Paieomagnetic data from Triassic strata, Zuni uplift, New Mexico: Further evidence of large-magnitude Triassic apparent polar wander of North America

September 6, 2017 | Autor: Roberto Garza | Categoria: Multidisciplinary, New Mexico, North America, Colorado Plateau, Geophysical
Share Embed


Descrição do Produto

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 103, NO. B10, PAGES 24,189-24,200, OCTOBER 10, 1998

Paieomagneticdata from Triassicstrata, Zuni uplift, New Mexico: Further evidenceof large-magnitude Triassic apparent polar wander of North America Roberto S. Molina Garza and John W. Geissman Department of EarthandPlanetary Sciences, University of NewMexico,Albuquerque Alfred

Gomez

Department of Geological Sciences, University of TexasatAustin Brian Horton

Department of Geosciences, University of Arizona,Tucson

Abstract. Upper Carnian (-225 Ma) strataof the BluewaterCreek Formationof the Chinle Groupof the ColoradoPlateau,westernNew Mexico, containpredominantlyreversepolarity characteristic magnetizationsof high coercivityanddistributedunblockingtemperatureup to 695øC.Data from a syndepositional structuresuggestacquisitionof a stableremanence duringor soonafterdeposition.The meanpaleomagnetic pole for 13 virtual geomagnetic poles(VGP) accepted(of 17 sitescollected)is locatedat 55.2øN, 87.5øE(A95=6.7ø, K=39.7). The angulardistancebetweenthis pole andthe meanof recentlypublishedmiddle andlate Norian (-210 Ma) polesfrom overlyingstratais 12.5ø, supportingthe hypothesisthat significantapparentpolar wanderoccurredduringLate Triassictime. Furthermore,the BluewaterCreekpolelies to the west(6.1o, angulardistance)of thecratonicreferencepole for Carniantime supportingthe hypothesisof a smallColoradoPlateaurotationsincethe earlyMesozoic.Anisianstrataof the MoenkopiFormationcontaindualpolarity magnetizations of highcoercivityanddistributedunblockingtemperatures up to 690øC.The meanVGP of six sitesyields is locatedat 53.1øN, 96.3øE (A95=6.4ø, K=109.2), which is similarto previouslydeterminedMiddle Triassicpoles.Triassicpaleomagnetic polesfrom southwest North Americafrom stratain continuousstratigraphic succession, bothon andoff the ColoradoPlateau,are not consistentwith the hypothesisof a Late Triassicstandstill of the geomagneticpole.

includesAnisian to latest Norian strata of the Moenkopi Formation and the Chinle Group, records -25 ø (angular

1. Introduction

Recentestimatesof Colorado Plateau (CP) rotation based distance)of APW between -240 and -208 Ma [Molina Garza

on directpaleomagnetic pole comparisons havefocusedon a relativelylarge data set from Upper Triassic strata,a time intervalduringwhichapparentpolarwander(APW) of North Americahas been interpretedto be slow to negligible[Kent and Witte, 1993; Kent and Olsen, 1997]. Paleomagneticdata for the NewarkSupergroup,on whichthe hypothesis of small to negligibleAPW is based,includethe mid to upperCamian Stockton and Lockatong formations, the lower to upper Norian PassaicFormation, and overlying Hettangianbasalts

et al., 1996].

and sedimentaryrocks (an interval from -228 to 205 Ma).

Althoughdepositionof the Newark SupergroupandChinle Groupwas almostentirelycontemporaneous, recentestimates of largeCP rotationbasedon Triassicdatamaybe affectedby problemsin stratigraphic correlationandincompletesampling of the Triassicsegmentof the North AmericanAPW path. Available poles for the Colorado Plateau, and thus included in theanalysisof TriassicAPW andCP rotationperformedby Kent and Witte [1993], are entirely middle to latestNorian (-215-205 Ma). These poles have been obtained from the

Otherpaleomagnetic data,however,havebeeninterpretedto

Owl Rock and the Church Rock formations

indicate

Group. The Owl Rock overlies lower Norian strata.Because of its stratigraphicposition,it is assumedto be of mid-Norian age [Lucas,1993]. The overlyingChurchRock is uppermost Norian and possibly Rhaetian. Kent and Witte [1993]

that

Late

Triassic

APW

of

North

America

is

significant.Kodama et al. [1994] showedevidenceof Late Triassic

APW

from

Mesozoic

rocks

of

noaheast

Noah

of the Chinle

America. Also, a long successionof Triassic strata in the Sangrede CristoMountainsof east-central New Mexico, that comparedthesedata with the mean of three cratonicpoles Copyright1998by theAmerican Geophysical Union. Papernumber98JB02047. 0148-0227/98/98JB-02047509.00

assumed to be of the sameage as the CP poles:the upper shalepole of Bazard and Butler [1991] (lower Norian), the -214 Ma (mid-Norian) ManicouaganImpact pole, and the polefor theupperPassaicFormation(lower-upperNorian)of Witteet al. [1991]. The age assignedto the Passaicpole is 24,189

24,190

MOLINA GARZA ET AL.: TRIASSIC PALEOMAGNETIC DATA ZUNI UPLIFT

based on the observation

that the Raritan

and Jacksonwald

locally named the McGaffey member. The Bluewater Creek

localities of Witte et al. [1991] include lower Norian strata.

Formation

Althoughthe age differencesbetweencratonicand CP poles seem minor, only one of the cratonic poles included in this analysis sampled the latest Triassic segment of the North AmericanAPW path. Estimatesof the durationof the Norian stage vary. Harland et al. [1990] estimateda duration of about 14 million years. This and the more recent geologic timescaleof Gradsteinet al. [1994] suggestthat the baseof the early Norian is about 10 m.y. older than the base of the late Norian. Therefore the comparisonof Kent and Witte [1993] is based on results for strata of unquestionably different age. A few million yearswould not affect previous estimates of large CP rotation if Late Triassic APW was indeednegligible,but the age differencebetweencratonicand CP polesis sufficientto bias a rotation estimateif APW was rapid. The new pole for the upper Carnian Bluewater Creek Formation reported here provides a datum of crucial importanceto (1) test the hypothesisof a Late Triassic stand still in the North American APW path and (2) improve

faunachron [Lucas,1993] andfossilplantsof the Dinophyton floral zone [Ash, 1980], which establishits age as late

estimates

of

CP

rotation

based

on

Triassic

results.

This

manuscript focuses on the first issue; regardlessof the magnitudeof CP rotation,paleopolesfrom rocks on and off the plateaushouldrecordsimilar amountsof APW. From the determinationof two new pole positionsand teevaluationof previouslypublisheddata, we suggestthat APW was neither small nor slow during the Late Triassic.This is importantnot only for understandingthe kinematicsof deformationalong the westernmargin of North America but also in determining the motion of the North American craton during the Mesozoic.In a companionpaper [Molina Garza et al., this issue] we argue that the assumptionof a large magnitude (>10ø) rotationof the ColoradoPlateauis not supportedby Late CarboniferousthroughLate Jurassicpaleomagneticdata.

contains

vertebrate

fossils

of

the Adamanian

Carnian.

