摘要:

An essential clue to the uppermost Silurian in the submarine Baltic arca is theBeyrichienkalk.According to recent investigations it constitutes a glacial drift boulder sequence characterized by four ostracode associations with about sixty species. In the correlation of ostracode zones of Baltoscandia these associations form a connecting link and thus are also of biozonal character. In the terms of regional stratigraphic units (East Baltic arca). the lower stratigraphic boundary of this sequence lies approximately at the beginning of the Kuressaare beds and the top in the upper Ohesaare beds. The termBeyrichienkalkshould be used for those glacial erratics that are characterized by typical ostracodes of the four associations defined here.

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1985.tb00705.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

A model of Early Cambrian trilobite biogeography in the North Atlantic region (Theokritoff 1979.Lethaia 12, 281–295) is reviewed and modified in the light of new data. The presence ofWanneriain conglomerates bearing theElliptocephala asaphoidesfauna strengthens correlation of theE. asaphoidesfauna as well as, by implication, the upper part of theCalluviaZone with the middle part of theBonnia‐OlenellusZone. The faunas of the Bastion Formation of East Greenland and of the Devil's Cove Limestone of northern Newfoundland are reinterpreted as shelf faunas. Additional occurrences of Archaeocyatha are noted in Spain and northwest Scotland but reports of Archaeocyatha in northern Norway and East Germany are not authenticated. NeitherSalterellanor ‘Volborthella’ are now recognized as characteristic of any trilobite province. Although Ordovician acritarch provinces show congruence with trilobite provinces, available data on Early Cambrian plankton are not sufficient to support algal provincialism. Interpretation of the geological record suggests that the Early Cambrian lapetus Ocean was stratified with a well‐mixed oxygenated zone overlying a phosphate‐rich oxygen minimum zone and that theElliptocephala asaphoidesfauna should be reinterpreted as a warm

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1985.tb00706.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1985.tb00707.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Patterns of shell formation and the chemical composition of the shell deposited during early post‐larval life were investigated in laboratory‐reared cultures of the Recent articulate brachiopodTerebraralia transversa(Sowerby). A non‐hinged protegulum averaging 148 pm in length is secreted by the mantle within a day after larval metamorphosis. The inner surface of the protegulum exhibits finely granular, non‐fibrous material. A rudimentary periostracum constitutes the outer layer of the primordial shell. and concentrically arranged growth lines are lacking. By four days post‐metamorphosis, a brephic type of juvenile shell develops from periodic additions of shell material to the anterior and lateral edges of the protegulum. Imbricated secondary fibers occur throughout the inner layer of the newly formed juvenile shell, and a rudimentary hinge apparatus is present posteriorly. The external surface of the shell exhibits concentric growth lines anterior to the caudally situated protegulum, and unbranched punctae begin to form in the subperiostracal region of the shell. At 23 days post‐metamorphosis, the shell weighs an average of 1.7 μg and measures 318 μm in length. Electron microprobe analyses reveal that the protegulum is calcified. Minor amounts of sulfur, magnesium, iron, chlorine, aluminum, and silicon are also present in protegula and juvenile shells. Based on electron diffraction data, the mineral phase of juvenile shells consists of calcite, and protegula also appear to co

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1985.tb00708.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1985.tb00709.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The post‐mortem history of a prolific Maastrichtian ammonite and nautiloid fauna preserved as phosphatic steinkerns in chalk of the upper Miria Formation of Western Australia is described. Sediment infilling of phragmocones, required for their fossilisation, was accomplished by means of perforations in the shell wall induced by the activity of abundant endoliths. These include borings ascribed to clionid sponges(Entobia), thallophytes, polychaete worms (includingCaulostrepisand probableMaeandropolydora), phoronids(TalpinaandGnathichnus)and others of conjectural origin. Sediment infilling by this mechanism is considered to be more applicable to the taphonomy of phragmocones in general than sediment entry through the siphuncle and to be indicative of low sedimentation rates for the hosting strata. Nonheteromorph ammonites, and the nautiloidCimomia, are preserved almost exclusively as phragmocones in the upper Miria Formation, and are numerically subordinate to the heteromorphEubaculiteswhich, together withGlyptoxoceras, is preserved predominantly as body chambers. This phragmocone/body chamber preservational contrast is attributed to the influence of shell shape on pre‐burial mechanical abrasion. The apparent dominance ofEubaculitesis considered to be largely a preservational artifact and ascribed to the ease with which body chambers were infilled, and thereby favoured for steinkern formation, relative to phragmocones. Phragmocones, or parts thereof. not filled with sediment were eliminated from the fossil record by diagenetic aragonite dissolution. Many ammonites with open umbilici have the early whorls missing. This we attribute to the trapping of sediment in the umbilicus prior to burial, preventing endolith attack whereby the early whorls avoided a sediment infilling. However, the protected inner whorls of involute ammonites andCimomia, which have closed umbilici, and the inner whorls of evolute ammonites where a cemented umbilical plug supported the mouldic cavity left by shell dissolution, were preserved and were commonly infilled with calcite spar later in diagenesis. The dearth of cephalopod fossils in chalk underlying the upper Miria Formation is ascribed to diagenesis in which aragonite dissolution was not preceded by cementat

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1985.tb00710.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Most arthropod burrows show a marked preferred orientation: they are not random in alignment. A recent burrow made byJaxea nocturnaNardo is compared to three fossil burrows from the Austrian Tertiary. In each system very steep and very flat burrow sections can be distinguished. In three cases, including the Recent one, flat burrow sections dominate in length. In all burrow sections the distribution of trend angles is also not uniform but indicate preferred directions. In those cases where two mean vectors exist their position is nearly orthogonal, in systems with three mean vectors they form angles of nearly 60°. A relationship between these preferred directions to coastline orientation and current direction is likely

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1985.tb00711.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1985.tb00712.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Middle Eocene, non‐marine sediments from southern England contain examples ofTeredolitesborings in two contrasting palaeoenvironmental settings, viz.: (A) asin situborings in an allochthonous lignite in an abandoned river channel and (B) as bored logs in cross‐bedded fluvial sandstones of probable point‐bar origin. The lignite is 0.30 m thick, of which the upper 0.20 m is intensely bored. Rounded pebbles of ?charcoal at its base also show small borings. A log in a fluvial sandstone shows densely‐packed. radial club‐shaped borings. now filled with sandstone. The wood substrate has subsequently been oxidized away. To our knowledge, this is the first detailed account ofTeredolitesfrom an ancient freshwate

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1985.tb00713.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1985.tb00714.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY