This is a sediment core from late holocene outer shelf of East China Sea. The water depth is around 80 m. It shows a overall fining-upward sequence (normal graded). It is like Ta, however I can't see any Tb Tc and Td. There are many rip-up mud clasts. No tractional flow (cross lamination) can be seen. The grain size distribution shows a double peak style.
Hi Xin,
In my opinion, deposit is neiter storm related or a soft sediment deformation. It looks more as a debrite even though the overal fining-up is suspicious. Anyway, the combination of basal erosion, mud clasts and faint laminations suggests a tractional feature. Turbidite to debrite for me.
Hope it will help you
Cheers
Alexis
Dear Dr. Xin Shan:
we found similar core section in the outer/mouth part of a large estuary in central Germany in a deep drill hole (sorry for the poor photographs in the publication, which you can download from the RG server).
DILL H.G., KÖTHE A., GRAMANN, F. and BOTZ, R. (1996) A palaeoenvironmental and palaeoecological analysis of fine-grained Palaeogene estuarine deposits of North Germany.- Palaeogeography, Palaeoclimatology, Palaeoecology, 124: 273-326.
DILL H.G. SCHEEL M., KÖTHE A., BOTZ R. and HENJES-KUNST F. (1997) An integrated environment analysis-lithofacies, chemofacies, biofacies-of the Oligocene calcareous-siliciclastic shelf deposits in northern Germany.- Palaeogeography, Palaeoclimatology, Palaeoecology, 131: 145-174.
It has nothing to do with turbidites
With kind regards
H.G.Dill
Dear Xin,
I would suggest you to empty your head from terminology and enjoy the story which core narrates you. So, you can see: 1) truncated strata in a "semibrittle like" manner 2) flowing blocks and clasts 3) not clearly graded grains
In my point of view, clasts and truncated strata does not favor the storm explanation but a relatively tectonical active depositional environment. I don't think it's possible for storm waters to disturb-erode in a depth where your sediments are clearly semi-consolidated.
The depositional environment could be turbiditic (although it doesn't seem so, because in this meter-scale core I can't see any cyclicity). But if you lean into this explanation for your reasons, I would suggest you to think of the possibility of a fresh "wild flysch", which explains the not-so-typical turbidite cyclicity.
So, soft-sediment deformation in an relatively active depositional environment, no storm impact, and I guess, not a depositional environment which could favor turbidity currents.
Regards
Ioannis
Hi Xin,
The Ioannis suggestion is correct - do not wary if You are not fixed to terminology. These are obviously redeposited sediments and I will name painless "event deposits". The truncated lower bed surface, the rip-up clasts, "softly" deformed strata indicate some event - storm, flood, earthquake or whatever be sure that the trigger generated some kind of destroying of background deposition and redeposition. Such rocks are hard for 100% correct interpretation due to very fast changes in characteristics basin- and land ward and laterally as well. Every basin and facies association are specific.
Good luck
Dian
In addition to previous comments about an erosional base and evidence of transport, I would also add that the texture at the top of photo D looks like it could be burrow mottling, signifying a change in environment. In terms of interpretations as to triggering mechanisms, scales (events or cyclicity), you need to integrate with your other data.
I do not have much data to go on but it looks like a debris flow, muddy matrix, ripped up intraclasts, poor sorting, slightly contorted bedding, the erosional base is kind of odd but I have seen debris flow with slightly erosional bases. What caused the failure on the slope does not really matter (storm, earthquake, hurricane who cares). I am also curious as to why the broadly defined term "Wild Flysch" is trying to be resurrected. I was told one time by my mudlogging boss that if we used the work greywacke or wild flysh we would be fired.
Good luck
Finally, I have studied the X-ray radiographs of these sediments. X-ray image shows that most of the mud are formed by soft sediment deformation. Alexis told me to read tailing's paper, which is so good for interpretation of these sediments. I now agree with him that these sediments are debrites formed by en masse process.Although I still dont know about the triggering mechansim of these debrites, I tend to think it is the storm which induced these debris flow.
I agree that it is not so easy to see what happen and I do not undestand your Ta, Tb but it appears to have similarities with a muddy layer I observed in a combined sewer channel. Did you quantified the organic fraction?
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