RACHEL C. BENTON (1), EMMETT EVANOFF (2), CARRIE L. HERBEL (3), AND DENNIS O. TERRY, JR.(4)
(1)Badlands National Park, Interior, SD 57750
(2)University of Colorado Museum, Boulder, CO 80309
(3)South Dakota School of Mines & Technology, Rapid City, SD 57701
(4)Temple University, Philadelphia, PA 19122
AbstractThrough a three-year grant with the Natural Resources Preservation Program (NRPP), Badlands National Park has begun documenting the extent and location of its fossil resources. Due to the great size of the park and the extent of exposed bedrock, the scope of this project is limited to the lowest horizons within the Scenic Member of the Brule Formation. To date, our team has documented the distribution, composition, stratigraphic position, and depositional setting of numerous fossil sites within three designated areas, covering 3.5 map sections. In the coming years, this survey will provide the basis for an effective paleontological inventory and monitoring program and a predictive model for locating other fossil accumulations within the lower Scenic Member of the Brule Formation. After one summer of fieldwork, 351 new paleontological sites have been documented and recorded into the Park's the Geographic Information System (GIS) database. Many of these sites consist of bone horizons with hundreds of specimens; however, only 231 specimens were collected. The criteria used to collect specmimens included; threats from erosion or poaching and the overall scientific value of the fossil. Six stratigraphic marker beds occur over 30 km2 of the Scenic Member outcrop. The marker beds provide stratigraphic control for locating fossil localities within 1 meter vertical resolution. A broad spectrum of paleosol development was also noted during the sedimentological survey and it appears that the Scenic Member was deposited on an irregular erosional surface, consisting of several topographic highs and lows. Sedimentological interpretations of particular marker beds and bone horizons will serve as valuable tools for interpreting ancient climates and regional basin evolution.
Paleontological resources were a major reason for originally establishing Badlands National Monument in 1939, for adding the 133,000 acre Stronghold District in 1976, and obtaining National Park status in 1978. Thousands of specimens have been legitimately collected and are housed in museums and universities throughout the world. These fossils have provided valuable information in the understanding of mammalian evolution and diversity, paleoecology and paleoclimates.
For the first time in its history, Badlands National Park has begun the process of documenting the extent and location of its fossil resources. The goals of this project include a paleontological site inventory including the identification and taphonomic analysis of each paleontological specimen found. It also includes the collection of baseline data including stratigraphic position, depositional environment and degree of preservation. This survey is providing the basis for an effective paleontological inventory and monitoring program, as well as a predictive tool for discovering additional fossil accumulations within the lower Scenic Member of the Brule Formation. All locality information has been recorded into the Park's GIS paleontological data layer, which is a database that contains many of the known park paleontological sites. Detailed fossil locality information is omitted in this manuscript to protect paleontological resources at Badlands National Park.
The NRPP bone bed mapping project has provided insight into many aspects of the geology and paleontology of the lower Scenic Member in Badlands National Park. Foremost, we have gained a better understanding of the distribution and condition of fossil resources in one part of the park. From a geologic standpoint, we have gained information on the geologic history, depositional environments, and paleoclimatic conditions at the time these bone beds were formed. The three field teams covered 3.5 map sections within Conata and Tyree Basins and far exceeded their expectations in the number of sites documented, scientifically significant specimens collected and general geologic interpretations made (Fig. 1).
The project has been limited in scope stratigraphically, to gain a better understanding of the depositional setting within the lower Scenic Member of the Brule Formation. Future surveys will be designed to examine other stratigraphic units under a similar approach. The bone beds survey has already generated interest in two additional Masters projects within the lower Scenic Member.
