Mammoth Moments

Field Reports from Holmes Semken

 

Mammoth Moments 17- Second Tusk September 11, 2012

This Tuesday dig was organized to coincide with the morning and afternoon laboratory sections of Janet Ewart’s Anatomy class, William Penn University. Janet met David and Holmes at 9:00 with about 20 students; they were given a 15 minute review on the differences between mammoths and mastodons and then walked 200 yards to the excavation. Farmer John had pumped entrapped water down the night before but two feet of water had refilled the excavation. The sump pump was restarted and the water removed. Unfortunately, the pump did not work on the two feet of underlying slop, described by Wm. Penn TV anchor Maureen McKamey, as ‘disgustingly repugnant.’ Jason Madison filmed the activities anyway. The students went into the muck without hesitation and shortly bones were being excavated on the east (downstream) and south (right bank) walls. Sarah arrived just after noon having participated in a video production featuring the Museum of Natural History for a televised production on the best places in Iowa to visit.  The east wall area yielded a rib and a vertebra and the south area a second tusk (broken into at least four parts), a piece of skull (nasal?), two vertebrae and three ribs or rib fragments.  All remains in this jumble were more gently sloping down to the north (picture Sarah & Jim North) than those collected last week, some of which were nearly vertical. These also weathered blue-clay slump clasts separated by sand stringers (as those which the Archaic projectile point recovered previously) as opposed to from coarser-grained, fluvial-like material with more organics. Overall, the top of the bone bed is higher here than toward the Discovery Pit. Upon completion of the dig, the tusk was removed to Farmer John’s basement and the previously collected mammoth cranium, residing in Farmer John’s barn since the last dig, was loaded onto Sarah’s truck for transport to the UI Museum of Natural History. We departed the site around 6:30 PM.

 

Mammoth Moments 16- Cranium and Retouched Tusk, September 6, 2012

Sarah, David and Holmes left Iowa City at 7:00 am and arrived at the site shortly after nine; road repairs required taking the scenic route to Farmer John’s, but Sarah’s GPS kept us on track. Half of the volunteers were already on hand when we arrived and had Jim’s pickup loaded with all tools needed for the excavation. The excavation area had three feet of water from seepage and a sump pump was employed to drain the site. A large portion of the woolly mammoth’s cranium, found under the previously removed palate, reappeared partially resting on a detached tusk as the water dropped. While the volunteers removed slop from around the bones, Sarah loaded GPS coordinates for exposed elements. Work then began to pedestal the cranium, difficult because of the tusk’s juxtaposed location. The cranium, lying sideways, was undercut on three sides and plaster bandages were applied with the idea of rolling the specimen into a topographic low opposite the tusk. Holmes then felt sinus box-work extending into the matrix below the cast. Further bad news occurred when the plaster on the tusk side failed to cure properly, probably because of local humidity. The specimen would be under a foot of water by morning so rolling the specimen to a safer area was the lesser of evils. The box-work came up with the specimen but fell out of the poorly cured portion of the cast as a single unit; it was stable. The tusk was then cleared, covered with wet burlap and rolled onto another board. The cranium was placed on a heavy blanket for handling and gently carried out of the excavation. The tusk was moved to Farmer John’s damp basement and the cranial element to his barn because it required five people to lift it. We decided not to move the specimens to the museum in Iowa City because President Obama was holding a pep rally beside the museum and the secret service had secured the building. It would have been a trying experience for both groups involved. Three ribs also were removed and several other elements, apparently ribs and a vertebra, were discovered and will be collected at a later date.

The geology at the site still is perplexing. Both the west (upstream) and east (downstream) walls of the excavation were modeled ‘smurfic’ blue and black and the downstream exposure contained a well preserved rib. The south (right hand) wall was composed of sand stringers in a much coarser grained matrix with plant fragments and bone at the same level of the downstream slump. This may be the wall of the plunge pool or creek deposits that cut the bone-bearing deposits. This bone-bearing deposit is four feet, three inches thick and deep enough to accommodate a standing rib (70°).  Cobbles are intermingled with bones of all sizes as if all items gently settled into the deposit. As noted earlier, there is no evidence of abrasion on the bones but dry fracture on some elements indicates surface exposure prior to burial.

Participants were Laura DeCook, Mike Goudy, Peter Eyheralde. James North. Jim Roberson, Lee Wymore, Mary Jane Sullivan and Leanne Van Donselaar. 

 

 

Mammoth Moments 15- Liquefied Matrix, Palate # 2 Removed, Thursday, Aug 30, 2012

Dave returned to the site at 8 AM meeting Jim Roberson and sloth/mammoth veteran Pete Eyheralde.  They were shortly joined by five staff members from the Clinton County Conservation Board (CCCB).  The pit was full of hundreds of gallons of water however a combination of pumping and hand bailing soon emptied it. Once again the bottom of the pit had "liquefied" under the water and a large amount of sloppy muck covered the bottom of the pitFarmer John had to return the portable generator at the end of the day so we need to find another solution to the pumping challenge before we go out again. The ICNC sump pump is still at the farm.

