[Todos] Rv: [Geoinfo] Conferencia Dr. Archer

[Roberto A. Scasso]

La Asociación 
Argentina de Sedimentología y el Departamento de Ciencias Geológicas
de la 
UBA tienen el agrado de invitar a la conferencia del Dr. Allen W. 
Archer:


"TIDAL RHYTHMITES IN MODERN AND ANCIENT 
HYPERTIDAL ESTUARIES"

 Aula Amos del Departamento de 
Ciencias Geológicas, FCEyN, UBA. Ciudad
Universitaria, Pabellón II. Ciudad 
Autónoma de Buenos Aires.

 Viernes 19 de Marzo, 14 
hs.


El Dr. Allen W. Archer (PhD University of Indiana) es 
actualmente profesor de
Estratigrafía y Sedimentología en la Univesidad de 
Kansas, USA. Se ha especializado
en ciclicidad y ritmicidad en depósitos 
originados por mareas (tidal rhythmites), de
edades que van desde el 
Precámbrico hasta el presente, particularmente en estuarios
con rangos de 
mareas extremos.


Resumen de la conferencia:

Tidal rhythmites, 
which exhibit systematic variations in lamina thickness, are most
common in 
hypertidal estuaries. Modern examples include the Bay of Fundy in 
eastern
Canada (tidal range >13 m), Ungava Bay in northeastern Canada 
(>12 m), Bay of Mont
Saint Michel in France (>11.5 m), estuaries along 
the Atlantic coast of southern
Argentina (>11 m), and Cook Inlet in 
south-central Alaska , USA (>10 m). These
modern examples provide analogs 
for ancient rhythmites, which have been documented
from the Proterozoic and 
Phanerozoic eons. Within the spectrum of astronomically
forced cycles, 
short-term periods exhibited by tidal rhythmites include semi-daily,
daily, 
half lunar month (neap-spring), and several lunar monthly cycles. All 
of
these periodicities have been reported from modern and ancient of tidal 
rhythmites.
Short-term tidal periods have quite consistent magnitude and 
frequency and thus can
directly affect sedimentation. Over geologic time, 
however,
tidal periods have changed. Examples of very ancient rhythmites 
indicate that the
paleotidal day was significantly shorter and that there 
were more solar days per
year. The rates of sedimentation within hypertidal 
estuaries can be very high,
particularly in the fluvio-estuarine transitional 
zones. Because of the high
turbidity and high sedimentation rates, sediment 
reworking by the biota can be
limited. Thus, bioturbation is minimal. These 
deposits are dominated by physical
sedimentary structures, such as tidal 
bedding, ripples, and thin laminae.


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