INSIGHTS INTO THE PALEOGEOGRAPHY OF LAURENTIA DERIVED FROM U-PB AGES OF DETRITAL ZIRCONS IN MESOZOIC STRATA OF THE COLORADO PLATEAU

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Crossing North America Transcontinental Fluvial
Transport of Laurentian Sand to Floodplains and
Deltas Deflated to Feed Jurassic Ergs Colorado
Plateau Eolianite DZ Signature and Interpretation)
RECYCLING OF EOLIANITE SAND
Mixing Pre-Arc and Arc-Derived Grains see
accompanying youngest age poster for age
populations of grains derived from Cordilleran
Mesozoic and East Mexico Permian-Triassic arc
assemblages
Mogollon and Ouachita Provenances
INSIGHTS INTO THE PALEOGEOGRAPHY OF LAURENTIA
DERIVED FROM U-PB AGES OF DETRITAL ZIRCONS IN
MESOZOIC STRATA OF THE COLORADO PLATEAU Wiliam R.
Dickinson and George E. Gehrels (University of
Arizona) Individual U-Pb ages for 5199 detrital
zircon (DZ) grains in 59 samples of Mesozoic
sandstone from the Colorado Plateau, plus the
contiguous High Plains and eastern Great Basin,
provide insight into paleogeographic relations
across southwest Laurentia. U-Pb ages were
determined for 100 DZ grains per sample by
LA-ICP-MS using a beam diameter of 35µ, but ages
gt20 discordant or with analytical uncertainties
gt10 were rejected (average of 88 grain ages
retained per sample). Middle Triassic
fluviodeltaic facies (Moenkopi) and Upper
Triassic fluvial facies (Chinle) of the southern
plateau contain DZ populations derived dominantly
from Proterozoic basement of SW Laurentia and
either the Permian-Triassic East Mexico arc or
the nascent Cordilleran arc within a provenance
lying up-paleocurrent from the Colorado Plateau.
Upper Triassic Chinle-Dockum sandstones from
SSE-to-WNW paleodrainages crossing the High
Plains and Colorado Plateau from headwaters in
the Ouachita foreland contain more heterogeneous
DZ populations that reflect recycling of detritus
from the Ouachita orogen plus contributions of
arc-derived DZ. Even more heterogeneous DZ
populations in Jurassic eolianites are dominated
by Paleozoic, Neoproterozoic, and Grenvillean
grains blown southward across the Colorado
Plateau from floodplains or deltas of
transcontinental paleorivers heading in the
Appalachian region, but also contain
non-Appalachian DZ grains contributed by
tributaries to the paleorivers during transit
across the craton. Western plateau eolianites
lack arc-derived grains, but eastern plateau
eolianites contain admixed DZ derived ultimately
from the East Mexico arc. Lower Jurassic fluvial
facies displaying SSE-to-NNW paleocurrents
contain DZ reflecting either mixture of East
Mexico arc detritus with reworked eolian sand
(Kayenta) or derivation largely from the
Cordilleran arc assemblage (Springdale). Upper
Jurassic and Lower Cretaceous fluvial and Upper
Cretaceous fluviodeltaic facies derived from the
west and southwest contain varied DZ populations
that reflect both recycling of eolianite DZ, off
the Sevier thrustbelt to the west and the
Mogollon highlands to the south, and derivation
from Proterozoic basement of the Mogollon
highlands, together with variable admixtures of
arc-derived DZ of Cordilleran origin.
Age-Distribution Curves of DZ Populations in
Jurassic Eolianite Samples and Samples Derived
from Mogollon Highlands Provenance South of
Colorado Plateau note subdued Paleozoic-Neoproter
ozic-Grenville peaks in latter (top) coupled with
enhanced peaks for Yavapai-Mazatzal basement
(1725 Ma) and associated anorogenic granite (1450
Ma)
Cumulative Age Curves of Dominant gt285 Ma DZ
Grains in Ten Colorado Plateau Jurassic
Eolianites (Aztec, Bluff, Entrada, Navajo,
Nugget, Page, Wingate)
Reworking of Eolian Sand into Marine Curtis
Formation from Underlying Entrada
Sandstone (sharp Curtis age spike at 165 Ma
reflects minor contributions from backarc
eruptive centers of Great Basin to west not
present in Entrada Sandstone with paleowinds from
northeast)
Redistribution of Eolian Sand from Coeval Glen
Canyon Ergs into Fluvial Kayenta Fm (P0.65 for
gt285 Ma grains) note admixture of 288-231 Ma
grains from 284-232 Ma East Mexico arc lying to
southeast of Colorado Plateau with gt285 Ma
grains in Kayenta Formation with WNW
paleocurrents
ACKNOWLEDGMENTS Sample Collection and
Analysis (students and ex-students in
NSF-supported undergraduate Colorado Plateau
Seminar in Department of Geosciences at
University of Arizona) Joseph R. Amar
Linette C. Ancha Carl E. Anderson
Erin V. Brenneman Jessica J. Bressmer
Richard A. Brown Carla M. Eichler
Jennifer D. Fox Erin
H. Gleeson Owen V. Hurd
Jennifer L. McGraw Michael
B. Norton Jaika Ojha
Gregory R. Schmidt Kelley N.
Stair Selected Sample Providers Gerald Bryant
(University of Toronto) Sample DOL Thomas M.
Lehman (Texas Tech University) Sample COO Nancy
Riggs (Northern Arizona University) Sample
SR Stratigraphic Context Confreres Ronald C.
