Sedimentologyandpaleontology of Lower Permian fluvialredbeds of north-centralNew Mexico- preliminaryreport by DaaidA. Eberth,Graduate Student, Department of Geology, University of Toronto, Toronto, Ontario, and Daaid S. Berman,Associate Curatot Sectionof VertebrateFossils, Carnegie Museum of Natural History, Pittsburgh,Pennsylvania Introduction from sedimentologists.The goals of this mian) in the San Diego Canyon region of foint application of sedimentologicaland projectare to: L) reconstructthe depositional SandovalCounty and centraland northeast paleontologicalprinciples to researchinvolv- environmentsof these beds by means of a SocorroCounty, and in the Cutler Formation ing terrestrialfluvial units is currently being multivariatebasin analysisapproach (Miall, in El Cobre Canyon near Abiquiu, Rio Arriba employed by many workers who desire a 1980);2)utilize a knowledge of depositional County.The depositsof theseareas also have more complete understanding of paleoen- stylewithin faciesto locatefossiliferous sed- provided a basisfor planning future field re- vironmental and depositional conditions iments; 3) gain a comprehensivepicture of search.All specimenshave been cataloged (Dodson, 1971; Dodson and others, 1980; the vertebratefauna and insights into envi- into the collectionsof the CarnegieMuseum Bown and Kraus, 1981.;Behrensmeyer and ronmental factors that may be affectingthe of Natural History, Sectionof VertebrateFos- Tauxe, 1982).The perspectivegained from distributionpatterns of someof its members; sils; the abbreviationCM is used to refer to such a union is of unquestionablevalue to and 4) provide an understanding of sand- that repository. biostratigrapherand paleoecologistand stone-bodymorphology and geometry as a the Sedimentology servesas an additional tool for the sedimen- possibleguide to mineral and/or hydrocar- tologist investigatinglocal faciesvariations. bon exploration in this resion and in other Sedimentologicalinquiry and data collec- This past summer (7982)a field party rep- u."ur dith similar historiei of deposition. tion in the Cutler Formationexposures of the resentingthe CarnegieMuseum of Natural Field research was carried out in two RioPuerco drainage area resulted in the com- History and the University of Toronto initi- phases.The thick, laterally extensiveexpo- pilation of 32 vertical sections(totaling 2,892 ated a joint researchprogram in the Lower iures of the Cutler Formatiohin the Rio Puerco h) and 17 horizontal sections(documenting Permian redbed fluvial faciesof north-cen- drainageof central Rio Arriba County were three-dimensional sandstone-body mor- tral New Mexico (fig. 1). The excellentex- the subjectof intensivepaleontological, sed- phology). A total of more than 1,100paleo- posuresin this region have in the past received imentological, and stratigraphic investiga- iurrent directionswere measuredduring the only sporadicattention from paleontologists tion. Similar,but cursory,examinations were courseof these investigations.In addition, and stratigraphersand virtually no attention alsomade in the Abo Formation (Lower Per- individual fossil-bearinglocalities, varying widely in taxa and in quantity of individuals yielded, were mapped and sampled in an effort to address the hydraulic controls on fossil distributions within these fluvial de- 'posits. Severaltentative conclusionscan be drawn from the vertical sectiondata of the Rio Puerco drainagearea (fig. 2). Theseconclusions are: Alsoin this issue: FloridaMountains overthurst belt p.26 Oiland gas discovery wells drilledin 1982 p. 30 Geologyand uranium potential of Sabinosodistrict p. 35 Service/News p. 39 I Comingsoon A Bryozoanand Crustaceanfrom Fruit- landFormation Magnetostratigraphyof Raton Basin core il Uraniumindustry in NewMexico FIGURE 1-LocArtoN oF STUDYAREAA, El Cobre Canyon and B, Rio Puerco drainage area; open circles CoyoteCreek State Park in B represent locations of the three vertical sections oI fig.2. L) sandstone bodies are concentrated at par- ity and channeltrends, and, to a lesserextent, stones and minor sandstones containing var- ticular horizons in a given vertical section river geometry.All recordedsections, as well iable concentrations of vertebrate, and lateral continuity of a sandstone horizon as casualobservations, indicate the presence invertebrate, and plant fossils were sampled, is uncommon, suggesting regular avulsion of two distinct types of channel sandstone mapped, and measured. Previous reference and splay events typical of ephemeral river bodies.One type is U-shaped,of limited lat- (Lahgston, 1953)to these fossil-rich deposits systems; 2) sandstone to mudstone ratios in- eral extent, and of very low sinuosity.The as "pond deposits" can be considered erro- crease upsection; 3) grain sizes