INVESTIGADORES
PONCE Juan Jose
congresos y reuniones científicas
Título:
Phymatoderma-bearing turbidites (Oligocene, Tierra del Fuego): Ichnologic implications for discrimination of sustained and episodic gravity flow deposits.
Autor/es:
PONCE, J.J.; OLIVERO, E.B.; MARTINIONI, D.R.
Lugar:
Trelew
Reunión:
Congreso; First International Congress on Ichnology; 2004
Resumen:
Distinguishing
sustained, long-lived, from episodic, short-lived, gravity flow deposits only
through physical sedimentary features could be problematic. Careful ichnologic
analysis is an important tool for discrimination of sustained and episodic
gravity flow deposits, as shown from two stacked first order cycles in
deep-water Oligocene turbidites at eastern Tierra del
Fuego. A 91m thick, mudstone-sandstone lower cycle (a)
consists of an upward coarsening-thickening succession, followed by an 81m
thick cycle (b) with a reverse trend and an erosive base.
Cycle (a)
consists of episodic flow deposits (a1, classical turbidites, distal lobe
facies); and sustained, flow deposits (a2, channel fill with lateral accretion
structures), arranged in minor (3m thick) upward coarsening-thickening (a1) and
fining-thinning (a2) cycles. Phymatoderma, Zoophycos, Chondrites,
Tasselia, and a vertical spreite structure are preserved at the top
of cycle (a), typically in episodic flow deposits. Bioturbation is
absent within the channelized deposits of long duration flows (a2) and only the
topmost layer of these deposits is bioturbated.
Cycle (b) consists of fine conglomerates and medium
sandstones, covered by sharp based rhythmically bedded fine sandstones and
mudstones. Only the basal 4m bear burrowed levels, mainly with Phymatoderma
and subordinated Zoophycos, Chondrites and Tasellia. The rest of
cycle (b) lacks bioturbation, recording abundant interstitial fluid
escape structures (convolute bedding) indicating rapid deposition. Overall,
cycle (b) most likely reflects the main back-stepping of long-lived
flows, whose deposits agradationally filled a major channel. Continuous, high
sedimentation rates avoid or reduce suitable conditions for colonization of the
substrate by organisms.