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Home , Minnekahta Formation, Permian, Watrous Formation, Williston Basin

PERMIAN TO REDBEDS OF THE

C. G. Carlson

North Dakota Industrial Commission Oil and Gas Division

MISCELLANEOUS SERIES 78 GEOLOGICAL SURVEY John P. Bluem1e, State Geologist 1993 INDUSTRIAL COMMISSION OF NORTH DAKOTA

Eclward T. SclWer Heidi Heitkamp Sarah Vogel GOVERNOR ATTORNEY GENERAL COMMISSIONER OF AGRICULTURE

NORTH DAKOTA GEOLOGICAL SURVEY

John P. Bluemle, State Geologist William A. McClellan, Asst. State Geologist

SURVEY STAFF

Richard A. Baker, Drafting Tedmicilm Robert F. Biek, Geologist Randolph B. Burke, CArbonate Geologist Paul E. Diehl, Geologist LaRae L Fey, Infrn'm4tion Processor Operator Phillip L Greer, Geologist Thomas J. Heck,. Geologist Tracy A. Henman. Infot7/Ul.tion Proassor Operator Darby A. Henke, Infot7lUl.tUm Processor Operator John W. Hoganson, Paleontologist Kent E. Hollands, Core Library Tedmtdan Karen M. Gutenkunst, Business MlUUlger Julie A. LeFever, Geologist/Core Library Director Jim S. Lindholm, Data Processing Coordinator Mark R. Luther, Geologist/GIS Manager Eula M. Mailloux, Clerk Annette M. MAter!, Receptionist Sharon M. Murfield-Tyler, GIS Analyst Edward C. Murphy, Environmental Geologist Russell D. Prange, Lab Tedrnicilltl Evie A. Roberson, Administrative Offiar Dean J. Tyler, GIS AtlIllyst

NORTH DAKOTA GEOLOGICAL SURVEY 1993 600 EAST BOULEVARD, BISMARCK ND 58505~ Mountain Association of Geologists, tion of Geologists, Denver, Colorado, p. Denver, Colorado, p. 166-176. 177-189.

Nordquist, J. W., 1955, Pre-Rierdon Jurassic Seager, O. A., el al" 1941: American Association in Northern and Geologists BuUetin, v. 26, p. Williston Basin: Billings Geological 1415, 1421. Society, Sixth Annual Field Conference Guidebook, p. 96-106. Slott, D. F., 1955, Jurassic Stratigraphy of Manitoba: Manitoba Mines Branch Publi­ Peterson, J. A., 1957, Marine Jurassic of Northern cation 54-2, 78 p. and Williston Basin: American Association ofPetroleum Geolo­ Vail, P. R., Mitchum, R. M., and Thompson, S. gists BuUelin, v. 41, p. 399-440. lII, 1987, seismic Stratigraphy and Global Changes ofSea Level, Part 4; Global Cycles Peterson, J.A., 1972, Jurassic : in Geologic of Relative Change of Sea Level: American Atlas of the Rocky MounlJlin Region; Association Petroleum Geologists Treatiseof edited by Mallory, W. W.; Rocky Moun­ Petroleum Reprint Series No. I, p. tain Association of Geologists, Denver, 313-327. Colorado, p. 177-189. Zieglar, D. L., 1956, Pre-Piper post-Minnekahta Rascoe, Bailey, Jr., and Baars, D. L., 1972, Redbeds in the Williston Basin: in First System: in Geologic Atlas of the Williston Basin Symposium, North Dakota Rocky Mountain Region; edited by and Geological Societies, p. Mallory, W. W., Rocky Mountain Associa­ 170-178.

21 CONTENTS

ILLUSTRATIONS ...... iv

ABSTRACT 1

INTRODUCTION ...... 1

PREVIOUS WORK ...... 1 1 Manitoba...... 1 Saskatchewan 2 North Dakota 2

NEW INTERPRETATIONS...... 3

STRATIGRAPHIC REVIEW...... 5 Permian...... 5 Permo- 5 Jurassic ...... 5 13

CONCLUSIONS ...... 18

REFERENCES ...... 20

III ILLUSTRATIONS

Figure Page 1. Typical log characteristics and stratigraphic nomenclature of redbed strata as defined by Zieg1ar (1956) and Dow, 1967 ...... 3 2. Typical log characteristics and revised stratigraphic nomenclature for Jurassic to Permian redbed strata 4 3. Isopach map of the Opeche Salt 6 4. Isopach map of the Opeche Formation 7 5. Isopach map of 8 6. Isopach map of Belfield Member of the ...... 9 7. Isopach map of "G" Salt " 10 8. Isopach map of "P" Salt ...... 11 9. Isopach map of Member of the Spearfish Formation ...... 12 10. Isopach map of Reirdon Formation and Bowes through Kline Members of the Piper Formation 14 11. Log of Phillips Petroleum Corp. - O. Saude No. 1 well (NW SE 19-158-74) with revised definition of Saude Member of Piper Formation ...... 15 12. Log of Amerada Petroleum Corp. - Pederson, Cater No.1 well (NE SW 21-158-95) showing revised definition of Saude Member of Piper Formation 15 13. Isopach map of Saude Member, Piper Formation " 16 14. Isopach map of Dunham Salt, Piper Formation 17 15. Log characteristics of Jurassic and strata in the Herman Hanson - Welder No. I well (NE NW 20-133-72) in Logan County...... 18

