authordate1 bibstyle generate bibliographies between "()" and not between "[]"

Hi,

I am using Miktex 2.7. My gool is to use the authordate1 bibstyle. So,
I installed the package authordate1-4 and I wrote this code:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\documentclass[a4paper,12pt,oneside]{book}
....
\usepackage{authordate1-4}

\begin{document}
....
....
\bibliographystyle{authordate1}
\bibliography{mybib}
\end{document}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

When I taped \cite{Granger03,Zhang93}, I got: (Granger, 2003; Zhang,
1993).

What I'm expecting is [Granger, 2003; Zhang, 1993].

Is it possible that authordate1 bibstyle generate bibliographies with
"[]" in stead of "()"?

If not, please provide me the name of another bibstyle ?

Thanks,

.