『Abstract
　A vast sheet of mature quartz sand blanketed north Africa and Arabia from the Atlantic coast to the Persian Gulf in Cambro-Ordovician times. U-Pb geochronology of a representative section of Cambrian sandstone in southern Israel shows that these sediments are dominated by 550-650 Ma detrital zircons derived from Neoproterozoic Pan-African basement. The short time lag between magmatic consolidation of a Pan-African source and deposition of its erosional products indicates that, despite their significant mineralogical maturity, the voluminous quartz-rich sandstone on the northern margin of Gondwana are essentially first-cycle sediments.
　Mass production of these voluminous first-cycle quartz-rich sandstones resulted from widespread chemical weathering of the Pan-African continental basement. We suggest that conditions favoring silicate weathering, particularly a warm and humid climate, low relief and low sedimentation rates prevailed over large tracts of Gondwana in the aftermath of the Pan-African orogeny. An unusually corrosive Cambro-Ordovician atmosphere and humid climate enhanced chemical weathering on the vegetation-free landscape. we infer that late Neoproterozoic-Cambro-Ordovician atmospheric pCO2 rose as a consequence of widespread late Neoproterozoic volcanism, followed by an uptake of CO2 by chemical weathering to produce the Cambro-Ordovician sandstones as a negative feedback.

Keywords: Cambro-Ordovician; sandstone; Gondwana; chemical weathering』

1. Introduction
2. The Cambro-Ordovician quartz-rich sandstone
3. Quartz sandstone petrogenesis - insights from detrital zircon geochronology
4. The role of chemical weathering in formation of quartz arenites
5. Field evidence for chemical weathering in late Neoproterozoic-Cambrian times
6. Evidence from Sr isotopes
7. Paleoenvironmental implications
Acknowledgements
References