Base Of Mound Research Articles

Tetrahedron baked-clay objects from an early woodland context at the Jaketown site, Mississippi

ABSTRACTExcavations undertaken in 1951 at the Jaketown site revealed a dense deposit of fragmented and intact pyramid-shaped baked-clay objects (BCOs) at the base of Mound A. This deposit was associated with the site’s Early Woodland component. Recent fieldwork at Jaketown also encountered the same tetrahedron deposit and identified an additional and distinct pit feature filled with the objects. In this article, we present the results of analyses that examine the production, composition, chronology, and function of these enigmatic baked-clay artifacts. Following a hiatus associated with massive flooding in the Mississippi Valley ca. 3200–2850 cal B.P., Jaketown was re-occupied by people who shared ceramic affinities with groups to the south and to the east and, who like many contemporaries, used BCOs as a part of their cooking technology. The tetrahedron deposit represents one of the earliest dated Tchula contexts at ca. 2600 cal B.P., and was used over a short time for a social purpose that brought populations together for food consumption as a means of encouraging cooperation.

Mineralogy, morphology and stratigraphy of the light-toned interior layered deposits at Juventae Chasma

Juventae Chasma is a deep depression located north of Valles Marineris on Mars, with four bright mounds or light-toned interior layered deposits (ILDs) extending upwards from the Canyon floor. We present here the results of long-term imaging of Juventae Chasma including mounds A, B, C, and D using multiple datasets. Monohydrated sulfates (MHS) were deposited first on the canyon floor, followed by polyhydrated sulfates (PHS). The upper PHS-dominated units are largely eroded away at Juventae Chasma, but this material is still present in significant abundance at mound B. PHS are observed mixed with MHS in some areas of mounds A and C. Terraces are observed at the upper elevations of mound B that contain PHS at the steeper slopes and appear to be covered with dust on the horizontal surfaces. Current analyses of the MHS-rich unit indicate that kieserite (MgSO4⋅H2O) is the primary sulfate component, rather than szomolnokite (FeSO4⋅H2O) as previously thought. Formation of kieserite at Juventae Chasma likely required temperatures in the 150–200°C range. Geochemical modeling is most consistent with dissolution of mafic materials followed by precipitation of kieserite from solution. The dust exhibits ferric signatures and the sand is largely mafic material. Outcrops of olivine- and pyroxene-bearing rocks are best observed along the base of mound C and in the chaotic terrain surrounding mound D. This study summarizes the current understanding of Juventae Chasma and its ILDs using HRSC, HiRISE and CTX data, an expanded laboratory spectral library, and the latest calibrations available for CRISM.

Bismuth and cobalt minerals as indicators of stringer zones to massive sulphide deposits, Iberian Pyrite Belt

The stringer zones and commonly the interaction zone at the base of the massive sulphide mounds in the Iberian Pyrite Belt contain bismuth and cobalt minerals that are not found in the overlying massive sulphides. These are fairly rare cobalt sulphoarsenides (cobaltite, alloclasite, galucodot) that were formed at the beginning of the massive sulphide genesis, and fairly common bismuth sulphides (bismuthinite, hammarite, wittichenite, cosalite, kobellite, joseite, etc.), including species rare at world scale (nuffieldite, giessenite, jaskolskiite) that were deposited from last stage high-temperature (> 300 °C) copper-bearing fluids containing Bi (Te, Se). The last stage fluids precipitated chalcopyrite containing Cu, Bi, Te, (Se) sulphosalts at the base of the sulphide mound to form a high cupriferous zone. Their interaction with the massive sulphides is reflected by the formation of an exchange zone, a few metres thick, showing chalcopyrite disease textures, at the base of the mound; this zone forms the upper limit of potentially economic copper enrichment and of bismuth minerals. Gold is undoubtedly in part, if not totally, related to this last phase. The bismuth concentrations being equivalent in the massive sulphides and the stringers, the presence of bismuth minerals in the stringer zones results from high-temperature conditions combined with a rarity of galena, which impedes absorption of available Bi. The distribution of these bismuth minerals provides a basic mineralogical zoning in the stringer zone, with a deep, low-aS2 zone containing native bismuth and tellurides and a shallow, higher-aS2 zone in contact with the massive ore sensu stricto and containing complex bismuth sulphides. These results make it possible to distinguish between sulphide veinlets belonging to stockwork zones of massive orebodies and veinlets of an ambiguous nature, and provide mineralogical criteria for the proximity of copper-rich zones. They enrich the very complex mineralogy of the Iberian Pyrite Belt.

Calcium Carbonate in Termite Mounds

THE presence of appreciable quantities of calcium carbonate in termite mounds on non-calcareous soil has intrigued pedologists for many years. Milne6, for example, found a termite mound with 7% calcium carbonate and estimated that it contained about 2 t of calcium carbonate excluding the hard limestone (53% CaCO3) base of the mound. The soil below the base of a termite mound may also be calcareous. The soil underneath one termite mound in an area of non-calcareous soil was found to have a mean of 1.7% calcium carbonate to a depth of 6 m, or about 20 t of calcium carbonate9.