photo courtesy of Thalia Sutton

Thanks to Thalia  for sending in these photos of the September excavation.  Lots more in Flickr.

Holmes,

We encountered three stratigraphic units (SU’s)–for convenience I’ll call these SU’s 1 through 3, in order of ascending age. All three are channel facies, meaning that they have sedimentary characteristics of having been deposited by swifter currents of water than were encountered in the blue clay where the sloth remains were found.

SU3 is a channel facies that is perhaps correlated with the sloth-bearing (slotheriferous?) blue clay. The blue clay represents a slackwater facies, where clayey sediments settled from suspension in a low energy environment with only very slight currents represented by micromorphologically visible laminations and oriented sand grains. In SU3, the blue-gray colored sediment matrix has sufficient very fine sand that it will not ribbon. There are also macroscopically-visible, discontinuous, laminations and lenses of fine to medium sand with rare pebbles. These materials were deposited near, and possibly within the stream channel.

 SU2 overlies SU3. It is a grayish brown silt loam that is finely laminated. In the south half of the island, SU2 has an abrupt, unconformable boundary with SU3, and appears to fill a small (ca. 1.5 wide by 30 cm deep) trough incised into SU3. This is perhaps an overflow channel scoured by floods and filled with more oxidized sediment that was probably reworked from a nearby, better drained sedimentary facies. The abrupt SU2-SU3 contact fades to the north in the profile, and in the north part of the island, has a conformable contact with SU3. This suggests that SU2 may be contemporaneous with the upper part of SU3. The SU2-SU3 contact trended northwest across the excavated surface, and seems to have been thicker in the west part of the excavated area of the island.

SU1 was encountered along the north side of the island. It is a laminated blue gray loam or very fine sandy loam. It is similar to SU3, but sandier, less consolidated, with more distinct laminations in the lower part. It yielded finely-divided flecks of bone and small bits of wood, and Euroamerican ceramics (undecorated whiteware). The latter suggests a historic channel fill deposit, perhaps of the 1917 excavated channel, or a post 1917 channel. At the south end of where we’d excavated, SU3 did have a very abrupt contact with what looked like SU2, which clearly indicates a historic age.

Thanks again,

Joe

I’ve long pondered the  improbability of 4 ft. of clay accumulating without a break–500 years (?) without a flood?! It’s comforting to find some evidence finally that they were indeed occurring. I expected a more dramatic signature–sand and rocks–but  Joe says the small differences seen here aren’t unusual for western Iowa at this time.  Flood water transports what’s available, and several thousand years of wind-borne deposits left a thick unstable blanket of loess in the region.  The hills literally melted away with the rain and spring thaws and for a long time the Tarkio was thick with loess sludge and not much else.   Thanks Joe for a vivid new picture of the Valley. . . . Dave

 

 

 

 

 

 

 

 

 

 

 

 

 

 The rain gods smiled on us all day Saturday, keeping thunderstorms west  of the site and downstream until nightfall.  No bones were found, but good fortune located the dig  in a section of the ancient Tarkio streambed unlike anything we’ve uncovered previously and the excavation produced a wealth of new information about the history of the watershed  thanks to the efforts of geoarchaeologist Joe Artz, Geospatial Program Director in the  Office of the State Archaeologist who assisted us on the dig.

A large crew of enthusiastic volunteers cleared the  target area quickly and then dug several deep trenches into our clay deposit for Joe to examine.  He used the walls like a professor with a blackboard tracing the evidence of the long and often violent history of erosion and deposition in the Tarkio Valley.

Slight color variations of the sediment and subtle differences in sand and clay content confirm a story that contrasts sharply with our long-held impression of placid water in the sloths’ valley.  The evidence points to multiple floods  cutting deeply into the  clay on many occasions.  

The Tarkio Valley has often been called  a  “hungry canyon” for its soil-devouring proclivities, but who would have guessed that history went back over 10,000 years!    More photos and Joe’s preliminary report tomorrow. . . Dave

 We have the crawler reserved for this Friday to prepare the Tarkio Valley site for a dig on Saturday. This could last into Sunday (but not likely). We will meet at the Days Inn parking lot at 7:30 on Saturday September 12 and caravan to the site. We will provide water, sunscreen and Deet. You should bring your own light tools (trowel, etc.).  Dave, Will and I believe that we have dug up to the north bank excavation cleared a few years ago but that bone may still lie below one of our old levees. This area will be the target this trip. Will should have the overburden cleaned down to this level by Friday afternoon.  Sloth on.  Holmes

Holmes and I were accompanied on the trip out by Meghann Mahoney, UI Museum of Natural History and Jan Ailes, Education Facilitator, Indian Creek Nature Center, Cedar Rapids.   We were joined in preparing the site for Saturday’s dig by our long-time Bobcat operator Will Mott, Council Bluffs, Bill Wiechman from the Greater Shenadoah Historical Society,  and Mary Brenzel the co-PI’s sister, who drove up from Fayetteville, Arkansas to help.

 14 intrepid volunteers joined the prep crew on Saturday, enduring intermittent rain and extremely mucky working conditions.  Working until nightfall, they moved a mountain of clay and cleared an area of approximately 400 sq. ft.  The bones were deposited on an undulating surface, which necessitates carefully shoveling through at least a foot of the dense clay matrix in their pursuit.

 As Holmes wrote in his letter to volunteers last week, digging at the site is rapidly approaching its conclusion.  It has taken 6 years, but we have now cleared a wide area surrounding the main deposit and only have a couple of narrow bands immediately under the berm  left to excavate.  We hope to take advantage of the seasonably low water levels and return to the site in a couple of weeks.   Until we can discover the location of the Paramylodon that we know is nearby, it looks like we have reached the final act of the excavation phase of the project.

 Thanks to the Des Moines area Central Iowa Mineral Society for organizing a large contingent of members for the dig.  As ever, thanks also to the Iowa Archaeological Society, the Shenadoah-area community, Evans Rental, Glenwood, IA, which supplied the Bobcat and Will Mott, the Rembrandt of Bobcat operators. . . . Dave

 Participant list:  

Jan Ailes, Pam Belknap, Mary Brenzel, Harold and Kandyce  Decuir, Charles Krauth, Meghann Mahoney, Lee McNair, Dennis Miller, Will Mott, Ed Peterson, Monica and Mica  Post, Don Raker, Chuck Safris, Randy, Cheryl and Ryan Shanks, Marie Tiemann, Bill Wiechman, Holmes Semken, David Brenzel.

 Megalonyx Matters 20

The week of July 6 was predicted to be sunny and apparently an ideal time for a two day excavation to recover additional remains of the baby and toddler discovered at the end of the May dig. As in the past, Evans Rental hauled the rented crawler to the site a day in advance.  Will Mott arrived mid-morning with a large gas-powered pump which rapidly pumped the accumulated water from inside the levee.  He estimated the capacity at about 100 gallons/minute. After the pit was ‘dry,’ Will relocated the levee protecting the previous dig north about 12 feet and then removed the muck resulting from two floods from off the floor of the  excavation area. This was accomplished by 7:00 PM. Unfortunately, overnight thunderstorms produced heavy rains which lasted into the following day. While the creek did not overtop the levee, the rain was sufficient to flood the excavation and render the area inaccessible for the pump, crawler and people.  More storms were predicted later in the day. The volunteers vowed to return as soon as possible after the area dried. Participants were William Mott, Lee McNair, Bill Wiechman, Aaron Last, David Brenzel and Holmes Semken.

Holmes Semken and David Brenzel, July 9, 2009.