Avetoichnus luisae ichnocoenosis in Paleogene bottom nepheloid layer deposits, Scaglia Toscana Formation, central Italy

• Main Authors: MONACO, Paolo, F. J. Rodríquez Tovar, A. Uchman, T. Trecci
• Other Authors: Neto de Carvalho, Monaco, Paolo, F. J., Rodríquez Tovar, A., Uchman, T., Trecci
• Format: Conference Object
• Language: English
• Published: Neto de Carvalho et al. 2016
• Subjects: Ichnology; North Atlantic
• Online Access: http://hdl.handle.net/11391/1377750; http://ichnia2016.org

Bottom nepheloid layers (BNL) are deep dense waters transporting suspended clay, silt or fine sand with organic matter particles in the central part of basins, with usual suspended sediment concentrations of <0.1 mg/l above background levels, reaching higher concentrations close to the continental rises, with near-bottom peaks >1 mg/l and lesser concentrations < 1 mg/l progressively towards the basin plain (Puig et al., 2013). BNL are very common in recent basin margins (e.g. the continental rise of French Mediterranean, North Atlantic), but poorly studied in the geological record. Some authors think that turbulent flow in BNL is more responsible for deposition of mud in flat basin plains than fine-grained turbidites (P. Pilgrim, personal communication 2010). The thickness of BNL deposits depends on bottom current velocity and the balance between gravitational settling of particles, basin plain morphology and turbulence of the current. Burrowing organisms intensively exploit the organic matter deposited in the sea floor by BNL; in Canadian Atlantic basin plain, the upper surface is extremely bioturbated with hundreds of burrow openings per m2 (Hunkins et al., 1969, figs 3, 4). In the Paleogene Scaglia Toscana Formation (central Italy; Trasimeno area, Montanare, M. Solare, M. Maggio, Fig. 1), grey to red mudstones occur in beds which are 40 to 60 cm thick (Fig. 2). They are much thicker than typical mud turbidites of overlying Macigno Formation (Amendola et al. 2015). A typical increasing upward density of trace fossils (Monaco et al., 2012) has been detected. In lower tiers dominate deep endichnia (Zoophycos, Taenidium, Planolites); in middle and shallow tiers dominate very common Avetoichnus luisae, Chondrites targionii, C. intricatus, and Cladichnus. Then, utilizing ichnocoenoses is possible differentiate turbulent flow deposits (see Shanmugam, 2002; turbidites versus BNL deposits), because currents caused variation in food resources and the presence or absence of nutrient-rich fine-grained ...