MUDSTONE PETROLOGY OF THE …eps et al_Journal of... · mudstone petrology of the mesoproterozoic...

Journal of Sedimentary Research, 2006, v. 76, 1106–1119

Research Article

DOI: 10.2110/jsr.2006.107

MUDSTONE PETROLOGY OF THE MESOPROTEROZOIC UNKAR GROUP, GRAND CANYON, U.S.A.:PROVENANCE, WEATHERING, AND SEDIMENT TRANSPORT ON INTRACRATONIC RODINIA

JOHN D. BLOCH,1 J. MICHAEL TIMMONS,1* LAURA J. CROSSEY,1 GEORGE E. GEHRELS,2 AND KARL E. KARLSTROM1

1Department of Earth & Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, U.S.A.2Department of Geosciences, University of Arizona, Tucson, Arizona 85721, U.S.A.

e-mail: [email protected]

ABSTRACT: The synthesis of mudstone petrology and interbedded sandstone detrital zircon geochronology provides insightsinto the provenance, weathering regime, hydrodynamic effects, and diagenesis of the Mesoproterozoic Unkar Group. Unkarmudstones were derived largely from the Grenville Orogen (GO) of southwest Texas and the adjacent Yavapai–Mazatzal (YM)and Southern Granite Rhyolite (SGR) terranes. Detrital zircon data indicate distinct pulses of GO-derived sediment duringHakatai and Dox Formation deposition whereas Shinumo sediment contains a larger component of YM and SGR material. Anincrease in plagioclase and biotite abundances in the Dox further suggest an orogenic pulse. Bulk chemistry, including elevatedCr and Ni abundances and REE systematics, implicate a heterogeneous provenance for Unkar sediment best approximated bya mix of granite or granodiorite with some basalt.

Weathering of Unkar sediment, as determined from mudstone and crystalline-source bulk-chemical trends, is characterizedas moderate (CIA values between 55 and 70) indicative of a temperate climate in an orogenic setting. Small (less than 10 wt %)amounts of detrital kaolinite and chlorite are consistent with a moderate (temperate) weathering regime. Illite, the dominantclay mineral in the Unkar Group, is largely the 2M1 polytype and detrital in origin. However, it is estimated that , 7% of theK in the Escalante Creek Member results from K-metasomatism and may form up to , 15 wt% authigenic 1M or 1Md illite.

The clay-size fraction and zircon are the chief contributors to the REE budget in Unkar mudstones. Lithostratigraphicvariations in the HREE distributions can be attributed partially to variable zircon abundance in the silt-size fraction, a likelyfunction of hydrodynamic sorting. Age constraints on the duration of Unkar Group sedimentation range from 30 to100 My forthe , 1100 m conformable Shinumo–Dox succession and result in compacted sedimentation rates of between 1.0 and 3.6 cm/103 yr. These rates are comparable to Mesozoic foreland-basin settings.

INTRODUCTION

The Grand Canyon Supergroup is one of the best-preserved and well-exposed Proterozoic sedimentary successions in the southwestern UnitedStates and has provided significant insights into Precambrian paleogeog-raphy and the evolution of the North American continent (e.g., Beus andMorales 2003 and references therein). Mudstones (sensu stricto Potter etal. 2005, Appendix A.2) constitute greater than 50% of the Grand CanyonSupergroup and are an underutilized resource in evaluating the tectonicand sedimentary evolution of Rodinia and southwest Laurentia. Thisstudy begins to address that deficiency.

Recent work on the Grand Canyon Supergroup (Timmons et al. 2001;Timmons et al. 2005; Dehler et al. 2001) and other Proterozoicsedimentary successions in the southwestern United States and Mexico(Stewart et al. 2001) provides insights into the tectonic and structuraldevelopment and demise of the supercontinent Rodinia and thesubsequent evolution of southwest Laurentia. Much of this work hasutilized sandstone detrital zircon geochronology to evaluate provenance

and reconstruct sediment distribution patterns (e.g., Bickford et al. 2000;Stewart et al. 2001; Fletcher and Heizler 2004). Refined geochronology ofGrand Canyon Proterozoic sedimentary successions (Karlstrom et al.2000; Timmons et al. 2005) permits a more detailed evaluation ofProterozoic basin development, interbasin correlations, and associatedsedimentary paleoenvironments. In addition, new details of the southernportion of the Grenville Orogeny are being revealed by geochemical(Smith et al. 1997; Barnes et al. 2004a; Barnes et al. 2004b), geo-chronological (Bickford et al. 2000; Fletcher et al. 2004), thermochrono-logical (Grimes and Copeland 2004), and tectonic (Mosher 1998) studiesof the remnants of the orogenic belt. All of these studies provide a refinedframework in which to evaluate Mesoproterozoic mudstone compositionand the implications it has for Rodinian tectonics, climate, andweathering.

This study integrates the geochronology, chemistry, and mineralogy ofMesoproterozoic Unkar Group mudstones with some of the existinggeochemical data of coeval Proterozoic ‘‘basement’’ terranes to determinethe sources of Unkar sediment, the influence of Grenvillian orogenesis oninboard Rodinian sediment distribution during Unkar Group (ca. 1.25–1.10 Ga) deposition, and the effects of weathering, transport, anddiagenesis on sediment chemistry.

* Present address: New Mexico Bureau of Geology and Mineral Resources,

Socorro, New Mexico 87801-4796, U.S.A.

Copyright E 2006, SEPM (Society for Sedimentary Geology) 1527-1404/06/076-1106/$03.00

Background

Timmons et al. (2005) link the southern portion of the GrenvilleOrogen (GO) (Texas Grenville of Mosher 1998 and Bickford et al. 2000—, 1360–1070 Ma) with inboard intracratonic basin formation duringdeposition of the Unkar Group (Fig. 1). Sandstone detrital zircongeochronology identifies specific source-area age populations that are, insome cases, coeval with Unkar Group deposition (Timmons et al. 2005).

Unroofing of proximal basement terranes just prior to Unkar Groupdeposition is inferred from Ar40/Ar39 K-feldspar thermochronology anddetrital muscovite thermochronology (Timmons et al. 2005; Fletcher andHeizler 2004; Fletcher et al. 2004) and continued into overlyingNankoweap Formation deposition (Grimes and Copeland 2004). De-position of carbonates and volcanics (ca. 1.25 Ga Allamore andTumbledown formations, Castner Marble), in a back-arc basin orepicontinental seaway, and foreland-basin sandstones (Apache [, 1.30–1.26 Ga] and De Baca [1.40–1.15 Ga] groups) occurred to the southeastof the Unkar basin more proximal to the orogenic front (Timmons et al.2005; Pittenger et al. 1994). This period of sedimentation was coeval withor followed closely by widespread emplacement of ca. 1.16–1.07 GaGrenville-related granites, rhyolites (Shannon et al. 1997; Smith et al.1997; Bickford et al. 2000), and mafic intrusives (Barnes et al. 2004b).

Within the Grand Canyon, the underlying Granite Gorge Meta-morphic Suite (GGMS; Fig. 2) and associated plutonic rocks representdeformation and intrusion related to Paleoproterozoic island-arc de-velopment, amalgamation, and stabilization of juvenile crust (Karlstromet al. 2003). Grand Canyon basement rocks range in age from , 1.84to , 1.40 Ga (Brown et al. 1979; Hawkins et al. 1996; Ilg et al. 1996)and include gabbro and supracrustal metasedimentary and metavolcanicrocks intruded by synorogenic peraluminous granites and aplite. Theserocks are part of the YM Crustal Province (Condie 1992).

Exhumation of basement rocks from mid-crustal depths postdatesemplacement of ca. 1.4 Ga granitoids in the Grand Canyon and predatesthe onset of Unkar Group deposition at , 1.25 Ga. To date, thermo-

chronology suggests that basement exhumation in the Grand Canyon wascontemporary with earliest Grenville orogenesis between 1.30 and1.25 Ga (Fletcher and Heizler 2004; Fletcher et al. 2004).

Deposition of Unkar Group sediments occurred in shallow-watermarine, marginal marine, and fluvial environments. Bass Formationconglomerate, limestone, and mudstone indicate shallow-water deposi-tion in marine to nearshore or marginal marine environments. Hakataimudstones and sandstones may represent prodeltaic to deltaic sedimen-tation and are unconformably overlain by Shinumo nearshore quartzsandstones. The Dox Formation is a complex sequence of marine,estuarine, and fluvial mud-dominated deposits that represent depositionat the prograding margin of the Unkar Basin (Timmons et al. 2005).

The burial history of the Unkar Group is recorded in the Neoproter-ozoic and Phanerozoic rocks of the western Colorado Plateau. Maximumburial depth of , 5.5 km most likely was reached in the Late Cretaceous(Morales 2003), and organic thermal maturation data from the overlyingNeoproterozoic Chuar Group are consistent with a maximum burialtemperature of , 170uC (Wiley et al. 1998; Wiley et al. 2002).

