Increasingly, ad-hoc online task groups must make decisions about jointly created artifacts such as open source software and Wikipedia articles. Time-consuming and laborious attention to textual discussions is needed to make such decisions, for which computer support would be beneficial. Yet there has been little study of the argumentation patterns that distributed ad-hoc online task groups use in evaluation and decision-making. In a corpus of English Wikipedia deletion discussions, we investigate the argumentation schemes used, the role of the arguer's experience, and which arguments are acceptable to the audience. We report three main results: First, the most prevalent patterns are the Rules and Evidence schemes from Walton's catalog of argumentation schemes , which comprise 36% of arguments. Second, we find that familiarity with community norms correlates with the novices' ability to craft persuasive arguments. Third, acceptable arguments use community-appropriate rhetoric that demonstrate knowledge of policies and community values while problematic arguments are based on personal preference and inappropriate analogy to other cases.