AMC, glad you're pretty much unhurt. It does happen to everyone, especially at slow speed. The only way to learn to ride though gravel is to do it. Great advice from other posters on not using the front brake when in the stuff but to concentrate on the rear.
You can safely navigate though it, look where you want to go, but also keep the bike as up right as possible. Try to angle yourself to take as straight as a line as possible though the gravel. If that is not possible, keep your movements and bar inputs as smooth and deliberate as possible.