PRIOR RESEARCH IN THE PARK
The long history of research in the White River Badlands has contributed greatly to the science of vertebrate paleontology in North America, beginning with the discovery and description of a brontothere mandible in 1846 by, St.Louis physician, Dr. Hiram Prout. In 1847, Dr. Joseph Leidy published a description of a small fossil camel collected from the Badlands. Both specimens were collected by Alexander Culbertson of the American Fur Company on his journey between Ft. Pierre and Ft. Laramie. As explorations continued and collections were made of White River fossils, Joseph Leidy would describe the great majority of new taxa that were discovered. Since then, thousands of fossils have been collected and have served to define this geologic interval.
|Figure 1. Map of Badlands National Park showing the location of the study area (arrow).|
|Figure 2. Generalized stratigraphic column of the White River Group in Badlands National Park. The column is not to scale, but is drawn instead to show the regional paleogeomorphic relationships of various units. Abbreviations as follows: AM, CJM, and PPM = the Ahearn, Crazy Johnson, and Peanut Peak Members of the Chadron Formation, respectively. BBLB = Bloom Basin Limestone Beds, CPF = Chamberlain Pass Formation, LNZ = Lower Nodular Zone, MU = marker unit, RF = Rockyford Ash, UNZ = Upper Nodular Zone.|
Stratigraphic nomenclature for White River sediments has evolved greatly over the past century of study (Fig. 2). Darton (1899) formally named the Brule Formation after "a series of pink clays" that lie above the Chadron Formation. Bump (1956) divided the Brule Formation into the Scenic Member and the Poleslide Member. The Scenic Member extends between the top of the Chadron Formation and the top of the "upper nodular zone;" and the Poleslide Member which includes the siltstone beds above the Scenic Member and below the Rockyford Ash Member. The "upper nodular zone" was originally described by Osborn and Matthew (1909) and Wanless (1923) as the "upper nodular layer". The development of nomenclature of the White River Group is described in detail by Harksen and Macdonald (1969a, 1969b), Emry and others (1987) and Terry and others (1995).
Several depositional models have been proposed for the origin of the White River deposits. Hayden interpreted the widespread uniform layering of White River Group sediments as the result of lucustrine deposition following the withdrawal of the Cretaceous seas (Tedford, 1970). Based on his studies in Colorado, Matthew (1901) proposed that the White River deposits were mostly fluvial and eolian loess "formed on grass covered prairies." Matthew noted that the White River contained mostly terrestrial faunas and very few aquatic animals within thick siltstone deposits.
Clark and others, (1967) examined the relationship between structural and geomorphic controls on sedimentation in the Badlands. They developed several models for various facies packages found within the area. From the early 1930's through the 1960's, Clark developed extensive paleontological collections from the Badlands to assist with paleoenvironmental interpretations. He felt that many of the earlier paleontological collections lacked the necessary stratigraphic and locality data needed to make valid interpretations.
Recent work on paleosols in the White River Deposits has been performed by Retallack (1983), Terry and Evans (1994) and Terry (1998, 2001). Retallack (1983) developed a soil classification scheme for the White River Group and used these for interpreting climate conditions throughout the Eocene and Oligocene. He established his paleosols on the U.S. Department of Agriculture's standard soil mapping unit, the soil series (Retallack, 1983). He described five different paleosol series for the Scenic Member. Retallack's evidence for soil formation included; fossil root traces, fossil burrows, soil horizons, cracking and veining of soil units, soil structures, concentration of calcareous layers and invertebrate remains and burrows. The work of Terry and Evans (1994), described lateral changes in paleosol types within the Chamberlain Pass Formation of Evans and Terry (1994). They concluded that paleosols of the Chamberlain Pass Formation could be divided into proximal and distal floodplain settings, each with distinctive pedological characteristics. Terry (in press) evaluated a series of paleosols across the Eocene/Oligocene boundary in the White River Deposits of NW Nebraska. He found that paleosols record a shift from humid to dryer conditions across the Eocene/Oligocene boundary, and that certain parts of the strata found in Nebraska are not preserved in the Big Badlands of South Dakota.
Kruse (1996, 1997) tested the model proposed by Retallack (1983), that fossils from the Scenic Member accumulate and are preserved on old land surfaces. Kruse proposed an alternative model that the mechanisms responsible for the accumulation of fossils in the Scenic Member in Conata Basin are the product of flood transport and later soil development.
