I've got two membranes under my gravel, a weed proof one....allegedly! and a thick plastic sheet, but this weed seems to grow within the gravel, probably in the dirt between to be honest, being coarse pitch I suspect there's quite a lot of nooks and crannies it can live and breed in, yours being a finer pitch will not probably trap as much dirt. I'm going to guess yours is 10mm drain shingle, looks just like the 100 Kg I just tipped down around my restored drainage under a collapsed drive

yesterday LOL I don't know what the weed is I'll grab a photo of it tomorrow, on second thoughts I wont as it now has a ton of soil on it from above drain works LOL but I expect one of the little critters will be poking out somewhere.