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101.
N. Malarkodi G. Keller P. J. Fayazudeen U. B. Mallikarjuna 《Journal of the Geological Society of India》2010,75(6):851-863
Intertrappean beds exposed between upper and lower traps of the Government and Sunnamrayalu quarries of Rajahmundry were analyzed
based on benthic and planktic foraminifera, ostracodes and algae observed in thin sections. Planktic foraminifera indicate
deposition occurred in the early Danian Parvularugoglobigerina eugubina (P1a) zone shortly after deposition of the lower trap flows. The most diverse planktic assemblages were deposited in limestones
of the middle intertrappean interval and indicate an upper P1a age, or subzone P1a(2), as marked by the co-occurrence of P. eugubina, Globoconusa daubjergensis, Parasubbotina pseudobulloides and Subbotina triloculinoides. Reworked late Maastrichtian planktic foraminifera are common in a limestone interval and suggest erosion of uplifted Cretaceous
sediments. Benthic foraminiferal assemblages indicate deposition occurred predominantly in shallow inner shelf to brackish
environments. Similarly, ostracodes indicate variable environments ranging from inner neritic to brackish with fresh water
influx, as also indicated by the presence of fresh water algae. These data confirm an overall deepening from restricted shallow
marine to estuarine, lagoonal and finally open marine conditions followed by abrupt emersion and paleosoil deposition prior
to the arrival of the upper trap flows at or near the base of C29n. 相似文献
102.
S. Marchi C. Barbieri F. Marzari H.U. Keller P. Lamy M. Massironi 《Planetary and Space Science》2010,58(9):1116-490
The cratering history of main belt asteroid (2867) Steins has been investigated using OSIRIS imagery acquired during the Rosetta flyby that took place on the 5th of September 2008. For this purpose, we applied current models describing the formation and evolution of main belt asteroids, that provide the rate and velocity distributions of impactors. These models coupled with appropriate crater scaling laws, allow the cratering history to be estimated. Hence, we derive Steins’ cratering retention age, namely the time lapsed since its formation or global surface reset. We also investigate the influence of various factors—like bulk structure and crater erasing—on the estimated age, which spans from a few hundred Myrs to more than 1 Gyr, depending on the adopted scaling law and asteroid physical parameters. Moreover, a marked lack of craters smaller than about 0.6 km has been found and interpreted as a result of a peculiar evolution of Steins cratering record, possibly related either to the formation of the 2.1 km wide impact crater near the south pole or to YORP reshaping. 相似文献
103.
Abundant and regionally unique dolostone lithoclast breccias occur throughout the shallow-marine, Lower to Middle Ordovician Pogonip Group in the Nopah Range and adjacent ranges in eastern California and southern Nevada. Breccia bodies display sharply cross-cutting relationships with host dolostone bedrock stratigraphy. They also show stratigraphic variability in size, shape and dolostone clast composition, but similarity in breccia matrix composition and framework texture and fabric. These characteristics are consistent with a palaeokarst origin. Upsection changes in breccia clast lithology as well as multiple occurrences of associated quartz sand-filled grikes (solution-widened fissures) indicate multiple episodes of carbonate platform exposure and karstification. Repeated karstification is also indicated by stratiform bodies of quartz sand and thin terra rossa palaeosols that locally truncate breccias and grike systems, thus bracketing karstified exposure surfaces. Facies successions and stacking patterns between recognized exposure surfaces are developed as transgressive–regressive cycles and thus show depositional sequence architecture. Hence, these breccias and other associated palaeokarst features are related to a succession of disconformities that provide a sequence-stratigraphic framework for assessing Ordovician relative sea-level history of the south-western Cordilleran margin of Laurentia. 相似文献
104.
W. I. Rose Jr. S. Bonis R. E. Stoiber M. Keller T. Bickford 《Bulletin of Volcanology》1973,37(3):338-364
The 1971 eruptions of Cerro Negro volcano in Nicaragua and Fuego volcano in Guatemala produced ash blankets with minimum volumes of 7 × 107 m3 and 6 × 107 m3, respectively. Seven new chemical analyses show that ash produced by both eruptions was basaltic and similar to previously — erupted lavas of both volcanoes. Both ash blankets were sampled areally and stratigraphically before they were affected by rain. Chemical analyses of soluble materials leached from these ashes show that near the end of both eruptions the concentrations of soluble materials increased by about an order of magnitude. These changes are believed to reflect changes in the composition of eruptive gases. 相似文献
105.
Analysis of State and Provincial Atlas Reviews* 总被引:1,自引:0,他引:1
Ninety-eight reviews of state and provincial atlases are examined in order to address several questions. Reviews are subjected to content analysis to identify the judgement criteria that experts use in evaluating a provincial or state atlas, and the aspects of each criterion that reviewers praise or condemn. An attempt is made to search for expert consensus and to identify a provincial or state atlas review recipe. The research reported here is part of a larger study undertaken to assist those in the process of planning a new provincial or state atlas initiative. This paper also assists individuals who are searching for rules and guidelines when undertaking an atlas review. 相似文献
106.
107.
H. Michael Keller R.A.K. Tahirkheli Mohammad A. Mirza Gary D. Johnson Noye M. Johnson Neil D. Opdyke 《Earth and Planetary Science Letters》1977,36(1):187-201
Over 1000 m of fluvial molasse, exhibiting a stable detrital remanent magnetization, is exposed in a mammal-bearing sequence in the Upper Siwalik Group of the Pabbi Hills, Pakistan. The magnetic polarity chronology reveals that the sequence records a time period of 2.6 m.y., extending from the early Gauss Normal Epoch into the Brunhes Normal Epoch. During this period, sedimentation rates increased upward in time from 0.25 m/1000 yr to 0.45 m/1000 yr. The sudden disappearance of red beds and a change in the lithoclastic composition of basal channel sands suggests that about 800,000 years ago the primary source area began shifting from the metamorphic terrane of the Himalayan Orogen to a more local sedimentary terrane on the folded margins of the Himalayan foredeep. About 500,000 years ago the anticlinal Pabbi Hills attained surface expression. Uplift continued at a minimum rate of 1 m/1000 yr.A local Pliocene/Pleistocene boundary based on the Olduvai Normal Event is clearly recognized. Local fossil finds reveal thatEquus, diagnostic element of the Pinjor faunal zone, appeared locally about 1.8 m.y. ago and thatHipparion, a faunal element of the Tatrot and earlier faunal zones, persisted locally until at least 3.0 m.y. ago. 相似文献
108.
Dr P. Keller Prof. Dr. H. Hess Dr. P. Süsse Dr. G. Schnorrer P. J. Dunn 《Mineralogy and Petrology》1979,26(1-2):51-58
Zusammenfassung Das neue Mineral Koritnigit ist ein wasserhaltiges Zinkhydrogenarsenat der Formel Zn[H2O|HOAsO3]. Die chemische Analyse (Elektronenmikrosonde und T.G.A.) ergab: As2O5 51,75%, ZnO 35,97% und H2O 12,3%, Summe 100,0%. Die HOAsO3-Ionen wurden IR-spektroskopisch nachgewiesen. Koritnigit ist löslich in kalter, verdünnter HCl und HNO3.Die Gitterkonstanten sind:a
0=7,948(2),b
0=15,829(5),c
0=6,668(2) Å, =90,86(2), =96,56(2), =90,05(2)o,V=833,2(4)Å3,V=8. Die Raumgruppe ist
. Die stärksten Linien des Pulverdiagramms sind: 7,90(10) (020,100), 3,83(7) (
), 3,16(9) (
) 2,926(4) (150), 2,679(4) (
), 2,461(6) (
), 2,186(5) (
), 1,969(4) (400), 1,649(3) (004).Koritnigit ist wasserklar bis durchscheinend weiß. Idiomorphe Kristalle sind nicht bekannt. Die Spaltbarkeit nach {010} ist ausgezeichnet und auf {010} sind Spaltspuren nach [001] und nach [100] erkennbar. Härte 2.G=3,54 g·cm–3,D
x
=3,56 g·cm–3. Koritnigit ist optisch zweiachsig positiv, 2V70(5)o. Die Werte der Lichtbrechung sind:n
=1,632(5),n
=1,652(3) undn
=1,693(3).Koritnigit wurde auf der 31. Sohle der Tsumeb-Mine, Südwestafrika gefunden. Er kommt als Sekundärmineral in Paragenese mit Cu-Adamin, Stranskiit und drei weiteren, vorerst nicht identifizierten mineralen in Zersetzungshohlräumen von Tennantit vor.
