The impact of the impact (I love doing that) was multiple, and had a long reach. According to the late Eugene Shoemaker, an object about a mile in diameter would, as a consequence of an impact on land, produce a deep, thick cloud cover totally obscuring the sky within a couple of hours, and that cloud cover would last for weeks or months.
IOW (’Civ adds), the surface of the Earth would be in nearly pitch darkness, the temperature would fall, and the hydrologic cycle would slow to a nearly imperceptible crawl — hence, all the rivers and streams would dry up. As a consequence, land-based plants would die or go dormant due to lack of light and water. Living creatures would chew off the bark from all the trees, eat up all the other plant remains, and the oxygen levels in the oceans would drop. Possibly (depending on the duration), the oceans would themselves freeze over.
Chicxulub is estimated at six miles (as you noted) diameter — meaning the mass would approximate six cubed of a one mile object...
Thanks for the thorough explanation! I hadn’t considered the chain reaction(s) that are set off from the initial event. Almost like dominoes in a way.
Fortunately, we(and our children’s children, children) will likely never see such a thing!
IMO, the greatest immediate threat to humans, given our numbers and mobility is deadly communicable diseases... and Leftists. lol