  We show that there are vast families of contact 3-manifolds each member of
which admits infinitely many Stein fillings with arbitrarily big euler
characteristics and arbitrarily small signatures ---which disproves a
conjecture of Stipsicz and Ozbagci. To produce our examples, we set a framework
which generalizes the construction of Stein structures on allowable Lefschetz
fibrations over the 2-disk to those over any orientable base surface, along
with the construction of contact structures via open books on 3-manifolds to
spinal open books introduced in [24].