Plate (2 total in separate packet) 1. Cross Section A-A'; a north-south section from Williams to Slope Counties ...... envelope Cross Section B-B'; a northwest-southeast section from McKenzie to Grant Counties Cross Section C-C'; east-west section from Williams to Renville Counties 2. Cross Section D-D'; east-west section from Renville to Bottineau Counties ...... envelope Cross Section E-E'; northwest-southeast section from Ward to Wells County

iv ABSTRACT or Lower Watrous in Saskatchewan are physically equivalent to strata referred to as Saude or Spearfisb Redbeds of Permian to Jurassic age are in North Dakota. No paleontological evidence has present in outcrops in the Black Hills of South been found to reconcile tbe differing age interpreta­ Dakota. Redbeds. which have been referred to as tions, so conclusive resolution ofthis question is not Jurassic in age, are present in outcrops in southern yet possible. However, a careful examination of Manitoba. In the subsuiface. equivalent strata are physical evidence provided by Dual Laterologs referred to as the Spearfish Formation of Triassic suggests a most likely solution. or Permo-Triassic age in Nonh Dakota and the lower Watrous or Amaranth Formations ofJura­ Nearly all exploration wells penetrate the Triassic or Jurassic age in Saskatchewan and complete section so wells with Dual Manitoba. Paleontological data are lackingfor age Laterologs were randomly selected at one or two resolution. A careful examination of physical per township in areas of active exploration. All evidence from the subsuiface indicates that previous­ available logs were used in less active areas. This ly unrecognized regional unconfonnities occur density is sufficient to provide a regional pattern for within the clastic redbeds. Areal distribution most of the strata. The halites have erratic patterns patterns ofthese lithogenetic unitsfavorthe Jurassic in some areas due to solution so details of presence age assignmentfor a pan ofthe Lower Watrous and or absence of halite cannot be shown in all areas on Amaranth Formations. tbese maps.

The Spearfish Formation, as originally de­ fined. includes redbeds, which have been correlated PREVIOUS WORK with stratafrom Permian to Jurassic age in eastern "yoming. although these beds were originally South Dakota generally assigned a Triassic age. The Spearfish Formation will retain its greatest utility in the The term Spearfish Formation was introduced subsuiface ifit is restricted to strata of Permian to by Darton (1899. p. 387) to refer to redbeds present Triassic age. Redtifinition ofthe Belfield and Pine between lbe Minnekahta (Permian) and units would avoid the introduction of new names the (Jurassic) in the northern and, by applying them to the two lithogenetic units Black Hills, South Dakota. The name is derived within the Spearfish. would more accurately portray from tbe town of Spearfisb, but no type section was the depositional history ofthese strata. Similarly designated. Lacking paleontological evidence a a redefinition ofthe Saude. closely resembling the Triassic (?) age assignment was given on the basis original definition. would preserve the utility ofthat of stratigraphic position. A portion of the strata term. referred to as Spearfisb in the outcrops of the Black Hills has been correlated with Gypsum Spring (Jurassic) strata ofWyoming (Imlay, 1947, p. 237). INTRODUCTION The Minnekahta Limestone and overlying redbeds of tbe Spearfisb Formation of South Dakota have Since the eatliest days ofexploration in the been shown as correlative with the Goose Egg Williston Basin the age and correlation of redbeds Formation of Permo-Triassic age of Wyoming has been controversial. Zieglar (1956. p. 170) (Rascoe, 1972, p. 160). noted at the First Williston Basin Symposium that "on the basis of stratigrapbic position and gross Manitoba lithology the pte-Piper, post-Minnekahta redbeds in the subsurface ofthe Williston Basin are considered Seager and others (1942, p. 1415) introduced by many American geologists to be correlative with tbe term Amaranth Formation for redbeds and the Spearfisb Formation ofPermo-Triassic age. On which he referred to as . Stott the other hand, Canadian workers believe that the (1955, p. 7) defined the term Amaranth Formation pre-Piper redbeds in Manitoba and Saskatcbewan as redbeds, evaporites, and carbonates of Jurassic are lower middle or lower Jurassic in age." The or older age overlying strata in Manitoba. strata referred to as Lower Amaranth in Manitoba Stott divided tbe Amaranth into an upper carbonate

