REE and Sr isotope characteristics of carbonate within the Cu–Co mineralized sedimentary sequence of the Nchanga Mine,Zambian Copperbelt

Carbonate, largely in the form of dolomite, is found throughout the host rocks and ores of the Nchanga mine of the Zambian Copperbelt. Dolomite samples from the hanging wall of the mineralization show low concentrations of rare-earth elements (REE) and roof-shaped, upward convex, shale-normalized REE patterns, with positive Eu*_SN anomalies (1.54 and 1.39) and marginally negative Ce anomalies (Ce*_SN 0.98,0.93). In contrast, dolomite samples associated with copper and cobalt mineralization show a significant rotation of the REE profile, with HREE enrichment, and La/Lu_SN ratios <1 (0.06–0.42). These samples also tend to show variable but predominantly negative Eu*_SN and positive cerium anomalies and an upwardly concave MREE distribution (Gd-Er). Malachite samples from the Lower Orebody show roof-tile-normalized REE patterns with negative europium anomalies (Eu*_SN 0.65–0.80) and negative cerium anomalies (Ce*_SN 0.86–0.9). The carbonate ⁸⁷Sr/⁸⁶Sr signature correlates with the associated REE values. The uppermost dolomite samples show Neoproterozoic seawater-like ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.7111 to 0.7116, whereas carbonate from Cu–Co mineralized samples show relatively low concentrations of strontium and more radiogenic ⁸⁷Sr/⁸⁶Sr, ranging between 0.7136–0.7469. The malachite samples show low concentrations of strontium, but give a highly radiogenic ⁸⁷Sr/⁸⁶Sr of 0.7735, the most radiogenic ⁸⁷Sr/⁸⁶Sr ratio. These new data suggest that the origin and timing of carbonate precipitation at Nchanga is reflected in the REE and Sr isotope chemistry. The upper dolomite samples show a modified, but essentially seawater-like signature, whereas the rotation of the REE profile, the MREE enrichment, the development of a negative Eu*_SN anomaly and more radiogenic ⁸⁷Sr/⁸⁶Sr suggests the dolomite in the Cu–Co mineralized samples precipitated from basinal brines which had undergone significant fluid–rock interaction. Petrographic, REE, and ⁸⁷Sr/⁸⁶Sr data for malachite are consistent with the original sulfide Lower Orebody being subject to a later oxidizing event.     

Major- and trace-element characterization, expanded distribution, and a new chronology for the latest Pleistocene Glacier Peak tephras in western North America

The Glacier Peak tephra beds are among the most widespread and arguably some of the most important late Pleistocene chronostratigraphic markers in western North America. These beds represent a series of closely-spaced Plinian and sub-Plinian eruptions from Glacier Peak, Washington. The two most widespread beds, Glacier Peak ‘G’ and ‘B’, are reliably distinguished by their glass major and trace element abundances. These beds are also more broadly distributed than previously considered, covering at least 550,000 and 260,000 km², respectively. A third bed, the Irvine bed, known only from southern Alberta, is similar in its major-element composition to the Glacier Peak G bed, but it shows considerable differences in trace element concentrations. The Irvine bed is likely considerably older than the G and B tephras and probably records an additional Plinian eruption, perhaps also from Glacier Peak but from a different magma than G through B. A review of the published radiocarbon ages, new ages in this study, and consideration in a Bayesian framework suggest that the widespread G and B beds are several hundred years older than widely assumed. Our revised age is about 11,600 ¹⁴C yr BP or a calibrated age (at 2 sigma) of 13,710-13,410 cal yr BP.     

