The indigenous origin of Witwatersrand "carbon"

In the Witwatersrand approximately 40% of the gold is intimately associated with so-called "carbon" in "carbon seam reefs, which occur in over a dozen paleoplacers, many of them concentrated at two stratigraphic levels in the 7000-m-thick succession of Archean siliciclastic sedimentary rocks. This is reduced carbon, present as kerogen admixed in various proportions with derivative (now solid) bitumen(s). Oil generation and migration were active geological processes during Early Earth history. Numerous possible source rocks for oil generation, including the carbon seams themselves, occur within the Witwatersrand basin. In the Witwatersrand ore, oil-bearing fluid inclusions are also present, derived like the bitumen, by thermal maturation of the kerogen. The presence of kerogen and bitumen in the Witwatersrand sedimentary rocks, together with a wealth of observations on the spatial distribution of the carbon seams confirm that the carbon originated in situ from living organisms in microbial mat cover, as opposed to flowing in from elsewhere as liquid hydrocarbons as some researchers have suggested. Paleochannels, which truncated auriferous carbon seams early in the depositional history, are of widespread occurrence, and micro-synsedimentary faults offset carbon seams. The carbon seams are thus indigenous biogenic markers that grew contemporaneously with placer development. The various features highlighting the nature and spatial distribution of Witwatersrand carbon seams provide a classic case where field evidence trumps laboratory data in the reconstruction of geological processes.14 page(s

Sorghum Transformation: Overview and Utility

Over the past decade genomics resources available for sorghum have rapidly expanded (Paterson Int J Plant Genomics 2008:6, 2008), these resources, coupled with the recent completion of the genome sequence which is relatively small in size (730 Mb) (Paterson et al. Nature 457:551–556, 2009) makes sorghum a rather attractive species to study. Moreover, the USDA germplasm system maintains 42,614 accessions, of which more than 800 exotic landraces have been converted to day length-insensitive lines to facilitate their use in breeding programs. In addition, a set of EMS mutation stocks developed by the USDA Plant Stress and Germplasm Development Unit in Lubbock, TX (Xin et al. Bioenerg Res 2:10–16, 2009) will be a valuable resource for functional genomics studies in sorghum. However, in order to be a robust system for study a suite of functional genomics tools are necessary to complement these other resources to aid in down-stream hypothesis testing. A key functional genomics tool is the ability to modulate gene expression through the introduction of transgenic genetic elements. This is exemplified by recent work (Cook et al. Plant Cell 22:867–887, 2010) in which RNAi experiments were employed to specifically reduced expression of two alkylresorcinol synthases to demonstrate their role in the synthesis of the allelopathic molecule sorgoleone. In addition to its value as a functional genomics tool, plant transformation offers a route to broaden access to novel input and output traits for sorghum breeding programs