Time series analysis of mantle cycles Part I: Periodicities and correlations among seven global isotopic databases

In this study, seven isotopic databases are presented and analyzed to identify mantle and crustal episodes on a global scale by focusing on periodicity ranging from 70 to 200 million years (Myr). The databases are the largest, or among the largest, compiled for each type of data – with an objective of finding some samples from every region of every continent, to make each database as global as conceivably possible. The databases contain zircon Lu/Hf isotopic data, whole-rock Sm/Nd isotopic data, U/Pb detrital zircon ages, U/Pb igneous zircon ages, U/Pb non-zircon ages, whole-rock Re/Os isotopic data, and large igneous province ages. Part I of this study focuses on the periodicities of age histograms and geochemical averages developed from the seven databases, via spectral and cross-correlation analyses. Natural physical cycles often propagate in exact integer multiples of a fundamental cycle, referred to as harmonics. The tests show that harmonic geological cycles of ～93.5 and ～187 Myr have persisted throughout terrestrial history, and the cyclicities are statistically significant for U/Pb igneous zircon ages, U/Pb detrital zircon ages, U/Pb zircon-rim ages, large igneous province ages, mean ε_Hf(t) for all samples, mean ε_Hf(t) values for igneous-only samples, and relative abundance of mafic rocks. Equally important, cross-correlation analyses show these seven time-series are nearly synchronous (±7 Myr) with a model consisting of periodicities of 93.5 and 187 Myr. Additionally, the similarities between peaks in the 93.5 and 187 Myr mantle cycles and terminal ages of established and suspected superchrons provide a framework for predicting and testing superchron periodicity.     

Zeolite zones in East Greenland: use of native copper by pre‐contact Inuit?

Zeolites are a diverse group of calcium and sodium aluminosilicate minerals. They are tectosilicates (3‐D arrays of SiO₄ tetrahedra), but vary in chemistry and crystal symmetry. Some readily exchange sodium for calcium and are used as water softeners. They also find applications as molecular sieves in petroleum refining, although the bulk of zeolites used industrially today are synthetic. These minerals form at low temperatures under well‐defined conditions and can be used as indicators of palaeotemperatures. In the same environment, but at higher temperatures, other minerals form including quartz, calcite, prehnite and even native copper. The Inuit of East Greenland, a Stone Age people, may have utilized native copper from this environment as did the Copper Inuit of the central Canadian Arctic.     

Normal fault growth and linkage in the Gediz (Alaşehir) Graben,Western Turkey,revealed by transient river long‐profiles and slope‐break knickpoints

The Gediz (Ala?ehir) Graben is located in the highly tectonically active and seismogenic region of Western Turkey. The rivers upstream of the normal fault‐bounded graben each contain a non‐lithologic knickpoint, including those that drain through inferred fault segment boundaries. Knickpoint heights measured vertically from the fault scale with footwall relief and documented fault throw (vertical displacement). Consequently, we deduce these knickpoints were initiated by an increase in slip rate on the basin‐bounding fault, driven by linkage of the three main fault segments of the high‐angle graben bounding fault array. Fault interaction theory and ratios of channel steepness suggest that the slip rate enhancement factor on linkage was a factor of 3. We combine this information with geomorphic and structural constraints to estimate that linkage took place between 0.6 Ma and 1 Ma. Calculated pre‐ and post‐linkage throw rates are 0.6 and 2 mm/yr respectively. Maximum knickpoint retreat rates upstream of the faults range from 4.5 to 28 mm/yr, faster than for similar catchments upstream of normal faults in the Central Apennines and the Hatay Graben of Turkey, and implying a fluvial landscape response time of 1.6 to 2.7 Myr. We explore the relative controls of drainage area and precipitation on these retreat rates, and conclude that while climate variation and fault throw rate partially explain the variations seen, lithology remains a potentially important but poorly characterised variable. Copyright © 2016 John Wiley & Sons, Ltd.     