A detailed synopsis of Unkar Group stratigraphy and inferredsedimentary environments is given in Timmons (2004) and Timmons etal. (2005). Additional descriptions of Unkar lithostratigraphy andpaleoenvironments are provided by Hendricks and Stevenson (2003).

Methods

Mudstone samples from multiple locations were collected fromdescribed and measured sections (Timmons 2004), commonly in tandemwith interbedded sandstone samples. U–Pb geochronology of sandstonezircons was conducted by laser ablation multicollector inductivelycoupled plasma mass spectrometry (LA-MC-ICP-MS). A detaileddescription of the method, sources of error, age uncertainties, andinterpretation is provided in the data repository of Timmons et al. (2005).

Complete characterization of the bulk chemistry and mineralogy ofUnkar Group mudstones includes bulk chemical analysis of major and

FIG. 1.— Rodinian paleogeography modifiedafter Timmons et al. (2005) showing inferredfluvial connections between source terranes(see Table 1) and Unkar Basin during depositionof Hakatai, Shinumo, and Dox formations.GC 5 Grand Canyon, FM 5 FranklinMountains, VH 5 Van Horn area,SDC 5 Sierra del Cuervo, PMIC 5 PecosMafic Intrusive Complex, LU 5 Llano Uplift.Solid arrows represent dominant source (Gren-ville Orogenic Front) during Hakatai and Doxdeposition. Open arrows represent dominantsource(s) during Shinumo deposition (Yavapai–Mazatzal and Southern Granite Rhyolite). Sea-way boundaries are speculative.

UNKAR GROUP MUDSTONE PETROLOGY 1107J S R

minor elements by X-ray fluorescence (XRF), bulk X-ray diffraction(XRD) of whole-rock powders, selective clay-mineral analysis by XRD of, 2 mm separates, trace-element and rare-earth-element (REE) analysisof a subset of samples by ICP-MS, and petrographic analysis bybackscattered electron microscopy (BSEM). Bulk chemical and mineral-ogical data are used as input to determine quantitative mineralabundances by linear programming (LPNORM; de Caritat et al. 1994).

Major-element XRF analysis was done on Li-metaborate fused beadsprepared by standard procedures, and minor-element analysis was doneon pressed powder pellets (Baedecker 1987). Comparison of standardanalyses (NBS-688) and replicate analysis of unknowns indicatesaccuracy to within 1.0% for major-element abundances, except Na(4.0%), and , 10% for minor elements. Tabulated bulk major-element,minor-element, and rare-earth-element data are available in the JSRdigital data archive (see Acknowledgments section for URL).

Bulk XRD was done with CuKa radiation generated at 35 mA, 40 kVaccelerating voltage, using a Scintag PAD-V diffractometer on unor-iented powder mounts from 4 to 64u 2h at 2u/minute. Clay-mineral

separates (, 2 mm) were analyzed with identical power settings from 2to 35u 2h at 1u/minute on oriented mounts (millipore method) underconditions of relative humidity, ethyelene glycol saturation, and heatingat 550uC for one hour (Moore and Reynolds 1989). Partial characteristicbulk-rock X-ray diffractogramas are available in the JSR Data Archive.

REE and minor-element analysis (Rb, Sr, Y, Zr, Nb, Ba, Th, U) weredone by ICP-MS on whole-rock digestions (HF and HNO3) usingstandard addition to correct for matrix effects (Jenner et al. 1990).Comparison with standard analysis (MRG-1) and replicate analysis ofunknowns indicates accuracy to within 10% of actual values for allelements except for Zr and Nb (15%), Ba (24%), and Th (, 30%).

Mudstone petrography was done by standard light-microscopy andbackscattered electron microscopy (BSEM) on polished sections. BSEMwas done on carbon-coated sections using a Jeol 5800 LV SEM equippedwith an annular 2 kV-threshold BSE detector. Operating conditions were20 kV, 75 mA filament current, spot size 12, and a working distance of, 10 mm. The SEM is equipped with an Oxford ISIS 300 ultra-thinwindow EDS detector for mineral and matrix characterization.

FIG. 2.—Unkar Group stratigraphy, generalized lithologies, and representative detrital zircon U–Pb age probability distribution plots. Maximum depositional ages arefrom Timmons et al. (2005).

1108 J.D. BLOCH ET AL. J S R

Quantitative mineral abundances are calculated using LPNORM (deCaritat et al. 1994) from bulk major-element oxide data using a mineralsuite that is determined from bulk and clay XRD and petrographic data.Mineral modes determined by linear programming are very sensitive tomineral compositions used as input. Minerals with variable compositionsand that form solid solutions can be problematic. Solid-solutioncompositions (micas, feldspars, carbonates) are calculated using end-member components (e.g., albite–anorthite; calcite–magnesite–siderite)and then combined to give a total abundance and average composition.Chlorite can be similarly modeled using chamosite (Fe) and clinochlore(Mg) end members. For Unkar samples, K-feldspar is determined as pureKAlSi3O8, based on BSEM and EDS analysis. Additional K-bearingminerals used as input to determine Unkar mineral modes includemuscovite (KAl3Si3O10(OH)2) and illite (K0.85Mg0.30Fe3+

0.60Al2.10-Si3.10O10(OH)2. This average illite composition is determined by adjustinginterlayer K and octahedral Al, Mg, and Fe, while minimizing interlayercharge, to reduce or eliminate residual oxides (see de Caritat et al. 1994for details of this method). Based on analyses of standard clay-mineralmixtures and well-characterized clastic sediment, calculated modes areestimated to be within , 15% of actual values. The LPNORM input andoutput files, as well as the tabulated mineral modes, are available in theJSR Data Archive.

RESULTS

Geochronology

Selected age-distribution plots are shown in Figure 2 with estimatedminimum ages of deposition and associated errors. Additional age-distribution data and corresponding concordia diagrams are available inthe JSR Data Archive.

There are three distinct populations of detrital zircons that directlytie Unkar Group sediments to specific source terranes. Older zircon agesto , 1850 Ma indicate sediment input from adjacent tectonic provincesof southwest Rodinia including the Yavapai–Mazatzal (YM; Condie1992) and Southern Granite–Rhyolite (SGR; Van Schmus et al. 1996)terranes (Fig. 2, Table 1). Archean-age zircons may be recycled fromolder sedimentary rocks and the above Mesoproterozoic tectonicprovinces or sourced from the Wyoming Craton or other unknownArchean terranes.

There is a significant population of , 1300 Ma zircons in the HakataiFormation, linking this unit with Grenville-age detritus. The Shinumo

Formation has three distinct populations , 1950 Ma but is dominatedby zircons from 1600 to 1950 Ma, suggesting a significant detrital inputfrom the adjacent YM and SGR terranes. The Dox Formation,represented by the sandstone-rich Solomon Temple Member, has zirconslargely , 1300 Ma, signifying another pulse of GO detritus.

Petrography and Mineralogy

Petrographic characteristics of Unkar mudstones are summarized inTable 2, and average mineral modes are shown in Figure 3. Unkar Groupsediments broadly can be described as red beds with lithologies that rangefrom claystone to fine-grained sandstones but include medium-grained,well-sorted quartzite (Shinumo Formation) and mudchip wacke (Co-manche Point Member). Shallow-water sedimentary structures (wave andcurrent ripples, centimeter-scale foresets) and exposure surfaces (mud-cracks and tension cracks) are common throughout the Unkar Group(Fig. 4A, C). The Shinumo Formation unconformably overlies theHakatai and exhibits intervals of extensive bedding deformation, water-escape structures, and probable seismites (Timmons 2004). The EscalanteCreek Member has numerous thin (, 5 m), stacked, fine-grainedsandstone channels that may be cut and filled with mudstone. TheOchoa Point Member of the Dox Formation has numerous surfaces withexquisitely preserved salt casts (Fig. 4B) and mudcracks.

Most mudstones are matrix supported, and framework grains aredominantly angular to subangular (Fig 4). Graded bedding is common(Fig. 4D). Pseudomatrix is abundant and results mainly from thedeformation of mudstone intraclasts (Fig. 4E, F). Matrix and mudstoneintraclast compositions are very similar (Fig. 4F). Compaction de-formation is minimal, as evidenced by common undeformed micas(Fig. 4D, G), well-preserved mudstone intraclasts (Fig. 4F), minimalframework-grain contacts and suturing (Fig. 4G), and well-preservedearly diagenetic, matrix-hosted dolomite cement (Fig. 4F).

Obvious silicate-mineral authigenesis is restricted to the Bass andHakatai formations in proximity to intrusions of Cardenas basalt andfeeder dikes and sills. These samples have significant K-feldspar cementand, in some cases, a hornfels texture and associated metasomatizedmineral assemblage (see JSR Data Archive). Rare illitization of feldspar isobserved (Fig. 4E).