We collected27 sitesfrom SanAndres(4 sites),Moenkopi (6 sites)and Bluewater Creek (17 sites) stratafrom localities nearBluewaterLake StateParkandnearFortWingate(Figure 1). At most sites, strata dip gently (2ø to 12ø) to the north. Sitesof BluewaterCreek strataat the Fort Wingate locality were collected from beds informally referred to as Lake Ciniza [Ash, 1978]. Six sites have near vertical dips associated with a syndepositional slump.The slumpconsists of about10 m of siltstoneand fine sandstonelayersoverlain by horizontallying mudstones[Ash, 1978; Lucas and Hunt, 1993]. At each site, 4 to 12 sampleswere cored using a portablegas-powereddrill. Orientationwas recordedusing a clinometer,magneticcompass,andSuncompass. Samples were subjected to alternating field (AF) demagnetizationup to 110 mT, and progressivethermal demagnetization(10-20 steps) up to 690øC. Principal component analysis was used in the interpretation of demagnetization results. Site mean directions and mean virtualgeomagnetic poles(VGPs) were determinedassuming bothFisherand Bingham statisticaldistributions.

3. Paleomagneticresults 3.1. Upper Carnian Bluewater Creek Formation

Our highest quality pole is based on data from the Bluewater Creek Formation. Demagnetization results for theserocksare of variedqualitybut consistently yield nearly uniform reverse polarity characteristic magnetizations (ChRMs) of high coercivity and distributedunblocking temperatures (Figure 2). About 25% of the samplesused in the final calculations, mostly from the Bluewater Creek 2. Geology and Sampling locality (bw sites), have simple nearly univectorial The north margin of the Zuni uplift in the easternCP remanences directedto the origin with maximumunblocking (Figure1) is characterized by continuousexposureof Permian temperatures in excessof 650øC and line fits that yield low and Triassicstrataassignedto the San Andresand Moenkopi (less than 5ø) angular dispersions(Figure 2a). These rocks Formationsand to the Chinle Group. The Upper PermianSan contain nonuniform distributionsof hematite pigment as Andres Formation consists of massive, tan colored, allochem-

color-banded

crossbeds and laminations.

Most samplesfrom the Fort Wingatelocality(fw sites)and red sandstones, siltstones, and mudstones of the Middle somefrom BluewaterCreek lack hematitepigmentand have Triassic Holbrook Member of the Moenkopi Formation, morecomplex,multivectorial,magnetizations bestdefinedby which in turn is disconformably overlain by the Upper combiningAF and thermaldemagnetization (Figures2b-2c). Triassic Chinle Group [Lucas and Heckert, 1994]. The Demagnetization first removesa low unblockingtemperature Chinle-Moenkopi contact is marked by quartz-pebble (< 200øC) and low coercivity (100 mT) but low unblocking The Chinle Group in western New Mexico includes, in temperaturecomponent is subsequentlyremoved between ascendingorder, the Shinarump,BluewaterCreek, Petrified about100ø and 300øC (Figures2b-2d). This componenthas rich limestone.It is disconformablyoverlainby purple-grayto

Forest, Owl Rock, and Rock Point (Church Rock) formations

(Figure 1). The Bluewater Creek Formation (formerly the Monitor Butte member of the Chinle Formation) consists

predominantlyof quartzo-feldspathic mudstonesranging in color from gray to reddishbrown and is less hematiticthan strata of the younger formations of the Chinle Group. The

steep negative inclination and south-southeastdirected declinations(Figure 3d). The ChRM is isolatedat temperatures of above400øC,but above 550øC demagnetizationbehavior is sometimeserratic (Figure2d). The linear trajectoriesdefinedbetweenthe 400 ø

and 550øC steps of the demagnetization sequencesmay (Figures2b and2c) or may not (Figures2e and2f) be directed depositedin lacustrineenvironmentsundervaryingoxidation to the origin.Demagnetization resultssuggest thatthe signal conditions.Interfingered lenses of micaceoussandstoneare remainingat temperatures above-600øCin samplesthatlack common.A prominent,ledge-formingsandstonesequenceis hematite pigment is randomly scattered. Trends of

Bluewater

Creek Formation

is less than 100 m thick. It was

MOLINA GARZA ET AL.: TRIASSIC PALEOMAGNETIC DATA ZUNI UPLIFT

24,191

108øW 35o30'N --

Tr

bw•

0

10

I

I

20km 35øN -108øW ,

•1 --"""• •

i Entrada Sandstøne Unconformity

Rock Point Fm. Unconformity Owl Rock

50m

Fro.

Petrified Forest Fm

Painted Desert Member

Sonsela Member

Unconforrnity

Magnetic polarity

• iiiii :ii ii!i ii!i i!i i! i Blue Mesa Mbr. • :!'i'!'i'!'i'i' bw03,bw7 Bluewater McGaffey Mbrbw02, bw04-06

CreekFm.

------:••••01 Shinarump Fm. bw18



Moenkopi Fm. fwl2 fwl3, fwl6;

fw06,fw09-fwl 1

fw01-fw05, fw07-fw08

Unconformity



Unconformity

SanAndres Fm bwl0, fwl4-fwl5,

fwl7

Figure 1. Schematicgeologicmap of the Zuni Mountainsindicatingsamplinglocalities(stars).The inset showsa simplified tectonic map of the Colorado plateau (light gray pattern) and surroundingregion, showing main structuraltrendsand areasof Tertiary volcanism(dark gray pattern).P, Permian;Tr, Triassic;J, Jurassic;K, Cretaceous;and the stippledpatternis Precambrianbasement.A schematicstratigraphicsectionof the Chinle Group in western New Mexico [after Lucas and Heckert, 1994] indicates sampling sites and the interpreted magnetostratigraphy of the BluewaterCreek Formation.

demagnetizationtrajectories are not consistent,with some endpoints directed to steeper and more south-southwest directions(Figure 2e) and othersbecomingmore shallow and moresouth-southeast directed(Figure2f). This suggests that a component of higher unblocking temperature cannot be resolved in these rocks, and measurements above about

600øCprobablylack any significance.

