The relationship of bionts and taphonomic processes in molluscan taphofacies formation on the continental shelf and slope: eight-year trends: Gulf of Mexico and Bahamas

Abstract

The Shelf and Slope Experimental Taphonomy Initiative (SSETI) deployed a suite of molluscan species in environments covering a range of depths and sediment types in the Bahamas and on the Gulf of Mexico continental shelf and upper slope for 8 years. Taphonomic state rarely correlated with the distribution of biont guilds among environments. The preservable and nonpreservable biont guilds were also routinely orthogonal. Several coincidences of taphonomic trait and biont guild occurred, including green discoloration that consistently co-occurred with boring algae and bacterial Wlms associated with the development of chalkiness and a soft shell surface. Environments of preservation (EOPs) of disparate taphonomic signature and biont guild complement occur in similar sediment types and environments with similar rates of burial. A paucity of biont coverage is no more a reliable indicator of rapid burial than is a limited degree of shell degradation. The suggestion that preservable bionts might protect shells from taphonomic processes is not well supported. Certain EOP groups are delineated from others most readily by a combination of biont guild and taphonomic trait. Thus, biont guilds augment taphonomic analysis in diVerentiating EOPs. Shell preservational state, including taphonomic signature and biont coverage, is inXuenced in a complex way by environment. The analysis conWrms an expectation that the diversity of EOPs should be greater in shallow water. Clustering of EOPs reveals that visually distinctive environments may be taphonomically and biotically similar. Visually similar environments may be quite disparate in taphonomic state and biont complement. EOPs grouped by similarity in taphonomic signature and biont coverage very likely deWne geographically widespread biological and taphonomic regimes, which, however, are everywhere restricted locally in areal dimension.

Encrustation patterns on Late Cretaceous (Turonian) echinoids from southern Poland

“…Intensity of encrustation is often linked with time of exposure of the substratum and taphonomic processes in general are related in some way to the degree of exposure (e.g., Powell et al 2011). It is predicted that substrates exposed for longer on the sea floor, including redeposited substrates, will have a greater chance to be colonized/ recolonized or more heavily encrusted (e.g., Reolid et al 2005;Rodland et al 2006).…”

Assinaturas tafonômicas em moluscos recentes e seu significado paleoambiental

“…Como a organização da matriz orgânica produz padrões diferentes de dissolução em conchas, há um potencial para a introdução de vieses conforme grupos ecológicos e linhagens evolutivas de moluscos, pois esses diferem na microestrutura de suas conchas (Flessa à precipitação química de óxidos e hidróxidos ricos em ferro (produzindo cores avermelhadas), sulfeto de ferro (produzindo cores cinza e preta) e filmes de minerais aluminossilicatos (produzindo uma grande variedade de cores; Lecinsky et al 2002, Best 2008, Powell et al 2011a). Certas cores (como a marrom) possuem origem duvidosa, possivelmente relacionada à deposição de biofilmes carbonáticos (Aller 1982), ou presença de matéria orgânica vegetal (Best 2008).…”

“…Entretanto, grande parte do conhecimento adquirido tem focado a ação de fatores particulares sobre assinaturas também específicas (e.g. Powell et al 2011aPowell et al , 2011bPowell et al , 2011c. A influência de um conjunto de fatores ambientais sobre o perfil tafonômico de uma associação ainda não é tão bem compreendido.…”

“…Embora seja claro que o dano em moluscos pode ser atribuí-do mais facilmente ao tipo de ambiente do que com sua constituição específica, as taxas de alteração e o efeito do tempo de exposição no sedimento são de difícil compreensão, mesmo em estudos de longo prazo (e.g. Powell et al 2011aPowell et al , 2011b.…”

“…Não obstante, o poder explicativo e a qualidade de vários tipos de dados paleobiológicos têm sido mais bem compreendidos com a intensificação de pesquisas que integram informações do registro fóssil com estudos em ambientes modernos (Cumem ambientes modernos (Cummins et al 1986, Fürsich & Flessa 1987, Flessa et al 1993, Fürsich & Oschmann 1993, Best 2008, Rodrigues et al 2008, Tomašových e Zuschin 2009, Powell et al 2011a, 2011b, 2011c. Recentemente, o núme-ro de trabalhos tafonômicos atualísticos aumentou consideravelmente, por exemplo, com iniciativas como o SSETI (Shelf and Slope Experimental Taphonomy Initiative) (veja Parsons-Hubbard et al 2011 e suas referências).…”