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170 6.1. Photographs of various taphonomic states. (A) Isolated limb bone. (B) Articulated limb bones. Pocket knife is approximately 7 cm long. (C) Tortoise (T) resting on former soil surface (S) and buried by fining upward flood deposits. Note photo scale next to shell. (D) Gnaw marks (G) on underside of a jaw bone. (E) Scratch marks (M) on a limb bone. (F) A fragment of tortoise shell that was heavily weathered before burial and fossilization. (D), (E), (F), scale in centimeters. Photos by the authors. 171 6 Death on the Landscape: Taphonomy and Paleoenvironments Paleoecology is the study of the interactions, habits, and lifestyles of extinct species and the ancient communities they formed. Paleoecologists, using data from the fossil and geologic record, reconstruct these communities of plants and animals to gain a better understanding of the relationship between members of that community (Shipman, 1981) and how they responded to environmental changes. Before the paleoecology of an assemblage can be interpreted, the paleoecologist must gain a better understanding of the events that intervened between death and fossilization and what effects these events have on the retrieval of information about the past (Shipman, 1981). This process is called taphonomy . Efremov (1940) introduced the concept of taphonomy as the study of embedding or burial. It is the analysis of the transition of organics from the biosphere into the lithosphere to become part of the geologic record. The term taphonomy can be broken down into the Greek words taphos (burial) and nomos (laws). Clark, Beerbower, and Kietzke (1967) made the first attempt at describing the ancient environments preserved in the White River Badlands. They proposed four different environments of deposition within the Chadron Formation. These included streams represented by channel fills of the Red River and its tributaries; limestone deposits near channels and channel margin facies; channel margin sands and silts from riverbanks; and massive to bedded clays and silts along ancient floodplains. Clark, Beerbower, and Kietzke (1967) proposed four general biotic structures, including aquatic, semiaquatic, river-border forest, and forest–savanna. They divided the paleoecology of the lower nodular zone of the Brule Formation into three different facies: near stream, open plains, and swampy plains. (See chapter 1 for a more detailed description on Clark and his colleagues’ research contributions.) Refinements to geochronology (such as paleomagnetism and radioisotopic dating), the application of paleopedology to deep time records, and an expanded paleobotanical archive have since fine-tuned paleoclimatic interpretations of the Cenozoic and refined our understanding of the paleoecological changes indicated by the fossils in the White River Badlands. Fossil Preservation in the White River Badlands During the uplift of the Black Hills, which began during the later phases of the Laramide Orogeny, Paleozoic rocks were exposed to weathering, and the resulting sediments were transported by streams and rivers flowing from west to east. These sediments are preserved within a slightly northwest –southeast-trending asymmetric basin that makes up much of what we call the White River Badlands (Fig. 4.2). The basin is bound to the north by the Sage Ridge Fault in the Badlands Wilderness Area and to the south along the Sandoz Ranch, White Clay, and Pine Ridge fault system (Clark, Beerbower, and Kietzke, 1967). A significant amount of White River Badlands sediment consists of reworked ash, which was carried via eolian and fluvial processes from volcanoes in eastern Nevada and Colorado. This combination of geologic factors promoted rapid rates of sedimentation, which aided in the fossilization process, allowing carcasses to be buried quickly after death and protecting them from destructive forces (Clark, Beerbower, and Kietzke, 1967; Shipman, 1981). The fossilization process is a rare event and requires a series of steps to occur. The preservation potential of a fossil is the balance between the factors of preservation and destruction . Chances of preservation tend to increase if organic remains can be buried rapidly in a particular sedimentary environment (Shipman, 1981). Some of the most frequent causes of death associated with White River vertebrates include predation, flood events, starvation, and dehydration. Regardless of the cause of death, the key ingredient in the process of fossilization is water. Once buried, and with the flesh removed, bones begin to interact with either water that is percolating downward through the soil zone (vadose water), or if the depth of burial is sufficiently deep, the bones are completely saturated and interact with groundwater (phreatic water). Most bones will experience both as they are progressively buried with additional sediment. The bone material, which is a...


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