I and member of Jurassic age and a lower, North Dakota unfossiliferous redbed member, which was also assigned a Jurassic age. The Lower Amaranth was Laird (1951) referred to the redbeds and further subdivided (Barchyn, 1982, p. 5) into an evaporites overlying the Permian Minnekahta upper shaIy unit and a lower sandy unit. He agreed Limestone as the Spearfish Formation of Triassic with the Jurassic age assignment ofthe entire Ama­ age. Zieglar (1956, p. 177) proposed a revision, ranth based on a conformable relationsbip of the restricting Spearfish to a portion of those strata and Upper and Lower Members of the Amaranth introducedthe terms PineSalt, SaudeFormationand Formation. Barcbyn (1982, p. 107) suggested Dunham Salt (fig. 1) for the rest ofthese strata. He variable depositional conditions for the lower sandy recognized a pre-Jurassic regional , sequence whereas the consistency oflog characteris­ which he considered as coincident with the base of tics of the upper shaly sequence was regarded as the Pine Salt. evidence for more stable conditions in a marine­ associated environment. Husain (1991, p. 152) Dow (1967, p. 14) introduced the currently referred to the Lower Amaranth as Jura-Triassic accepted nomenclature for these redbeds and while noting a lack of paleontological evidence for evaporites in North Dakota (fig. 1). He recognized an age assignment. the Dunham Salt as a facies of the Poe evaporite member of the Piper Formation so he transferred Saskatchewan the Dunham Salt to the Jurassic Piper Formation. He redefined the Saude to include the "G marker Milner and Thomas (1954, p. 255) bed" and the clastics between the "G marker bed" introduced the term to refer to and the main halite bed, which he then referred to Jurassic redbeds together with carbonates and as the Pine Salt. He introduced the term Belfield evaporites overlying Paleozoic strata in Saskatche­ Member for the clastics between the Minnekahta wan (= Amaranth of Manitoba). Francis (1957, p. Limestone and Pine Salt. He used the terms 376) referred to the lower portion of Watrous strata Belfield, Pine, and Saude as members of the as the Jura-Triassic redbeds while noting that the Spearfish Formation. He assigned a Permo-Jurassic contact with the overlying non-clastics member of age to these strata as he did not recognize any the Watrous was gradational. Carlson (1968, p. unconformity within the redbeds and evaporites. He 1978) referred to the Lower Watrous as "equivalent used Saude and Spearfish synonomously in the area to the Triassic Spearfish southward where the north and east of the limit of Pine Salt. Jurassic-Triassic boundary is undisputed. Because it has been established that the Spearfish is of Late Rascoe (1972, p. 148) accepted a Permian and age ..." (Presumably disconformity at the base of the Pine Salt, but referring to the South Dakota-Wyoming correla­ considered it to be an intra-Guadalupe discon­ tions). Christopher (1982, p. 85-87) reviewed the formity. He placed the pre-Jurassic unconformity age questions and equated the Lower Watrous of at the base of the Poe or Dunham evaporites. Saskatchewan to the Upper Spearfish floored by the Pine SaIt in North Dakota (Saude ofcurrent usage). The Williston Basin nomenclature cbart He noted that this interpretation suggests an early (Bluemle, et aI., 1981) places the Triassic-Permian Triassic age for the lower Watrous and implies an boundary at the top of the Pine Salt with a conform­ unconformity and a hiatus spanning able relationship between the Spearfish and and between the Lower and Upper Minnekahta Formations. The North Dakota Watrous. However, on his stratigraphic cross Stratigraphic Column (Bluemle, et aI., 1986) has the section (1982, fig. 5, p. 87) Christopher places an Saude, Pine, and Belfield as members of the unconformity at the base of the Watrous, but does Spearfish Formation, and assigns a Permo-Triassic not separate the Lower and Upper Watrous with an age to these strata. They recognize a pre-Jurassic unconformity. Kreis (1991, p. 167) considered the unconformity, which they place at the base of the Lower Watrous as largely Early Triassic based on Dunham or Poe Members of the Jurassic Piper stratigraphic considerations "with an undefined Formation. portion of the uppermost part possibly being Early to ."

2 DOW. 1967 COMPOSITE LOG ZIEGLER. 1956 1078 AMERADlPSlXlIIA Ne),! 2·...... co. G.R. L.L. ,...... \ SALT i \ i

z g !c z " PINE SAlT ~ ~ " ...... p,,,, ii SALT --­ ~ " L IIELRELll...... m

Figure 1. Typical log characteristics and stratigraphic nomenclature of redbed strata.

NEW INTERPRETATIONS conformities present within the strata currently re­ ferred to as the Spearfish Formation in North Three episodes of halite deposition have Dakota. The unconformities, rather than being at occurred in the Williston Basin from the Permian the base of the halites, are within the clastics through Jurassic time span. The halites and the currently referred to as the Belfield and Saude Minnekahta Limestone are distinctive lithologies that Members of the Spearfish Formation. Recognition have been used to divide these strata into strati­ ofthese unconformities shows that the Dunham and graphic units. These recognized subdivisions have "P" (Pine) salts, like the Opeche Salt, are part of provided useful mapping units where the halites are depositional episodes which begin and end with present. However, these units are not lithogenetic clastics. The areal extent of the "G Salt" and the units, their use tends to mask the geologic history, presence of clastics between the "G Salt" and the and the clastics ofthe Belfield and Saude units have underlying halite clearly indicate that they are part been combined as Saude in areas to the north and of the same depositional episode. Referring to the east of the limit of the halite. main halite bed as the "P Salt" eliminates duplica­ tion of the term Pine. Careful examination of Dual Laterologs indicates that previous interpretations have either I would propose that the terms Saude, Pine, misplaced (Zieglar, 1956; Rascoe, 1972; Bluemle, and Belfield should be redefined to reflect litho­ etal., 1981,1986), or ignored (Dow, 1967), un- genetic units. The Saude and Belfield should be