For sampleswith erraticbehaviorat high temperatures the directionof the ChRM was calculatedin two ways.First, line fits were anchoredto the origin. In a secondcalculation,free segmentswere computedusing all pointsbetweenthe 400ø and 550øC steps.Resultsyield indistinguishable site means, typicallywithin a few degreesof oneanother(Figure3). If the directionswere systematically biasedby an unresolvedhigh-

24,192

MOLINA GARZAET AL.: TRIASSICPALEOMAGNETICDATA ZUNI UPLIFT c-fwS.07

up/W

2•5560 0mT

• up/W

Mo=l.42mA/m f-fwll.08

Mo=0.86mA/m

up/W'

N35c•160

O0

,_

• 59v•65 50

up/W

•.,,•05_50m •5 T N

575 65 u

560

g-fw9.01A

N

up/W

c•0



l-fw10.SA

9,,100-350C

O•nn"'•u'" '"•'•.

h-fw9.04B

Mo=0.47mA/m

.... 2 0•r

N

m up/W

-

o

160

3

Mo=0.81mA/m • NFITI

Nrm

Mo=0.42mA/m

Nan

Figure 2. Orthogonaldemagnetization diagrams[Zijderveld, 1967] of selectedspecimensof the (a-f) Bluewater CreekFormation,(g-i) MoenkopiFormation,and (j, k) SanAndresFormation.All diagramsin in situcoordinates. Open (solid) symbolsare projectionson the vertical(horizontal)plane.In Figures2b and 2c, threecomponents of magnetizationsare easily identified. Examples in Figures 2g and 2i are interpretedas normal polarity magnetizations.

temperature (>600ø) magnetization, we would expect statisticallydistinctand about35ø (angulardistance)from the anchoredline fits to be systematicallydisplacedtoward that restof the BluewaterCreek sites(Figure 3a and Table 1). Tilt direction,but they are not. Resultsusingthe secondmethod correction restores these directions to within 20 ø of the mean were used in the final calculations(Table 1). Overall, the for shallowlydipping strata (Figure 3b). The tilt correction averagemaximumangulardeviation(MAD) value for free does not produce a statistically significant fold test line segments for samplesof the BluewaterCreekFormation [McFadden and Jones, 1981]. However, the k parameter is 7.9ø, attestingto the qualityof the data.Only 18% of the increases from an in situ value of 16.6 to a tilt corrected value includedsampledirectionshave MAD valuesbetween10ø of 27.3, with a maximumof 29.3 at 59% unfolding.In bothin and 15ø. Sampleswith MAD valuesgreaterthan 15ø were situ and tilt correctedcoordinatesthe means are statistically excluded from all calculations.

In field coordinates,the five sites collected from beds

distinct. We note, however, that in situ site means for sites on

theslumphavepositiveinclinationsandarefar removedfrom

formingpart of a syndepositional slumphavea clustered expectedLate Triassicor youngerdirections.Tilt-corrected group of southeast-directed mean directionsthat are site means, on the other hand, are consistent with

MOLINA GARZA ET AL.: TRIASSICPALEOMAGNETICDATA ZUNI UPLIFT

24,193

ß ß

t

k= TM 16.6 s!tu-- D=166.9, 1=5.8

'

b-Tiltcorrected

D=1•1.4, 1=-3.0 =2•7.31 i I

I

Insitu. .

d-Fort Wingate Overprint

I

I

I

I

Figure 3. Equal-areaprojectionsof sitemeandirectionsin the (a-b) BluewaterCreekand(c) Moenkopiformations. Sitescollectedfrom a syndepositional slumpin the BluewaterCreeksectionare plottedas squaresand diamonds; diamondsare calculationsanchoringline fits to the origin which resultsin nearlyidenticalsite means,(seetext for explanations). In Figures3a and 3b, we alsoshowthe meandirectionof sitesfrom the syndepositional slumpand

the meanfromgentlynorthdippingsites.Aftertilt correction the an.gular distance between directions foundin slumpedand flat lying stratais less than 20ø. (d) Directionsof magnetizations interpretedas late Mesozoic overprintsin Triassic(circles)and Permian(triangles)strata.Open(solid)symbolsare lower (upper)hemisphere projections.

paleolatitudes expected forthesampling locality. Thefactthat that fine- to coarse-grainedhematite is the main remanence the fold test producesinconclusive resultsis not readily carrier.The high coercivityand low unblockingtemperature interpretable, but the weightof the evidencesuggests that (100-300øC) of the steep, south directed overprint suggests acquisition of the remanence was nearlycompletebefore that this is also carried by fine-grainedhematite.Notably, slumping.Data for the syndepositional slumpthussuggest however, many of these rocks lack hematite pigment. that the characteristicmagnetizationin nonhematitic Microscopicobservationsshow that small concentrationsof Bluewater Creek strata was locked in during or soon after deposition.

Acquisitionof isothermalremanentmagnetization (IRM) indicates thatmostsamples of theBluewaterCreekFormation containcontributionsfrom low- and high-coercivityphases

(Figure4). AF demagnetization of the IRM suggests that contributions from a high-coercivity phase are more

important.The high coercivitybut distributed unblocking temperatures of theChRM of BluewaterCreekstratasuggest

hematiteas speculariteare presentin the immediatevicinity of some ferromagnesianand iron oxide detrital grains. The contributionof a low-coercivity phase to the IRM suggests that magnetiteis the possiblecarrier of viscouscomponents of recentorigin. A large percentage(-60-70%) of hematitegrains contain ilmenite intergrowths and typically show evidence of transport(e.g., rounding);we infer that theseare of detrital origin. These grains are possibly the carriers of the

24,194

MOLINA GARZA ET AL.' TRIASSIC PALEOMAGNETIC DATA ZUNI UPLIFT

polarity.The interpretationis tentativebecausethey may also reflect acquisitionof a secondarymagnetizationof uncertain origin. It is unclear whether or not these sites are in continuousstratigraphicsequence,but both are below the McGaffey member. These sites, as well as sites fw8, fw18, and bw3, yield demagnetizationresults of inferior quality (Table 1; only site fw10 was included in the overall mean). Their polarityis, for the mostpart, interpretedfrom endpoint directions. These are poorly resolved north directed and shallow magnetizations(Figure 2g); the magnetic moment remainingafter heating to 500øC is near the magnetometer

0.8 .

