University of Portland Pilot Scholars Environmental Studies Faculty Publications and Environmental Studies Presentations 5-1981 Magnetic Polarity Stratigraphy and Biostratigraphy of Paleocene and Lower Eocene Continental Deposits, Clark's Fork Basin, Wyoming Robert F. Butler University of Portland, [email protected] Philip D. Gingerich Everett H. Lindsay Follow this and additional works at: http://pilotscholars.up.edu/env_facpubs Part of the Earth Sciences Commons Citation: Pilot Scholars Version (Modified MLA Style) Butler, Robert F.; Gingerich, Philip D.; and Lindsay, Everett H., "Magnetic Polarity Stratigraphy and Biostratigraphy of Paleocene and Lower Eocene Continental Deposits, Clark's Fork Basin, Wyoming" (1981). Environmental Studies Faculty Publications and Presentations. 3. http://pilotscholars.up.edu/env_facpubs/3 This Journal Article is brought to you for free and open access by the Environmental Studies at Pilot Scholars. It has been accepted for inclusion in Environmental Studies Faculty Publications and Presentations by an authorized administrator of Pilot Scholars. For more information, please contact [email protected]. MAGNETIC POLARITY STRATIGRAPHY AND 40K-40AR DATING OF LATE MIOCENE AND EARLY PLIOCENE CONTINENTAL DEPOSITS, CATAMARCA PROVINCE, NW ARGENTINA' ROBERT F. BUTLER, LARRY G. MARSHALL, ROBERT E. DRAKE, AND GARNISS H. CURTIS Departmentof Geosciences, The Universityof Arizona, Tucson, Arizona85721 Departmentof Geology and Geophysics, Universityof California,Berkeley, California94720 ABSTRACT Magnetostratigraphicand 40K- 40Ardata on a 2300 m thick sequenceof continentalsediments at Puerta de CorralQuemado in CatamarcaProvince, NW Argentinapermit calibration of landmammal faunas of late Tertiary(Huayquerian and Montehermosan)age. The sequence represents(from oldest to youngest) the ChiquimilA, Araucanense,and CorralQuemado Formations. Paleomagnetic samples were collected from 99 stratigraphiclevels. Strong-fieldthermomagnetic and isothermalremanent magnetization experiments indicatethat the dominantferrimagnetic mineral is magnetite.Progressive alternating-field (AF) and themal demagnetizationof the naturalremanent magnetism (NRM) demonstratesthat AF demagnetizationto 20 mT peak field is sufficient to isolate the primaryNRM which is of depositionalorigin. The resulting paleomagneticdata provide a well-definedmagnetic polarity zonation, although sampling is less dense in the upperhalf of the section. 40K-40Ar data obtainedfrom mineralseparates of four tuffs withinthe section allow reliableage determinationsfor those levels. The combinedmagnetostratigraphic and 40K- 40Ardata allow the magneticpolarity zonation to be correlatedwith the magneticpolarity time scale. This correlation indicates a nearly constant rate of sediment accumulationbetween -8.0 Ma and 3.5 Ma. The boundary between the Araucanenseand CorralQuemado Formations approximates the boundarybetween the Huay- querianand Montehermosanland mammalage faunas at this locality. The data presentedhere allow the boundarybetween the Araucanenseand CorralQuemado Formations to be datedat 6.4 Ma. Combinedwith geochronologicdata from similarage rocks and faunasfrom San Carlos, MendozaProvince, west-central Argentina,the geochronologicdata from Puerta de CorralQuemado allow the Huayquerian-Monteher- mosanland mammal age boundaryto be placedtentatively at 6.0 Ma. A specimenof the fossil land mammal Cyonasua(family Procyonidae) from unit 14 of the AraucanenseFormation is dated at 7.0 to 7.5 Ma. This specimenis the earliest known representativeof this North Americangroup in South Americaand repre- sents the oldest dated participantin the GreatAmerican Faunal Interchange on that continent. INTRODUCTION the appearance of the land bridge and in- The continents of North and South volved most of the interchange participants, America are today connected by the Panama- which dispersed north and/or south after 3.0 nian land bridge, a structure which has per- Ma. The other phase occurred prior to emer- mitted the reciprocal interchange of terres- gence of the land bridge and involved fewer trial biotas following its final emergence participants. The land mammals in this phase about 3.0 Ma. This biotic event is known as were waif immigrants in the Late Miocene the Great American Faunal Interchange and dispersed on rafts of vegetation and/or by (Webb 1976), and it represents the best docu- island hopping along island chains. The par- mented example in the fossil record of an in- ticipants are known to include members of terchange of two long separated continental the North American raccoon family Procy- faunas. onidae (and possibly the rodent family Two primary phases of the Great American Cricetidae), which dispersed to South Amer- Faunal Interchange are recognized, the