; (2) improve boundary conditions by extending models to include natural hydraulic boundaries; and (3) couple groundwater flow models with surface-water flow models so that the entire terrestrial water cycle can be accommodated during water-resource management scenario assessment.
Biology and ecology of the Edwards Aquifer
Authors: Krejca* Jean , Reddell† James
Published: October 2019

The Edwards Aquifer supports an important ecosystem with rarely seen faunas that have unique adaptations to a dark and thermally stable environment. We tallied over 60 species of aquifer-adapted (stygobitic) species in the Edwards Aquifer, and 30 more in other Texas aquifers, including snails, flatworms, worms, crustaceans, mites, and beetles. Exploration and research continue, with nine new species described in the last two years. Vertebrate species include Eurycea salamanders and ictalurid catfish, including a blind species (Prietella phreatophila) recorded for the first time in the United States from the Edwards–Trinity Plateau Aquifer in 2016. Contributing to the stygobite diversity are ten state or federally listed species, including the Texas blind salamander (Eurycea rathbuni), which was one of the first species to be listed as endangered by the U.S. Fish and Wildlife Service (USFWS) in 1970. Major springs of the Edwards (Balcones fault zone), Edwards–Trinity Plateau, Trinity, and other aquifers are under constant threat of drying due to aquifer overdraft and climate change. These springs provide habitat for 26 state or federally listed spring-adapted species. Aquifer species in general are known to provide ecosystem services, including water purification, nutrient cycling, and biological indication; however, the function and biology of these species in central Texas have not been studied. Considering the Edwards Aquifer ranks among the top aquifers in the world for number of species, the gaps in understanding remain enormous.
Geologic structure of the Edwards (Balcones Fault Zone) Aquifer
Authors: Ferrill David A. , Morris Alan P. , McGinnis Ronald N.
Published: October 2019

The Edwards (Balcones Fault Zone) Aquifer is structurally controlled by the system of normal faults following the Balcones Escarpment, with major domains, including contributing, recharge (unconfined), and artesian (confined) zones, dictated by the large-displacement (50 m to >250 m throw) normal faults and depth of erosion. Faults and extension fractures, in many cases enhanced by dissolution, localize recharge and flow within the Balcones fault zone and into the subsurface of the artesian zone. Juxtaposition of the Edwards with other aquifers provides avenues for interaquifer communication, while juxtaposition against impermeable layers and concentration of clay and mineralization along faults locally produce fault seals for compartmentalization and confinement. Fault block deformation, including small faults and extension fractures, leads to aquifer permeability anisotropy. Faults also locally provide natural pathways for groundwater discharge through springs above the confined (artesian) zone. Although the importance of joints and faults in the Edwards (Balcones Fault Zone) Aquifer system is recognized, there has not been a systematic analysis of the meter-scale structures in the Edwards and associated confining units and their influence on groundwater flow. Here, we review evidence from several key areas showing that an analysis of faults and fractures in the Edwards (Balcones Fault Zone) Aquifer and associated aquifers and confining units is needed to characterize structural fabrics and assess the permeability architecture critical for the next generation of groundwater modeling of the aquifer.
The Edwards Aquifer Habitat Conservation Plan: Its planning and implementation
Authors: Payne Shaun , Pence Nathan , Furl Chad
Published: October 2019

The Edwards Aquifer Habitat Conservation Plan (EAHCP) protects the federally listed species in the Comal and San Marcos Springs. The plan was developed through the Edwards Aquifer Recovery Implementation Program, a consensus-based process involving a diverse body of stakeholders including industries, agricultural users, municipalities, water purveyors, river authorities, environmental organizations, four state agencies, and downstream interests. Since 2013, the partners of the EAHCP have implemented a multifaceted program mainly focused on spring-flow protection and habitat improvements to ensure the persistence of the covered species and to create more certainty in the region’s water supplies.
The use of water from the Edwards Aquifers, Texas
Authors: Mace* Robert E.
Published: October 2019