Mit 2 Abbildungen
Herrn Univ. Prof. Dr.H. Meixner zum 70. Geburtstag gewidmet. 相似文献
Koritnigite, Zn[H2O|HOAsO3], a new mineral from Tsumeb, South West Africa
Summary The new mineral koritnigite is a hydrated zinc hydrogen arsenate with the formula Zn[H2O|HOAsO3]. Chemical analysis (electron microprobe and t.g.a.) gave: As2O5 51.75%, ZnO 35.97%, and H2O 12.3%, total 100.0%. The HOAsO3 ions were determined by IR spectroscopy. Koritnigite is soluble in cold diluted HCl and HNO3. The unit cell dimensions are:a 0=7.948(2),b 0=15.829(5),c 0=6.668(2)Å, =90.86(2), =96.56(2), =90.05(2)o,V=833.2(4) Å3,Z=8. The space group is . The strongest lines of the powder pattern are: 7.90(10) (020, 100), 3.83(7) ( ), 3.16(9) ( ), 2.926(4) (150), 2.679(4) ( ), 2.461(6) ( ), 2.186(5) ( ), 1.969(4)(400), 1.649(3) (004).
Mit 2 Abbildungen
Herrn Univ. Prof. Dr.H. Meixner zum 70. Geburtstag gewidmet. 相似文献
109.
George V. Keller 《Physics of the Earth and Planetary Interiors》1975,10(3):201-208
The use of Schlumberger and dipole arrays for crustal-scale resistivity soundings is considered. Advantages and disadvantages of the two methods are described. The depth to which resistivity may be determined from field measurements is discussed as well as the determination from the sounding curves of various parameters associated with layered structure. The interpretation of experimental data using reference curves as well as two approaches used in computer assisted interpretation are discussed. 相似文献
110.
P.?SchulteEmail author W.?Stinnesbeck D.?Stüben U.?Kramar Z.?Berner G.?Keller T.?Adatte 《International Journal of Earth Sciences》2003,92(1):114-142
Spherule deposits, commonly interpreted as ejecta from the Chicxulub impact at Yucatán, Mexico, are present in many K-T (Cretaceous-Tertiary) sections. Geological mapping of the northern La Sierrita area, NE Mexico, revealed the presence of (1) multiple spherule deposits embedded in late Maastrichtian marls, which are folded or disaggregated (breccia-like). They are up to 6 m thick, locally present in two outcrop areas, and show limited lateral continuity. These deposits consist of mm-cm sized spherical to drop-shaped vesiculated spherules, angular to filamentous (ejecta-) fragments and abundant carbonate. They are interpreted as primary ejecta fallout deposits that have been affected by subsequent local slumps-slides, liquefaction, and debris flows; welded components suggest an initial ground surge-like ejecta-dispersion mode. (2) A spherule deposit, 10-60 cm thick that constitutes the base of a channelized sand-siltstone deposit at, or close to, the K-T boundary and is characterized by wide lateral continuity. It is of similar petrologic composition to deposit (1), though slightly enriched in terrigeneous detritus, thus reflecting influx from proximal shelf areas. It is interpreted to result from debris flows and turbidite currents, though no size sorting and abrasion of ejecta has been observed. Petrological, mineralogical, and geochemical criteria suggest that ejecta components from both types of spherule deposits are similar and originated from the Chicxulub impact, with multiple deposits produced by subsequent remolding, reworking, and redeposition. Spherules and fragments have an Fe- (25-30 wt%), Al-, Mg-rich and Si-poor (<25 wt% SiO2) composition, and are altered to chlorite and iron-oxides, though rare K-rich mafic glass (~50 wt% SiO2; 5-8 wt% K) is also present. They contain Ti-, Fe-, K-rich schlieren, Fe-, Mg-rich globules, and rare µm-sized metallic and sulfidic Ni-, Co-rich inclusions. Carbonate as clasts and within spherules and fragments shows textures indicative of quenching and/or liquid immiscibility. Although potential ejecta fractionation and alteration make accurate evaluation difficult, this composition suggests an ejecta origin mainly from mafic lithologies and carbonaceous sediments, in addition to a contribution from intermediate felsic rocks and the possibility of meteoritic contamination. 相似文献