Blakey (No Ariz Univ) Brian S. Currie
(Miami Univ) Peter G. DeCelles (Univ Ariz)
Charles M. Gilbert (Univ Okla)
Timothy F. Lawton (NM State Univ) Thomas M.
Lehman (Texas Tech Univ) Spencer G.
Lucas (NMMNHS) Fred Peterson (USGS)
John H. Stewart (USGS)
Robert J. Stern (Univ Texas Dallas)
Christine Turner-Peterson (USGS) Sample
Collection Permits Anton Chico Land Grant
Hopi Tribe Grand Staircase-Escalante NM
Navajo Nation Pueblo of
Laguna Research Funding Support National Science
Foundation Grants EAR-0341987 and EAR-0443387
DZ Populations in Age Groups of Samples with
Mogollon Provenance (note consistent
Yavapai-Mazatzal and anorogenic granite age peaks)
Age-Distribution Curves (Above) and Cumulative
Age Curves (Below) showing similarity of mixed DZ
grain populations (pre-arc and arc-derived) in
Middle to Upper Jurassic Entrada-Bluff Sandstones
(eastern Colorado Plateau ergs) and Lower
Jurassic Kayenta Formation (fluvially
redistributed erg sand admixed with minor arc
detritus from southeast) P0.3 from K-S Analysis
Recycling Lower-Middle Jurassic Eolian Sand into
Fluvial Upper Jurassic Morrison
Formation (Tidwell-Recapture-Salt Wash-Fiftymile
Members) sources along Sevier thrust belt and/or
Mogollon highlands P0.7 from K-S analysis)
Net Eolianite DZ Age Distribution (gt285 Ma Grains)
Similar Eolianite Recycling into Fluvial Lower
Cretaceous Strata (Cedar Mountain Fm off Sevier
thrust belt Burro Canyon Fm off Mogollon
highlands) see accompanying youngest age poster
for arc-derived grains lt285 Ma
Age Distributions of gt285 Ma DZ Grains in Western
Plateau Eolianites Lacking Arc-Derived Grains and
Eastern Plateau Eolianites Containing Arc-Derived
Grains grains derived from Cordilleran
Triassic-Jurassic and/or East Mexico
Permian-Triassic magmatic arcs admixed with older
grains from eastern and central North America
Principle Paleorivers of Chinle-Dockum Deposystem
Age-Distribution Curves for Chinle-Dockum Samples
of Northeastern Paleodrainages prominent
Cambrian (515-525 Ma) age peaks from
Amarillo-Wichita granite provenance Cambrian
zircon grains probably reworked from Permian
granite-wash sediments overlying Pennsylvanian
Amarillo-Wichita uplift
Grenville-Aged Grains Age distributions of
Mesoproterozoic grains of Grenvillean age that
form prominent age peaks in DZ populations of a
majority (75) of the Colorado PlateauHigh
Plains Mesozoic sandstones are effectively
indistinguishable in groups of samples of varying
ages (see age-probability plots above and
cumulative age plots below) the integrated DZ
signal of detritus from the Grenville orogen
provides no reliable guide to the segment or
segments of the orogen from which detritus was
ultimately derived (plus or minus varied
dispersal paths and intaregional sediment
recycling)
Similar DZ Signatures in Redistributed (Lower
Jurassic Kayenta) or Recycled (Upper
Jurassic-Cretaceous) Eolianite Zircons (Eolianite
Standard at Bottom) prominent 1600-1800 Ma age
peak for fluviodeltaic strata of Sevier foredeep
probably reflects additional reworking of zircons
from Paleozoic and/or Neoproterozoic strata also
incorporated into Sevier thrust belt
Age-Distribution Curves (Above) and Cumulative
Age Curves (Below) showing similarity of mixed DZ
grain populations (pre-arc and arc-derived) in
Middle to Upper Jurassic Entrada-Bluff Sandstones
(eastern Colorado Plateau ergs) and Upper
Jurassic Morrison Formation fluvial sandstones
containing recycled eolianite sand admixed with
minor arc detritus P0.7 from K-S Analysis
Cumulative Age Curves of gt285 Ma DZ Grains in
Western and Eastern Plateau Eolianites (showing
common provenance for pre-arc grains)
Bedrock Zircon Sources in North America
Age-Distribution Curves for DZ Populations of
Chinle-Dockum Samples from Trends of Major
Paleostreams with Headwaters in Ouachita Foreland
(Paleozoic-Neoproterozoic-Grenville grains
probably recycled from sedimentary assemblages
of Ouachita orogen exposed along Eagle Mills rift
shoulder in Texas) see accompanying youngest age
poster for younger arc-derived grains
DZ Age Populations of Paleozoic-Neoproterozoic
Grains in Colorado PlateauHigh Plains Mesozoic
Strata full interpretation uncertain but Upper
Triassic Chinle-Dockum deposystems with
headwaters in Ouachita foreland of Texas display
somewhat different age peaks than Jurassic
eolianites and younger recycled strata with DZ
derived ultimately from eastern North America
Special Note calculation of P-values from
Kolmogorov-Smirnoff statistics allows objective
comparison of two DZ age populations to
supplement visual impressions of age-probability
plots and cumulative-age curves where Pgt0.05,
one cannot be 95 confident that two age
populations were not sampled randomly from the
same parent population (P1.0 for identity)
Linked Transcontinental Fluvial (to WNW)Eolian
(to SSW) Sand Dispersal System for gt285 Ma DZ
Grains in Colorado Plateau Jurassic Ergs
(Stippled)