3 NDF 12178 -Sec.18,Twp.139 N.,Rg.IOOW. GR. LAT.

RIERDON ll!IOO

J

u It: I R CI) .... CI) Q. POE

7000

p

Z

~ a::: MINNE lJJ a. -¥~----) - -\ .-:""'=--''='~~. OPEC HE

BROOM

Figure 2. Typical log characteristics and revised stratigraphic nomenclature for Jurassic to Permian redbed strata. restricted to portions of the strata currently referred of the Spearfish Formation of Permo-Triassic age. to these units with the remaining portions added to I would transfer the Saude as a member to the Piper the Pine. I would use Belfield and Pine as members Formation of Jurassic age (fig. 2).

4 STRATIGRAPIDC REVIEW The "G Salt" (fig. 7) appears to have depositional thicknesses preserved. The "P Salt" Permian (fig. 8) also has depositional thicknesses preserved in most areas. The eastern margin of the "P Salt" Deposition of the Opeche Formation began is likely a solution margin and there are some areas, with red clastics followed by halite in the central particularly along the Nesson , where basin area and then red clastics before deposition of solution may have altered thicknesses. The the Minnekabta Limestone. Current extent of the preservation of depositional thicknesses of these halite (fig. 3) indicates depositional thicknesses have halites in most areas indicates that clastic deposition been preserved except for the southeast margin must have succeeded evaporite deposition before any through Stark and Dunn Counties where rapid eFosional episode. thinning from 100 feet to absent indicates a solutional margin. Depositional thicknesses of the The red clastics between the Belfield Member Opeche Formation are preserved where the and the "P Salt" are approximately the same Minnekabta Formation is present (fig. 4). Similar­ thickness as the Pine clastics to the east of the limit Iy, depositional thicknesses of the Minnekabta of the "P Salt" in southwestern North Dakota. If Formation have been preserved where the Belfield we accept the Permian age ascribed to the Pine Salt Member of the Spearfish Formation is present (fig. (Rascoe, 1972), then these clastics must also be of 5). Permian age.

Two distinct laterolog characteristics (see The area of greatest thickness of the Pine cross sections A-A' and B-B', plates I and 2) are Member (fig. 9) is in the area where the "G Salt" present within the clastics between the Minnekabta is present and in the area of maximum thickness of Limestone and the halite referred to as the Pine Salt. the "P Salt." In those areas, clastics are relatively I believe this marks an unconformity and I believe thin in the upper portion of the Pine Member. that the term Belfield will retain its utility if it is Proceeding northward, as the "P Salt" thins, the redefined as the clastics between the Minnekabta clastics below the "P Salt" thin while the clastics Limestone and the unconformity. It is recognized overlying the "P Salt" thicken (plate I). Assuming by higher resistivity readings on the laterolog. The a facies relationship between the evaporites and the overall distribution of tbe redefined Belfield Mem­ clastics, this would imply a Permian age for most ber with it' zero edge closely parallel to the 35-foot of the Pine clastics where halite is absent. contour of the Minnekabta Limestone and the rapid thinning from 50 feet to a zero edge to the north The "G Salt" has been correlated with the and east indicate erosional limits for the Belfield Little Medicine Tongue ofthe Goose Egg Formation Member in those areas (fig. 6). of Wyoming which is considered to be Triassic in age. This correlation would imply a Triassic age The Opeche and Minnekabta have always for the overlying clastics and a Permo-Triassic age been assigned a Permian age. The Pine Salt bas assignment for the redefined Pine Member (fig. 2). been correlated as Permian (Rascoe, 1972, Bluemle, et aI., 1981) which then requires that the Belfield Jurassic Member, as redefined, be assigned a Permian age. The Rierdon and Piper Formations are ofun­ Permo-Triassic questioned Jurassic age and have depositional thick­ nesses preserved in most areas of western North The term Pine would have its greatest utility Dakota. The Piper Formation, as currently if it were redefined similar to its original definition recognized in North Dakota, is equivalent to the to include halites and associated clastics. Deposition Nesson Formation as defined by Nordquist (1955) would then begin with the clastics between the plus the Dunham Salt. Nordquist (1955) defined six Belfield Member and the "P Salt" continuing members and these members are recognizable in the through the "G Salt" and concluding with clastics central basin area, but facies changes make it above the "G Salt" (see cross sections A-A' and B­ difficult to trace the units south and eastward. B', plate 1). Current Montana usage is to restrict the term

5 ",:row' 11:.I0'lt __ -- lII:..~W. .- --...." - - --­ I : ! !

