Sedimentology and Palaeoecology of Ernietta-Bearing Ediacaran Deposits in Southern Namibia: Implications for Infaunal Ve
The Ediacaran was a period of wide soft-bodied biota development in marine siliciclastic environment. The reconstruction of palaeoecology, lifestyle and environment settings of these organisms are among the challenges in characterising the earliest metazo
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1 Introduction The Ediacaran was a period of wide soft-bodied biota development in marine siliciclastic environment. The reconstruction of palaeoecology, lifestyle and environment settings of these organisms are among the challenges in characterising the earliest metazoan life on Earth. The biota colonised sea bottoms and were living as benthic communities occurring in a wide spectrum of environmental settings (e.g. Gehling 2000; Waggoner 2003; Narbonne 2005; Grazhdankin 2004; Droser et al. 2006). In the classical localities (e.g. Newfoundland, Namibia, White Sea and Australia), the fossils occur in rock successions with distinct depositional settings ranging from distributary mouth-bar of braid-delta systems to deep-water slope (Gehling 2000; Grazhdankin 2004; Narbonne 2005). However, the preservation style of this biota in the sedimentary record as well as their lifestyle and palaeoecology are still unclear for some assemblages and genera of which data are mainly coming from isolated float samples. According to various features including among others taphonomy, ecology, functional morphology and style of preservation within the rock record, two main benthic faunas with contrasting lifestyles are distinguished: (1) epifaunal disc-shaped to sessile leaf-shaped communities, living at the water-sediment interface, generally buried as in situ biota in their habitat and preserved as epireliefs. Such types of palaeocommunities are well recognised in the Avalon-type assemblage where deep-water frondose biota are smothered in their habitat and preserved in turbiditic successions as
E.H. Bouougri Department of Geology, Faculty of Sciences Semlalia, Cadi-Ayyad University, 40020 Marrakech, Morocco H. Porada, K. Weber, and J. Reitner (*) Geowissenschaftliches Zentrum G€ ottingen, Universit€at G€ ottingen, Goldschmidtstrasse 3, 37077 G€ottingen, Germany e-mail: [email protected]
J. Reitner et al., Advances in Stromatolite Geobiology, Lecture Notes in Earth Sciences 131, DOI 10.1007/978-3-642-10415-2_29, # Springer-Verlag Berlin Heidelberg 2011
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casts on bedding surfaces (Narbonne 2005; Hofmann et al. 2008); (2) infaunal bagshaped to canoe-shaped communities commonly preserved as three-dimensional moulds and reported in fossil-bearing rocks as reworked entities or in life position. Exclusively mouldic preservation was suggested for quilted organisms of Namatype fossils like Rangea, Namalia, Pteridinium and Ernietta interpreted as epifaunal or infaunal biota (Jenkins et al. 1981; Jenkins 1992; Buss and Seilacher 1994; Dzik 1999; Grazhdankin and Seilacher 2002, 2005). Although the infaunal or epifaunal lifestyle of some shallow-marine genera is still controversial (e.g. Laflamme and Narbonne 2008), it is necessary to note that various factors have been suggested to explain the diversity and distribution of the Ediacara assemblages, including biogeography, biostratigraphy, ecology and taphonomic processes (Jenkins 1992; Buss and Seilacher 1994; Gehling 1999; Waggoner 2003; Grazhdankin 2004; Narbonn
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