--> ABSTRACT: Recognition of Miocene and Pliocene Sturzstrom Deposits in Anza-Borrego Desert State Park, California, by Patrick L. Abbott, David A. Rightmer, and Dennis R. Kerr; #91019 (1996)

Datapages, Inc.Print this page

Recognition of Miocene and Pliocene Sturzstrom Deposits in Anza-Borrego Desert State Park, California

Patrick L. Abbott, David A. Rightmer, and Dennis R. Kerr

Sturzstroms are some of the most stunning events on Earth. Rock volumes in excess of one million m3 fall down a steep slope, shatter, and travel distances up to 25 times their vertical fall at velocities up to 280 km/hr.

The Neogene stratigraphic section in the Split Mountain area exposes sturzstrom deposits up to 12 km long with volumes up to 300×106 m3. The sturzstrom deposits have L/W^approx8. Shattered-rock domains still portray the bedrock distribution of lithologies. A unique jigsaw-puzzle fabric occurs on a variety of scales. Stretched and broken pegmatites, as well as bedrock clasts with sworled fabric, step up in the downflow direction.

Purely subaerial sturzstroms up to 70 m-thick disturbed the underlying strata to depths of only a meter, including grooved and decapitated stones and rare sandstone dykes drawn up into the sturzstrom. The basal 2 m of a sturzstrom display elongated, sheared clasts including "comet-like" masses with leading "tails" of shredded debris.

A Pliocene sturzstrom that ended in an inland sea deformed the underlying sediments by injections and sunken sturzstrom masses that caused, tightly folded, bottom-sediment packages >35 m thick to rise diapirically. The terminus is a more traditional, layered sandy conglomerate formed as turbulence caused a rapid stacking of beds.

The sturzstrom deposits present some unique features such as lithologic domains and jigsaw puzzle fabric; they both require laminar flow. For shattered dry rock masses to flow many kilometers at high velocities in laminar flow requires a unique mechanism. Acoustic fluidization best fits the observed features.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California