0 ! ! I - I 1 I I!'U - I - -- .-~. i i T- 0 - - i • 0 ; I • • - --1-­ .-! • wr' I • • • : o • • I • J.-! .:r. • •• • • IT '\. • : I'\. • • : b' • : l • '7 .\ • 1"1 •• I l :'1---J-...... II-..:-•..jL..-l-'~- ....,..j..-+_.!..l-.r+~--l--Jo..- ~'t":":,+=-:+L_-l---- ~--+-- I-1- -+--1---1-t-· ... ~r ~ •••••• • l'-..... :.-:-": I Mo:I£A' rl-.-.1"~'-I.--.L.,:·J-,;'~~Ei·~tLr_·[, ...L:;' i. l . _L r. • 1./" :CUI" , • ~ r • • I ./ :. • • • • • rio. .: :.~ .: • ,

! I.:" I~ );~~ l' IV • /~ i : i. ~ C:::;'flj .' Ie ••;~ 1--1--1--. MON.I·~It)d :_ • ~Ie. • -1/ -. sr+nK:­ l/' :--:----;.... ")\7. • • • 1

!o c: - .... ""I • • • .: r I : • I L._.L.-.!_-.J _­ ._ 0 0 ! .~1 __ . .I!j'_--l---+-+-+-+-i r I

Contour Interval 100 feet

Figure 3. Isopach map of the Opeche Salt.

6 1l.111""'• ...o~ 11.100\11; R.llO\!('

, U),JL,1,J,-J=?-r-Y-r-Y-n-lTt J .," • •

• • • • • • • • • • • • • • • 1-4fN. • • • • • •

1'1.100. R.NW.

Contour Interval 100 feet

Limit of Minnekahta ---­

Figure 4. Isopach map of the Opeche Formation.

7 1I.:,f1":W. _ __ .....0'«:-_ __ __"IO:)V( I : ! ! ! -, I ,

o 0 o 0 . : '. j~ft. , 0 • Itc • .: • • ":: 14tL~ 10 • !,:O:LIo./,..L,. -; , • 0 '"i. J ° : • • • / i .1" ~ ° . • • •. I o i· 0 • o 0 0 • • ••

",-,,1/ ,>ON. o • • 0 • • 1- • ••• ' • II ''-_I_~ L..._L... __ ,,= __1- L _,-_ J:b. -­ ...ow• ..lOIIoW ..IOOW. IUIOW,

Contour Interval 10 leet

Limit of Beilield---­

Figure s. Isopach map of the Minnekahta Fonnation.

8 IUISVl. ...ow. --,­ ruoow. __ -­ ~81W. -­ ! ! : i ! . i """II F -j \ i I • • -­ - I wrc> --I-­ I i i I i 1 i L-­ • i i I> IL ) i ) ! i L ; ...... ;.:...:-. ! --I-­ • . - - 1-1- ­ • • • 'fU"t" i • • ;r.... I· • _L ." . •• • • if l -lao. j•••• ~ I

I'--, . r·-" I -1-.

1 .\ I •• i·...... '" • \. olMl i r i - • • I· • i :" ..... ~ • i ~-1-J-..--l-. -t-.I{~. L,-.;;~ ;~'" l-, -+--4--..,]-,-:-. -t-'T.-t,/71'--l(ojir-• -M- fri . .. ~~ i ~., . .L -. 1"1 ~ IG """i • • j • ! i ,....Jj...... ~ :--'?.. /.y i ! t'.... ~ : i· • i

• • i. • ISON..j" •••• 1 I •• • 1.0.. I • I"" .-L ~ L-_Jtt.Iiii.,,- .1.-_1_ --:UOOw.-- .... ,

Contour Interval 25 feet

Figure 6. Isopach map of Belfield Member of the Spearfish Formation.

9 ,-1Il.1'1lW. ~"'. _tt.!.~ .. o."", ":,.eJw. -- ;:::::: ------­ i ! . •I • : ! • . : ..b.ou.l, • ! • I I NO l>~i I I I . - I 1- --1-­ , T .1... • i i l - - -- - i I ! I i i ­ .~ - . I l I ; i 1 I ! i, ....,~ I i i , - ,. i ; -- ! I , j ! T ~. . : : - --I-. - - ­ i ... .. "-- :...... i i ._L ! I l> ~ .1 ; i't.- .1.--1'--. ! .. IICI r i ... ~ ; ! 1'1 .. - "'" r-'~ , ~i I i I . f.-. j i i l ; •: IT i i i • \. M3 ~ L-_I-_ ~ -~ ,.t­ I i "" "" i . ·i - r i -0'.. • - - 1~A1 - NO.. ' • • •...e-;. • I 10-" .... • .L-"' •. :··I\· : ~ • .- 'c..:-.I _ i .- ,- f-. •• i i ,~ ~ , GR~ :;; '.' . -"..1'" oT ~ · ~ .... ! i • i •156M. , -\O';;....V • : 5 • : ! : • • 1 , • _~ o.:'LoP 'I _.1. , ..... • I-" ! IAo,y. ! .- I .", 0 .- ---1 " 0 I r7 ,>0"Lj 10 • •• • i L-- l.---' • ~~ I ••• ~L-_ ~.. t1-! I-J _!_L~J_ •__ ,= -_..I- ._1..J_ --'-- U--,­ R.,", •• .. . k.lOOW 'l,IooW. -

Contour Interval 25 feet

Figure 7. Isopach map of "G" Salt.

10 ...... --~.

I

....' Ianile: ; I l I . _ l r-j5::;;;I-j-:±-I-~--~~·f·~-·~-~I~~~~~t!=t3jt-~I±-j~llUio<~E;t~·~;ttttt·!'f±3je~!!J3j t ~ ·.~t ~ -- - i . i i . v.. .•: V - •• ri .;.1 -,-I--+w-+r-> 1---\I-+--+-+-+-jHj ~ •• I...... •• .--t • ,I- . • • I" ~ :;:., • • • i -•• i 10 ~o\,::=:: _ •• •• " l¥"i ,1.. • • i ...... •• • 'j I' • • I .• ~:Y l-".. • • VO-.-+'-J...i • • " t . . . r ~ a. •: : : • : r •[) Il.: ~. !

L • Ibo • • 1~~ ••• .-.i L

L.. ~. _. •S~Ol'I. 11:, ~V" I'A "1 I

I •• '//f / -r I ._ . _ _ !--I---+-+-----1-----1---j1----l I .:. Yo ~9'f .."u.s ,....:. • ~ '/ I ,.,. i ,. i.-- I,..J /"

~ • ::::,;-jlL-.l~1l::uoo.,d__ L_~. '.:;0.. --'- --4....~ ._ SIOOx .....

Contour Interval 50 feet

Figure 8. Isopach map of "P" Salt.

11 R70W It.la,", . '. - .- _ . ...._-.:__ __ _".n..... __ II• .oW< ":..~ ...- " ­ -- -- - ­ • I. • ~ • • . .. .!. .1' ~ I • • ! • '" • .

- • i • j• • • 1, • .J , I V • e. I• • _-l-_J l .... 'V ; I o i • I

,r-; r/'Jll r... fi!l ~/VA..W • J./ ,q\: """ :1 : '/1,( r/ '-,M r/ POll "-1--1-4:-+--+-+-1-1--1-'\~ r. l'Y'I. -.,1/ r.t V •• 1-- ~1.-k...J-..' - NO f - r.M... • < • ...... , ... 11".,... ;V, ..... ". i • • J •• If • .....It ~~~.\;'j-,\0.'I--\:;\+-.h•.-1--;' ....1---+--1-1 Wi - J:.-• ..:' ..... i

• Ii • .'.-V I : '·0 --Y-\!-l-l--.I-+-I--l ,~

Area of "G" & 'p' Salt 1::::~J] Area of 'p' Salt ~

Figure 9. Isopach map of Pine Member of the Spearfish Formation,

12 Nesson Formation 10 the Kline, Picard and Poe the Saude 10 be Jurassic in age. Members with the upper members transferred10 the Piper Formation. The lower Piper, as currently I would redefine the Saude Member of the defined in North Dakota, is a redbed and evaporite Piper Formation as the interval from 2802 10 2848 depositional episode which includes the Picard feet in the Phillips Petroleum Company - O. Saude , Poe Evaporite, and Dunham Salt. The upper No. I well (fig. 13). This interval is equivalent to Piper consists of a normal marine depositional an upper portion ofDow's type section, the interval sequence of and IimeslOnes of the Bowes, from 6290 to 6405 feet in the Amerada Petroleum Firemoon, Tampico, and Kline Members. The top Corporation - Pederson, Cater No.1 well (fig. 12). of the Rierdon Shale and the top of the Picard Shale As thus defined, the Saude is generally less than 100 provide two consistent picks to provide the normal feet thick, but extends south and east of the limit of marine Jurassic regional depositional pattern. It the Pine Member of the Spearfish Formation and shows a gradual northwest to southeast thinning of represents the initial Jurassic deposition in the these strata from nearly 500 feet in northwestern Williston Basin (fig. 13). North Dakota to less than 200 feet at the South Dakota border (fig. 10). The Dunham Salt (fig. 14) i;limited to the central basin area and has an erratic distribution due Zieglar introduced the term Saude to refer 10 dissolution in many areas. One ofthese areas has to clastics between the Dunham and Pine Salts been demonstrated as Post-Piper dissolution (Dow, assuming a Jurassic age for both salts. Subsequent 1967, pI. 11), but no attempt has been made to interpretations have agreed with the Jurassic age of document time ofdissolution in other areas. Where the Dunham Salt, but the clastics have generally depositional thicknesses of the Dunham Salt are been regarded as Triassic in age in North Dakota. present the Dunham Salt thickens with compensated The term Saude is derived from the Phillips thinning of Poe anhydrites (plate 2) This demon­ Petroleum Company - OliviaSaudeNo. I well (NW strates the facies relationship of the evaporites and SE 19-158-74) where salts are absent and redbeds accounts for the Jurassic age assignment for this lie unconformably on the Tilston Interval of the salt. Madison Formation (Mississippian). Presumably the name was chosen because of the cored interval Unconformities in that well (fig. 11) although Zieglar did not desig­ nate this as the type section. Zieglar used a The subtle lithologic changes within the composite log from an area of the basin where all redbeds make recognition of unconformities the salts are present to define the Saude (fig. 1). difficult, but log characteristics on Dual Laterologs Dow used a well in the same area to redefine the (plates 1-2) are consistent with regional uncon­ Saude and then designated the interval between 6290 formities within the redbeds. Recognition of the feet and 6610. feet in the Amerada Petroleum unconformity between the Belfield and Pine Corporation - Pederson, Cater No. I well (NE SW Members of the Spearfish Formation is aided by the 21-158-95) as a type section (fig. 12). Presumably areal extent of the higher resistivity redbeds to the he chose that well because he wanted to redefine the areal extent of the underlying Minnekahta Lime­ Saude as the interval between the Poe Evaporite and stone. Recognition oftheunconformity betweenthe the "P" rather than the "G" salt (fig. I). As thus Saude and Pine redbeds is more tenuous, but utilizes defined, the Saude was considered to be Triassic a combination of the gamma ray and resistivity since the top of the Permian was placed at the top characteristics. There is also generally a higher of the "P" (Pine) Salt. Dow described the upper 60 resistivity below this unconformity and the gamma feet, based on cuttings, as moderate reddish brown, ray characteristics are consisteut with the generally slightly calcareous, silty shale. The remainder of noted more shaly lithology of strata immediately the Saude was described as moderate reddish orange below the Poe (or Amaranth) Evaporites. Place­ siltstone, sandy in part, with rounded, frosted sand ment of pre- "P" (Pine) and pre-Dunham grains. Dow (1967, p. 19) thought it probable that unconformities witbin the red clastics provides a the Jurassic-Triassic boundary was in the upper part more logical depositional sequence than initial thick of the Saude. Zieglar placed the Jurassic uncon­ salt deposition. formity at the base of the Pine Salt so he considered

