I have worked in Alaska for several decades and have excavated more than a thousand fossils. Often I have responded to calls about discoveries that sounded exciting but that turned out to be an isolated tusk protruding from a cliff or part of a bison skull among the gravels. In fact, these fossil finds are usually interesting and informative. But Mr. Roman’s find was a first for both of us. He had found a true mummy, and it was a rare event.
From the time of the Alaskan Gold Rush to the late 1950s, thousands of gold miners laboriously washed away acres of silty overburden to gain access to gold-bearing rocks. Several frozen mummies of large mammals had been found earlier in this century, but not many. In recent decades, since the biggest of the gold mining operations had shut down, nothing had been found of much importance, even though there are many small placer mines like the one Walter Roman operates with his wife, Ruth, and son, Ron. Pearl Creek, where the bison was found, is a tributary (fig. 2.3) of the Chatanika River. Latitude and longitude are 65° 59’ N and 47° 19’ W.
Like all good things, the frozen bison was a mixed blessing. It certainly caught me at an awkward time. I was getting ready to leave for a year’s sabbatical in Europe, and other constraints made the time seem terribly short. Roman was near the end of his summer cleanup, and he needed to finish sluicing before water ran out or froze up. Frozen silt surrounding the bison was in the way, but Roman was able to wash out around the bison and gave us a few weeks’ grace to excavate the mummy The university was not in session, and volunteer help was difficult to find because of the economic boom created by the Alaska pipeline. I finally enlisted my wife and son as assistants. We spent the long midsummer evenings out at the mine, screening silt from the daily thaw zone (fig. 2.4).
Fig. 2.1. Walter Roman, the gold miner who found Blue Babe, standing next to one of his giant “monitors.” The powerful jet of water helps to thaw and wash the silt. Many acres of frozen ground must be stripped away in his manner to reach gold-bearing gravels.
Fig. 2.2. Blue Babe emerging from the muck.
Fig. 2.3. Schematic map of bison site. Blue Babe was found north of Fairbanks, Alaska, in the uplands between two major interior Alaskan rivers, the Yukon and Tanana. The hills around the Pearl Creek locality rise above the present tree line, but Blue Babe, was found well below this tree line.
The walls of frozen ground cooled the air, and it settled to a cold layer. Approaching the mine was like walking from a warm July evening into autumn. We had to take jackets, boots, and rain gear even on the brightest days. Shedding, thawed ground plipped and plopped from the overhanging walls of muck. A rich, pungent rottenness, like nothing else I have smelled, filled the air. It was a rottenness aged for millennia in the frost—not a stench, but a sweet, intense tang. We worked in a canyon of ice-cold, blue-black mud, and the water used to wash away the silt was a mud-laden stream at our boots (fig. 2.5).
Fig. 2.4. Collecting thawed silt. After getting photographs and maps of the exposure, we started to wet screen the silt around Blue Babe which had already thawed and collapsed. Here, Mary Lee, my wife and emergency assistant, collects mud to be screened back at the lab.
Fig. 2.5. Walter Roman’s mine. A photo of the Pearl Creek mine and its exposures shows the scene on a gray day. Blue Babe was found to the right of the monitor.
We had to plan fast. Mud around the bison was melting inexorably, and the miner’s big water jet was waiting. First, in a field notebook I tried to record every bit of stratigraphic information. It changed daily. All the silt around the bison had to be washed through a small mesh screen. Soon we realized we could save time by collecting silt now and washing later. We saved every shred of material, but that meant arranging freezer space. And of course we had to plan for enough freezer space to accommodate the mummy once it was excavated. At the same time, I was trying to sort out what to do with the mummy while I was on sabbatical.
Mr. Roman and the owner of the ground from whom he had leased the mine, Alaska Gold Co. (Dan Eagan, president), were willing to donate the bison to the university. When part of the bison began tearing loose from the rest still solidly frozen in the bank, I realized I had to get the exposed portion back to the university and into the freezer. But the museum director was reluctant to sign the donation form because the miner stipulated that the mummy always be displayed. It was an impasse, and I was stuck in the middle of it with the thawing bison. Finally, a solution occurred to me: the biology department could promise to display the bison if the museum did not always want to. The museum director signed. That same evening the legs and torso of the bison came loose from the bank, and we brought it to the freezer at the Institute of Arctic Biology.
