A ferrotantalite-ferrotapiolite intergrowth from Spittal a.d. Drau,Carinthia, Austria

Summary Intimate intergrowths of ferrotantalite and ferrotapiolite occur in a pegmatite in Spittal a.d. Drau, Carinthia. They are associated with muscovite, albite, smoky quartz, cassiterite, and microscopic uranmicrolite, zircon and uraninite. An assemblage of secondary uranium minerals is also present, generated by extensive alteration and leaching of the uranmicrolite and zircon. Textures of the ferrotantalite-ferrotapiolite intergrowths suggest considerable recrystallization that obliterated most of their primary features; neither coprecipitation nor exsolution can be recognized with certainty. Despite intersecting tielines indicating disequilibrium, the ferrotantalite and ferrotapiolite compositions show very restricted ranges (Mn/(Mn + Fe) 0.08–0.11, Ta/(Ta + Nb) 0.53–0.57 for ferrotantalite, and 0.01–0.04, 0.84–0.89 for ferrotapiolite, respectively), particularly in comparison with compositions from other localities featuring primary textures. A degree of compositional equilibration could have been attained during recrystallization. This process may also explain the high level of structural order characterizing both minerals; they are considerably disordered in other localities. Extensive deformation typical of pegmatites in the southern Ostalpen in general, and specifically of the Spittal pegmatite, is probably responsible for the recrystallization phenomena in the Ta, Nb, Sn-bearing mineral assemblage.

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Eine Ferrotantalit-Ferrotapiolit Verwachsung von Spittal a.d. Drau, Kärnten, österreich

Zusammenfassung In einem Pegmatit von Spittal a.d. Drau, Kärnten, treten enge Verwachsungen von Ferrotantalit und Ferrotapiolit auf. Diese werden von Muskovit, Albit, Rauchquarz, Zinnstein sowie-in mikroskopischem Masstab-von Uranmikrolith und Zirkon begleitet. Die Textur der Verwachsungen lässt Rekristallisation erheblichen Ausmasses erkennen, die die primären Merkmale weitgehend auslöscht. Weder eine gemeinsame Auskristallisation der beiden Mineralphasen noch eine Bildung durch Entmischung kann mit Sicherheit erkannt werden. Trotz einander kreuzender Verbindungslinien, die einen Hinweis auf Ungleichgewicht darstellen, zeigen die Zusammensetzungen des Ferrotantalits und des Ferrotapiolits lediglich geringe Schwankungsbreiten: Mn/(Mn + Fe) 0,08–0,11, Ta/(Ta + Nb) 0,53–0,57 für den Ferrotantalit beziehungsweise 0,01–0,04 und 0,84–0,89 für den Ferrotapiolit. Dies gilt insbesondere für den Vergleich mit Zusammensetzungen solcher Mineralphasen mit jenen von Fundarten, die primäre Verwachsungstrukturen aufweisen. Bis zu einem gewissen Ausmass ist diese homogene Zusammensetzung möglicherweise auf die Rekristallisation zurück zuführen. Diese Rekristallisation könnte auch den hohen strukturellen Ordnungsgrad der beiden Mineralphasen erklären. An anderen Fundorten zeigen diese Minerale strukturell merklich geringeren Ordnungsgrad. Intensive metamorphe überprägung, wie sie für die Pegmatite in den südlichen Ostalpen und insbesondere für jenen von Spittal typisch sind, kann wahrscheinlich als Ursache der Rekristallisationsphänomene der Ta-Nb-Sn Mineralparagenese angenommen werden.

     

Upper Albian OAE 1d event in the Chihuahua Trough,New Mexico,U.S.A.