par- ica, and members of the ground sloth families ticipants in which are identified on the basis Megalonychidae and Mylodontidae, which of their time and means of dispersal (Simpson dispersed to North America. In this paper we 1940, 1950, 1980). One phase occurred after provide geochronologic data that securely calibrates the beginning of this early phase of the Great American Faunal Interchange in 1 Manuscript received February 22, 1984; re- vised June 11, 1984. South America. Late Tertiary land mammal faunas which [JOURNALOF GEOLOGY, 1984, vol. 92, p. 623-636] © 1984 by The University of Chicago. All rights include fossil Procyonidae have been re- reserved. corded from a thick sedimentary sequence 0022-1376/84/9206-001$1.00 at Puerta de Corral Quemado and Chiquimil 623 This content downloaded from 64.251.254.77 on Mon, 28 Oct 2013 18:33:29 PM All use subject to JSTOR Terms and Conditions 624 R. F. BUTLER ET AL. FIG. 1.-Map of Catamarca Province, northwest Argentina showing Puerta de Corral Quemado and Chiquimil localities. in CatamarcaProvince, northwestArgentina corded 1,525 m of sediment and that from (fig. 1). A largecollection of fossil vertebrates Puerta de Corral Qeumado 1,913 m. Fossil from these localities was made by Elmer S. mammalsand tuff beds were indicatedto be Riggs in 1926 and is deposited in the Field especially abundantin the upper half of each Museum of Natural History, Chicago. De- section. tailed stratigraphicprofiles of each locality These published data indicated potential were made by RudolphStahlecker, geologist for calibrating the age of these mammal- on the Riggs' expedition, and recordwas kept bearingrocks using magnetostratigraphicand of the position of most fossils collected within 40K- 40Ar dating techniques. In May 1977, this stratigraphic framework. Stahlecker's Butler, Marshall, and personnel from the sections were publishedby Riggs and Patter- Museo de La Plata and Museo Municipalde son (1939) along with a preliminarystudy of Ciencias Naturales "Lorenzo Scaglia" in the faunas. The section from Chiquimilre- Argentina visited these localities to deter- This content downloaded from 64.251.254.77 on Mon, 28 Oct 2013 18:33:29 PM All use subject to JSTOR Terms and Conditions MAGNETIC POLARITY STRATIGRAPHY 625 mine the feasibility of such a study. The re- results of that trip are reportedhere. A 2,300 sults of that trip are reported by Marshall et m thick composite paleomagneticsection, in- al. (1979). The rocks at Puerta de Corral cluding the two sections collected in 1977, Quemado proved particularly suitable for was obtained. This section correlates with paleomagnetic analysis, and two sections, the upper half of Stahlecker's section, span- each including a securely dated tuff, were ning his units 13 through30 (see below) and sampled. The dated tuff in the upper part of includes four securely dated tuffs. We our lower 400 + m section we believed to be confirmedthe identityof the tuff in our upper Stahlecker's unit 8, and the dated tuff in the section of Marshallet al. (1979) as Stahleck- top of our upper 500 + m section we believed er's unit 29, but found that unit 8 in the lower to be his unit 29. Correlation of our two sec- section of Marshall et al. (1979) is actually tions with units in Stahlecker's section was Stahlecker's unit 15. The unit identified as based largely on the identity of these tuff unit 15 by Marshallet al. (1979) cannot be levels. securely correlated with a specific unit in Our preliminary study demonstrated the Stahlecker's section, although we believe ideal nature of these rocks for magnetostrati- that unit is correlativewith Stahlecker'sunit graphic and 40K- 40Ar analyses. We felt 20. confident that additional work at Puerta de Stratigraphicnomenclature of the late Ter- Corral Quemado would permit us to sample tiary sedimentsat Puertade CorralQuemado the sequence between our upper and lower and Chiquimilhas had a confused history as sections. The anticipated results would pro- reviewed by Marshall and Patterson (1981, vide a more secure correlation of our data pp. 14-15) and Bossi and Palma(1982, fig. 1). with Stahlecker's section and would permit We follow the terminologyused by Riggs and chronostratigraphic calibration of the fossil Patterson (1939) because it is the one which faunas, including three specimens of Procy- appears most frequently in paleontological onidae. The mammal faunas are assigned to literature. the Huayquerian and Montehermosan Land The following abbreviations are used: Mammal Ages (see below). Thus, the oppor- FMNH, Field Museum of Natural History, tunity existed to date the Huayquerian-Mon- Chicago;MACN, Museo Argentinode Cien- tehermosan boundary at this locality. cias Naturales "Bernardino Rivadavia," An unpublished manuscript