| Harold L. (Hal) Mansfield, Ph.D. | |
| 7366 North County Road 27, Loveland, CO 80538 | |
| Phone: 970.667.3878 | E-mail: hal.mansfield3@gmail.com |
Most of us have "special places," places that evoke especially powerful emotions and memories. A visit to the Bisti/De-Na-Zin Wilderness Area (Bisti, for short), about 40 miles south of Farmington, in New Mexico, USA, is such a place for me. There, centuries of wind and water erosion have opened the "pages" of a history long past.
As I walk from the parking lot into the Bisti, an almost hypnotic state engulfs me because the geologic and paleontology history from the time of the Cretaceous/Tertiary Boundary (75 to 65 million years ago) lies open before me. The present eerie silence of this secluded, mystical place gives no indication of the immense natural powers that formed it. It was a time of great cataclysms and changes. Those events led to the massive die off of many of the living plants and animals of that distant time.
I reflect on the tragedies that human beings are causing to countless species recently made extinct and those swiftly moving toward extinction from our thoughtless misuse of the earth, its resources and its ecologies.
According to Webster's New Twentieth Century Dictionary, Unabridged, Second Edition, 1977, "geology is the science dealing with the structure of the earth's crust and the formation and development of its various layers: it includes the study of individual rock types and early forms of life found as fossils in the rocks. Paleontology is the branch of geology that deals with prehistoric forms of life through the study of plant and animal fossils."
Information gathered and synthesized from both of these sciences is necessary for describing, characterizing and understanding the Bisti/De-Na-Zin Wilderness Area, its long past and its present, stark beauty. The Bisti/De-Na-Zin was created in 1996 when the Bisti and De-Na-Zin Wilderness
Areas were joined, through land acquisitions. The Bisti covered less than 4,000 acres and the De-Na-Zin about 24,000 acres. With the joining of the two through land acquisition additions, the total area is about 45,000 acres.
The old saying that beauty is in the eye of the beholder certainly applies to the Bisti/De-Na-Zin Wilderness Area and the larger, surrounding Chaco Basin. Stark it is. Some would say bland. Those who favor the lushness and greenery of areas that receive high levels of annual rainfall would not look favorably on the dry and forbidding landscapes - the "badlands" look - of the Bisti/De-Na-Zin. But for those who appreciate that which is dry and stark and which was formed - first - from 75 to 65 million years ago, and - second - that which emerged through the powerful processes of erosion over the past few thousand of years, the beauty is "obvious." So is the challenge of studying the past through the records that are there.
The geology of the earth began some 4.5 billion years ago. This immensity of geologic time is divided into ages. Ages are divided into eons. Eons are divided into eras. Eras are divided into periods.
The age covered in this essay is the Geochronologic Age. It covers the last 600 million years. The eon covered is the Phanerozoic Eon. The time that is the focus of attention extends across the boundaries of two eras, which are the last years of the Mesozoic and the early years of the Cenozoic eras. Parts of two periods occur within the time frame covered. These are the Cretaceous (symbolized with the letter K) and the Tertiary (symbolized with the letter T).
In fact, it is the Cretaceous/Tertiary boundary (the K/T boundary) that is the specific focus because it is in that time period, some five million years of geologic and paleontologic time, when the presently exposed layers of the Bisti/De-Na-Zin Wilderness Area were laid down. It is in that time frame that a great upheaval occurred. It is in that time frame that the many of the dinosaurs died off, setting the stage for the evolutionary developments that led to the earth's present biota, including what is often referred to as the Age of Mammals, our present age.
The K/T extinction is one of five great, mass extinctions that are recorded in the geology and paleontology records. The other four occurred millions of years before the K/T extinction. Perhaps, in part because of the human impact on the Earth, a sixth great, mass extinction may - even as I write this - be underway. If so, will there be intelligent life to analyze the record from this period 65 million years from now?
What is certain is that the geology and paleontology history of the earth is a history of change. Some of those changes are relatively slow as measured in geologic time. Some are, however, of relatively short duration - a few million years. And, some of them are times of great geologic upheaval and of mass extinction. It has estimated that 99 per cent of all of the species that ever have lived are now extinct.
It is not known exactly why the K/T boundary extinction occurred. It is not even known, for certain, how long it took the extinction process (or processes) to run its course (their course). What is known, from the records found in places like the Bisti/De-Na-Zin Wilderness Area is that many of plants and animals of that era - including what are today's best-known dinosaurs - became part of "history's past" and that the Age of Mammals was launched.
In science, as in the rest of life, when facts fail to provide a definitive answer, theories come into play. That is the case with the K/T extinction. Three of the most popular theories are: 1) That the extinction may have been caused by climate changes. 2) That a period of massive volcanic eruptions may have been the cause. 3) That a huge "missile" (either a meteorite or a comet) may have struck the earth, causing great clouds of dust and other debris, blanketing much of the earth's atmosphere, reducing the amount of solar energy coming to the Earth and, thusly, leading to dramatic climate changes, changes which created unfavorable circumstances for some forms of life and favorable circumstances for other forms.
