Distribution of mtDNA U5:
U5 peaks in northern Scandinavia/the Baltic region and in northern Spain/southern France among the Basques.
“The age of U5 is estimated at between 25,000 and 35,000 years old, roughly corresponding to the Gravettian culture (…) U5 was the predominant mtDNA of mesolithic Western Hunter Gatherers (…) Haplogroup U5 and its subclades U5a and U5b today form the highest population concentrations in the far north, among Sami, Finns, and Estonians. However, it is spread widely at lower levels throughout Europe. This distribution, and the age of the haplogroup, indicate individuals belonging to this clade were part of the initial expansion tracking the retreat of ice sheets from Europe around 10,000 years ago (…) The modern Basques and Cantabrians possess almost exclusively U5b lineages”
https://en.wikipedia.org/wiki/Haplogroup_U_(mtDNA)#Haplogroup_U5
“Haplogroup U5 is considered to be one of the most ancient haplogroups in Europe and is believed to have arisen there… It is not uncommon in Mesolithic European populations, particularly those from Central and Eastern Europe... the highest frequency of the haplogroup U5b today is in the Iberian peninsula and U5b2c1 was also present there in Mesolithic hunter gatherers… It is very plausible that descendants of the Mesolithic hunter-gatherers carried U5b1b1 and sister lineages across the Straits of Gibraltar into North Africa.”
(Matisoo-Smith et al. 2016)
“With regards to the mtDNA, the high incidence of H1 and H3 in Northwest Africa, together with some other West European lineages (i.e. V and U5b), reveals a possible link with the postglacial expansion from the Iberian Peninsula, which not only directed north-eastward into the European continent, but also southward, beyond the Strait of Gibraltar, into North Africa. ... the maternal pool of Northern Africa appears to be characterized by at least two major components: (i) a Levantine contribution (i.e. haplogroups U6 and M1), associated with the return to Africa around 45 kya, and (ii) a more recent West European input associated with the postglacial expansion.”
(Ottoni et al. 2010)
"modern Basques and Cantabrians possess almost exclusively U5b lineages. What's more, all the Mesolithic U5 samples from Iberia whose subclade could be identified belonged to U5b.(...) Carriers of haplogroup U5 were part of the Gravettian culture, which experienced the Last Glacial Maximum (LGM, 26,000 to 19,000 years ago). During this particularly harsh period, Gravettian people would have retreated into refugia in southern Europe, from which they would have re-expanded to colonise the northern half of the continent during the Late Glacial and postglacial periods. (...) founder effects among the populations of each LGM refugium would have amplified the regional division between U5b and U5a. U5b would have been found at a much higher frequency in the Franco-Cantabrian region."
U5b2b: found in Epigravettian Italy, in Epipalaeolithic south-eastern France, in Mesolithic Sicily and Croatia, in Neolithic France, Croatia and Ukraine, in EBA England, and in Bronze Age Poland.
U5b2b1: found in northern and central Europe / found in Mesolithic Sweden (Pitted Ware culture), in Early Neolithic France and Ukraine, in the Globular Amphora culture (LN Poland), in the Corded Ware culture (Chalcolithic Poland) and in Bronze Age Poland
U5b2b1a: found in Mesolithic Sicily
U5b2b2: found in EBA England
U5b2b3: found across western Europe / found in Megalithic Spain, Neolithic Italy and Late Neolithic France
U5b2b4: found in the England, Scandinavia, Germany and Poland
U5b2b5: found in Chalcolithic Sardinia and Spain, and in the Egyptian Middle Kingdom
https://www.eupedia.com/europe/Haplogroup_U5_mtDNA.shtml