The team extracted the remaining ribs discovered last Friday. One "rib" turned out to be a portion of a shoulder blade bearing the spine.   A small fragment of bone was found bearing clear signs of a green fracture, also some wood in the area of the tusk.

In the process of clearing the muck from the pit, diggers uncovered another complete rib and a large rib piece west of the tree location. The fragment rests about 1-1/2 ft. from the wall and 6 in. lower than another rib fragment which was later discovered protruding from the wall directly west.  It was determined that the two ends match and the remainder of the rib was left embedded in the wall for future recovery. Three feet south of the scapula (spine) fragment and two feet higher in blue clay, a digger found a complete foot bone tentatively identified as a left cuneiform.

The Clinton CCB gang had to depart at 12:30PM. They were replaced after lunch by two representatives of the Mahaska CCB in the form of Director Dave Sedivec and Administrative Assistant Jenny Snyder.  Pete and Jenny applied a plaster bandage to upper jaw/tooth #2 and, while they waited for it to dry, they prepared to excavate the ribs found that morning. With the bottom of the pit "liquefying" every night, the team was concerned about leaving them in what was already a very mucky location.  In the process they encountered several large bones protruding from the south corner of the pit.  These were partially excavated as time allowed and included a small piece of tusk/ivory, a couple of portions of ribs and a massive triangular limb bone which upon inspection proved to be split in half lengthwise, with a large fragment of the same bone sitting nearby.  As darkness approached, the other portion had to be left in the ground for future recovery. With many hands helping, the diggers carried maxilla #2 up from the pit and transported it back up to the farm where it was loaded into the back of Dave's car along with maxilla #1 which had been stored in John's pole barn for transport back to Iowa City.  The team departed the site at approximately 8 PM.

 

Mammoth Moments 14- Plunge Pool, Upper Jaw 2 Recovery, Wednesday, August 29, 2012

The team did not return to the site until Wednesday to give the site and surrounding area some time to dry after over two inches of rain Saturday.  Farmer John and Dave traded numerous text messages and phone calls Monday and Tuesday discussing the problem and possible solutions.  John finally located an electric generator from a co-worker and Dave borrowed a sump pump from the Indian Creek Nature Center (ICNC). Dave arrived at 8 AM accompanied by Jan Aiels from the ICNC.  They met Jim Roberson and were soon joined by Farmer John's neighbors Leanne and Shirley. The pit was quickly pumped dry but the water left a large quantity of muck that had liquefied and slumped under water, on the bottom of the pit.

Unlike the Tarkio Valley sloth site, which stayed dry after pumping, the mammoth site has sprouted a number of leaks both on the bottom and on the sides. Apparently, Saturday's rain recharged the ground water and flowing down from the western uplands it has found the path of least resistance into the pit.  One cannot dig long without stopping to bail out water--sloppy conditions will be a permanent challenge ahead.

Shirley recovered a portion of a vertebra while clearing the drainage ditch downhill from the discovery pit.  Jan recovered some skull fragments in the muck directly under where the tree had grown.  One piece still has roots attached. 

The team began extracting the ribs found the previous dig so they could renew their attack on upper jaw #2.  The team was joined at 1 PM by Indian Hills Community College Professor Lee Wymore and veteran mammoth digger Jenn, a nursing student and President of the IHCC Science Club.  The team continued extracting ribs, while making clean cuts on the pit walls in anticipation of the arrival of Art Bettis later in the PM.  Leanne discovered a new rib less than one ft. north of the main rib deposit and 6 inches higher, resting in clay rather than the gravel. It was left in place for Art to see.

UI Professors Art Bettis and Frank Weirich with graduate student Phil Kerr arrived at the site at 4:30 PM with the goal of determining the nature of the skull/rib deposit.  They scraped and sampled the wall. They also used a hand auger to collect samples, comparing their observations from Phil's notes related to the core they collected approximately 20 ft. west and uphill from the skull.  Art confirmed the importance of the tree that was excavated last week for marking the date of the slump.  He recommended collecting and saving any pieces of wood found directly associated with the bones to date the deposit with greater precision.

Art suggested that the bones may simply be sitting in a large block of slump which was undercut, broken apart and transported by a flood in one of the two ancient streams that bordered the site.  It is also possible the bones are sitting in a plunge pool created by the junction of the prehistoric Skunk River tributary that still runs east of the site and the prehistoric predecessor of the dry gulley coming down from the uplands overlooking the site from the west.  An ancient flood on the Skunk may have created a nick point which eroded uphill (much as occurred after the 1993 flood which ultimately exposed the bones) causing the bone-bearing deposit to collapse into the plunge pool.  This scenario would account for the large range of depth of the bones and the large angles from horizontal in which some are sitting. Art requested that as we move west we continue to take wide-angle photos of the sediments/walls and send them to him.   He asked if any of the diggers had a 35mm camera to take a high resolution photo of the west wall.  No one had one on them, but Osky News reporter Ken Allsup, who arrived with William Penn reporter Maureen McKamey at 5:30PM to interview Art, volunteered to come back in the AM to take the photo. Leanne extracted the rib she had found for the reporters and the team departed at 6:15 PM.

