In a medium skillet over medium heat, warm the oil.
Sprinkle the venison with the pepper and kosher salt. Sear the venison until golden brown all over, about 8 minutes total.
Add the shallot to the skillet and cook until golden brown, about 2 minutes.
Arrange the orange slices, oregano, and garlic around the meat in the skillet, and cook 4 minutes, turning the oranges after 2 minutes.
Carefully spoon the blackberry-balsamic vinegar reduction over the venison, and cook, basting with reduction mixture in the skillet, until the venison is done to the desired doneness, preferably when the internal temperature is between 130° and 140°F (54° and 60°C), about 4 minutes, for medium-rare.
Transfer the venison to a cutting board and let stand at least 10 minutes.