Field Trips

1. A Look at Critical Zone Processes in the NW Sierra Nevada.
Sat.–Sun. 18–19 May.
Canceled.
2. Granite, Glaciation, and Rockfall in Yosemite Valley, California.
Sat.–Sun., 18–19 May.
Canceled.
 
3. From Deep to Modern Time along the Western Sierra Nevada Foothills between the San Joaquin and Kern River Drainages.
Sat.–Sun., 18–19 May. Cost: $240, Max: 24.
Jason Saleeby, Zorka Saleeby, Frank Sousa, Div. of Geological and Planetary Sciences, California Institute of Technology.
The western Sierra Nevada Foothills preserve ~500 m.y. of diverse geologic history initiating with the interaction of Panthalassa abyssal lithosphere with the passive margin of the SW Cordillera and accented today by rapidly evolving epeirogenic displacements arising from the ongoing removal of the mantle lithosphere that formed beneath the Cretaceous Sierra Nevada batholith. Our field trip will survey basement exposures that display key stages in western Sierra Nevada lithospheric evolution and geomorphic-stratigraphic relations that reflect geologically recent mobilization of the underlying mantle lithosphere. Key elements surveyed in the basement include (1) a deformed abyssal Moho section interpreted to represent an oceanic spreading ridge-transform intersection core complex; (2) a regional ophiolitic mélange interpreted to have formed along a major transform zone that truncated the SW Cordilleran margin and along which the California Mesozoic convergent margin nucleated; and (3) Early Cretaceous mafic intrusions that are typical of the western Sierra Nevada batholith and its extension into the Great Valley subsurface. Key geomorphic-stratigraphic elements include (1) An exhumed end of Cretaceous pediment surface and its implications on the remnants of Cretaceous paleo-relief throughout the greater Sierra Nevada; (2) anomalous subsidence along the eastern margin of the southern Great Valley interpreted to have arisen from initial mobilization of the underlying mantle lithosphere; and (3) rapid Quaternary uplift and hydrothermal fluxing along part of the southeastern Great Valley arising from the most recent focused phase of mantle lithosphere detachment from the lower crust.
Relevant Theme Sessions: T1 Tectonic Processes that Build the Stratigraphic and Structural Record of Ancient and Modern Convergent Margins; T2 Mélanges: Comparison and Contrast Between Circum-Pacific and Tethyan Chaotic Rock Bodies, and Modern Submarine Analogues; T3 Oceanic Petrogenesis of Pacific-Type Convergent Margins; T4 Ophiolites and Suture Zones; T6 Using Detrital Zircon Age Data to Reassemble the Cordilleran Jigsaw Puzzle.
4. Middle Irvingtonian Fairmead Landfill Fossil Site and Fossil Discovery Center of Madera County, California.
Sun., 19 May. Cost: $50 Max: 24.
Robert G. Dundas, CSU Fresno, rdundas@csufresno.edu; James C. Chatters, CSU Fresno Foundation, paleosciatgmail.com; Eric Scott, San Bernardino County Museum, escottatsbcm.sbcounty.gov.
Celebrating the 20th anniversary of the Fairmead Landfill fossil locality’s discovery, participants will visit the Madera County Fairmead Landfill, the corresponding Madera County Paleontology Collection, and end at the Fossil Discovery Center of Madera County. The middle Irvingtonian aged (0.78 to .55 Ma) Fairmead Landfill fossil site was discovered in May 1993 during excavations for a new expansion cell at the landfill. Paleontological monitoring since 1993 has yielded thousands of fossil specimens representing 71 taxa (two fish, two amphibians, three reptiles, five birds, 29 mammals, one bivalve, one gastropod, 12 plants, and 16 diatoms). Fossils occur in distal alluvial fan channel, distal fan overbank flood or sheetflood, and marsh/lacustrine deposits of the upper unit of the Turlock Lake Formation. Fossils have been collected from a geographic area of more than 40 acres and stratigraphically from depths of 4 m to 20+ m below ground surface. The vertebrate fauna include Archoplites interruptus, Catostomus occidentalis, Caudata, Anura, Clemmys marmorata, Xerobates agassizi,Colubridae, Athene cunicularia, Branta canadensis, Tadorna tadorna,cf. Aythya sp., Zenaida macroura, Sorex sp., Paramylodon harlani, Nothrotheriops shastensis, Megalonyx wheatleyi, Canis latrans, Canis dirus, Vulpes velox, Homotherium sp., Smilodon sp., Miracinonyx sp., Lynx rufus, Panthera sp., Taxidea taxus, Arctodus sp., Spermophilus sp., Neotoma sp., Peromyscus sp., Microtus sp., Thomomys sp., cf. Dipodomys sp., Lepus sp., Mammuthus columbi, Equus sp., Camelops sp., Hemiauchenia sp., Tetrameryx irvingtonensis, Capromeryx sp., Odocoileus sp., and Platygonus vetus. The fauna is dominated by large herbivorous mammals, particularly open-country grazers and mixed feeders such as Equus, Camelops, Mammuthus columbi and Paramylodon harlani. Fairmead Landfill represents an age not well documented in the terrestrial vertebrate record of North America and helps to fill the gap in knowledge about the middle Irvingtonian.
Relevant Theme Session: T13 Irvingtonian Paleoecology of Western North America.
5. LOCKED ROCKS: Hard-to-Access Outcrops of the Mesozoic Metasedimentary Framework and Gabbroids of the Early Cretaceous Sierra Nevada Batholith.
Thurs., 23 May. Cost: $70. Max: 33.
Diane Clemens-Knott, Dept. of Geological Sciences, CSU Fullerton; Jason Saleeby, Div. of Geological and Planetary Sciences, California Institute of Technology.
This one-day trip will begin/end with a one-hour highway commute from Fresno to the greater Visalia area. As we travel back roads through private ranchlands of the Stokes Mountain region, we will track the Mesozoic evolution of depositional environments as recorded in the batholith’s metamorphic framework, progressing from (1) the Triassic ribbon cherts, carbonates, and distal turbidites of the Calaveras Complex; to (2) the Jurassic turbidites of the Kings Sequence; to (3) the Early Cretaceous siliciclastic and volcanic rocks of the Goldstein Peak Formation, which were deposited in a nonmarine, intra-arc basin during the earliest stage of Cretaceous arc activity. As we travel, we will inspect various Early Cretaceous rock types of the Stokes Mountain ring dike complexes, with the trip culminating at a spectacular outcrop of layered olivine-plagioclase cumulates—the most primitive rocks of the Cretaceous Sierra Nevada batholith. Various isotopic (igneous and detrital zircon U-Pb; Hf-Nd-Sr-O), geochemical, and geophysical data will be integrated into reconstructions of Mesozoic paleogeography, tectonics, and the dominantly gabbroic-to-tonalitic Early Cretaceous Sierra Nevada batholith.
Relevant Theme Sessions: T1 Tectonic Processes that Build the Stratigraphic and Structural Record of Ancient and Modern Convergent Margins; T3 Oceanic Petrogenesis of Pacific-Type Convergent Margins; T6 Using Detrital Zircon Age Data to Reassemble the Cordilleran Jigsaw Puzzle; T9 AFC Processes in the Formation of Intermediate Magmas from Mantle to Crust.
6. New Views on the Evolution of the San Andreas Fault Zone in Central California and the Carrizo Plain.
Thur.–Sat., 23–25 May.
Canceled.
 