 

 

Mammoth Moments 13- Palate Recovery Initiated, Friday, August 24, 2012

The team met at Farmer John's house at 9AM.  Dave and Jim Roberson returned with Lee Wymore, Indian Hills Community College, along with biology and nursing student Kylie Ratzloff and her husband Dustin.  John used the Titan Machinery backhoe to widen the shelf at the west side of the pit and cleared away approximately five ft. of overburden running the full length of the pit.  This gave the team more room to work around the skull safely and a place to throw the ever-growing pile of clay they were removing.

The immediate goal was to uncover the maxillary or upper jaw/tooth #2 as well as the adjoining tusk and skull portions.  To accomplish this, the team determined that the first priority was removing the tree stump which was accomplished in several large pieces which were saved topside.  The second step was extracting upper jaw/tooth #1.  Using a tile probe, Lee located a bone-free plane between maxilla #1 and #2.  Kylie applied a plaster bandage to #1.  The bone/plaster mass proved heavier than expected and the team used a 6 ft. length of 2X8 provided by Farmer John as a "stretcher" to carry the bone out of the pit and up to Jim's truck. Specimen #1 was wrapped in plastic bags and stored in Farmer John's pole barn to await transport to Iowa City.  Leanne Van Donselaar (UNI Earth Science grad) arrived after lunch to reinforce the crew.   A large number of small bone fragments were discovered sitting on top of #2, presumably fallen from #1.  They were collected in a bag.  A separate pile of large fragments was found to the west between #2 and the tusk and other skull masses.  These were photographed and bagged and labeled "#1."

As the team dug deeper under #2 they encountered several ribs resting in and on a thick (~6 in.) bed of gravel.  To the north (downstream?), larger cobble-sized rocks were encountered.  Diggers widened the hole and eventually found at least eight (8) ribs. The ribs are much deeper than we have previously dug in the Discovery Pit. Do we have to go back and look under the gravel layer we encountered underlying everything there?

Osky Herald reporter Duane Nollen came to the site mid-afternoon and took some notes and photos for a story to be published Saturday. Maureen and Jason returned to film for CRI.  The team departed about 7:30 PM.  At the end of the day maxillary #2 remained in the ground as well as the tusk and ribs 1-8. 

 

 

Mammoth Moments 12- Woolly Mammoth Identified, Tusk, Thursday, August 23, 2012

Dave returned to the site with two MNH student-employees Kelsy Westman and Andrew Blodgett, both veterans from previous digs. They met Jim Roberson and Lee Wymore at 9 AM with the goal of further excavating and extracting the tree stump and maxillary/tooth which Dr. Chris Widga, Illinois State Museum, had confirmed via emailed photos was an elderly Woolly Mammoth.

The team had speculated on Monday that perhaps the large block of blue clay represented the edge of the intact fossil deposit but this hope was dashed as diggers widened and deepened the hole and discovered gray clay flecked with specks of blue and sand stringers intermingled.  Clearly the maxillary is simply resting in a large block of slump.  The other half of the upper jaw and tooth (#2) was uncovered almost directly under the first.  As diggers worked around the jaw they uncovered the tip of a well-preserved tusk--approximately 5-6 inches in diameter.  The tusk appears broken off at one time but re-sharpened and polished by the animal through use.  Approximately 24 in. of the tusk was exposed by the end of the day.  Diggers also encountered islands of other large bones, assumed to be other portions of the skull.  The team departed about 5 PM leaving tree and all bones in-place and made hasty plans to renew their attempts to extract the jaw the next day.

 

Mammoth Moments 11- Small Mammoth Tooth, Monday, August 20, 2012

Dave returned to the site, meeting volunteers Jim Roberson (Muscatine) and Rich Sawyer (Oskaloosa) at 9 AM with the goal of further excavating and extracting the tree stump uncovered near the end of the previous day along with the unidentified bones/fragments uncovered nearby.  Farmer John joined the team.  After a couple of hours of digging it became clear the bone was a large portion of an upper jaw.  This was confirmed when an associated mammoth tooth was uncovered just before lunch. A toe bone was found inches away.  Dave took close-up photos of the tooth to expedite identification of the species.  These were sent to Dr. Chris Widga, Illinois State Museum, that evening. The tooth was unusually small--approximately half the length of an adult tooth, sparking conjecture that the jaw/tooth might belong to a juvenile.  The jaw is resting approximately 5 ft. from the east line of Frank Weirich's first GPR grid and thirteen ft. south of the NE corner (see photos). It may show up on the grid he ran on the shelf Farmer John cleared, but the flags from that grid have been disturbed and it's impossible to say where it falls without consulting Frank's notes and or the GPS map.

The tree, maxillary and toe are buried in a large block of "smurfic" blue clay that slopes upward to the west, away from the Discovery Pit. A layer of silt that ranges from approximately one ft. pit-side to just a few inches westward covers the clay.  The tree grew on top of this silt.  The roots follow the top of the clay for the most part but penetrate it in places. The tree is a cloning species and suckers where uncovered in several places nearby.   A local resident who stopped by offered the observation that the stump looks like that of an Osage orange tree, renowned for its durability and rot-resistance. 

