Weird shadow on chunk border

I was exploring the new biomes. When I found the border to the new world, I found this weird shadow. It was a big black square covering the mountain border. I tried mining the blocks it covered and it split up. I don`t know where it came from, maybe some chunk error. Please fix this bug, I would be very thankful. Please respond if you have found out what it is.

Sincerely,

Ivan

Minecraft Username: Dr_Orwells

P.S.: My crosshair is on the weird shadow to help you find it.