Showing papers in "The mountain Geologist in 1978"

Taphonomic and Ecologic Information Form Bone Weathering

Abstract: Bones of recent mammals in the Amboseli Basin, southern Kenya, exhibit distinctive weathering characteristics that can be related to the time since death and to the local conditions of temperature, humidity and soil chemistry. A categorization of weathering characteristics into six stages, recognizable on descriptive criteria, provides a basis for investigation of weathering rates and processes. The time necessary to achieve each successive weathering stage has been calibrated using known-age carcasses. Most bones decompose beyond recognition in 10 to 15 yr. Bones of animals under 100 kg and juveniles appear to weather more rapidly than bones of large animals or adults. Small-scale rather than widespread environmental factors seem to have greatest influence on weathering characteristics and rates. Bone weathering is potentially valuable as evidence for the period of time represented in recent or fossil bone assemblages, in- cluding those on archeological sites, and may also be an important tool in censusing populations of animals in modern ecosystems.

Uranium in western colorado

Abstract: Uranium deposits in western Colorado occur in rocks of many geologic ages and lithologic types. Bedded, vanadiferous deposits in continental, fluvial sandstones of the Salt Wash Member of the Morrison Formation of Jurassic age are the most important. A cluster of deposits in Mesa, Montrose, and San Miguel Counties comprises the Colorado segment of the Uravan mineral belt, the largest uranium area in Colorado. During the period 1948 through 1976, 15,589,100 tons of ore with an average grade of 0.23% U/sub 3/O/sub 8/ and containing 71,132,400 pounds of uranium oxide (U/sub 3/O/sub 8/) have been produced from western Colorado. This amounts to 12% of the total United States' uranium ore production. In addition, 350,522,000 pounds of vanadium oxide (V/sub 2/O/sub 5/) have been recovered. The discovered ore reserves and the favorable geology for undiscovered potential resources are expected to maintain western Colorado as a significant source of uranium for years to come.

Barrier and b ack-barrier environments of deposition of the upper- cretaceous almond formation, rock springs uplift, wyoming

Abstract: Detailed analysis of t he detrital rocks associated with coal deposits in the upper part of t he Upper Cretaceous Almond Formation of the Mesaverde Group has resulted in the identification of coal depositional settings. The several lithofacies indicate t hat depositional environments of this interval in the upper part of the Almond Formation include shoreface, barrier island, tidal inlet, tidal delta, washover fan, tidal f lat, lagoon, tidal creek, overbank, pond, and marsh. Tidal delta, tidal-inlet-chan nel, washover-fan, and tidal-creek deposits signif- icantly affected back-barrier accretion and lagoon filling. The complete filling of the lagoon led to coalescing of marsh on the back side of the barrier island with the marsh on the landward side of the lagoon. Thin, dis- continuous c oal beds which rapidly prade into carbonaceous shale formed in t6e marsh in close proximity to the barrier island. Thin to thick, lateral l y extensive coal beds t:mt Ic~cal iv graJe into carbonaceo~~s shale formed in the marsh on emergent levee, overbank, and bayfill deposits at the landward side of the lagoon. Deposition of the above detrital Seposits as well as tidal-creek chanrlel sandstones caused splittino and merging of the c oal beds. The depositional process and rate of sedimentation aod subsidence in the d epositional basin influenced to some degree the lateral variation of t he coal beds. tiinability and resource potential of coal beds in the Almond Formation can be better assessed if the precise distribution of the sedimentary environments is recognized.

Rb-Sr GEOCHRONOLOGIC INVESTIGATION OF PRECAMBRIAN SILICIC ROCKS FROM THE ZUNI MOUNTAINS, NEW MEXICO

Abstract: The Rb--Sr whole rock isochron age for metarhyolite from the Zuni Mountains, New Mexico, is 138 +- 003 by with initial /sup 87/Sr//sup 86/Sr = 0721 +- 0009 The metarhyolite is intruded by a cogenetic suite of gneissic granites, biotite granites, and aplites which yield a Rb--Sr whole rock isochron age of 149 +- 009 by with initial /sup 87/Sr//sup 86/Sr = 07062 +- 00008 Although the errors overlap, the metarhyolite has apparently been incipiently altered resulting in its apparent lower age As the silicic plutonic rocks are all fresh (based on petrographic examination) and clearly intrusive into the metarhyolite, then 149 +- 009 by is assigned as the minimum age for the Precambrian silicic rocks from the Zuni Mountains