Sarah arrived after lunch to reinforce the excavation team.  A Des Moines CBS affiliated television crew, responding to the Oskaloosa Herald story published that morning about the discovery of mammoth #2, called late in the afternoon and asked to come to film site activities.  Permission was granted by Farmer John and Sarah was interviewed.  The reporter had also called Jim North who came to the site.   The diggers departed about 7:30 PM leaving the tree stump, jaw/tooth and toe in the ground for recovery the next day.

 

 

Mammoth Moments 10- Tree Stump, Sunday, August 19, 2012

A crew of approximately 27 volunteers met at the site at 9 AM.   Sarah, Holmes and Dave were joined by Andrew Blodgett (MNH student staff), faculty and students from ISU, William Penn University, Indian Hills Community College and Oskaloosa High School along with staff from the Mahaska and Story County Conservation Boards. Once again Titan Machinery supplied the vital backhoe. 

Volunteers used probes to explore the bench John had previously cut overlooking the west side of the discovery pit, but encountered only gravel and iron deposits until early afternoon when the stump of a buried tree was uncovered. It was resting 5-6 feet below the modern ground level and is in excellent condition.  Further excavation disclosed the tree was growing on a layer of silt approximately 1 ft. thick on the downhill (east) side and only inches thick on the uphill (west) side, overlying a large sloping mass of smurfic blue clay.  The tree roots mostly follow the silt/clay boundary but a few penetrate deeply into the clay.  The team resolved to collect the stump for analysis but late in the afternoon the excavators encountered a bone concentration downhill and NE of the stump. Time ran out and the team resolved to return with a small group of volunteers the next day to continue digging. The team departed at approximately 5:30 PM.

 

Mammoth Moments 9- Site Preparation, Friday, August 17, 2012

Sarah, Dave and Holmes joined Jim North of William Penn University and Farmer John at 3:00 PM to look at the site in preparation for a dig on Sunday, August 19. We found water in the pit and noted that there are still areas in the west end of the Discovery Pit that need to be examined, especially since bone has continually been found deeper than expected. The drainage ditch was cleaned and water began to slowly flow out of the excavation area.  John plans to deepen the channel before we arrive on Sunday. He has the keys to the Titan Machinery backhoe and will cut the bench above the Discovery Pit floor down to within 1.5 feet of the bone bearing deposits.  This will give the volunteers two main areas to excavate on Sunday. Jason Madison and Maureen McKamey from Communication Research Institute (CRI), the William Penn University affiliated television news station, filmed site preparation activities as well as the scapulae from both mammoths. The program should air Friday, August 24. The Iowa City group left the site about 6 PM.

 

Mammoth Moments 8- Geological Assault, Excavation and Second Right Scapula, July 20-22, 2012

On Friday, July 20, a small crew from the Museum of Natural History and the Department of Geoscience descended on the site to conduct geological exploration of the bone-bearing deposits, clear the Discovery Pit and test new probes, funded by Frank Weirich, especially made for the excavation Essex Rock Bit of Monroe, NY. Additional geological analysis was essential because the depositional situation is not clear. The Discovery Pit was attacked but efforts to complete excavation of the area were not finished.  Since then, Farmer John has uncovered mammoth bones 18 inches below the level previously deemed to be the bottom of the bone bed. The thickness of the deposit, at least under the modern deposits in Bone Gulley (previously called tributary), is much greater than anticipated .Perhaps Farmer John was excavating in an older channel of Bone gulley channel. All of the bones discovered so far have been moved from their original position, initially as slump blocks which would not sort skeletal elements. Subsequent fluvial activity, some of which is historic has either cut into the bone-bearing slump or undercut the unit which then collapsed into Bone Gulley. As yet, there is no indication of the direction of the source. Also, as noted previously, the specimens were coming from or are surrounded by two historic deposits, possibly facies of each other, but likely distinct units. As previously reported, one contained historic ceramics, plastic and calf bones. The other did not have historic artifacts but Dick Baker, Geoscience, found invasive plant macrofossils. How often has the bone bed been modified over time?

 

The Friday crew left Iowa City in time to arrive at the site when Farmer John got off work at three o’clock. We were early and John found us in the café.  Dave drove with him to Titan Machinery to borrow the backhoe for the weekend. John then cleared a bench seven feet wide (backhoe’s reach) down to about two feet above the bone bed and smoothed the surface for Saturday’s GPR surrey closer to the bone bed. Sarah Horgen, Andrew Blodgett, Museum Natural History student/staff, and Ryan Bozer, museum volunteer & West High student, began draining the Discovery Pit and shovel-testing small areas of the Discovery Pit floor. Tom Jorgensen, University writer/photographer reviewed our operation and took pictures for the Spectator, an e-magazine for UI staff and alumni. Art Bettis and Phil Kerr, UI Department of Geoscience, shaved the nick point section, the only undisturbed sediments exposed, and hand cored the subsurface sediments to a depth of almost five meters. They bottomed in sand that was under sufficient hydrologic pressure to induce flow into the Discovery Pit. This is the local groundwater that is capped and confined by the silty sediments that are part of the upper layer yielding the mammoth remains. On Sunday, Art and Phil returned to take two cores, one on the high ground 10 meters southwest of the Discovery Pit and another about 50 meters almost due west of the Discovery Pit. Art and Phil’s coring documented a consistent stratigraphic succession of fine-grained pre-Gunder alluvium grading downward into sandy alluvium that is more than 5 meters thick.  The zone where the fine grained deposits grade into sandy alluvium contains abundant organic matter and plant fossils and is the same layer where organic remains crop out in the lower part of the knickpoint profile in the Discovery Pit. Art also verified that we are not digging in primary deposits but in reduced, reworked, sediments. The bones were originally upslope, in as yet to be defined direction.  We completed Friday’s work around 6:30 PM. Excavations on Saturday and Sunday ended between 2:30 and 3:00 PM because of the extreme heat. The discovery Pit still is not cleared.