13 Il.N",__ ...." • • . , • ! • . \'. '. " i ! N • ~ D~ • . I " ,. " 0 -~ . -! -. . ,~ • • .: • • ! •wt~ ~. • • • • • ~ • • 1H-.-+.3,jI"'Iort-","--"\--1-~h+-::1-+--I-.a.+--tI~• .I=-.--+-.,.--I!;' ~.&--I--+....-l~f--+-+-++-t-t-l\ • LJ - • .; • • • 10 • 1'\ i • ~ i • • • I • ~ • - 1/ . --I-­ ...... I 1\ 1 V I + ...... :';;r,;z. ;" ,I . / / j' • • ~ ·.r 1/ ! • :. •• "'. 0 1Il;RO!R • !• to • r • .V' •1/1" • r, .: I.. 1.-'. • /.' ;'JI-";;:;!."I'""l.!f-::Lr-t.iIR~·lij:";-l.I""r: V K....!;"". .0 ;.- .' -, • S1jUI« ..... ! 1-. te... r. . . L... I. l./ 1t-+-l-~-f--l.-...j:I-:-i--b"'/-"':f:I-:::::l~~.~-+~.~.~+ !­ j' - + - ...... "l---J--+-+r:.;--::I Fio.l.,...L,...J.",-L, .:. V •• I I' l v L_I-.~!=r~~.It·r·r[E1.~~t~·~~~r~~~-~~"ri' .158N.1 ~... I • ~ 1 .!~-1-.-i~v-::;;"",q.~I-+.4-\;--1j.--i=---I-Io.t-:-1y-;>+-.-..k"",i-"''1,=r+--+.--JI-.-l-t--I,

"""..r •• V • I • L-h lJl/' I I.....· ,IOU ~ ~lsooIn< c L.~lL- _.-'-_J_ ••L",." _.L . --1-. J ~ __ __,-- __ J.-,-"~..l- rUGaw III.IOOW...... ~ ""~. R.n*.

Contour Interval 50 feet

LImit of Picard Shale --­

Figure 10. Isopach map of Reirdon Formation and Bowes through Kline Members of the Piper Formation.

14 PHILLtPS-o. SAUDI MO. 1 SEC. ll,T. 158 N.,.R. 74 w. BO'nDfEAU COURTY'. NORTH DAKOI'.I......

E

Figure 11. Log of Phillips Petroleum COEp. - O. Saude No. I well (NW SE 19-158-74) with revised definition of Saude Member of Piper Formation.

AMERADA l'I!ROL. OORP.-I'IIlIIlSClM, CA.'IZR 110.1 NI sw BI!lC. 21. T.I68 N..Jl 86 Y. THIS WIIUAKS COUJC1T. NORI'H DAlCor" PAPER !OOW.IN7.f11.51 OR. LL :i POE IIBR POE J1BR. rz.. 0: Pi! SAUDE ll. ~ YIlR. ll.

