INVESTIGADORES
PONCE Juan Jose
artículos
Título:
Bivalve trace fossils from an early Miocene discontinuity surface: Burrowing behaviour and implications for ichnotaxonomy at the firmground-hardground divide
Autor/es:
CARMONA, N.B.; MÁNGANO, M.G.; BUATOIS, L.A.; PONCE, J.J.
Revista:
PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY
Referencias:
Año: 2007 vol. 255 p. 329 - 341
ISSN:
0031-0182
Resumen:
Ichnofossils developed in a firmground at
the contact between the middle Eocene-lower Miocene continental Sarmiento
Formation and the lower Miocene marine Chenque Formation, in central-eastern
Patagonia, Argentina, are assigned to Gastrochaenolites ornatus Kelly
andBromley [Kelly, S.R.A., Bromley, R.G., 1984. Ichnological nomenclature of
clavate borings. Palaeontology 27, 793807.], and interpreted as dwelling
structures of suspension-feeding bivalves. These record the activities of
pholadids, most likely belonging to the Pholadinae. Bivalves are usually
preserved as casts and external molds within the biogenic structures. The
details of the internal ornamentation in G. ornatus allow identification of two
sets of scratch patterns, permitting comparison with the boring behavior of
modern pholadids.
In terms of ichnotaxonomy, when the same
organism is able both to excavate and to bore, and the excavation technique is
identical to the mechanical perforation technique, the same name should be
used. Accordingly, Gastrochaenolites, whilst more commonly assigned to
bioerosion structures in hard substrates, is herein regarded as available also
for bivalve burrows in firm, but unlithified substrates. The firmground studied
here represents a co-planar surface of lowstand erosion and transgressive
erosion that produced exhumation of deposits belonging to the Sarmiento
Formation, providing appropriate conditions for the development of the
Glossifungites ichnofacies. Differential erosion of the apertural necks, the
heterogeneity of the available casting material, and the wide size range of
ichnofossils suggest a complex history of colonization and erosion for this
surface.