The previously cut bench in the overburden to reduce overburden thickness above the bone bed to two feet also provided a flat platform to refine the GPR analysis. Frank dragged this bench with two antennae (250 &  500 Mhz) in an area where bone is anticipated and will be exposed over the weekend,  Frank returned Friday with his highest resolution antenna GPR antenna (2.3 GHz) to explore the floor of the Discovery Pit. On Sunday, Frank, along with Geoscience graduate student, Megan Schettler, used a 5 cm grid drawn on a two meter square plastic sheet for a level base to scan the exposed floor of the Discovery Pit. The subsequent discovery of a second partial scapula and two ribs under the bench and several small bones under the Discovery Pit floor should permit detailed evaluation of the effectiveness of GPR at the mammoth site.  Hopefully, both Art and Frank will be able to integrate their findings before the next excavation.

A large body of volunteers arrived both Saturday and Sunday. Those on Saturday were largely from the Cedar Rapids Gem and Mineral Society and those on Sunday were primarily provided by the Indian Creek Nature Center in Marion, Iowa. The latter arrived as a morning and afternoon shifts. Working in the Discovery Pit and underneath the bench, volunteers uncovered a second partial right scapula (We have two Individuals!), two ribs, several foot/ankle bones and segments of a deformed tusk over the course of two days.

 

 

Mammoth Moments 7- Clearing the Discovery Pit , June 30, 2012

The goals of the trip were to finish screening all bone-bearing matrix from the Discovery Pit piled on the overlying terrace and to clear unexcavated areas in the bottom of this pit so we can launch into virgin deposits on the south side. The cleared pit will provide space to toss overburden when we dig the next trench parallel to the Discovery Excavation. Hopefully, the skull will be there so that we can establish its condition and how far we can dig through the overburden without hitting any bone.  It's a real tribute to the volunteers who have worked this spring/summer that they've been willing and eager to endure the tedious work of this "cleaning up," especially at 100 degree plus temperatures.

 One rib and some chunks of a large limb bone, one with strange post-mortem marks, were recovered. The rib was standing almost on end, vertebral articulation up, and clearly was reworked from the primary deposit into the tributary cutting into the site. A rib recovered on the first excavation was similarly orientated and visible protruding from the stream, close to the limb bone chunks. During the mapping expedition, on June 24, a fragmented vertebra was collected just above the ‘standing rib’ and above the level of the bone bearing matrix. The ‘standing rib’ was visible when the vertebra was removed. How did the vertebra get above the level of the bone bed? The vertebra that John recovered with the backhoe on the first dig appeared to be above the level of the other recovered bones as well.  The definition of the bone-bearing unit is not clear at this point. 

The bone bed has been partially exposed at least twice previously. During our first excavation, historic ceramic fragments, remains of a modern calf and plastic debris were collected from mammoth bone-bearing fill in the Discovery Pit. Today (June 30) we pulled honey locust seed pods from two areas of the tributary, one under the nick point of the little creek and the other from dark matrix, also bone-bearing, previously regarded as the mother lode. These seed pods were better preserved than other plant macrofossils recovered and Dick Baker, UI-Geoscience, indentified European plant species in an associated matrix sample.  Thus, there are two historic lithologies associated with mammoth bone and modern plant macros. Primary deposits are present and exposed because the plant macro sample that Art collected in January was not contaminated. The bottom line - We do not currently understand the deposit.  

The two hotspots that Frank Weirich had previously identified with high resolution, 1.3 GHz GPR were probed and excavated but yielded nothing. The radar anomaly is apparently below the mammoth layer. Frank is working with his software vendor to get a glitch fixed and can't calibrate his maps right now with depth measurements.  He was tied up in another project this Saturday but will be back to try again the next time we go out.

There were 31 volunteers present,  representing the usual broad mix of MNH volunteers, OSA staffers, local residents/students and teachers, nature center naturalists and representatives from state agencies. Lee Wymore, Professor of Biology at Indian Hills Community College, Ottumwa, brought five students and some supporting staff members who spent almost the entire day with us.  Professor Jim North was back from Wm Penn, as ever, teaching down in the pit.  

