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61.
62.
BARRY B. MILLER WILLIAM D. McCOY NED K. BLEUER 《Boreas: An International Journal of Quaternary Research》1987,16(2):133-138
Miller, Barry B., McCoy, William D. & Bleuer, Ned K. 1987 06 01: Stratigraphic potential of amino acid ratios in Pleistocene terrestrial gastropods: an example frpm West-Central Indiana, USA. Boreas , Vol. 16, pp. 133–138. Oslo. ISSN 0300–9483.
The terrestrial gastropods Catinella spp., Stenotrema leai and Hendersonia occulta have been studied from 10 Wisconsinan and pre-Wisconsinan sites in west-central Indiana to determine if amino acid racemization values from these fossils would have stratigraphic utility in this area. The ages of the samples range from about 20,000 years B.P. for materials collected from radiocarbon-dated deposits of the Trafalgar Formation, to >730,000 years B.P. for fossils obtained from magnetically reversed silts of the Jessup and Banner Formations. The shell samples have yielded four groups or aminozones based on the ratio of D-alloisoleucine to L-isoleucine in both the free fraction and the total acid hydrolysate from the shell samples. The results of this preliminary study appear to be consistent with the previously assumed age of the strata from which the fossils were collected and suggest that the technique has great promise as a chronostratigraphic tool in Quaternary sequences that contain terrestrial pulmonate and prosobranch gastropods. 相似文献
The terrestrial gastropods Catinella spp., Stenotrema leai and Hendersonia occulta have been studied from 10 Wisconsinan and pre-Wisconsinan sites in west-central Indiana to determine if amino acid racemization values from these fossils would have stratigraphic utility in this area. The ages of the samples range from about 20,000 years B.P. for materials collected from radiocarbon-dated deposits of the Trafalgar Formation, to >730,000 years B.P. for fossils obtained from magnetically reversed silts of the Jessup and Banner Formations. The shell samples have yielded four groups or aminozones based on the ratio of D-alloisoleucine to L-isoleucine in both the free fraction and the total acid hydrolysate from the shell samples. The results of this preliminary study appear to be consistent with the previously assumed age of the strata from which the fossils were collected and suggest that the technique has great promise as a chronostratigraphic tool in Quaternary sequences that contain terrestrial pulmonate and prosobranch gastropods. 相似文献
63.
Metamorphism and deformation at different structural levels in a strike-slip fault zone, Ross Lake fault, North Cascades, USA 总被引:1,自引:0,他引:1
S. M. GORDON D. L. WHITNEY R. B. MILLER N. McLEAN N. C. A. SEATON 《Journal of Metamorphic Geology》2010,28(2):117-136
Continental crust is displaced in strike-slip fault zones through lateral and vertical movement that together drive burial and exhumation. Pressure – temperature–deformation ( P–T–d ) histories of orogenic crust exhumed in transcurrent zones record the mechanisms and conditions of these processes. The Skagit Gneiss Complex, a migmatitic unit of the North Cascades, Washington (USA), was metamorphosed at depths of ∼25–30 km in a continental arc under contraction, and is bounded on its eastern side by the long-lived transcurrent Ross Lake fault zone (RLFZ). The P–T–d conditions recorded by rocks on either side of the RLFZ vary along the length of the fault zone, but most typically the fault separates high-grade gneiss and plutons from lower-grade rocks. The Ruby Mt–Elijah Ridge area at the eastern margin of the Skagit Gneiss exposes tectonic contacts between gneiss and overlying rocks; the latter rocks, including slivers of Methow basin deposits, are metamorphosed and record higher-grade metamorphism than in correlative rocks along strike along the RLFZ. In this area, the Skagit Gneiss and overlying units all yield maximum P–T conditions of 8–10 kbar at >650 °C, indicating that slices of basin rocks were buried to similar mid-crustal depths as the gneiss. After exhumation of fault zone rocks to <15 km depth, intrusion of granitoid plutons drove contact metamorphism, resulting in texturally late andalusite–cordierite in garnet schist. In the Elijah Ridge area of the RLFZ, an overlapping step-over or series of step-overs that evolved through time may have facilitated burial and exhumation of a deep slice of the Methow basin, indicating that strike-slip faults can have major vertical displacement (tens of kilometres) that is significant during the crustal thickening and exhumation stages of orogeny. 相似文献