It is possible that a complex of causes led to the mass extinction. It is also possible that the process of change - and therefore of extinction - took many years, even though some of the theories listed above suggest that the extinction was quite rapid by geologic standards. Since evidence of previous extinctions exists in the paleontology records, the K/T extinction may have been a "normal" event, extending out from "normal" causes.
For our purposes, the length of time the extinction took is not as important as is an understanding of the conditions and processes that led to the laying down of the geology and paleontology records. To do this, it is necessary to talk about four distinct ecology zones that existed in the place that is now known as the Bisti/De-Na-Zin Wilderness Area (the Bisti, for short).
The Bisti contains four distinct rock formations. Each of these formations is related to one of the four zones mentioned in the previous paragraph. Each formation bears the name of a location where the rocks are well exposed. Lewis Shale, the oldest of the layers, was named after a non-defunct military post. (Fort Lewis College, in Durango, Colorado, was originally located on the site of the old fort.)
Lewis Shale was laid down when the present Bisti area was tiny part of a great, shallow ocean (or, salt sea, if you prefer) covering most of what is now the United States. Plant and animal life teemed in this shallow, fecund ocean. Great rivers flowed into this ocean. These rivers deposited masses of silt, rock, plant and animal detritus. In addition, layers of ocean dwelling plant and animal remains sank to the bottom of the ocean. As plants and animals, or their partial remains, were covered by layers of mud, the stage was set for geologic processes to turn these into paleontology records, such as fossils and oil and natural gas deposits. And, the geologic processes of time, compaction, heat and chemical alteration turned the mud into the rock termed Lewis Shale.
On the edges of this shallow ocean were large river estuaries. Here, life on a giant scale existed. Huge plants, including massive trees, abounded. So did the dinosaurs, ranging in size from the humongous to the small. As these areas were covered with deposits, they eventually became a formation known as Pictured Cliffs Sandstone, named for some cliffs west of Farmington, New Mexico. These sandstones overlie the Lewis Shale.
Adjacent to the estuaries and higher in elevation were the K/T forests. These forested areas, across 65 million years, became a layer of rocks now known as the Fruitland Formation. This layer is found above the Pictured Cliffs Sandstone and was named for Fruitland, New Mexico, which is a small-town located a few miles west of Farmington, New Mexico. The immense amounts of plant and animal life in this ecological niche provided the "raw material" from which - through geologic time and processes - oil and natural gas was formed. Most of the carboniferous deposits in this part of New Mexico are found in the Fruitland Formation rocks.
During the K/T period, there was a fourth ecological area that was relatively "high and dry." The vegetation was sparse, compared with the other three zones. This zone had fewer animals and animal species, also. As this area was covered over and as the geologic processes unfolded, the formative material was turned into Kirtland Shale, the uppermost formation found in the Bisti.
In summary, there are four distinctive formations in the Bisti: Lewis Shale, typically, is found at the deepest level. Above that is the Pictured Cliffs Sandstone formation. Next, is the Fruitland Formation. And, above that is the Kirtland Shale formation.
The actual picture is somewhat different than the simplistic narrative just presented. Through the formation years - 65 to 70 million years ago - there were many times of chaotic change. What this means is that the ocean regressed and expanded. Local climates underwent dramatic changes. Habitants expanded, contracted and otherwise changed. So, the laying of the four formations was neither uniform nor orderly. In addition, through the 65 million years, there were subsequent times of massive upheavals. While the formations are distinctive, as to type, they are not uniform in the order of Lewis Shale, Pictured Cliffs Sandstone, Fruitland Formation and Kirtland Shale, even though that is the general, overall pattern.
The dominant colors of the Bisti include off-whites, tans, light yellows, grays, muted browns, reds and blacks. The blacks are associated with coal deposits. The reds are associated with carboniferous deposits that were super heated, while covered. The other colors are mixed throughout the Bisti in the four rock formations.
The K/T boundary time was a time when the dominant life form in the sea was giant marine lizards. On the land, the dominant life form - that life form that still excites enormous interest in fact and fiction - was the dinosaurs. The K/T boundary time was characterized by high ocean levels. As mentioned, most of what is now the United States was an ocean. The climate, generally, was a hot, humid "greenhouse" climate, again on a global scale. The greenhouse climate fostered the growth of enormous, by today's standards, life forms. (However, it must be said that today's largest whales are larger than the largest known dinosaur.)
As mentioned, some of the plant and animal material from these five million years became oil and natural gas deposits across the millions of years and through the action of time, compaction, heat and chemical alteration. More importantly, some of the plant and animal remains became fossilized. As the four basic formations resurfaced through the process of erosion, the fossil records emerged.
