A geochemical study of island-arc and back-arc tholeiites from the Scotia Sea

first_imgElsevier Earth and Planetary Science Letters Volume 36, Issue 2, September 1977, Pages 253-262 Earth and Planetary Science Letters A geochemical study of island-arc and back-arc tholeiites from the Scotia Sea Author links open overlay panel C.J. Hawkesworth 1, R.K. O’Nions 2, R.J. Pankhurst 3, P.J. Hamilton 2, N.M. Evensen 21Department of Earth Sciences, University of Leeds, Leeds Great Britain2Lamont-Doherty Geological Observatory of Columbia University, Palisades, N.Y. 10964USA3British Antarctic Survey, c/o Institute of Geological Sciences, London, WCIX 8N6Great BritainReceived 22 April 1977, Revised 9 June 1977, Available online 23 October 2002.Show lesshttps://doi.org/10.1016/0012-821X(77)90207-2Get rights and content Abstract 87Sr/86Sr and143Nd/144Nd ratios, REE and selected minor and trace elements are presented and compared for present-day volcanic rocks in the Scotia Sea. Tholeiitic basalts from the South Sandwich Islands show widely ranging contents of some lithophile elements, e.g. K2O (0.09–0.55%) and Rb (1.55–14.2 ppm), but fairly constant Na2O and Sr. Total REE contents range from about 4–20 times chondritic abundances with significant light-REE depletion and both positive and negative Eu anomalies. The variations in minor and trace element abundances are consistent with low-pressure fractional crystallization of plagioclase and clinopyroxene but only minor amounts of olivine. The87Sr/86Sr and143Nd/144Nd ratios of the parental magmas are thought be 0.7038–0.7039 and 0.51301–0.51314 respectively, and indicate derivation of at least some87Sr from subducted ocean crust. The back-arc tholeiites in the Scotia Sea have lower87Sr/86Sr ratios (0.7028–0.7033), similar143Nd/144Nd ratios (0.51305) and are variably light-REE-enriched(CeN/YbN= 1.0–1.6). Total REE contents are comparable to those of the South Sandwich Islands tholeiites.last_img read more

Fire-prone plant communities and palaeoclimate of a Late Cretaceous fluvial to estuarine environment, Pecinov quarry, Czech Republic

first_imgThe botanical identity and facies distribution of fossil charcoal is described from Middle to Late Cenomanian (90–94 Ma) fluvial to estuarine units at Pecínov quarry, near Prague, Czech Republic. Braided alluvial facies associations contain charred conifer woods (family Pinaceae) possibly derived from upland forest fires, and abundant charred angiosperm woods, flowers and inflorescences (families Lauraceae and ?Platanaceae) derived from riparian gallery forest fires (Unit 2). Retrogradational coastal salt marsh facies associations contain abundant charred conifer wood (families Cheirolepidiaceae and Cupressaceae/Taxodiaceae) derived from fires in halophytic backswamp forest, and rare pinaceous charred cones and lauraceous angiosperm wood washed downstream from fires further inland (Units 3–4). Progradational coastal facies associations within an estuary mouth setting contain abundant charred conifer wood (family Cupressaceae/Taxodiaceae), common taxodiaceous conifer and angiosperm leaves, fern rachises, and lycopsid stems derived from fires in mesic backswamp taxodiaceous forests and supra-tidal fern-lycopsid thickets (Unit 5). Growth rings in angiosperm and conifer woods, leaf physiognomy and computer models indicate that climate was equable, warm and humid, but that there was a short annual dry season; most fires probably occurred during these annual drought periods. The abundance of charcoal and the diversity of taxa preserved in this state indicate that nearly all plant communities were fire-prone. Physiognomically, the Pecínov flora resembles present-day seasonally-dry subtropical forests where fires are a common occurrence.last_img read more

Stratigraphic landscape analysis: charting the Holocene movements of the Nile at Karnak through ancient Egyptian time

first_imgGeological analysis of 5-10-m-long sediment cores in the context of the anthropologically derived materials within them has allowed us to identify ancient landscape features in the Theban area around Luxor, Egypt. From these observations we propose a sequence of island formation and northwestward movement of the Nile from the Middle Kingdom onward in the area of the temple complexes of Karnak. The geoarchaeological techniques used appear to document the Holocene lateral migration and vertical aggradation of the Nile. Our method can be used to test postulated movements and is applicable to sites in river or coastal plains where sediments were being deposited during the occupation of the site. The sediments were sieved to retrieve sherds and numerous other small items (2 mm and larger), which included worked stone fragments, rootlet concretions (rhizocretions), desert polished sand grains, and occasionally beads. The small stone fragments can be correlated with buildings and sherds of known age within the site, while the rhizocretions and desert sand grains indicate environmental conditions prevailing at the time of deposition.last_img read more