SAUDE PINE MEMBER

YIlR. :i :i rz.. rz.. :r: :r: rt.l rt.l ~ ~ rz.. rz.. 'p SAL'l" ~ ~ Pi! Pi! ll. ll. rt.l rt.l

Figure 12. Log ofAmerada Petroleum Corp. - Pederson, Cater No.1 well (NE SW 21-158-95) showing revised definition of Saude Member of Piper Formation.

15 - ­ -­ -. .­ _ lII.!.''t '. _.IOW, -­ - ~~.. -­ -­ M'" - - -­ ~.. 0 10: 0 ,I 0 '(.. , • J • • !­ '0 0 ~ Cll..! ...1'---. • • • • ' 10 • I 0 0 0 , ! • • ~ i • • lColt.le • - - T ...JJ : • • J 0 • . - I i • T . - '\ • )l -'io 0, j • j \, t­ \ • " E- • 0 I 0 ~.. • L -->-i • ·1 • • i i • ~ • i ;, ~-- - - • • ! :." .: ~"l .: i -r. • • y • l.--r­ • • i • • oT • ... 0 "7 • • • : J • ~ • • • ~ i • i "/ ~ - .­ : "J ,51 • • • : v • j\r. . 0 0 10 . ! ~ i T : • • • .. . • ---. ... 0 - • - / 0 " • r--.. '-, ."'"" fAN i • i 1 _L I 0 , It 0; ""'I. • • ./ • • : • 10 r- t... _..f~ ! I. ! M """I" , • .. - • • T • • ! •, i i i I L., r--' - ou >Eft "', it:i : : : " : i i • i : \ , i II.lJ s . i - . -­ - i - • ._ L , : "I • r 0 ! I :. • '" :. i f' ~ i~ / ~- ,;' " . y, i~ .... ~ . .;.. • oif"'), ~jI ,..J T ! -0 ~AN , ~ 'V! i F+ ! I : ! 0 : . • I : sc~ 0 l ~ - · 0­ : 1 , T -.. lAI , .- •.- .- ­ I I !­ • 0 .'.soM.. i : 0 l-­ l----' L_l.-_ ,_ ~ ~ilux !- -­ R:iOi --­ -,­ ___ -.L __ __ .J. ___ w IUOOW. ..""'­ R.8S"

Contour Interval 50 feet

Figure 13. Isopach map of Saude Member, Piper Formation.

16 ll.76W. ~"".., --,­ I : ! : : ! IH-H--+--I--,f-++-+-+-+--j--H-+--l I •• ! i I I : --1-­ i I i " ; I W i"" i i "

"

:. ;

I \ I " ,...irl~Ou~fERiJr-~ r" "o"II_~ ! f4--f-!lif.:'WIF"4iImrJ'-"I---+-"+=i''''''-+-~+-+''-+-++-+--I-i' -­ __ 1--+--11--1--+--1 i ,.~r: ~~~~l}'i:;;'m" _"~+JsL-+(I'e_--i::--l-1r-I--1----+--t--t--+-t--t-1G1i--tfN'--t'""1; :! .; Ii

OW"}i'+-++-+--1-1-+-+-1-;'-j---.JI--t-++-I---Ir-fLL---:..=...t'-"""'1>=ril.---l::::tV-j....!~~ !. _.'_'- --- __---"-'_' --~._..J-J..-'-_Ji -'-- --L....-J,"-'-I I _ . _ _=_.•••_ fllO.. fl.:lllW. ..as.. 1I.ea..

Contour Interval 100 feet

F"Jgure 14. Isopach map of Dunham Salt, Piper Formation.

17 The unconformity between the Opeche NDF NO. 1835 Formation or older Paleozoic strata and overlying H. HANSON.WELDER NO.f redbeds has been referred to as a pre-Mesozoic NENW SEC. 20, T.133N., R.72W. event (Anderson, 1974). The nature ofthe contact in southeastern Saskatchewan, southwestern S.P. RES. Manitoba, and north-eentral North Dakota is one of essentially unweathered Mississippian carbonates with only minor secondary anhydrite in areas where the overlying redbeds are referred to as the Pine Member. This is in sharp contrast to south-central North Dakota where a karst topography has developed to a depth of 130 feet in the Herman Hanson - Welder No. I well (NE NW 20-133-72; Carlson, 1958) where red shales of the Saude Memberofthe PiperFormation overlie Mississippi­ an carbonates (fig. 15). This indicates a significant age difference in different areas for the uncon­ formity between redbeds and Paleozoic strata in North Dakota. I would SUbmit that the elusive pre­ Middle Jurassic unconformity is at the horizon which I have designated as the pre-Saude uncon­ formity.

Global sea level lowstands of Early , Mid-LeonardianandSinemurianage with associated unconformities fit nicely with unconformities at the base of the Tyler, Opeche, and Piper (Saude Member) Formations. The unconformity at the base of the Pine, if associated ~ z 0 z !! with the relative sea level fall al the base of the o~ -==: Q -~ ~ o~ ~ Middle Triassic would indicate a Triassic age for No; O!! ~ the Pine Member. Preservation of depositional ~ < ...... !! thicknesses of the Pine halites below the