KNITTING WITH REBAR

Improving the strength and stability of the QVC involves better anchoring of the building’s steel skeleton to the ground. One part of that will involve increasing the size of the concrete footers and adding concrete substructure between the beams. To that end, long boxes of rebar will be set into concrete and serve as attachment points for the steel pillars. However, there are several steps to this seemingly simple action.

First is the rebar itself. What appears at first as a jumbled mass of rods scattered across our parking lot is actually a well organized and thought out erector set.

Each rebar box is made up of many separate rods of different shapes and lengths. And each has ends that are bent to very precise angles that are dictated by that rod’s position in the framework. Reference must be made to some very visually confusing blueprints to determine where each piece of rebar is to be placed.

To form a rigid structure each piece of rebar needs to be tied to others. Welding isn’t necessary because in the end all this will be set in concrete. However, the wiring keeps the pieces in place. Hundreds of ties need to be done for each box.

At first the wiring can be done on saw horses.

But when the longer pieces of rebar are added the whole structure needs to be suspended.

Once a box is completed, work starts on the next. Eventually each will be set in the ground and concrete poured into the trench. We will come to that in a future post.

Photos: National Park Service.

THEN AND NOW (INTERMEZZO)

The QVC project is in a transition phase. The major demolition actions (gutting of building, removal of administrative wing, extraction of the crane, and demolition of the Rotunda) are completed. Presently we are strengthening the steel skeleton of the building with pilings, new footers, etc. This will continue for another month or more. The final phase will involve rebuilding and rehabilitating what will become the new building, installing new museum exhibits, and uncovering and cleaning the quarry face and its dinosaur bones.

So this is probably a good point at which to take a look at how far we have come.  Remember, some of the former building will not be replaced and is now just space!

THE EXHIBIT HALL

 THEN ...

... AND NOW

THE ROTUNDA AND ENTRANCE RAMP

THEN ...

... AND NOW

THE ADMINISTRATIVE WING

THEN ...

... AND NOW

EXHIBIT AREA

THEN ...

... AND NOW

THE PALEONTOLOGY LAB

THEN ...

... AND NOW

THE QUARRY FACE

THEN ...

... AND NOW

THE GRAND VIEW

THEN ...

... AND NOW

Photos: National Park Service

THE TIE THAT BINDS

Well the QVC project is continuing to focus on work that will improve the future stability of the QVC. The forty 60+ foot deep pilings just put in will be the anchors for the repaired building.

Each cement piling has a long, threaded, steel rod in it that will be bolted to the steel framework. The hose next to the threaded pipe was used to inject the cement into the drilling hole.

Steel beams are being placed horizontally at the base of each existing upright. The horizontal and vertical beams will be bolted together and the pilings will be bolted to the horizontal beams. When completed, these two systems will form a much stronger skeleton for the building, one that should resist any movement due to wetting and swelling of the bentonitic mudstone beneath it.

However, the concrete footer beneath each upright beam is only about 3 feet thick, too thin for the new design. So each the footer will need to be removed and a deeper one poured. The horizontal beams already in place will play an important role in how the replacement footers are put it. More on that later.

Photos: NPS

DRILL, BABY, DRILL

It has been a few weeks since I’ve posted anything here but we’ve been finishing up a busy and very productive summer field season in the paleontology operation at Dinosaur. It has been a banner year with a number of very exciting and interesting discoveries. We shall be reporting on some of these at the Society of Vertebrate Paleontology and Geological Society of America meetings this fall. At any rate, here are a few photos from the summer's fieldwork.

My colleague Dr. George Engelmann on the side of a canyon wall examining scorpion trackways in the Early Jurassic Nugget Sandstone.

Yours truly musing over some Brachychirotherium tracks on the underside of an overhang in the Nugget Sandstone.


Since the demolition of the Rotunda, work at the Quarry Visitor has been more mundane and less dramatic, although of no less importance. One of the problems that plagued the old QVC had to do with the foundation and footers for the vertical steel beams that form the skeleton of the building. For some unknown reason, when the building was constructed in 1957 the footers never went deep enough to anchor into hard sandstone. Rather the footers were placed in the bentonitic mudstone, a rock that simply loves water. Once water seeped under the building the bentonite swelled and expanded --- and contracted as it dried out. Thus began the cycle that ultimately doomed the structure.

