Carbonate SeqStrat

7/31/2019 Carbonate SeqStrat

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ABSTRACT

The Middle Ordovician St. Peter Sandstone andGlenwood Formation (Ancell Group) represent a sig-nificant target for gas exploration at the base of the

Tippecanoe sequence in the Michigan basin. Coreand well log data show that the St. PeterGlenwoodinterval contains numerous carbonate units that pro-vide the basis for both regional correlation and subdi-vision of the section into at least 20 high-frequencysequences. The temporal resolution afforded bythese sequences allows a detailed analysis of sedi-ment partitioning as the basin evolved. The spatialdistribution of the basal sequences illustrates the pro-nounced east-to-west onlap of the Wisconsin arch.An abrupt increase in sequence thickness upsectionindicates that a major episode of basin-centered sub-sidence began during middle St. Peter deposition andcontinued through the deposition of the Glenwood

Formation. The upper sequences show a significantbeveling of the Glenwood Formation and the top ofthe St. Peter Sandstone in the north, south, andsoutheast areas of the basin prior to deposition of theoverlying Black River carbonates. Although eustaticsea level changes were undoubtedly operating at sev-eral scales, the facies distribution of this mixed clas-tic/carbonate system also documents significantchanges of local and regional tectonics.

975AAPG Bulletin, V. 84, No. 7 (July 2000), P. 975996.

Copyright 2000. The American Association of Petroleum Geologists. Allrights reserved.

1Manuscript received August 20, 1998; revised manuscript receivedAugust 18, 1999; final acceptance November 15, 1999.

2Department of Geological Sciences, Ohio University, Athens, Ohio45701.

3Department of Geology and Geophysics, University of Wisconsin, 1215W. Dayton St., Madison, Wisconsin 53706.

This paper stems from research of basin compartments and seals fundedby the Gas Research Institute under contract 5089-260-1810. The projectcould not have been completed without the foresight of W. B. Harrison,Western Michigan University, in collecting the numerous St. Peter cores andhis generosity in allowing access to this core repository. Our thanks to ShellResources, Unocal, and Marathon Oil companies for access to core, thecolleagues and students at the University of Wisconsin, and the otheruniversities that participated in this project for numerous discussions andcritiques. The reviews of P. Catacosinos, P. Daniels, and J. May helpedsharpen the focus of the paper.

High-Resolution Sequence Stratigraphic Analysis of theSt. Peter Sandstone and Glenwood Formation(Middle Ordovician), Michigan Basin, U.S.A.1

G. C. Nadon,2J. A. (Toni) Simo,3 R. H. Dott, Jr.,3 and C. W. Byers3

INTRODUCTION

The Middle Ordovician St. Peter Sandstone is anhistorically famous and economically significant for-mation of the north-central cratonic portion of the

United States. The St. Peter is a classic blanket orsheet sandstone that covers most of six states; eitherit or correlative sandstones extend into several morestates (Dapples, 1955). The St. Peter is famous for itsextreme compositional and textural maturity, as wellas the fact that it is the basal unit of the Tippecanoesequence (Sloss, 1963, 1982). In most of its outcroparea the formation is of the order of 3040 m thick,but in the Michigan basin it is over 350 m thick(Figure 1). The overlying Glenwood Formation is onlya few meters thick where exposed on the Wisconsinarch, but reaches about 60 m in Michigan. In contrast,in outcrop the St. Peter is a very homogeneous, cross-stratified quartzarenite, but the Glenwood Formation

contains interstratified green shale and fine sand-stones with considerable bioturbation.

Although the St. PeterGlenwood interval hasbeen well documented from exposures during thepast century, it was not until a resurgence of deepdrilling for hydrocarbons that its character in theMichigan basin could be determined. Commercialgas accumulations in anticlinal structures within theSt. PeterGlenwood interval spurred explorationduring the 1980s and early 1990s (Catacosinos et al.,1991). During the earliest stages of this phase ofdeeper drilling, the mistaken identification of thenewly discovered gas reservoir as Upper Cambrianto Lower Ordovician (Jordan Sandstone, Prairie duChien Group, or Knox sandstone) caused much con-fusion (Catacosinos, 1973; Fisher and Barratt, 1985;Catacosinos and Daniels, 1991). Harrison (1987) cor-rected this confusion and showed that the MiddleOrdovician St. Peter Sandstone and GlenwoodFormation names should be applied to the strata inquestion.

In addition to a marked contrast in thicknessbetween outcrops and the subsurface, the St.PeterGlenwood interval also displays significant


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changes of lithology. In south-central Wisconsin,fine- to medium-grained eolian sandstones dominatethe St. Peter (Mai and Dott, 1985), whereas the

Glenwood is a bioturbated medium- to coarse-grained sandstone with sporadic phosphatic gran-ules and some very sandy dolomite. In centralMichigan, by contrast, much of the upper St. Peterand the Glenwood are intensely bioturbated. Bothunits in the subsurface contain a greater variety oftrace fossils than in outcrop. In Michigan eoliansandstones are inferred only in the western counties;there, the St. Peter is a monotonous, unbioturbated,homogeneous, pure quartz sandstone with rareadhesion structures. Carbonate facies (mostly

dolomite) are entirely absent in outcrop, but in thesubsurface they occur widely within the south andeast portions of the Michigan basin, representing the

northwestward extension of equivalent, entirely car-bonate, Middle Ordovician strata.In a broad sense the St. PeterGlenwood interval

represents a transgressive systems tract onlappingthe Wisconsin arch and capped by a condensed sec-tion (Barnes et al., 1992, 1996; Schutter, 1996). Thebase of the St. PeterGlenwood interval, which formspart of the craton-wide Sauk-Tippecanoe sequenceboundary, lies on the Shakopee Formation of thePrairie du Chien Group, a complex surface that isprobably locally karsted (Nadon and Smith, 1992).

976 Sequence Stratigraphy, Michigan Basin

25

25

25

2550

100

150

250

300

350

50 50

50

10025

Chicago

2000 100 Km

1000 Mi

Madison

200

150

200

IllinoisIndiana

Michigan

Wisconsin

A

B

Figure 1Location map showingthe thickness variations in theSt. PeterGlenwood interval inthe midwestern United States.Contour interval 50 m (afterDapples, 1955; Willman et al.,1975; Mai and Dott, 1985; Droste

et al., 1982; Bricker et al., 1983).


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The carbonate and black shale facies of the BlackRiver formation define the top of the interval.

Thermal modeling (Cercone and Pollack, 1991;Wang et al., 1994) and backstripping (Coakley et al.,1994; Howell and van der Pluijm, 1999) show thatthe Michigan basin underwent basin-centered subsi-dence during deposition of both the Prairie duChien and Ancell groups. Postdepositional variationsin fluid f low influenced by both compaction and

orogenesis along the eastern and southern marginsof North America produced a complex diageneticoverprint. Fluid inclusion and isotopic data fromquartz overgrowths and carbonate cements provideevidence of a complex history of fluid flow and dia-genesis after burial (Drzewiecki et al., 1994; Winteret al., 1995). One result of this diagenetic complexi-ty is the variation of porosity and permeability with-in the St. PeterGlenwood interval from 2 to 21%and 0.001 to 4 md over relatively short intervals(Moline et al., 1994; Bahr et al., 1994).