0.6

0.4

.

noiselevel(10-9 A m-2kg), but a similarbehavior was

0.:

• •

Z• t

/

-.-w03 -c•-fwl 1 --•- fwl 3

observedin at least one other specimenfrom this site. Other samples from this site give east directed magnetizations

0 I

1

10

100

1000

Induction(roT) Figure 4. Isothermalremanentmagnetization (IRM) acquisition curvesandAF demagnetization of theIRM for selected samples of the Late Triassic Bluewater Creek Formation,the Middle Triassic

Moenkopi Formation, and the Lower Permian San Andres Limestone.

characteristicmagnetization.Some of thesegrainshave been partiallycorrodedand hematitehas been remobilized(Figure 5). Hematite is also found at grain boundaries,as alteration rims on ferromagnesiansilicategrains,but this occurrenceis relatively rare. A common occurrenceof hematite (in some specimensmaking 40 to 50% of all the grains)is as aligned inclusions in detrital mica and chlorite (Figure 5). Some inclusionsare lensoidalin shape,othersare planar.Inclusions are oftentruncatedat grainboundariesand in somecasesthey are deformed through compaction. There is almost no evidence

of hematite

dissolution

and no cases of hematite

forming around the mica grains except for small stainsof hematitepigmentin the most oxidized grains.These grains are completely enclosed in calcite cement, and, in some instances, cement crosscuts inclusions. These observations

suggestthat hematiteinclusionsformedbefore depositionof sheet silicate grains; they may thereby contribute to a depositional remanence(DRM). Magnetiteis presentin other, less altered, ferromagnesiansilicate grains. Pigmentary hematite is rare even at the microscopic level and is concentrated in the immediatevicinity of specularhematite grains. A less common occurrence of hematite is as a relatively"late" diageneticphasein veinsthat crosscutearlier

calcitecement.Late diageneticfine-grainedhematitemay carry the steep south directedoverprintunblockedbetween 100 ø and 375 øC.

The mean virtual geomagneticpole (VGP) derived from of commonhematiteoccurrences in sites in hematitic Bluewater Creek strata with high Figure 5. Photomicrographs unblocking temperature (>650øC) magnetizations is indistinguishableat a 95% confidencelevel from that derived from nonhematiticsites; the angular distancebetween the means is only 3ø. The characteristicmagnetizationof

sandstone beds of the Bluewater

Creek Formation

near Fort

Wingate. (top) Rounded to subroundedspecularitegrains showing extensive remobilization and recrystallization of hematite(specularite)at grain margins.Late diagenetichematite bearingveinsarein the lower right comer.(bottom)Inclusionsof hematiticsamplesis thus also interpretedas an "early specularhematitealong cleavageplains of chlorite grains.In acquired"magnetization. someof the grainsinclusionsappearto be isotropicsuggesting Some specimens from sites fw9 and fw10 have that somemagnetiteis also presentin similar forms. Scalebars magnetizationswe tentatively interpret to be of normal are approximately40 gin.

MOLINA GARZA ET AL.' TRIASSIC PALEOMAGNETIC DATA ZUNI UPLIFT

24,195

Table 1. PaleomagneticData and StatisticalParameters In Situ

Site

Tilt Corrected

n •nd Declination,deg.Inclination,deg k

VGP

o[95Declination, deg.Inclination,degLatitude, deg.Longitude,deg.

BluewaterCreekFormation,Fort Wingate(35.46øN,108.54øW) fw01'• fw02'•

5W 4\7

139.7 149.1

14.9 14.9

fw03'• fw05-•

3\5 7\8

144.1 151.0

28.0

fw06

3\6

175.4

3.0

19.3

28.8

fw07'•

3\6

156.7

13.7

45.7

18.4

10.7

73.2 45.5

9.0 13.8

157.3 157.6

-3.1 -12.1

50.1 54.2

108.4 111.8

26.4 24.5 9.1

153.2 171.1

-7.4 -12.8

49.7 59.9

115.6 89.3

175.6

8.6

50.0

78.3

156.9

-20.6

57.5

117.3

44.7

fw08'•*

1\6

12.9

6.6

12.7

-2.9

fw09*

1\5

344.6

-2.9

344.3

- 11.6

fw10

5\8

180.1

5.2

12.4

22.6

179.1

2.1

53.5

73.0

fwll

4\8

188.4

10.4

37.7

15.2

181.3

18.0

43.3

69.6

fw18*

3W

167.4

18.8

14.0

34.3

168.6

30.5

fw12

3\5

161.9

-3.8

fw 13

2\8

159.2

-20.7

fw16

5W

160.4

MoenkopiFormation,Fort Wingate(35.46øN, 108.54øW)

3.6

34.7

21.2

11.2

24

161.9

2.2

49.7

100.2

159.1

- 15.0

56.2

111.0

160.5

9.6

45.7

99.9

SanAndresFormation,Fort Wingate(35.46øN,108.54øW) fw14

3\4

359.8

54.6

1150

3.6

356.8

fw15

3\4

352.8

57.7

1354

3.4

350.4

49.1 51.9

fw 17

3\4

156.2

17.8

7.3

50

156.2

23.8

bwO1

6\6

169.0

-11.0

26.4

13.3

169.1

-9.1

57.7

92.6

bw02

7\7

184.0

-0.1

43.5

9.3

184.0

1.9

53.6

65.2

bw03*

2\11

166.8

27.7

166.5

29.6

BluewaterCreek Formation,BluewaterCreekLake (35.29øN, 108.06øW)

bw04

5\8

187.5

0.5

31.3

13.9

187.5

2.5

52.8

59.5

bw05

5\8

181.4

-14.5

18.7

18.2

181.4

-12.5

61.0

69.1

bw07

4\4

168.6

-1.1

39.3

14.8

168.6

0.8

52.8

91.0

78.1

MoenkopiFormation,BluewaterCreekLake (35.29øN,108.06øW) bw8

3\3

176.3

0.4

5.5

176.3

2.4

53.3

bw9

5\8

350.8

10.8

501.1

11.4 23.6

350.9

8.8

58.0

89.3

bwll

7\8

344.4

10.6

26.5

344.5

8.7

55.9

100.3

bw10

4\9

306.3

4.4

31.7

139.5

11.9

San AndresFormation, BluewaterCreekLake (35.29øN, 108.06øW) 15.4

9.8

30.9

308.1

Other Directions

bw10Hi-T

3\9

337.4

58.0

675.5

4.7

340.0

43.3

70.7

135.7

fw Lo-T

19

163.4

-61.8

32.6

6.0

162.1

-55.9

75.5

170.6

fw17Hi-T

5\8

169.5

-57.4

143.6

6.4

167.5

-51.5

79.1

147.4

k =39.7

A 95=6.7 ø

55.2

87.5

Mean Bluewater

Creek Formation

Binghamstatistics Mean MoenkopiFormation

(k 1=-102.7; k2=-14.3;ov-az=85 ø; {x13=2.8ø;{x12=7.6ø) k=109.2

A 95=6.4 ø

53.1

96.3

Here n (nd) is the numberof samplesused(demagnetized)in meancalculations;VGP is the virtual geomagneticpole;k anda95 areFisher's precisionparameterandradiusof the 95% coneof confidence. •- Sitessampledin a syndepositional slump. * Sites excluded from calculations.