 

 

Mammoth Moments 6- GPS Mapping & More GPR, June 24, 2012

Frank Weirich and Frank Jr. used the GPR to map the terrace on the north side of the discovery pit, above the opposite bank previously worked. They plan to return on Saturday, June 30, hopefully with 3-D maps from the microgrid over the hot spot test explored on June 16 if they can get a vendor to fix a software bug.  The Franks used their super-precise 1.3 gHz GPR antenna on a small area (approx 1 m. X 1 m.) down in the discovery pit directly on top of the bone-bearing clay layer.  It doesn't penetrate as far as the 250 and 500 MHz so it cannot be used from ground level, but is accurate within mm down on the clay. They predicted location of two bones, although John then probed without results.  Frank Sr. will take the data and process it to calculate the depth; John may not have probed deep enough, but it could be deeply buried rocks. We will test this area on Saturday, June 30.

Bill Whittaker, of the UI Office State Archaeologist, used his Total GPS equipment to capture GPS coordinates for the dig area, some previously excavated bones, Frank's GPR grids and a wide area of the surrounding terrain including the ravine and creek.   His equipment uses a highly accurate GPS base station, a laser and a reflector that Sarah Horgen and Dave Brenzel carried up and down through the pasture, bushes, poison ivy and mud to measure distance, bearing, and height of any point that's in the laser's line of sight with an accuracy of a few centimeters.  Bill will supply us with a very accurate map that we can use and add on all the GIS data that's available.  Sarah contacted Don Wirth to get his map from the bones recovered on June 16th so we can integrate everything at hand into one official map. Don sent his map to Iowa City promptly and Museum staff will reconcile all geographic data. 

John and his son probed the bottom of the discovery pit prior to the 24th and found another bone, broken in several pieces. Sarah took it back to the museum to be glued if possible. Digging with John Doershuk, they found three more ribs (in perfect condition) lying on top of each other which were then photographed and collected.  Another bone, a badly weathered mammoth vertebral centrum, was recovered on top of a vertically-orientated rib. It could be the rest of the vertebra John gave Sarah to glue on the Inaugural Dig. At this point it is estimated that 20% of the mammoth skeleton has already been recovered -- not a bad start!  The diggers were still amazed by the condition of associated plant material and a large sample of locust seed pods was collected to give to Dick Baker, who studies plant macrofossils in the UI Department of Geoscience. 

Dave is impressed, as are all of us, that there are two ice age orphans/ghosts on top of the site-a honey locust and a hawthorn.  Dave also discovered another classic orphan--an osage orange just 50 feet uphill to the west. We plan to show Dave Sedivec, Mahaska County Conservation Board, the next time he visits.  It will be a terrific way to tie the mammoth to the kind of woodlands/ educational opportunities he could create at the Mahaska County's new nature center.  Dave promised to bring the landowner some pawpaw and Kentucky coffee seeds on the next dig and plant them to add to his ice age collection.  

Objective number one for Saturday, June 30, is to clear the rest of the mammoth-bearing clay down on the bottom of the Discovery Pit. There is room for 6-8 people to work down there.  A few volunteers should bring their mud boots; the pit sprouted some springs after a half inch rain the previous night. It is an easy bail though.   John left one rib in place for us to dig out. It is not laying flat but rather on its ventral surface. Sarah remarked that the way the bones are dispersed in "packages" and resting at odd levels and angles is strikingly similar to the sloth site, but not kicked around and mixed up quite as much.  We need Art or Joe to look at the clay deposit.   

If we have extra bodies the next time we dig, John wants us to screen the small amount of material sitting within about 1 m. of the ravine and kicked down into the bottom by the cattle. All the rest of the spoil piles can be ignored. John does not think that we need to screen excavated clay from the discovery pit, especially if we probe the clay and then shave.  John is going try to get the backhoe back so we can throw matrix into the bucket like we did on the Inaugural Dig.  Once we finish in the Discovery Pit we can start pulling back overburden lying immediately to the south and attempt to locate the skull. We will be able to shovel overburden down into the now empty Discovery Pit. More ‘sloth’ probes will help.

 

Mammoth Moments 5- Screening backfill & Radar Field Check, June 16, 2012

Thirty-six volunteers, primarily from William Penn University’s Division of Health and Life Science and the University of Iowa Office of State Archaeologist with help from University of Iowa Department of Geoscience, joined the museum establishment at the mammoth site. The primary objective was to screen previously excavated matrix, calibrate the Ground Penetrating Radar (GPR) maps made on a previous trip, and fine-tune the GPR by running a microgrid over a hot spot in the discovery pit. The volunteers signed waivers and examined selected bones that John brought for inspection. After a few minutes of orientation on mammoths in general, the group moved to the dig area, set up tripod screens as well as shaker screens borrowed from the UI Office of State Archaeologist (OSA) and began screening matrix previously excavated from the discovery pit. Foot bones had been discovered in the spoil piles and the piles needed to be re-examined. Also, the spoil piles were located on top of the area to be excavated next. Light brown backfill produced a few artifacts and some bison/cow bones, but clods from the grey matrix contained mammoth sesamoids. A neighbor of John’s saw the difficulty of screening the quantity of spoil so he went home and built a four by eight foot screen with a much coarser mesh. Since anything that we were looking for is at least the size of a walnut, this was more efficient for mammoth bone recovery and was much appreciated by the project leaders.

