Allochthonous Elements Research Articles

Plant mega- and microfossil assemblages from the Brunssumian of `Hambach' near Düren, B.R.D.

A series of 19 carpological samples, 9 of them from a 50 cm thick section, were collected from Late Brunssumian deposits in the browncoal open-cast mine `Hambach'. They were analyzed together with two leaf assemblages collected from the same horizon. They reveal a change from wetland forest to reed vegetation together with an increasing influence of allochthonous elements. Some plant species new to the region were found: Carex appropinquata, Euphorbia palustris, Salix sp. (seeds), Urtica dubia. The difference between the composition of leaf and carpological assemblage from the same deposits is elucidated. The incorporation of palynological data helps to clarify the nature of the vegetation.

Taphonomy of Jack's Birthday Site, a diverse dinosaur bonebed from the Upper Cretaceous Two Medicine Formation of Montana

Jack's Birthday Site is a diverse vertebrate assemblage from the Upper Two Medicine Formation of western Montana. Age is roughly 74 Ma. The site covers roughly 3000 m 2 , and excavations over 140 m 2 . A large bone sample (> 1600 skeletal elements) allowed statistical evaluation of the preservational and compositional variation within the site. Evidence, including sedimentary facies, plant and invertebrate fossils, and bone orientation and condition, indicates Jack's Birthday Site represents part of a small, shallow floodplain lake. Lithologies and fossil preservation vary from northwest to southeast over a distance of 50 m. This variation represents a transition from lake through shoreline to marginal shoreline/floodplain environments. Containing ten dinosaur taxa and a variety of non-dinosaurs, Jack's Birthday Site provides one of the best single faunal samples of the region. The vertebrate assemblage includes two taphonomic fractions. The first, consisting of attritional, predominantly isolated and allochthonous elements, represents a time-averaged assemblage. The other consists of associated, parautochthonous remains restricted to a single horizon. Taxa represented by associated remains include three iguanodontoids, Hypacrosaurus, Prosaurolophus , and Gryposaurus , and the theropod Troodon . Associated individuals of these taxa have non-random distributions within the site (Fisher's Exact Test, p < 0.01) and observed taxonomic clustering may reflect group behavior and/or event mortality. The four or more Troodon represent the first described multi-individual troodontid occurrence. The diversity and spatial complexity of the parautochthonous fraction of the Birthday Site assemblage is difficult to explain. Discussion of possible event mortality mechanisms focuses on three: drought, botulism and cyanobacterial toxicosis. These share an ability to act over an ecologically significant period of time, affect a variety of species and concentrate mortality along water sources, aspects that may have been important in generating the Birthday Site assemblage. Evidence at the site favors drought or perhaps a drought/botulism hypothesis. However, taxonomic clusters could represent completely separate events with a variety of causes.

Paleobiology of a Neoproterozoic tidal flat/lagoonal complex: the Draken Conglomerate Formation, Spitsbergen.

Carbonates and rare shales of the ca 700-800 Ma old Draken Conglomerate Formation, northeastern Spitsbergen, preserve a record of environmental variation within a Neoproterozoic tidal flat/lagoon complex. Forty-two microfossil taxa have been recognized in Draken rocks, and of these, 39 can be characterized in terms of their paleoenvironmental distributions along a gradient from the supratidal zone to permanently submerged lagoons. Supratidal to subtidal trends include: increasing microbenthic diversity, increasing abundance and diversity of included allochthonous (presumably planktonic) elements, decreasing sheath thickness of mat-building organisms (with significant taphonomic consequences), and an increasing sediment/fossil ratio in fossiliferous rocks. Five principal and several minor biofacies can be distinguished. The paleoecological resolution obtainable in the Draken Conglomerate Formation rivals that achieved for most Phanerozoic fossil deposits. It documents the complexity and diversity of Proterozoic coastal ecosystems and indicates that both environment and taphonomy need to be taken into explicit consideration in attempts to understand evolutionary trends in early fossil record. Three species, Coniunctiophycus majorinum, Myxococcoides distola, and M. chlorelloidea, are described as new; Siphonophycus robustum, Siphonophycus septatum, and Gorgonisphaeridium maximum are proposed as new combinations.

Zur Inaktivierung von Erregern übertragbarer Krankheiten in Gewässern

Germs of infectious diseases are not adapted to the environment of waters but to their hosts. Therefore, as allochthonous elements they survive there only for a short time for the most part; individual germs, however, are much more resistant under these environmental conditions, in dependence on their species or type. At a higher initial germ content the period of survival in general is longer than at a lower one. For inactivation in waters e.g. the following causes may be responsible: nutrient deficiency, unfavourable water temperature, redox potential, saprobity, chemical constituents, including metabolic products of aquatic organisms, solar light osmotic pressure, settling material and suspended solids, bacteriophages.

