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199 A horizon mixed zone of mineral and organic matter at the top of a soil profile. Commonly referred to as topsoil. acidic chemical condition in soils denoted by higher concentrations of hydrogen protons than base cations, such as sodium, calcium, and potassium. alfisol soil order in semiarid to humid areas, typically under a hardwood forest cover. It has a clay-enriched subsoil and a relatively high native fertility. “Alf” refers to aluminum (Al) and iron (Fe). alkaline chemical condition in soils in which base cations, such as sodium, calcium, and potassium, are more abundant than hydrogen protons. anoxic environment lacking oxygen. anterior near or toward the front of something (such as the body) antorbital vacuities openings in front of the orbit within a skull. aperture opening of a snail shell. apomorphy in cladistics, a derived character state, or one that evolved later. Any feature novel to a species and its descendants. See synapomorphy. aragonite form of calcium carbonate that makes up mother-of-pearl shells. arboreal living in or often found in trees. argillan film of clay on the surfaces of peds that form by the translocation of clays downward in a soil profile. argillic horizon pedogenic horizon (Bt) that is enriched in clays that have been translocated downward. aridisol soil most commonly found in association with arid environments, such as deserts; often have accumulations of carbonate or gypsum in their profiles. articulation degree of connectivity between various bones in a fossil deposit. Articulated bones retain their original life position on the organism, and disarticulated bones are freefloating but generally in the same area as other bones. avulsion process by which a river changes its overall course of flow by breaching the natural levee that contains it. B horizon primary horizon of accumulation (illuvial horizon) in a soil profile. The type of materials that concentrate in the B horizon reflect dominant climatic conditions. bed load portion of sediment transported by a river that is in contact with the stream bed as it moves. benthic foraminifera microscopic single-celled organisms that precipitate a calcite shell (test) and live on the seafloor. bentonite particular type of swelling clay (smectite) named for Benton, Wyoming. bicipital groove groove on the anterior border of the proximal humerus between the medial and lateral tuberosities. bioapatite apatite is a group of phosphate minerals, calcium apatite is the mineral that forms bone. The individual crystals are held together by collagen, which decays upon death and burial. biochronology correlation of rock units based solely on the presence of fossils, either individual taxa or an assemblage. biomineralization process by which living organisms produce minerals, often to harden or stiffen existing tissues; an extremely widespread phenomenon, it occurs in all six taxonomic kingdoms, and over 60 different minerals have been identified in organisms. Examples include silicates in algae and diatoms, carbonates in invertebrates, and calcium phosphates and carbonates in vertebrates. biostratigraphic unit rock units defined solely by their fossil content. Biostratigraphic units are not required to adhere to lithologic boundaries. biostratigraphy branch of stratigraphy focusing on correlating and assigning relative ages of rock strata by using the fossil assemblages within the strata. bone bed accumulation of fossil bone that has a higher-than-normal concentration within a given area relative to the volume of sediment. brachyodont having teeth with low crowns, well-developed roots, and only narrow canals in the roots, typically found in browsing mammals. bunodont mammal with cheek teeth with low, rounded cusps on the occlusal surface of the crown, typical of omnivores. C horizon bottom of a soil profile; has little to no modification from its original parent material state. C3, C4 vegetation particular photosynthetic pathways utilized by certain types of plants. C3 plants include most shrubs and trees, whereas C4 plants are dominated by grasses. These differences in photosynthetic pathways, which are a response to general climatic conditions (such as moisture availability) can be preserved in the rock record as distinct ranges of carbon isotopic values of preserved organic matter. Measurement of the amount of carbon 13 in tooth enamel can provide information about an extinct animal’s diet. caldera cauldronlike volcanic feature usually formed by the collapse of land after a huge volcanic eruption. cambic horizon beginning stages of subsurface accumulation of translocated materials to form a B horizon. The cambic horizon (Bw) is sufficiently different from either the A or C horizon but has not reached a diagnostic stage of accumulation. caniniform of or bearing similarity to the shape and appearance of a canine...


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