Both people and the environment require water. The environment in Texas depends upon water discharged from the Edwards Aquifers, including ~1.5 million megaliters per year (ML/yr) from the Edwards-Trinity (Plateau) Aquifer and ~1 million ML/yr from the Edwards (Balcones Fault Zone) Aquifer. The first people in the area used the aquifer springs as drinking water and subsequently irrigated with the springs’ flow and then began drilling and pumping wells. Well production in the Edwards (Balcones Fault Zone) Aquifer was ~120,000 ML/yr in the 1930s and steadily increased over the next three decades to ~500,000 ML/yr, which is the average use from 1970 to 2015. Production from the Edwards-Trinity (Plateau) Aquifer was ~250,000 ML/yr from 1984 through 2016, while production from the Edwards-Trinity (High Plains) Aquifer was ~25,000 ML/yr from 1984 through 2016. The Interstate 35 growth corridor, extending from Bexar County (San Antonio) through New Braunfels, San Marcos, and Austin, Texas, and up to Bell County, is expected to grow from 4.6 million people in 2020 to 8.7 million in 2070. Despite the needs of this growing population, groundwater availability and regional water planning information suggests that pumping from the Edwards (Balcones Fault Zone) Aquifer over the next 50 yr will be limited. Groundwater availability numbers suggest that pumping in the Edwards-Trinity (Plateau) Aquifer could double from current levels, although planning information currently projects a more modest increase. Unsettled groundwater law and climate change could also affect future levels of pumping.
Evidence for the sinistral Porcupine shear zone in North Yukon (Canadian Arctic) and geotectonic implications
Authors: von Gosen* W. , Piepjohn* K. , McClelland* W.C. , Colpron* M.
Published: October 2019

Structural analysis of Neoproterozoic to lower Paleozoic rocks near Old Crow, in North Yukon, show that they were affected by widespread, but distributed sinistral shear zone deformation. This tectonic event occurred under brittle-ductile conditions, in the early Paleozoic, prior to intrusion of Late Devonian granitoids of the Old Crow plutonic suite (368–375 Ma). Although outcrops are scattered, the shear zone deformation can be inferred to extend over a broad ~W–E corridor, ~10–20 km-wide and ~145 km long, from eastern Alaska into northern Yukon. The sinistral Porcupine shear zone is interpreted to represent a major, early Paleozoic crustal structure along which elements of NE Laurentian and Caledonian affinities in the Arctic Alaska terrane were transferred across the Arctic region during the Paleozoic. Our observations do not support major Paleogene dextral strike-slip deformation along the Porcupine River near Old Crow.
Synsedimentary deformation in Upper Cretaceous–Lower Paleogene limestones within a thrust anticline of the Umbria-Marche Apennines, Italy
Authors: Tognaccini Sofia , Tavarnelli Enrico , Montanari Alessandro
Published: October 2019

The geometry of collisional mountain belts, which were formed at the expense of passive continental margins, is often complex because orogenic structures, such as thrusts and related folds, commonly interfere with pre-orogenic extensional structures, namely, normal faults, resulting in kinematically complex, composite structural assemblages. In these settings, analysis of the relationships between depositional and structural features may provide very useful tools to correctly unravel the local sedimentary and deformational history and relative ages of structures. Analysis of the relationships between minor normal faults and slumps near Frontale in the Umbria-Marche Apennines of Italy made it possible to correctly unravel the local chronology of events and hence to infer the depositional and deformation history of a part of the Upper Cretaceous–Paleogene Scaglia Rossa Formation pelagic basin. The results of this investigation made it possible to ascribe the normal faults to events that predate the construction of the Umbria-Marche mountain belt. Therefore, the normal faults at Frontale are distinct from those that overprint the main compressional structures responsible for the present-day seismicity of central Italy.
Expansion breccias in Lower Cretaceous Apennine pelagic limestones: II. Geochemical constraints on their origin
Authors: Belza J. , Alvarez W. , Tavarnelli E. , Vanhaecke F. , Baele J.-M. , Claeys P.
Published: October 2019

