Dienekes has an interesting post which summarizes a recent paper that surveys "African" (north and sub-Saharan) mtDNA lineages in Ibera. Here is a snip of interest:

...However, the observed geographic structuring for one of the haplogroups does not fit the expected distribution provided by simplistic historical considerations. In fact, although for haplogroup L the north-south increasing frequency is corroborated by historical data, the opposite trend, observed for haplogroup U6, is more difficult to reconcile with the magnitude and time span of the Islamic political and cultural influence, which lasted longer and was more intense in the south....

U6 seems to be of north African origin, and the researchers are curious as to its north-to-south gradient. Let us grant that U6 is north African (as opposed to an ancient Iberian variant which they lacked resolution to distinguish) and that the north-south gradient is not an artifiact of methodological error. It might interest the researchers that in Infidels : A History of the Conflict Between Christendom and Islam the author (who seems to be well versed in Iberian history) asserts that the Berber soldiers who first crossed over into Iberia were settled in the north of the peninsula (the Arab generals and tribes who crossed over received the choice southern regions). And it is also relevant that the first Berber settlers were likely "converted" to Islam within their lifetimes,¹ so their fidelity to their new faith might not have been reinforced by custom, habit or tradition.

1 - I put converted in quotes because all histories that mention these Berber soldiers recruited by the general Tariq ibn-Ziyad offer that their embrace of Islam was quite pro forma.