Paleosols and prehistoric populations in the high plains

Excavations in 1980–1981 at sites (32MZ319 and 32MZ380) along Cinnamon Creek Ridge in the Little Missouri River Badlands of McKenzie County, North Dakota, unexpectedly revealed at each locality the presence of one or more deeply buried paleosols with associated cultural materials. At both sites, 32MZ319 and 32MZ380, multiple paleosols are present, each of which is terminated by an episode of aeolian deposition. Fifteen radiocarbon dates on these paleosols establish an incipient chronology for paleosol development in the study area and permit correlation with other High Plains archaeological complexes. Geological and archaeological data for the two multiple paleosol sites are summarized.     

Vacuum testing of the permeability of the excavation damaged zone

Summary The vacuum permeability method provides a new approach to assessment of permeability in the near-field of rock excavations. The method, which resembles leak testing of vacuum lines, is based on the measurement and interpretation of the pneumatic response to evacuation of a rock mass. As the induced drainage area is in order of meters, the method is particularly suitable on the scale of the excavation damaged zone. The data can be evaluated either analytically or numerically. The evaluation is similar to the approach used in the analysis of drill stem tests in gas wells. Experiments on large scale laboratory models corroborated the validity of the method and the evaluation procedure. Field tests were conducted at a wide range of geomechanical conditions. The collected data indicate that there are three characteristic types of permeability distribution in the excavation damaged zone.     

Cesstibtantite—a geologic introduction to the inverse pyrochlores

Summary The crystal structure of cesstibtantite has been solved from diffractometer data collected on samples from Leshaia, Russia and the Tanco pegmatite, Manitoba. Cesstibtantite from the Leshaia pegmatite (type locality) hasa 10.515(2) Å, space groupFd3m, composition Cs_0.31(Sb_0.57Na_0.31Pb_0.02Bi_0.01)_O.91(Ta_1.88Nb_0.12)₂(O_5.69[OH, F]_0.31)₆(OH, F)_0.69, Z 8; its structure was refined toR 3.8,wR 4.3% using 96 observed (F > 3[F]) reflections (MoK). Cesstibtantite from the Tanco pegmatite hasa 10.496(1) Å, space groupFd3m, composition (Cs_0.22K_0.01)_0.23(Na_0.45Sb_0.39Pb_0.14· Ca_0.06Bi_0.02)_1.06(Ta_1.95Nb_0.05)₂(O_5.78[OH,F]_0.22)₆(OH,F)_0.55,Z 8; its structure was refined toR 3.9w R 3.7% using 104 observed reflections. Cesstibtantite differs from the normal pyrochlores in that it contains significant amounts of very large cations such as Cs. As these cations are too large (^VIII[r] > 1.60 Å) for the conventional [8]-coordinated A site, they occupy the [18]-coordinated site, which normally contains monovalent anions. Natural cesstibtantite samples are non-ideal in that both Cs and monovalent anions occur at the site; thus cesstibtantite is intermediate to thenormal pyrochlores (with only monovalent anions at the site) and theinverse pyrochlores (with only large cations at the site).

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Cesstibtantit—eine geologische Einfiihrung in die inversen Pyrochlore

Zusammenfassung Die Kristallstruktur von Cesstibtantit wurde auf der Basis von Diffraktometerdaten von Proben von Leshaia, Russland and dem Tanco Pegmatit, Manitoba, gelöst. Cesstibtantit aus dem Leshaia Pegmatit (Typlokalität) hat a 10.515(2) Å, RaumgruppeFd3m, die Zusammensetzung CS_0.31(Sb_0.57Na_0.31Pb_0.02Bi_0.01)_0.91(Ta_1.88Nb_0.12)₂· (O_5.69OH, F_0.31)₆(OH, F)_0.69 Z 8; die Struktur wurde aufR 3.8,wR 4.3% verfeinert unter Benützung von 96 beobachteten Reflexen. Cesstibtantit vom Tanco Pegmatit hat a 10.496(1) Å, RaumgruppeFd3m, die Zusammensetzung (Cs_0.22K_0.01)_0.23(Na_0.45· Sb_0.39Pb_0.14Ca_0.06Bi_0.02)_1.06(Ta_1.95Nb_0.05)₂(O_5.78OH,F_0.22)₆(OH,F)_0.55,Z 8; seine Struktur wurde aufR 3.9wR 3.7% auf der Basis von 104 beobachteten Rettexen verfeinert. Cesstibtantit unterscheidet sich von normalen Pyrochloren insofern, als er signifikante Mengen von sehr großen Kationen, wie z.B. Cs enthält. Da these Kationen zu groß sind (^VIII r 1.60 Å) für eine konventionelle [8]-koordinierteA Stelle, nehmen she die [18]-koordinierten Positionen ein, welche normalerweise monovalente Anionen enthalten. Natürliche Cesstibtantitproben sind nicht ideal insofern als sowohl Cs als auch monovalente Anionen in der Position vorkommen. Somit ist Cesstibtantit intermediär zu den normalen Pyrochloren (mit nur monovalenten Anionen auf der Position) and den inversen Pyrochloren (mit ausschließlichen großen Kationen an der Position).

     

Dimorphism in Placenticeras mintoi from the Upper Cretaceous Bagh Beds, central India

The Upper Cretaceous Bagh Beds yield many biota of which ammonoids are particularly well known. Previously Bagh ammonoids were grouped into many genera and species within several families. The present study, however, shows that failure to recognize dimorphism and a wide range of interspecific variation within the single genus Placenticeras perhaps results in taxonomic oversplitting. Specific dimorphism in P. mintoi has been established.     