The geochemical signatures of sparry calcite-sealing expansion breccias, calcite veins, and host clasts were analyzed for their strontium (87Sr/86Sr) and oxygen and carbon (δ18O, δ13C) stable isotopic signatures. The breccias occur within the Lower Cretaceous Maiolica Formation. Related but different breccias are found in a few places in the Upper Cretaceous to Eocene Scaglia Rossa Formation of the Umbria-Marche Apennines fold-and-thrust belt (Italy). We propose hydraulic fracturing by fluid overpressure as a possible mechanism for generation of the breccias in these formations. Our data are compatible with the hypothesis of a hydraulically fractured breccia formed by cyclic buildup and rapid decompression of CO2-rich fluids, with overpressures generated by entrapment of CO2 by structural and stratigraphic seals. Strontium and oxygen isotope ratio data suggest that the CO2-rich fluids may have originated from carbonate metasomatism of the mantle, resulting from subduction of carbonate-rich lithologies constituting the downgoing slab. This is consistent with previous conceptual models inferring that in the central part of the Northern Apennines, which is characterized by thick continental crust, CO2-rich fluids derived from mantle metasomatism would become trapped in structural seals, creating high fluid overpressures.
Late Eocene impact ejecta in Italy: Attempts to constrain the impactor composition from isotopic analyses of spinel-rich samples
Authors: Koeberl* Christian , Montanari Alessandro , Schulz Toni , Tusch Jonas , Mougel Berengere , Moynier Frédéric
Published: October 2019

The late Eocene was marked by multiple impact events, possibly related to a comet or asteroid shower. Marine sediments worldwide contain evidence for at least two closely spaced impactoclastic layers. The upper layer might be correlated with the North American tektite-strewn field (with the 85-km-diameter Chesapeake Bay impact structure [USA] as its source crater), although this is debated, whereas the lower, microkrystite layer (with clinopyroxene [cpx]-bearing spherules) was most likely derived from the 100-km-diameter Popigai impact crater (Russia). The Eocene-Oligocene global stratotype section and point is located at Massignano, Italy, and below the boundary, in the late Eocene, at the 5.61 m level, shocked quartz and pancake-shaped smectite spherules that contain (Ni- and Cr-rich) magnesioferrite spinel crystals are found. These are associated with a positive Ir anomaly in deposits with the same age as the Popigai-derived cpx spherule layer. This layer is overlain by another Ir-rich layer, likely due to another large impact event. From a large amount of “pancake-bearing” rock, we isolated a few hundred milligrams of this spinel-rich material. The tungsten isotopic composition of this material shows more or less a terrestrial composition. However, the spinel-rich materials have excess 54Cr values (expressed as ε54Cr, which is the per ten thousand deviation of the 54Cr/52Cr ratio from a terrestrial standard) of around –0.4 to –0.5 ε54Cr, which distinctly point to an ordinary chondritic impactor. This result supports the asteroid impact interpretation but not the comet impact hypothesis.
Popigai impact ejecta layer and extraterrestrial spinels recovered in a new Italian location—The Monte Vaccaro section (Marche Apennines, Italy)
Authors: Boschi*,† Samuele , Schmitz† Birger , Terfelt† Fredrik , Ros† Linus , Elfman† Mikael , Kristiansson† Per , Sulas† Camilla , Monechi† Simonetta , Montanari† Alessandro
Published: October 2019

The Popigai (100 km in diameter) and the Chesapeake Bay (40–85 km diameter) impact structures formed within ~10–20 k.y. in the late Eocene during a 2 m.y. period with enhanced flux of 3He-rich interplanetary dust to Earth. Ejecta from the Siberian Popigai impact structure have been found in late Eocene marine sediments at numerous deep-sea drilling sites around the globe and also in a few marine sections outcropped on land, like the Massignano section near Ancona in Italy. In the Massignano section, the Popigai layer is associated with an iridium anomaly, shocked quartz, and abundant clinopyroxene-bearing (cpx) spherules, altered to smectite and flattened to “pancake spherules.” The ejecta are also associated with a significant enrichment of H-chondritic chromite grains (>63 μm), likely representing unmelted fragments of the impactor. The Massignano section also contains abundant terrestrial chrome-spinel grains, making reconstructions of the micrometeorite flux very difficult. We therefore searched for an alternative section that would be more useful for these types of studies. Here, we report the discovery of such a section, and also the first discovery of the Popigai ejecta in another locality in Italy, the Monte Vaccaro section, 90 km west of Ancona. The Monte Vaccaro section biostratigraphy was established based on calcareous nannoplankton, which allowed the identification of a sequence of distinct bioevents showing a good correlation with the Massignano section. In both the Monte Vaccaro and Massignano sections, the Popigai ejecta layer occurs in calcareous nannofossil zone CNE 19. The ejecta layer in the Monte Vaccaro section contains shocked quartz, abundant pancake spherules, and an iridium anomaly of 700 ppt, which is three times higher than the peak Ir measured in the ejecta layer at Massignano. In a 105-kg-size sample from just above the ejecta layer at Monte Vaccaro, we also found an enrichment of H-chondritic chromite grains. Because of its condensed nature and low content of terrestrial spinel grains, the Monte Vaccaro section holds great potential for reconstructions of the micrometeorite flux to Earth during the late Eocene using spinels.
Distribution of chrome-spinel grains across the 3He anomaly of the Tortonian Stage at the Monte dei Corvi section, Italy
Authors: Boschi*,† Samuele , Schmitz† Birger , Montanari† Alessandro
Published: October 2019

The present-day ocean-climate system configuration took shape during the Miocene Epoch. Toward the end of the epoch, in the late Tortonian at ca. 8.5 Ma, there was an exceptional event: collisional disruption of an >150-km-diameter asteroid, which created the Veritas family of asteroids in the asteroid belt. This event increased the flux of interplanetary dust particles rich in 3He to Earth and probably caused a period of increased dust in the atmosphere, with consequent alteration of global and local environmental conditions. A late Miocene 3He anomaly likely related to the Veritas event has been registered in deep-sea sediments from Ocean Drilling Program (ODP) Site 926 (Atlantic Ocean), ODP Site 757 (Indian Ocean), and in the late Tortonian–early Messinian Monte dei Corvi section near Ancona, Italy. Here, we report the results of a study in the Monte dei Corvi section aimed to recover extraterrestrial chrome-spinel grains across the 3He anomaly interval, as has been done for the similar late Eocene 3He anomaly in the nearby Massignano section. In this study, three ~100 kg samples were collected from the Monte dei Corvi section: two within the 3He peak interval and one outside the anomaly interval as a background reference sample. In total, 1151 chrome-spinel grains (>63 µm) were recovered, but based on chemical composition, none of the grains has a clear extraterrestrial origin. This supports the inference that the 3He anomaly is indeed related to the Veritas event and not to an approximately coeval breakup of a smaller H-chondritic body in the asteroid belt, an event registered in meteoritic cosmic-ray exposure ages. Spectral studies of the Veritas asteroids indicate that they are made up of carbonaceous chondritic material. Such meteorites generally have very low chrome-spinel concentrations in the grain-size range considered here, contrary to the very chromite-rich ordinary chondrites. The terrestrial grains recovered were classified, and their composition showed that all the grains have an ophiolitic origin with no substantial compositional and distributional change through the section. The source area of the terrestrial grains was probably the Dinarides orogen.
Paleoclimate implications of earliest Pleistocene tree rings from the Dunarobba Fossil Forest, Umbria, Italy
Authors: Bice* David , Csank* Adam , Macalady* Alison , Montanari* Alessandro , Tierney* Devin , Baldanza* Angela
Published: October 2019

