Studies in Devonian Stratigraphy: Proceedings of the 2007 International Meeting of the Subcommission on Devonian Stratigraphy and IGCP 499 D. Jeffrey Over, editor
;,, "' / · Numh~r 6:i, Decemb_~r 2009 ~ 1,.,.
ABSTRACTS COMPARATIVE STRATIGRAf>HY OF EIFELIAN SUCCESSIONS IN SOUTHERN MOROCCO AND THE APPALACHIAN BASIN: IMPLICATIONS FOR GLOBAL EVENTS G. C. Baird1, C. E. Brett2, R. T. Becker3, Z. S. Aboussalam3, M. DeSanris2, & A. ]. Bartholomew4 1 Department of Geosciences, SUNY Fredonia, Fredonia, New York 14063, USA,
[email protected]; 2 Department ofGeology, University ofCincinnati, 500 Geology/Physics Building, Cincinnati, Ohio 45221-0013, USA,
[email protected]; 3GeologischPaläonrologisches Institut, Westfalische Wilhelms-Universität, Corrensstrasse 24, D-48149, Münster, Germany,
[email protected]~ 4 Department of Geological Sciences, SUNY College at New Palrz, New Paltz, New York 12561 , USA, barthola@newpaltz. edu A new Middle Devonian section has been discovered in the western Dra Valley (southwestern Morocco) during a mapping project of geology smdents from Münster. A detailed measuremenr and sampling of rhythmic shale-carbonate outcrops of the Eifelian ro early Givetian Timrhanrhart succession southeast of the Rich Touimiliht and south ofHassi Mouf (south ofAouinet Torkoz) was subsequently undertaken by a joint American-German research group. This investigarion has rhe following objecrives: first, to document the derailed pattern of sequence and cycle stratigraphy; second, ro document rhe succession of faunas and ro establish biostratigraphic relationships, rhird, ro mal5e detailed comparisons between the Moroccan sections and classic Middle Devonian successions in the Appalachian Basin, and thereby, fourth, to shed light on the local versus global origin of cycles, facies changes, and bioevenrs. Although much of this analysis is preliminary, a detailed lithostratigraphy has been established and the sampling for conodonts and goniatites permirs comparison with coeval sections of the eastern Dra Valley, sourheasrern Morocco (Tafilalr) and the Onondaga Limestone and Marcellus Shale (lower Hamilron Group; Eifelian-lower Givetian) in rhe Appalachian Basin of eastern North America (Becker & H ouse, 1994; Brett & Ver Straeten, 1994). Tue new Hassi Mouf-south section is exposed along a sourhtrending rriburary wadi to the Oued Draa, approximately 11 km south of Torkoz. Above a rhick siliciclastic succession of upper Emsian to basal Eifelian units (topmost Khebchia Formation, Rich 4 Sandstone Member) is a 46 m-thick interval of repetitive limestone-shale alternations spanning rhe Eifelian to lower Givetian Yeraifa and lower Ahrerouch Formations (Becker & H ouse, 1994). Resistant sandstones of rhe Rich 4 Member grade upward inro a gray, calcareous shale and siltstone unir yielding shell lags characterized by crinoid ossicles, rhenopyrgid edrioasteroids, diverse brachiopods, proetid (Gerastos sp.) and phacopid trilobites, gastropods, solirary rugose corals, and !arge, distinctive ostracodes. This argillaceous interval (Crinoid Marl Member, basal Yeraifa Formation) is abruptly overlain by shell and pelmarozoan-rich limestones (Pinacites Limestone Member); calcareous shale and limestone beds rich in robust bivalves (Panenka sp.), goniatites (Fidelites sp.), rugosans, rhynchonellids, bryozoans, trilobires, and pelmatozoans
characterize this basal imerval. These beds contain an admixture of pelagic (goniatites, nowakiids, polygnathids) and rich benthic faunal elements. This interval is approximately equivalent ro the richly fossiliferous upper Onondaga Limesrone. Above this interval, succeeding limestones become disrinccly darker and marly, nodular or concretionary (Grey Marl Member). Tue diverse benthos gives way ro a biota of sryliolines, very, small brachiopods, some phacopids, and both straight and coiled cephalopods. This dysoxic fades concinues ro the highest strata examined at this seccion but there are discinctive changes between dark grey, black and light grey beds and changes in fossil conrenc. Approximately 10.9 m above the base of the Pinacites Limesrone Member, a !arge arthrodire skull and shoulder girdle was discovered by one of us (GCB) in a dark limestone interval with the goniacite Fidelites, small ambocoeliid brachiopods, orthocones, and small solitary rugose corals. lt overlies direccly a marly limestone with large orthocones that is characterized by the firsr mass occurrence of a small, smoorh brachiopod, which resemble forms of the two Givetian "pumilio Beds" of southern Morocco and Germany. Eifelian "pumilio Beds" have previously been found at Bou Tserfine near Assa and in the eastern Dra Valley. Approximarely 1.6 m above the arthrodire bed is a thin limesrone with numerous small and poorly preserved cabrieroceratids suggesting, at