Whisk together flour, baking soda, cinnamon, nutmeg, allspice, and salt. Set aside. In another bowl, combine both sugars, oil, and blackberry jam. Mix on medium speed until well blended. Add eggs and vanilla extract; mix well. Add half of flour mixture and half of buttermilk. Mix until ingredients are just blended. Repeat with second half of flour and buttermilk. Mix until batter is smooth. Fold in pecans.