7. Mélanges, HP Metamorphism, Subduction Accretion and Erosion, Subduction Megathrusts, and Ophiolites: The Franciscan and Related Rocks.
Thur.–Fri., 23–24 May. Cost: $205 Max: 50.
John Wakabayashi, California State University, Fresno, jwakabayashiatcsufresno.edu.
We will visit exposures that highlight the rock record of convergent plate margin processes on round-trip from Fresno through Panoche Pass to the San Francisco Bay area. The trip will feature multiple stops with exceptional exposures of mélange matrix of Franciscan subduction complex showing evidence for sedimentary origins of block in matrix fabric and introduction of exotic blocks/clasts, as well evidence of two and possibly three burial-exposure cycles to blueschist facies or greater depth. At least one of these stops will view exposures that may represent the exhumed subduction megathrust. We will see the large-scale architecture of the preserved trench-forearc system and its implications for non-accretionary versus accretionary episodes, preserved ocean plate stratigraphy within different parts of the system, and the high-grade metamorphism that may record Franciscan subduction initiation. We will also view exposures of the Coast Range ophiolite, considered a good example of a supra-subduction zone ophiolite, along with the forearc basin cover of the Great Valley Group, including the basal olistostrome of the latter that includes high-grade metamorphic blocks.
Relevant Theme Sessions: T1 Tectonic Processes that Build the Stratigraphic and Structural Record of Ancient and Modern Convergent Margins; T2 Mélanges: Comparison and Contrast between Circum-Pacific and Tethyan Chaotic Rock Bodies, and Modern Submarine Analogues; T3 Oceanic Petrogenesis of Pacific-Type Convergent Margins; T4 Ophiolites and Suture Zones; T6 Using Detrital Zircon Age Data to Reassemble the Cordilleran Jigsaw Puzzle.
8. Debris Flows in Recently Burned Watersheds in the Southeastern Sierra Nevada.
Thur.–Sat., 23–25 May.
Canceled.
 

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