(Figure 2h). It is possible that these are composite shallow,however,to be a recent overprint.Thereforewe magnetizations,reflecting "long-term" acquisition of a tentativelyinterprettheseas normalpolaritymagnetizations. chemical remanence [Larson et al., 1982]. If the normal polarity event theserocks record is indeed short, as we have

assumed, theeastdirectedmagnetizations canbe explainedas the sumof normal and reversepolarity chemicalremanences. Samplesfrom site fw10 are predominantlyreverse(Figure 2j), but in two samplesa moderateto high coercivity(>30 mT), north directed magnetization(also poorly defined) is removedover the range of temperaturesbetween 350ø and 550øC (Figure 2i). The north directedendpointvectorsand the componentremovedin site fw10 couldbe interpretedas overprintsof uncertainnature. Their magnetizationsare too

The late Carnianis characterized by predominantly reverse polarity;normal polarity subchronsare interpretedto be relativelyshort(e.g., - 500 kyr) to averagesecularvariation. The circular

standard deviation

of

the VGP

distribution

der Voo, 1990]. The Moenkopi Formationis one of the best paleomagnetically characterizedrock unitsin North America, and data for the small number of sitesreportedhere are not anomalous.The angle between the mean of normal and reversedirectionsis 9.2ø. The datapassa reversaltest with a C classification[McFaddenand McElhinny, 1990]. Some workers have suggestedthat remanence in the

(12.9ø) also suggestsa reasonablyadequateaveragingof secularvariation.It appears,moreover,that our collectionof data spansat leasttwo reversechronsand one shortnormal polarityevent.Thereby,despitethe relativelysmallnumberof accepted sites,themeanrepresents an accurateestimateof the Moenkopi Formationwas acquiredsoon after or during late Carnianpaleopoleposition. deposition[Purucker et al., 1980]. Others have shown that Becauseof the sampling schemeand the lack of well- remanencecarriers are secondary(diagenetic) and that induratedlayers, the Bluewater Creek magnetostratigraphy acquisitionlong postdatesdeposition[Larson et al., 1982]. may lack sufficientresolutionfor rigorouscomparisonwith Moreover, some stratigraphicintervals of the Moenkopi proposed Triassicpolaritysequences. It is permissible thatthe Formation have been selectively, and pervasively, reverse-shortnormal-reverse sequence correlates with remagnetizedin late Mesozoic time [Molina Garza et al., intervalsbetweenzonesE8 and El2 of the Newark polarity 1991]. We are not in the position to contribute to this record [Kent et al., 1995]. discussion becauseno field testsare possiblefor Moenkopi A steepnegativeand southdirectedmagnetization(in situ: Formation strata in the localities studied here. D=163.4 ø, I=-61.8ø;

tilt corrected: D=162.1 ø, 1=-55.9ø)

removedat low temperaturesduring demagnetizationis well defined in 19 samples(Figure 3d). Tentatively, we interpret this magnetization as a late Mesozoic to early Cenozoic overprint of diagenetic origin. Similar directions of magnetizationhave been identified in Permian and Triassic strata in central New Mexico [Molina Garza et al., 1991].

3.2. Middle Triassic Moenkopi Formation and Middle

San Andres Formation specimenscollected near the Permian-Triassicdisconformitycontain single component, north directedand steep positive magnetizationsof high coercivity (>110 mT) and moderatelyhigh but distributed unblockingtemperature. Thesesamplesarehighlyalteredand containoxidizedphases,suchas hematiteand goethite.Less oxidizedsamplesfrom site fw 17 in the San AndresFormation contain two components(Figures 6d and 6e), a shallow

southeast directedmagnetization, and a high coercivityand intermediate unblockingtemperature magnetization of steep In specimensof the Moenkopi Formation the ChRM negativeinclinationandsoutheast directeddeclination(Figure unblocks over a distributedrange of temperaturesbetween 3d). The IRM of thesesamplesis characterized by a large Permian

San Andres

Limestone.

300ø and 670øC (Figure 6a) or over a narrow range of unblockingtemperaturesbetween 625øC and 670øC (Figure 6b). The ChRM is south or north directed and shallow in inclination (Figure 6c). Componentsof magnetizationin the direction of the presentdipole field (•=55 ø) are presentin some of the samples.The six Moenkopi sites yield a wellgroupedmeanpole at 53.1øN, 96.3øE (Table 1). The number of sitesinvolvedin the pole calculationis small,but the pole is similar to previouslypublishedMiddle Triassicdata [Van

contributionfrom a cubic phase.For site bw10, also in the San AndresFormation,magnetizations are either of high unblocking temperature (-650øC) and north-northwest

directedandsteeppositive,or of low unblocking temperature (-400øC) andnorthwestdirectedandshallowpositive.North to northwestdirectedand steeppositivemagnetizations in SanAndresstrataaremostlikelyrecentin origin.The steep negativesouth to southeastdirected,high unblocking temperature magnetizationof site fw17 is indistinguishable 11ø

a-bw8.4

M o =4.64m A/m

Nrta

e-fw17.6

u

500

150 • 3•

0up/W N

Nrm

up/W

•__•685 N

b-fw12.06

up/W

55•-•.2• 0'•

625 •70 •Nrm

.•

Mo=l.78mA/m Figure 6. Orthogonaldemagnetization diagrams[Zijderveld,1967] of selectedspecimens of (a-c) Moenkopi Formationand (d, e) San AndresFormation.All diagramsin in situ coordinates.Open (solid) symbolsare projections on the vertical(horizontal)plane.

MOLINA GARZA ET AL.' TRIASSIC PALEOMAGNETIC DATA ZUNI UPLIFT

24,197

plains of the craton interior but it is statistically indistinguishable from them (Table 2). Data for the southwestern plainsincludethelateCamianandearlyNorian

polesfor the SantaRosa,Trujillo,and GafitaCreek

formations [Motina Garza etat.,1996], and theBullCanyon Mexico, and the late CarnianDockum Grouppole-A, in west Texas [Motina Garza et al., 1995]. The mean of thesepoles

falls at55.1øN -94.0øE, and the angular distance tothe support thehypothesis of a "large"rotation of theColorado The angular distancebetween the new Bluewater Creek

indicating, within statistical uncertainty, thatat leastthat

obtained from the stratigraphic succession ofTriassic and much APW occurred during Late Triassic time. Poles

Lower Jurassicstrataon the CP, including the SmithJanto Figure 7. Paleomagneticpoles with 95% confidenceregions Anisian Moenkopi Formation (mean calculatedfrom Table from Lower Triassic (Smithian) through Lower Jurassic (Sinemurian) strata of the Colorado Plateau (solid symbols) 2), the upperCarnianBluewaterCreek (this study),the midsuperimposed on the paleomagnetic Euler pole track of Gordon Norian Owl Rock [Bazard and Butler, 1991], the upper et al. [ 1984].We includethe meanof Moenkopistrataon the CP Norian Church Rock [Kent and Witte, 1993], and the (calculatedusingthe dataof Table 2). CP dataare comparedwith resultsfor the Newark Supergroup(opensymbols),interpretedto indicatesmall to negligibleLate Triassicapparentpolar wander [Kent and Witte, 1993] and a pole interpretedto show'evidence of the J-1 cusp in the APWP [Kodama et al., 1994]. The BluewaterCreek pole of this study(bw) is indistinguishable from the mean of equivalentstratain central New Mexico (bw*). The sequenceof poles, in ascendingstratigraphicorder are: m, Moenkopi Formation;bw, Bluewater Creek Formation, western