Preservation of a heavily bored belemnite rostrum from the upper Maastrichtian of north-east Belgium

The robust calcite rostra (or guards) of belemnites were attractive substrates for some boring organisms in the Mesozoic. The rostra of belemnitellid coleoids are common at certain levels within the Gulpen and Maastricht formations of the extended type area of the Maastrichtian Stage (Upper Cretaceous) in the south-east Netherlands and north-east Belgium. A range of episkeletozoans have been reported from these substrates hitherto. A new specimen preserved as a natural mould in flint from the province of Liège, north-east Belgium, is distinctive, preserving a dense three-dimensional infestation of long, slender, unbranched and unsculptured borings of constant diameter, Trypanites? isp. These may be the spoor of polychaetes. Variations in diameter between borings suggests that the traces in this specimen may represent four separate infestations.     

Enigmatic clastic pipe swarms and implications for fluidization dynamics in aeolian deposits

Soft‐sediment deformation of contorted and massive sandstone is common throughout much of the siliciclastic record, but clastic pipes represent a distinctive class of pressurized synsedimentary features. Remarkable centimetre to metre‐scale clastic pipe exposures in the Jurassic Navajo Sandstone of Utah (USA) establish a range of pipe sizes, expressions and relationships to the host rock in an erg margin setting, traditionally thought to be just a dry desert system. In particular, the field and laboratory characterizations of cylindrical pipes show internal concentric, annular rings that imply water fluidization, with alignment of long grain axes due to shear flow along pipe margins. Central interior parts of decimetre‐scale pipes appear massive in plan view, but display weakly developed pseudobedding from post‐pressure release, gravitational settling in the cross‐sectional view. Deformation features of conjugate fractures, ring faults, hypotrochoid patterns (geometric arcs and circles) and breccia in the host material reflect both brittle and ductile behaviour in response to the fluidization and injection of the clastic pipes. The stratigraphic context of individual pipes and the stratabound intervals of pipe features imply dynamic deformation nearly coincident with deposition in this Early Jurassic aeolian system related to multiple factors of groundwater expulsion, timing and local host sediment properties that influenced pipe development. Although the pipe features might be easily overlooked as a smaller scale feature of soft‐sediment deformation in dune deposits, these are valuable environmental indications of disrupted fluid pathways within porous, reservoir quality sands, associated with possible combinations of periodic springs, high water‐table conditions and strong ground‐motion events. These pipe examples may be important analogues where exposures are not so clear, with applications to diverse modern and ancient clastic settings internationally on Earth as well as in planetary explorations such as on Mars.     

Stable and clumped isotopes in desert carbonate spring and lake deposits reveal palaeohydrology: A case study of the Lower Jurassic Navajo Sandstone,south‐western USA

Carbon, oxygen and clumped isotope (Δ₄₇) values were measured from lacustrine and tufa (spring)‐mound carbonate deposits in the Lower Jurassic Navajo Sandstone of southern Utah and northern Arizona in order to understand the palaeohydrology. These carbonate deposits are enriched in both ¹⁸O and ¹³C across the basin from east to west; neither isotope is strongly sensitive to the carbonate facies. However, ¹⁸O is enriched in lake carbonate deposits compared to the associated spring mounds. This is consistent with evaporation of the spring waters as they exited the mounds and were retained in interdune lakes. Clumped isotopes (Δ₄₇) exhibit minor systematic differences between lake and tufa‐mound temperatures, suggesting that the rate of carbonate formation under ambient conditions was moderate. These clumped isotope values imply palaeotemperature elevated beyond reasonable surface temperatures (54 to 86°C), which indicates limited bond reordering at estimated burial depths of ca 4 to 5 km, consistent with independent estimates of sediment thickness and burial depth gradients across the basin. Although clumped isotopes do not provide surface temperature information in this case, they still provide useful burial information and support interpretations of the evolution of groundwater locally. The findings of this study significantly extend the utility of combining stable isotope and clumped isotope methods into aeolian environments.     

Climatic and sea‐level control of Jurassic (Pliensbachian) clay mineral sedimentation in the Cardigan Bay Basin,Llanbedr (Mochras Farm) borehole,Wales

Early Jurassic climate is characterized by alternating cold and warm periods highlighted by studies based notably on oxygen isotopes measured on belemnite guards and other marine invertebrate shells. These climatic changes include changes in the hydrological cycle, and consequently weathering and runoff conditions. In order to clarify the erosion and weathering conditions during the Pliensbachian, this study determined the mineralogical composition of the clay fraction of 132 samples taken from the entire stage drilled in the Llanbedr (Mochras Farm) borehole (Cardigan Bay Basin). The clay mineral assemblages are composed of various proportions of chlorite, illite, illite/smectite mixed‐layers (R1 I–S), smectite and kaolinite, with possibly occasional traces of berthierine. The occurrence of abundant smectite indicates that the maximum burial temperature never exceeded 70°C. Consequently, clay minerals are considered mainly detrital, and their fluctuations likely reflect environmental changes. The variations in the proportions of smectite and kaolinite are opposite to each other. Kaolinite is particularly abundant at the base of the jamesoni Zone, in part coinciding with the δ¹³C negative excursion corresponding to the Sinemurian/Pliensbachian Boundary Event, and through the davoei Zone, whilst smectite is abundant in the upper part of jamesoni and base of ibex zones and through the subnodosus/gibbosus subzones of the margaritatus Zone. The kaolinite‐rich intervals reflect an intensification of hydrolysis and an acceleration of the hydrological cycle, while the smectite‐rich intervals indicate a more arid climate. The spinatum Zone is characterized by a distinct clay assemblage with abundant primary minerals, R1 I–S, kaolinite reworked from previously deposited sediments or from Palaeozoic rocks, and probably berthierine originating from contemporaneous ironstone‐generating environments of shallower waters. This mineralogical change by the end of the Pliensbachian likely reflects a transition from a dominant chemical weathering to a deeper physical erosion of the continent, probably related to a significant sea‐level fall consistent with a glacio‐eustatic origin.     

Contrasting definitions for the term ‘karst aquifer’

It is generally considered that karst aquifers have distinctly different properties from other bedrock aquifers. A search of the literature found five definitions that have been proposed to differentiate karst aquifers from non-karstic aquifers. The five definitions are based upon the presence of solution channel networks, hydraulic conductivities >10^?6 m/s, karst landscapes, channels with turbulent flow, and caves. The percentage of unconfined carbonate aquifers that would classify as ‘karst’ ranges from <1 to >50%.     

Deep hydrothermal activity in hydrocarbon reservoirs,South Kuwait

Fluid inclusion (FI) data provide insights into the origin of hot fluids in Cretaceous and Jurassic reservoirs in south Kuwait. FI data for Cretaceous reservoirs show anomalously high temperatures exceeding 200 °C compared to samples from the Jurassic. In addition, formation water chemical geothermometry data also show anomalous water-rock equilibration temperatures. The preservation of high temperatures indicates rapid migration from depth through deep-seated fault systems. This implies that very hot fluids probably migrated up-fault from near basement to the Cretaceous section. This approach helps to understand the role of hydrothermal activity associated with basement faults in south Kuwait.     

Reappraising the geomorphology‐ecology link

This thematic Virtual Special Issue highlights a personal selection of 18 recent (2007–2009) contributions to Earth Surface Processes and Landforms. These papers provide a flavour of recent research that is concerned with furthering our understanding of the many ways in which the biosphere interacts with the physical and chemical processes of sediment transfer/transformation. Much of this research has focused on understanding the mechanics by which the biota can modulate sediment transport and the strength of earth surface materials, often with the aim of applying that knowledge to enhance bioremediation methods of erosion control. This work continues to be fundamentally important in enhancing our understanding of earth surface processes, but often treats the biosphere and physical world as uncoupled entities. This selection therefore also provides samples of work that point to an ongoing but significant disciplinary reappraisal in which it is the interactions between ecological and geomorphological realms that are of primary interest. Copyright © 2009 John Wiley & Sons, Ltd.