www.acsprf.org

This ACS-PRF grant supports a field- and laboratory-based project focused on characterizing a recently discovered sedimentary and volcanic formation preserved in a metamorphic pendant in the western Sierra Nevada batholith. Specific goals of the study are to confirm whether an independent estimate of the Goldstein Peak formation's Early Cretaceous depositional age is correct, as well as to assess where the ancient river sediments were originally derived from (i.e., the sedimentary provenance). The overarching goal of the study is to assess whether these rivers could have contributed sediment to California's oil-rich Great Valley Group. As of August 30th, 2011, all of the fieldwork has been completed. By February 2011, approximately half of the laboratory work (conducted at the University of Arizona Laserchron facility) was completed; the remaining half was completed in September 2011. To date, 9 undergraduate students and 5 graduate students have participated in research associated with this grant.

Substantial tasks completed during the grant's second year include the following:

1. completion of 1 MSc thesis (Mike Martin), 1 undergraduate thesis (Crystal Castellanos), and 1 undergraduate thesis proposal (Kevin Tomita);
1. Martin's thesis completed 1 of the main objectives of this study (confirming the Early Cretaceous age of the Goldstein Peak formation).
2. completion of fieldwork for four new undergraduate theses (Hector Fernandez, Natalie Hollis, Isaac Shirley, Josh Sobolew) and one masters thesis (Chris Buchen);
1. 4 of these student projects (Buchen, Fernandez, Shirley, Sobolew) are directed at
   1. characterizing the older zircons in the local metamorphic framework of the arc, in order to study the provenance of the Goldstein Peak sediments;
   2. determining the depositional age and provenance of the oldest distal sediments in the Great Valley Group of the San Joaquin basin, the Gravelly Flat formation;
   3. assessing whether Goldstein Peak rivers contributed sediment to the Great Valley Group.
2. 1 undergraduate thesis (Hollis) is directed at exploring the provenance of Late Cretaceous proximal forearc sediments associated with the Peninsular Ranges arc, a southern continuation of the Sierra Nevada arc.
3. analysis of 8 detrital zircon samples at the University of Arizona's Laserchron Lab
   1. 4 undergraduate students (Tomita, Gevedon, Hensley, Prior) and one graduate student (Buchen) participated in this Feb. 2011 research experience.
      1. Note: an additional 11 dz samples were analyzed in September 2011; 3 undergraduates (Fernandez, Hollis, Shirley) and 3 new graduate students (Gevedon, Murphy, Moran) participated.
4. submission of 7 abstracts reporting results of this study
   1. 3 presentations, to be made by the PI, 2 undergraduates, and 1 graduate student at the November 2011 ACS meeting in Pasadena, CA.
      1. Presentations will be made in a session co-convened by the PI entitled Frontiers in Geochemistry: The Growing Legacy of PRF-funded Research.
      2. 29 abstracts have been submitted to this session.
   2. 4 presentations, to be made by four undergraduate students and 3 graduate students, at the April 2012 national meeting of the American Association of Petroleum Geologists, in Long Beach, CA.

Preliminary results of this study (2009-2011) are as follows:

1. Mike Martin's detrital zircon data confirm that the depositional age of the Goldstein Peak (GP) formation is indeed Early Cretaceous (140±2 Ma). As such, the GP formation is the oldest recognized nonmarine deposit in the Sierra Nevada arc-Great Valley forearc system.
2. Approximately half of the GP zircons have ages consistent with local derivation from the Jurassic arc.
3. The remaining GP zircons have crystallization ages that date as far back as 3.5 Ga. We consider the stratigraphically underlying Jurassic Kings Sequence and the Paleozoic Calveras Complex as potential sources for older detrital zircons.
   1. The detrital zircon population in a Jurassic turbidite deposit from the Lake Kaweah pendant provides a good match (Kolmogorov-Smirnoff statistical test = 0.90) to one subset of dz samples from the GP formation.
      1. There is significant, and unanticipated, variation within the detrital zircon (dz) populations from the nonmarine GP formation. Such intra-formation variation seems sedimentologically reasonable, but does not appear to have been documented elsewhere.
   2. Good matches to another Goldstein Peak formation dz subset are provided by samples of the Calveras Complex (?), collected 40 km east of the Lake Kaweah pendant (Kolmogorov-Smirnoff statistical test = 0.89).
   3. We are in the process of characterizing detrital zircon populations in the neighboring metamorphic pendants (Tule River, Slate Mountain) in order to determine whether these pendants could represent local sources for all of the older zircons within the GP formation.
      1. We have found it challenging to extract zircon from these older metasediments.
4. We have accidentally discovered one Early Cretaceous metamorphosed ash (125 Ma) and two mid-Cretaceous metamorphosed sandstones (112 Ma; 98 Ma). Though a few metamorphosed ashes of similar ages have been recognized in other roof pendants further east in the arc, this discovery extends the geologic history of the region.

Efforts during the third year of the grant (2011-12) will be directed at making 7 presentations at professional meetings, writing 6 student theses (5 undergraduate; 1 graduate), and completing the first publication on the age and provenance of the Goldstein Peak formation (Martin and Clemens-Knott, in prep.).

2011-2012 Abstracts

Western Regional ACS meeting (November 2011)

• Detrital zircon investigations of Early Cretaceous (?) sediment provenance and delivery to the southern Great Valley forearc basin; Clemens-Knott, Martin, Buchen, Sobolew, Shirley, Fernandez)
• Detrital zircon investigation of metasedimentary rocks at SCICON (Tulare County Office of Education): Using detrital zircon data to enrich the sixth-grade science experience (Tomita, Clemens-Knott)
• Detrital Zircon Study of the Oldest Sediments in the Peninsular Ranges Forearc Basin, Orange Co., CA (Hollis, Gevedon, Clemens-Knott)

National AAPG meeting (April 2012)

• A Detrital Zircon Study of the Age and Provenance of the Gravelly Flat Formation, Great Valley Group and Metasedimentary Rocks of the Tule River and Slate Mountain Pendants (Fernandez, Shirley, Sobolew, Clemens-Knott)
• Age and Provenance of the Oldest Sediments in the Peninsular Range Forearc Basin, Orange Co., CA (Hollis, Gevedon, Clemens-Knott)
• Kings Sequence and Calaveras Complex Rocks of the Southern Lake Kaweah Roof Pendant, Tulare County, California (Buchen & Clemens-Knott)