Tridimentionally integrated trace-fossils from-shallow marine deposits in the Lower Cretaceous of the Neuquén Basin: Hillichnus agrioensis isp. nov.

PAZOS, P.J. AND FERNÀNDEZ, D.E

ACTA GEOLOGICA POLONICA

WYDAWNICTWO NAUKOWE INVIT

Lugar: Warsava; Año: 2010 vol. 60 p. 105 - 118

0001-5709

A complex trace fossil that requires a 3D reconstruction is described and interpreted. The specimens studied are assigned to a new ichnospecies (Hillichnus agrioensis) of Hillichnus BROMLEY et al. 2003. Most of them are uncollectable and a compound iconotype was designed to identify the new ichnospecies. The three-dimensional trace fossil has been recorded in marginal-marine deposits close to the top of the Agrio Formation, Lower Cretaceous of Neuquén Basin, Argentina. The new ichnospecies shows a different pattern of feeding and records defecation downward in the deeper preservational level (level 4). Feather-like forms (level 2) that typify the ichnogenus also record the activity of an inhalant siphon and indicate a retractile movement. The vertical shafts (level 1) are scarcely recorded. Aligned double rings also document the infaunal habit of the tellinid bivalves that are considered the most likely producers of the trac. It is clear that when only level 2 is exposed, sometimes this form can be assigned to Jamesonichnites heinbergi DAM 1990, consequently,  this ichnospecies is interconnected to more than one ichnogenus. Vertical projections recorded in branches differ from the type ichnospecies H. lobosensis BROMLEY et al. 2003. The occurrence in marginal-marine facies is congruent with the record of Jamesonichnites but not common in the type species and similar to those more frequent in deep-sea deposits (e.g. Polykampton alpinum OOSTER 1869).