A local newspaper reporter had got wind of the find and aggressively sought information. Roman, however, had stipulated that I release nothing to the press because his mining operation was about to start sluicing gold—an understandably delicate time in gold mining—and he did not want a lot of strangers walking by the sluice boxes. Again I was in the middle. I tried explaining the situation to the reporter, but he only became more angry, saying the public had a right to the information. The very night the head of the mummy was freed, the reporter found out via Mr. Roman’s wife where the site was located and arrived with his cameras. The photographs of Blue Babe were in the news the same day the bison’s head went into the freezer. Still I needed to record more information about other sediments beyond the spot where the bison lay before they too thawed and were washed downstream. We asked for a little more time, which Roman graciously granted.
Although it was frustrating to lock the mummy in a freezer and fly off for a year, the sabbatical provided essential time and access to information. I needed time before the necropsy to organize questions; before I took it apart, I wanted to be thoroughly alert to clues the mummy might contain. And I needed time to obtain funds to hire assistants. Coincidentally, I had already planned to spend time with Soviet researchers who had worked on similar Siberian frozen mummies. I would also be able to study museum collections of European Mammoth Steppe fossils. These European fossils are similar to many found in Alaska because the continents of North America and Asia were once connected.
The bison mummy and numerous bags and buckets of silt were securely stowed away in a freezer at the university, but that big walkin freezer had broken down in the past. The Institute of Arctic Biology director, John Bligh, suggested a double alarm system and came up with funds for it from the Institute’s budget. It would not be the last time Bligh would come through on the Blue Babe project.
Roman’s find and the rare opportunity he gave us to carefully excavate Blue Babe meant we were able to collect much information that was later pieced into a complete story about the mummy. The necropsy revealed a fascinating scenario of how and in which season the bison died, how the carcass was scavenged, and finally, how it happened to be preserved. Following the necropsy, the mummy was expertly mounted by Eirik Granqvist, then conservator of the Zoological Museum in Helsinki, Finland. Blue Babe is now displayed at the University of Alaska Museum in Fairbanks.
Fig. 2.6. The great Pleistocene bison belt. Fossil remains of Pleistocene bison are concentrated across Eurasia in a wide east-west belt. This is the main axis of the arid Pleistocene Mammoth Steppe. In North America, however, bison remains are concentrated in the rain shadow on a north-south belt. Although bison occurred elsewhere in North America, they were never so abundant as bison in the shortgrass plains east of the Rocky Mountains.
Although bison are not now associated with the far north, that was their prehistoric homeland. Their distribution across northern Eurasia formed a vast bison belt that ran through Alaska and followed the rain shadow of the Rocky Mountains (fig. 2.6). Indeed, bison may not be the only bovine that consistently used these northern arid regions. A species of cattle, the yak (Bos poephagus), ventured into the Asian north on occasion (fig. 2.7). Yak skulls are easily distinguished from bison, but are very similar to cattle. New radiocarbon dates on Alaskan specimens show
that these “yak fossils” are stained skull fragments from cattle that early miners brought to Alaska.
Fig. 2.7. Yak distribution in Beringia. Yak (Bos poephagus) bones are found in late Pleistocene sediments in the far north of eastern Eurasia, indicating a range considerably larger than the present. Yak skull identification is complicated because they are so similar to cattle skulls, but skulls of bison and yak are quite diagnostic. Alaskan “yaks” seem to be miner’s cattle (see text).
The Geological Context of Blue Babe
During the Tertiary the last 65 million years, the landmasses of the eastern and western hemispheres have been periodically connected via Alaska and the Soviet Far East when low sea levels exposed the Bering-Chukchi Platform. This vast area comprised a large and complex biotic province known as Beringia. Some of the richest deposits of Pleistocene fossils in the world occur in these unglaciated northern regions. Fortunately this abundance of fossils occurs at the right location to provide clues about animal and plant movements between hemispheres. Because Eurasia and North America have exchanged faunas and floras across this northern avenue, it is sometimes difficult to categorize Alaska as Eurasian or North American in its biogeographic affinities. But these large expanses of Arctic landscape have been more than a turnstyle or corridor for animals and plants. The region has been home as well as highway sustaining a characteristic fauna and flora (Guthrie and Matthews 1971).