Hydrocarbons, mainly gas, are found within fieldsdefined by small anticlines (Catacosinos et al., 1991).Gas has been recovered from two main horizons,one near the middle and one near the top of theinterval. Pressure data within the St. Peter Sandstoneand Glenwood Formation indicate the presence ofoverpressured compartments (Bahr et al., 1994).The overpressures occur mainly in the deepest por-tion of the basin. The regional distribution of over-

pressures, which are in excess of 1034 kPa (150 psi)above hydrostatic, suggests formation by glacialloading. Within individual wells, the overpressuredzones are highly variable over a few tens of meterswithin formations (Bahr et al., 1994).

Exploration and development of potential reser-voirs from such vertically limited compartments with-in a thick succession require more detail than a gener-alized transgressive systems tract (TST) frameworkprovides. A high-resolution sequence stratigraphicanalysis of the St. PeterGlenwood can provide the

Nadon et al. 977

Figure 2Isopach mapfor the St. Peter Sandstoneand Glenwood Formationin the Michigan basinshowing the distributionof wells used in this study.The locations of cross

sections of Figures 1012and the Ruppert well(Figure 5) are shown.

350

Figure11

Figure9

St. Peter Sandstone

Bevel Edge

Figure10

St. Peter SandstoneBevel Edge

Glenwood Fm.

Bevel Edge

Contour Interval50 m

60 kilometers

50 Miles

Erosional Limit

of the

St. Peter Sandstone

250

300

200

150100

250

200

150

10050

Ruppert

Well Locations

Glenwood Fm. TruncatedSt. Peter Sst. TruncatedGlenwood Absent

St. Peter/Glenwood Absent

JEM


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Table1.

Lithofacieswithin

theSt.

PeterSandstoneandGlenw

oodFormationandTheirTypicalLogResponses*

Depositional

Well-Log

Lithofacies

Description

Environment

Respo

nse

Faciese1

Massivesandstone

Fine-

tocoarse-grained,well-sorted

toverywellsortedsandstone.

Shallowsubtidal

Gamma-ray=1

5

20APIunits

Occursasbeds0.1

to>10mthick

.Noburrowsobserved.

tononmarine.

PEF**=2

2.6

MostcommoninthelowerSt.

PeterSandstone.

Density=2.4

2.5g/cm

3

Porosityrangesfrom1to14%

Bioturbated

Fine-

tocoarse-grained,well-sorted

toverywellsortedsandstone.

Shallowsubtidal.

massivesandstone

Occursasbeds0.1

to>10mthick

.Denselybioturbatedby

Skolithos.

MostcommonintheupperSt.

Peter(Figure3A).

Horizontallybedded

Paralleltohorizontallylaminatedfine-tomedium-grainedwell-

Shallowsubtidal,

sandstone

sortedtoverywellsortedsandsto

neinbeds0.1mtoseveral

highenergy.

metersthick.

RareSkolithosburro

ws.Presentthroughoutthe

St.

PeterSandstone(Figure3B).

Cross-bedded

Planartabulartotroughcross-bedd

ed,

fine-

tocoarse-grained

High-energyshallow,

sandstone

sandstone.

Rareadhesionripples.

Well-sortedtoverywellsorted.

subtidaltoeolian.

Rarebioturbation(Skolithos).MostcommoninSt.

PeterSandstone.

Faciese2

Clay-rich

Massivetopoorlybedded,veryfinetomedium-grainedsandstone.

Shallowsubtidal,

Gamma-ray=2

0

90API

sandstone

Abundantdetritalclaysasclastsanddispersedbybioturbation.

lowenergy.

(usually309

0)

SkolithosandPlanolitescommon

.Mostcommoninthebasal

PEF**=2.5

2.7

GlenwoodFormation.

Density=2.42

2.6

9g/cm

3

Porosity=11

6%

Faciese3

Interbeddede1&e2

Thinlyinterbeddedsetsoffaciese1

ande2atthescaleofresolution

Serratedgamm

a-raylogprofile

ofthegammalog(9

0API

andveryfinegrainedsandstone.B

urrowsarerare.

Occursin0.1m

lowenergy,

PEF**=2.5

2.

bedsinthemiddleandupperGlenwood.

subtidal.

Density16%

Faciese5

Interbedded

Intervalswithvariableproportions

ofsiliciclasticsandcarbonates

Logresponses

characteristically

siliciclasticsand

inbedsof0.5

0.3mthick.

Thecarbonatebedsincreaseinnumber

serratedwith

anincreasing

carbonates

andthicknessupsection.

gamma-rayva

lueupsection

(finingupward).


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Nadon et al. 979

Table1.

Continued

Depositional

Well-Log

Lithofacies

Description

Environment

Response

Faciese6

Sandycarbonate

Dolomitizedcarbonatemudstonewithupto60%quartzgrains.

Relativelyshallow,

Lowtohighgammaray

Grainsrangefromsilttocoarsesand.

Rarehorizontalbedding

subtidal.

PEF**=3

3.6

(BlackRiver

preserved.

Rareooids,coatedgra

ins,andfossils(bivalveand

LimestonePE

F=4.5

5)

trilobitefragments).Mostcommo

ninthelowerSt.

PeterSandstone

Density>2.74

andupperGlenwoodFormation(Figure4A).

Porosity=13

%(Glenwood

porosity=3

6%)

Dolomite

Mudstones,wackestones,grainstones,andalgalboundstones.

Rangesfrom

Mudstonesarethinlylaminatedtomassive.

Rareshaleintraclasts.

intertidalto

Bivalveandtrilobitefragments,ooids,andcoatedgrains

shallowsubtidal.

common.

Burrowsrangefromco

mmontoabsent.Rareanhydrite

crystalsinlowerSt.

PeterSandsto

ne.

Presentinboth

formations(Figure4B).

Faciese7

Interbedded

Intervalswithvariableproportionsofsiliciclasticsandcarbonates

Shallowmarine.

Logresponses

carbonatesand

inbedsof0.5

0.3mthick.

Thes

andstonebedsincreaseinnumber

characteristicallyserrated

siliciclastics

andthicknessupsection.

withanupwarddecreasein

gamma-rayvalues

(coarsening-upward).

Faciese8

Limestone

Samefaciesasdolomite,

butunaltered.

Shallowmarine.

Low-density,h

igh-porosity

values.Lowgamma-rayand

highPEF**va

lues.

Faciese9

Anhydrite

Bedsofanhydritegreaterthan0.6

m.

Evaporiticponds.

Lowgamma-rayvaluesdensity

greaterthan3.0andPEF**

valuesgreate

rthan6.

*LithofaciescompiledfromV

an

drey(1991),Barnesetal.(1992),andDrzewieckietal.(1994).

**PEF=Photoelectricfactor.


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necessary detail to enhance both exploration and pro-duction strategies, but requires a means of accuratecorrelation. The carbonate rocks within this mixedsystem provide the means for the correlation and sub-division of the St. PeterGlenwood interval within thebasin. This paper presents a detailed stratigraphicanalysis based on 30 cores and 74 well logs, with theinterpretation of facies from well log analysis receiv-ing special emphasis (Figure 2).

FACIES

The St. Peter Sandstone and Glenwood Formationtogether contain 13 lithofacies (Table 1). Faciesdescriptions and interpretations, which are brieflysummarized here, are presented in more detail byBarnes et al. (1992) and Drzewiecki et al. (1994). Thetwo main lithologic components in core are quartz-arenites and carbonates, with minor amounts of

shale and siltstone. The depositional environment ofthe siliciclastics ranged from marine to possiblyeolian, whereas the carbonates were all shallowmarine and are largely dolomitized. The log respons-es for the lithofacies are represented by a suite ofnine electrofacies (Serra, 1986; Moline et al., 1994)that are presented in Table 1.

The siliciclastics range from massive to parallel lam-inated and trough cross-bedded, quartz-cemented,medium- to coarse-grained sandstones (Figure 3A) tomedium- to fine-grained sandstones with a highly vari-able clay and silt component and intensity of biotur-bation (Figure 3B). All of these may be presentthroughout the St. Peter Sandstone, with the massive

sandstones most common low in the section. The bio-turbated sandstones are characteristic of GlenwoodFormation and are common in the upper St. Peter.The ichnofacies include zones ofTeichichnus,Asterosoma, Planolites, Terebellina, and Chondrites,which are typical of Ordovician normal marine condi-tions (MacEachern et al., 1992), and zones whereonly abundant Skolithos are present. The amount ofnonmarine sandstone facies within the section isunknown. Barnes et al. (1992) and Drzewiecki et al.(1994) interpreted all the nonbioturbated massiveand cross-bedded sandstones as marine deposits;however, the possibility of a fluvial component in thisfacies, especially in the more proximal sections to thenorth and northwest, cannot be eliminated. Cross-bedded sandstones with adhesion ripples in one corein southwestern Michigan may represent eolian strata.Shales with little or no carbonate content are rare(


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result of local restriction due to fault movement inthat area (Nadon et al., 1991).

The carbonate and anhydrite electrofacies weredefined by a combination of gamma-ray, density, andPEF logs. The carbonate units within the sectioncommonly have the highest gamma-ray responsesdue to the presence of silt-size feldspar grains(Drzewiecki et al., 1994). All the facies variationswithin the dolomites and the limestones group intotwo electrofacies, facies e6 and e8, respectively.The anhydrite beds (electrofacies e9) are easily

determined from the density logs.The siliciclastic and carbonate intervals display

transitional zones within which both lithologies areinterbedded. Intervals of increasing carbonate orincreasing sandstone are present throughout thecentral portion of the basin; however, variations inrates of sedimentation and subsidence within thebasin produced several distinct types of transition.In the center of the basin, these zones are relativelythick. Toward the margins of the basin, the transi-tion zones become thinner until, just before thecarbonates disappear to the north and northwest,the transitions are absent and the end-member

lithologies are in abrupt contact. Similarly, abruptcontacts occur in the southeastern portion of thebasin where carbonates are the predominate lithol-ogy. Figure 5 illustrates one of the cores that con-tain these abrupt transitions.

The electrofacies classification includes thesiliciclastic/carbonate transitional zones (Table 1).A serrated log response that shows an increase ingamma-ray values coupled with an increase in den-sity upsection is designated facies e5. A similar ser-rated log style, but one showing a decrease in

gamma ray and density response upsection, com-poses facies e7. Both record interbedded siliciclas-tics and carbonates at or near the limit of resolutionof the logs (approximately 0.6 m). Facies e5 reflectsan increase in the amount of carbonate upsection,whereas facies e7 is a result of a decrease in car-bonate.

A SEQUENCE STRATIGRAPHIC MODEL

The overall depositional framework for the St.PeterGlenwood interval is one of a shallow rampwith a clastic source to the north and northwest anda carbonate factory to the south and southeast(Drzewiecki et al., 1994) (Figure 6). The core and logfacies are arranged in recurring vertical patterns. Anideal vertical succession in the central Michigan basin(Figure 7) consists of a basal clean quartz sandstone offacies e1, which is gradationally overlain by eithersandstones of facies e2 or the interbedded sandstonesand carbonates of facies e5. The interbedded litholo-gies give way to a zone of predominantly carbonatedeposition (facies e6, e8) that usually contains the

maximum gamma-ray response in the sequence.Facies e7, which overlies the carbonates, records aninflux of siliciclastics (facies e2, e3). The upperboundary of the sequence is marked by an abruptshift to facies e1.

The facies assemblages are interpreted in sequencestratigraphic terms to represent lowstand systemtracts (LST = massive + parallel laminated sandstone),transgressive system tracts (TST = bioturbated sand-stone + increasing carbonate transition zones), andhighstand system tracts (HST = increasing sandstone

Nadon et al. 981

Figure 4Examples ofcarbonate lithofacieswithin the St. PeterSandstone and GlenwoodFormation in theMichigan basin.(A) Algal boundstone from

the Glenwood Formation(facies e6) in Brinks 1-3,Missaukee County. (B)Oolites and coated grainsfrom the St. PeterSandstone (facies e6) inState Foster 6-21, OgemawCounty.


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transition zones + massive, bioturbated, and troughcross-bedded sandstones) (Table 1). The variationsin character of the systems tracts within the basinrecord the local and regional changes in the rate offormation of accommodation space. The resultingmodel, although similar to others interpreted forramp settings (Posamentier and Allen, 1993a, b),can be used to interpret the well-log data wherecore data are absent.

The sharp contact at the base of facies e1 sand-stones is interpreted to be a sequence boundary fol-lowed by an abrupt basinward shift of facies. Faciese1 constitutes an LST (Posamentier and Allen, 1993a,b; Mitchum et al., 1993). As the rate of formation ofaccommodation space then increased, a TST wasdeposited composed of either clastics with a highersilt component (facies e2) or interbedded sandstonesand carbonates (facies e5). The increase in carbonate


Figure 5Coredescription and welllog from the Ruppertwell, Tuscola Countyin the southeasternportion of the studyarea (see Figure 2 for

location). A completesequence is coredthat illustratesthe siliciclastic/carbonate transitionsin the St. PeterSandstone.