Part of the fix for the rehabbed QVC involves better anchoring of the steel framework. To that end, pilings are being placed deep enough down to be in hard sandstone layers beneath the building. That required drilling holes down to the right level, sometimes in excess of 60 feet!

Next the holes are lined with steel casing, a threaded steel rod is inserted, and the hole is filled with cement. Ultimately some 40 new pilings will be put in and they will be bolted to the steel infrastructure via the threaded rods. This should strengthen the building and prevent future movement. However, the actual connecting of the pilings to the steel beams will require a few more rather interesting steps which we’ll follow in an upcoming post.

Photos: NPS

THE GREAT OPHIOMORPHA DANCE FLOOR

We’ve looked at various aspects of the relationship between architecture and fossils at Mesa Verde. Here we will discuss the most spectacular example of fossils in the service of architecture in the entire park, yet one most visitors never see – even though it is literally under their noses.

The Fire Temple at Mesa Verde is an unusual cliff structure in that it is a large open plaza that was not a dwelling but may have served as an area for ceremonial dances and other communal activities. The whitewashed back wall bears painted clouds, animals, cactus, and humans. Fire Temple dates from 1250 AD, only a few decades before the Mesa Verde area was completely evacuated by the Ancestral Puebloans.

Fire Temple can best be seen from a stop on the popular Mesa Top auto tour route. However, just a short distance before the Fire Temple stop, is the Sun Point View pullout. From this stop one can get a panoramic view of a dozen cliff dwellings in the alcoves of Cliff and Fewkes Canyons. Of the millions of visitors who have stood here over the decades, few have ever looked down at the rocky surface they were standing on, except maybe to avoid tripping. Too bad for them.

Trace fossils are fossils resulting from organismal activities. Dinosaur footprints are a well known example. However, most trace fossils are formed by marine invertebrates living in and on ocean floor sediments. One of the more common fossil burrows goes by the scientific name Ophiomorpha. These are complicated burrows that run both vertically through sediments and along bedding planes within the sediments. The can run for several meters in length and have a distinctive pustulose or bumpy texture to the burrow walls. In today’s oceans Ophiomorpha-like burrows are made by callianassid shrimp. These shrimp press their own fecal pellets into the walls of the burrow, not only strengthening it, but giving it a distinctive bumpy texture. Given the great similarity between the modern burrows and Ophiomorpha fossils burrows, the inference is that the fossil burrows were also made by shrimp. Not necessarily callianassid shrimp but by shrimp with a similar burrowing lifestyle.

Remember that virtually all of the geology of Mesa Verde is made up of sediments laid down on the floor of Cretaceous seas that flooded the vast interior of North America. The broad and wide surface of the Sun Point View overlook is an exposed sandstone bedding surface of one of those seafloors. And it is rife with Ophiomorpha burrows. The red arrows in the photo above point to the most obvious of those burrows. They have been worn down by erosion, weathering, and foot traffic, but to the trained eye they stand out clearly.

The most obvious Ophiomorpha fossils are those burrows that run parallel to the bedding surface. They appear as tubes or grooves, some with the characteristic bumpy texture.

However, as we noted above, Opihomorpha burrows run both horizontally and vertically. Thus vertical tubes appear as circular structures on the bedding plane. They are about 1.5 -2.0 inches in diameter and show the characteristic texture. This can be best seen on some of the steps leading to the viewing area (see photo above). These circular fossils are sections through vertical parts of the burrow that run down to horizontal burrows still unexposed at a deeper levels.

So while 700+ years ago the Ancestral Puebloans danced their communal ceremonies on the plaza floor of Fire Temple, this rich deposit of extinct Ophiomorpha slept in its ancient sandstone tomb until centuries later it was exposed by modern man to form a place where people could gaze upon the architectural remains of that same extinct Puebloan culture. Ironic.

Photos: Dan Chure

RUMINATIONS ON THE RELATIONSHIP OF ARCHITECTURE AND FOSSILS

Continuing with revelations uncovered during my visit to Mesa Verde, let’s reflect upon the relationship between fossils and architecture. At Dinosaur National Monument architecture has been placed in the service of fossils. The 1957 QVC was designed to enclose and protect the great wall of fossils of the Carnegie Quarry. Extensive walls of glass took advantage of ambient light to illuminate the bones. The V-shaped roof was intended to reflect the topography of hills and gullies in the area and at the quarry site specifically.

