Showing papers by "Randall F. Miller published in 2011"

New biostratigraphical constraints on the lower Cambrian Ratcliffe Brook Formation, southern New Brunswick, Canada, from organic-walled microfossils

Abstract: Organic-walled microfossils from the Ratcliffe Brook Formation of southern New Brunswick enable recognition of the three lowest Cambrian acritarch-based zones established in southeastern Poland and on the East European Platform. This is the first re- cord of these zones in Avalonia. The distribution of acritarchs of the Asteridium tornatum-Comasphaeridium velvetum, Skiagia ornata-Fimbriaglomerella membranacea ,a ndHeliosphaeridium dissimilare-Skiagia ciliosa zones leads us to propose a revised correla- tion of sections of the Ratcliffe Brook Formation, in which an ash bed dated at 531 Ma now predates rather than postdates an assemblage of small shelly fossils that had been previously attributed to the Watsonella crosbyi Zone. The small shelly fossils are here suggested to belong to a younger biozone as they occur with acritarchs of the Skiagia ornata- Fimbriaglomerella membranacea Zone, the base of which is currently thought to approximate in time to the global appearance of trilobites. The occurrence of acritarchs of the Helio- sphaeridium dissimilare-Skiagia ciliosa Zone close to the top of the Ratcliffe Brook Formation suggests that the upper part of this forma- tion and the overlying Glen Falls Formation are younger than previously thought and that their correlation with strata in Newfoundland is in need of revision. Biostratigraphic constraints are currently insufficient to position the 531 Ma ash bed with precision with respect to the Watsonella crosbyi Zone in Newfoundland, but it is likely that the date is within this zone.

Hypothesized Cambrian medusae from Saint John, New Brunswick, reinterpreted as sedimentary structures

Abstract: More than a hundred radial and discoidal structures occur on bed tops of shales and very fine sandstones of the Cambrian (Series 3) King Square Formation in New Brunswick, Canada. These structures typically contain a central sediment plug, radial lineations that extend outward from the central plug, concentric rings, and a broad trough surrounding or underlying ring margins. Originally interpreted as fossils of scyphozoan medusae, these structures could represent one of only a half-dozen mass strandings documented from the fossil record. Instead, re-evaluation of their sedimentology and morphology suggests that they are likely sedimentary structures known as Astropolithon. These sand-volcano-like structures formed by subsurface blistering, cracking, and failure of a near-surface or surface bed, triggered by the upward movement of gases or other fluids from underlying beds. RESUME Plus d’une centaine de structures radiales et discoides apparaissent au sommet des couches de schiste et de gres tres fins de la formation King Square du Cambrien (Serie 3), du Nouveau-Brunswick, au Canada. Ces structures contiennent generalement un culot sedimentaire central, des lineaments radiaux qui se deploient vers l’exterieur a partir du culot central, des anneaux concentriques, et une vaste cuvette qui ceinture le bord des anneaux ou qui se trouve en dessous. On estimait initialement qu’il s’agissait de meduses scyphozoaires, mais ces structures pourraient correspondre a l’une de la demi-douzaine d’echouages massifs de l’ichnofaune dont les vestiges fossiles ont ete retrouves. La reevaluation de leur contexte de sedimentation et de leur morphologie porte plutot a croire que ce sont vraisemblablement des structures sedimentaires connues sous le nom d’astropolithon. Ces structures apparentees a un volcan de sable ont ete formees par l’apparition d’alveoles souterraines, le fendillement et la rupture d’une couche pres de la surface ou a la surface, et qu’aurait provoquee le deplacement vers la surface de gaz ou d’autres fluides provenant des couches inferieures. [Traduit par la redaction]