Backscattered electron microscopy (BSEM) reveals well-preservedlabile framework grains that include plagioclase, biotite, muscovite, andmudstone intraclasts in addition to quartz and K-feldspar (Fig. 4E–G.).Secondary (resulting from weathering and/or diagenesis) framework

TABLE 1.—Data sources for Mesoproterozoic terranes of southwest Rodinia.

Name Age (Ma) Reference

Yavapai–Mazatzal Provinces 1842–1650 Condie 1992 and refs thereinGranite Gorge Metamorphic Suite Babcock et al. 1979

Hawkins et al. 1996Ilg et al. 1996

Southern Granite–Rhyolite Terrane 1450–1350 Anderson and Morrison 1992 and refs. thereinBarnes et al. 2004a

Van Horn AreaCarrizo Mtn. Group 1380–1330 Rudnick 1983

Mosher 1998 and refs. thereinAllamore and Tumbldown fms. 1256–1247 Mosher 1998 and refs. thereinSierra del Cuervo 1333–1080 Blount 1993

Mosher 1998Pecos Mafic Intrusive Complex 1165–1120 Barnes et al. 2004bFranklin Mountains

Red Bluff Granitic Suite , 1120 Shannon et al. 1997Thunderbird Rhyolite , 1111 Roths 1993

Llano Uplift 1120–1070 Smith et al. 1997Mosher 1998Mosher 1998


minerals include illite, chlorite, and kaolinite. Matrix constituents includeclay-size detrital micas, quartz, K-feldspar, and chlorite as well as illiteand kaolinite.

Qualitative mineral variation (as shown by bulk-rock X-ray diffracto-grams; see JSR Data Archive), in conjunction with petrographicobservations and calculated modes, indicate the following:

1. Primary, ash-rich intervals of the Bass Formation have been alteredto an assemblage of K-feldspar and Mg-aluminosilicates that mayinclude diopside, anthophyllite, saponite, and talc. Dolomite maybe a major component, and quartz is less than 20 wt%. Ash layersare recognized by sharp basal contacts, some graded bedding, andmineralogical changes from carbonate or calc-silicate dominated toa more diverse silicate assemblage.

2. The Hakatai Formation has up to , 40 wt% K-feldspar andabundant illite. Illite occurs as 2M1 and 1M or 1Md varieties, anddetrital muscovite is also common. The K-feldspar occurs as detritalgrains, overgrowths, and cement, is predominantly authigenic, andmost likely results from K-metasomatism associated with contactmetamorphism.

3. The Shinumo Formation is characterized as a quartzite, butmudstone-rich intervals in the upper Shinumo, near the contactwith the overlying Dox Formation, contain a significant amount ofdetrital muscovite and/or illite. Similar to the Hakatai, the Shinumocontains virtually no plagioclase feldspar.

4. A major change in mineralogy occurs at the conformable transitionof Shinumo to Dox (Fig. 3). The basal Escalante Creek Member ofthe Dox Formation is very ‘‘immature’’ relative to the Shinumo inthat the mudstone quartz content is lower and the plagioclasecontent is much higher. Detrital biotite and muscovite are alsocommon in the Escalante Creek Member. Total clay content ishigher. The Solomon Temple Member is similar in composition tothe Escalante Creek Member but has a higher sandstone/mudstoneratio, higher hematite abundances, and noticeably less mica.

5. Another distinct compositional change occurs at the SolomonTemple–Comanche Point contact within the Dox Formation. TheComanche Point and overlying Ochoa Point members are finergrained and show a significant increase in K-feldspar contentrelative to the lower Dox. In addition, the abundance of authigeniccarbonate, both dolomite and calcite, increases.

6. The Comanche Point Member has a substantial population ofcoarse-sand-size mudchip intraclasts and therefore can be classifiedas a mudchip wacke, and, uniquely, contains detrital calcite.

Bulk Chemistry

Major Elements.—Tabulated bulk chemical data are available from theJSR Data Archive. Whole-rock major-element variations among Unkar

Group formations and members are readily attributable to variations inmineralogy. Mineralogical variations, in turn, may be controlled byprovenance, weathering, transport and depositional hydrodynamics,diagenesis, and, in the case of the Bass Formation, contact meta-morphism.

Weathering effects, which are dominated by the hydrolysis ofplagioclase, can be assessed by evaluation of major-element variationon A–CN–K and A–CNK–FM ternary diagrams (Fig. 5; Nesbitt 1995).In addition, the Chemical Index of Alteration (CIA; Nesbitt and Young1982) has been superimposed on the A-CN-K ternary to quantify thedegree of weathering (Fedo et al. 1995).

Figure 5 shows the normalized molar bulk oxide composition in A–CN–K and A–CNK–FM space for Unkar samples as well as coevalcrystalline source rocks listed in Table 1. (The molar Ca, Fe, and Mgvalues are corrected to a carbonate and apatite-free basis.) Most of thesource-rock samples fall at or below the A50 line (the feldspar join; Fedoet al. 1995), indicating virtually no alteration of these samples. Three ofthe source-rock samples have A or CIA values of between 50 and 55,indicating a minimal degree of alteration. One sample, a gneiss from theGGMS, is significantly altered (CIA . 75). Excepting this latter sample,all the source-rock values represent viable baseline compositions fromwhich weathering and other alteration trends can be evaluated (Nesbitt1995). A similar conclusion is drawn from the A–CNK–FM ternary,where most source-rock samples fall at or below the biotite–feldspar join,indicating a dominantly unweathered mineralogy.

In A–CN–K space (Fig. 5), Unkar Group samples fall into threegroups. The majority of the samples show a moderate degree ofweathering with CIA values between 55 and 70 and plot above thecenter of the feldspar join. A second group of samples representing theShinumo and Hakatai formations lie along the A–K join and have CIAvalues similar to those of the Dox samples. The third group includes allof the Bass Formation, one sample each from the Ochoa Point andComanche Point members, and a Hakatai Formation sample. These plotbelow the feldspar join and form a trend towards the CN corner,indicating reverse weathering (CIA values , 50); that is, significantdiagenetic and/or contact metamorphic alteration. The mineralogy ofthese samples confirms significant alteration (see JSR Data Archive).

The weathering of plagioclase, the primary alteration process ofcrystalline source rocks, is expressed as a vector parallel to the CN–A join(Nesbitt 1995). The addition of K (K metasomatism) is similarlyexpressed by a vector parallel to A–K. Dox Formation samples (Fig. 6)lie along vectors away from the CN (plagioclase) corner parallel to theCN–A that indicate weathering of plagioclase from a range of granitic torhyolitc compositions, as represented by vector #1 in Figure 6. TheEscalante Creek samples form an oblique (to CN–A) linear trend (#2,Fig. 6) that intersects the feldspar join at a plagioclase/feldspar ratio of, 5:1; a granodiorite. This composition would represent an averageunweathered source (Fedo et al. 1995) of the Escalante Creek sediment.

TABLE 2.—Summary of Unkar Group petrographic characteristics.

Unit Lithology* Sorting Alteration Carbonate1

Bass Claystone–mudrock excellent significant (hornfels) dolomiteHakatai siltstone–f.g. sandstone moderate moderate (authigenic K-feldspar) dolomiteShinumo arenite to sublitharenite w/minor

siltstonewell minor dolomite

Dox Fm.Escalante Creek siltstone well to moderate minor noneSolomon Temple siltstone to f.g. sandstone poor minor noneComanche Pt. siltstone to mudchip wacke poor minor dolomite and detrital calciteOchoa Pt. mudrock to siltstone well to moderate minor dolomite

* see Potter et al. (2005), Appendix A.2, for lithology definitions1 all dolomite is authigenic


The oblique trend of this vector indicates that there is both plagioclaseweathering and a small component of K-metasomatism in EscalanteCreek mudstone alteration, as shown by trend #3. Similar alterationpaths can be traced for the Hakatai and Shinumo samples that indicateeither simple weathering of a more potassic source (#4) or moderate (#5)to intense (#6) weathering and K-metasomatism. Illite is the mostabundant mineral in Unkar mudstones (Fig. 3 and JSR Data Archive),and therefore it is likely that the sequestration of K in illite (or a precursorphase such as smectite or mixed layer illite–smectite) before or afterdeposition (metasomatism) is a factor in Unkar mudstone alteration (seeClay Mineralogy section below).

