In this paper, we prove an existence theorem for a mixed-type fractional integrodifferential equation of the form: \( {\phantom {a}}_T^C \varDelta ^\alpha x(t) =f(t,x(t),(Hx)(t),(Kx)(t)), \) with the initial conditions \( x(0)=x_0, x_0\in E, t\in I_a=[0,a]\cap T,a>0, \alpha \in (0,1]. \) Here, \((Hx)(t)=\int _0^t k_1 (t,s)g(s,x(s))\varDelta s,(Kx)(t)= \int _0^a k_2 (t,s)h(s,x(s))\varDelta s\) , where T denotes a time scale (a nonempty closed subset of the real numbers R), \(I_a\) is a time scale interval. The functions f, g, h, x are assumed to be weakly-weakly sequentially continuous. All integrals are understood in the sense of the Henstock-Kurzweil-Pettis delta integral. Moreover, the functions f, g, h satisfy suitable boundary conditions formulated in terms of measures of weak noncompactness.