Have you seen something like this in Lowland Mesolithic?

We are used to strange and exceptional Mesolithic structures at the site Paliwodzizna 29, but this time we are really surprised! After four months of excavation (that should be finished after two…), it appeared that the last of the Mesolithic pits that we have is something different than we thought. On the deepness of 1,70 cm (what is really huge deepness for Mesolithic sandy sites in Poland) the feature breaks through the moraine pavement, which was removed. Then as it seems, only the biggest stones (without the gravel) were put back into the pit with admixture of some strange (probably not local?) loamy soil, that includes a lot of humus (please see the pictures attached, sorry for the quality – they are from the mobile phone, and sorry for the mess on the trench, it is already a kind of rescue excavation in its final stage). The structure is surrounded by the series of very deep postholes. There are also a few hearths with stone constructions around, including really huge ones (for example with a diameter of 2,5 meter) and some almost for sure ritual pits (like the one that included about 2000 of intentionally crushed flints). We have no idea what is under the level of stones because we had to finish the excavation for this year and we will come back to this feature next summer. However, before we do it we would like to be prepared for the different possibilities. So, we would like to ask what the people, particularly experts in Mesolithic think about it? Of course, if anybody has any ideas… For now, we think that it can be a kind of ritual pit/structure, in a type of ritual well? Perhaps a kind of strange grave? We can’t find any explanation for this type of economic activities. The only things that we know for sure (almost) now that this is not a natural structure (the level of stones saw also the geomorphologist) and it is Mesolithic. I would be very grateful for any opinions.

Thank You in advance.

With my best regards