Preheat your oven to 350 degrees Fahrenheit.
In the bowl of your stand mixer, or in another large bowl, mix together the flour, sugar, cocoa powder, baking soda, vanilla and salt until well combined.
Add the vegetable oil, orange juice, marmalade, vinegar and orange zest. Turn the mixture speed to medium and using the paddle attachment whisk until well combined.
Prepare your loaf pan by lining it with parchment paper and then spraying any parts of the pan that are not lined with the parchment paper with cooking spray.
Pour batter into pan and spread evenly.
Bake in middle rack of your oven for 50 - 60 minutes until a toothpick inserted into the center comes out clean.
Remove from oven when baked and allow to cool in the loaf pan for 5 minutes and then transfer the cake to a cooking rack to cool completely.