Exceptional preservation of photosynthetic organisms in silicified carbonates and silicified peats

Carbonaceous cherts in Proterozoic carbonate sequences provide an exceptionally clear record of early microbial life, but one that is significantly biased with respect to the range of environments inhabited by contemporary organisms. Many of the best preserved Proterozoic microfossil assemblages come from microbial mats and organicrich muds that accumulated in protected coastal areas where a combination of high productivity, limited water circulation, and, often, hypersalinity limitedpost mortemdegradation. The close distributional relationship between early diagenetic silica and organic matter can be explained in terms of a model developed by Leo and Barghoorn for the silicification of wood. Three factors appear to control the distribution of early diagenetic chert in Proterozoic sequences: sediment permeability, availability of silica in ground water solution, and locally high concentrations of organic matter in near-surface sediments. Of these, organic content appears to impose the major environmental bias. In terms of their excellent preservation, geochemistry of formation, and limited environmental coverage, Phanerozoic silicified peats bear comparison with their Proterozoic counterparts. Swamp dwellers may be the plants most likely to be preserved exceptionally well, but they may also be the plants least likely to give rise to new populations that will become ecologically widespread and evolutionarily important in subsequent periods. Allochthonous elements in permineralized peats may be unusually important to palaeobotany because they combine the exceptional preservation conferred by peat permineralization with ecological representation of floodplain and upland evolutionary cradles rather than swampland museums.

Stromatolitic microbiota from the middle Proterozoic Wumishan Formation (Jixian Group) of the Ming Tombs, Beijing, China

A relatively diverse microbiota, preserved in-situ, has been discovered in cherty stratiform stromatolites of the middle Proterozoic Wumishan Formation (c. 1200–1300 Maold), Jixian Group, in the Ming Tombs area of Beijing. This microfossil assemblage consists of two parts: (1) the mat-building and mat-dwelling benthos which mostly belong to “long-lasting” taxa and are mostly common with those of other Proterozoic microbiotas; and (2) allochthonous elements including some plankton and peculiar structures which are either new forms first described here or taxa shared with some contemporaneous or penecontemporaneous microbiotas elsewhere. The latter may have more stratigraphic significance. Bivariate analysis on two characters measured (length and width) has been used in the classification of the elongate microfossils, and the results demonstrate that biometrical methods are effective in the taxonomy of some Precambrian microfossils. The following new taxa are described: Archaeoellipsoides obesus sp. nov., Archaeoellipsoides conjunctivus sp. nov., Bactrophycus oblongum gen. et sp. nov., Bactrophycus dolichum gen. et sp. nov., Callosicoccus crauros gen. et sp. nov.

Origine autochtone et allochtone des argiles récentes de haute altitude en Corse

In high-altitude lakes from Corsica, clay minerals can be subdivided in three groups : mainly autochthonous minerals (stilpnomelane, chlorite, illite, irregular mixed-layers, vermiculite), mixed autochthonous and allochthonous minerals (smectite), essentially allochtho-nous minerals (kaolinite, palygorskite). Allochthonous elements are transported from Africa by the Sirocco, and chiefly deposited during rainfalls. The corsican lakes, located close to the crests of the mountains and dependent on short drainage-basins, favor the accumulation of eolian particles, which can be used as indicators of the wind activity in course of time.

Stratigraphical analysis of island arc—continental margin collision in eastern Indonesia

Eastern Indonesia is a sinuous plate margin interpreted as a collision between the northern margin of the Australian continent and an Asian island arc. Detailed stratigraphical analysis of the collision zone in Timor reveals that pre-Pliocene deformation phases affected members of the allochthon before they were overthrust together onto the Australian margin in the middle Pliocene. The Australian facies para-autochthon below the thrust sheets was not involved in these pre-Pliocene deformations. The distinction within the collision zone of elements having different structural histories and opposite facies polarity permits identification of the plate margin which has been overthrust and folded after the initial collision. The lowest thrust sheet emplaced in Timor and other islands of the Outer Banda Arc appears to be part of an Asian outer arc ridge overthrust by fragments of a continental margin metamorphic basement and volcanic-sedimentary cover. Stratigraphical studies provide the basis for an explanation of the origin, transport and emplacement of a major olistostrome, for the sequence of allochthonous elements emplaced on the underthrusting continental margin and for post-collision deformation phases in the arc. A speculative model interprets a progressive Mio-Pliocene collision between the Australian margin and an island arc migrating away from SE. Asia by spreading of the marginal-type Banda Sea. The Asian arc was underthrust by the Australian continental margin but buoyancy probably restricted the process to overthrusting slivers of rocks from the trench and trench-arc gap. This model could be tested by seismic and magnetic studies of the Banda Sea region. The Indonesian

The significance of the metamorphic rocks of Timor in the development of the Banda Arc, Eastern Indonesia

The metamorphic rocks of Timor are reinterpreted in the light of reconnaissance mapping of the whole island. All metamorphic rocks that crop out in Timor are allochthonous. Several metamorphic massifs are reported for the first time, the outline of others is revised. On the basis of their grade, three distinct groups can be mapped: lustrous slate, amphibolite-serpentinite, and a granulite-amphibolite-greenschist complex. Each group has distinctive structural relations to other allochthonous elements. The granulite facies meta-anorthosite in Timor must have originated near the boundary between the continental mantle and the crust. These and related high-grade metamorphic rocks may represent slices of an ancient Asian continental basement. These rocks imply that the history of the Mesozoic-Cinozoic fold belt of the Outer Banda Arc extends into the Precambrian Era. The metamorphic rocks of Seram appear to be remarkably similar to those of Timor in grade, distribution and structural relations. The overthrust directions of the metamorphic rocks in Timor is southwards, in Seram it is northwards. As the islands are separated by the 4–5 km deep Banda Sea, these directly opposite thrusts may be explained in terms of the Banda Arc acquiring its sinuosity after the emplacement of the metamorphic rocks.