Bioturbation

Intense

None

Rare

Moderate

Structures

Parallel lamination

Trough cross-beds

Intraclasts

Low-angle lamination

Shell material

Ripple cross-lamination

3225

claysilt

vfmcv

sandgranulepebble

GRAIN SIZE

3195

3196

3199

Sequence

#10

3175

Ruppert(Tuscola Co.)

3200

PEF

Density

Intensity ofBioturbation

3201

3200

3198

3197

3194

3191

3193

3192

0 150GR

GAPI

0 10PEF

0.450

2.00 3.00

45 -15NPHI

RHOB

NPHI

Compensation

DRHO

Sandstone Siltstone Carbonate

Gamma-Ray


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sedimentation is a result of the trapping of coarse clas-tic material farther landward by rising base level.Continued high rates of formation of accommodation

space ultimately resulted in a zone of predominantlycarbonate deposition (facies e6 and e8). The maxi-mum gamma-ray values that occur within the carbon-ates are the result of an influx of silt-size material(Drzewiecki et al., 1994), which entered the basin asrelative sea level began to fall and the materialtrapped landward was flushed into the basin. In thisscenario, the gamma-ray maxima is therefore justabove, rather than coincident with, the maximumflooding surface (MFS) (Mitchum et al., 1993).

A further decrease in rate of formation of accom-modation space resulted in the deposition of an HSTrepresented by facies e7, e2, and e3. The decreased

carbonate content and gamma-ray response upsec-tion record the arrival of coarse clastics, whichwere once again transported into the basin. TheHST is capped by another sequence boundarymarked by an abrupt shift to facies e1.

Variation in the rates of formation of accommoda-tion space within the basin led to predictable lateraland vertical variations of electrofacies withinsequences and stacking patterns of sequences(Figure 8). The transitional facies (e5 and e7) occuronly where the rate of formation of accommodation

space was a maximum. To the north and northwest,where high rates of siliciclastic input lowered therate of formation of accommodation space, the

entire section is composed solely of facies e1. Thecarbonates used for correlation are absent, and theidentification of sequence boundaries is problemat-ic. Sequence boundaries were extrapolated into thenorthern area based on curve matching rather thanelectrofacies variations. To the south and southwest,similar problems occur because of the distance froma siliciclastic source. The absence of siliciclastic sedi-ments within some sequences poses as many prob-lems for correlation as the absence of carbonates.

In addition, even in the basin center, where themaximum rate of formation of accommodation spaceis expected to form and preserve the sequences,

many sequences are attenuated. The maximumgamma-ray response seen in the middle of sequence11 of the Weingartz well (Figure 9 near 3436 m)marks a major change in the thickness of sequenceswithin the interval. Above this level the sequencesare both thicker and more complete than thesequences below. This marker, which is widespreadthroughout the basin, informally subdivides the St.Peter Sandstone into upper and lower members.

The 20 sequences correlated within the basin arethose present in the zone of maximum preservation

Nadon et al. 983

Sequence

NW SE

100-200 Km

Clean Sandstones

Interbedded Carbonates & Siliciclastics

Shale-prone Siliciclastics & Carbonates

HST

HST

LST

LST

Carbonates

TST

TST

e1

e2/e3

e4

e5

e7

e6/

e8

10'so

fmeters

Figure 6Sequencestratigraphic model of theSt. Peter Sandstone andthe Glenwood Formationacross the Michigan basin.LST = lowstand systemstract, TST = transgressive

systems tract, HST =highstand systems tract.Letters and numbers referto electrofacies describedin the text.


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of section. There are, however, significant changesthat occur within wells that are not predictable.These changes include abrupt thickening or thin-ning of facies, the presence of additionalsequences, or the absence of sequences within thesection (Nadon et al., 1991).

RESULTS

Lithostratigraphic correlation throughout the St.PeterGlenwood interval used the quasiregional car-bonate beds that contain the maximum floodingsurfaces (Figures 911). Correlation along thesouthern margin of the depocenter, where signifi-cant thickness changes occur over relatively shortdistances, requires multiple overlapping datums(Figures 10, 11). The sequences thin and undergo afacies change to the south. This change is interpret-ed as the result of onlap of the topography forming

the southern margin of the basin in the lower St.Peter interval. The maximum thinning occurs at andjust above the boundary between the lower andupper St. Peter Sandstone.

The chronostratigraphic implications of sequencestratigraphy were the impetus to extend the well-loginterpretations beyond simple lithologic correlation(Van Wagoner et al., 1988). The extension of the 20sequences throughout the basin allows for the con-struction of a series of maps that illustrate the natureof the controls on basin infill. Map views of the con-tact of the basal sequences with the underlyingPrairie du Chien Group (Figure 12A) and the accom-panying Wheeler diagram (Figure 12B) show the pro-

gressive basal onlap of the St. Peter Sandstone ontothe Wisconsin arch. A similar map of the uppersequences directly below the Black River formation(Figure 13A) and Wheeler diagram (Figure 13B) doc-ument the erosional truncation of both theGlenwood Formation and St. Peter Sandstone alongboth the northern and southern margins of the basin.

The chronostratigraphic subdivision of the sec-tion also enabled us to document the temporal andspatial variations in sediment types throughout thesection. This was accomplished by partitioning thesiliciclastic and carbonate sediments within indi-vidual sequences using clastic/carbonate ratiomaps of each sequence (Figures 1416). Thesemaps show (1) the variations in the extent of car-bonate deposition, (2) areas where siliciclasticdeposits are absent within specific sequences, and(3) areas where each sequence is absent.

DISCUSSION

The sediment partitioning displayed in Figures1416 reveals significant trends in the basin. These


Compensa

tion

1

6

2

5

7

3

e-FACIES

JEM

Weinga

rtz

Sequence1

4

Gamma-

Ray

PEF De

nsity

LowstandSystems

Tract

Transgressive

Systems

Tract

Highstand

Systems

Tract

Model

e-FACIES

1

6

2

5

7

3

MFS

S

equenceBoundary

S

equenceBoundary

Gamma-

Ray

Density

PEF

50 25

3375

3400

San

dstone

Car

bonate

Figure7Modelforasequencebasedonelectrofaciesdata

comparedtoawell-preservedsequ

encewithintheJEMWeingartzwe

ll,

ClareCounty.

SeeFigure2forwellloca

tion.


11/22

trends include (1) variations in thickness of the lowerSt. Peter Sandstone in the center of the basin, (2) ver-tical changes in thickness and facies within the St.PeterGlenwood interval, and (3) changes in siliciclas-tic source direction and basin geometry through time.The onlap of the lower St. Peter Sandstone (Figure

12B) is consistent with the overall transgressivenature at the base of the Tippecanoe sequence (Sloss,1963; Barnes et al., 1992, 1996). The spatial pattern ofsequences (Figure 12A) may represent the infilling ofa valley system with local highlands in the south andnorth of the basin. The presence of incised valleys ina similar stratigraphic position on the Wisconsin arch(Mai and Dott, 1985) suggests that an incised valley fillmodel is a logical extrapolation, but too few data areavailable to evaluate fully this hypothesis.