Diachronous isotopic and sedimentary responses to topographic change as indicators of mid‐Eocene hydrologic reorganization in the western United States

Early Cenozoic terrestrial deposits in the western United States represent well‐preserved archives of climatic and tectonic processes that together shaped the Earth's surface during the demise of a large continental plateau. This study examines a Cenozoic terrestrial sedimentary sequence in the central part of the Cordilleran orogen (Montana) using sedimentologic and geochemical techniques. At ～49 Ma, we observe rapid major shifts in oxygen, carbon and strontium isotope records that are too large to directly reflect changes in meteoric water composition due to simple orographic rainout. The transition to low‐δ¹⁸O values in pedogenic carbonate in concert with changes in the composition of clastic material at ～49 Ma points to the input of evolved meteoric water to the hydrological cycle due to a change in the source of waters reaching Cordilleran intermontane regions in southwestern Montana. This drainage reorganization coincides with the initiation of magmatism and extension to the west in what is now Montana and Idaho. The sedimentological record shows evidence that depositional gradients increased in the study area ～46 Ma, ～3 Myr after the drainage reorganization occurred. This interval is most likely the time it took for extensional deformation to propagate to the study area itself. Evidence of freshening events in Laramide Basins to the southeast suggests that this drainage reorganization diverted waters to progressively fill these basins and highlights the impact of post‐plateau extension‐related landscape reorganization on river networks and lake dynamics. This study also emphasizes the importance of using multiple tools in deciphering topographic history through the study of terrestrial basin deposits, in that interpretation based on any single method employed would have compromised our ability to successfully identify the regional evolution of topography and drainage networks.     

DROUGHT DURING THE 1930s AND 1950s IN THE CENTRAL UNITED STATES

The Palmer Index was used to compare the droughts of the 1930s and the 1950s in the central United States. A series of maps was produced to compare the droughts in terms of location, severity, and duration. The results indicated the 1930s drought lasted longer and consisted of three distinct waves. The 1950s drought, although shorter in overall duration, was actually more intense over a larger area for a longer period. There were changes in the size and configuration of the drought-affected area, but both droughts were especially persistent in a core region on the High Plains. A simple index of overall drought impact was developed based on the drought-affected area and the Palmer value from each climatic division. The probability of drought occurrence was calculated for each of the 76 climatic divisions in the study area. [Key words: drought, Palmer Index, Great Plains.]     

Tracing groundwater discharge in a High Arctic lake using radon-222

In the High Arctic, groundwater fluxes are limited by the presence of continuous permafrost, although it has been hypothesized that there may be localized groundwater flow and hydraulic connectivity beneath large lakes, due to the presence of taliks, or large regions of unfrozen ground. However, due to the logistical difficulty of employing seepage meters and piezometers in deep, ice-covered lakes, relatively little is known about groundwater discharge to polar lakes. One method of assessing groundwater discharge is through the use of geochemical tracers. We conducted a pilot study to quantify groundwater discharge into a High Arctic lake using dissolved radon gas as a geochemical tracer. Lake water was collected in 15 L polyvinyl chloride (PVC) bags with minimal atmospheric interaction from a 25-m deep lake near Shellabear Point, Melville Island, Northwest Territories, Canada. Sample bags were aerated through a closed water loop for 60 min to allow sufficient radon to equilibrate in a coupled air circuit. Radon in air concentrations were measured on a Durridge RAD7 portable alpha spectrometer. The field trial in a remote setting and separate tests with groundwater samples collected from a temperate site demonstrate the utility of the methodology. The limited results suggest that radon levels in the lower water column are elevated above background levels following nival melt in the surrounding watershed. Although these results are insufficient to quantify groundwater discharge, the results suggest subsurface flow may exist, and further study is warranted.     

Bioaccumulation of nitroarenes in bivalves at Osaka Bay, Japan

This paper reports for the first time the detection and occurrence of nitroarenes (NPAHs) in marine organisms. Mussels and oysters collected from Osaka Bay, Japan, had total NPAHs concentrations that ranged from 2380 to 24,688 pg/g dry and 2672 to 25,961 pg/g dry, respectively. Relatively higher concentrations were detected in sampling sites located near the central district and suburbs of Osaka City implying that the most probable sources of NPAHs in the two bivalves are exhaust gases and smokes emitted by automobiles and industrial plants. Bivalves had relatively higher residues of 1-nitronaphthalene, 2-nitronaphthalene, 3-nitrophenanthrene, and 9-nitrophenanthrenes. Residues of 2-nitrofluorene, 1-nitropyrene, 4-nitropyrenes, and 6-nitrochrysene were much lower compared to nitronaphthalenes and nitrophenanthrenes. Inter-species differences was only observed for 2-nitronaphthalene with oysters exhibiting significantly higher residues than mussels.