Named after P. Briault - French astronomer (d. 1922).
The dark areas seen in the images are dunes; the curved dunes are called barchans. (wikipedia entry)
A crater is a circular depression likely created by an impact event. On Mars large craters are named after deceased scientists, writers and others who have contributed to the lore of Mars. Small creaters (less than 60km) are named after small towns and villages.