Abstract-We review induced thermoluminescence (TL) data for 102 unequilibrated ordinary chondrites (UOCs), many data just published in abstracts, in order to identify particularly primitive DOCs and further explore TL systematics that may have implications for the history ofthe chondrites and their parent body. We have identified 11 DOCs ofpetrologic types 3.0-3. These samples represent an important new resource for researchers interested in the nature ofprimitive solar system materials. Previously reported trends in which TL sensitivity increases with TL peak temperature and TL peak width, which we interpret in terms of crystallization of feldspar in the ordered or disordered forms during metamorphism, are confirmed by the new data. Importantly, the present data strengthen the trend described earlier in which the mean level of metamorphism experienced by DOCs increases along the series LL, Land H. This suggests either different burial depths for the DOCs from each class, or formation at similar depths in regoliths of different thickness.
Some of the most primitive solar system materials available for study in the laboratory are the ordinary chondrites, the largest meteorite class. The size and distribution of the chondrules (silicate beads) and metal, which leads to the definition of the H, L, and LL classes, suggest sorting before or during aggregation. We suggest that meteorite parent bodies (probably asteroids) had thick dusty surfaces during their early evolution that were easily mobilized by gases evolving from their interiors. Density and size sorting would have occurred in the surface layers as the upward drag forces of the gases (mainly water) acted against the downward force of gravity. The process is analogous to the industrially important process of fluidization and sorting in pyroclastic volcanics. We calculate that gas flow velocities and gas fluxes for the regolith of an asteroid‐sized object heated by the impact of accreting objects or by 26Al would have been sufficient for fluidization. It can also explain, quantitatively in some cases, the observed metal‐silicate sorting of ordinary chondrites, which has long been ascribed to processes occurring in the primordial solar nebula. Formation of the chondrites in the thick dynamic regolith is consistent with the major properties of chondritic meteorites (i.e., redox state, petrologic type, cooling rate, matrix abundance). These ideas have implications for the nature of asteroid surfaces and the virtual lack of asteroids with ordinary chondrite‐like surfaces.
The identification of human graves in situations where there is little or no evidence of skeletal material or coffins has been a problem for archaeologists. In the spring of 1998, the Arkansas Archaeological Survey was hired to find the location of the "lost" Anderson family slave cemetery on property slated for a new airport. Field methods included front end loader blading and hand excavated units. The location of the slave cemetery on a low knoll in an agricultural floodplain was only identifiable by three features of disturbed soil thought to be grave-fill and the chemical remains of human burials. One feature contained a light colored stain identified as the archaeological phenomenon referred to variously as a ghost, silhouette, shadow, or degraded burial. In an attempt to confirm human burial by soil analysis, chemical tests were run on a limited number of samples for total digestion and exchangeable levels of elements present in human bodies. This study examines several elements that previous investigators have suggested as reliable indicators for silhouette burials. Because of frequent inundation and the addition of phosphorus to the field as a fertilizer, only the ratio of Zn/Cu is indicative of possible human burial. Zn/Cu ratios show clearly elevated levels at burial depth in the suspected cemetery features relative to control samples. 323
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