2014 Pacific Cell FOP

The masses have spoken and the masses voiced loud support for the Tecopa Basin proposal put forth by Marith Reheis on the behalf of John Caskey and others.

We all look forward to an epic trip this November. Look forward to an official announcement.

Here is the original proposal as composed by Reheis (also here: http://www.fop.cascadiageo.org/?p=79#comments)

From Marith:

OK folks, the moment you’ve all been waiting for! or rather, holding your breath so that you won’t feel guilty…

Tecopa Basin Stratigraphy, Chronology, and Structure: A Work in Progress

Leaders: John Caskey, Marith Reheis, Dan Larsen, Gary Scott, Jack Hillhouse, others?

The Tecopa basin and its well-exposed basin-fill sediments have been studied for decades and is a favorite target of Western geology field trips. Sheppard and Gude first examined the chemical alteration of the sediments and recognized three tuffs, A, B, and C, by which to correlate around the basin. Hillhouse and Sarna-Wojcicki (and Izett) correlated these tuffs to the Lava Creek, Bishop, and Huckleberry Ridge tephra layers using glass chemistry and paleomagnetic data. Roger Morrison reconstructed a lacustrine history for the basin, and claimed that the last major highstand reached ~540 m early in OIS 6. Finally, Dan Larsen recently refined the lacustrine history using detailed sedimentology and degree of diagenetic alteration.

For the last 5 years or so, some of us have been looking at other evidence for lake history by analyzing sediments for ostracodes as an indicator of depositional and chemical environment and by looking for preserved beach deposits and (or) strandlines around the basin as an indicator of true lake level. From ostracode analysis, the only sedimentary intervals that contain lacustrine ostracodes as opposed to those that can live in waters derived from groundwater discharge include (1) just below the Huckleberry Ridge ash on the east side of the basin, (2) a several-meter interval just below the Lava Creek ash (with a highstand during or just after LC deposition); and (3) a unit 10-15 m stratigraphically above the Lava Creek. This youngest unit is of uncertain age and possibly could represent similar highstand elevations at different times (we’re working on dating). All three of these intervals are also represented by beach sands and gravels.

For additional FOP stimulus, some of us also think that (1) the shoreline elevations as defined by beach sediments have been warped and (or) faulted; (2) the published stratigraphy of lake units below the Bishop ash as correlated from east to west may be incorrect because the tephra identified as “tuff C” on the western side of the basin is not the Huckleberry Ridge and is probably much younger; (3) the OIS-6 highstand, if there was one, did not exceed 510 m; (4) observations indicating that two (?)lakes, both younger than that associated with the LCB, reached a similar 510 m-high stand elevation, suggesting that lake levels were controlled by a bedrock sill on the “Tecopa hump.”

Recent studies by the proposed trip leaders and others that will also be the focus of discussion on the trip include the timing of Amargosa River integration with the Tecopa and Death Valley basins, and new observations tying the OIS 6 lake-level (shoreline) history of pluvial Lake Manly to the well-dated and studied Badwater core.

All of this is in progress and much of it conflicts with previous work. So the goal of this FOP is to host open discussion of all interpretations, to invite comment, suggestions, and criticism, and hopefully to enable collaborations that will lead to better understanding of this long-lived sedimentary basin. The guidebook will be MINIMAL!

We propose to do this trip in early November 2014, around Veteran’s Day weekend, because delaying till next March won’t see us any more prepared and because March is more commonly typified by howling winds than November.

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