The contact between the Chadron and Brule Formations is marked by a regional unconformity that lasts at least 400,000 years, but maybe as long as 1 My, in duration (Prothero and Whittlesey, 1998). This unconformity produced paleotopography on the underlying Chadron Formation. Once deposition resumed, the Scenic Member of the Brule Formation filled in the uneven ancient land surface. Some parts of the Scenic Member are thicker than others due to the infilling process. We are presently using magnetostratigraphy, to determine the temporal relationships of the subunits of individual bone beds in the Scenic Member above this unconformity.
Many of the fossils from the White River Badlands appear to be concentrated as bone beds within a fairly thin stratigraphic layer within the Scenic Member of the Brule Formation. One of these bone beds, known as the Conata Picnic Area Paleontological Site, or the "Big Pig Dig", was discovered in 1993. The site is a dense accumulation of fossils which differ from the traditional models for bone preservation (i.e. attritional bone accumulations on ancient ground surfaces or fluvial accumulations within ancient channel systems). The bones instead occur as semi-articulated to disarticulated elements which show no preferred orientation (Stevens, 1995; Stevens 1996a, 1996b). The site has moderate diversity with the bones of several types of animals greatly intermixed. Based on the sedimentary analysis completed by Terry (1996a, 1996b) the site is interpreted as a watering hole. These conclusions are based on the relict bedding lamination, the lenticular shape of individual units and the lack of pedogenic features such as root traces, soil structure, soil fabric and geochemical trends within the bone bed. Thousands of fossils have been collected from this site and valuable information on bone preservation and accumulation has also been acquired (Bjork, 1994-1996; Herbel, 1997-1998). The information from the Big Pig Dig is currently being compared with sites of similar origin in Northeastern Colorado. Further surveys have indicated that several other bone beds of similar significance occur in the park but are less completely documented.
Several sites within the Badlands Wilderness Area were originally documented by Clark and others (1967) and later by surveys the South Dakota School of Mines and the Denver Museum of Nature and Science. One of the newest locations is the Brian Maebius bone bed within Tyree Basin. In contrast to the Pig Dig, this site contains a greater diversity of fauna along with trace fossils (coprolites), pollen and fossilized wood (DiBenedetto, 1997, 1998, 2000, DiBenedetto and Wrenn, 2000). Fossils were deposited in discrete pods or surface swales and many individual bones contain gnaw marks from scavenging activity. Paleosols are easily identified at the site as indicated by coprolites, root casts and in situ fossil tree stumps. A detailed analysis of the paleosols is currently underway.
PALEONTOLOGICAL SITE SURVEY
Objectives - The objectives of the paleontological site survey are to document the fossil resources within the confines of the lower Scenic Member of the Brule Formation in select sections of the North Unit of Badlands National Park. The paleontological field team also developed methodologies to be used for future paleontological field documentation. The localities selected for this study are highly fossiliferous and easily accessible from nearby roads and visitor areas. By doing a thorough baseline mapping and fossil survey, the staff at Badlands National Park can identify areas that are threatened now, in the near future, or are potentially stable for many years to come.
This survey will attempt to develop a basic understanding of how these sites fit into the overall geologic time scale and regional depositional models. These sites will also be used as a predictive model when looking for new paleontological sites within the selected study area.
Methods - The paleontological team divided into two or three groups of 2 to 3 individuals each (Fig. 3). One team of two members was in charge of collecting GPS field data. Other teams prospected new areas for vertebrate fossils and documented fossil sites on aerial photographs and within field notebooks. Other information, such as associated geological, stratigraphic and bone surface features, were also noted. Bone horizons, bone beds, and important single fossil specimens were flagged to alert the GPS team. The GPS team would follow the prospecting team(s) and entered locality data in the form of a point, line or polygon within the GPS units. The GPS data will be integrated into a GIS layer and incorporated into the final report to the Park at the end of the three-year project.