The local and regional variability in the sequencessuggests several spatial and temporal scales for thetectonic control of the rates of formation of accom-modation space. Howell and van der Pluijm (1999)

used the similarity of basin-centered subsidencestyle to group the St. PeterGlenwood interval withthe underlying Shakopee Formation as a single tec-tonic sequence. They argued there was no evidenceof the major Sauk-Tippecanoe sequence boundaryin the central basin and suggested this was consis-tent with the increased subsidence rates calculatedfor both units; however, the pattern of sequences ofthe basal St. Peter Sandstone in contact with theShakopee Formation (Figure 12) suggests otherwise.

The regional variations in sequence thickness inFigures 9 and 11 show that there were also higherorder variations in subsidence rate, at least withinthe St. PeterGlenwood interval, that must be takeninto account when considering regional patterns offormation of accommodation space.

At the local or field scale, penecontemporaneousmovement on fault-cored anticlines determined thethickness and preservation potential of individualsequences within wells (Nadon et al., 1991). Al-though this complexity makes detailed correlationsmore difficult, it also presents the possibility of addi-tional hydrocarbon traps within the basin. Structuraland stratigraphic traps resulting from either erosion-al truncation or thinning of sequences over the crestof structures or the changes in facies due to sedi-ment partitioning as a result of changes in rates offormation of accommodation space may be presenton the flanks of the major structures.

Spatial variations in the sequences at the top of

the section (Figure 13B) occur in parallel tracts thatare essentially orthogonal to the onlap at the base ofthe section. Detailed cross sections in the southeast(Figure 11) illustrate the removal of the entireGlenwood Formation and the erosion of the uppersequences within the St. Peter Sandstone. A similargeometry is developed on the northern margin ofthe basin (Figure 2). This pattern reflects the bevel-ing of the strata due to uplift prior to, or in somecases possibly contemporaneous with, deposition

Nadon et al. 985

?

?

DistalProximal

Electro-Facies Associations

e1 Clean Sst. (gamma-ray >98%)

e2 "Dirty" Sst. (gamma-ray 50%)

e7 Carbonate with Interbedded Sst. (e1 and/or e2)

e6, e8, e9 Carbonate = Dolomite + Limestone + Evaporites

e5 Sst. with interbedded Carbonate (e6)

HST

TST

LST

??

MFS

Figure 8Model for the variations expected in a single sequence across the Michigan basin. Sections proximal tothe siliciclastic source area preserve only sandstones (facies e1, e2, or e3). The sections toward the center of thebasin preserve the entire sequence. The increasing deposition of carbonates (facies e5, e6, e8, and e9) reflectsincreasing distance from a clastic source. The reduction of facies in both proximal and distal sections makessequence boundary identification difficult.


12/22


2850

2875

2975

2900

2925

2950

3000

3

150

3175

3125

3025

3075

3050

3100

2.0 3.0

45.0 -15.0NPHI

0.0 10.0PEF

-0.050 0 .450DRHO (G/C3)

RHOB (G/C3)

Boyce(Osceola Co.)

upper

St.Peter

lower

St.Peter

GlenwoodFm.

Black RiverFm.

Prairie du ChienGroup

Gamma-Ray

Compensation

PEF

Density

St.PeterSandstone

0.0 150.0

1 50 .0 3 00 .0

GR(GAPI)

NPHI

PEF

357

5

3350

3550

3525

3500

3475

3450

3425

3400

3375

3225

33

25

3250

3275

3300

Weingartz(Clare Co.)

Gamma-Ray

Compensation

PEF

Density

3375

3400

3425

3450

3475

3500

3525

3575

3550

3600

3625

3650

3675

3700

3725

3375

16 km 10 kmWest 63 km

Grout(Gladwin Co.)

19

18

17

16

15

14

13

10

9

8

7

6

4

20

3

Gamma-Ray

Compensation

Density

11

5

12

0.0 150.0

1 50 .0 3 00 .0

GR(GAPI)

0.0 150.0

1 50 .0 3 00 .0

GR

(GAPI) 2.0 3.0

45.0 -15.0NPHI

0.0 10.0PEF

-0.050 0 .450DRHO (G/C3)

RHOB (G/C3)

2.0 3.0RHOB (G/C3)

0.0 10.0PEF

-0.050 0 .450DRHO (G/C3)

NPHI

Datum

Figure 9East-west well-log cross section through the central portion of the Michigan basin (see Figure 2 for loca-tion). Note the basal onlap at the base of the western end of the section. The producing intervals in the region bor-dering Saginaw Bay are marked on the Whyte well. The stratigraphic datum is the maximum gamma-ray responsewithin sequence 11 that lies just above the MFS (maximum flooding surface).


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Nadon et al. 987

3175

3075

Producing IntervalsSequence Boundaries

Lithostratigraphic Boundaries

0.0 150.0

1 50 .0 3 00 .0

SGR

2.0 3.0

45.0 -15.0NPHI

0.0 10.0PEF

-0.050 0 .450DRHO (G/C3)

RHOB (G/C3)

South Almer(Tuscola Co.)

3225

3200

3150

3125

3100

3050

3025

3000

Gamma -Ray

Compensation

PEF

Density

3300

3400

*

0.0 150.0

1 50 .0 3 00 .0

GR(GAPI)

2.0 3.0

45.0 -15.0NPHI

0.0 10.0PEF

-0.050 0 .450DRHO (G/C3)

RHOB (G/C3)

*

3350

3450

3425

3375

3325

3225

3250

3275

3200

3175

Whyte(Bay Co.)

Compensation

PEF

NPHI

Hunt-Martin(Gladwin Co.)

3425

3450

3475

3500

3575

3525

3550

3

600

3625

3650

3675

3700

37

25

20

19

18

16

15

14

13

10

9

8

7

6

4

3

11

3400

Gamma-Ray

Compensation

PEF

Density

Gamma-Ray

East38 km 49 km

17

12

5

0.0 150.01 50 .0 3 00 .0

GR(GAPI) 2.0 3.0

0.0 10.0PEF

-0 .050 0 .450

DRHO (G/C3)

RHOB (G/C3)

Density

NPHI

Datum

Figure 9Continued.


14/22


PrairieduChien

Group

2100 21752125 22002150

0.0

150.0

150.0

300.0

GR

(GAPI)

2.0

3.0

0.0

10.0

PEF

-0.050

0.450

DRHO(

G/C3)

RHOB(G/C3)

Gamma

-

Ray

Compensa

tion

Densi

ty

PEF

22252075

23002200 2225 22502175

Woodruff

1-19

0.0

150.0

150.0

300.0

GR

(GAPI)

2.0

3.0

RHOB(G/C3)

-0.050

0.450

DRH

O(

G/C3)

Gamma-

Ray

Compensa

tion

Densi

ty

2275

24502375 24002325 2350230022752225 2250

0.0

150.0

150.0

300.0

GR

(GAPI)

2.0

3.0

RHOB(G/C3)

0

0.25

DRHO(

G/C3)

BlackRiver

Fm.

upper

lower

Glenwood

Fm.

