That's really -211.3 m - why the abrupt change in color? Diane Winters, one of the scientist authors explains:
The abrupt change from green to grey at that point in the core is partially why we liked that section. It shows a lovely erosional contact where some diatomite was scoured away, in this case I think the interpretation was by current activity as diamictite is not deposited on top of it, with a clear change in sediment type to the mudstone above. The environment obviously changed quite dramatically, from open ocean with high productivity to a high terrestrial sediment input seen in the grey silt and sand above being brought out to the site by currents associated with glacial growth and advance. This growth certainly had associated increased sea ice at the site, which would stop the diatom productivity in the overlying waters as well. This erosion of material and creation of an unconformity is illustrated mostly by by the advancing glacier and little grey bits coming off of the underside of the ice as it moves across the sea floor in the animation. Not the same as what happened here, but it is a simple but nice animation. As for dating, the diatom species with their know first and last occurrences in other parts of the southern ocean, provide relative age to the sediment. Some absolute ages using isotopes can be determined from volcanic material, this is where many age tie points came from for this core.
The abrupt change from green to grey at that point in the core is partially why we liked that section. It shows a lovely erosional contact where some diatomite was scoured away, in this case I think the interpretation was by current activity as diamictite is not deposited on top of it, with a clear change in sediment type to the mudstone above. The environment obviously changed quite dramatically, from open ocean with high productivity to a high terrestrial sediment input seen in the grey silt and sand above being brought out to the site by currents associated with glacial growth and advance. This growth certainly had associated increased sea ice at the site, which would stop the diatom productivity in the overlying waters as well. This erosion of material and creation of an unconformity is illustrated mostly by by the advancing glacier and little grey bits coming off of the underside of the ice as it moves across the sea floor in the animation. Not the same as what happened here, but it is a simple but nice animation. As for dating, the diatom species with their know first and last occurrences in other parts of the southern ocean, provide relative age to the sediment. Some absolute ages using isotopes can be determined from volcanic material, this is where many age tie points came from for this core.
4128:14204
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