Oceanic anoxic events are clues to ocean processes and are correlation datums. In North America only OAE 1a and 2 are well documented. Based on a low-resolution sampling program, a multi-proxy geochemical approach constrained by a biostratigraphic framework was utilized to identify OAE 1d in the upper part of the upper Albian Mesilla Valley Formation near El Paso, Texas. Chronostratigraphic and biostratigraphic evidence indicate that the OAE 1d event in the Mesilla Valley section is located in the lower part of the upper Albian–Cenomanian Ovoidinium verrucosum zone, which correlates with the uppermost Albian Parathalmanninella appenninica and Stoliczkaia dispar zones. The chronostratigraphic age of the geochemical event in the Mesilla Valley Formation is uppermost Albian (97.39–97.30 Ma).The classic geochemical signatures for OAEs are enriched total organic carbon (TOC) concentrations and coupled positive δ¹³C excursions. OAE 1d at this location records TOC values ranging from 0.25 to 0.69 wt.% throughout the Mesilla Valley Formation, where TOC increases during the OAE (21.0–40.0 m) to more than 0.40 wt.%. Interestingly, the organic matter in the Mesilla Valley is dominantly type III, which indicates a pervasive terrigenous source. Although marine organic matter is abundant from the base into the middle of the proposed OAE interval, it is progressively replaced by terrestrial material above the OAE section during progradation. The δ¹³C_organic values record a positive δ¹³C shift of +1.6‰ from −26.41 to −24.80‰ across the stratigraphic interval from 21.0 to 40.0 m, which correlates with OAE 1d.Mn and Fe geochemistry suggest the depositional conditions of the Mesilla Valley Formation were dominated by anoxic and possibly Fe-rich bottom waters, specifically during the time period associated with the OAE 1d event. This interpretation is supported by the presence of Fe enrichment recorded by Fe_Total/Al and Fe_{Highly Reactive}/Fe_T with the lack of Fe_pyrite/Fe_{Highly Reactive} associated with Mn depletion.     

Evidence for cyclic reactions between andalusite, “sericite” and sillimanite, mount franks area, willyama complex N.S.W

In the Mt. Franks area of the Willyama Complex, microfabric evidence suggests that the alteration of andalusite to sillimanite has taken place by a process similar to that suggested by Carmichael (1969). Andalusite is pre- to syn-S₂ in age. Alteration to “sericite” has resulted in the formation of “sericite” laths, some of which are crenulated about S₂, and some which are syn- and post-S₂. “Fibrolite” occurs in these andalusite—“sericite” aggregates within the sillimanite zone and is wholly embedded in “sericite”. “Fibrolite” is pre- to syn-S₂ in age. This evidence is interpreted as suggesting that the formation of sillimanite from andalusite took place via a “sericite” phase.Further microfabric observations are interpreted to imply constant volume for the reaction aluminosilicate → “sericite”. This suggests a situation in which Al³⁺ is relatively mobile but Al⁴⁺ is relatively immobile. This suggestion differs from Carmichael's (1969) idea of Al³⁺ immobility.     

Morphologic and stratigraphic evidence for Allerød and Younger Dryas age glacier fluctuations of the Cordilleran Ice Sheet, British Columbia, Canada and Northwest Washington, U.S.A.

The late Wisconsin deglaciation of the Fraser Lowland is reconstructed by integrating surficial mapping, stratigraphic, palynological, oceanographic (from previous studies), radiocarbon, and shaded digital topographic data. Moraines associated with glacier fluctuations along the southwestern margin of the Cordilleran Ice Sheet are recognized for the first time and their chronology is established from 70 radiocarbon dates secured by morphologic and stratigraphic evidence. Following emergence of the lowland at c. 11.6 14 C kyr BP, three periods of glacier readvance occurred 11.6-11.4 and 10.9-10.2 14 C kyr BP during the Sumas interval. The spatial and temporal relationships of Sumas Drift indicate four recognizable phases, which unifies and extends the surficial geology across the U.S.-Canadian border.     

Reply to comments by R. Von Herzen, E.E. Davis, A.T. Fisher, C.A. Stein and H.N. Pollack on “Earth's heat flux revised and linked to chemistry”

The lengthy comment by Von Herzen et al. does not address the most important conclusions of the paper by Hofmeister and Criss [Hofmeister, A.M., Criss, R.E., 2005, Earth's heat flux revisited and linked to chemistry. Tectonophys. 395, 159–177.]. These are 1) that actual measurements better describe the Earth than do simplistic models with demonstrably unrealistic boundary conditions that diverge markedly from the data; and 2) that the models are unconstrained, resulting in a series of papers proposing values for the global flux that have become increasingly disparate from the growing data base over time (Fig. 3 in our paper). We disagree strongly with penultimate concluding statement of Von Herzen et al., “that it is preferable to base surface heat flow analysis not only on the extensive measurements but also on well understood processes that are known to bias the values and statistics of the measurements,” as our Fig. 3 demonstrates that no consistent magnitude has been assigned to the alleged advective flux, so that neither the processes nor the correction are “well understood”. We do not deny the existence of submarine hydrothermal systems, but we disagree strongly with the scales over which they are alleged to operate, and with the large Rayleigh and Nusselt numbers Von Herzen et al. assign to them.     

The geoarchaeology of Iron Age “moated” sites of the Upper Mae Nam Mun Valley,N.E. Thailand. I: Palaeodrainage,site–landscape relationships and the origins of the “moats”

The study focuses on the “moated” Iron Age sites of N.E. Thailand, first identified as significant prehistoric settlement sites in the 1940s from aerial photography. Two more recent photograph sets are used to map the surficial geology and prehistoric site distribution for a study area west of Phimai, N.E. Thailand, with a focus on site–landscape relationships and, in particular, relationships between site location and form and patterns of palaeodrainage. The derived record of the surficial geology reflects several phases of palaeodrainage, characterized by differing locations and types of former river channels. Of note is the differentiation between a recent period in which river channels, including those presently active, are single-string meandering channels, and an older period of broad belts of meandering multistring channels. The prehistoric site distribution correlates closely with the older drainage, and for many, the encircling channels (the “moats”) are closely associated with former river channels. These relationships provide a critical and novel model for site distribution; several implications arise, supported by emerging field evidence, and introducing issues for archaeological debate: (i) there is no need, as has been done in the past, to invoke prehistoric artificial forms of drainage associated with the sites; (ii) the definition of the encircling channels as “moats” is seriously called into question; and (iii) the inferred geomorphological evolution of the floodplain implies past changes in environmental parameters such as run-off, climate or biophysical environments. Since the sites are all located in or beside ancient meander belts, these parameters should now be introduced into archaeological discussions regarding the establishment, history, evolution, and abandonment of the Iron Age sites. Methodologically, this article illustrates the need to be aware of the complexity of aerial photograph interpretation in archaeological survey, showing that careful analysis of aerial photograph information may have a significant impact upon the modeling of prehistoric interpretations. Further stratigraphical studies will be reported subsequently, and will refine the models presented here. © 1999 John Wiley & Sons, Inc.     

三维地震勘探技术在新疆沙吉海井田中的应用

针对沙吉海井田以往未开展过地震勘探,煤层多、局部间距小特点,介绍了研究区主要地震反射波与煤层对应关系.通过对T13、T12、T10、T6反射波研究,采用地震波阻抗反演技术对该区煤层厚度及煤层结构进行解释,查明井田构造形态和主要煤层赋存变化特征,取得了较好地震勘探效果.     

“Traditional” women, “modern” water: Linking gender and commodification in Rajasthan, India

In this paper, I analyze the connections made between women and water in a Rajasthani drinking water supply project as a significant part of drinking water’s commodification. For development policy makers, water progressing from something free to something valued by price is inevitable when moving economies toward modernity and development. My findings indicate that water is not commodified simply by charging money for it, but through a series of discourses and acts that link it to other “modern” objects and give it value. One of these objects is “women”. I argue that through women’s participation activities that link gender and modernity to new responsibilities and increased mobility for village women involving the clean water supply, a “traditional” Rajasthani woman becomes “modern”. Water, in parallel, becomes “new”, “improved” and worth paying for. Women and water resources are further connected through project staff’s efforts to promote latrines by targeting women as their primary users. The research shows that villagers applied their own meanings to latrines, some of which precluded women using them. This paper fills a gap in feminist political ecology, which often overlooks how gender is created through natural resource interventions, by concerning itself with how new meanings of “water” and “women” are mutually constructed through struggles over water use and its commodification. It contributes to critical development geography literatures by demonstrating that women’s participation approaches to natural resource development act as both constraints and opportunities for village constituents. It examines an under-explored area of gender and water research by tracing village-level struggles over meanings of latrines.