Official report: last dig and preparation

Since we started excavating in 2003, Holmes has been keeping an official log he calls Megalonyx Matters documenting  our significant activites. This is publication #17, covering the preparation work leading up to our last expedition and its results. Lest anyone be concerned, the stubborn beaver discussed below is alive and well, and continuing to safeguard the site with a cover of at least a foot of water . . . .  Dave

Megalonyx Matters 17Site preparation (Aug. 27, Oct. 3, Dec. 4) and excavation (Dec. 6)

Site Preparation
On August 27, 2008 Dave Brenzel, Holmes Semken, Phil Mather (Mather and Sons) and Bob Athen (landowner) met at the site and devised a plan to extend the sloth excavation about 30 feet into the south bank to search for more juvenile remains. The first obstacle proved to be a downstream beaver dam that substantially increased the water level over the bone-bearing, blue-grey clay. Bob had experimented with removing the dam by hand. This worked but the beavers repaired it overnight. It was clear that each excavation would be initiated by attacking the dam.

On October 3, Holmes and Dave returned to oversee the Mather’s levee repair and overburden removal. Dave waded in and breached the beaver dam by the time the excavator arrived (8:00 am); the water dropped 2.5 feet at the site. We were delighted because this exposed the bone-bearing matrix. Phil (name of operator), who operated the excavator, got the machine to streamside (and back out) via some creative road repair over very mucky terrain resulting from the infamous 2008 flood. By the end of the day there was a combination dam/entrance ramp both up and downstream from the future excavation area. The ramps were about 30 feet apart. The old lateral (midstream) levee was largely removed by flooding but it was traceable and was also reinforced by the excavator. Sloth bone, predicted to be under this levee, appeared safe. At the end of the day, the south bank was pulled back about 30 feet and the dig floor appeared accessible for a crawler to enter, clear remaining overburden (approximately one foot) and build a stream side levee to protect south bank excavations. Phil noted, “We now have a big hole to play in on the next dig.”

The crawler, operated by Will Mott, arrived December 4. Dave drove to Shenandoah a day early to reopen negotiations with the resident beaver. Will started clearing overburden by 9:30 AM and worked until nightfall. Dave and Will both noted the clay was more varied in color and, except for an occasional patch, less blue than previously seen. There was also a distinct up-tilt in the clay layer upstream (East). In the afternoon, after the bulk of the overburden had been moved, Will attached a blade he had fabricated to the bucket of the crawler and began shaving off thin layers of clay to reduce the amount the weekend recruits would have to remove. Dave stood by watching for traces of bone. At the end of the day Will used the bucket to dig a sump to collect melt water and satisfy Dave’s curiosity about the depth of the clay. He dug through approximately four feet of clay, all as homogenous as the surface layers, before striking a layer of fine white sand. The sand began to seep into the hole from the sides under the pressure of a slow flow of water that eventually filled the hole (so much for the sump idea). Dave and Will left the site by 6PM.

The Sloth Rapid Response Team journeyed to Shenandoah on Friday, Dec. 5th and they were on site at 8:00 Saturday morning. After bailing out the hole, and starting the pumps to keep up with Dave’s spring, the volunteers formed a line facing the stream side levee and began cutting a trench toward the south bank of the cut parallel to the levee. Spoil was thrown onto the levee. By the end of the day the area, except for a snapping turtle bone, proved barren.

While disappointing in terms of sloth bone recovery, the dig did define the south boundary of the bone scatter. This boundary is now defined to the north and east as well as to the south. Bone has been probed in the partly excavated intermediate areas where the juvenile bone has been concentrated. Another positive note: Ron Vogel performed a feasibility test on the clay using ultrasonic equipment he borrowed from his department. The results were promising and Ron hopes to construct a prototype of an ultrasonic bone detector in time for our next venture to the site. The next dig will occur after the spoil that forms the south levee is pushed back into the south excavation and a new levee created between the two entrance ramps. The crawler will again be required and we are working on ways to facilitate its access and egress.

Participants on the December 6, 2008 dig:  Lynn Alex (OSA), Bob Athen (landowner), Cyril Below (grandson of Herb Dircks), David Brenzel (Co-PI, NSF grant), Andy Clack (Ancient DNA Centre, McMasters University), Herb Dircks (UI Rapid Prototyping Laboratory), Harold Decuir (President, Board of Directors, Greater Shenandoah Historical Museum, Kandyce Decuir (daughter), Pete Eyheralde (Naturalist, Mahaska County Conservation Board) , Elizabeth Fox (OSA), Cherie Haury-Artz (OSA), Sarah Horgen (UI Museum Natural History), Don Johnson UI Hospitals and Clinics, aka the Fossil Guy, and President, Eastern Iowa Paleontology Project, Meghann Mahoney (Museum of Natural History student-staff, Anthropology Major), Robert McAfee, Ph.D. (Faculty, Doane College), Holmes Semken (UI-Geoscience, Emeritus; PI, NSF grant), Austyn Slaybaugh CR High School student), Jennifer Sweet (OSA), Ron Vogel UI-Dept.of Physics and Astronomy), and Mary Weber (OSA).

Holmes A. Semken, Jr and David J. Brenzel, January 5, 2009

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