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
thesis (scanned
text) - 16.4MB pdf file
Plate 1 - Geologic
map of the Galice and Rogue Formations near Galice, Oregon
coloured geological map (scale 1:31,680) 8.5MB
pdf file
Plate 2 - Station
locale map, Galice, Oregon
uncoloured outline map (scale 1:31,680) 0.5MB
pdf file
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