For purposes of this essay, three "levels" of sea life - as seen in the fossil records - are of interest:
1) Invertebrate animals, such as worms, clams and snails lived in the mud at the ocean's bottom. These invertebrates fed on the rich organic matter found in the mud. As they died (or were killed) some of them were buried, encased and preserved.
2) Above the mud, swam ammonoid cephalopods (extinct species related to presently living octopi and squid). These were the most numerous species in the K/T boundary oceans. Also present were a great variety of fishes, including sharks.
3) At the top of the food chain in this teeming ocean of life were giant lizards. The lizards, mosasaurs by name, are the extinct "ancestors" of the monitor lizards of today. The highest profile monitor lizard is the Komodo dragon, a large, fearsome lizard found primarily on the Island of Komodo, in Indonesia. However, there are many living species of monitor lizards in Africa, southern Asia and Australia. Those of which I am aware live primarily on land.
The mosasaurs were huge. Some of the fossilized skeletons of these fearsome denizens of the ancient oceans measure fort feet in length. The skeletal remains suggest that they were capable of swimming at high speeds and with startling maneuverability. Apparently, they were voracious eaters, with an omnivorous diet. The examination of mosasaur stomachs in the fossil records provides ample evidence of the range of the mosasaur's diet.
Although the surface of the shallow K/T boundary ocean was generally calm, there were times of cataclysms. The massive rainstorms generated by the monsoons of that time and climate flooded rivers with incredible amounts of mud and debris. As dead plants and animals were buried in the mud of the ocean bottom and in sand bars and bogs, it is remarkable that any fossil records were laid down.
There were periods when the mud and sand were churned causing the break up of both the softer organic matter and, also, the tougher body parts. Only a tiny fraction of the total, potential record remained intact. And, of that tiny record, only an almost infinitely small sample has been found or extracted.
As our focus shifts away from the ocean and to the estuaries and onto the land surfaces, a large array of plant and animal life is revealed in the fossil records. These include everything from giant dinosaurs to the tiny "ancestors" of mammals! True, the many dinosaur species were the dominant and most visible life forms. And, in some sense, they were most important. Dinosaur fossils have been found ranging from those that were amphibious herbivores of the marshes through those with horns and armor plates, all the way to Tyrannosaurus Rex. There were also bird-like dinosaurs, the "ancestors" of today's birds. There were small carnivorous dinosaurs. However, even though dinosaurs "ruled," there were many species (turtles, snakes, lizards and the tiny precursors of today's dominant species, the mammals).
However quickly or slowly it happened, the Age of the Dinosaurs passed. That is not to say that all dinosaurs died out. That is a common, mistaken belief. Birds, among other present-day species, are "descended" from the dinosaurs.
Over the 65 million years, the ocean receded for a final time and tremendous volcanic eruptions occurred. The volcanic eruptions covered the four K/T boundary deposits with deep ash and other volcanic eruptive materials. As the early, K/T boundary deposits were covered, the processes of fossilization occurred. In addition, continental shelves collided pushing up vast mountain chains. Many climate changes occurred, including several Ice Ages and several periods when greenhouse-like times reappeared.
In the area that is now the Bisti/De-Na-Zin, erosion of the millions of years of cover began. Eventually, the four dominant rock formations of the Bisti "emerged" through the erosion processes. And, along with the rock formations - imbedded in them, in fact - the fossil records became evident.
The common way to enter the Bisti is at the parking lot near the southwest corner. After signing in, the visitor has many choices to make. Typically, I walk across a relatively flat drainage plain toward the low hills on the southern boundary of the area. By skirting these low hills, it is possible to hike with ease into the heart of the original Bisti part of the area.
The dominant colors of the Bisti are muted tans and grays. In addition to these colors are some very light, unsaturated yellows and some fairly bright reds. These reds occur where carboniferous deposits experienced high temperatures. Finally, there are the black colors of the carboniferous deposits.
About a mile into the area, the area takes on a true "badlands" look. Here there are many different shapes, including the "mushroom-like" hoodoos, grottos, domes and other "weird" and unusual shapes and configurations. It is to these badland areas that most visitors are attracted.
Along the way, the visitor encounters petrified wood. The astute and knowledgeable visitor may even find a fossilized shark's tooth or a range of other fossil records.
The dominant vegetation of the Bisti is rabbit bush. However, there is comparatively little vegetation of any sort. The visitor will occasionally see birds, small lizards, butterflies and small insects. Anthills are a common sight. But both plant and animal life is sparse-to-rare.
It is the rich record to be found in the geology and the paleontology of the Bisti that attracts the professionals. It is the "moon-like surface" and "badlands" character of the Bisti that attracts and fascinates both amateur and casual visitors. For me, visits to the Bisti never fail to trigger those strong emotions, memories and thoughts mentioned in the opening paragraphs of this essay.
Author note: Harold L. "Hal" Mansfield retired from Fort Lewis College, in Durango, CO in 1993, where he was professor of psychology and chair. A Colorado native, he has lived in Green Valley only since September of 2005. One of his retirement regimens is freelance writing.