ABSTRACT
The western Jurassic belt of the Klamath Mountains is an ideal locale
for the study of ophiolite genesis, island arc development, and study of
flysch deposition from a nearby eroding island arc and continental margin.
Closure and imbrication of an inferred back-arc basin coincided with the
Late Jurassic Nevadan orogeny (ca 150 Ma). The Galice Formation is the
youngest formation involved in the Nevadan orogeny (Lanphere et al., 1968).
In the type section in southwestern Oregon, the Galice structurally overlies
the Rogue Formation volcaniclastics. The Rogue Formation has been previously
interpreted as an island arc assemblage (Garcia, 1979). The type Galice
consists of thin-bedded, dark grey to black slaty shales with a prominent
cleavage. Chert-pebble conglomerate is found locally and most probably
represents the basal Galice. Coarse-grained pebbly sandstone beds with
large shale rip-up clasts are interpreted as representing water-cut channels.
Paleoflow data were calculated from measurements of flute casts, parting
lineation, grooves, and longitudinal ridges found across from the town
of Galice and along Grave Creek. Paleoflow was found to be dominantly towards
the west (Grave Creek section) and north (Galice type section) after corrections
for local folding and overturned bedding.
The Galice is dated as late middle Oxfordian to middle Kimmeridgian
on the basis of Buchia concentrica (Sowerby) (Imlay, 1980). Plant
fragments consisting of carbonaceous broken stems and possible leafy material
are preserved in Galice shales. Apparent trace fossils are found parallel
to sub-parallel to bedding.
The Galice Formation contains minor interbedded volcaniclastics which
appear indistinguishable from the Rogue Formation volcanics. Flattened
shale clasts were observed locally in the tuffaceous units within the Galice.
The Rogue and Galice Formations generally strike N to NE and dip to
the SE. The Rogue-Galice contact is a probable high-angle fault whose exact
displacement and times of displacement are uncertain.
Nevadan folds are found throughout the study area cut by an axial-planar
cleavage. Post-Nevadan folds are defined as those folds that have refolded
the axial-planar cleavage. Bedding-cleavage intersection lineations were
used to describe the trend and plunge of Nevadan fold axes. An asymmetric
Nevadan fold overturned to the NW was identified across from the town of
Galice. The Grave Creek section reveals tight to isoclinal Nevadan folds
and fold vergence alternates in a systematic way from NE to SW. Proposed
F3 or post-Nevadan folds trend NW-SE and account for the dispersal
of Nevadan fold axes.
The Nevadan axial plane AP1 strikes 022º and dips 060ºSE.
The orientation of the post-Nevadan axial plane AP3 is 119º/080ºNE.
F1 and F2 fold axes have similar orientations as
they both trend SSW and plunge gently SW at 4-10º. The F1
and F2 fold axes are interpreted as Nevadan fold axes with F2
representing a late-stage Nevadan folding episode. The mean F2
fold axis trends 303º and plunges 14ºNW. The fold interference
pattern is transitional between types I and II of Ramsay (1967).
XRF and INAA analyses show differences exist between the type Galice
and "Galice" shales that overlie the Josephine ophiolite to the south.
The type Galice and "Galice" shales have higher V, Cr, and Ni abundances
than the standard SCo-1, which is thought to represent an arc volcaniclastic
component or ophiolitic component. Differences were noted in the mean values
of the type Galice and "Galice" in the abundance of Mn, Mg, Na, K, Sr,
and Rb, but these differences are not significant at the 2sigma level.
Comparison of immobile elements showed differences in geochemical behavior
between the type Galice and "Galice" shales in the plots of Zr versus A12O3,
K2O versus TiO2, K2O versus A12O3,
Y versus A12O3, and K2O versus V. These
differences in geochemical behavior are presented as preliminary, general
findings worthy of more detailed study to more accurately characterize
the similarities and differences between the type Galice and "Galice" shales.
Park-Jones, R., 1988. Sedimentology, structure, and geochemistry of
the Galice Formation: sediment fill of a back-arc basin and island arc
in the western Klamath Mountains. Unpublished MSc. thesis, State
University of New York at Albany. 166 pp., +vii; 2 folded plates (maps)
University at Albany Science Library call number: SCIENCE Oversize
(*) QE 40 Z899 1988 P37
Return to MS Theses completed in the Geological
Sciences Program, University at Albany