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Thursday, August 20, 2009

Fossil Plants At Buffalo Canyon, Nevada

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Visit an extraordinarily productive 15-million-year-old fossil locality in Churchill County, Nevada, a number of miles from Fallon--a place that has yielded some 54 species of ancient plants from the Middle Miocene Buffalo Canyon Formation.
Buffalo Canyon lies in the heart of the arid Great Basin physiographic province a number of miles from Fallon, Nevada--home to the Navy's Top Gun fighter pilot program and County Seat of Churchill County. This is a land characterized by three widely distributed botanic species: sagebrush , juniper and pinion pine. But roughly 15.5 million years, during Middle Miocene geologic times, present-day Buffalo Canyon was the site of a large fresh-water lake around which flourished a great variety of plants, including spruce, fir, pine, ash, maple, zelkova, willow and evergreen live oak.
Today, the fossilized remains of these trees and shrubs, along with commercially minable quantities of diatomite can be found in the sedimentary layers deposited in that ancient lake. In addition, several diatomite beds in Buffalo Canyon have been changed to prized opal through the geologic forces of heat and pressure, a geologic process that has created abundant, colorful material for hobby, recreational lapidary use.
All of the fossil plants occur in the diatomite member of the Middle Miocene Buffalo Canyon Formation, a regional badlands-forming deposit originally named by K. L. Barrows in 1971. The flora was most recently analyzed by the late paleobotanist Daniel I. Axelrod in an excellent monograph. Axelrod concluded that the fossil floral association most closely resembles conifer-deciduous forests now living in three widely separated areas of the United States: the Klamath Mountains of northwestern California, the Adirondack Mountains of eastern America, and the Porcupine Mountains of Michigan. Based on the environmental preferences of modern analogs of the fossil flora, precipitation in the ancestral Buffalo Canyon Basin was approximately 35 to 40 inches per year, a figure that contrasts radically with the scant 15 inches delivered there today--and most of that amount is in the form of winter snow. A major difference in the rainfall patterns 15.5 million years ago was that storms dropped significant amounts of precipitation during both the winter and summer months--enough rain during those seasons to account for such sensitive indicators as elm, birch, hickory, black locust and zelkova in the local fossil record.
Temperatures were also apparently much more moderate some 15.5 million years ago. A good indication of this can gained from comparing the average monthly temperatures for the fossil site today with those estimated for the Middle Miocene geologic times. For example, today Buffalo Canyon has an average June-July temperature of some 77 degrees, but the fossil plants there prove that 15 million years ago the average monthly reading for that specific time of season could not have been any higher than 63 degrees. And while today's average January temperatures range downward to a frigid, arctic-style 10 degrees, the mid-Miocene plants demonstrate that 15.5 million years ago a typical January mean would have been a rather chilly, but tolerable 37 degrees.
As far as estimating elevations of the ancestral Buffalo Canyon Basin goes--Axelrod originally determined that the plants preserved in the Middle Miocene Buffalo Canyon Formation accumulated at an elevation of roughly 4,200 feet; today, the fossil site lies at an altitude of 6,060 feet, suggesting, according to Axelrod's analysis, that the region has undergone an uplift of approximately 1,900 feet since Middle Miocene times 15.5 million years ago. But, recently, paleobotanists Howard E. Schorn and the late Jack A. Wolfe (passed away in August, 2005) have demonstrated that the present-day Great Basin region of Nevada stood just as high, if not higher, during Middle Miocene times than it does today--accordingly, they propose that the Buffalo Canyon plants accumulated at an elevation of roughly 9,000 feet, that in fact the entire Miocene Great Basin area has dramatically dropped, collapsed in elevations since 13 million years ago.
Altogether, some 54 species of fossils plants have been secured from the Buffalo Canyon district. The two most conspicuous--and abundant--forms encountered are intact leaves from an evergreen live oak, ,Quercus pollardiana a species that is practically identical to the living maul oak now native to the western foothills of the Sierra Nevada, Cascade Mountains and Coast Ranges of California, and leaves from a birch, Betula thor, whose vegetation is identical to the the modern paper birch. Other less commonly observed specimens include the leafy twigs of cypress, a juniper, in addition to the leaves of cattail, four species of cottonwood, six species of willow, an alder, three additional species of birch, a hornbeam, a hickory, a black walnut, two more species of oak, an elm, a zelkova, two species of holly grape, a water lily, a hydrangea, four species of currant, a Catalina ironwood, three species of bitter cherry, a rose, a mountain ash, a leadplant, a black locust, a tropical cypress, a madrone, a stopper, two species of ash, a sparkleberry, and a snowberry. Also present, but rarely recovered, are the winged flying seeds of two species of fir, one species of larch, three species of spruce, two species of pine, one species of Douglas-fir, one species of hemlock, and five species of maple.
According to paleobotanists Howard E. Schorn (retired Curator of fossil plants at the University California Museum of Paleontology) and Dr. Diane M. Erwin (present Curator of fossil plants at UCMP), credit for discovering the fossil plant-bearing beds at Buffalo Canyon goes to a Mrs. Beulah Buckner, who came across the productive diatomaceous beds during a rockhounding excursion in either the 1940s or very early 1950s. After she eventually directed writer Harold O. Weight and his wife Lucile to the locality, Mr. Weight wrote up an article on the subject of fossil plants in Buffalo Canyon for a noted national publication, in which he named one of the primary fossil-bearing sites Fossil Leaf Hill.
The most efficient way to locate fossil plants here is to split the soft shales along their natural bedding planes. Use the pick end of a geology rock hammer or a broad putty knife to split the poorly indurated, often crumbly sedimentary material. If you should happen to accidentally fracture a fossil specimen, use Duco Cement or some other fast-drying, reliable glue to mend the break. But try to be especially careful not to crack the fossils. Attempting to glue pieces of diatomaceous shale back together is usually a messy, delicate chore. Several coats of glue applied along the fractured surfaces may be required to get the job done, since the porous, powdery rocks often soak up glue like the proverbial sponge.
Not every sedimentary rock layer in the Buffalo Canyon area is fossiliferous--as a matter of fact there appear to be many more barren horizons than plant-bearing ones. But, generally speaking, if you can find the fine-grained, whitish diatomaceous shales that outcrop in proximity to narrow beds of blue-gray volcanic ash, you're chances of finding superior fossil plant specimens will increased dramatically. The "paper shales" observed in parts of the section closely resemble the plant and insect-bearing shales exposed in the Middle Miocene Savage Canyon Formation, Nevada, and Florissant, Colorado--noted insect-yielding deposits of world-wide renown--although I've yet to locate anything significant in the Buffalo Canyon sediments, save for a few poorly preserved leaf fragments. Still, those paper shales may well be worth some special explorations. Excellent specimens could yet show up in them, due to the fact that they lie in such close stratigraphic proximity to the plant-bearing beds higher in the geologic section. Adding to the paper shales' potential interest is the fact that, recently, a graduate student on a field trip to Buffalo Canyon uncovered an exquisitely preserved dragonfly wing--the very first fossil insect reported from the Middle Miocene Buffalo Canyon Formation.
The shales in the Buffalo Canyon Formation grade upward into geologically younger tan to gray clays and sandstones bearing five distinct beds of lignite, a brownish-black coal whose alteration of the original vegetal matter has proceeded farther than in peat but no so far as in subbituminous coal. All five layers of the lignite have been analyzed for possible uranium content, but only two of the beds show any potential economic interest, averaging 0.052 to 0.1 percent uranium. The ashy-gray mudstones in this part of the geologic section frequently yield abundant remains of reeds from a species of cattail, a scouring rush.
Taken together as evidence, the lignites and fossil cattails indicate ponded, swampy conditions during deposition of the younger phases of the Middle Miocene Buffalo Canyon Formation. The regularly bedded diatomaceous shales lower in the section--rocks which represent the older periods of deposition--were likely laid down in a large lake whose shoreline supported a dense growth of deciduous hardwood trees and shrubs such as maple, birch, ash, cottonwood, willow, serviceberry, hawthorn, Oregon grape, bitter cherry, currant, rose and sparkleberry. Slightly higher slopes bordering the basin of deposition were covered by a rich mixed conifer forest of fir, larch, spruce, cypress, hemlock, maple, alder, birch, black locust, elm, zelkova, serviceberry, hawthorn, Oregon grape, bitter cherry, and mountain ash. On the more exposed, drier south and west-facing hillsides the mesic vegetation graded into an evergreen woodland consisting of madrone, mountain mahogany, cypress, stopper, juniper, catalina ironwood and evergreen live oak.
During my last extended exploration of the Buffalo Canyon Flora, I spent a couple of productive days opening a modest-sized fossil quarry. The digging was good. Among my keepers were several nice birch leaves, winged spruce seeds, a few relatively rare Zelkova leaves and many nice evergreen live oak leaves. A few years later I made a brief stopover at Buffalo Canyon to check out my quarry, which had lain dormant all that time. Unfortunately, I found it had been obliterated by heavy rains. All that was left to mark the site of my past digs were several large slabs of shale I remember having yanked out while attempting to expose a particularly fossiliferous layer upon which were plastered some fine specimens of oak leaves. The slabs of shale had been washed way down slope into a newly formed gully far below where I had dug--the result of intense, short-lived rampaging runoff that had taken advantage of the softer sedimentary rocks there, cutting into them with potent ease: acts of natural erosive power on full display here. I spent a couple of hours digging in the same general area as my original quarry and was pleased to learn that the fossil plants were still "alive and well;" they could still be found there, much to my delight.
It should be pointed out, perhaps, that I recently donated practically all of my fossil plants from the Buffalo Canyon district to the archival paleobotanical collections at the University California Museum of Paleontology. As a general rule, all particularly well-preserved plant remains collected from the Middle Miocene Buffalo Canyon Formation should be brought the attention of a professional paleobotanist; who knows, perhaps you might have uncovered a species that is new to science?
All of the collecting sites in Buffalo Canyon are presently accessible: as far as I am aware, there are no collecting restrictions, save the common-sense courtesy all the conscientious fossil hunters abide by: always obtain permission from the owners before collecting on private property. Of course, should commercial collecting parties begin to raid and desecrate the fossil plant localities, the Bureau of Land Management will most certainly close the Buffalo Canyon district to all but professional paleontologists.
An excellent reference is a very informative and well-written guidebook by Howard E. Schorn and Dr. Diane M. Erwin, A Field Trip Guidebook To The Buffalo Canyon Fossil Plant Locality, 10 May 1997, published by The Nevada Paleontological Association in conjunction with the Carson City District Bureau of Land Management. For some additional images of fossil plants from the Buffalo Canyon district, check out a web page called, Leaf Fossil Photos-Cenozoic.
A field trip to Buffalo Canyon, Nevada, will provide visitors with something out of the ordinary: a chance to collect a large selection of middle Miocene plant remains, plus an abundance of very colorful specimens of opal, as well. As you dig into the fossiliferous diatomaceous shales of the Middle Miocene Buffalo Canyon Formation, you will bring fossil leaves and winged seeds to their first light of day in some 15 million years, species which tell of a time when the plant life in this part of arid west-central Nevada resembled the modern-day Klamath Mountains of northwestn California and the humid, moist forests of the Adirondack and Porcupine Mountains of the northeastern United States.
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