Recent developments in quantitative interpretation of fluvial dune deposits: an application to the Quaternary Loire River, France Suzanne F. Leclair Tulane.

Recent developments in Recent developments in quantitative interpretation of quantitative interpretation of

fluvial dune deposits: an fluvial dune deposits: an application to the Quaternary application to the Quaternary

Loire River, FranceLoire River, FranceSuzanne F. Leclair

Tulane University, New Orleans, LA http://www.tulane.edu/~eens/geol/faculty/leclair.html

Eric C. Straffin1 and Michael D. Blum2

1. Edinboro University of Pennsylvania 2. Louisiana State University, Baton Rouge, LA

Context of this studyContext of this studyFluvial response to allogenic forcing over Fluvial response to allogenic forcing over the last glacial cycle: large rivers of the last glacial cycle: large rivers of southern Francesouthern France

Objective of this studyObjective of this studyUsing characteristics of preserved cross-sets to Using characteristics of preserved cross-sets to reconstruct the paleohydraulic response of the reconstruct the paleohydraulic response of the Loire River to changes in flood regime during the Loire River to changes in flood regime during the late Quaternary.late Quaternary.(using methods described in(using methods described in Leclair and Blom, Leclair and Blom, IAS spec. Publ. 35, in press; Leclair & Bridge, IAS spec. Publ. 35, in press; Leclair & Bridge, JSR, 2001)JSR, 2001)

Results from 2 downstream sites near OrleansResults from 2 downstream sites near Orleans Observed Mean Cross-set Thickness = 0.12 m

Estimated Mean Dune Height 0.35 mEstimated Mean Flow Depth 1m

Lower unit: Obs. Mean Cross-Set Tk= 0.1 mEst. Mean Dune Height 0.3 mEst. Mean Flow Depth 0.8 m

Holocene

Late Pleistocene

(Near-bank situation)

Late Pleistocene LoireLate Pleistocene Loire Predicted mean dune Predicted mean dune

height averages 0.5m height averages 0.5m (0.3 – 0.8m)(0.3 – 0.8m)

Predicted flow depth Predicted flow depth ranges from 1 - 3 m ranges from 1 - 3 m

Modern Loire channelModern Loire channel

Conclusion: Modern floods are Conclusion: Modern floods are typically typically 2 times as deep as late Pleistocene 2 times as deep as late Pleistocene floodsfloods

Flow depth Flow depth 2 - 6 2 - 6 mm

Preliminary results from 7 downstream sites near Preliminary results from 7 downstream sites near OrleansOrleans

Questions for future Questions for future researchresearchWhat are the criteria to distinguish deposits What are the criteria to distinguish deposits

from ‘distinct’ events within a channel?from ‘distinct’ events within a channel?What is the preservation potential for deposits What is the preservation potential for deposits

from a single event?from a single event?What is the effect of partial record of event What is the effect of partial record of event

deposit on analysis?deposit on analysis?

I plan to address these issues by doing I plan to address these issues by doing research on modern rivers, laboratory research on modern rivers, laboratory experiments, and modeling (computer experiments, and modeling (computer

simulation) simulation) If you are interested, please contact me at If you are interested, please contact me at

[email protected]