Sunday, April 11, 2021

Winter Whale Excavation, part 3: making, flipping, and moving some uncomfortably large jackets

See Part 1 here.

See Part 2 here.

See Part 4 here.

Day Four – finally some real progress

We took over a week off this time and returned with a larger crew, with the capability of flipping the block over. The normal museum crew consisting of myself, Sarah, our curator Scott, and preparator Shelley had come out, joined by Ashby Gale Schuyler and Josh Basak also joined us – they, and Mark Bunce, had indicated they could use a reciprocating saw to help speed up the excavation. I was skeptical of anything battery powered; my own battery powered drill conks out after about an hour of use, after all. I shelved it for the time being – besides, the priority was to dig the trench deeper, and then we could talk about power tools. We spent a couple of hours deepening the trenches – using the estwing ‘super pick’ to remove large blocks of limestone about 3-4 lbs in weight, and then someone on standby with a shovel would remove them while the picker took a breather for a minute – and then repeat. An issue we were quickly finding to be a problem was drainage: the upper 2-4” of the ramp was lose mud rather than bedrock. Because the bedrock was impermeable, the water would flow at the bottom of this loose mud layer rather than on top. Further complicating this was that this was continuously trickling into the trenches we were digging. On the second day, we had dug a trench around the entire pit, thinking that if we dug down deep enough we could channel all the water in a circle around the pit. It definitely helped – the pit didn’t fill up enough – but it took a good half hour of picking to make that trench. And, after another hour, our trenches began to fill again – albeit at a slower rate. This time, we decided to systematically excavate the trenches so that water would flow downhill rather than pool up in the trench. I also spent the first hour undercutting and popping out Rich’s two jackets, which came out without incident.

Back to work on the blocks: our trenches are approaching the lower limit of the bones, which would mark a turning point in the excavation. From left to right: Sarah Boessenecker, Scott Persons, Shelley Copeland, I'm at the bottom in blue hardhat, and Josh Basak's arm off to the right. Below Shelley are "Rich's lumps", which we removed within an hour of taking this photo.

The second largest block (housing mostly cervical and thoracic vertebrae, and ribs) after flipping - being trimmed by Curator Scott Persons. A major gamble here was how many or how few bones were in the trench between these two blocks: fortunately when it flipped over all we could see were a couple of ribs in the fracture.

This gorgeous tooth of the Eocene mako shark Isurus praecursor was found sticking out of the limestone on the underside of the second largest block! I tapped it out with a chisel.

Scott (right) and I (left) continuing work on the two largest jackets. Note how much deeper the trench is compared to the first photo in this post above.

By about 1pm, we had come close enough on the second largest block to undercut it. We began undercutting with chisels, and then Josh offered to use the saw – I was skeptical until I saw how quickly it cut through the limestone. After some undercutting, we put on one more rim of plaster to get a skirt under the undercut parts of the block – this would help prevent cracking of the block during flipping. Once the plaster was cured, Josh began undercutting the secondary block by first using a drill (again, battery operated) with a 12” long, ½” wide masonry bit to drill a series of radial holes underneath the block. These were all in the same plane. Once this was done, he used the hole to allow the Sawzall to be stuck into the rock a few inches, and then connected up the holes into a single long saw cut – remarkable! He then made a second row of drill holes about 2-3” below the first, and repeated the sawing process. A few vertical cuts, and we were able to pick out the horizontal slices of rock. Now that these slabs were removed, the pedestal under the block was only about a foot wide or so – and there was enough space to fit the sawzall in again. One more cut was made, and then a series of large stakes – not suitable for chiseling but fine for cracking pedestals – were hammered in carefully into the pedestal. The jacket was freed relatively quick – it took about three of us to flip it and four to move it up onto the rim of the excavation pit, which now had significantly more free space. This jacket was just shy of 3x4 feet and about 10-12” thick – and probably weighed about 150 to 200 lbs or so. Our difficulty in moving this block was starting to give me serious concerns about the large block. While we were clearly not going to flip the largest block, we were close – and we quickly continued to undercut the big block. By 4:45 or so we had removed three jackets, with the big one remaining. We would need to return, with probably at least two more days budgeted. Rich indicated that he discussed the excavation with the mine, and some of the mining contractors would probably be able to help us remove the big block – thank god, because that behemoth was going to weigh in excess of three or four hundred pounds.

The quarry wall, perhaps 50 yards away from the dig. The resistant rock is mostly the Tupelo Bay Formation; the overlying Parkers Ferry Fm., which is yellowish, has been scraped away and dumped elsewhere - along with the highly fossiliferous (but thin and patchy) Harleyville Formation.

Someone had gone off and found this spot a couple hundred yards away that was a post-Eocene (likely Pleistocene, in my opinion) bonebed above the hard matrix with large concretions and loads of shark teeth - chiefly Carcharocles auriculatus, like this nice specimen. This secondary site would later cause some complications.

The first few hours of Day 5 were spent digging down at a faster rate than we could before, by virtue of being completely below the bone-bearing layer. Dr. Scott Persons clears debris from the downhill trench, and Ashby is starting to uncover Shelley's bone & tooth cluster on the high side.

Sarah supervises while Ashby (left) and Dr. Persons (right) deepen the high side trench and clean up Shelley's bone cluster.

