What kind of event is this? I would think it should be 70% marketing driven or more in most cases. If you are running high end events with few people, then sales might be more, but 70%?
In our case, marketing puts on our user conference and develops/distributes promo materials - but I'd guess that it's about 60-70% driven by conversations our Client Advocates (account managers) have. Our sales team invites prospects, but only those that are far along in the buying process. With prospects, it's 100% sales, utilizing marketing's promo materials.