In a large bowl, combine the flour, oats, pecans and brown sugar. Add butter; mix well. Spread in a thin layer in a 15x10x1-in. baking pan. Bake at 400° for 15 minutes or until golden, stirring occasionally. Crumble while warm; cool., Press half of crumb mixture into a 13x9-in. dish. Drizzle with half of caramel sauce; spread with ice cream. Top with remaining caramel sauce and crumb mixture. Cover and freeze until firm. Remove from the freezer 10 minutes before serving.