Ferromagnesian (FM) alteration trends can be evaluated on the A–CNK–FM ternary (Fig. 5). Unkar samples plot in two groups here. Thesamples affected by diagenesis and contact metamorphism lie near orbelow the feldspar–biotite join, as do most of the source-rock samples.The weathered samples lie above the feldspar–biotite join and showa range of Fe and Mg compositions consistent with plagioclaseweathering. However, the FM component is enriched relative to mostof the granite and rhyolite source-rock compositions that are implicatedon the A–CN–K ternary. There are two possible explanations for this.The first is Fe-enrichment by the addition of adsorbed Fe-oxide on claysthat are preferentially sequestered in mudstones (e.g., Fig 4F). Fe-enrichment (ferrallization) occurs in tropical weathering profiles in situ asmore mobile elements are removed from regolith under intenseweathering conditions (Chesworth 1992). Sediment recycling, as indicatedby common to abundant mudstone intraclasts, may enhance this affect.The second explanation is the mixing of a more mafic source componentwith granitic detritus. As shown on the A–CNK–FM plot, there is a rangeof potential sources with increasing Fe and Mg contents that includeGGMS Fe-rich granites (Brown et al. 1979), intermediate to mafic schists,amphibolites (Clark 1979), and basalts (Rudnick 1983; Mosher 1998 andreferences therein; Barnes et al. 2004a).

Rare Earth and Trace Elements.—Representative chondrite-normalizedREE (Fig. 7A) plots of each lithostratigraphic unit indicate LREEenrichment (5.5 , LaN/YbN , 8.6), a moderate negative Eu anomaly(0.6 , Eu/Eu* , 0.8; m 5 0.67), and generally flat HREE distribu-tions characteristic of sediment derived from dominantly granitic sources(Condie 1991; Taylor and McLennan 1985). The variation in HREEdistributions shown in PAAS normalized plots (Fig. 7B) is consistentwith both more variable heavy-mineral abundances and perhaps thepresence of a mafic component (Totten et al. 2000). The mean LaN/YbN

of 6.8 is well below the average shale value of , 13 (Taylor andMcLennan 1985).

Cullers et al. (1975) and Condie (1991) demonstrate the importance ofclay minerals in determining bulk REE in mudstones. In Unkar Groupsamples, comparison of the clay fraction and bulk REE abundanceshighlights the variable REE distribution in the clay-size fraction (Fig. 8).

In all units except the Escalante Creek Member, the LREE are enrichedin the clay-size fraction (Fig. 8). It is therefore likely that illite, the mostabundant clay mineral (see below), is LREE-enriched. In the Ochoa Pointand Comanche Point members and the Hakatai Formation, HREE alsoare concentrated in the clay-size fraction, as shown by clay/whole rockvalues . 1. Zircon, significantly enriched in HREE, is the most abundantheavy mineral in the Unkar Group and has been shown to be a significantcontributor to the REE budget in mudstones (e.g., Taylor and McLennan1985). Hf systematics (Fig. 8), as a proxy for zircon, (Zr–Hf correlationcoefficient 5 0.978; see JSR Data Archive) suggest that zircon occurslargely in the silt-size fraction in the Shinumo Formation and theEscalante Creek and Solomon Temple members (Hfclay/Hfwhole-

rock , 0.6) and therefore a significant portion of the HREE budget inthese units is in the silt-size fraction, not the clay-size fraction. In theHakatai Formation and Ochoa Point Member, most zircon is apparently

FIG. 3.— Four-component average Unkar mudstone compositions after Shawand Weaver (1965). Total clay includes illite, kaolinite, and chlorite. Carbonateincludes dolomite, siderite, and calcite. The Bass Formation contains additionalphases (diopside, anthophyllite) not included in the key. Complete tabulatedmineral modes are provided in the JSR data archive.


FIG. 4.—Outcrop photos and backscattered scanning electron micrographs. For all images, A 5 apatite, B 5 biotite, C 5 calcite, D 5 dolomite, K 5 K-feldspar,M 5 muscovite, P 5 plagioclase, dominantly albite, Q 5 quartz, MI 5 mudstone intraclast. A) Wave ripples, Hakatai Formation; clinometer staff is 50 cm. B) Saltcasts, Ochoa Point Member; chapstick bar code is 3 cm. C) Mudcracks, Comanche Point Member; pencil is 15 cm. D) Graded bedding in Escalante Creek Membersiltstone–claystone, #T017201. Micas are exceptionally large due to hydraulic equivalence. E) Framework-supported coarse-grained siltstone with abundantpseudomatrix, Solomon Temple Member, #T017203, MI is Fe-rich and appears as incipient pseudomatrix. ILL 5 illitized K-feldspar, Kao 5 kaolinite is a detritalclast. F) Mudchip wacke, Comanche Point Member, #T017204; large mudstone intraclasts (MI) are the dominant grain type with authigenic dolomite (D) that consumesor displaces matrix. Circles indicate locations for EDS analysis. EDS show similar compositions for intergranular matrix and MIs. Note large scale bar. G) Matrix-supported mudstone, Shinumo Formation, #K027607; detrital micas show minimal compaction effects.


in the clay-sized fraction (Hfclay/Hfwhole-rock $ 1) and therefore extremelyfine grained. The Comanche Point Member shows a consistent 20%increase in the clay-size REE abundances and an intermediate Hfclay/Hfwhole-rock value of , 0.8. This is a common attribute of manymudstones (Taylor and McLennan 1985).

These observations highlight the complex interplay between mineralogyand grain-size distribution on REE abundances in mudstones. There is nosignificant mineralogical variation within the clay size fraction (see JSRData Archive) consistent with the conclusions of Cullers et al. (1975) thatclay mineralogy is not a controlling factor of REE distributions and thatthe clay size fraction may contain other REE-bearing mineral phases.Further, these observations seem to be at odds with Condie (1991), whosuggests that clays are more important than zircon in controlling bothLREE and HREE distribution in mudstones.

Cr and Ni values show a positive correlation but limited range of valuesin relation to potential sources (Fig. 9). All Unkar Group samples areenriched in Ni and Cr relative to potential granite and rhyolite sources,

and the Dox Formation has a Cr/Ni value of , 1.7, which is consistentwith mixing of upper crustal and total or lower crustal sources (Taylorand McLennan 1985). These data, in addition to Fe enrichment (Fig. 5)and elevated HREE abundances relative to PAAS (Fig. 7B), areinterpreted to indicate a mafic component in the sediment mix. TheHakatai Formation has elevated Cr values relative to the Dox (Cr/Ni , 4.3), suggesting a Cr-enriched mafic component that is distinctfrom that of the overlying Unkar units.

Clay Mineralogy

In most Unkar samples, the , 2 mm fraction consists dominantly ofillite with variable amounts of kaolinite and chlorite (see JSR DataArchive). The Bass Formation contains significant well-crystallizedchlorite and little illite. Illite in shales and mudstones is commonlya mixture of both detrital (allogenic) and authigenic (neoformed in situ)phases (Bailey et al. 1962). K–Ar dating of illites in mudstones confirms

FIG. 5.—A–CN–K and A–CNK–FM ternaries (Nesbitt 1995) with normalized molar abundances for Unkar Group units and potential protolith. Shaded zone is rangeof CIA (Chemical Index of Alteration) values for weathered Unkar samples (see Fedo et al. 1995). Kao 5 kaolinite, Ill 5 illite, Mus 5 muscovite, Ksp 5 K-feldspar,Plg 5 plagioclase feldspar, Chl 5 chlorite, Hem 5 hematite. Line at A 5 50% is feldspar join. See Table 1 for references for source-terrane data and textfor discussion.


that the 2M1 polytype is largely detrital and the 1M and 1Md polytypesare dominantly authigenic in origin (Pevear 1999; Grathoff and Moore1996).

2M1 illite is the most abundant polytype in Unkar mudstones (Fig. 10)and has both detrital and authigenic origins. The Bass, Hakatai, andShinumo formations have very-well-crystallized 2M1 illite, which, in thecase of the Bass and some Hakatai samples, can be attributed to contactmetamorphic conditions. The Shinumo has up to , 50 wt% muscovite,matrix 2M1 illite (JSR Data Archive), and the sampled sections are notproximal to, or crosscut by, intrusive igneous bodies, all of which suggestthat much of the matrix material is detrital. Illite pseudomorphs after

feldspar and/or kaolinite are rare. This is consistent with maximum burialtemperatures of , 170uC. These mineralogical and petrographic char-acteristics, in addition to bulk chemical trends, suggest that the Shinumo

FIG. 6.— Potential weathering and alteration paths (numbered arrows) forUnkar Group sediments. Black arrows represent simple weathering. Red arrowsrepresent weathering and K-metasomatism. White circles and ellipse representpotential source compositions. The Escalante Creek member is the only unit witha linear trend (vector #2). See text for discussion.

FIG. 7.— A) Chondrite and B) PAAS normalized REE distributions forrepresentative Unkar samples.

FIG. 8.— Ratios of REE and Hf clay size (, 2 mm) to whole rock. Units are color-coded to key in Figure 7. See text for discussion.


is derived largely from a more potassium-rich source (trends # 4 and/or#5 in Fig. 6) rather than resulting from significant K-metasomatism (trend#6), and the abundance of muscovite and 2M1 illite further suggestsa significant schist or phyllite protolith component.

