I was on Delta.com signing up for the double Skymiles for Lyft and I noticed that Marriott is on the list also, so I figured i'll share this information with my teaminsiders . Use this link https://www.delta.com/mypromos/acelanding.action?offer=PartnerDoubleMiles
Earn double miles on eligible transactions between March 20 and May 31, 2018 with any participating partner with which you did not earn miles with during 2017.
Offer: Registered SkyMiles members will earn a 100% bonus on eligible transactions with any new participating partner they earn miles with between March 20, 2018 and May 31, 2018. The term "New" refers to a partner the member has not earned miles with during the period January 1, 2017 to December 31, 2017.
Step 1- SIGN UP
Step 2-LINK MARRIOTT
I'm not familiar with Marriott , so from here, you guys are on your own. LOL. As it states "Go to your Marriott Reward profile"
Don't forget with SPG and Delta SkyMiles Crossover Rewards program . SPG Platinum and Gold members earn 1 Starpoint for every dollar spent on Delta flights. So when transferred over, that's another 3 points per dollar for Marriott Reward members
updated March 27:
**only base miles earned on hotel stays qualify, and not other types of hotel points transfers