ICHNOLOGY OF THE LOWER MIOCENE CHENQUE FORMATION, PATAGONIA, ARGENTINA: ANIMAL - SUBSTRATE INTERACTIONS AND THE MODERN EVOLUTIONARY FAUNA

Noelia B. Carmona, Luis Buatois, María G. Mángano, Richard G. Bromley

Abstract


The lower Miocene Chenque Formation of Patagonia contains superbly preserved and diverse
ichnofaunas, including the ichnogenera Asterosoma, Balanoglossites, Chondrites, Gastrochaenolites, Gyrolithes,
Helicodromites, Macaronichnus, Nereites, Ophiomorpha, Palaeophycus, Phycosiphon, Planolites, Protovirgularia,
Rhizocorallium, Rosselia, Schaubcylindrichnus, Scolicia, Siphonichnus, Skolithos, Spongeliomorpha, Taenidium,
Teichichnus, and Thalassinoides. Wave-influenced open-marine deposits are characterized by intense bioturbation,
complex tiering structures and a very high diversity. Restricted, brackish-water, tide-dominated
deposits display lesser degrees of bioturbation, less complex tiering structures and lower ichnodiversity.
Both marginal- and open-marine deposits are commonly punctuated by discontinuity surfaces delineated
by firmground ichnofaunas. The complex tiering structure of open marine ichnofaunas shows the
development of a finely partitioned infaunal niche and an increment in bioturbation by the Neogene,
which is consistent with trends revealed by body fossils. However, further expansion of the Cenozoic ichnologic
database is necessary in order to evaluate the role of evolutionary and latitudinal controls.

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