In the Dox Formation, the illite001 peak morphology broadens to thelow-angle side, and distinct 1M (or 1Md) and 2M1 peaks are be discerned(see JSR Data Archive). Some Dox samples reveal small but diagnosticpeaks for 1M illite in unoriented diffractograms (Fig. 10). In conjunctionwith BSEM images, these data are interpreted to reflect a greaterabundance of authigenic 1M illite in Dox matrix.

The low abundance of kaolinite (JSR Data Archive) throughout theUnkar Group is inconsistent with intense weathering, but these lowabundances may, in part, reflect some illitization of kaolinite andmoderate K-metasomatism during diagenesis (see below). Significantlyhigher chlorite abundances, particularly in the Dox Formation, are alsoinconsistent with an intense weathering regime and likely reflect moderateweathering conditions and/or more rapid erosion and deposition ofsediment associated with orogenesis.

DISCUSSION

Weathering Effects

Detrital zircon geochronology ties Unkar Group sediment directly tothe adjacent tectonic provinces (YM, SGR) and the Grenville Orogen(GO), consistent with paleocurrent data (Timmons et al. 2005; Hendricksand Stevenson 2003). The primary concern then is how faithfully Unkarmudstones reflect source composition. The Dox Formation, particularlythe Escalante Creek Member, preserves labile minerals including biotiteand plagioclase feldspar, has a lower abundance of hematite, and minimalcompaction and diagenetic alteration. Bulk chemical trends (Figs. 5, 6) ofthe Dox are similar to other Mesoproterozoic mudstone compositionsthat record provenance information and the degree of weathering andalteration (Fedo et al. 1997; Fedo et al. 1996; Nesbitt 1995).

Unkar CIA values (Fig. 5) are similar to those of the glaciogenicPaleoproterozoic Gowganda Formation (CIA 5 , 70;Young andNesbitt 1999) and Neoproterozoic Mineral Fork Formation shales anddiamictites (CIA , 60–75; Young 2002) that are interpreted to representweathering in a temperate climate but are distinctly lower than overlyingChuar Group (Grand Canyon) CIA values (, 70–90; Dehler et al. 2005)that record wet to dry climatic variations in a non-orogenic environment.

Studies of element mobility in weathering profiles show that whereerosion rates are high, elemental fractionation is minimal, and sedimentchemistry reflects provenance chemistry (e.g., Brimhall and Dietrich1987). Nesbitt and Young (1984) demonstrate that despite chemicalweathering and associated mineralogical alteration of protolith, bulkchemical composition may be preserved under a variety of weatheringregimes and climatic conditions. Where annual precipitation rates arehigh, mass flux within soil profiles rapidly approaches elementalequilibrium that reflects parent-rock composition (Stiles et al. 2003),and paleosols are commonly used to evaluate paleoclimate andweathering regimes (e.g., Retallack 1990). Protracted pedogenesis mayresult in loss of mobile elements that includes iron, magnesium, sodium,calcium, and phosphorus (e.g., Sheldon 2003), and REE can befractionated within the pedogenic profile (Morey and Setterholm 1997;Nesbitt 1979), but relatively rapid rates of erosion, particularly intectonically active settings, can mitigate local chemical weathering effects(West et al. 2005; Pasquini et al. 2005; Taylor and McLennan 1985).

Dox Formation CIA values indicate minimal to moderate weathering,and their position on the A–CN–K ternary, relative to potential protolith,are consistent with variable plagioclase weathering and minor K-meta-somatism (trends #3 and #5, Fig. 6). The linear trend of Escalante Creekvalues on the A–CN–K ternary indicates less mixing of sources of variablecomposition (Fedo et al. 1995) and points to a granodiorite source.

Some K-metasomatism has occurred (trend #3, Fig. 6) duringdiagenesis and is the likely source of the 1M illite in the Dox (Fig. 10).Sediment K-uptake during early diagenesis has been documented inestuarine (Hover et al. 2002), deltaic (Johns and Grim 1958), andproximal marine (Drever 1971) environments. It is estimated fromFigure 6 that , 7% of the potassium in the Escalante Creek Membermay result from metasomatism. Using a 1M illite composition with, 0.66 K per unit cell (Grathoff and Moore 1996), approximately 12–15% of the illite in the Escalante Creek could be authigenic. This isconsistent with XRD data that indicate that detrital 2M1 illite is thedominant polytype (Fig. 10).

The close proximity of Unkar bulk chemical values to protolith arguesagainst intense chemical weathering associated with equatorial climatesand ferrallization of weathering residue. The low abundance of kaolinite,significant chlorite content, preservation of labile framework minerals,and the dominance of detrital 2M1 illite suggest a more moderate,temperate weathering regime.

Provenance

The intersection of the Escalante Creek mudstone trend with thefeldspar join in Figure 6 suggests a dominantly granodiorite source forthese sediments, but this composition can be mimicked by the mixing ofmore mafic sources with granite (see below) or chemically equivalentmetamorphic rocks. A mixed source is supported by Fe enrichment andCr/Ni values and is the simplest interpretation of the bulk chemical trendsshown in Figure 5. Totten et al. (2000) identified a similar range of Crvalues in the Mississippian Stanley Group with a mafic (oceanic crust)component, as did Fedo et al. (1996) in the Archean Buhwa Group.

Focusing on immobile elements, a simple mass balance of averagerock-type compositions (Table 3) can be matched to Dox Formationaverage values, as shown in Figure 11. Al and a suite of REE show a goodfit to a mixture of 2:1:1 granite:granodiorite:basalt. Dox REE abundances

FIG. 9.— Cr versus Ni with alkaline source values (shaded area). Intermediateand mafic source terrane values cover the entire graph area beyond (see Table 1 fordata references). Total-crust and upper-crust values are from Taylor andMcLennan (1985). Hakatai Formation (dotted line) has much higher Cr/Ni valuesthan the Dox Formation, represented by Solomon Temple regression (solid line).


are adjusted to 80% of their actual values to compensate for the observed, 20% enrichment in REE relative to crustal sources that commonlyoccurs in moderately weathered mudstones (Nesbitt and Markovics 1997;Taylor and McLennan 1985). This compositional coincidence may notdemonstrate a specific mix of detrital sources, but it does illustrate theviability of a mixed provenance for Unkar mudstones.

Ti, Cr, Ni, and the HREEs Tb and Yb show greater than 40%enrichment from the expected composition of the 2:1:1 source mix. This ismay be due to hydrodynamic sorting, which can result in an increasedmica content (Garver et al. 1996) in the finer fraction, and the presence offiner-grained heavy minerals, particularly zircon, in the silt fraction. Theclay fraction/whole rock REE systematics (Fig. 8) indicate that zircon isa significant contributor to the HREE budget. Both biotite and chlorite,which occur in the clay and silt size fractions, may contain significantamounts of Cr, Ni, and Ti. Clay-sized anatase is also a common matrixconstituent in Unkar sediment.

The exceptional degree of preservation of Dox Formation mudstonesis consistent with rapid erosion and deposition of source material,particularly the increased plagioclase abundance in the EscalanteCreek and Solomon Temple members. In situ exposure and weatheringwere variable, but not intense. The abundance of well-preservedmudstone intraclasts indicates that reworking and deposition offine-grained sediment was also rapid. The persistent occurrence ofintraclasts throughout most of the Dox Formation indicates relativelyrapid, intraformational recycling of mudstones. The similarity ofmudstone clast and Unkar matrix (Fig. 4F) compositions indicates thatintraformational recycling of sediment occurs without significantfractionation of mineralogy or bulk chemistry. Without the definitiveidentification of primary mineral components (detrital plagioclase,biotite, muscovite, apatite) indicative of crystalline protolith, it wouldnot be possible to discern a crystalline from a sedimentary source forUnkar mudstones.

FIG. 10.—Partial unoriented , 2 mm diffrac-tograms comparing diagnostic peaks for 2M1

(arrows) and 1M (dashed lines) illite. Verticalscale bars are 200 cps. Q 5 quartz, F 5 K-feldspar, D 5 dolomite.


Sedimentation in the Unkar Basin

The data on zircon age distribution (Fig. 2) suggest that much of thebasal Hakatai sediment is GO-derived and, therefore, that fluvial systemswere delivering Grenville detritus from the orogenic front across theinferred foreland, a distance of some 800 km (Fig. 1). As the forelandmatured, and perhaps orogenesis slowed, distributary systems developedwithin the YM and SGRT that mixed this detritus with GO material. Ifthe zircon age-distribution data are representative of sediment volumes,during Shinumo time YM and SRGT detritus dominated the sedimentaryinput into the Unkar Basin. This implies a shift from southern to moreeasterly sources for sediment that may have included an Archeancomponent from the Wyoming Craton. Alternatively, Archean zirconsare an inherited component of the YM terrane (e.g., Hawkins et al. 1996).At the onset of Dox deposition, perhaps in response to renewedorogenesis, GO detritus again surged into the Unkar Basin. Paleocurrentdata from the lower Dox Formation indicate flow directions to thenorth and northeast (Timmons et al. 2005). The increased abundanceof plagioclase and biotite in the Escalante Creek Member is consistent

with this scenario. The compositional change between the SolomonTemple and Comanche Point members, characterized by an increasein K-feldspar, muscovite, hematite, and diagenetic dolomitization, isconsistent with a slower sedimentation rate and a lull in orogenesis.Detrital calcite in the Comanche Point Member indicates erosion andrecycling of uplifted marine sediment from the evolving foreland. Coarse-sand-size mudchips indicate localized, intraformational recycling ofmudstone.

Age constraints on the duration of Unkar deposition are tenuous(Fig. 2) but could be as short as , 30 My or as long as , 100 My. Theapproximate thickness of the conformable Shinumo–Dox succession is1.1 km, which yields a compacted sedimentation rate of between 1 and3.6 cm/103 yr. This range is comparable to modeled subsidence rates forthe Western Canada Sedimentary Basin (Jervey 1992), and the higher rateis comparable to Cretaceous foreland basin deposits (e.g., Schroder-Adams et al. 1996) of western Canada.

CONCLUSIONS

The synthesis of geochemistry, mineralogy, and petrography withdetrital zircon U–Pb data allows specific provenance information,constraints on weathering characteristics, and the effects of transportand hydrodynamic sorting on Unkar Group sediment. Sandstone detritalzircon geochronology implicates the Grenville Orogen (GO) of southwestTexas as a primary source of Hakatai and Dox Formation sediment.Additional sediment sources include the adjacent Yavapai–Mazatzal(YM) and Southern Granite Rhyolite (SGR) terranes and possibly theArchean Wyoming Craton.

Weathering effects in source areas and during Unkar deposition wereminimal to moderate, consistent with a temperate climate in an orogenicsetting. The hydrolysis of plagioclase and micas resulted in a secondarymineral assemblage dominated by quartz and clay minerals. Petrographiccharacteristics and the dominance of 2M1 illite, in addition to chlorite andkaolinite, indicate that the clay fraction is largely detrital in origin. Bulkchemical trends for K, Ca, Na, and Al suggest, however, that up to, 7 wt% of the K, or , 12–15 wt% of the illite in the Dox Formation,may result from K-metasomatism. The Bass and, to a lesser extent, theHakatai formations locally have been altered by contact metamorphismto hornfels facies.

The chemistry of remnant GO point sources located in west andsouthwest Texas, as well as crystalline igneous and metamorphicbasement from the adjacent YM and SGR terranes, are representative

FIG. 11.— Comparison of immobile-element abundances in Dox Formationsamples and a calculated protolith composed of 2:1:1 granite:granodiorite:basalt.Dox chondrite-normalized REE abundances are reduced to 80% of their actualvalues (Taylor and McLennan 1985). Elements with . 40% enrichment in Doxsamples are white boxes. See Table 3 for numerical values and text for discussion.

TABLE 3.—Compositional data for mixing mass balance (ppm).

Element Granite1 Granodiorite1 Basalt1 Dox average m Dox w/ 80% REE Mix 2:1:13

Al2O32 14.2 16.9 17.6 15.7 15.7 15.7

TiO22 0.2 0.6 0.7 0.8 0.8 0.4

Th 17.0 10.0 2.2 11.0 11.0 11.6Nb 20.0 20.0 20.0 17.9 17.9 20.0Y 40.0 30.0 25.0 30.1 30.1 33.8La4 68.1 98.1 27.2 111.0 88.8 65.4Nd 25.3 36.6 25.3 42.0 33.6 28.1Sm 13.0 30.3 17.3 23.0 18.4 18.4Eu 11.5 13.8 14.9 13.0 10.4 12.9Gd 6.5 24.2 15.4 17.0 13.6 13.2Tb 0.9 22.4 10.3 15.0 12.0 8.6Yb 0.2 14.5 4.4 15.0 12.0 4.9Cr 4.0 20.0 200.0 98.0 98.0 57.0Ni 0.5 20.0 150.0 63.0 63.0 42.8

1 data from Levinson (1980).2 weight percent.3 granite:granodiorite:basalt.4 REEs chondite normalized.


of Dox sediment sources. Bulk chemical trends and mineralogy indicatethat the Dox Formation, particularly the Escalante Creek Member, bestpreserves a provenance signature. Simple mass-balance calculations usingimmobile elements suggest that a mix of granite, granodiorite, and basaltin proportions of 2:1:1, respectively, may approximate the protolith ofDox Formation mudstones. A high Fe content, Cr/Ni values, and perhapselevated HREE abundances, relative to PAAS, are consistent witha mixed source. The Hakatai and Shinumo formations most likely werederived from a more potassic source. The abundance of muscovite anddetrital 2M1 illite in the Shinumo Formation suggests a significant schistor phyllite provenance component. The Hakatai Formation has a higherCr/Ni ratio, suggesting a different mafic source in the mix.

Hf and REE distributions indicate that the clay-size mineral fractionand variable zircon content and size distribution control the REEsystematics in Unkar samples. Although the REE signatures preserveprovenance information, they are perturbed by hydrodyamic effectsduring transport and deposition that fractionate clay-size material andthe heavy-mineral suite. Ni, Cr, and Ti, in addition to Tb and Yb, areenriched relative to a potential mixed protolith, most likely due tovariable zircon and increased biotite and chlorite content. Unkar Groupmudstone geochemical compositions and mineralogy reflect a mixedprovenance signature subtly altered by weathering, transport, deposition,and diagenesis. Without detailed petrographic examination and de-termination of quantitative mineral modes, it would not be possible todiscern a sedimentary from a crystalline source for much of the Unkarsedimentary package.

ACKNOWLEDGMENTS

Funding for this research was provided by the National ScienceFoundation, grant number EAR-0208463 to K. Karlstrom, L. Crossey, andJ. Bloch with additional support by Ben Donegan Consultants. The authorswish to thank the National Park Service and particularly the staff of GrandCanyon National Park for their cooperation and support of UNM fieldresearch. R. Rudnick is thanked for providing data on the Carrizo MountainGroup. R.L. Cullers, an anonymous reviewer, and Associate Editor L. Lynchare thanked for their constructive comments on an earlier draft of thismanuscript. The data described in this paper have been archived, and areavailable in digital form, at the SEPM data archive at http://www.sepm.org/archive/index.html. This work is dedicated to George B. Dantzig, the creatorof the simplex algorithm and linear programming.

REFERENCES

ANDERSON, J.L., AND MORRISON, J., 1992, The role of anorogenic granites in theProterozoic crustal development of North America, in Condie, K.C., ed., ProterozoicCrustal Evolution: New York, Elsevier, Developments in Precambrian Geology, no.10, p. 263–299.

BABCOCK, R.S., BROWN, E.H., CLARK, M.D., AND LIVINGSTON, D.E., 1979, Geology ofthe older Precambrian rocks of the Grand Canyon: Part II—the Zoroaster plutoniccomplex and related rocks, Precambrian Research, v. 8, p. 243–275.

BAEDECKER, P.A., 1987, Methods for geochemical analysis: U.S. Geological Survey,Bulletin 1770, p. 4–6.

BAILEY, S.W., HURLEY, P.M., FAIRBAIRN, H.W., AND PINSON, W.H., 1962, K–Ar datingof sedimentary illite polytypes: Geological Society of America, Bulletin, v. 73, p.1167–1170.

BARNES, M.A., ROHS, C.R., ANTHONY, E.Y., VAN SCHMUS, W.R., AND DENISON, R.E.,2004a, Isotopic and elemental chemistry of subsurface Precambrian igneous rocks,west Texas and eastern New Mexico: Rocky Mountain Geology, v. 34, p. 245–262.

BARNES, C.G., SHANNON, W.M., AND KARGI, H., 2004b, Diverse Mesoproterozoicbasaltic magmatism in west Texas: Rocky Mountain Geology, v. 34, p. 263–273.

BEUS, S.S., and MORALES, M., eds., 2003, Grand Canyon Geology: New York, OxfordUniversity Press, 432 p.

BICKFORD, M.E., SOEGAARD, K., NIELSEN, K.C., AND MCLELLAND, J.M., 2000, Geologyand geochronology of Grenville-age rocks in the Van Horn and Franklin Mountainsarea, West Texas: implications for the tectonic evolution of Laurentia during theGrenville: Geological Society of America, Bulletin, v. 112, p. 1134–1148.

