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16. CONTINENTAL 1CIINOLOGY: PUNDAMENTAL PROCESSES AND CONTROLS ON TRACĘ FOSSIL DISTRTBUTION

currents and abundnnt plant debris and other aąuatic insects for the caddisfly larvae to feed on. If spherical termite nests are the dominant tracę fossils, the trace-tossil association would be called the Termiticlmus ichnocoenosis. This type of nest denotes areas with ample vegetative materiał for termites that expand their nests by building new nest centers connected by a gallery system.

The application of this approach produces a mosaic of juxtaposed ichnocoenoses, each with unique physical, Chemical, and biologie properties character-ized not only by the tracę fossils present, but by cross-cutting relationships with each other and their sedimentologic, pedogenic, and geochemical co-con-stitutes. For instance, in fig. 16.2, a few examples of ichnocoenoses are provided and modeled after exam-ti the Upcer Jurassic Morrison Formation in transitional, shoreline environments, three examples for proximal aąuatic settings, and three examples of distal aąuatic settings are provided. Many morę can be constructed for these and other deposits in the Morrison Formation (Hasiotis, 2004). The most impor-tant trend to notę is that the diversity, depth, and tiering of tracę fossils decreases toward shoreline and aąuatic settings. Also important to notę is that the terraphilic and hygrophilic behavioral zones are literally compressed out of the environments because the soil-moisture and water-table level in sediments inerease towards periaąuatic and aąuatic environ-ments. Interestingly, the epiterraphilic zonę can con-tinue to a water depth in aąuatic settings where terrestrial organisms can produce footprints on the surface of the sediment in subaąueous settings.

Ichnocoenoses could be used to develop a hierarchy of trace-fossil associations with community and ecological significance, indicating the high degree of spatial and tern porał heterogeneity that exists in most Continental environments. This hierarchy may become part of an ichnofacies scheme, or replace it altogether, in order to reflect better the naturę of processes and life in the Continental realm. A newly constructed hierarchy based on ichnologic, palaeontologic, sedimentologic, palaeopedologic, and geochemical data will track the evolution of terrestrial and aąuatic ecosystems through geologie time. The new hierarchy can assess the response of different portions of Continental ecosystems to such perturbations as climate change, extraterrestrial impacts, superplume activity, caldera collapse, and tectonic reconfiguration.

CONCLUSION: TWO DISTINCT PARTS BUT ONE ICHNOLOGY

Although Continental and marinę tracę fossils and bioturbation pattems may generally appear similar, their genesis and significance are distinctly different because the biological and physicochemical condi-tions that influence the organism behaviors are sperific to those depositional realms, as well as the behaviors themselves (e.g., Hasiotis and Bown, 1992; jiotis, 2002, 2003, 2004). For example, a bumów posed of backfilled menisd of minimafly altered iment altemating with pelleted sediment, assigned ćhc ichnogenus Taenidium, was produced by a posit-feeding marinę organism (e.g., Ekdale et aL, 4). A burrow composed of tightly backfilled idles of adhesive menisd of minimally altered /diment (AMB) found in a paleosol, however, was produced by a terrestrial organism moring freąuently through the soil in the vadose zonę while feeding occasionally (e.g., Hasiotis and Bown, 1992).

Although these two tracę fossils are similar because of their meniscate backfill, their detailed intemal and external morphologies, genesis, constructors, and significance are distinctly different. The interpretation of Taenidium is based on the behavior of marinę organisms and physicochemical conditions of the sediment common in marinę environments. The interpretation of AMB is based on experiments designed to test the burrowing ability of insects with respect to soil types and variable soil moistures common to terrestrial environments (e.g., Willis and Roth, 1962; Hasiotis and Bown, 1992; Hasiotis, 2004). If all backfilled burrows were interpreted as the product of deposit-feeding, sediment-ingesting aąuatic organisms, then this would lead to incorrect interpretations of organism behavior and paleoenrir-onmental settings for Continental deposits (e.g., Miller et al., 2002; Buatois and Mangano, 2004; Genise, 2004; Genise et al., 2004).

Thus, terrestrial and aąuatic tracę fossils and their relationship to the sedimentary and palaeoped characteristics of the strata must be incorporated i integrative and iterative process to understand accurately their significance in the Continental real*. Comparison of tracę fossils to the structures