Aspects of a Middle Cambrian Thanatotope on Öland

Abstract

The Paradoxissirnus Siltstone, representins the Middle Cambrian zone with Tomagnostusjssus and PQcha,onostus alaius in the Oland area, was deposited in a bay under the influence of rhythmic or pendulating curtent action from NE. Longer periods of mud deposition and a n abundant animal life alternated with short periods of silt influx causing a devastation of the mud-burrowing zoocoenoses over large areas. Occasionally the currents turned, transporting some silt in the opposite direction. Among the characteristic animals of the muddy bottoms was the large trilobite Paradoxides parndoxissimur which is found in abundance in the siltstone but only as fossil exuviae; in the shale, representing the environment in which it lived, shelly and trace fossils have been obliterated by diagenetic processes. The silt coiitent in the Paradoxissirnus Beds shows lateral variations within the a l a n d area, and the mainly shaly portions, mostly in the lower part of the sequence, contain better preserved dead trilobites and esuviae in situ.Primary sedimentary structures in connection with the current activity (ripples of different types, traction m a r h , and priels) are briefly discussed, and the trace fossils are dealt with in more detail. Practical problems in the treatment of trace fossils and ichnocoenoses are discussed as well as some ichnosystematic aspects of the Cambrian "genera" Halopoa and Scotolithus.

Kinneyia: A Flow-Induced Anisotropic Fossil Pattern from Ancient Microbial Mats

“…Kinneyia patterns are often found to exhibit a preferred crest orientation. In Kinneyia from Öland, this orientation could be shown to run perpendicular to the paleocurrents from which the event layers were deposited (Martinsson, 1965). The results suggest that the different patterns may arise from variations in the flow conditions under which the microbial mat or film is deformed and depend upon the amount of sediment suspended in the flowing water.…”

Systematic ichnology of the Middle Ordovician Trenton Group, St Lawrence Lowland, eastern Canada

“…Since its original description, it has been shown to intergrade with Phycodes (Hantzschel andReineck 1968, Hofmann 1979), Thalassinoides, Ophiomorpha and Gyrolithes (Hester and Pryor 1972, Frey et al 1978, Frey and Seilacher 1980, Rhizocorallium (Chisholm 1970, Sellwood 1970 and even Cruziana (Garcia-Ramos 1976). As such, its producers are probably polyphyletic, though annelids and arthropods are usually most favoured (Martinsson 1965, Chisholm 1970, Chamberlain 1977.…”

Paleoecologic and Biostratigraphic Significance of Trace Fossils From Shallow- to Marginal-Marine Environments From the Middle Cambrian (Stage 5) of Jordan

“…Ichnogenus MONOMORPHICHNUS Crimes, 1970 Remarks.-In the original description of Monomorphichnus, Crimes (1970) referred to trace fossils observed by Martinsson (1965) who suggested trilobites ''caught up in the current'' producing these scratch marks by raking up the sediment surface with their endopodites. This interpretation was subsequently endorsed by Osgood (1970).…”