Bill,

>Holocene marl d13C values from Bolivia varies from a high of about +16 per
>mil PDB
>Our question is.....has anyone obtained similar data or know of any
>published explanation for such values?

As far as the marls are concerned, values of +16” are somewhat rare for the
environment you describe, but some have been reported. Values of up to +18”
have been analysed for Permian limestones in Brazil (Ferrarresi de Giovani
et al., 1974; Unusual isotopic composition of carbonates from the Irati
Formation, Brazil. Geol. Soc. Amer. Bull, 85, 41-44). The limestones in the
Irati Fm. are  also associated with substantial amounts of organic matter
which have relatively enriched d13C values ranging between -23 to -20” (my
own unpublished data). Ferrarresi de Giovani et al. suggest that the 13C
enriched carbonates are a consequence of ppt from heavey CO2 produced by
the isotopic exchange between CO2 and methane which was produced during
alteration of the organic matter.

Kevin




**********************************************************
Dr Kevin Faure
Department of Geochemistry
Geological Survey of Japan
1-1-3 Higashi
Tsukuba
Ibaraki 305
Japan

Tel. and Fax: +81-298-54-3726