HR: 17:45h
AN: H54A-08 INVITED     [Abstracts]
TI: Recording of Climatic Signals in Physical Stratigraphy: Experimental Results
AU: * Paola, C
EM: cpaola@umn.edu
AF: St Anthony Falls Lab/Geology & Geophysics, 2 3rd Ave SE, Minneapolis, MN 55414 United States
AB: We review results from experimental stratigraphy studies that bear on interpreting physical-sedimentary climate records. Superposition of base-level cycles driven at comparable but distinct frequencies, such as those associated with climatic glacioeustatic cycles, leads to ambiguously superposed major stratal surfaces. High-frequency cycles grouped on the falling limbs of lower-frequency tend to be highly amalgamated while those on rising limbs are relatively distinct. Preserved erosional "valleys" are highly composite surfaces representing, in some cases, multiple base-level cycles as well as autogenic scour events within a single cycle. One problem in interpreting paleoclimate from preserved physical-sedimentary signals is the interference between relatively high-frequency climatic signals and internally generated (autogenic) signals. In channelized flow systems these autogenic signals, mainly associated with sediment storage and release, have time scales ranging from very short to at least a few thousand years. The upper limit for autogenic variability in terms of time and space scales is not known at present. Experimental data suggest the possibility of long-period cycles involving changes in the overall organization of the channel system. A key feature of autogenic variability is that it cannot be thought of as "noise" that passively masks climatic and other external signals. Rather, autogenic variation actively smears externally forced signals falling within the autogenic frequency range. In some respects the process is analogous to turbulent mixing in fluids. Depending on amplitude, frequency, and location relative to the sampling site, high-frequency climatic signals may be "mixed" to the point of being undetectable.
DE: 8105 Continental margins and sedimentary basins
DE: 4558 Sediment transport
DE: 3022 Marine sediments--processes and transport
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting