tag:blogger.com,1999:blog-8712540294522210240.post2016421047302568000..comments2024-03-06T22:08:30.648-08:00Comments on The Dynamic Earth: Death Valley Day 3: The Break-up of RodiniaErichttp://www.blogger.com/profile/01969672173684293621noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-8712540294522210240.post-42221835708900099372008-04-07T13:23:00.000-07:002008-04-07T13:23:00.000-07:00AMEN on the diamictite. Here in South Africa, til...AMEN on the diamictite. Here in South Africa, tillite and diamictite are used pretty much interchangeably and it drives me up the wall. thanks for calling them on it.Christie Rowehttps://www.blogger.com/profile/17131186132737346311noreply@blogger.comtag:blogger.com,1999:blog-8712540294522210240.post-37594089500284348112008-04-04T12:33:00.000-07:002008-04-04T12:33:00.000-07:00I agree with Kaufman; the use of Diamictite has be...I agree with Kaufman; the use of Diamictite has been fairly sloppy in the literature (SOME of it, at least; there are certainly folks who use it without any genetic connotation).<BR/><BR/>There was no evidence for faceted clasts, glacial striations, or any of the usual "glaciogenic" textures listed. Interestingly, there were clear changes in clast types through the section, with some intervals having many more granite clasts than quartzite clasts, etc.<BR/><BR/>All in all, enigmatic rocks!Erichttps://www.blogger.com/profile/01969672173684293621noreply@blogger.comtag:blogger.com,1999:blog-8712540294522210240.post-6777303882523533762008-04-04T11:14:00.000-07:002008-04-04T11:14:00.000-07:00An additional thought: Do any of these cobbles app...An additional thought: <BR/><BR/>Do any of these cobbles appear faceted, or display glacial scratches?Callan Bentleyhttps://www.blogger.com/profile/11750106265915456172noreply@blogger.comtag:blogger.com,1999:blog-8712540294522210240.post-64447613957034371882008-04-04T11:12:00.000-07:002008-04-04T11:12:00.000-07:00Great post, awesome rocks, and it sounds like a fu...Great post, awesome rocks, and it sounds like a fun trip.<BR/><BR/>After extended conversation on this topic with Jay Kaufman (UMD College Park), who has worked on the Noonday Dolomite and associated units in Death Valley, here are the terms as I understand them:<BR/><BR/><B>DIAMICTITE</B> : Poorly sorted sedimentary rock that is matrix-supported (as opposed to clast-supported -- like the one seen in Chris Rowan's <A HREF="http://scienceblogs.com/highlyallochthonous/2008/04/geopuzzle_10.php" REL="nofollow">geo-puzzle #10</A> today). No genetic assumptions made: Diamictites can be glacial in origin, or they can result from landslides or debris flows, too. <BR/><BR/><B>TILLITE</B> : A diamictite with clear glacial origins.<BR/><BR/><B>DROPSTONE</B> : An individual clast which shows clear evidence of truncating lower finer-grained sedimentary layers, indicating it dropped in from above. Overlying (finer-grained) strata are "draped" atop the dropstone. <BR/><BR/>A big clast in a poorly sorted rock is not a dropstone. The clasts in a tillite are not even dropstones. The term "dropstone" should be reserved specifically for this situation where we observe the truncation of underlying layers. <BR/><BR/>People who use "diamictite" when they mean "tillite" are being sloppy. And we shouldn't call a diamictite a tillite just because we want it to be one. We need clear evidence (including, in my mind, dropstones) to interpret a diamictite as a tillite. <BR/><BR/>That's my two cents! Thanks again.Callan Bentleyhttps://www.blogger.com/profile/11750106265915456172noreply@blogger.com