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The AAPG/Datapages Combined Publications Database

CSPG Special Publications

Abstract


Pangea: Global Environments and Resources — Memoir 17, 1994
Pages 967-982
Biostratigraphy

A Late Pennsylvanian Encruster: Terminal Paleozoic Calcified Demosponge?

Ann Molineux

Abstract

The presence of Incrustospongia meandrica, n. gen. and sp., a late Desmoinesian to early Virgilian stromatoporoid-like encruster in north-central Texas, provides an important opportunity to investigate a rare late Paleozoic encrusting organism and to postulate possible modern relatives. The fossil remains undescribed despite its collection in Texas by F. T. Plummer as early as 1942.

Diagenetic alteration of these encrusters has destroyed much of the original micro-architecture, yet distinct layering and pillar-like structures are observed. These are stromatoporoid characteristics; however astrorhizae and mamelons are absent. Tentative relicts of fascicular aragonite structures within the layered basal skeleton, together with meandroid surface processes and traces of spicules, all point to an affinity with modern calcified demosponges (“sclerosponges”).

Faunal composition and sediment characteristics indicate a shallow water, muddy bottomed environment, with shelled organisms providing a hard substrate for encrustation. Competition for these limited hard surfaces may explain the paucity of other types of encrusters. Thick multi-layered encrustations, often overgrowing both sides of shells, generate an undulating surface with pronounced lobes. Growth on both sides of a shell requires a mechanism for periodic overturning, for example tropical storms.

Sessile organisms such as rugose corals form preferred attachment sites, as do gastropods, bivalves and brachiopods. Evidence points to encrustation of both live and dead hosts, with species-specific selection indicating the importance of host behavior or skeletal chemistry. Few borers are associated with the encrusters, but serpulid worms are often present.

Despite a considerable stratigraphic range, their lateral extent within any unit appears to be rather constrained. This implies a highly specific niche within the community, or a particular environmental constraint.


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