Channel incision in the Rio Atenguillo, Jalisco, Mexico, defined by Cl-36 measurements of bedrock
Geomorphology 120,3-4 (2010) 279-292;
The Jalisco Block of western Mexico has undergone uplift in the Tertiary, in response to subduction tectonics. The Atenguillo River, interior to the Jalisco Block, has incised the bedrock units of the Jalisco Block, including Cretaceous ash flow tuff, granite, as well as younger volcanic lava flows. To study incision rates, knickpoint propagation, and the uplift rate of the region samples from nine different points along the Atenguillo channel were collected for Cl-36 exposure age dating. Exposure ages along the length of the channel are high near the head of the basin where the river meanders in a broad plain. Ages are younger at the knickpoints and downstream where the river cuts deeply and forms a canyon. Incision rates measured at different points along the channel also correlate with channel slope and age. Low incision rates are measured in the oldest part of the channel near the head (station B; 2.5 mm/year), and just above the knickpoints (station C; 0.6 mm/year and station G; 1.4 mm/year). The incision rates are highest just below the knickpoints (station F; 2.4 mm/year) and farther downstream (stations H and I; 5.6 and 2.9 mm/year, respectively). The high incision rates can be attributed to subduction-related uplift of the Jalisco Block. Other features attributable to uplift are emergent paleoshorelines and uplifted marine sediments along the coast; and relatively lower incision rates were measured north of the Jalisco Block. Published by Elsevier B.V.
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