  In early eighties, Belavin and Drinfeld showed that nonskewsymmetric
classical r-matrices for simple Lie algebras are classified by combinatorial
objects which are now called Belavin-Drinfeld triples. Later the second author
of the present paper generalized this result to the case of dynamical
r-matrices, and showed that they correspond to generalized Belavin-Drinfeld
triples. The dynamical r-matrix corresponding a triple is given by a certain
explicit formula, which works for any symmetrizable Kac-Moody algebra. In
special cases, this formula gives the Felder and the Belavin r-matrix.
  In 1994, Felder associated with every dynamical r-matrix a system of
differential equations called the KZB equations. In the case of the Felder and
Belavin r-matrix, solutions of these equations are known to have a
representation theoretical presentation, as conformal blocks (i.e. traces of
products of intertwining operators between representations of Lie algebras).
  In this paper, we propose such a presentation for ANY dynamical r-matrix
given by the second author's formula. In particular, the paper sheds light on
the Belavin-Drinfeld classical r-matrices of 1984.
  This paper begins a series of papers. In the next paper, joint with
T.Schedler, we will give an explicit quantization of the dynamical r-matrices
for simple Lie algebras (in particular, Belavin-Drinfeld r-matrices), which has
been an open problem for a number of years. In another paper, we plan to
generalize the results of the present paper to quantum groups. This should
yield quantum KZB equations which involve quantum R-matrices obtained by
quantizing the classical r-matrices that appear in this paper.
