Structure of trilobite communities along a delta-marine gradient (Lower Ordovician; Northwestern Argentina)

SERRA, F; BALSEIRO, DIEGO; VAUCHER, ROMAIN; WAISFELD, BEATRIZ G.

PALAIOS

SEPM-SOC SEDIMENTARY GEOLOGY

Lugar: Lawrence; Año: 2021 vol. 36 p. 39 - 52

0883-1351

Throughout their long history, trilobites occupied various ecological niches, colonizing a wide variety ofmarine environments. However, the paleoecology of this group is mostly based on shelf?slope environments and less isknown about their distribution in marginal environments. To understand how trilobite communities respond to adeltaic influence, we studied changes in the taxonomic composition and structure of a diverse and well-known LowerOrdovician olenid-dominated fauna from the Argentine Cordillera Oriental along a delta?marine gradient. Clusteranalysis revealed two distinct associations, and ordination analysis revealed a clear biotic gradient within each. Theecological structure and diversity trends of both associations follow a predictable response to a depth-related gradient.Impoverished communities with a highly nested structure characterize the lower offshore, whereas rich and evencommunities occur in the upper offshore. The trend towards higher diversity and greater taxonomic turnover inshallower environments corresponds to greater habitat heterogeneity. Towards the other extreme, only the ubiquitousgenusJujuyaspiswas  a  successful  colonizer  in  deltaic  settings.  This  marked  contrast  with  the  more  diverse  andabundant  assemblages  of  fully  marine  deposits  indicates  stressful  physiological  conditions  in  marginal-marineenvironments,  where  alternating  and  contrasting  normal-marine  to  brackish-water  conditions  and  high  input  ofsiliciclastic material were among the key factors controlling the distribution of these early trilobite communities.