I am flying from US to Marseille through Amsterdam. Single ticket but we fly Delta first leg and partner AirFrance for the second leg. We arrive Amsterdam mid morning on a Thursday and and have a 1 hour 40 min layover. I see from the comments that there is a chance of missing connecting flight, and a greater chance that any checked bags will miss the connecting flight. In this scenario will it be Delta's responsibility to get us on the next flight and to get our bags to our Marseille location?
Simple answer: yes. Since klm is handling amsterdam, they will be responsible for dealing with delays.
1h 40 seems like a reasonable transfer time though. Your biggest worry should be to enter the schengen area. I would advise you to do that asap and enjoy schiphol after getting through. Typically someone will be waiting at the gate with instructions if you arrive. Schiphol - Amsterdams main business comes from transfer traffic, so the airport is quite efficiently organized. You might want to study the airport layout to find your way.