300

280

260

240

220

200

[] MV

S0'

[]

50'

B o 4.0'

NewMexico (thisstudy); bw*, Bluewater Creek Formation o•4ø' equivalent strata,centralRio Grande rift, NewMexico[Motina Garza et at., 1991]' or, Owl Rock Formation[Bazard and Butler,

1991]'ch3,Church RockFormation [KentandWitte,1993];my,

-30'

30'

Moenave Formation [Ekstrand and Butler, 1989]. The Newark polesare nwl, Newark lower beds [Witte and Kent, 1989]; nwm,

middleNewark[WitteandKent, 1990]' nwu,NewarkHettangian

M3

zone [Witte etat.,1991]' ncp,Newark Culpeper Basin baked •ø•0'

M1

20'

sediments[Kodama et at., 1994]. -10'

10' CUl

from the overprint found in Chinle strata and is also interpretedto be of late Mesozoic-earlyCenozoicage.

E CU2

O'



200

4. Implications for North America APW

Age (Ma)

The paleomagnetic pole for the Bluewater Creek Formation(55.2øN - 87.5øE) comparesfavorably (Figure 7) with results for correlative

strata in central New Mexico.

The

lowermostChinle pole of Molina Garza et al. [ 1991] falls at 60.8øN - 88.9øE. The validity of this pole for interpretations of APW had been questionedbecausedata were collected from localitieswithin or alongthe marginsof the Rio Grande rift, at the eastern edge of the CP. We had previously suggested that this area"was rotatingrigidly with the plateau, or it experiencedsimilar senserotation via an independent deformationmechanism"[Molina Garza et al., 1991, p. 14254] The fact that Early Permian, Middle Triassic, and, now, Late Triassic poles in central New Mexico are indistinguishable from coevalpolesfor the plateaureinforces that conclusion.

The paleopolefor the Bluewater Creek Formationfalls to the westof polesfor equivalentage stratain the southwestern

Figure 8. Angular progression of Colorado Plateau paleomagnetic polesalong the small circle paleomagnetic Euler pole (PEP) track of Gordonet al. [1984] as a functionof pole age. We used the PEP in column B of Table 5 in Gordon et al. [1984], which gives a model North American APWP for the CarboniferousthoughTriassic.The data are shown with (solid squares)and without (hollow squares)a correction for the rotationof the plateau.The correctionis made by rotatingthe plateaupolesby 4.6ø aboutan Euler pole at 34øN, 100øW.The solidline is the bestfit polynomialthroughthe data from North Americacraton,which is digitizedfrom Figure 2 of Bryan and Gordon [ 1990]. Note how well this curve fits the correcteddata, including our new Late Triassic data point. Labels are as in Bryan and Gordon [1990] with the addition of our new data, whereBW is BluewaterCreek and M3 is our Moenkopidatum. We havealsoaddedthe ColoradoPlateaudatagiven in Table 2 whereCH3 and CH4 are the ChurchRock data [Kent and Witte, 1993] and OR is the Owl Rock datum[Bazardand Butler, 1991].

24,198

MOLINA GARZA ET AL.: TRIASSIC PALEOMAGNETIC DATA ZUNI UPLIFT

Table 2. Summaryof Paleomagnetic datafor TriassicandLower JurassicNonmarineStrata from West and Southwestern North America Colorado Plateau

Poles

Early Jurassic(205-185 Ma) 61.9,74.4 Dockum B overprint(2)

KayentaFm. KayentaFm. (1)

Poles

59.7,65.7

59.0,66.6

Fm.

58.2,51.9

Wingate Fm.

59.0,63.0

Moenave

Craton Platform Interior

Late Triassic, Norian-Rhaetian (220-205 Ma) Chinle, ChurchRock Fm. (3) 57.5,63.3 Chinle, RedondaFm. (4) Chinle,ChurchRock Fm. (1,10) (61,64) 59.0,67.0 $ UpperChinleFm. (5)

Chinle,Owl RockFm. (1)

56.5,66.4

Chinle,Bull CanyonFm. (1)

(59,77) 58.3,68.9 57.7,79.1 57.4,87.8

Late Triassic, Late Carnian (227-220 Ma)

Chinle,BluewaterCreekFm. (6) Chinle, lower beds (7)

55.2,87.5 60.5,88.9

PopoAgie Fm. Garita Creek Fm. (4) SantaRosa-Trujillo Fm. (4) DockumGroupA (2)

Middle-Early Triassic(245-235 Ma) UpperMaroonFm 60.0,102.0 AntonChicoMbr. (4) UpperMoenkopiFm. 54.8,103.3 AntonChicoMbr. (8) Lower MoenkopiFm. 57.2,98.0 AnkarehFm MoenkopiFm., AZ 58.0,101.0 UpperRed PeakMbr. MoenkopiFm., drillcore 56.0,101.3 LowerRed PeakMbr. MoenkopiFm., NM (7) 57.6,100.3 ChugwaterFm. MoenkopiFm., NM (6) 53.1,96.3 ChugwaterFm.

Moenkopi Fm.,AZ (9)

55.5,95.5 54.0,86.7

(53,104) 54.4,97.3 56.4,96.3

48.0,113.5 43.2,121.4 50.8,104.6 48.5,104.7 45.8,121.1 46.6,113.5 45.4,115.3

58.5,94.8

References:1, Bazard and Butler [ 1991]; 2, Molina Garza et al. [ 1995]; 3, Kent and Witte [ 1993]; 4, Molina Garza et al. [1996]; 5, Reeveand Helsley [1972]; 6, thisstudy;7, Molina-Garzaet al.

[1991]; 8, SteinerandLucas [1992]; 9, Steineret al., [1993]; 10,Reeve [1975].Unreferenced poles arefromVander Voo [ 1990].Polesin parentheses indicateanalternative paleomagnetic result. ? The alternative poleis notcorrected by estimated 4øof southward plunge. $ Polesrecalculated from theoriginalpublication(in parentheses).

HettangianMoenaveformations[Ekstrandand Butler, 1989] showa smoothprogression from eastto west(Figure7) along the paleomagnetic Eule pole (PEP) track of Gordon et al.

the dataequallywell, withoutrequiringabruptchangesin the motion of North America.

[1984].