BLOUNT, J.G., 1993, The geochemistry, petrogenesis and geochronology of thePrecambrian meta-igneous rocks of Sierra del Cuervo and cerro El-Carrizalillo,Chihuahua, Mexico [Ph.D. dissertation]: University of Texas at Austin, 242 p.

BRIMHALL, G.H., AND DIETRICH, W.E., 1987, Constitutive mass balance relationsbetween chemical composition, volume, density, porosity, and strain in metasomatichydrochemical systems: Results on weathering and pedogenesis: Geochimica etCosmochimica Acta, v. 51, p. 567–587.

BROWN, E.H., BABCOCK, R.S., CLARK, M.D., AND LIVINGSTON, D.E., 1979, Geology ofthe older Precambrian rocks of the Grand Canyon, Part 1. Petrology and structure ofthe Vishnu Complex: Precambrian Research, v. 8, p. 219–241.

CHESWORTH, W., 1992, Weathering systems, in Martini, I.P., and Chesworth, W., eds.,Weathering, Soils and Paleosols: New York, Elsevier, p. 19–40.

CLARK, M.D., 1979, Geology of the older Precambrian rocks of the Grand Canyon, PartIII—petrology of mafic schists and amphibolites: Precambrian Research, v. 8, p.277–302.

CONDIE, K.C., 1991, Another look at rare earth elements in shales: Geochimica etCosmochimica Acta, v. 55, p. 2527–2531.

CONDIE, K.C., 1992, Proterozoic terranes and continental accretion in southwesternNorth America, in Condie, K.C., ed., Proterozoic Crustal Evolution: New York,Elsevier, Developments in Precambrian Geology, no. 10, p. 447–480.

CULLERS, R.L., CHAUDHURI, S., ARNOLD, B., LEE, M., AND WOLF, C.W., JR., 1975, Rareearth distributions in clay minerals and in the clay-sized fraction of the lower PermianHavensville and Eskridge shales of Kansas and Oklahoma: Geochimica etCosmochimica Acta, v. 39, p. 1691–1703.

DE CARITAT, P., BLOCH, J., AND HUTCHEON, I., 1994, LPNORM: a linear programmingnormative analysis code: Computers & Geoscience, v. 20, p. 131–347.

DEHLER, C.M., ELRICK, M., KARSTROM, K.E., SMITH, G.A., CROSSEY, L.J., AND TIMMONS,J.M., 2001, Neoproterozoic Chuar Group (, 800–742 Ma), Grand Canyon: a recordof cyclic marine deposition during global cooling and supercontinent rifting:Sedimentary Geology, v. 141, p. 465–499.

DEHLER, C.M., ELRICK, M., BLOCH, J.D., CROSSEY, L.J., KARLSTROM, K.E., AND DES

MARAIS, D.J., 2005, High-resolution d13C stratigraphy of the Chuar Group (, 770–742 Ma), Grand Canyon: implications for mid-Neoproterozoic climate change:Geological Society of America, Bulletin, v. 117, p. 32–45.

DREVER, J.I., 1971, Early diagenesis of clay minerals, Rio Ameca Basin, Mexico: Journalof Sedimentary Petrology, v. 41, p. 982–994.

FEDO, C.M., NESBITT, H.W., AND YOUNG, G.M., 1995, Unraveling the effects ofpotassium metasomatism in sedimentary rocks and paleosols, with implications forpaleoweathering conditions and provenance: Geology, v. 23, p. 921–924.

FEDO, C.M., ERIKSSON, K.A., AND KROGSTAD, E.J., 1996, Geochemistry of shales fromthe Archean (, 3.0 Ga) Buhwa Greenstone Belt, Zimbabwe: implications forprovenance and source-area weathering: Geochimica et Cosmochimica Acta, v. 60,p. 1751–1763.

FEDO, C.M., YOUNG, G.M., AND NESBITT, H.W., 1997, Paleoclimatic control on thecomposition of the Paleoproterozoic serpent Formation, Huronian Supergroup,Canada: a greenhouse to icehouse transition: Precambrian Research, v. 86, p.201–223.

FLETCHER, K., AND HEIZLER, M.T., 2004, Probing the secrets of Rodinia: pieces of thesupercontinent puzzle extracted from 40Ar/39Ar geochronology of detrital muscovites:New Mexico Geological Society, 2004 Annual Spring Meeting, Proceedings Volume,p. 16.

FLETCHER, K.E., HEIZLER, M.T., KARLSTROM, K.E., TIMMONS, J.M., CROSSEY, L.J., AND

BLOCH, J.D., 2004, Provenance and geochronology of Mesoproterozoic sedimentaryrocks from across the southwest United States revealed by 40Ar/39Ar dating of detritalmuscovites [abstract]: Geological Society of America, v. 36, no. 5, p. 405.

GARVER, J.I., ROYCE, P.R., AND SMICK, T.A., 1996, Chromium and nickel in shale of theTaconic Foreland: a case study for the provenance of fine-grained sediments with anultramafic source: Journal of Sedimentary Research, v. 66, p. 100–106.

GRATHOFF, G.H., AND MOORE, D.M., 1996, Illite polytype quantification usingWildfire calculated X-ray diffraction patterns: Clays and Clay Minerals, v. 44, p.835–842.

GRIMES, S.W., AND COPELAND, P., 2004, Thermochronology of the Grenville Orogeny inwest Texas: Precambrian Research, v. 131, p. 23–54.

HAWKINS, D.P., BOWRING, S.A., ILG, B.R., KARLSTROM, K.E., AND WILLIAMS, M.L.,1996, U–Pb geochronologic constraints on the Paleoproterozoic crustal evolution ofthe Upper Granite Gorge, Grand Canyon, Arizona: Geological Society of America,Bulletin, v. 108, p. 1167–1181.

HENDRICKS, J.D., AND STEVENSON, G.M., 2003, Grand Canyon Supergroup: UnkarGroup in Beus, S.S., and Morales, M., eds., Grand Canyon Geology: New York,Oxford University Press, p. 39–52.

HOVER, V.C., WALTER, L.M., AND PEACOR, D.R., 2002, K uptake by modern estuarinesediments during early marine diagenesis, Mississippi delta plain, Louisiana, U.S.A.:Journal of Sedimentary Research, v. 72, p. 775–792.

ILG, B.R., KARLSTROM, K.E., HAWKINS, D.P., AND WILLIAMS, M.L., 1996, Tectonicevolution of Paleoproterozoic rocks in the Grand Canyon: insights into middle-crustalprocesses, Grand Canyon, Arizona: Geological Society of America, Bulletin, v. 108, p.1149–1166.

JENNER, G.A., LONGERICH, H.P., JACKSON, S.E., AND FRYER, B.J., 1990, ICP-MS:A powerful tool for high-precision, trace-element analyses in earth sciences: evidencefrom analysis of selected U.S.G.S. reference samples: Chemical Geology, v. 83, p.133–148.

JERVEY, M.T., 1992, Siliclastic sequence development in foreland basins, with examplesfrom the Western Canada Foreland Basin, in Macqueen, R.W., and Leckie, D.A.,eds., Foreland Basins and Fold Belts: American Association of Petroleum Geologists,Memoir 55, p. 47–80.


JOHNS, W.D., AND GRIM, R.E., 1958, Clay mineral composition of recent sediments fromthe Mississippi River Delta: Journal of Sedimentary Petrology, v. 28, p. 186–199.

KARLSTROM, K.E., BOWRING, S.A., DEHLER, C.M., KNOLL, A.H., PORTER, S.M., DES

MARAIS, D.J., WEIL, A.B., SHARP, Z.D., GEISSMAN, J.W., ELRICK, M.B., TIMMONS,J.M., CROSSEY, L.J., AND DAVIDEK, K.L., 2000, Chuar Group of the Grand Canyon:record of breakup of Rodinia, associated change in the global carbon cycle, andecosystem expansion by 740 Ma: Geology, v. 28, p. 619–622.

KARLSTROM, K.E., ILG, B.R., WILLIAMS, M.L., HAWKINS, D.P., BOWRING, S.A., AND SEAMAN,S.J., 2003, Paleoproterozoic rocks of the Granite Gorges, in Beus, S.S., and Morales, M.,eds., Grand Canyon Geology: New York, Oxford University Press, p. 9–38.

LEVINSON, A.A., 1980, Introduction to Exploration Geochemistry: Wilmette, Illinois,Applied Publishing Ltd., 924 p.

MORALES, M., 2003, Mesozoic and Cenozoic strata of the Colorado Plateau near theGrand Canyon, in Beus, S.S., and Morales, M., eds., Grand Canyon Geology: NewYork, Oxford University Press, p. 212–221.

MOREY, G.B., AND SETTERHOLM, D.R., 1997, Rare earth elements in weathering profilesand sediments of Minnesota: implications for provenance studies: Journal ofSedimentary Research, v. 67, p. 105–115.

