Selmer groups for elliptic curves in Z_l^d-extensions of function fields of characteristic p

Let F be a function field of characteristic p>0, \mathcal{F}/F a \mathbb{Z}_l^d-extension (for some prime l\neq p) and E/F a non-isotrivial elliptic curve. We study the behaviour of the r-parts of the Selmer groups ( r any prime) in the subextensions of \mathcal{F} via appropriate versions of Mazur's Control Theorem. As a consequence we prove that the limit of the Selmer groups is a cofinitely generated (in some cases cotorsion) module over the Iwasawa algebra of \mathcal{F}/F.