7.7

km

11.6

km

N

orth

South

29.3

km

19

18

17

16

15

14 31

312

10 9 8 7 6 5 4 2

St.PeterSandstone

2375 2450

0.0150

.0G

R

(GAPI)

150.0

300.0

2.0

3.0

-0.050

0.450

DRHO(

G/C3)

RHOB(G/C3)

2275 2300 2325 2350 24252250

Datum

Litho

stra

tigrap

hicBoun

dar

ies

Sequence

Boun

dar

ies

11

Volmering

RichardHewettetUx

ShaddUnit1-20

Fro

stic1-30

Compensa

tion

Densi

ty

Gamma-

Ray

Gamma-

Ray

Compensa

tion

Densi

ty

2425

2400

Figure10North-southwell-logcrosssectionthroughthe

southeasternportionofthestudyin

tervalintheMichiganbasin(seeFig

ure2forloca-

tion).Notetheabrupt

andsequentialtruncationoftheup

perthreesequencestothesouth.Th

istruncationreflectsupwarping,probablydueto

faulting,ofthebasinm

arginthatwascontemporaneouswithdepositioninthecentralportionofthebasin.T

hedatumisthesamea

sinFigure9.


15/22

Figure 11North-south well-log cross section through the southwestern portion of the St. Peter Sandstone in the Michiganbasin (see Figure 2 for location). Note the marked thinning or truncation of the sequences within the Butler Highland well.The sequences within the lower St. Peter Sandstone are composed largely of carbonate sediments. Sequence 10 illustrateshow abruptly the transition from terrigenous to carbonate sedimentation can occur. The datum is the same as for Figure 9.

2375

2400

2425

2450

2525

2075

2100

Lithostratigraphic Boundaries

Sequence Boundaries

2450

2275

2250

2300

2350

2325

2400

2375

2425

WolverineWise et al.

Gamma-Ray

NPHI

Compensation

PEF

Density

2050

2125

2025

2000

ButlerHighland

GlenwoodFm.

15 kmNorth South18 km

2600

2575

2550

2500

2475

Patrick & StateNorwich

Black RiverFm.

St.P

eterSandstone

upper

Prairie du ChienGroup

5

12

6

7

8

10

11

14

15

20

19

18

17

16

4

13

9

lower

0.0 150.0

1 50 .0 30 0. 0

GR(GAPI)

2.0 3.0

45.0 -15.0NPHI

0.0 10.0PEF

- 0.05 0 0 .4 50DRHO (G/C3)

RHOB (G/C3)

0.0

150.0

GR(GAPI)

150.0

300.0

2.0 3.0

45.0 -15.0NPHI

0.0 10.0PEF

- 0.05 0 0 .4 50

DRHO (G/C3)

RHOB (G/C3)

0.0 150.0

15 0. 0 3 00. 0

GR(GAPI)

2.0 3.0

30.0 -10.0NPHI

0.0 10.0PEF

- 0.05 0 0 .4 50DRHO (G/C3)

RHOB (G/C3)

Gamma-Ray

NPHI

Compensation

PEF

Density

Gamma-Ray

NPHI

Compensation

PEF

Density


16/22

of the carbonates of the Black River formation. Thepreservation of sequences in the central basin, butnot the distal (southeastern) margin, eliminatesbase-level fall as a possible cause. The result is theformation of another series of untapped potentialstratigraphic traps on the basin margins.

The clastic/carbonate maps illustrate the dynam-ic nature of the basin during deposition of thesequences. The western source for the St. Petersand component, the Wisconsin arch, should haveproduced a monotonous blanket of siliciclastics tothe west (Figure 6). Instead, substantial variationoccurred in the accumulation and preservation ofsandstone in the basal St. Peter Sandstone (Figure14). The causes for these departures from themodel include (1) sediment partitioning related tothe filling of an incised drainage system and (2)local concentration of sandstones over anticlineswi thi n the bas in (Catacosi nos et al. , 1991) in


2

6

3

7

8

4

C

D

Prairie du Chien GroupSauk

Tippecanoe

230 km

West East

C D

Sequence 5

43

2

1

B

A

1

2

5

4

5

2

18

1816

15

14

1516

E

F

A

B

Black River Fm.

Sequence 19

FrosticShadd WoodruffVolmering

North South

18

17

16

Sequence 15

49 kmE F

19

20

19

17

Figure 12(A) Map view showing the distribution andextent of the basal sequences of the St. Peter Sandstone.The general trend within the basin center is one of pro-gressive onlap of the Wisconsin arch to the west. Theabrupt changes in the north and south are inferred to rep-resent nondeposition (or subsequent erosion) over activebasement structures. Numbers refer to sequences shownon Figures 911. (B) Wheeler diagram showing the east-to-west onlap of the arch by successive sequences.

Figure 13(A) Map view at the base of the Black Riverformation carbonates showing the sequences that formthe top of the St. Peter Sandstone and Glenwood Forma-tion. The absence of the upper sequences on the north-ern and southern margins of the basin are interpretedto reflect truncation due to uplift (see also Figure 12).Numbers refer to sequences shown on Figures 911. (B)Wheeler diagram summary showing the sequentialsouthward truncation of the upper sequences of theGlenwood Formation and St. Peter Sandstone.


17/22

Nadon et al. 991

50%

0%

100%

50%

75%

50%

100%

100%

7

75% 25%

75%

100%

100%

75%

75%100%

8

75%

100%

0%

100%

5

0%

0%

25%

50%

75%

3

100%

50% 100%

75%

100%

50%

50%

4

100%

50%

25%

25%

75%

100%

675%

25%0%

25%

50%

75%

100% Siliciclastics

0% Siliciclastics

Sequence Absent

St. Peter-GlenwoodInterval Absent

75%

75%

25%

50%

25%

25%

50%

25%

75%

50%

Figure 14Clastic/carbonate ratio maps for sequences 38 within the lower St. Peter Sandstone. Contours are at25% intervals from 0 to 100% siliciclastics. Within the St. Peter Sandstone the 100% siliciclastic regions are essen-tially sandstones. Shales are restricted to Glenwood Formation. The two lowest sequences are not presentedbecause of such limited areal extent. Note the onlap signified by the reduction in the areas with diagonal stripingwhere a particular sequence is absent.


