Trace fossil diversity in hyperpycnites: ethologic implications and comparison to trace fossil in episodic gravity flows

CARMONA, NOELIA; PONCE, JUAN J.; LÓPEZ C., MARÍA I.; OLIVERO, EDUARDO B.

Ushuaia, Tierra del Fuego

Conferencia; AAPG Hedberg Research Conference: Sediment Transfer from Shelf to Deepwater - Revisiting the Delivery Mechanisms; 2008

American Association of Petroleum Geologists

Hyperpycnal flows, generated by extraordinary fluvio-derived discharges, are characterized by sustained sedimentation, fluctuations in flow velocity, and usually have high concentration of phytodetrital influx. On the contrary, “classical turbidites” are generated by episodic gravity flows, after slump events or other gravitational collapses in unstable depositional slopes, and are characterized by a rapid deceleration due to the short-lived sediment influx and the growing friction with the sea floor. In the lower Miocene of the Austral Basin foredeep, thick hyperpycnal deposits generated by hydraulic jumps were recognized at the toe of depositional slope breaks. Six sedimentary facies were identified; each one characterized by transitional and recurrent passages of sedimentary structures, without sharp rheological boundaries and with distinctive trace fossil associations. Particularly, the composition of the trace fossil suites and their distribution in these deposits, differ from the typical associations identified in episodic gravity flow deposits (e.g. classical turbidites).Consequently, the main objectives of this study are to discuss and determine the implications of these fluvio-derived flows in the spatial distribution of the biogenic structures, and to compare these trace fossil suites to those found in episodic gravity flows deposits.