ranging pre- sandsare medium grained and well sorted. neous simply on the basis of their channel- dominantly from medium to coarse in the Bedformsand biogenicindicators consist pri- like morphologies and discontinuous lateral sandstone bodies, as well as infrequent con- marily of medium to large scale trough extent. Preliminary evaluation of vertical and glomerates,and abundant channel scouring crossbedding,abundant dewatering struc- horizontal sections, as well as taphonomic suggest a midfan fluvial environment; 4) ca- tures, and calcareoustubular nodules. Low data recorded from fossils collected by us liche beds of varying maturity and lateral width/depth ratios, as well as internal scour and by the University of California (Berkeley) extent are abundant in mudstone deposits surfaces,^suggestvertical accretionperhaps nearly a half century ago, strongly suggest throughout all of the vertical sections but similar to that found in modern anastomos- that these deposits are the remnants of prox- become noticeably rare in the highest por- ing rivers. The second type of sandstone imal crevasse splays. The subsequent rec- tions of the thickest sections; 5) local corre- channelfill is laterallyextensive and flat based ognition of lithologically and morphologically lations of up to 6-7 km are possible using and representsa channel unit that has ex- similar deposits elsewhere in the section, laterally extensive caliche beds; 6) dark stain- perienced longer periods of lateral accretion which are devoid or very sparsely fossilifer- ing of grains, probably because of hematite than the U-shapedunits. Textural parame- ous, demonstrates that crevasse-splay de- (not displayed in fig. 2), becomes noticeably ters and bedformsof the secondtype appear posits are a common feature associated with reduced upsection, a condition that also was comoarableto those of the U-shapedunits, these sandstone units (as would be expected) noticed in the San Diego Canyon and So- perhapsexhibiting more largescile trough and that their fossil content can be highly corro County areas. crossbedding.Paleocurrent measurements variable. Horizontal section data provided the most of scourssuggest low sinuosity. Preliminary sedimentological studies of useful insights into general channel mor- In addition to the studv of the sandstone Lower Permian redbed facies in San Diego phology, bedform interrelationships, sinuos- bodies, U-shapedCeposit! of reducedmud- Canyon, El Cobre Canyon, and northeast and central Socorro Couniy provided us with a 6/l 5/27 means of evaluating some of the strati- graphic data from the Rio Puerco drainage area. These studies also raised questions that will help to direct future field research. Thick (120 m), exclusively fluvial facies in El Cobre Canyon are tentatively considered to be stratigraphically lower than those beds in the Rio Puerco drainage on the basis of their larger grain size and darker color (hematite stain- ing). One other line of evidence suggeststhis relationship. Within the Rio Puerco drainage area, the Chinle Formation (Triassic) cuts New A4exfic@ CAL,CHE GEOLOGV . Scionceand Service Volume 5, No. 2, May 1983 published quarterly by New Mexico Bureau ofMines and Mineral Resources a division of New Mexico lnstitute of Mining & Technology BOARD OF REGENTS Ex Officio Toney Anaya, Goverror of Ne|| Mexico Leonard Delayo, Slpeintendeil of Public Inslruction Appointed Judy Floyd, Prcs., 1977-1987, Ias Cruces Willim G. Abbott, Secty/Ireas., 1961-1985, Hobbs Donald w. Moris, 1983-1989, Los Alamos Robert Lee Sanchez, 1983-1989, Albuquerque Steve Tores, 196'7-1985, Socorro New Mexico lnstitute of Mining & Technology ActinqPrcsident ....... CharlesR.Holmes New Mexico Bureau of Mines & MineralResources Director . .. FrankE.Kottlowski Deput) Dircctor George S. Austin M M _ fu1UDSTONE Subscriptions: lssued quarterly, February, May, August, E November; subscription price $6.00/yr. SS- SANDSTONE T possible Dalerial for E Editoriol matte.: Contributions of C - CONGLOMERATE consideration in future issues of NMG are welcome. R .t CoBBLES Address inquiries to Marla D. Adkins-Heljeson, editor of s Nee Mexico Ceology, New Mexico Bureau of Mines & IKM olo- CALICHE Mineral Resources, Socorro, NM 87801 Published as public donain, thercfore rcproducible without permission. Sou rce cred i t rcques ted. FIGURE 2-SrnarrcnerHrc CoLUMNSrnov Lowrn Prmanx Curun FonrraerroNor Rro Putnco DRATNAGE Ciculation: l.4OO (fig. 1); note lateral continuity of thick caliche horizon (datum marker) and lateral discontinuity of P.ntel. University of New Mexico Printing Plant sandstone units. May 1983 NewMexico Geology down into the underlying Lower Permian tool. However, the relationship between this New Mexico, both from the Cutler Forma- beds, thus forming an