18/22


100%

50%

0%

0%

50%

100%

11

25%

75%

25%

0%

100%

50%

50%

100%

14

75%

25%0%

0

50%

100%

0%50%

100%

13

25%

75%

50%

50%

50%

75%

25%

10

100%

75%

50%

0%

100%

75%

50%

9

75%

25%

100%

100% Siliciclastics

0% Siliciclastics

Sequence Absent


100%12

75%

75%

25%

0%

50%

50%100%

25%

Figure 15Clastic/carbonate ratio maps for sequences 914 in the St. Peter Sandstone. Sequence 9 marks the onsetof a significant and long-lasting northwestern source area for terrigenous material. The absence of sequences 9 and12 in some wells is interpreted to be a consequence of fault movement. Note that the consistent boundary of 100%siliciclastics in the west-central portion of the basin is orthogonal to the onlap pattern of Figure 12A.


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Nadon et al. 993

100%

50%

15

75%

25%

25%0%

100%

50%

50%75%

19

75%

50%

50%

50%

75%

20

25%

100%

50%

100%

17

75%

100%

18

75%

75%

100%

50%

16

75%

100% Siliciclastics

0% Siliciclastics

Sequence Absent


75%

75%

100%

75%

75%

Figure 16Clastic/carbonate ratio maps for sequences 1520 in the upper St. Peter Sandstone and Glenwood For-mation. Note the infill of the basin by sandstone from sequences 1517, followed by a transgression in sequences 18and 19. Truncation of the upper sequences along the southern margin provided a source of reworked St. Peter ter-rigenous material to the central basin as shown by the 100% siliciclastics contour of sequences 19 and 20.


20/22

response to a decrease in rate of formation of accom-modation space. Limestones are present in the west-ern sections throughout sequences 36 (Figure 14).If the Wisconsin arch is a source area, the sandsbrought into the basin had to bypass these areas. Anincised valley system may be the reason, but too fewwells are available in critical areas to test that hypoth-esis. The ramp geometry depicted in Figure 6 wasestablished by the time sequence 9 was deposited.

The termination of terrigenous deposition coincid-ed with the start of uplift along the northern andsouthern margins of the basin by the time sequence16 was deposited (Figure 16). The final two se-quences, which occur solely within the GlenwoodFormation, show that the former terrigenous sourcearea to the north was shut down, and local sourcesaround the rising margins of the basin provided moresiliciclastic input to the basin. The subsequentremoval of strata from the margins of the basin byerosion is a consistent pattern throughout the history

of the Michigan basin (Wang et al., 1994).Diagenetic alterations and the patterns of pressurecompartmentalization were both controlled by thedistribution and preservation of the high-frequencysequences. The diagenesis scenarios proposed byDrzewiecki et al. (1994) and Winter et al. (1995) illus-trate the control on cements by both local and re-gional facies variations evident in the sediment parti-tioning. These facies variations were a function ofboth high-frequency relative sea level changes andlong-term tectonic subsidence. The regional over-pressures within the St. PeterGlenwood interval areprobably a transient effect of glacial loading (Bahr etal., 1994). Maintenance of the pressure anomalies is

due in part to lateral seals created by both small-scalestructure and regional truncation patterns (Bahr etal., 1994).

CONCLUSIONS

The presence of carbonate rocks within the pre-dominantly clastic Middle Ordovician cratonic sec-tion allows a high-resolution sequence stratigraphicanalysis of the St. Peter Sandstone and GlenwoodFormation at a much higher chronostratigraphic reso-lution than was previously available. The mapping of20 sequences within the St. Peter Sandstone andoverlying Glenwood Formation shows lateral and ver-tical facies changes that are the result of a combina-tion of preexisting geography, syndepositional inter-action of sediment supply with tectonics, andeustatic sea level change. The distribution of sand-stone in the basal St. Peter was probably controlledlargely by deposition in a preexisting drainage systemrather than by a simple ramp geometry. The increasein thickness and completeness of sequences at thebase of the upper St. Peter Sandstone reflects an

increase in rate of formation of accommodationspace due to increased subsidence rates, especially inthe central basin. The change in sedimentary regimeduring deposition of the Glenwood Formation was aresponse to a significant deepening within the basin(or retreat of the source area from near the basin cen-ter), which ultimately led to deposition of the car-bonates of the Black River formation.

Tectonic influence was manifested on several spa-tial and temporal scales. The local abrupt variationsin sequence thickness and facies over structuralhighs within the basin and the truncation of theupper sequences along the margins of the basin mayprovide additional structural and stratigraphic traps.The basin margin was probably a significant localsediment source of the Glenwood Formation. On alarger scale, eustatic control on the rate of formationof accommodation space can be inferred for thebasal onlap pattern, which corresponds to the overallrise in sea level seen in the Middle Ordovician (Sloss,

1963).The result of the interaction of the tectonic andeustatic rates within the Michigan basin is theproduction of low-permeability carbonates that actas vertical seals for pressure compartments. Trun-cation of sequences over anticlines or adjacent tobasin margins provide lateral seals.

REFERENCES CITED

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Bahr, J. M., G. R. Moline, and G. C. Nadon, 1994, Anomalouspressures in the deep Michigan basin, in P. Ortoleva, ed., Basin

compartments and seals: AAPG Memoir 61, p. 153165.Barnes, D. A., C. E. Lundgren, and M. W. Longman, 1992,

Sedimentology and diagenesis of the St. Peter Sandstone, centralMichigan basin: AAPG Bulletin, v. 76, p. 15071532.

Barnes, D. A., W. B. Harrison III, and T. H. Shaw, 1996,LowerMiddle Ordovician lithofacies and interregionalcorrelation, Michigan basin, U. S. A., in B. J. Witzke, G. A.Ludvigson, and J. Day, eds., Paleozoic sequence stratigraphy:Geological Society of America Special Paper 306, p. 3554.

Bricker, D. M., R. L. Milstein, C. R. Reszka, Jr., 1983, Selected studiesof CambroOrdovician sediments within the Michigan basin:Michigan Geological Division Report of Investigation no. 26, 54 p.

Catacosinos, P. A., 1973, Cambrian lithostratigraphy of the Michiganbasin: AAPG Bulletin, v. 57, p. 24042418.

Catacosinos, P. A., and P. A. Daniels, Jr., 1991, Stratigraphy ofmiddle Proterozoic to Middle Ordovician formations of the

Michigan basin: Geological Society of America Special Paper 256,p. 5372.Catacosinos, P. A., W. B. Harrison III, and P. A. Daniels, Jr., 1991,

Structure, stratigraphy, and petroleum geology of the Michiganbasin, in, M. W. Leighton, D. R. Kolata, D. F. Oltz, and J. J. Eidel,eds., Interior cratonic basins: AAPG Memoir 51, p. 561601.

Cercone, K. R., and H. N. Pollack, 1991, Thermal maturity of theMichigan basin: Geological Society of America Special Paper 256,p. 112.

Coakley, B. J., G. C. Nadon, and H. F. Wang, 1994, Spatial variationsin tectonic subsidence during Tippecanoe I in the Michiganbasin: Basin Research, v. 7, p. 131140.

