http://slothcentral.com/archives/1281 A 12,000 year-old mystery in SW Iowa Mon, 05 Dec 2011 21:09:54 -0700 http://wordpress.org/?v=2.8.4 hourly 1 http://slothcentral.com/archives/1281/comment-page-1#comment-2131 David Sun, 20 Sep 2009 21:58:27 +0000 http://slothcentral.com/?p=1281#comment-2131 Good question Trav. I wondered about that myself and had to ask. We would have found them if the water had been perfectly still, but those conditions are rare in Iowa. You need to eliminate wind, current, and especially animals burrowing into the bottom or wading around and stirring things up. Deep lakes are your best bet. The channel here was uneven and shallow in places. It dried out completely sometimes (some of the bones show signs of weathering)—that means erosion and more movement. In winter the shallows would freeze—water and top layers of sediment would fuse and move with the spring thaw. It all adds up to plenty of forces homogenizing the top 9-12 inches and erasing the small annual changes. I picture the layers Joe found as major floods--100-year events, cutting deep enough not to be completely erased by all the subsequent activity. Good question Trav. I wondered about that myself and had to ask. We would have found them if the water had been perfectly still, but those conditions are rare in Iowa. You need to eliminate wind, current, and especially animals burrowing into the bottom or wading around and stirring things up. Deep lakes are your best bet. The channel here was uneven and shallow in places. It dried out completely sometimes (some of the bones show signs of weathering)—that means erosion and more movement. In winter the shallows would freeze—water and top layers of sediment would fuse and move with the spring thaw. It all adds up to plenty of forces homogenizing the top 9-12 inches and erasing the small annual changes. I picture the layers Joe found as major floods–100-year events, cutting deep enough not to be completely erased by all the subsequent activity.

]]> http://slothcentral.com/archives/1281/comment-page-1#comment-2120 travis foxx Fri, 18 Sep 2009 18:43:05 +0000 http://slothcentral.com/?p=1281#comment-2120 Dave, Why don’t you find more layers in the clay? Floods are a common event there aren’t they? Annually at least Dave, Why don’t you find more layers in the clay? Floods are a common event there aren’t they? Annually at least

]]>