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The Middle Jurassic Summerville Formation, Northern New Mexico--A

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The Middle Jurassic Summerville Formation, Northern New Mexico--A TheMiddle Jurassic Summerville Formation, northern New Mexico -a rebuttalof Gondon,1993 by SpencerG. Luus,New Mexico Museum of NaturalHistory & Science,1801 Mountain Road NW, Albuquerque, NM87104; and 1rin J. Anderson,New Mexico Bureauof Minesand Mineral Resources. Socono. NM 87801 Introduction no way carefully defined as a stratigraphic unit, and Redwall Nothing new is presented in Condon's reply (Condon, 7993) Limestone, introduced by Gilbert (1875)but not named for a ge- to our paper on the Summerville Formation and related strata in ographic location, would have to be considered invalid using northern New Mexico (Anderson and Lucas, 1992). Condon re- Condon's criteria. sorted to trivializing our objection to using preoccupied strati- Condon failsto understandthat long-usedand widely accepted graphic names, calling it specious, and also to searching the stratigraphic names, such as Grabau's term Wanakah, are valid stratigraphic code (NACSN, 1983) for loopholes in order to justify and take priority over later usageseven if the original definitions perpetuating his confusing duplication of names. Clearly usage do not meet current or (what Condon imagines to be) earlier of the name Wanakah as a stratigraphic unit in New York has standards. Failure to understand and implement this basic con- precedence over usage in southwest Colorado. Significantly, Con- cept is a recipe for nomenclatural chaos.Condon's claim that "the don did not choose to defend regional correlations proposed by Wanakah of the eastem Colorado Plateauhas been the subject of workers at the U.S. Geological Survey based on the "Bed at Black much more study than the New York unit" can only mean that Steer Knoll." We interpret this as an admission that regional cor- he is unaware of extensive geological and paleontological litera- relations based on the "Bed at Black Steer Knoll" are unsupport- ture on the New York Wanakah. able. Generally, arguments set forth by Condon only strengthen our The "Beclabito Member of the Wanakah" is correlative with conclusion that the last 25 years of effort bv workers of the U.S. the Summerville Geological Survey to revisi Middle and Lipper Jurassic stratig- At the heart of our disagreementwith Condon and his col- raphy and sedimentation models on the Colorado Plateau have leagues is the correlation of San Rafael Group units on the Col- been based (1) on continued use or creation of redundant and orado Plateau from west-central New Mexico to southwestern parochial stratigraphic names, (2) purported tracing of marker Coloradoto east-centralUtah. The correlationwe proposeis sup- beds that cannot be traced by other investigators in the field, (3) ported by all availablelitho- and biostratigraphy and is advocated postulating regional unconformities for which no stratigraphic or by most workers, including Harshbargeret al. (1957),Imlay(1980), geochronologic evidence exists and using these "unconformities" Kocurekand Dott (1983),and Ridgley(1989), among others.This as formation contacts, and (4) creating sedimentological models correlation (Fig. 1a) recognizesthe main body of the Entrada to which stratigraphic units are retrofitted regardlessbf the actual Sandstone across the Colorado Plateau. The overlying Todilto stratigraphic relationships. Formation in northern New Mexico/southwesternColorado rep- resentsa salinalake (Lucaset al., 1985)or a marine embayment Preoccupied stratigraphic names should not be used (Harshbargeretal.,1,957; Ridgley, 1989) related to a risein regional We pointed out that the term "Wanakah Shales," introduced base level due to the transgressionof the CurtirStump (early- by Grabau (1977) for Devonian strata in New York, has priority middle Callovian) seaway.The SundanceFormation of South Da- over Burbank's (1930) "Wanakah Member of the Morristrn Foi- kota-Wyoming was also deposited during this transgression;the mation." Indeed, the Middle Devonian Wanakah Member of the ichthyofauna of the Todilto Formation is also found in the Sund- Ludlowville Formation (the Hamilton Group) is a well recognized anceFormation, lending further support to the correlation(Schaeffer stratigraphic unit used in many publications, including the Ge- and Patterson, 1984). ologic Map of New York published by the New York State Mu- The Summerville Formation of our usage overlies the Todilto seum of Science/New York Geological Survey (Rickard and Fisher, Formation or, where the Todilto is absent, the main body of the 7970a, b) and more recently by Miller (1991) in a discussion of Entrada Sandstonefrom Cimarron County in western Oklahoma Devonian stratigraphy. Grabau (1917,p.338) introduced the name to near Moab in east-centralUtah. West of Moab, to the SanRafael in a footnote to refer to an already well known unit, "the lower Swell, however, the Summerville overlies the shallow-marine Curtis Hamilton Shales" of western New York. Cooper (1930, p. 225) Formation which, not surprisingly, occupies the same strati- subsequently designated and described a type section foi what graphic position as the Todilto Formation. Regional stratigraphic he termed the Wanakah Member of the Ludlowville Formation relationships, fossils, and lithology thus support the correlation of the Hamilton Group. This unit is listed and described in the advocated by most workers between west-central New Mexico most recent U. S. Geological Survey Lexicon of Geologic Names and the San Rafael Swell of Utah: Entrada : Entrada, Todilto : (Keroher, 1955) and has never been recommended foiabandon- Curtis, and Summerville : Summerville, with the recognition merrt by the original author nor the U. S. Geological Survey. that part of the upper Curtis may grade eastwardor southeast- Condon challenges the idea that Grabau's use of Wanakah has ward into lower Summerville strata (Fig. 1a). priority over Burbank's on the ground that Grabau's introduction Condon and his colleagues (especially O'Sullivan, 1,980a,b), of the name Wanakah Shales did not constitute "an adequate however, propose a very different correlation (Fig. 1b). They claim definition of a new stratigraphic name . in 7917." Obviously, that careful tracing of key marker beds shows the "Wanakah For- Condon is alone in this belief, since all stratigraphers who have mation" of southwestern Colorado (and west-central New Mex- worked in western New York, and geologisti o] the New york ico) to be older than the Summerville Formation of east-central Geological Survey, have recognized Grabau's Wanakah Shales as Utah. According to Condon, the Wanakah is correlative with the a valid stratigraphic, unit. Fven Burbank (1930) acknowledged Curtis. This apparently indicates to him that the Todilto is older Grabau's priority, although he thought no confusion would aiise than the Curtis and that the Entrada Sandstone of west-central from giving the same name to two geographically disparate units. New Mexico is older than the Entrada of Utah (Fig. 1b). Ironically, Much confusion would arise if the criteria demanded bv Con- it was Condon's predecessors(Baker et al., 1947)who correlated don were applied to many of the stratigraphic names introduced the Entrada Sandstoneinto the southern San Juan Basin. in the 1800s and early 1900s. Well understood and widely used In our original article we refuted the Wanakah-Curtis corre- names such as Shinarump, casually used by Powell (1876lbut in lation by pointing out that the so-called"marker bed"-"Bed at August 1993 Nan Merico Geology SanRafael Swell, Utah SanJuan Basin, New Mexico Condon reasserts the erroneous correlation (locally) of the "Bed BrushyBasir at Black Steer Knoll" of O'sullivan (1980b)and refers to O'sullivan Morrison Member MorrisonFormation and Pierce (1983) to argue that strata, which McKnight labelled Formation owermembers Zuni Sandstone Summerville (and which lie above the Moab Tongue of the En- BluftSandstone cross SummervilleFormation trada Sandstone on the southwestern end of McKnight's This is an assertion for which Con- Formation section), are not Summerville. A Summerville don presents no evidence. Furthermore, Condon's statement that CurtisFormation of Moab, which we termed Summerville, "consist TodiltoFormation rocks southeast of Entrada, Curtis, and Summerville equivalents and therefore EntradaSandstone EntradaSandstone cannot be called Summerville" runs contrary to established strat- igraphic practice. These rocks are lithologically similar to, and continuous with, Summerville strata and should be mapped as Summerville Formation even if they include strata correlative with the Curtis Formation. SanRafael Swell, Utah SanJuan Basin, New Mexico The rather superficial reasons for the Summerville-to-Wanakah name change are discussed by Condon and Peterson (1986, p. MorrisonFormation MorrisonFormation 15). In addition, a written communication from Condon to An- derson (February, 1986) states "Had O'Sullivan's revised inter- pretation been known to me earlier, I wouldn't have gone ahead SummervilleFormation CowSprings Sandstone with the name change in the San Juan Basin." The "revisions" B HorseMesa Member alluded to by Condon are those of O'Sullivan in which he ac- CurtisFormation Er knowledged that the Summerville was not cut out entirely by pre- Beclabito*Member four-corners area. The "name change," 6L Morrison erosion in the >c refers to the change from Summerville to Wanakah. A Entrada TodiltoMember of course, Sandstone subsequent written communication from Condon to Anderson 'Although (February, 1988) includes the following: the interpre- EntradaSandstone tation now
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