Research ArticleGEOLOGY

The Mississippi River records glacial-isostatic deformation of North America

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Science Advances  30 Jan 2019:
Vol. 5, no. 1, eaav2366
DOI: 10.1126/sciadv.aav2366
  • Fig. 1 Schematic of drainage integration and forebulge incision.

    (A) An ice sheet dams rivers on one side of a divide, ponding their waters into lakes that overtop the drainage divide. This sediment-poor proglacial lake outflow incises into the paleodivide and the glacial-isostatically uplifting forebulge. (B) When the ice retreats, glaciofluvial erosion has cut a gorge across the divide, permanently integrating drainage. The eroded forebulge subsides and aggrades, leaving a sediment-filled cast of part or all of its shape.

  • Fig. 2 Pleistocene drainage evolution in the upper Mississippi drainage basin.

    (A) The pre-Pleistocene continental divide extended from southern Wisconsin to southern Minnesota (30) and had been stable throughout the Cenozoic (101). The pre-LGM Mississippi River followed the course of the Illinois River over erodible shales; LGM ice advance pushed it into its current course (13). (B) Ice advance (drawn schematically; exact pattern unknown) dammed and rerouted former tributaries to the St. Lawrence, causing them to overtop and incise through the paleodivide (1). (C) Modern rivers and depth to bedrock data points. (D) Location map. In map (A to C) backgrounds, shading indicates shale (easily erodible), and carbonate bedrock underlies most of the paleodivide region (fig. S4).

  • Fig. 3 Upper Mississippi long-profile evolution.

    The Pliocene long profile was reconstructed by identifying ancient river courses and buried strath terraces in statewide depth-to-bedrock data and gridding these sparse elevation markers into a hydrologically consistent DEM (20). The modern mainstem alluvial surface lies above the bedrock long profile of the upper Mississippi, which includes the now-abandoned Princeton Channel–Illinois River course. The bedrock long profile may be split into three zones, as indicated on the figure. Downstream of the forebulge-induced overdeepening, a uniform incision signal dominates. Above the forebulge-induced overdeepening, buried bedrock elevations frequently align with the downstream bedrock long profile, indicating that forebulge incision created a narrow inner gorge that lies within a longer-occupied valley floor.

  • Fig. 4 Modeled long-profile evolution.

    Simulated Pleistocene evolution of the long profile of the upper Mississippi River. Light gray dashed lines indicate lithologic boundaries; shale is the most erodible and limestone and dolostone are the least erodible of those rock units encountered by the river. The pre-integration long profile was modified from our Pliocene surface to account for ~65 m of Pleistocene incision, calibrated to match the elevations of the Bridgeport Terrace in the Wisconsin River Valley (16) and the bedrock profile of the upper Mississippi south of St. Louis (Fig. 3). The incision model used a stream-power law with variable lithology and was forced by a GIA simulation based on the algorithm of (23) and the ICE-6G/VM5a ice-Earth model pairing (11) during the drainage reversal. pЄ, Precambrian (Midcontinent Rift) basement; ss, sandstone; ls&ds, limestone and dolostone.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/1/eaav2366/DC1

    Supplementary Materials and Methods

    Fig. S1. GPS.

    Fig. S2. Bedrock cross section along the Princeton-Illinois course of the upper Mississippi River.

    Fig. S3. GIA-induced deflection during maximum forebulge uplift.

    Fig. S4. Bedrock geologic map.

    Fig. S5. Model tests with two components.

    Data file S1. Bedrock topography data.

    Data file S2. Bedrock geology.

    Data file S3. Generalized bedrock geology.

    Movie S1. Glacial-isostatic adjustment from the Mississippi to the Gulf of Mexico.

    References (41101)

  • Supplementary Materials

    The PDF file includes:

    • Supplementary Materials and Methods
    • Fig. S1. GPS.
    • Fig. S2. Bedrock cross section along the Princeton-Illinois course of the upper Mississippi River.
    • Fig. S3. GIA-induced deflection during maximum forebulge uplift.
    • Fig. S4. Bedrock geologic map.
    • Fig. S5. Model tests with two components.
    • Legends for data files S1 to S3
    • Legend for movie S1
    • References (41101)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Data file S1 (Microsoft Excel format). Bedrock topography data.
    • Data file S2 (Microsoft Excel format). Bedrock geology.
    • Data file S3 (Microsoft Excel format). Generalized bedrock geology.
    • Movie S1 (.mp4 format). Glacial-isostatic adjustment from the Mississippi to the Gulf of Mexico.

    Files in this Data Supplement:

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