A 500 yr speleothem-derived reconstruction of late autumn–winter precipitation, northeast Turkey

A verified instrumental calibration of annually resolved δ¹⁸O for a stalagmite from Gümü?hane in northeast Turkey is presented and cross-validated using a ‘leave-one-out’ technique. The amount of late autumn to winter precipitation is negatively correlated with stalagmite δ¹⁸O between AD 1938 and 2004. The observed relationship is extrapolated back to ~ AD 1500 leading to the first long winter precipitation reconstruction for this region. Modern day October to January precipitation is linked to pressure fields in Western Russia. Anomalously lower reconstructed rainfall is recorded in AD 1540–1560 at which time higher pressure over the Caspian Sea region is inferred.     

New OSL dating of UK loess: indications of two phases of Late Glacial dust accretion in SE England and climate implications

Windblown dust deposits or loess, locally known in the UK as brickearth, blanket many parts of southern England outside the limits of the British and Irish Ice Sheet. The best‐studied loess exposures occur in Kent, southeast England, where the deposits are believed to be Late Glacial in age. New sedimentological evidence is presented for phases of accretion with two distinct units, a calcareous brickearth exhibiting periglacial cryoturbation and a non‐calcareous, massive brickearth. Optically stimulated luminescence (OSL) dating has been applied to chemically isolated modal quartz silts to derive a chronology for sediment accretion and to better understand the palaeoclimatic significance of these deposits. © British Geological Survey/Natural Environment Research Council copyright 2007. Reproduced with the permission of BGS/NERC. Published by John Wiley & Sons, Ltd.     

The Purpose and Age of Underwater Walls in the Bay of Elaia of Western Turkey: A Multidisciplinary Approach

Pergamum (modern: Bergama) was operating an important harbour used by military forces and merchants at the city of Elaia during Hellenistic and Roman Imperial times. Harbour‐related facilities such as warehouses, breakwaters and wharfs document the importance of this harbour site not only for the Pergamenians. This paper focuses on the purpose and age of six submerged wall structures situated approximately 1 km south of the ancient closed harbour basin of Elaia. Geoelectric cross‐sections and semi‐aquatic coring near these walls failed to detect any solid basement under the walls which excludes their possible use as breakwaters or wharfs. Instead, the walls were most likely delineating and separating evaporation ponds of salt works, which compares well with similar structures from other periods and places around the Mediterranean. Combined OSL and ¹⁴C‐dating determined the construction age of the installation between the 4th and 6th centuries A.D. Subsequent (re‐)uses are likely and are in agreement with findings from archaeological surveys.     

Remote sensing of Carhuarazo volcanic complex using ASTER imagery in Southern Peru to detect alteration zones and volcanic structures – a combined approach of image processing in ENVI and ArcGIS/ArcScene

A combined approach to detect hydrothermal alteration zones and their mineral distribution is proposed for a relatively remote area around the Carhuarazo volcanic complex in southern Peru encompassing 2222 km². In this region, tertiary volcanic structures associated with hydrothermal alteration are well known to host epithermal ore deposits. We make an attempt to detect and to quantify alteration minerals based on spectral analysis using ASTER reflectance data product provided by LP-DAAC. Besides commonly used ratio images, mineral indices (MI) and relative band depth images (RBD), we also extracted endmember spectra using Pixel-Purity-Processing preceded by minimum noise fraction transformation. These spectra are thought to represent the spectrally purest pixel of the image and show the typical absorption features of the main constituents. Based on this assumption, we used different spectral analysis methods in order to extract the most important alteration minerals for such an environment. These minerals were then used for matched filter processing in areas showing high values in MIs and RBDs. Using this method, we detected and mapped argillic alteration and variations in the distribution of important minerals like alunite, kaolinite or nacrite. There were no indications for the presence of propilitization at ASTER spatial resolutions. Our method can be applied easily to any ASTER scene and provides information about the intensity of alteration and the character of alteration zones. The intensity is highest in the centre of the Carhuarazo volcanic complex and is mostly argillic with a high content of alunite, dickite and other clay minerals.     

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.     

Inter-laboratory comparison of oxygen isotope compositions from biogenic silica

Several techniques have been introduced in the last decades for the dehydration and release of O₂ from biogenic silica (opal-A) for oxygen-isotope analysis. However, only one silica standard is universally available: a quartz standard (NBS28) distributed by the IAEA, Vienna. Hence, there is a need for biogenic silica working standards. This paper compares the existing methods of oxygen-isotope analyses of opal-A and aims to characterize additional possible working standards to calibrate the δ¹⁸O values of biogenic silica. For this purpose, an inter-laboratory comparison was organized. Six potential working standard materials were analysed repeatedly against NBS28 by eight participating laboratories using their specific analytical methods. The materials cover a wide range of δ¹⁸O values (+23 to +43‰) and include diatoms (marine, lacustrine), phytoliths and synthetically-produced hydrous silica. To characterize the proposed standards, chemical analyses and imaging by scanning electron microscopy (SEM) were also performed. Despite procedural differences at each laboratory, all methods are in reasonable agreement with a standard deviation (SD) for δ¹⁸O values between 0.3‰ and 0.9‰ (1σ). Based on the results, we propose four additional biogenic silica working standards (PS1772-8: 42.8‰; BFC: 29.0‰; MSG60: 37.0‰; G95-25-CL leaves: 36.6‰) for δ¹⁸O analyses, available on request through the relevant laboratories.     

