AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Coeval Deepwater Slope Channel and Transient Fan Successions in the Eocene Juncal Formation, Coast and Transverse Ranges, Southern California
(1) Geology, Colorado School of Mines, Golden, CO.
The Eocene Juncal Formation, well exposed in the Transverse and Coast mountain ranges of Southern California, consists of a deepwater (500->1500 m water depth) continental slope succession that shallows overall to outer shelf deposits (~100 m water depth). On the Pine Mountain fault block, at least two coeval slope successions are preserved within the Juncal Formation; an Eastern slope succession dominated by conglomeratic channel bodies, and a Western slope succession dominated by sandy, sheet-like channel and fan deposits. The Eastern slope succession is characterized by conglomeratic channel bodies sitting within erosional confinement (50-150 m deep) interbedded with thick intervals (10s m - ~100 m) of fine-grained shale and thin-bedded intervals. Mass-transport deposits are common, and range up to 10s of meters thick. The Western slope succession is characterized by thin (few meters) to thick (~100 m) sandstone bodies that only locally sit within modest (5-15 m deep) confinement, and laterally tend to exhibit interfingering margins. These sandstone bodies are interbedded with thin-bedded intervals (10s-~100 m thick) which exhibit high-energy features such as erosive bases and eroded tops and margins, pebble lags, and injections, although within relatively fine-grained deposits. We interpret the Eastern slope succession as deposits primarily of deeply confined slope channels and their associated overbank, and the Western slope succession as the deposits of an intraslope, transient fan system. Here we compare these coeval continental slope systems, and discuss how their radically different grain-size populations, body geometries, and architectural features relate to their respective depositional environments.