The earliest Pleistocene fossil forest of Dunarobba (Umbria, Italy) consists of a set of more than 70 tree trunks of an extinct species of sequoia or cypress with original cellulose still preserved. Spectral analyses of tree-ring series (325 and 448 yr in duration) combined with oxygen isotope analyses of the cellulose provide a glimpse into the mean annual temperature and the interannual climate variability that characterized this region at the beginning of the Pleistocene, when the concentration of atmospheric CO2 was ~400 ppm. The high-frequency variability of the ring width time series shows significant spectral components that are consistent with the influence from the North Atlantic Oscillation, and to a lesser extent, solar cycles and El Niño–Southern Oscillation. The mean annual temperature estimate of ~19 °C, based on a model that combines ring widths and oxygen isotope values, is a full 6 °C warmer than the present-day value for this region. These elevated temperatures are consistent with estimates from pollen analyses and with estimates from higher latitudes.
Extreme thermal metamorphism associated with Gondwana assembly: Evidence from sapphirine-bearing granulites of Rajapalayam, southern India
Authors: Li Shan-Shan , Palin Richard M. , Santosh M. , Shaji E. , Tsunogae T.
Published: October 2019

The Madurai block is the largest composite crustal block in the Southern Granulite terrane of India, where granulite-facies rocks metamorphosed at ultrahigh-temperature (UHT) conditions occur in several localities. Here, we investigated UHT rocks from Rajapalayam, in the southern domain of the Southern Granulite terrane, using integrated thermobarometry and in situ monazite geochronology to precisely constrain the nature and timing of this extreme metamorphism and its implications for regional tectonics. Conventional thermobarometry and petrological phase equilibrium modeling reveal prograde pressure-temperature (P-T) conditions at 0.75–1.2 GPa and <900 °C, followed by peak/postpeak UHT metamorphism at 0.72–0.82 GPa and 1025–1050 °C, and retrograde reequilibration at 0.72–0.80 GPa and 875–895 °C. The granulites thus record a clockwise P-T path defining geothermal gradients of 1200–1500 °C/GPa at peak metamorphism, indicating the presence of an extreme thermal perturbation in the middle to lower continental crust. In situ monazite dating indicates prograde metamorphism at 607–585 Ma, peak metamorphism at 546–543 Ma, and retrograde cooling and exhumation at 539–483 Ma. As such, the entire tectonothermal cycle was complete within ∼120 m.y., although temperatures exceeding 900 °C were likely sustained for at least 30 m.y. Such extreme thermal events preserved in geological terranes worldwide are commonly associated with lithospheric extension, although our data show that prolonged heating can occur during continental convergence instead, supporting inferences made by thermomechanical models. Thus, supercontinent formation may act as a driver for spatially distributed UHT tectonometamorphism, as shown by the episodic records in geological history. The age of peak metamorphism constrained here was synchronous with UHT metamorphism in other localities in the Southern Granulite terrane, Sri Lanka, Madagascar, and Antarctica, indicating their correlation with the final amalgamation of eastern Gondwana at ca. 550 Ma.
Hungry bone syndrome after thyroidectomy for thyroid storm
Authors: Kusuki Kazuhisa , Mizuno Yuzo
Published: October 2019

A 39-year-old man was admitted to our hospital with the diagnosis of thyroid storm due to Graves’ disease. Near-total thyroidectomy was performed after 1 month’s pharmacological treatment, and he presented with tetany next morning. Serum corrected calcium value was 5.7 mg/dL. Procollagen type 1 N-terminal propeptide increased considerably, while tartrate-resistant acid phosphatase 5b decreased. These changes indicated that bone formation exceeded bone resorption in reverse after thyroidectomy. Calcium gluconate was administered intravenously for 14 days, before the patient was discharged. Oral administration of calcium and active forms of vitamin D was continued for 4 months. Rapid skeletal uptake of calcium from blood caused severe and persistent hypocalcaemia, which is called hungry bone syndrome. When patients with Graves’ disease have severe thyrotoxicosis, high serum alkaline phosphatase levels and low bone mineral densities, they are at high risk for hungry bone syndrome after thyroidectomy, and should be educated for the symptoms of hypocalcaemia.