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Alkali extractions on sediments will remove any unbound carbon that is alkali-soluble.The source of this carbon can be from more recent humic and fulvic acids or ancient labile carbon that is alkali-soluble.However, many times what happens is the opposite; the alkali-extracted sediment yields a younger date due to the factors above.
In some cases, it is wise to date both separately to see if the macrofossils or sediment is yielding the best (most reliable) date.
You are welcome to contact us to discuss the pretreatment or request that we contact you after the pretreatment to discuss options for radiocarbon dating. However, knowing the dry weight will better allow you to estimate the amount of material to send.
If you want to dry your samples, heating at 90°C to 100°C for 4-24 hours is recommended.
In general the plant dates are usually more reliable as they typically represent a more unique event in time.
The plants were relatively short-lived as compared to the time it may have taken for the sediment to form.
For sediment samples, the lab performs flotation in water then progressive sieving through 225-micron, 180-micron, and then 125-micron sieves to see if there are any macrofossils that can be extracted.