5. Late Triassic data and Colorado Plateau For comparison, we considerresultsfor the Newarkbasin, rotation includingthe lower Newark [Witte and Kent, 1989], middle Kent and Witte [1993] comparedthe meanof polesfor Newark [Witte and Kent, 1990], and upper Newark Supergroup(HettangianZone) [Witte et al., 1991], and the Norian strataof the Chinle Groupon the CP with the meanof Newark-Culpeperbaked sediments[Kodama et al., 1994] Norian poles from the Newark Supergroupand the craton (Figure7). The poleprogression in the Newarkrecordmay be interior and concluded that about 13.5 ø of CP rotation has If APW wasslowduringLateTriassictime,asthey interpretedto indicateabruptAPW in latestTriassic-earliest occurred. Jurassictime, but North American data from the high plains invoked,thenslightdifferencesin the ageof the poleswould of the craton interior suggest a continuous westward induce negligible bias in their rotation estimate, but that progression. Triassic and Early Jurassic poles for assumption is notsupported by datafromtheCP andthehigh southwestern North America (Table 2), ostensiblyfrom on the Coloradoplateau,indicatefairly continuousAPW as well. The continuousprogressionof late Paleozoic to early Mesozoic poles is demonstratedby plotting the anglesthat polessubtendalong the apparentpolar wanderpath (Figure 7), for which we use the small circle APW path proposedby Gordonet al. [1984]. If the time intervalencompassed by the Carnian and Hettangian(about 225 to 203 Ma in Figure 8) is interpretedto have slow or negligibleAPW, then extremely rapidAPW (>2ø/m.y.)would be requiredfor the time periods before and after this interval. Although suchan interpretation is permissible,a simplermodel with nearlycontinuousAPW at rates of 0.65 to 0.75ø/m.y. over the period from the Early Permian to earliest Jurassic,about 290 to 200 Ma, explains

plains of the Craton interior and shouldbe reexamined.As a

first stepin suchreexamination, we makebasiccomparisons of meanpolesfor Norian and Carnian data for the cratonwith

those from the plateau. A far more robust approachis presentedby Molina Garza et al. [this issue]. We calculateda mean cratonic Norian pole for North America that incorporatesthe three poles included in the

averageof Kentand Witte[1993] (theBull CanyonFormation in easternNew Mexico, the Manicouaganimpactstructure, and the PassaicFormationof the Newark Supergroup) and two additionalpoles.One of themwasomittedby Kentand Witte [1993] (the upperChinle pole of Reeveand Helsley [1972]), the other was obtained from the Redonda Formation

in the Sangre de Cristo mountains [Molina Garza et al.,

MOLINA GARZA ET AL.: TRIASSIC PALEOMAGNETIC DATA ZUNI UPLIFT

24,199

Jurassicgeomagneticpolarity sequenceand paleolatitudesfrom 1996]. The Norian North America reference pole falls at drill cores in the Newark rift basin, eastern North America, J. 58.9øN, 84.3øE (A95=4.3ø).For the referencepole, recently Geophys.Res., 100, 14965-14998,1995. publisheddata from the Newark Basin drillcores[Kent et al., Kodama, K. P., M. T. Cioppa, E. Sherwood,and A. C. Warnock, 1995] were excludedbecausetheir orientationis indirectly Paleomagnetismof baked sedimentaryrocks in the Newark and Culpeperbasins:Evidence for the J1 cusp and significantLate determined.The angulardistanceto the meanof Norian poles Triassic apparent polar wander from the Mesozoic basins of for the plateau(Table 2) is 9.9ø. North America, Tectonics, 13, 917-928, 1994. Similarly, we calculatedthe mean cratonicpole for North Larson, E. E., T. R. Walker, P. E. Patterson, R. P. Hoblitt, and J. America for the Carnian. The pole is located at 52.2øN, Rosenbaum, Paleomagnetismof the Moenkopi Formation, 96.7øE (A95=3.2ø).In additionto Carnian polesof the Chinle ColoradoPlateau:Basis for long-termmodel of acquisitionof CRM, J. Geophys.Res.,87, 4819-4836, 1982. Groupoff the Coloradoplateau(Table 2), the pole calculation

includes data for the Dan River Basin [Kent and Olsen,

Lucas, S. G., The Chinle Group: Revised stratigraphy and biochronologyof Upper Triassic nonmarinestratain the western UnitedStates,in Aspectsof MesozoicGeologyand Paleontology of the ColoradoPlateau, editedby M. Morales, Bull. Mus. North.

1997], Triassicintrusionsin Maine [Fang and Van der Voo, 1988], the Fundy Group [Symonset al., 1989], and the lower Ariz. 59, 27-50, 1993. bedsof the Newark Supergroup[Witte and Kent, 1989]. The angulardistanceto the combinedBluewaterCreek result,the Lucas,S. G., and A. B. Heckert, Triassicstratigraphyin the Lucero uplift, Cibola, Valencia, and Socorro counties, New Mexico, only Carniandata availablefor rockson the plateau,is 6.2ø. Field Conf Guideb.N.M. Geol. Soc.45, 241-254, 1994. In total, Camian and Norian data suggestthat rotationof the Lucas,S. G., and A. P. Hunt, Field guideto nonmarineTriassicstrata Coloradoplateauis lessthan 10ø. Direct comparisonbetween of the southernColorado Plateau, New Mexico and Arizona, in The nonmarine Triassic, edited by S. G. Lucas, and M. Morales, any two polesfrom on and off the plateaudoesnot provide, however, the most robust estimate of the amount of CP

Bull. N.M. Mus. Nat. Hist. Sci. 3, Albuquerque,N.M., G20-G23, 1993.

rotationbecauseeach pole has associateduncertaintiesin its McFadden,P. L., and D. L. Jones,The fold test in paleomagnetism, age and position. As other workers have previously Geophys.J. R. Astron.Soc.,67, 53-58, 1981. concluded,a rotation of 5ø about an Euler pole in eastern McFadden, P.L., and M. W. McElhinny, Classification of the reversaltest in paleomagnetism,Geophys.J. Int., 103, 725-729, New Mexico or west Texas brings Triassic poles of the 1990. plateauinto agreementwith the cratonicreference. Molina Garza, R. S., J. W. Geissman, R. Van der Voo, S. G. Lucas, Acknowledgments.We thank Grant Meyer who kindly assistedin the field collection and Spencer Lucas for suggestingsampling localities. The reviews of K. Kodama and H. Hagstrum and the commentsof G.D Acton improvedthismanuscript.

