Food deteriorates in the freezer. So you are positing that the temperature for this particular patch of earth remained constantly at an extremely deep freeze for 70 million yrs?
Btw, how do you know that even if it did remain in a constant deep freeze for 70 million yrs, it wd be this well preserved? Has there been a test case?
To find anything that has been cold for that long you almost have to leave Earth. Even Antarctica was tropical 65 million years ago. I suppose when they start to study the chemistry of the ices in the outer solar system they will find out how long spans of time causes change in the cold.