MOORE, D.M., AND REYNOLDS, R.C., JR., 1989, X-ray Diffraction and the Identificationand Analysis of Clay Minerals: New York, Oxford University Press, 332 p.

MOSHER, S., 1998, Tectonic evolution of the southern Laurentian Grenville orogenicbelt: Geological Society of America, Bulletin, v. 110, p. 1357–1375.

NESBITT, H.W., 1979, Mobility and fractionation of rare earth elements duringweathering of a granodiorite: Nature, v. 279, p. 206–210.

NESBITT, H.W., 1995, Diagenesis and metasomatism of weathering profiles, withemphasis on Precambrian paleosols, in Martini, I.P., and Chesworth, W., eds.,Weathering, Soils and Paleosols: New York, Elsevier, p. 127–154.

NESBITT, H.W., AND MARKOVICS, G., 1997, Weathering of granodioritic crust, long-termstorage of elements in weathering profiles, and petrogenesis of siliciclastic sediments:Geochimica et Cosmochimica Acta, v. 61, p. 1653–1670.

NESBITT, H.W., AND YOUNG, G.M., 1982, Early Proterozoic climates and plate motionsinferred from major element chemistry of lutites: Nature, v. 299, p. 715–717.

NESBITT, H.W., AND YOUNG, G.M., 1984, Prediction of some weathering trends ofplutonic and volcanic rocks based on thermodynamic and kinetic considerations:Geochimica et Cosmochimica Acta, v. 48, p. 1523–1534.

PASQUINI, A.I., DEPETRIS, P.J., GAIERO, D.M., AND PROBST, J.-L., 2005, Material sources,chemical weathering, and physical denudation in the Chubut River basin (Patagonia,Argentina): implications for Andean rivers: Journal of Geology, v. 113, p. 451–469.

PEVEAR, D.R., 1999, Illite and hydrocarbon exploration: National Academy of Sciences,Proceedings, v. 96, p. 3440–3446.

PITTENGER, M.A., MARSAGLIA, K.M., AND BICKFORD, M.E., 1994, Depositional historyof the middle Proterozoic Castner Marble and basal Mundy Breccia, FranklinMountains, west Texas: Journal of Sedimentary Research, v. 64, p. 282–297.

POTTER, P.E., MAYNARD, J.B., AND DEPETRIS, P.J., 2005, Mud and Mudstones: NewYork, Springer, 297 p.

RETALLACK, G.J., 1990, Soils of the Past: Boston, Unwin Hyman, 520 p.ROTHS, P.J., 1993, Geochemical and geochronological studies of Grenville-age (1250–

1100 Ma) Allamore and Hazel formations, Hudspeth and Culberson counties, westTexas, in Soegaard, K., Nielsen, K.C., and Marsaglia, K.M., eds., PrecambrianGeology of Franklin Mountains and Van Horn Area, Trans-Pecos, Texas: GeologicalSociety of America, South-Central Meeting Guidebook, University of Texas atDallas, p. 1–35.

RUDNICK, R., 1983, Petrography, geochemistry, and tectonic affinities of the meta-igneous rocks of the Carrizo Mountain Group, Van Horn, Texas [MS Thesis]: SulRoss State University, Alpine, Texas, 100 p.

SCHRODER-ADAMS, C.L., BLOCH, J.D., LECKIE, D.A., CRAIG, J., MCINTYRE, D.J., AND

ADAMS, P.J., 1996, Paleoenvironmental changes in the Cretaceous (Albian toTuronian) Colorado Group of western Canada: microfossil, sedimentological andgeochemical evidence: Cretaceous Research, v. 17, p. 311–365.

SHANNON, W.M., BARNES, C.G., AND BICKFORD, M.E., 1997, Grenville magmatism inwest Texas: petrology and geochemistry of the Red Bluff Granite Suite: Journal ofPetrology, v. 38, p. 1279–1305.

SHAW, D.B., AND WEAVER, C.E., 1965, The mineralogical composition of shales: Journalof Sedimentary Petrology, v. 35, p. 213–222.

SHELDON, N.D., 2003, Pedogenesis and geochemical alteration of the Picture Gorgesubgroup, Columbia River basalt, Oregon: Geological Society of America, Bulletin,v. 115, p. 1377–1387.

SMITH, D.R., BARNES, C., SHANNON, W., ROBACK, R., AND JAMES, E., 1997, Petrogenesisof Mid-proterozoic granitic magmas: examples from central and west Texas:Precambrian Research, v. 85, p. 53–79.

STEWART, J.H., GEHRELS, G.E., BARTH, A.P., LINK, P.K., CHRISTIE-BLICK, N., AND

WRUCKE, C.T., 2001, Detrital zircon provenance of Mesoproterozoic to Cambrianarenites in the western United States and northwestern Mexico: Geological Society ofAmerica, Bulletin, v. 113, p. 1343–1356.

STILES, C.A., MORA, C.I., DRIESE, S.G., AND ROBINSON, A.C., 2003, Distinguishingclimate and time in the soil record: mass-balance trends in Vertisols from the Texascoastal prairie: Geology, v. 31, p. 331–334.

TAYLOR, S.R., AND MCLENNAN, S.M., 1985, The Continental Crust; Its Composition andEvolution: Boston, Blackwell Scientific, 312 p.

TIMMONS, J.M., 2004, Intracratonic deformation and basin formation during protractedGrenville Orogenesis: sedimentary and tectonic regional inferences from the ca. 1254–1100 Ma Unkar Group, Grand Canyon [Ph.D. Thesis]: University of New Mexico:Albuquerque, New Mexico, 325 p.

TIMMONS, J.M., KARLSTROM, K.E., DEHLER, C.M., GEISSMAN, J.W., AND HEIZLER, M.T.,2001, Proterozoic multistage (ca. 1.1 and 0.8 Ga) extension recorded in the GrandCanyon Supergroup and establishment of northwest- and north-trending tectonicgrains in the Southwestern United States: Geological Society of America, Bulletin,v. 113, p. 163–180.

TIMMONS, J.M., KARLSTROM, K.E., HEIZLER, M.T., BOWRING, S.A., GEHRELS, G.E., AND

CROSSEY, L.J., 2005, Tectonic inferences from ca. 1254–1100 Ma Unkar Group andNankoweap Formation, Grand Canyon: Intracratonic deformation and basinformation during protracted Grenville orogenesis: Geological Society of America,Bulletin, v. 117, p. 1573–1595.

TOTTEN, M.W., HANAN, M.A., AND WEAVER, B.L., 2000, Beyond whole-rock geo-chemistry of shales: The importance of assessing mineralogic controls for revealingtectonic discriminants of multiple sediment sources for the Ouachita Mountain flyschdeposits: Geological Society of America, Bulletin, v. 112, p. 1012–1022.

VAN SCHMUS, W.R., BICKFORD, M.E., AND TUREK, A., 1996, Proterozoic geology of theeast-central mid-continent basement, in Van Der Pluijm, B.A., and Catacosinos, P.A.,eds., Basement and Basins of Eastern North America, Geological Society of America,Special Paper 308, p. 7–32.

WEST, A.J., GALY, A., AND BICKLE, M., 2005, Tectonic and climatic controls on silicateweathering: Earth and Planetary Science Letters, v. 235, p. 211–228.

WILEY, B.H., RAUZI, S.L., COOK, D.A., CLIFTON, E.H., KUO, L.-C., AND MOSER, J.A.,1998, Geologic description, sampling, petroleum potential and depositional environ-ment of the Chuar Group, Grand Canyon, Arizona: Arizona Geological Survey,Open-File Report 98-17, 83 p.

WILEY, B.H., DEHLER, C.M., GHAZI, S.A., KUO, L.-C., AND RAUZI, S.L., 2002, Geologicdescription, sampling and petroleum source rock potential of the Awatubi andWalcott members, Kwagunt Formation, Chuar Group of the Sixtymile Canyonsection, Grand Canyon, Arizona: Arizona Geological Survey, Open-File Report 02-01, 84 p.

YOUNG, G.M., 2002, Geochemical investigation of a Neoproterozoic glacial unit: theMineral Fork Formation in the Wasatch Range, Utah: Geological Society ofAmerica, Bulletin, v. 114, p. 387–399.

YOUNG, G.M., AND NESBITT, H.W., 1999, Paleoclimatology and provenance of theglaciogenic Gowganda Formation (Paleoproterozoic), Ontario, Canada:a chemostratigraphic approach: Geological Society of America, Bulletin, v. 111, p.264–274.

Received 22 November 2004; accepted 20 April 2006.


MUDSTONE PETROLOGY OF THE …eps et al_Journal of... · mudstone petrology of the mesoproterozoic...

Documents

Transcript of MUDSTONE PETROLOGY OF THE …eps et al_Journal of... · mudstone petrology of the mesoproterozoic...