References

and S. Hayden, Paleomagnetismof the Moenkopi and Chinle Formationsin central New Mexico: Implications for the North American apparent polar wander path and Triassic magnetostratigraphy, J. Geophys.Res.,96, 14239-14262, 1991. MolinaGarza,R. S.,J. W. Geissman, andR. Van derVoo,Paleomagnetism of the DockurnGroup (Upper Triassic),northwestTexas: Further evidencefor the J-1 cuspin theNorthAmericaapparentpolarwander path and implicationsfor rate of Triassicapparentpolarwanderand Coloradoplateaurotation,Tectonics,14, 979-993, 1995.

Ash, S. R., Stratigraphyof the Ciniza Lake Beds and relatedstrata, in Geology,Paleontology,and paleoecologyof a Late Triassic Molina Garza, R. S., J. W. Geissman, S. G. Lucas, and R. Van der Lake, westernNew Mexico, editedby S.R. Ash, Brigham Young Voo, Paleomagnetismand magnetostratigraphy of Triassic strata Univ. Res.Stud.Geol. Set., 25, Provo,Utah, pp. 1-14, 1978. in the Sangrede Cristo Mountainsand TucumcariBasin, New Ash, S. R., Upper Triassic floral zones of North America, in Mexico, USA, Geophys.J. Int., 124, 935-953, 1996. Biostratigraphy of fossil plants, successional and Molina Garza, R. S., G. D. Acton, and J. W. Geissman,Carboniferous paleoecologicalanalysis,editedby D.L. Dilcher and T.N Taylor, through Jurassic paleomagneticdata andtheirbearingon rotationof the Van NostrandReinhold,New York, pp. 153-170, 1980. Coloradoplateau,J. Geophys.Res.,this issue. Bazard, D. R. and R. F. Butler, Paleomagnetism of the Chinle and KayentaFormations,New Mexico andArizona,J. Geophys.Res., Purucker, M. E., D. P. Elston, and E. M. Shoemaker,Early acquisitionof characteristicmagnetizationin redbeds of the 96, 9847-9872, 1991. Mowenkopi Formation (Triassic), Gray Mountain, Arizona, J. Bryan, P., and R. G. Gordon, Rotation of the Colorado Plateau: An Geophys.Res.,85, 997-1005, 1980. updatedanalysisof paleomagneticdata, Geophys.Res.Letts., 17, Reeve,S.C., Paleomagneticstudiesof Cambrianand Triassicage, 1501-1504, 1990. Ph.D. thesis,426 pp., Univ. of Tex., Dallas, 1975. Ekstrand,E. J., and R. F. Butler, Paleomagnetismof the Moenave Formation: Implications of the Mesozoic North American Reeve,S.C., andC. E. Helsley, Magneticreversalsequence in the apparentpolarwanderpath,Geology,17, 245-248, 1989. upper portion of the Chinle Formation,Montoya, New Mexico, Geol. Soc. Am. Bull., 83, 3795-3812, 1972. Fang, W., and R. Van der Voo, Paleomagnetismof Middle-Late Triassicplutonsin southernMaine, Tectonophysics, 156, 51-58, Steiner,M. B., and S. G. Lucas, A Middle Triassicpaleomagnetic pole for North America, Geol. Soc. Am. Bull., 104, 993-998, 1,988. 1992. Gordon,R. G., A. Cox, and S. O'Hare, Paleomagneti½ Euler poles and the apparentpolar wanderand absolutemotionof North Steiner, M. B., M. Morales, and E. M. Shoemaker, Magnetostratigraphic, biostratigraphic, andlithologiccorrelations America sincethe Carboniferous,Tectonics,3,499-537, 1984. in Triassic strata of the western U.S., in Applications of Gradstein,F. M., F. P. Agterberg,J. G. Ogg, J. Hardenbol,P. van Paleomagnetism to SedimentaryGeology,editedby D. McNeil, Veen, J. Thierry, and Z. Huang, A Mesozoictime scale,J. D. Aissaoui,and N. Hurley, Spec, Publ. Soc. Econ. Paleontol. Geophys. Res.,99, 24051-24074,1994. Mineral., 49, 41-57, 1993. Harland,W. B., R. L. Armstrong,A. V. Cox, L. E. Craig, A. G. of Smith, and D. F. Smith,A GeologicTime Scale 1989, 263 pp., Symons,D. T. A., R. E. Borman,andR. P. Jans,Paleomagnetism the Triassic redbedsof the lower Fundy Group, and Mesozoic CambridgeUniv. Press,New York, 1990. Kent, D. V., and P. E. Olsen, Paleomagnetismof continental tectonismof the Nova Scotia platform, Canada,Tectonophysics, 164, 13-24, 1989. sediments of Late Triassicagefrom the Dan River-DanvilleRift Basin(easternNorthAmerica),Geol.Soc.Amer.Bull., 109, 366- Van der Voo, R., Phanerozoicpaleomagneticpolesfrom Europeand 379,1997. North America and comparisonswith continentalreconstructions, Kent,DoV., andW. K. Witte, Slow apparentpolarwanderfor North Rev. Geophys.,28, 167-206, 1990. Americain the Late TriassicandlargeColoradoplateaurotation, Witte, W. K., and D. V. Kent, A middle Carnian to early Norian Tectonics, 12, 291-300, 1993. (-225 Ma) paleopole from sedimentsof the Newark Basin, Pennsylvannia,Geol. Soc. Amer. Bull., 101, 1118-1126, 1989. Kent, D. V., P. E. Olsen, and W. K. Witte, Late Triassic-earliest

24,200

MOLINA GARZA ET AL.: TRIASSIC PALEOMAGNETIC DATA ZUNI UPLIFT

Witte,W. K., andD. V. Kent,Thepaleomagnetism of redbedsand basalts of the Hettangian Extrusive zone, Newark Basin, New Jersey,J. Geophys.Res., 95, 17533-17545, 1990. Witte, W. K., D. V. Kent, and P.E. Olsen, Magnetostratigraphy and paleomagnetic polesfrom the Late Triassic-earliestJurassicstrata of the Newark basin, Geol. Soc. Amer. Bull., 103, 1648-1662, 1991.

J. W. GeissmanandR. S. Molina Garza, Departmentof Earth and PlanetarySciences,Univeristyof New Mexico, 203 NorthropHall, Albuquerque,NM 87131-1116.(email: [email protected]) A. Gomez,Departmentof GeologicalSciences,Universityof Texas, Austin, TX 78712.

B. Horton, Departmentof Geosciences,University of Arizona, Tucson, AZ 85721.

Zijderveld, J. D. A., A.C. demagnetizationof rocks: Analysis of results, in Methods in Rock Magnetism and Paleomagnetism, editedby D.W. Collison, K.M. Creer and S.K. Runcorn,Elsevier, (ReceivedNovember7, 1997;revisedMay 8, 1998; New York, pp. 254-286, 1967. acceptedJune9, 1998.)

Lihat lebih banyak...

Comentários

Copyright © 2017 DADOSPDF Inc.