Laboratory measurements of high-frequency, acoustic broadband backscattering from sea ice and crude oil

first_imgRecent decreases in summer sea ice cover are spurring interest in hydrocarbon extraction and shipping in Arctic waters, increasing the risk of an oil spill in ice covered waters. With advances in unmanned vehicle operation, there is an interest in identifying techniques for remote, underwater detection of oil spills from below. High-frequency (200–565 kHz), broadband acoustic scattering data demonstrate that oil can be detected and quantified under laboratory grown sea ice and may be of use in natural settings. A simple scattering model based on the reflection coefficients from the interfaces agrees well with the data.last_img read more

Evolutionary scenarios for the origin of an Antarctic tardigrade species based on molecular clock analyses and biogeographic data

first_imgThe origin of the Antarctic continental extant fauna is a highly debated topic, complicated by the paucity of organisms for which we have clear biogeographic distributions and understanding of their evolutionary timescale. To shed new light on this topic, we coupled molecular clock analyses with biogeographic studies on the heterotardigrade genus Mopsechiniscus. This taxon includes species with endemic distributions in Antarctica and other regions of the southern hemisphere. Molecular dating using different models and calibration priors retrieved similar divergence time for the split between the Antarctic and South American Mopsechiniscus lineages (32–48 Mya) and the estimated age of the Drake Passage opening that led to the separation of Antarctica and South America. Our divergence estimates are congruent with other independent studies in dating Gondwanan geological events. Although different analyses retrieved similar results for the internal relationships within the Heterotardigrada, our results indicated that the molecular dating of tardigrades using genes coding for ribosomal RNA (18S and 28S rDNA) is a complex task, revealed by a very wide range of posterior density and a relative difficulty in discriminating between competing models. Overall, our study indicates that Mopsechiniscus is an ancient genus with a clear Gondwanan distribution, in which speciation was probably directed by a co-occurrence of vicariance and glacial events.last_img read more

Relative paleointensity (RPI) and age control in Quaternary sediment drifts off the Antarctic Peninsula

first_imgLack of foraminiferal carbonate in marine sediments deposited at high latitudes results in traditional oxygen isotope stratigraphy not playing a central role in Quaternary age control for a large portion of the globe. This limitation has affected the interpretation of Quaternary sediment drifts off the Antarctic Peninsula in a region critical for documenting past instability of the West Antarctic Ice Sheet (WAIS) and Antarctic Peninsula Ice Sheet (APIS). Here we use piston cores recovered from these sediment drifts in 2015 during cruise JR298 of the RRS James Clark Ross to test the usefulness for age control of relative paleointensity (RPI) data augmented by scant δ 18 O data. Thermomagnetic and magnetic hysteresis data, as well as isothermal remanent magnetization (IRM) acquisition curves, indicate the presence of prevalent magnetite and subordinate oxidized magnetite (“maghemite”) in the cored sediments. The magnetite is likely detrital. Maghemite is an authigenic mineral, associated with surface oxidation of magnetite grains, which occurs preferentially in the oxic zone of the uppermost sediments, and buried oxic zones deposited during prior interglacial climate stages. Low concentrations of labile organic matter apparently led to arrested pore-water sulfate reduction explaining oxic zone burial and downcore survival of the reactive maghemite coatings. At some sites, maghemitization has a debilitating effect on RPI proxies whereas at other sites maghemite is less evident and RPI proxies can be adequately matched to the RPI reference template. Published RPI data at ODP Site 1101, located on Drift 4, can be adequately correlated to contemporary RPI templates, probably as a result of disappearance (dissolution) of maghemite at sediment depths >∼10 m.last_img read more

Morphological changes to the terminus of a maritime glacier during advance and retreat phases: Fox Glacier/Te Moeka o Tuawe, New Zealand

first_imgFox Glacier/Te Moeka o Tuawe is a fast-responding maritime glacier that has undergone multiple advance and retreat phases during recent decades. Here we use a combination of repeat photography, Structure from Motion (SfM), and ice discharge measurement, to identify key morphological differences associated with these repeated phase changes, and assess how much of the current terminus is still dynamically active. Increasing surface-debris cover at the margins and topographic shading result in the asymmetry of the retreating terminus, with central portions receding faster than the margins. In 2019, the glacier is shorter than at any time in recorded history, and ice flux is insufficient to sustain the current glacier length, with a further ∼300 m of the glacier terminus region potentially vulnerable to retreat. However, due to the high climate sensitivity of this maritime glacier, even a slight shift towards increasing mass flux could see this trend reverse.last_img read more

