Cut ends off oranges, then cut away peel and outer membrane of fruit in wide strips, following the curve of the orange with the knife. Discard peel; slice fruit crosswise 1/2 inch thick and arrange slices on a large rimmed plate.
Rinse fennel and thinly slice crosswise (or use a mandoline); arrange slices over oranges.
Drizzle olive oil evenly over fennel and sprinkle with salt and pepper to taste. Scatter olives over salad.