Beachrocks can give useful information on sea level and shoreline position, yet few works exist and in particular few have been dated.
Have you done any studies on recent (Holocene) beachrocks? Have you tried to date them? With what techniques and what results?
Thanks for sharing.
optically stimulated luminescence (single aliquot regenerative protocol approach has been a veritable tool to date holocene beach. mostly when they a well bleached. it was recently used to date the holocene siliciclastic sediment eastern Dahomey basin in southwestern Nigeria, it proved successful
Thx for you comment, I would be pleased to read this work I also ask myself about other type of datation.
What speaks against radio-carbon dating of the Holocene neomorphism. The process falls within its physical boundaries.
HGD
So apart from OSL dating, there is no option?
(for holocene beachrocks)
Problem with radiocarbon dating might be marine reservoir effect if dating the cement. One can correct for this, of course, but there could be also old carbon in the system from bedrock.
Regarding OSL, coastal deposits are indeed usually well-bleached and very suitable for dating. The problem with beachrock is mainly the disequilibrium in the Uranium decay chain that need to be corrected for. Besides practical issues (extracting and dissolving the carbonate under red-light), OSL properties could be a problem (but not necessarily). Maybe cosmogenic nuclide exposure dating could work (Cl-36) but this will depend on the particular setting.
The objective is obviously to date the cements and not the aggregate. We would gently reduce the rock by milling with a small mortar and pestle and sieve, followed by microscopic inspection. Repeat milling and inspection until few aggregate grains remain. 14C date the cements to approximate beachrock formation.
This article can be of use
Sharma, K., Bhatt, N., Shukla, A., Cheong, D., & Singhvi, A. (2017). Optical dating of late Quaternary carbonate sequences of Saurashtra, western India. Quaternary Research, 87(1), 133-150. doi:10.1017/qua.2016.12
Yes I have worked on a beach sediment in eastern Dahomey Basin. I used Single Aliquot Regenerative dose protocol (An improved Optically stimulated luminescence). The result has been very accurate. The rock was dated late Holocene Epoch of quaternary period
As you all know, there are pros and cons for every method, trying to date Holocene beachrocks. Accepting the uncertainties, the best estimate (most precise) can possibly come by combining methods:
- 14C-Dating of well-preserved cemented shells (if any): being 'well-preserved' most possibly reduces the probability that they are much older than the cementation. The 14C date of the shells means your beachrock is as old as the shell or younger. Dating multiple shells can reduce your uncertainty.
- OSL: a good 'grid' of OSL dates can provide an accurate time-window of cementation. However, you might get older dates due to the formation or location conditions too.
- 14C-Dating of the cement: the testing lab needs lots of experience with such material, to give the best estimate of all corrections (dead C, marine reservoir, cement type effect eg LMC, HMC, Ar etc).
Having a collection of data from the above will probably define an acceptable time-window of the cementation process.
If there is access to a good lab for radiogenic isotopes, other approaches might be interesting too (eg 226Ra).
good luck!
you may try 10Be-26Al surface exposure age dating for dating Holocene surfaces. It has to be exposed to surface. Target mineral is quartz. there are other cosmogenic nuclides also for non-quartz bearing rocks
This article might help : Evaluating optically stimulated luminescence rock surface exposure dating as a novel approach for reconstructing coastal boulder movement on decadal to centennial timescales, Brill, D. May, S. M. Mhammdi, N. King, G. Lehmann, B. Burow, C. Wolf, D. Zander, A. Brückner, H.
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