Geoscience Reports 30:5-6 (Winter 2000).

NOTES FROM THE SCIENTIFIC LITERATURE

Geochronology

Mukasa SB, Dalziel IWD. 2000. Marie Byrd Land, West Antarctica: evolution of Gondwana's Pacific margin constrained by zircon U-Pb geochronology and feldspar common-Pb isotopic compositions. Geological Society of America Bulletin 112(4):611-627.

    Forty-eight dates were reported from a variety of terrains and the information was used to evaluate previous models and constrain the conclusions. Of those dates, 14 were considered concordant using error-weighted means.
    Comment: Dates that were most directly related to the interpretations were reported in this paper. Discordant dates were attributed to Pb loss and inherited zircon components. Contamination and deformation effects on most granites have been documented in numerous previous studies. (An excellent volume dealing with the complexity of granites is: Brown M, Candela PA, Peck DL, Stephens WE, Walker RJ, Zen E-an, editors. 1996. The Third Hutton Symposium on the Origin of Granites and Related Rocks. Geological Society of America Special Paper 315, p 1-359.) The uncertainty of the reliability of the samples raises questions regarding the confidence placed in the conclusions drawn from the "good" dates.

Geology

Umino S, Lipman PW, Obata S. 2000. Subaqueous lava flow lobes, observed on ROV KAIKO dives off Hawaii. Geology 28(6):503-506.

    Rates for subaqueous lava flows were determined near the Hawaiian Islands. These results were compared with the flow rates previously documented for subaerial flows in Iceland. The Hawaiian subaqueous pahoehoe flows had a higher supply rate of thinner, less viscous lava by one to two orders of magnitude than the subaerial flows. The key factor seems to be the effectiveness of the heat capacity of water and its impact on the inflation properties (increased expansion rates and excessive pressure) of the lava as it moves. Rates as high as 8 cubic meters/minute were recorded. 
    Comment: These findings should be somewhat applicable to flood basalts, though a simple volume comparison would not provide an accurate picture of the flows. Since multiple flood basalt flows occurred synchronously, extrapolations from the observations to the geologic record should be used cautiously.

Paleontology

Sheehan PM, Fastovsky DE, Barreto C, Hoffmann RG. 2000. Dinosaur abundance was not declining in a "3 m gap" at the top of the Hell Creek Formation, Montana and North Dakota. Geology 28(6): 523-526.

    Researchers report a count of dinosaur remains within the upper 3 m of the Hell Creek Formation that is comparable with their surveys conducted lower in the record. They conclude that the distributions do not represent a gradual decline but rather an extinction event consistent with the K-T boundary impact theory.
    Comment: Despite the considerable amount of data collected in this research, there is a lack of data and analysis in the paper. The authors recognize concentrations or pockets of dinosaur remains but fail to plot the distributions relative to the associated sediments (and facies). In addition, the lower numbers in the upper 3 m of the Hell Creek Formation are attributed to their limited sampling of the upper 3 m relative to the underlying layers. Because of the limited analysis of the taxonomic, taphonomic and sedimentary relationships, their conclusions based on numerical comparisons may be premature.