This crustal weakness allowed unusually high heat flow from deeper mantle sources to «super-heat» the highly organic Niobrara source rocks, which in turn generated the significant oil and gas deposits now contained in the Niobrara and Codell formations. (pdce.com)
In contrast, the island basalts» ratios of uranium - 238 to uranium - 235 correspond to those of the meteorites used in the study and showed that these rocks could not have the same mantle source as the MORBs. (sciencedaily.com)
Holland acknowledges the limitations in the new data set: «These samples are just from one specific area of the southwest U.S.A.» But testing other mantle sources, he adds, is «our next line of work.» (scientificamerican.com)