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| Titel |
From stratigraphy to (inferred) processes: development of the late Pleistocene Po Delta clinothems at millennial to centennial scales |
| VerfasserIn |
Claudio Pellegrini, Alessandra Asioli, Tina Drexler, Kevin Bohacs, Michael Sweet, Vittorio Maselli, Fabiano Gamberi, Marzia Rovere, Giacomo Dalla Valle, Fabio Trincardi |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250150103
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| Publikation (Nr.) |
 EGU/EGU2017-14530.pdf |
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| Zusammenfassung |
| The 350-m thick succession of the late-Pleistocene Po River Lowstand Delta (PRLD)
deposited in just 17 k.y. encompassing the Last Glacial Maximum and contains stratal
architecture at a physical scale commonly attributed to much longer time intervals, with
complex, systematically varying internal clinothem characteristics. We document clinothem
characteristics, stacking patterns, and controls through the integration of seismic-reflection
data with sediment attributes, micropaleontology, regional climate, eustacy, and
high-resolution age control on the PRLD. Within the PRLD, three clinothem types are
characterized by distinctive topset geometry, shelf-edge and onlap-point trajectory,
internal seismic facies, and interpreted bottomset deposits: Type A) moderate topset
aggradation, ascending shelf-edge trajectories, and thin mass-transport bottomset
deposits; Type B) eroded topset, descending shelf-edge trajectories, and bottomset
distributary channel-lobe complexes; and Type C) maximal topset aggradation,
ascending shelf-edge trajectories, and draped concordant bottomsets. Measured
sediment accumulation rates suggest that Type A and C clinothems experienced
reduced sediment bypass and delivery to the basin, whereas, Type B clinothems were
associated with short intervals of increased sediment export from the shelf to deep water
and development of distributary channel-lobe complexes. This interpretation is
supported by micropaleontological analyses that highlight increased delivery of
sediment and fresh water to the basin during the progradation of Type B clinothems, as
suggested by the reduced occurrence of Cassidulina laevigata carinata and the peak
abundance of Nonion spp. Each clinothem formed in a very short interval, from
0.4 to 4.7 k.y., contemporaneous with significant eustatic and climate changes.
While changes in stacking patterns at these temporal scales have previously been
observed in modern deltaic clinothems, the significance of our study is that we have
for the first time documented changes to continent-margin-scale clinothems on
this time scale. Our observations have two significant implications for interpreting
older continental-margin-scale deposits: 1) As allogenic factors at millennial- to
centennial time-scales exert a substantial influence on the late Pleistocene continental
margin deposits of the PRLD, the deposits of ancient continental-margin-scale
systems could also record variations of eustacy and sediment supply at these short
time-scales; 2) while previous studies have focused on 100.000 year-scale cycles of
glaciation-deglaciation as temporal scale that determines the balance between shelf
aggradation and sediment export to the deep basin, data from the PRLD show that
sediment export to the basin can be episodic, even over centennial to millennial
time-scales. |
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