After noting position, the fossils were also identified to family or genus as well as element, and examined for taphonomic information (weathering, bone modification, fracture pattern, position within the bone bed, etc.). Additional documentation such as photographs and measurement within the section was also gathered. Specimens of scientific importance were collected. However, collecting was kept to a minimum because of the scope of the project. Each bone locality was plotted on detailed aerial photographs at a scale of 1:2400.
Figure 3A. Joe DiBenedetto and Sarah Black collecting GPS data. 3B. Carrie Herbel, Ellen Stark, and Jerry Mundt reviewing aerial photos.
3C. Partially poached fossil tortoise. 3D. Trench exposing unweathered portions of the lower Scenic Member at the Brian Maebius Site.
Specimens collected - Although the primary goal of the project was not to collect specimens unless scientifically significant, many fossils proved to be so. The 231 specimens that were collected, were threatened by erosion or poaching (well-traveled areas), and were scientifically important (e.g. Agriochoerus jaw). Bone modification by carnivores was noted on several specimens. A small number of skulls were jacketed with plaster bandages. All specimens are currently at the South Dakota School of Mines Museum of Geology's Vertebrate Preparation Laboratory and are being cleaned and stabilized for later analysis.
Number of new sites - Several new fossil sites were discovered within the lower part of the Scenic Member of the Brule Formation. A total of 351 new sites were documented during the first field season. Each plotted fossil site does not signify only one fossil. In many cases, a bone horizon was plotted as a line along the outcrops using the GPS unit. In several others, polygons plotted by the GPS unit encompassed a larger area of fossil accumulations. Several major multi-taxa bone beds were assigned locality names. Of additional interest, turtle fossils occurred in nearly every section surveyed and ranged from complete to partial shells, some of which were highly fractured. Extensive turtle/tortoise horizons could be traced over great distances. Some of these were plotted as a single line in many areas, while others as a single point. Only a few turtle specimens were collected during the first field season. Those not collected were either extremely large and/or highly fractured and were in poor condition.
Only the lowermost portion of the Scenic Member was surveyed in this project. Cursory examination of the upper sections proved that they contain some fossil material; however, the steepness of the upper Scenic outcrops and the need to focus on a discrete section eliminated these areas from the thrust of this study. In addition, the much greater threat of poaching in the lower section of the Scenic increases the necessity of documentation when surveying these sections. The major fossil-bearing units fall below a marker bed (marker unit 1) (Fig. 2) that occurs throughout and between the areas studied by the paleontological survey team. This marker unit is directly above the majority of the fossil-bearing strata and stratigraphically defines the lower Scenic member.
One of the major goals of this project is to provide information to the management team at Badlands National Park on the location of easily accessible fossil resources so that fossil sites within the Park can be protected. The data collected will assist park staff in monitoring sensitive fossil-rich areas and bone bed localities. In addition, the park paleontological staff can address various issues regarding these sites with knowledge garnered from this mapping project. After completing the first year of this 3-year project, results are already visible. GPS data and field notes have already been converted into a GIS layer usable by park staff. New insights into bone bed concentrations are currently being explored in great detail through projects developed by graduate students. These studies may be used as predictors of bone bed occurrences within the lower Scenic Member throughout the park.
Objectives - The purpose of the Stratigraphic Studies portion of the Baseline Mapping of Fossil Bone Beds Project is to recognize the detailed four-dimensional relations of rock units within the Scenic Member of the Brule Formation in the North Unit of Badlands National Park.. Documenting the stratigraphy is essential to understanding the position in space and time of the fossil-rich horizons within the most fossiliferous part of the White River Group. Stratigraphic analysis of the lower part of the Scenic Member compliments the associated paleontological survey and the sedimentology studies. As a result of the current stratigraphic work, the nomenclature of the Brule Formation will require revision. Previous studies based on work in limited areas can be understood in a broader regional framework, and patterns of bone accumulation are better known and may allow for prediction of occurrence in unstudied areas.
Methods - The area of study included the Hay Butte, Deer Haven, Dillon Pass, and northern Conata Basin areas, extending from sec. 2, T. 3 S., R. 16 E. on the southeast end to sec. 28, T. 2 S., R. 15 E on the northwest end. This study area includes the areas studied by the paleontological survey and the exposures between them. By the end of the field season, 6 stratigraphic marker horizons were documented in the Scenic Member, 30 square km of outcrops were mapped, and 20 stratigraphic sections were measured.
Results - Six widespread stratigraphic contacts and marker units occur
in the Scenic Member of the Brule Formation in the Hay Butte to Dillon Pass
area of the Park. They include the Chadron/Brule contact, three widespread mudstone
horizons, the contact between typical Scenic Member mudstone beds and siltstone
beds more typical of the Poleslide Member, and the "upper nodular zone,"
a widespread sequence of sandstone beds with a top contact that forms the traditional
top of the Scenic Member. The stratigraphic position of the scattered fossil
accumulations can be determined by their positions relative to these marker
units, typically to a resolution of less than 1 m.
SUBDIVISIONS OF THE SCENIC MEMBER
The marker units in the Scenic Member provide stratigraphic boundaries for the lower, middle and upper parts of the Scenic Member. The top contact of the Scenic Member is as yet uncertain, but the siltstones and the "upper nodular zone" traditionally included within the Scenic Member should be assigned to the Poleslide Member by lithologic criteria.
The lower Scenic Member is defined as the rocks between the contact with the underlying Chadron Member and the top of the first marker bed , called marker unit 1. Marker unit 1 is a widespread greenish gray noncalcareous mudstone bed containing abundant mudstone and claystone rip-up clasts and root traces, and scattered white limestone stringers. The lower Scenic ranges in thickness between 25 m in the deepest part of paleovalleys cut into the Chadron Formation, to a minimum of 8.7 m along the highest crests of the erosional paleotopography developed on the Chadron Formation. Lower Scenic rocks in these uplands include basal, red to brown clayey mudstone beds weathered to a strong popcorn surface (reflecting a high amount of swelling clays) that grades into tan massive mudstone beds which locally contain abundant bones. Basal clayey mudstones also floor the sequences in lower Scenic paleovalleys, but they are capped by a well-bedded sequence of red mudstone beds, red to gray, typically platy claystone beds, and interbedded thick very light gray sandstone and light brown-gray muddy sandstone beds. A well exposed cross section (Fig. 4) through a lower Scenic paleovalley sequence is seen in the northern Conata Basin between the Pig Dig (NW¼ sec. 34, T. 2 S., R. 16 E.) and the site of Retallack's (1983) measured section (SE¼ sec. 20, T. 2 S., R. 16 E.).
|Figure 4. A series of stratigraphic sections through the lower Scenic Member extending from near the Pig Dig (Karen W. section) to the stratigraphic section described by Retallack (Retallack Amphitheater). What is shown is the thickness variations and depositional features of the lower Scenic as it filled a paleovalley cut into the Chadron Formation. The total length of the cross section is 3.4 km. See Figure 5 for the location of this cross section.|
The middle Scenic is bounded by the top of marker unit 1 and the base of marker unit 3. Marker unit 3 is a very thick sequence of buff brown to green noncalcareous clayey mudstones interbedded with thin white limestone stringers and limestone beds. The base of the first limestone bed marks the top of the middle Scenic. The middle Scenic can be further subdivided into two parts by a mudstone marker bed (marker unit 2). The primary lithologies of the middle Scenic are very light gray very fine to fine sandstone beds interbedded with light brownish gray muddy sandstone beds. Secondary lithologies include gray to red, blocky to platy claystone beds and brown mudstone beds near the top. Marker unit 2 is a thick, brown, noncalcareous mudstone bed with green mottles and numerous claystone rip-up clasts. Thicknesses of the subdivisions of the middle Scenic vary widely. The lower sequence ranges from 8.1 to 17.4 m wiht no regional trends. The thick sandstone beds represent broad channel belf complexes. The claystone and mudstone beds represent overbank deposits.
