Preheat oven to 400 degrees F. Line muffin cups with muffin liners or spray with nonstick cooking spray.
In a medium bowl, whisk together ½ cup sugar, cornmeal, baking powder, baking soda, and salt; set aside.
Place cranberries, orange zest, and remaining ¼ cup suagr in the bowl of a food processor fitted with a metal blade. Process with six 1-second pulses, until mixture resembles cornmeal.
Transfer mixture to a large bowl and mix in the egg, milk, sour cream, oil, and marmalade until smooth. Add flour mixture and stir until just moistened.
Fill each muffin cup about 3/4 full. Bake in the center of the oven for 20-25 minutes, until lightly browned and a toothpick inserted in the center of the muffin comes out with a crumb or two attached.
Move the muffin pan to a cooling rack, and let cool for 10 minutes. Remove the muffins from the pan and let them cool on the cooling rack an additional 5 minutes before serving.