Surface melt and runoff on Antarctic ice shelves at 1.5°C, 2°C and 4°C of future warming

first_imgThe future surface mass balance (SMB) of Antarctic ice shelves has not been constrained with models of sufficient resolution and complexity. Here, we force the high‐resolution Modèle Atmosphérique Régional (MAR) with future simulations from four CMIP models to evaluate the likely effects on the SMB of warming of 1.5°C, 2°C and 4°C above pre‐industrial temperatures. We find non‐linear growth in melt and runoff which causes SMB to become less positive with more pronounced warming. Consequently, Antarctic ice shelves may be more likely to contribute indirectly to sea level rise via hydrofracturing‐induced collapse, which facilitates accelerated glacial discharge. Using runoff and melt as indicators of ice shelf stability, we find that several Antarctic ice shelves (Larsen C, Wilkins, Pine Island and Shackleton) are vulnerable to disintegration at 4°C. Limiting 21st century warming to 2°C will halve the ice shelf area susceptible to hydrofracturing‐induced collapse compared to 4°C.last_img read more

Weber State Football Hosts Sacramento State For Senior Day Saturday

first_img Tags: Elijah Dotson/Jake Constantine/Jay Hill/Jody Sears/Kevin Thompson/Pierre Williams/Sacramento State Football/Senior Day/Stewart Stadium/Weber State Football FacebookTwitterLinkedInEmailOGDEN, Utah-Saturday,  #4 Weber State football hosts Sacramento State on Senior Day as this will be the last home game for 16 seniors at Stewart Stadium Saturday.The Wildcats will be led by signal-caller Jake Constantine, who was named as the Big Sky Offensive Player of the Week as he went 27-41 for 318 yards and 3 TD’s, in Weber State’s 35-30 win at North Dakota.With a win, Weber State will have won seven or more games in three straight seasons for the first time in program history.This series dates back to 1996 with the Wildcats leading the Hornets 14-8 all-time, including a 10-1 mark at Ogden.The Hornets are coached by former Weber State head coach Jody Sears, whom Jay Hill replaced at the helm in Ogden five years ago.With a win, the Wildcats will go undefeated for only the third time in school history, having previously gone 6-0 at Ogden in 1991 and 1997.Sacramento State is led by tailback Elijah Dotson (153 car, 1,058 yards, 9 TD’s) and quarterback Kevin Thompson (1,253 yards, 7 TD’s/INT).Receiver Pierre Williams (25 rec, 442 yards, 4 TD’s) is Thompson’s favorite target on the season.The Hornets come in at 2-6 and 0-5 in Big Sky Conference play in what has been a trying season. October 31, 2018 /Sports News – Local Weber State Football Hosts Sacramento State For Senior Day Saturday Written by Brad Jameslast_img read more

Four-Run Seventh Leads to Win for BYU

first_img FacebookTwitterLinkedInEmailCORPUS CHRISTI, Texas – A two-out rally in the seventh helped give BYU a 6-2 victory over Texas A&M-Corpus Christi on Thursday at Whataburger Field. Written by February 21, 2019 /Sports News – Local Four-Run Seventh Leads to Win for BYU Tags: BYU Cougars Baseball One through eight in the Cougar lineup had at least one hit and the pitching staff combined for eight strikeouts and just one walk as BYU improved its record to 3-2. In his first career start as a Cougar, Lessar went 4.2 innings and struck out four. Freshman right-hander Reid McLaughlin picked up his first career win, throwing two strikeouts with no runs allowed in 2.1 innings. Senior right-hander Blake Inouye closed out the final two innings. With two outs in the fourth, sophomore DJ McNew singled to left field, then advanced a base on a wild pitch. Hill then singled through the left side, scoring McNew to make it 2-0. After giving up a single to the first Islander batter of the game, sophomore starting pitcher Jarod Lessar retired the next 10 Corpus Christi hitters until an infield single with two outs in the bottom of the fourth broke the streak. However, an outstanding play in the field threw the runner out one batter later at third base on a 7-6-3-2-5 sequence. Tied 2-2 with two outs and two on in the top of the seventh inning, senior Brock Hale hit the first pitch he saw back up the middle for a two-RBI single to give BYU the lead. After Hale stole second, sophomore Jackson Cluff hit a double down the right field line, scoring Hale. Senior Keaton Kringlen answered with another double, scoring Cluff, to extend the lead to 6-2. BYU will return to Whataburger Field on Friday, Feb. 22, at 2 p.m. CT to take on Ohio State (4-0). Eight Cougar batters had at least one hit, with Hale, Hill and senior Brian Hsu each tallying two apiece. A&M-Corpus Christi answered in the fifth, manufacturing a pair of runs to tie the game, 2-2, before BYU responded two innings later. BYU had an initial 2-0 lead, first scoring on a solo home run by sophomore Mitch McIntyre, his first homer of the year. “Jarod Lessar was pretty good in his first D-I start and set a great tone for us on the mound,” BYU head coach Mike Littlewood said. “We talk all the time about clutch hitting, solid pitching and playing catch; tonight, we did all three very well. Noah Hill did a great job tonight behind the plate and came up huge at the plate.” Robert Lovelllast_img read more