Integrated stratigraphy and palaeoenvironment of the P/E boundary interval, Rakhi Nala section, Indus Basin (Pakistan)

Marine sedimentary section across the Paleocene/Eocene (P/E) boundary interval is preserved in the Dungan Formation (Lower Indus Basin), Pakistan. Four dinoflagellate zones in the P/E interval of the Rakhi Nala section (Lower Indus Basin) are identified and correlated. The quantitative analysis of the dinoflagellate cyst assemblages together with geochemical data are used to reconstruct the palaeoenvironment across the P/E interval. The dinocyst assemblages allow the local correlation of the Dungan Formation (part) of the Sulaiman Range with the Patala Formation (part) of the Upper Indus Basin and global correlation of the Zone Pak-DV with the Apectodinium acme Zone of the Northern and Southern hemispheres. The onset of the carbon isotopic excursion (CIE) associated with Paleocene Eocene Thermal Maximum (PETM) is used globally to identify the P/E boundary. The CIE for the total organic carbon (fine fraction) δ¹³C_FF is of a magnitude of ?1.7‰ is recorded for the first time in the Indus Basin. The Apectodinium acme precedes and straddles the onset of the CIE in the Indus Basin. This Apectodinium acme is also accompanied by a planktonic and benthonic foraminifera “barren zone.” The CIE in the Indus Basin, coupled with the changes in the dinocyst distribution and the benthonic and planktonic foraminifera assemblages, provides evidence of the changes associated with the PETM in this little-known part of the world. The benthonic foraminiferal assemblage indicates bathyal environment of deposition at the time of P/E boundary interval; the presence of dominantly open marine dinoflagellates and high planktonic foraminiferal ratio suggest that the water column at this site was well connected with the rest of the Tethys.     

Naturally propped fractures caused by quartz cementation preserve oil reservoirs in basement rocks

Much silica precipitation in oil reservoirs occurred in the presence of hydrocarbons, evidenced by the entrapment of oil fluid inclusions in quartz. Also, silica in sedimentary basins is commonly precipitated at oil‐window temperatures. This spatial and temporal relationship between oil and quartz precipitation aids the entry of oil into fractured reservoirs, including fractured basement. Where quartz is precipitated as fracture linings, the fractures are propped open by bridging quartz crystals, creating high fracture porosity and permeability. Evidence from fossil fractured reservoirs shows a large proportion of oil residue is in such propped open fractures.     

Volatiles in a peralkaline system: Abiogenic hydrocarbons and F–Cl–Br systematics in the naujaite of the Ilímaussaq intrusion, South Greenland

Agpaitic rocks comprise most of the exposed part of the 1.16 Ga old, 8 × 17 km large and about 1700 m thick Ilímaussaq intrusion in South Greenland. Within these, more than 600 m thick sequence of sodalite-rich “naujaites” (mainly sodalite + arfvedsonite + alkali feldspar + nepheline + eudialyte + aenigmatite) are interpreted as a sodalite flotation cumulate. Sodalites show two to three different zones in cathodoluminescence (CL) and at least two zones in thin sections. The CL zones can be related to chemical differences detectable by electron microprobe, whereas relations with optical zonations are less obvious. Compositional trends in sodalite reflect trends in the evolution of volatile contents in the melt. The sodalite at Ilímaussaq is almost free of Ca and closely corresponds to the pure Na–Cl sodalite endmember with about 7 wt.% of Cl; S contents reach up to 0.9 wt.%. Cl/Br ratios range from 500 to 1700. Raman spectroscopy shows that S is present as [SO₄]²⁻ in sodalite, although sphalerite (ZnS) is a stable phase in naujaites. Peralkalinity and fO₂ conditions allow S²⁻ and [SO₄]²⁻ to be present contemporaneously.

The whole naujaite sequence is divided into two parts, an upper part with low, homogeneous S contents and Cl/Br ratios in the sodalite cores, and a lower part with strongly variable and higher S contents and with Cl/Br ratios, which are decreasing downwards. The details of the S content and the Cl/Br ratio evolution show that sodalite strongly influences the halogen contents of the melt by scavenging Cl and Br.

The naujaites were formed from a highly reduced, halogen-rich magma in equilibrium with magmatic methane at about 800 °C, which, upon ascent, cooling and fractionation, exsolved an aqueous fluid phase. Both fluids were trapped in separate inclusions indicating their immiscibility.

Micrometer-sized aegirine crystals and primary hydrocarbon-bearing inclusions are abundant in the crystal cores. The inclusions were trapped at pressures up to 4 kbar, although the emplacement pressure of the intrusion is about 1 kbar. This indicates growth of the sodalite during melt ascent and a very effective mechanism of trace element scavenging during sodalite growth. Sodalite rims are devoid of aegirine or primary hydrocarbon inclusions and probably reflect the emplacement stage.     

Lake evolution in a semi-arid montane environment: response to catchment change and hydroclimatic variation

Pollen, geochemical and sedimentological data from Sidi Ali, a montane Moroccan lake, provide a 7000 yr record of changes in climate, catchment vegetation and soil erosion intensity. Diatoms, non-silicious algae, macrophyte fossils and ostracods from the same core record the dynamics of the lake ecosystem. Oxygen isotope and trace-element ratios of benthic ostracods appear to be relatively insensitive to climatic variation in this open lake with low water-residence time, but diatom plankton / periphyton (P/L) ratios show lake-level variations that are probably climate controlled. At least two superimposed processes are recorded, but at different timescales: catchment vegetation and soils show long-term changes due to climate and human impact, whereas P/L ratios suggest century-scale oscillations in lake depth. The timing of changes in algal and macrophyte productivity and carbon cycling within the lake broadly corresponds to changes in terrestrial vegetation, suggesting either that lake nutrient status is linked to catchment vegetation and soils, or that both were influenced by climate. The lack of a sensitive and independent (non-biological) climate proxy makes it more difficult to assess the lake's ecological response to short-term climate variation. Overall, the lake's evolution has been influenced both by catchment-mediated nutrient flux and by changes in water balance, thus having characteristics in common with both temperate and arid zone lakes.