FACIES ARCHITECTURE AND GROUNDING-LINE FAN PROCESSES OF MORAINAL BANKS DURING THE DEGLACIATION OF COASTAL MAINE

Citation
Le. Hunter et al., FACIES ARCHITECTURE AND GROUNDING-LINE FAN PROCESSES OF MORAINAL BANKS DURING THE DEGLACIATION OF COASTAL MAINE, Geological Society of America bulletin, 108(8), 1996, pp. 1022-1038
Citations number
78
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geosciences, Interdisciplinary
ISSN journal
0016-7606
Volume
108
Issue
8
Year of publication
1996
Pages
1022 - 1038
Database
ISI
SICI code
0016-7606(1996)108:8<1022:FAAGFP>2.0.ZU;2-W
Abstract
Submarine jet processes are inferred from glaciomarine facies exposed in gravel pits in southwestern coastal Maine. The geometry and distrib ution of fan facies depend on (1) the proximity to the grounding line and stream effluxes, (2) the angle of jet trajectory from glacier cond uits, and (3) sediment remobilization processes. Syndepositional glaci otectonic deformation further augments morainal bank formation through pushing and squeezing of fan sediments at the grounding line. Complex process-sediment interactions along the temperate tidewater margin of the Laurentide ice sheet are recorded in the facies architecture of s edimentary sequences in morainal banks. Morainal bank accumulation was governed by rapid fluvial deposition, and outwash jet dynamics that c ontrolled the spatial distribution of sedimentary facies. Near the gro unding line, meltwater dynamics change rapidly where sediment-laden fr esh water is discharged at or near the sea floor. Turbulent mixing wit h ambient sea water and discharge fluctuations cause rapid changes in flow competence, accompanied by the dumping of bed-load gravel and san d at the apices of grounding-line fans in the morainal banks. Jet traj ectory relative to the morainal bank slope determines whether a jet wi ll make contact with the morainal bank. Gravel and sand remain in bed- load traction as long as the jet is in contact with the morainal bank. Bed-load dumping and settling of the coarse suspended load occurs whe re buoyant forces in the jet overcome momentum forces or where the jet is deflected by the morainal bank. Below these buoyant jets, backflow eddies can produce currents that drive ripple migration toward the gr ounding line. Abrupt facies changes record fluctuations in jet dischar ge and trajectory and sediment redistribution by sediment gravity flow s initiated near the grounding line.