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Succession of coral associations during a Givetian transgressive-regressive cycle in Queensland

100%

Zhen Y. Y.

Acta Palaeontologica Polonica

1996

tom 41

nr 1

59-88

The small solitary coral dominated, Grypophyllum-Chostophyllum association, a pioneer coral community, is widely distributed at the base of the Givetian Burdekin Formation of north Queensland in the mixed arkose-carbonate sediments. It is succeeded by fasciculate coral dominated, Dendrostella trigemne association, which is mainly associated with wackestone or bioclastic calcirudite of inner shelf, lagoonal or protected environments. The Australophyllum-Sanidophyllum association, Blysmatophyllunt-Iotuaphgllum schlueteri association, and Spongophgllstm association, all dominated by in situ, large massive coral colonies, formed biostromal deposits on the margins of the basin. They developed in nearshore environments during the maximum flooding in the region. The Aphyllum salmoni-Stringophgllum (Neospongophyllum) bipartitum association indicates relatively deeper, mid-outer shelf environments connected with maximum flooding in the depocentre and least terrigenous influx. The massive coral dominated Endophyllum columna-Stringophyllum (Stringophyllum) isactis association, developed in the initial regressive phase, forms a distinctive biostromal unit at the top of the Burdekin Formation. The Lekanophyllum association developed at the base of the Cultivation Gully Formation in a very shallow nearshore environment with a large terrigendus influx as a result of the basin wide, relatively rapid regression. It is characterised by the abundant occurrence of solitary corals and large sized, cerioid Endophyllum columna, which often formed micro-atolls. Rugose corals were better adapted than stromatoporoids to survive of mud inllux.

Cyanobacterial key to the genesis of micritic and peloidal limestones in ancient seas

100%

Kazmierczak J., Coleman M. L., Gruszczynski M., Kempe S.

Acta Palaeontologica Polonica

1996

tom 41

nr 4

319-338

The origin of micritic and peloidal limestones comprising the bulk of many ancient marine carbonate deposits represents a major unsolved problem of carbonate sedimentology. Our studies of such limestones from a sequence of Late Jurassic open marine sediments exposed in central Poland revealed them as products of in situ calcified mats of benthic coccoid cyanobacteria. Remains of the cyanobacteria are visible in scanning electron microscope (SEM) images as characteristic patterns closely resembling the common mucilage sheaths of modern entophysalidacean and/or pleurocapsalean cyanobacteria comparable to those we found producing micritic and peloidal microbialites in Lake Van, Turkey. We suggest, by analogy, that many subtidal micritic and peloidal limestones common in the marine sedimentary record might be products of similar in situ calcified cyanobactend microbiota. Such an intensive calcification of marine cyanobacteria could have proceeded only in environments more than modern seawater supersaturated with respect to calcium carbonate minerals. Advection of excess alkalinity, originating from deeper, anaerobic or dysaerobic zones to shallow water areas is proposed as the main factor enhancing colonization of extensive sea bottom areas by the alkaliphilic cyanobacteria and promoting their in uiuo calcification.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

1 Coleman M. L.

1 Gruszczynski M.

1 Kazmierczak J.

1 Kempe S.

1 Zhen Y. Y.

2 1996

Wyniki wyszukiwania

Succession of coral associations during a Givetian transgressive-regressive cycle in Queensland

Cyanobacterial key to the genesis of micritic and peloidal limestones in ancient seas