Salesforce Integration - Unable to Merge Contacts

I am trying to set up the native salesforce integration for our Marketo instance. I am experimenting with in our Sandbox instances first, which I connected over the weekend.

When I was playing with the people in Sandbox, I noticed that I could not merge a Marketo-only record with it's duplicate record that spanned both Marketo and Salesforce. I was told by support that this has to do with the permissions our integration user has inside of Salesforce. All the Marketo docs I can find only ever reference recommended read/create/edit/delete access for specific areas (like Leads vs Contacts vs Accounts, etc) but they don’t reference what standard field-level permissions we need to continue to utilize standard Marketo features as if it wasn't integrated into Salesforce (for example, merging a Marketo-only contact with it's duplicate record that exists in Salesforce).

Does anyone know where I can do to find this?