Dapples, E. C., 1955, General lithofacies relationships of St. Peter



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Droste, J. B., T. F. Abdulkareem, and J. B. Patton, 1982, Stratigraphyof the Ancell and Black River groups (Ordovician) in Indiana:Indiana Geological Survey Occasional Paper no. 36, 15 p.

Drzewiecki, P. A., A. Simo, P. Brown, E. Castrogiovanni, G. C.Nadon, L. D. Shepherd, J. W. Valley, M. R. Vandrey, B. L. Winter,and D. Barnes, 1994, Diagenesis, diagenetic banding, and

porosity evolution of the Middle Ordovician St. Peter Sandstoneand the Glenwood Formation in the Michigan basin, in ,P. Ortoleva, ed., Basin compartments and seals: AAPG Memoir61, p. 179199.

Fisher, J. H., and M. W. Barratt, 1985, Exploration in Ordovician ofcentral Michigan basin: AAPG Bulletin, v. 69, p. 20652076.

Harrison, W. B., III, 1987, Michigan deep St. Peter gas playcontinues to expand: World Oil, v. 204, no. 4, p. 5661.

Howell, P. D., and B. A. van der Pluijm, 1999, Structural sequencesand styles of subsidence in the Michigan basin: GeologicalSociety of America Bulletin, v. 111, p. 974991.

MacEachern, J. A., I. Raychaudhur, and S. G. Pemberton, 1992,Stratigraphic application of the Glossifungites ichnofacies:delineating discontinuities in the rock record, in S. G.Pemberton, ed., Applications of ichnology to petroleumexploration: SEPM Core Workshop 17, p. 169198.

Mai, H., and R. H. Dott, Jr., 1985, A subsurface study of the St. Peter

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Mitchum, R. M., J. B. Sangree, P. R. Vail, W. W. Wornardy, 1993,Recognizing sequences and systems tracts from well logs,seismic data, and biostratigraphy: examples from the lateCenozoic of the Gulf of Mexico, in P. Weimer and H.Posamentier, eds., Siliciclastic sequence stratigraphy: AAPGMemoir 58, p. 163197.

Moline, G. R., J. M. Bahr, and P. A. Drzewiecki, 1994, Permeabilityand porosity estimation by electrofacies determination, in P. J.Ortoleva, ed., Basin compartments and seals: AAPG Memoir 61,p. 201209.

Nadon, G. C., and G. L. Smith, 1992, Extending unconformities intobasin centers; an example from the Early to Middle Ordovician ofthe central Michigan basin, in M. Candellaria and C. Reed, eds.,Paleokarst, karst-related diagenesis, and reservoir diagenesis:examples from OrdovicianDevonian age strata from west Texasand the mid-continent: Permian Basin Section, SEPM Publication92-33, p. 153164.

Nadon, G. C., A. Simo, C. W. Byers, and R. H. Dott, Jr., 1991,

Controls on deposition of the St. Peter Sandstone (midLateOrdovician), Michigan basin: AAPG Bulletin, v. 75,p. 13881389.

Posamentier, H. W., and G. P. Allen, 1993a, Siliciclastic sequencestratigraphic patterns in foreland ramp-type basins: Geology,v. 21, p. 455458.

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Serra, O., 1986, Fundamentals of well-log interpretation 2; theinterpretation of logging data: Developments in PetroleumScience, v. 15B: Amsterdam, Elsevier, 684 p.

Sloss, L. L., 1963, Sequences in the cratonic interior of NorthAmerica: Geological Society of Amer ica Bullet in , v. 74,p. 93113.

Sloss, L. L., 1982, The midcontinent province, United States, inA. R.Palmer, ed., Perspectives in regional geological synthesis:Geological Society of America, Decade of North AmericanGeology, Special Publication 1, p. 2739.

Vandrey, M. R., 1991, Stratigraphy, diagenesis, and geochemistry ofthe Middle Ordovician Glenwood Formation: M.S. thesis,

University of Wisconsin-Madison, 239 p.Van Wagoner, J. C., H. W. Posamentier, R. M. Mitchum, P. R. Vail,

J. F. Sarg, T. S. Loutit, and J. Hardenbol, 1988, An overview of thefundamentals of sequence stratigraphy and key definitions, inC. K. Wilgus, B. S. Hastings, C. G. St. C. Kendall, H. W. Posa-mentier, C. A. Ross, and J. C. Van Wagoner, eds., Sea levelchanges: an integrated approach: SEPM Special Publication 42,p. 3945.

Wang, H. F., K. D. Crowley, and G. C. Nadon, 1994, Thermal historyof the Michigan basin from fission track ages and vitrinitereflectances, in P. Ortoleva, ed., Basin compartments and seals:AAPG Memoir 61, p. 167177.

Willman, H. B., E. Atherton, T. C. Buschbach, C. Collinson, J. C.Frye, M. E. Hopkins, J. A. Lineback, and J. A. Simon, 1975,Handbook of Illinois stratigraphy: Illinois State Geological SurveyBulletin, v. 95, 261 p.

Winter, B. L., J. W. Valley, J. A. Simo, G. C. Nadon, and C. M.Johnson, 1995, Hydraulic seals and their origin: evidence fromthe stable isotope geochemistry of dolomites in the MiddleOrdovician St. Peter Sandstone, Michigan basin: AAPG Bulletin,v. 79, p. 3048.

Nadon et al. 995


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Greg Nadon

Greg Nadon received his Ph.D. from the University ofToronto in 1991. He is currently an assistant professor at

Ohio University. His research interests are primarily in theanalysis of mud-rich fluvial deposits and the application ofsequence stratigraphic concepts to the Pennsylvanian ofthe Appalachian basin.

C. W. Byers

Charles Byers received his B.S. degree from MariettaCollege in 1968 and his Ph.D. from Yale University in1973. Since that time he has served on the faculty of theDepartment of Geology and Geophysics at the Universityof Wisconsin. He was department chair from 1987 to1990. His research interests include sedimentology andpaleoecology of shales, cratonic sequence stratigraphy,trace fossils, and the history of geology.

J. A. (Toni) Simo

Toni Simo is a full professor at the Department ofGeology and Geophysics, University of Wisconsin. He

received both an M.S. degree and a Ph.D. in geology fromthe University of Barcelona, Spain. Before joining theUniversity of WisconsinMadison, he was a consultinggeologist in Spain and a Fulbright Scholar. His researchfocuses on interpretation of stratigraphic sequences, dia-genesis, and fluid flow in sedimentary basins.

R. H. Dott, Jr.

Robert H. Dott, Jr., is Professor Emeritus at theUniversity of Wisconsin. His principal specialty is sedi-mentology, and he has studied the lower Paleozoic andProterozoic clastic rocks of the upper Mississippi Valleyregion for 40 years. He has long been active in AAPGand SEPM. Dott was president of SEPM in 19811982

and received its Twenhofel Medal in 1993.


ABOUT THE AUTHORS

Documents

Carbonate SeqStrat