Sedimentology of modern alluvial fans, Baja California, Mexico.

Abstract

<p>Five modern alluvial fans in Baja California have been examined In terms of their sedimentary characteristics.</p> <p>Three of the fans are located in Sierra Juarez. They are composed of very coarse boulders up to 5 m in diameter. The coarseness of these boulders is related to the joint weathering of the granite plutons which comprise the source area. The transport process is debris flows which are probably triggered by one of the few but intense summer rainfalls. The two other fans are less coarse and largely formed by sheetflows.</p> <p>Five alluvial-fan derived facies are defined. Two of them; facies A and C, represent debris flow in which the main clast-dispersion mechanism is thought to be dispersive pressure generated by particle collisions. Two more; facies B and D, represent debris flow in which the main clast-dispersion mechanism is thought to be matrix-strength. Finally, facies E represents sheetflow deposition.</p> <p>A remarkable ancient analogue to Sierra Juarez alluvial fans shows that given the same tectonic and climatic setting, similar debris flow ·processes would take place.</p>