|Figure 5. West to east cross section showing the distribution of marker beds in the Scenic Member from Sage Creek Pass to Conata Basin. The lithologies of the three most complete sections are shown. In many places the upper Scenic outcrops are unaccessible because of their steepness. The index map shows the locations of these sections (numbered sites) and the locations of the sections of Figure 4 (lettered sites).|
The upper Scenic Member is the sequence from the base of marker unit 3 to the base of the Poleslide Member (Fig. 5). The traditional top contact of the Scenic is the top of the light gray sandstone beds of the "upper nodular zone" (Bump, 1956). However, thick, massive siltstone beds typical of the Poleslide Member occur on average 5.3 m below the base of the "upper nodular zone" in the study area. These siltstones overlie a sequence of buff to tan typically clayey mudstone beds that lie above the uppermost limestone of marker unit 3. A lithologically more consistent boundary between the Scenic and Poleslide members would be the distinct contact between these mudstone and siltstone beds that occurs on average 11.9 m above the base of marker unit 3. This project will resolve this nomenclature problem after more regional stratigraphic studies are completed.
DISTRIBUTION OF FOSSILIFEROUS UNITS
The rich fossil assemblages of the Scenic Member are strongly associated with certain lithologies and stratigraphic units. Most of the rich bone accumulations occur in mudstone beds, either near the base of the Scenic member or directly below the widespread marker units. The most fossiliferous units include the basal brown to red mudstones informally called the "lower red layer" associated with the basal Scenic at the base of the paleovalley fills. The Pig Dig is associated with these "lower red" mudstone beds. Bone is also common in the massive tan mudstone beds of the lower Scenic on top of the Chadron Formation paleotopographic highs. Mudstone beds directly below marker unit 1, especially in the western Hay Butte area, are locally very fossiliferous and include the Brian Maebius site. Mudstones directly below marker units 2 and 3 on the west side of Hay Butte also have locally rich bone accumulations. Bones are almost always abundant in the siltstones just below the "upper nodular zone." The sandstones and claystones in the lower and middle Scenic are not bone rich. Bones can occur in the widespread marker units, but they are typically rare. Thus, the fossil assemblages occur in discrete stratigraphic intervals separated by poorly fossiliferous rocks.
NEW INSIGHTS ON PREVIOUS STUDIES
The regional stratigraphic perspective from this study brings new insight on previous studies of the Scenic Member. A good example is a reevaluation of the significance of the paleosols described by Retallack (1983). Marker unit 1, one of the most widespread units in the region, was considered a paleosol with a limited distribution indicating original wet local environments by Retallack (soil 23, a Gleska clay silty variety). Retallack reports (p. 31-32) that this soil "has been traced as far south as Conata Picnic Ground where it appears to be changing laterally into a Conata Series paleosol in a fossilized catena." He also reports that the Gleska Series soils in the Scenic member are lateral to channel deposits and grade into the weaker Conata Series paleosols which represent flood basin soils. Neither of these are corroborated by this study, for marker unit 1 retains its high clay content and soil features throughout the study area (even by the Conata Picnic Ground), and it is not associated with any channel deposits in the study area. Instead of representing a local environment, marker unit 1 probably reflects a regional change to wetter environments during depositional stability, allowing widespread forests to cover the area. Such changes may reflect long-term paleoclimatic variations (see the discussion below).
Soils in modern settings form from the interactions of five main factors: climate, organisms, relief, parent material, and time. This results in a soil profile that has distinct physical, chemical, and biological characteristics manifested as a vertical sequence of horizons within the profile. Common horizons include the A Horizon, a zone of mineral matter and organics at the top of a soil profile, the B Horizon, a zone of accumulation within the middle of the profile that forms by the downward movement of materials through the profile, and the C Horizon, which represents the least amount of alteration. Modern soils are classified into twelve main categories (soil orders) representing soil formation in humid to arid, and hot to cold environments. These in turn can be subdivided into increasingly more distinct soils representing particular changes in the five factors of soil formation (e.g. drainage, topography, and parent materials). In certain situations, soils can be buried and fossilized in the geologic record. These ancient soils, or paleosols, have preserved within them the clues to their original environment.
Paleosols are very common in ancient fluvial deposits, such as those in Badlands National Park. Since paleosols are the result of ancient soil forming conditions, they can be used to interpret the genesis of fossil bone beds by looking at the position of bones within an individual paleosol profile, as well as assessing their preservational state (degree of weathering, articulation, diversity). Common end-member associations of bones and paleosols in the White River Group include isolated bones at the top of profiles due to attritional accumulation on an ancient landscape, articulated skeletons within the middle of a profile due to catastrophic burial and subsequent pedogenic overprinting, and channel/proximal floodplain deposition of bones as clasts that have been reworked by lateral migration.
Objectives - The sedimentological field team documented the lithologic component of each of the major or informally named paleontological sites found within the Tyree and Conata Basin study areas. Each site was incorporated into the regional geology extending from Conata Basin, across the wilderness area and into Chamberlain Pass. Detailed studies of lithologies associated with the most significant bone accumulations were made by the sedimentological field team to determine depositional and preservational settings. Such features as layer thickness, lateral extent, rock type, bedding features and ancient soil features will be documented from exposed surfaces and through the use of test pits.
Methods - Nine trenches were excavated, described, and sampled for sedimentology and paleopedology. Five trenches were at the Brian Maebius Site, one was approximately 300 meters to the north of the Mabius Site within the "lower red layer" named the Buffalo Alley Bone Bed, and the remainder were within the "lower red layer" in Conata Basin. These include a site approximately 300 meters to the north/northeast of the Pig Dig in Dillon Pass, a site just south of the access trail to Deer Haven, and a site located in southeastern Conata Basin named Jerry's Bone Bed. Approximately 100 samples were collected from 16 paleosol profiles. In almost every case, bone material could be related to a definite position within a paleosol profile. As of yet we have not determined any preference for position vs. profile type, or degree of bone preservation/modification.
Paleosols in the lower Scenic Member ranged from extremely weak to extremely strong development (Fig. 6). The weakest degree of development (AC profiles to azonal: Entisols within the U.S.D.A Soil Taxonomy, 1998) was seen in southeastern Conata Basin (Jerry's Bone Bed). The strongest development (ABC profiles: Inceptisols within U.S.D.A Soil Taxonomy, 1998) was seen in the Brian Mabius Site. Of particular interest is the marker unit 1. Although not intimately associated with bone accumulation, the areal distribution and extreme pedogenic development (ABtC: Alfisols within the U.S.D.A Soil Taxonomy, 1998) of marker unit 1 throughout Tyree and Conata Basins may serve as a tool for interpreting the dynamics of regional basin evolution. This in turn may be a controlling factor on the genesis of these bone beds. Marker unit 1 is also interesting for the environmental conditions suggested by its paleopedology. Marker unit 1 contains an extremely well developed argillic horizon (Bt), a subsurface accumulation of clay material created by downward percolation of soil water. This type of soil forms under humid, forested conditions. Our present paradigm states that the Eocene/Oligocene transition was marked by a change to cooler and drier conditions (Prothero, 1994). Further study of marker unit 1 my help us refine the dynamics of this climatic change.
|Figure 6. Paleosol profiles associated with bone beds of the Scenic Member. Note that fossils occur at different positions within the profiles. A/C profiles are weakly developed soils, whereas A/Bw/C profiles are slightly more developed. Also note that the Pig Dig shows no signs of ancient soil formation.|
This project would not have been possible without the funding from the Natural Resources Preservation Program managed by the National Park Service. We would also like to thank the Superintendent of Badlands National Park, William R. Supernaugh for granting the three field teams access to National Park Service Lands. Field and lab work would not have been possible without the dedicated efforts of the following graduate students: Andrew Anderson, Jennifer Haessig, and Dave Daitch (Stratigraphic field team); Sarah Black, Ellen Starck, Jerry Mundt, Rob Meredith and Joe DiBenedetto (Paleontological Field Team); Lewis Factor (Sedimentological Field Team). Sarah Black and Lewis Factor have developed Masters research directly related to the project.
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