Dear Readers -
I have two related questions having to do with some unusually heavy del
C-13 values on continental ostracode valves. First, has there been any
study done on the effects of methanogenesis on the del C-13 value of
dissolved bicarbonate in continental aquatic (not diagenetic)
environments?  Hypothetically, heavy values could result with
limited exchange with carbon in isotopic communication with the atmosphere,
degraded organic matter, or with groundwater. Second, what are the heaviest
del C-13 values on biogenic carbonate from continental settings? I have
some ostracode valves from Sangamonian (last interglacial) lacustrine
sediments with del C-13 values as high as +16 per mil. The highest values I
have seen reported run at about +6 per mil or so. Thanks for your input -
Brandon Curry
Illinois State Geological Survey
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