Like most of the Soviet Far East, large expanses of Alaska and the Yukon Territory were not glaciated during the Pleistocene. Because these areas were bounded on several sides by enormous glaciers and glacial outwash streams, today much of Beringia is mantled with a thick deposit of eolian (wind-blown) silt called loess (Péwé 1975a). Loess sediments originated from glacial flow triturating underlying stone into tiny particles. These particles were deposited beyond the glacial terminus by outwash streams. Winds lifted this glacial dust from stream bars and carried it across the landscape, where it slowly accumulated in thick, buff-colored loess deposits (fig. 2.8).
An important aspect of northern loesses for the paleontologist is that when they are washed downslope to valley bottoms, they act as a preserving agent without peer. Although some bones have been preserved in the primary loess, these are rare and lack soft tissues. Frozen mummies and most fossils are found in the reworked silt. Preservation of both fauna and flora is exquisite in the loess that was washed downslope and accumulated in valley bottoms and broad colluvial cones. In such deposits one finds beds of tree roots and stumps, beaver dams and ponds, and countless large mammal bones; many with marrow inside, others with connective tissue, muscle, and skin still attached.
Fig. 2.8. Loess bank at a road cut near Fairbanks. The thick loess which settled in the Fairbanks area during the glacials forms a mantle over bedrock. One interesting feature of these loess deposits is that they stand vertically.
Fig. 2.9. Origins of Yukon-Tanana upland loess. The region where Blue Babe was found has especially thick loess deposits. Although most moisture from the Pacific air mass falls south of the Alaska Range, some is deposited on the north side. In Pleistocene times this moisture nourished great ice fields to the south and fed smaller glaciers that flowed north from the mountains. Glacial trituration grinds rock into sand and even smaller particles of silt. Meltwater carries this glacial flour to river deltas, where wind sorts sand into dunes and blows the silt aloft. Clouds of this dust were carried many miles across the Yukon-Tanana uplands.
The hills around Fairbanks, which these loesses mantle, are composed of a schist bedrock, penetrated by veins of quartz containing minute particles of gold. Prior to the Pleistocene this schist (1) decomposed to form its own thin soil mantle and (2) eroded along upper stream courses as coarse angular gravel. Heavier gold particles were concentrated at the base of these gravels, on top of bedrock in what we now call gold placer deposits.
Had the geological events of the Pleistocene not occurred, these hilly schist uplands would be a rougher landscape, with only thin soils of decomposed bedrock. But large Pleistocene glaciers in the Alaskan Range, 200 km to the south, indirectly altered the uplands in major ways. The northern Pacific air mass which flows into the state from the Gulf of Alaska carries a heavy load of moisture, but successive mountain ranges—the Chugach, Wrangell, Talkeetna, and Alaska ranges—catch most of this moisture (fig. 2.9). Air that reaches interior Alaska creates a dry, continental climate, and that lack of moisture is the reason the interior remained unglaciated during the Pleistocene. Conversely, moisture falling on the high mountain arcs created large glaciers that coalesced into an ice sheet the length of the Alaskan coast. On the north side of the Alaska Range, valley glaciers extended toward Fairbanks. As these flowed northward out of the mountains they carried with them large quantities of rock.
Rapid Pleistocene uplift of the Alaska Range increased the valley slope, which further accelerated aggradation of bedrock by glaciers and stream action. The sculpting of those north-facing drainage basins by glaciers carried large quantities of stone debris toward the Tanana River, which drains the north face of the Alaska Range. Sediments ground into smaller and smaller particles by glacial movement were deposited beyond the glacial terminus. Meltwater rivers carrying this rock powder fanned into broad deltas toward the north, crowding the Tanana River up against the hills near Fairbanks. Cooled, heavy air rolled over the mountains and funneled down valleys, gaining speed as it dropped into the lowlands. It blew sand into dunes and lofted clouds of silt out across the Tanana Valley onto the Tanana Hills (fig. 2.10). Over a million years, this fine rain of dust formed a thick mantle of loess over the hills and valleys. Loess deposits smoothed the landscape into gentle contours. Judging from exposed sections of mining cuts, deposition occurred mainly during the glacials. Spring runoff and rains carried some of this silt downslope—sometimes rapidly, at times slowly, and during interglacials, hardly at all. Silt movement downslope varied with the amount of wind and vegetation cover, and the quantity and intensity of rainfall or snowmelt.
