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Erstnachweis der Spurengattung Lingulichnus Hake, 1976 als Geschiebefund
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The formation rests unconformably on Precambrian gneiss and was deposited during a time of global sea-level rise. The Formation and its equivalents around the North American craton indicate that the craton margin was covered by a blanket of immature alluvium prior to the Early Palaeozoic transgression. The alluvium resulted from denudation of the barren, unvegetated North American craton under wet, tropical conditions.-from Authors
Several trace fossil assemblages from the clastic members of three Upper Pennsylvanian cyclothems in the state of Kansas are considered to represent marginal marine (brackish-marine) environments. Trace fossils were collected from several lenticular- or flaser-bedded siltstone and fine-grained snadstone horizons within the Rock Lake Shale, Timberhill Siltstone, and Lawrence Shale. These units were commonly thought to be nonmarine (freshwater to subaerial exposure) due to the general lack of marine body fossils. Common trace fossils are Asteriacites, Lingulichnus, Isopodichnus, Chondrites, Didymaulichnus, Pelecypodichnus and Planolites. The trace fossil assemblages are characterized by the following 1) small-sized members; 2) excellent preservation; 3) high to moderate diversity; 4) moderate abundance; 5) no preferential preservation; and 6) all ethological groups except grazing trails. The small size of these trace fossils is related to a lowering of salinity as a result of freshwater influx into a shallow marine environment accompanying the deposition of the silts and sands upon which the ichnofauna is preserved. The trace fossils may have been overlooked because of their small size, and it is proposed that they could be found elsewhere within similar shallow water stratigraphic sequences.-Author
Detailed analysis of modern and Pleistocene deposits at Willapa Bay, Washington concentrated on identifying ichnological and sedimentological characteristics of five estuarine subenvironments. These include: (1) intertidal flat deposits, which are typically thoroughly bioturbated by a somewhat diminutive suite of various vertical and horizontal shafts and burrows that are locally cross-cut by robust crustacean dwellings; (2) unburrowed to rarely burrowed tidal creek point-bar deposits, which are sporadically burrowed by minute Gyrolithes, Skolithos, Cylindrichnus, Planolites, Palaeophycus, and rare bivalve equilibrichnia; (3) fluvially- through tidally-influenced main point-bar deposits, which are sporadically bioturbated with vertical traces superimposed upon inclined heterolithic stratification; (4) well to thoroughly bioturbated bay deposits, burrowed by relatively robust forms of Ophiomorpha, Teichichnus, Skolithos and bivalve equilibrichnia; and (5) locally bioturbated channel-bar deposits, typically displaying robust bivalve equilibrichnia, rare Ophiomorpha, and deep-penetrating Skolithos. Traces from both the modern and ancient deposits display a marked reduction in size and diversity in the upper estuary. Ongoing research at Willapa Bay confirms the validity of the brackish-water model and provides data that potentially improve our understanding of these deposits. Our findings suggest that strong textural controls are overprinted by salinity stresses; commonly vertical deposit-feeding structures, made by infauna that are mining and / or stoping organic-rich laminae, are present; and there is a potential for the presence of large diameter crustacean burrows in brackish deposits. This research emphasizes ichnologic variability due to autocyclic changes and climatic variability, and urges caution when integrating ichnologic and sedimentologic data into a genetic stratigraphic model.
The environmental distribution of lingulide brachiopods in western Canadian Triassic marine successions, their relationship with other infaunal organisms occupying the same ecospace, and their role in the aftermath of the Permian-Triassic extinction event is summarized. Western Canada is an ideal location to assess lingulide distribution patterns as upper Paleozoic and lower Mesozoic strata are extensively exposed, and lingulides (cf. Lingularia Biernat and Emig) and the trace fossil Lingulichnus Hakes are both common. A distribution comparison of in situ lingulides and Lingulichnus Hakes with concordantly emplaced lingulide shells and shell beds shows clearly that the latter is a poor indicator of true environmental distribution of these infaunal suspension feeders. Lingulides are rare in uppermost Paleozoic strata in the study area. Most occurrences consist of isolated valves or abraded material in erosional lags. Lingulides remain minor components of infaunal Communities during the earliest Triassic (Griesbachian). Although lingulide valves and valve fragments are the dominant body fossil,Observed, trace fossil analysis indicates that lingulides were minor components of earliest Triassic infaunal communities. Lingulides increase in abundance and importance during the Dienerian and Smithian. Shallow and marginal marine trace-fossil assemblages of this age are dominated commonly by Lingulichnus. Lingulide fossils are less abundant but are found in many shallow and marginal marine lithofacies. Lingulides comprise only a minor component of late Smithian through Anisian infaunal communities. Canadian lingulide abundance reached an acme during the latest Middle Triassic (Ladinian). Fossil material is common in many environments, however, in situ lingulides and the trace fossil Lingulichnus occur primarily in tempestites in proximal offshore through lower shoreface settings and in intertidal flat settings. Although quantitatively more abundant in the Middle Triassic, lingulides were proportionally more abundant in Lower Triassic successions. Regardless of relative changes in abundance, the environmental distribution of lingulides did not differ between Early and Middle Triassic successions. Lingulides comprise only a minor component of Upper Triassic infaunal communities. Early Triassic lingulides did not occupy any environmental settings from which they were excluded prior to the Permian-Triassic extinction or after the postextinction recovery interval. Thus, lingulides were not postextinction disaster taxa but rather were ecological opportunists that dominated some Early Triassic shallow and marginal marine successions.
Log-probability curves of grain-size distribution have been analysed of sediments collected in three previously described localities occupied by either Lingula anatina or L. reevei (Brachiopoda, Inarticulata). The grain-size population transported by saltation (average about 92–223 μm), generally associated with traction load population, determines Lingula distribution. The two preferential substrates of both studied species (density > 100 individuals/m-2) are compact and stable sediments under moderate water currents: either coarse sands and gravels clogged by fine and very fine sands, or fine, very fine and clay sands (saltation populations more than 60%). As soon as the suspension population and/or traction increase in the sediment to the detriment of the saltation population, the density of Lingula decreases rapidly. Nevertheless, if grain-size distribution and populations have a primordial function for Lingula, other ecological features (i.e. the environmental fauna, high occurrence of digging species, the available nutrients) will affect the distribution and sometimes become prevailing. The absence of important changes in the shell shape of Lingula since its origin suggests that the grain-size requirements remained about the same.
All the specimens of Lingulasma tenuigranulata found at two localities in Meifod, Montgomeryshire (North Wales), are in original life position, with the burrow attituds ranging from vertical, inclined and vertical oblique to inclined oblique. The specimens are all extremely large in size for linguloids (over 3.9 cm in length) and this attributed essentially to an abundant food supply and possibly to vertical phosphate diffusion within the enclosing sediments. The unimodal size-distribution is attributed to an absence of predation and disease and to death by senility. The associated fauna shows that Lingulasma is part of a strophomenid-trilobite community rather than the normally expected gastropod-bivalve one. The trophic structure of this community is shown to be out of accord with that of recent communities. L. tenuigranulata represented chance spatfalls in an open shelf environment which was extremely conducive to its growth and development.