Architecture in the service of fossils. The natural order of things it seems to me. However, there are notable exceptions to this world view. In some areas of France farmers have long built walls using fossils of the giant rudist clams, one of the major reef building marine organisms from the time of the dinosaurs. Johnson (2002 fig. 2; http://www2.fiu.edu/~goldberg/coralreefs/Rudist%20Reefs.pdf ) contains a very nice photo of one of these amazing walls of fossils.

The Brazilian towns of Sao Carlos and Araraquara are extensively constructed of stone from quarries in the Lower Cretaceous Botucatu Formation. Literally thousands of fossil vertebrate footprints can be seen in the flagstone sidewalks, as well as walls of buildings, throughout these cities. As recounted by Leonardi et al. (1986), paleontologists have surveyed more than 200 miles of flagstone sidewalks in these towns and collected over 200 slabs of important fossil footprints from them.

Mesa Verde is another place where we can see expressed this most peculiar philosophy of fossils pressed into the service of architecture.

There are some 6000 cultural sites in Mesa Verde, although only about 10% of them are cliff dwellings. Here  we’ll concentrate on the cliff dwellings, where I spent most of my time. Sandstone blocks were gathered  by the Ancestral Pueblo peoples, shaped, and then usually mortared together to form a sturdy structure. Many of the complexes have long retaining walls along part or all of their front edges. On the top stones of these walls can be seen a pleasing diversity of paleontological curiosities, mostly in the form of invertebrate trace fossils. Here are a few examples.

BALCONY HOUSE

Nicely preserved section of an Ophiomorpha burrow. These tubular, pitted burrows were probably made by crustaceans. We will revisit a truly exceptional Mesa Verde Orphiomorpha deposit in a future post.

Also from Balcony House, a slab with abundant impressions of clam shells with ribbed ornamentation.

CLIFF PALACE

Narrow, curved, non-filled burrows in hypo-relief, crossing one another on bedding plane surfaces.

LONG HOUSE

 

Part of the rippled sandstone floor surface riddled with vertical burrows and with short segments of burrows running along bedding surfaces.

STEP HOUSE

This site is a veritable wonderland of Mesozoic marine trace fossils. Here is an Ophiomorpha burrow, about a meter in length, branching and cutting across bedding.

Two burrows in retaining wall. One is vertical, in hyporelief, about one-half inch in diameter. The other is an infilled non-meniscate burrow running diagnonally across bedding.

This is a very peculiar trace, or possibly multiple traces. In the center is a sinuous infilled burrow exposed in hyper-relief. This sinuous trace appears to be within a larger elongate burrow that may branch or be crossed by similar burrows. Maybe this is an oddly preserved Ophiomorpha.

SPRUCE TREE HOUSE

A sandstone block showing cross sections and natural external molds and infillings of various marine molluscs, mostly bivalves. The block is part of a retaining wall along the trail up from Spruce Tree House, near the bottom of the trail.

SUN POINT VIEW

Long, straight and gently curved, in-filled non-meniscate invertebrate burrows running along bedding planes. The burrows are exposed in hyper-relief on a sandstone block (red arrow) along the paved path leading to the viewpoint.

SEDIMENTARY STRUCTURES

In addition to fossils, sedimentary structures have also been pressed into service. Most notable of these are ripple marks that formed on the shallow Cretaceous ocean floors.

Here is a rippled slab used as the lentel of a doorway in a three story structure in Cliff Palace. It is situated such that the ripples are facing down in towards the doorway and facing whomever passes beneath it.

Sometimes these ancient rippled sea beds form large parts of the living floors and plazas of the dwellings. Here we can see ripples on the floor of the communal area of Long House. Similar extensive rippled surfaces can be seen on the floor of the southern part of Balcony House.

Photos: Dan Chure

Johnson, C. 2002. The rise and fall of rudist reefs. American Scientist 90(2):148-153 (freely available at http://www2.fiu.edu/~goldberg/coralreefs/Rudist%20Reefs.pdf)

Leonardi, G. and Sarjeant, W.A.S. 1986. Footprints representing a new Mesozoic vertebrate fauna from Brazil. Modern Geology 10: 73-84.