Effects of CO2-H2O and oblique collision on orogenesis—the european hercynides as an example

The European Hercynides are considered the collisional result of Baltica and the microcontinents of Southern Europe, after subduction destroyed the intervening Rheic Ocean during the early Paleozoic. Their geotectonic development is assumed to consist of four overlapping stages:

1. (1) lithospheric thinning, upwelling of hot asthenospheric material, subsidence along listric faults, and basinal and geosynclinal development on the opposing shelves of the Rheic Ocean starting in pre-Devonian time;

2. (2) intermittent subduction of the Rheic Ocean interspersed with episodes of fracturing, volcanism, local uplift and subsidence, and basement reactivation as a result of compression with dextral megashear, particularly since the earliest Devonian;

3. (3) several phases of folding with a northward vergence, and thrusting and overthrusting along listric surfaces, the true orogenic stage;

4. (4) post-orogenic stage of massive granite intrusions and subsequent volcanism in the Permo-Triassic

.The high clastic content (as opposed to carbonates) of the sedimentary sequences involved in the subduction and folding processes and the consequent release of large amounts of meteoric water are held responsible for the synorogenic and post-orogenic magma rise, and for the wide zone of anatectic granites and migmatites. The dominant dextral megashear, the constant re-adjustment of the microcontinents of Southern Europe (oblique collision) and the scarcity of back-arc basins, oceanic plateaus and microcontinents led to the poor preservation of ophiolites and ultrabasic rocks, and to a wide (over 1500 km) Hercynian Foldbelt.During the Paleozoic, the depositional center of the Rhenish Massif shifted from south polar latitudes in the early Ordovician to tropical positions within a period of about 100 m.y. The sediment facies reflects this paleogeographic development.     

Fission tracks in minerals: Annealing kinetics,track structure and age correction

It is shown that the annealing kinetics of fission tracks in apatite can be described by a sum of exponential decay functions. From an analysis of the temperature dependence of this annealing law it is concluded that the etchability of fission tracks is due to extended defects, i.e. systems of dislocation loops. The multiexponential annealing law is also applied to prove that the plateau correction method is basically correct, but rather as a method for determining a lower limit than the “true” fission track age.     

Primary productivity and phytoplankton size fraction dominance in a temperate North Atlantic estuary

The composition, productivity, and standing crop of net (>20 μm) and nano-(<20 μm) phytoplankton of Peconic Bay, Long Island, New York was examined from June 1978 through May 1979. Nanoplankton, primarily small solitary flagellates, chlorophytes, and diatoms, dominated from May through September accounting for 88.5% of the productivity and 88.1% of the standing crop (measured as chlorophyll a). An apparent net plankton bloom began in December and continued through March. The dominant organism through most of the winter bloom was the chain-forming diatom Skeletonema costatum (Grev.) Cl. Net plankton at this time represented 66.4% of the standing crop. For both size fractions, productivity/chlorophyll a (g C per g chl a per d, integrated through the euphotic zone) was a function of light energy over the year with the exception of a few sampling dates during the post-winter bloom period. Assimilation numbers (g C per g chl a per h at saturating light intensities) were a function of temperature between 0 and 20°C. Nitrogen deficiency did not appear to be a factor in regulating phytoplankton growth rate through the euphotic zone, as ratios of ¹⁴C assimilation for dark bottles enriched with NH₃ and with no enrichment exhibited no relationship to environmental dissolved inorganic nitrogen concentrations. Zooplankton grazing pressure appeared to have been an important factor in regulating the upper limit of phytoplankton biomass and in influencing size fraction dominance. Dominance of one phytoplankton size fraction over the other on any given date was not based on physiological differences between the two groups since both fractions were composed of the same species. Apparent net phytoplankton blooms (in terms of productivity and chlorophyll a) were artifacts of increased chain lengths of nanoplankton diatoms such as Skeletonema costatum, and to a lesser extent, Thalassiosira nordenskioldii Cl. and Detonula confervacea (Cl.) Gran, rather than to the dominance of large, solitary cells.     

Age of Gimli beach of Lake Agassiz based on new OSL dating

Gimli beach in Manitoba is one of the lowest elevation beaches in the southern Lake Agassiz basin, and is a distinct ridge composed of bedded sand and gravel that rises above the lake plain and extends for more than 40 km. Ten new optically stimulated luminescence (OSL) ages from Gimli beach yield ages mostly ranging from 9.7 ± 0.7 to 10.5 ± 0.8 ka (average 10.3 ± 0.5 ka), which is older by 0.6 to >1.0 ka than age estimates of previous researchers. Two of our new OSL ages are notably older than the others, dating to ~11.3 ± 0.8 and 13.9 ± 1.0 ka, which we attribute to poorly bleached sands. We ascribe an age of about 10 ka to Gimli beach, which is several centuries before overflow from Lake Agassiz and its vast drainage basin shifted from the western Great Lakes to glacial Lake Ojibway and the St. Lawrence Valley.     

Stochastic Local Interaction Model: An Alternative to Kriging for Massive Datasets

Mathematical Geosciences - Classical geostatistical methods face serious computational challenges if they are confronted with large spatial datasets. The stochastic local interaction (SLI) approach...