 Frank Weirich, of the UI Department of Geoscience and IIHR-Hydroscience and Engineering, scanned the area above one of the anomalies or "hot spots" discovered previously with GPR on a finer grid (one-half m) to be processed later.  John, using a loaned backhoe from Titan Machinery of Oskaloosa, [http://oskaloosa.titanmachinery.com/], then dug an exploratory pit over the anomaly primarily to calibrate the GPR maps and confirm the depth readings. At about mammoth level, several large rock cobbles were struck. As there is a boulder juxtaposed to mammoth remains in the discovery pit, the anomalies may indicate boulder/cobble beds located on the mammoth horizon. Subsequent analysis of the microgrid suggests that there may bone intermingled with the rock. This will be tested as we continue to systematically excavate the site. A thick sequence of blue clay-a pre-Gunder paleosol according to Joe Artz (e-mail communication)-was encountered above the cobbles. This coloration is typical of the deposits from which many ice-age mammals have been discovered in Iowa. There is still potential that the GPR will be refined to detect bone and Frank intends to refine the survey.

Another crew of volunteers excavated the remaining area of mammoth-bearing sediment around the discovery pit. One additional mammoth rib was recovered. Deposits abutting the dark black clay hosting the mammoth, while similar to the mammoth-bearing unit, are mottled in color and texture and contain historic stoneware (Ohio manufacture, 1905-Marlin Ingalls) and modern bovid remains. These probably are from a modern calf rather than bison. We initially thought that this was a slump deposit but Cherie Haury-Artz (OSA ) suggested that it was historic fill deposited in a previously cut valley, that was re-entrenched during the 2008 flood which also exposed the mammoth femur in the old valley wall. The density of the sediment suggests fill rather than recent slump.

 

 

Mammoth Moments 4-Radar Friday, June 8, 2012

Four members of Team Mammoth left Iowa City at 1:30 PM and arrived at the mammoth site at 2:45. Frank Weirich and David Brenzel went to the dig area immediately and began preparing a grid for the Ground Penetrating Radar (GPR) survey while Holmes Semken waited for the land owner to return from work and Sarah Horgen who came from Ottumwa.  A film crew from William Penn University arrived shortly thereafter and all were onsite by 3:30.

We laid out a 12 meter by 12 meter grid (approx.) and Frank surveyed the site three times with a Mala ProEx ground penetrating radar system. The grid on each survey was crisscrossed, first E-W then N-S, at 1 meter intervals, using 250 MHz, 500 MHz and 800 MHz antennas. The 250 MHz antenna penetrates further but 800 shows more detail.The GPR yielded some interesting anomalies but the raw data cannot separate mammoth bones from logs, cache pits, rocks or graves. Frank will process the raw data using several radar data processing software packages in order to filter, amplify and otherwise clarify the images as well as proceed to generate 2 and 3 D images of the mapped areas. We hope to have some pictures and a preliminary analysis in time for our next dig Saturday, June 15. Information from Art’s cores will help correlate the different lines with stratigraphic breaks in the core samples. Frank plans to return during the next dig to field check the results and refine data levels. We're fortunate to have Frank Weirich donating his time to the project.

The camera crew from William Penn University’s Communication Research Institute said that their organization specializes in documentary film. Holmes asked if they would like to document the dig and they were most interested and agreed. They are aware that reporters from other organizations will visit the site.

The survey was complete about 7:00 PM.

 

Mammoth Moments 3- June 2, 2012 Inaugural Dig

The Iowa City contingent arrived at the mammoth site about 8:45 AM to find some volunteers from the Ames and Des Moines areas already present. After introductions, the group walked to the dig area.Some volunteers began deepening the streamlet that cross cuts the site to better drain the bone concentration area. Others began removing spoil and overburden lying between the discovery excavation (femur) and the streamlet while another group screened spoil from the femur excavation the landowner had placed on the terrace overlying the bone bed. Screening back dirt from the discovery excavation was necessary because the landowner has recovered foot bones from the spoil. Two screens, borrowed from the Office of the State Archaeologist were assigned to each spoil pile.A backhoe with an extender for the bucket, borrowed from Titan Machinery of Oskaloosa [http://oskaloosa.titanmachinery.com/] assisted the creek side work by lifting matrix six feet from creek level up to screening areas on the terrace.

Volunteers working to deepen drainage from the area immediately discovered a vertically- oriented rib in the stream bed. The rib could have been reworked from either bank or 1-2 meters upstream where the mammoth bone concentration appears to be. The rib exhibited obvious evidence of gnawing by a large carnivore. By 10:45 a rib previously noticed in the bone bed by the landowner was encountered and, as the excavation area was expanded, another complete floating rib and two foot bones were collected. A vertebra, with epiphyses not fused, was struck by the backhoe while removing spoil at creek level. The pieces were recovered from the screens and the vertebra will be repaired in the MNH. A spruce (?) log about 2.5 feet long and 6 in. in diameter was collected from the bone-bearing deposit, also a couple of honey locust pods.Numerous other plant macrofossils appeared on the screens but none were collected because of possible contamination. Excavation ceased about 4:00 PM.

