Microendoliths in Lower Pliocene Oysters from the Alt Empordà Basin, NW Mediterranean: Paleoenvironmental InferencesIchnos

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Authors
Anna Rita Molinu, Rosa Domènech, Jordi Martinell
Year
2015
DOI
10.1080/10420940.2015.1030071
Subject
Palaeontology / Agricultural and Biological Sciences (all)

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Microendoliths in Lower Pliocene Oysters from the Alt Empordà Basin, NW Mediterranean:

Paleoenvironmental Inferences

Anna Rita Molinua, Rosa Domènecha & Jordi Martinella a Biodiversity Research Institute (IRBio) and Department of Stratigraphy, Paleontology and

Marine Geosciences, Faculty of Geology, University of Barcelona (UB), Barcelona, Spain

Published online: 01 Jun 2015.

To cite this article: Anna Rita Molinu, Rosa Domènech & Jordi Martinell (2015) Microendoliths in Lower Pliocene Oysters from the Alt Empordà Basin, NW Mediterranean: Paleoenvironmental Inferences, Ichnos: An International Journal for Plant and

Animal Traces, 22:2, 77-86, DOI: 10.1080/10420940.2015.1030071

To link to this article: http://dx.doi.org/10.1080/10420940.2015.1030071

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Microendoliths in Lower Pliocene Oysters from the Alt

Emporda Basin, NWMediterranean: Paleoenvironmental

Inferences

Anna Rita Molinu, Rosa Domenech and Jordi Martinell

Biodiversity Research Institute (IRBio) and Department of Stratigraphy, Paleontology and Marine

Geosciences, Faculty of Geology, University of Barcelona (UB), Barcelona, Spain

The study of traces made by microendoliths on Neopycnodonte cochlear shells from a coquina in the Vilacolum area (Alt

Emporda basin) has permitted us to identify for the first time 18 ichnotaxa in the Lower Pliocene sediments of the NW

Mediterranean. A shallow, euphotic environment with local shaded zones (corresponding to deep shallow conditions) is proposed for this shell bed, owing to the presence of abundant heterotroph microborings and rare cyanobacterial traces as well as to the high number of Rhopalia catenata and Ichnoreticulina elegans. This refines a former interpretation, mainly based on body fossils and macroborings, which suggested simply a shallow depositional environment. The ichnospecies Ichnoreticulina elegans, Rhopalia catenata, ?R. clavigera, Saccomorpha clava,

S. terminalis, Polyactina araneola, Entobia mikra, Orthogonum lineare and Aurimorpha varia are identified for the first time in marine Pliocene materials, thus furnishing a more complete picture of the temporal span of some microborers.

Keywords Microbioerosion, Marine paleonvironments, Pliocene,

NW Mediterranean

INTRODUCTION

Microbial euendoliths are defined by their microscopic size (<1 mm) (Wisshak, 2012) and belong to different prokaryotic (cyanobacteria and other bacteria) and eukaryotic (chlorophytes, rhodophytes, fungi and sponges) taxa. Some authors also include carbonate penetrating foraminifera and bryozoans within the microeuendoliths (Radtke, 1991; Bromley et al., 2007). Other microbial groups occupy cavities or fissures within hard substrates, but do not actively bore into them (Golubic et al., 1981).

There are a number of features that make microbioerosion a useful tool in paleoenvironmental interpretations, notably, a) abundance: microborings are abundant in the fossil record linked to calcareous substrates such as coral skeletons, mollusk and brachiopod shells, limestone, and ooids (Glaub and

Vogel, 2004); b) clue-morphology: borings made by recent microendoliths often fit very well with the morphology of the organism that produced the bore, which means they can be identified using specific morphological traits (Radtke, 1991); and c) evolution: taxa in these groups are very conservative over long (geological) time spans at low taxonomic levels (Golubic et al., 1975). Bradytelic evolutionary behavior is a key feature that enables ichnospecies to be identified within the fossil record and their distribution to be inferred by the study of modern counterparts.

Present microbial euendoliths are distributed worldwide and found in diverse ecosystems in marine, terrestrial and freshwater environments. They obtain nutrients from two different sources: cyanobacteria and algae (chlorophytes and rhodophytes) are photoautotrophs and depend mainly on the availability of light to survive; the remaining euendoliths are heterotrophs, and their source of energy is the organic matter within the substrate (Golubic et al., 2005).

Other important physico-chemical parameters that affect the presence of certain euendoliths include temperature and salinity (Gektidis et al., 2007). These parameters can be classified as ecological and environmental indicators (Golubic et al., 1975; Budd and Perkins, 1980; Glaub, 1994; see Wisshak, 2012, for a review). Perry and Hepburn (2008) emphasize the use of microbioerosion as a paleoenvironmental analytical tool, given its high preservation potential, environmental constraints, and role in the identification of taphonomic signatures in reef development.