Cycles of silt deposition and stabilization probably occurred throughout the Pleistocene, but episodes of extreme silt erosion stripped loess deposits from valley bottoms as well as hillsides. We find only patchy remnants of the early Pleistocene silts (Péwé 1975a, 1975b; Guthrie 1968). Most valley bottoms are filled only with late Pleistocene sediments overlying gold-bearing gravels.
Except on lower, well-drained south-facing slopes, these loess and reworked loess sediments exist as perennially frozen ground known as permafrost. Only the upper meter or two thaws in summer. The concept of permafrost is simple: the balance of annual heat gained versus heat lost in the soil becomes negative. Microclimatic dynamics of permafrost are complex. Permafrost is affected by a number of interacting variables, including insulation, moisture, degree of slope, and aspect. As my wife likes to picture it, we who live in the far north reside on the warm meringue crust of a Baked Alaska dessert. The cold ice cream is never far underfoot. Like a potted plant sitting on top of the home freezer, things can grow in the summer sun despite the frost just beneath (fig. 2.11).
Fig. 2.10. Dust blowing along the Delta River, Alaska. Pleistocene loess deposits were created by similar but larger-scale processes.
Fig. 2.11. Placer miner’s deep canyons in permafrost. Miners remove the insulating vegetation; then they use flowing water to cut into the frozen silt. Upstream from where Blue Babe was found, one can see the thin “icing” of thawed ground and vegetation and the much thicker layer of frozen “cake” below.
Frozen silt deposits in the Tanana Hills are like an irregular layer-cake, with thin lenses of earlier Pleistocene loess covered by thick layers of the latest Pleistocene. The “cake” part of the sections is the more homogenous glacial windblown silt with few obvious features, while the wetter and warmer interstadial and interglacial periods are usually represented by thinner “icing” layers of fossil soils, often including peat and stumps and roots of woody plants laid down when soils were more stable.
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We live on top of this cake. It is only along stream-cut banks and at mining operations, like the one where Blue Babe was found, that a slice can be studied. These vary considerably with topography, but generally form a repeated pattern (Péwé 1975a, 1975b).
The silts are so organically rich that they are black when wet and give off a thick pungent odor of incompletely composted litter. As they thaw, one is aware of decomposition that was arrested by freezing, thousands or tens of thousands of years ago.
Many of the lowland Pleistocene deposits around Fairbanks contain large ice wedges. As I mentioned in the first chapter, intense winter cooling of the ground causes contraction, producing cracks that penetrate a number of meters deep. Ice wedges are formed when surface meltwater flows into these polygonally patterned ground cracks and then freezes. When this pattern is repeated over thousands of years, gigantic subsurface wedge-shaped ice masses form which warp fossil sediments (Lachenbruch 1962). Ice-wedge development still occurs on the Arctic Coastal Plain, but not in the Fairbanks area. Ice wedges in the sediments around Fairbanks are “fossils,” that is, they developed in the Pleistocene and are now inactive. Thus Pleistocene sediments around Fairbanks not only contain cross sections of interglacial-glacial sedimentary cycles; they also include complex three-dimensional ice-wedge features, which are present at Pearl Creek where Blue Babe was found.
Another feature complicates this normally simple stratigraphy: valley bottoms occasionally shift within the main valley architecture. Pleistocene sediments moving downslope from one side of the valley can push a stream to the opposite side. Continued downcutting of the new stream channel leaves the gravel of the older channel behind on a gravel bench covered with sediment. Such was the case in the locality where Blue Babe was found (fig. 2.12). The stream channel was once near his carcass, but asymmetric movement of silt at right angles to the channel pushed the stream across the valley, leaving Blue Babe on a high bench under a thick deposit of silt.
Frozen Fauna of the Mammoth Steppe: The Story of Blue Babe Page 6