Vital information acquired is that any fractures in mammoth bones widen rapidly with desiccation and the fracture spreads. Uncovered bone will have to be shielded from the sun and kept moist unless collected and bagged immediately. Solid specimens hold up well upon exposure. It also is apparent the bone bed is normally above the water table as well as the level of the little creek that transects the site. Inundation should not be a problem during future excavations.

Holmes Semken, David Brenzel and Sarah Horgen, June 4 2012

 

Mammoth Moments 2- April 23, 2012 Core Samples

Art Bettis (Associate Professor, Geoscience), accompanied by Tiffany Adrain (Collections Manager, Geoscience), David Brenzel (Naturalist, Indian Creek Nature Center, Marion),, Sarah Horgen (Education Coordinator, UI Museum Natural History) and Holmes Semken (Professor Emeritus, Geoscience) met the landowner at his farm around 8:00 in the morning. The Giddings core rig that was towed from Iowa City was attached to the landowner’s tractor and pulled to the mammoth locality. One core (16 feet) was collected about 20 yards south of the outcrop with the mammoth remains on the terrace immediately above the mammoth. A second core (20 feet) was collected about 40 m further south from the outcrop on the next higher terrace. Art reports that both cores transgressed the unit containing the mammoth and bottomed in sand immediately below that unit.

After coring, we hatched an initial excavation plan with the landowner for our next trip. The mammoth bed lies on saturated gravel and beside a small streamlet that pours into the landowner’s excavation. Flooding is enhanced by a partial dam created when the specimens recovered to date were removed. The landowner says that there are mammoth-bearing sediments (including ribs) at the base of this dam and it is capped by back dirt from his excavation. The dam needs to be removed to facilitate drainage and recover the remaining specimens. The back dirt also needs to be screened because smaller bones have been recovered from the spoil. There is only one acceptable way to throw the dirt in the dam out and that is up (a long throw) to avoid impeding flow out of the pit downstream. Also, the streamlet and the creek are crystal clear and we do not want to muck it up. For those who have not seen the location, it is beautiful as well as pristine with the clear rippling creek. The landowner has a backhoe but it will not reach the target area. He can get close. Therefore, the plan is to get about 10 volunteers to shovel into the extended bucket of the backhoe and lift it to a dry screening area on the terrace. This should be fun for the volunteers as there will be bones at the bottom and probably in the fill. Hopefully, the site will drain after this operation. If not, an ADS system might be rigged. Pumps would be a last resort. As at the Tarkio, plans can change as we work.

Art has an undergraduate who is interested in describing the two cores. This will really facilitate our working knowledge at the site. Also, there is lots of organic material, good for dates and paleobotanical studies. I did not see any snails but who knows.

Dick Baker has looked at the grab sample of mammoth-bearing sediments that Art collected during our first visit and reports lots of spruce (probably both black & white), larch needles, probably fir, a violet seed and raspberry seed fragments along with a couple of unknowns. Pollen is undoubtedly present.

Dave Campbell (Adjunct Professor, Geoscience) is interested in exploring the site with radar. The bone bed is too deep for the system that he uses but Glenn Story (Associate Professor, Classics, Anthropology) and Frank Weirich (Associate Professor, Geoscience) may have a bigger antenna. He will investigate.

We are looking at weekends in early June for the first excavation.

Andy’s story appeared the next day can be viewed at http://oskaloosa.com/local/x130094254/A-discovery-of-mammoth-proportions

Holmes Semken, April 28, 2012

 

Mammoth Moments 1- December 16, 2011, Initial Site Visit

Tiffany Adrain, Art Bettis, Holmes Semken, all of the Department of Geoscience and David Brenzel of the Indian Creek Nature Center, Marion met the landowner at 3:00 PM on a clear Friday afternoon to examine the mammoth specimens that the landowner had collected, visit the locality and discuss the feasibility of the University of Iowa excavating the Mahaska County Mammoth Site. The meeting went well and all parties agreed that the site potentially is an outstanding scientific resource. We agreed to help excavate the mammoth and preserve all of the scientific information that could be extracted from the bone-bearing matrix (plant macrofossils, mollusks, chemistry) at the University of Iowa. At least one bone is to be donated to serve as a voucher specimen and to provide samples for geochemical analysis. We also agreed that the first step to careful excavation was to core the site to get a complete stratigraphic section. Art collected a grab sample of the matrix to test for plant macrofossils and other paleoecological indicators that may be present. A tree branch was collected as a potential source for a radiocarbon date. We looked at the landowner’s artifact collection as well as about 20 skeletal elements that he had excavated to date. The bones ranged in size from a femur to terminal phalanges. Thus, it is clear that the skeleton has not been sorted by fluvial processes. Gnawing by a carnivore on the tibia documented that the mammoth decayed on the surface before burial. Also, the landowner noted that the five cervical vertebrae were the only elements that were articulated.

Holmes A. Semken and David G. Brenzel, April 28, 2012

 

 

 

 

 


Last Updated: January 7, 2013