Day Five - flipping the big block

We returned again with a larger crew in order to get the big jacket undercut and flipped. In addition to the crew from the prior week, we now had Alex Mertz and Everett White – two large guys, and Jordy Taylor, a powerlifter – to help us out. In addition, we were also accompanied by two of our colleagues at Charleston Museum: Curator of Natural History Matt Gibson (a paleontologist/paleocetologist by training), and Natural History Collections Manager Jessie Peragine (a botanist by training, but working extensively with fossils by this point). We arrived, headed up the hill, and began trenching to get rid of ponded water, and to allow enough space for the Sawzall to be used. I had serious reservations about the thickness of this jacket – up to 14” in places – and its mobility. We would really need to trim it down after flipping to get it down to a remotely manageable weight. Regardless, we used pick, chisel, and the Sawzall to undercut the big jacket. After about an hour of work, there was perhaps an 18” wide rectangular pedestal underneath the approximately 5x4” jacket. Unbeknownst to us, one side was more extremely undercut than the other. After about only 10 minutes of undercutting with the saw, Josh started using the drill and just making a series of criss-crossed boreholes under the jacket, turning the rock into swiss cheese. Before we could even use a chisel to “pop” the jacket, we noticed the entire jacket was vibrating – this is a milestone in a jacket excavation as it means the block is now more likely to behave as an isolated block than as a pedestal still very much attached to the earth, but that you’ve given a cute plaster ‘hat’. The vibrations also mean you’re very close to being able to crack the block – normally using a series of chisels and a crow bar if necessary. However, Josh’s drill method was enough to do the trick – and owing to the lopsided trenching effort, the block “self-popped” – a perfect horizontal fracture ran right through the base of the pedestal! 

Ashby (top), Schuyler (left), and Josh (right) undercutting the big block, using hammer/chisel, masonry drill, and a sawzall (Josh is using one of two sawzalls, the other is in the foreground).

I even got some practice with the sawzall. What a fantastic tool! I was sold on this thing for the purpose of excavations.

One of our attempts in sliding the jacket up and out of the pit. Those two 2x4s used to be part of Ashby's house, and one of them broke immediately, sending me into a much needed fit of laughter during the most stressful part of an excavation. After about 10-15 minutes of jockeying we managed to slide it, a few inches to a foot at a time, up and out of the pit.

The entire crew tiredly relaxing and celebrating for a few minutes! Back row, from left to right: Matt Gibson, Everett White, Alex Mertz, Ashby Gale, Scott Persons, Schuyler Basak, Josh Basak, Rich Familia; foreground: Jessie Peragine, Mark Bunce, Sarah Boessenecker (on jacket), and yours truly (in recline; I almost passed out and took a nap in the mud).

A few minutes later we gathered up everyone, and got a couple of flat straps ready, and a couple of old wooden 2x4s to use as a ramp – though I had my doubts, as the wood was quite old. The block flipped quite readily, and immediately snapped one of the two 2x4s in half – I was captured on video laughing my ass off at this. After a few more minutes of straining, we managed to slide the jacket up and out of the pit with about six people – not encouraging, given how much effort it took. But, I was confident we could reduce the weight of the block by at least 25%. At this point it was 3:30 and getting cool – and, worse, several folks had to take off early. Schuyler, Josh, and I took turns using the Sawzall – we first trimmed off excess plaster, and then cut a grid into the top of the jacket: each cut was about 3” deep, and 3” apart, making for small cubes of sandy limestone that could easily be chiseled off with 2-3 taps of a hammer. We borrowed the Sawzall from Schuyler when she and Josh left, and we managed to cut in two more grid layers – removing about 8-10” from the jacket, before we found bone – and we knew we had to stop cutting. Within the next hour, as the sun went down, we jacketed the top (formerly the bottom) and completed that jacket. On our next return, we were set up well to remove the three largest blocks with help from the mine.

The mood may have been celebratory, but it was getting late, and we absolutely needed to complete the jacket. That required serious trimming. Make a jacket too much of a thin pancake shape prior to flipping and you risk cracking it: less risky to make it thicker, and just trim the hell out of it after flipping. So, we used the two sawzalls to cut a grid  3" deep into the limestone. Schuyler on the left, myself on the right. This tandem grid cutting ended up working like a very loud and very muddy ballet.

The sawzall takes a lot of effort to cut, and tends to turn your arms to jelly, so it was nice to trade off: Dr. Persons is now sawing, and the rest of us are popping off limestone cubes with hammer and chisel.

More chiseling. Here I am checking the underside for bone. I decided we would keep lowering the grid until we exposed bone: the minimum thickness of the block. We ended up trimming perhaps 8-10 inches of limestone, which is the equivalent volume/weight of the second to largest jacket. Jesus H Christ, the fisheye lens effect is not doing great things for my self esteem here... Me (left), Scott (behind my head), Jessie (green hardhat), and Ashby on right.

We got the top jacket finished just around 5pm - you can see there are no longer any shadows - whereas the prior photo, maybe 20 minutes earlier - was taken during the brief "golden hour". The sun is now behind the trees and it's starting to cool off a bit. Ashby on left, Matt Gibson on right.

All done! That doesn't look so bad, what was all the fuss about? Until you remember those are 2x4s...

We now had a three foot deep (~1 meter) pit the size of a king size mattress. Here is Josh Basak, surveying the crater. Nature abhors a vaccuum, and some blocks that had gotten in the way ended up back in the pit. We'd have to dig these out again upon our return.

No comments: