An occurrence of secondary sulfides from Leg 37 basalts

Two types of secondary sulfides occur on the walls of a vesicle in slightly altered basalt recovered from site 332A of DSDP Leg 37. The first consists of euhedral crystals of pure pyrite, with occasional small partial overgrowths of fibrous chalcopyrite, embedded within smectite (altered glass) which lines the vesicle. The second type occurs as small composite sulfide spherules lightly attached to the surface of the smectite. The spherules are composed of pyrite crystallites arranged in approximate pyritohedral symmetry, with marcasite crystallites decorating the pyritohedron edges. Precession camera photographs and optical studies suggest the marcasite and pyrite grew simultaneously from a pyrite nucleus, with marcasite adopting the pyrite growth habit. These spherules differ sharply from the magmatic sulfide spherules previously described.     

Do Stable Isotope Data from Calcrete Record Late Pleistocene Monsoonal Climate Variation in the Thar Desert of India?

Late Pleistocene terrestrial climate records in India may be preserved in oxygen and carbon stable isotopes in pedogenic calcrete. Petrography shows that calcrete nodules in Quaternary sediments of the Thar Desert in Rajasthan are pedogenic, with little evidence for postpedogenic alteration. The calcrete occurs in four laterally persistent and one nonpersistent eolian units, separated by colluvial gravel. Thermoluminescence and infrared- and green-light-stimulated luminescence of host quartz and feldspar grains gave age brackets for persistent eolian units I–IV of ca. 70,000–60,000, ca. 60,000–55,000, ca. 55,000–43,000, and ca. 43,000–25,000 yr, respectively. The youngest eolian unit (V) is <10,000 yr old and contains no calcrete. Stable oxygen isotope compositions of calcretes in most of eolian unit I, in the upper part of eolian unit IV, and in the nonpersistent eolian unit, range between −4.6 and −2.1‰ PDB. These values, up to 4.4‰ greater than values from eolian units II and III, are interpreted as representing nonmonsoonal¹⁸O-enriched “normal continental” waters during climatic phases when the monsoon weakened or failed. Conversely, 25,000–60,000-yr-old calcretes (eolian units II and III) probably formed under monsoonal conditions. The two periods of weakened monsoon are consistent with other paleoclimatic data from India and may represent widespread aridity on the Indian subcontinent during isotope stages 2 and 4. The total variation in δ¹³C is 1.7‰ (0.0–1.7‰), and δ¹³C covaries positively and linearly with δ¹⁸O. δ¹³C values are highest when δ¹⁸O values indicate the most arid climatic conditions. This is best explained by expansion of C₄grasses at the expense of C₃plants at low latitudes during glacial periods when atmosphericpCO₂was lowered. C₄dominance was overridingly influenced by global change in atmosphericpCO₂despite the lowered summer rainfall.     

Geographical reflections on Sir Edmund Hillary (1919–2008)

Abstract: During the past year, the media, public and officialdom have focused on Sir Edmund Hillary, his achievements, and what they mean to New Zealand. In this commentary, we reflect on how they relate to human geography. Although we acknowledge the obvious tensions that exist between adventuring and the contemporary concerns of the discipline, we also illustrate how Hillary's life and actions resonate with many of the discipline's current hopes, aims and challenges. Specifically, we discuss thematic overlaps in the fields of geopolitics and national identities, colonial histories and resistances, as well as the emerging public geography. We posit that ‘Hillary's geography’ is closer to human geography than is realized or at least acknowledged by geographers.     

Multiple deglaciations of the Hudson Bay Lowlands,Canada, since deposition of the Missinaibi (Last-integlacial?) formation

The stratigraphic record in the James and Hudson Bay Lowlands indicates that the sequence of glacial events at the geographical center of the 12.6 × 10⁶ km² Laurentide Ice Sheet may have been more complex than hitherto imagined. Isoleucine epimerization ratios of in situ and transported shells recovered from till and associated marine and fluvial sediments cluster into at least 4 discrete groups. Two alternative explanations of the data are offered, of which we strongly favor the first. Hypothesis 1: Setting the age of the “last interglacial” marine incursion, the Bell Sea, at 130,000 yr B.P. results in a long-term average diagenetic temperature for the lowlands of +0.6°C. Using this temperature enables us to predict the age of shells intermediate in age between the “last interglaciation” and the incursion of the Tyrrell Sea 8000 yr ago. Between these two interglacial marine inundations, Hudson Bay is predicted to have been free of ice along its southern shore about 35,000, 75,000, and 105,000 yr ago based on amino acid ratios from shells occurring as erratics in several superimposed tills and fluvial sediments. These results suggest (1) that traditional concepts of ice-sheet build-up and decay must be reexamined; (2) that “high” sea levels may have occurred during the Wisconsin Glaciation; and (3) that a critical reappraisal is required of the open ocean δ¹⁸O record as a simple indicator of global ice volume. An alternative, Hypothesis 2, is also examined. It is based on the assumption that the 35,000-yr-old deposits calculated on the basis of Hypothesis 1 date from the “last interglaciation”; this, in effect, indicates that the Missinaibi Formation, commonly accepted as sediments of the “last interglaciation,” are about 500,000 yr old and that the effective diagenetic temperature in the lowlands during approximately the last 130,000 yr has been close to ?6°C. We argue for rejection of this alternative hypothesis.     

The geochemistry of formation waters in the molasse basin of upper Austria

The geochemistry of formation waters in the Molasse basin of Upper Austria has been investigated to ascertain the extent of meteoric water replacement of the connate interstitial fluids in these sediments. The chemistry, isotopic composition, and dissolved gas contents of the groundwaters and of oil and gas associated brines have been determined. The most superficial sediments of the basin, the Innviertel (Miocene), have been completely flushed by meteoric waters within the last 200 ka. The underlying Hall and Puchkirchen formations (Miocene/Oligocene) form gas reservoirs for biogenic methane, and the associated formation waters are chemically and isotopically modified connate brines of the original marine deposition. In the northeastern part of the basin, the connate brines of the deeper sediments (Cretaceous/Jurassic) have been partially or completely replaced by meteoric waters, whereas in the south of the basin these sediments contain high salinity fluids which are substantially of connate origin. These conclusions are supported by the stable isotope composition of the various brines. Oil-associated brines from the Eocene sediments contain large amounts of dissolved radiogenic⁴⁰Ar, which suggests that the oils have migrated from high-temperature environments. This is in contrast with the Puchkirchen, for which the observed absence of radiogenic⁴⁰Ar suggests that the biogenic methane has been formed in situ. The⁴He contents of these brines and of the Cretaceous/Jurassic groundwaters are, however, less than those in the overlying Puchkirchen formation and suggest that He has been removed from the deeper sediments as a result of flushing by meteoric water. The ratios of dissolved methane and nitrogen to argon increase with increasing ammonium content of the formation waters. All of these parameters may be used as indices for the maturation of the system. The heavy noble gases, Kr and Xe, are abnormally abundant in the dissolved gases, and this is attributed to geochemical concentration of these gases by adsorption onto shales in the sediment sequence. The overall geochemical situation confirms the existence of separate hydraulic systems with little interconnection in the several overlying geological horizons.     

Land/ocean correlations during the last interglacial/glacial transition, Baffin Bay, northwestern North Atlantic: A review

Evidence from terrestrial sections, ice cores, and marine cores are reviewed and used to develop a scenario for environmental change in the area of the extreme northwest North Atlantic during marine isotope stages 5 and 4. The critical physical link between the landbased glacial chronology and marine events in Baffin Bay is the presence of carbonate rich drift along the Baffin Bay coast of Bylot Island and a detrital carbonate facies (Facies B) in Baffin Bay sediments. Cores from Baffin Bay/Labrador Sea can be dated by means of oxygen isotope variations and by peaks in the abundance of volcanic glass shards. One occurrence of Facies B is dated between late stage 5 and stage 4 and we correlate this event with the Eclipse Glaciation of Bylot Island and the Ayr Lake stade of the Foxe Glaciation of Baffin Island (= Kogalu aminozone). In contrast on West Greenland, amino acid racemization evidence suggests that the Greenland Ice Sheet developed throughout stage 4 and reached a maximum in stage 3 (Svartenhuk advance >40 ka). The oxygen isotope record in the Devon Island Ice Cap (northwest Baffin Bay) indicates that Baffin Bay was largely open during marine isotope stage 5. Analyses of shallow water molluscan and foraminiferal assemblages, deep-water foraminifera, pollen from Iand sections and deep-sea cores, and dinoflagellates from marine cores indicate that interglacial conditions prevailed during much of the stage glaciation.     

Sodium and strontium in mollusc shells: preservation,palaeosalinity and palaeotemperature of the Middle Pleistocene of eastern England

This paper revisits the utility of sodium (Na) content in aragonite and calcite mollusc shells as an indicator of palaeosalinity. The data come mainly from a related suite of Middle Pleistocene marine and freshwater fossils that have been subject to broadly similar diagenetic histories. Environmental salinity is re-affirmed as the primary factor in determining the sodium content of modern and ancient mollusc shells: values <2000 ppm Na are generally indicative of non-marine environments while values >2000 Na ppm are typically from marine shells. There is a positive relationship between Na (salinity) and Sr which is a helpful discriminator of palaeosalinity in the fossil data set. The Na and Sr data give confidence that the fossil shells have not suffered pervasive diagenetic alteration and that the marine fossils lived in fully marine conditions. Oxygen isotope values in the best-preserved, fully marine fossil shells, suggest Middle Pleistocene ‘eastern England’ seawater temperatures were broadly similar to those of the modern North Sea.