A unifying model for Neoproterozoic–Palaeozoic exceptional fossil preservation through pyritization and carbonaceous compression

A reexamination of Yuknessia from the Cambrian of British Columbia and Utah

“…Similar elemental compositions have been documented for non-biomineralizing fossils from Burgess Shale-type deposits, the material being preserved as carbonaceous compressions but including replication by clay minerals and overprinting by pyrite (e.g., Orr et al, 1998Orr et al, , 2009Gabbott et al, 2004;Hu, 2005;Zhu et al, 2005;Butterfield et al, 2007;Gaines et al, 2008;Page et al, 2008;Anderson et al, 2011;Cai et al, 2012;Meyer et al, 2012;Schiffbauer et al, 2014). The Utah material, however, seems to show a stronger iron overprint than non-biomineralized Burgess Shale material.…”

Exceptionally preserved fossil assemblages through geologic time and space

“…If these processes do not occur, soft tissues that survive early post-burial microbial degradation may be preserved as insoluble (i.e. kerogen) and/or soluble carbonaceous materials (Cai et al, 2012;Schiffbauer et al, 2014b;Stankiewicz et al, 2000), as observed in carbonaceous compressions (Xiao et al, 2002), small carbonaceous microfossils (Butterfield and Harvey, 2012), and organically preserved skeletal fossils . Non-biomineralized tissues are also sometimes preserved in siliciclastic rocks as casts, molds, and impressions (Gutiérrez-Marco and García-Bellido, 2015;Muscente and Allmon, 2013), such as Ediacara-type fossils (Laflamme et al, 2011;Narbonne, 2005).…”

“…The preservation of a single fossil may involve one taphonomic process or many (Cai et al, 2012), and the processes involved in exceptional preservation may vary among tissues within a single specimen (Cai et al, 2012;McNamara et al, 2009), among specimens in a single assemblage (Guan et al, 2016;McNamara et al, 2012b;Schiffbauer et al, 2014b), or among assemblages located proximally in geologic time and space . Well-known fossils, which express evidence of multiple taphonomic processes, include the carbonaceous/ pyritized/aluminosilicified fossils of the Ediacaran Gaojiashan Member (Dengying Formation) in South China (Cai et al, 2012); the carbonaceous/aluminosilicified fossils of the Burgess Shale (Orr et al, 1998); the phosphatized/calcified fossils of Libros in Spain (McNamara et al, 2009(McNamara et al, , 2012b; the carbonaceous/phosphatized fossils of some Burgess Shale-type localities (Butterfield, 2002;Lerosey-Aubril et al, 2012); the phosphatized/pyritized/calcified fossils of the Eocene London Clay (Allison, 1988b); and the fossils of the Carboniferous Mazon Creek and Montceau-les-Mines biotas (Cotroneo et al, 2016;Perrier and Charbonnier, 2014).…”

“…1) include silicification Rice et al, 2002;Strang et al, 2016;Xiao et al, 2010), phosphatization Dornbos, 2011;McNamara et al, 2009;Schiffbauer et al, 2014a), pyritization Guan et al, 2016;Schiffbauer et al, 2014b), aluminosilicification (Cai et al, 2012;Orr et al, 1998), and preservation of tissues with carbonate (i.e. calcite and siderite) minerals Cotroneo et al, 2016).…”

“…Geobiological agents, such as sediment-mixing animals and microbial mats, also influence exceptional preservation. These agents are geospatially variable in their local and regional distributions, and their evolution has shaped nearsurface preservational environments on global scales Schiffbauer et al, 2014b). Global controls, nonetheless, remain contentious (Butterfield, 2012;Pickerill, 1994) because, by and large, most studies have focused on particular assemblages (Schiffbauer et al, 2014b), regions , stratigraphic intervals (Butterfield, 2003), and preservational styles (Gaines et al, 2012b).…”