least, a middle Eifelian age for this unic. A higher, black, marly limesrone with abundant well-preserved Agoniatites and other goniatites (Cabrieroceras, Parodiceras) on its upper surface is upper Eifelian in age and allows correlacion with rhe latest Eifelian Agoniatites Zone of the Tafilalr (Becker & House, 1994). Ir could also correlate with the dysoxic Cherry Valley Member ("Agoniatites Limestone") of the New York succession (Baird et al , 1999; Ver Straeten et al., 1994). Overlying shales and black marls of the basal Ahrerouch Formation are much less fossiliferous but include some Trevoneites, a genus which first emers in cl1e Kacak Event beds of the eastern Dra Valley and southern Algeria. Tue subsequent gradual return ro light grey, marly nodular limesrone wirh pyrire-filled burrows, crinoid stems, brachiopods, solitary Rugosa, phacopids and goniatites [A. aff. vanuxemi (Hall 1879)) give evidence for an episodically improved seaf!oor vencilacion in the basal Givecian, perhaps correlating with the Halihan Hill Bed of the New York section (Brett & Ver Srraeten, 1994; Baird et al., 1999; Ver Straeten et al., 1994). Above a covered interval, limestones with pyritic burrows and nodules, black marls and thin "pumilio layers" return, indicating a brief episode of pronounced dysoxia during the basal Givetian. Overall, comparisons between the Moroccan section and those of the lare Eifelian-earliest Givetian in the Appalachian basin (Chlupac & Kukal, 1986; Walliser, 1990; House, 1996; Schöne, 1997; Garda-Alcalde & Soto, 1999; Bulrynck & Walliser, 2000; DeSantis et al. , 2007) provide a test of cycle and bioevent patterns. Such comparison indicates strong similariries of sequence and cycle stratigraphy, as well as bioevents that support a global origin for these features. LITERATURE CITED Baird, G. C., C. E. Brett, & C. A. Ver Straeten. 1999. NYSGA Fieldtrip Guidebook, pp. 155-175 .
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Becker, R. T., & M . R. House. 1994. CFS, 169: 79-135. Brett, C. E., & C. A. Ver Straeten. 1994. NYSGA Fieldtrip Guidebook, pp. 221-269. Bulcynck, P., & 0. H. Walliser. 2000. CFS, 225: 211-226. Chlupac, 1., & Z. Kukal. 1986. Springer- Verlag, Notes on Earth
Science, 8: 169-179. D eSantis, M. K., C. E. Brett, & C. A. Ver Straeten. 2007. Pages 83-104, in: Devonian Events and Correlations, R. T. Becker & W T. Kirchgasser, eds., Geological Sociecy of London, Special Publicarion 278 . Garda-Alcalde, J. L., & F. Soro. 1999. Revista Epafzola de Paleotol.ogia, n° extr.: 43-56. House, M. R. 1996. Proceedings ofthe Ussher Society, 9: 79-84. Schöne, B. R. 1997. Göttinger Arbeiten zur Geol.ogie und Paläontologie, 70: 140 pp. Ver Srraecen, C. A., D. H. Griffing, & C. E. Brett. 1994. NYSGA Fieldtrip Guidebook, pp. 271-321 . Walliser, 0. H. 1990. Springer Verlag, Notes on Earth Science, 30:
1-3.
DETAILED CONODONT BIOSTRATIGRAPHY AND CARBON ISOTOPE CHEMOSTRATIGRAPHYTHROUGH THE KLONK EVENT AND ACROSS THE SILURIAN/DEVONIAN BOUNDARY IN SOUTHWESTERN LAURENTIA
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J. E. Barrick 1, D. J. Jacobi2, M . A. Kleffner 3 , & H.R. Karlsson 1 'Department of Geosciences, Texas Tech Universicy, Lubbock, Texas 79409-1053, USA,
[email protected]; 2Baker Aclas, P. 0. Box 1407, Houston, Texas 77073-5100, USA; 3Department of Geological Sciences, 1he Ohio State Universicy at Lima, Lima, Ohio 45804-3576, USA Detailed sampling for conodonrs and carbon isotopes at three carbonate sections in southwestern Laurentia provides a wealrh ofbiostracigraphic and chemostratigraphic information chrough the Klonk Evenc and across ehe Silurian/Devonian boundary. Two sourhern Oklahoma outcrop sections span ehe Henryhouse-Haragan formational boundary and comprise a succession of argillaceous carbonate mudsrone and wackestone deposited in an outer carbonate ran1p setting that grade upward into interbedded wackestone and packstone. A core of ehe upper Frame Formation from Andrews County, Texas, contains a succession of carbonate mudstone and wackestone deposited in a slope setting souch of a shelf margin chac grade up inco interbedded wackescone and packstone. Three conodont faunal units characterize the Silurian/Devonian boundary interval, which ranges from 2-5 m thick. (1) A diverse late Pridoli conodont fauna characterized by Oul.odus elegans detorta (Walliser, 1964), Belodella coarctata Barrick & Klapper 1992, B. anfi"acta Barrick & Klapper 1992, Dapsilodus, and Dvorakia amsdeni Barrick & Klapper 1992, extends below ehe boundary interval. (2) Tue abrupt disappearance of many Pridoli species results in a lower diversicy fa una in which Dapsdodus and 0. e. detorta range slighrly above ehe base, B. resima? (Philip, 1966) and Dv. philipi? (Drygant, 1974) appear, and acmes of Decoriconus fi"agilis (Branson & M ehl, 1933) an d Pseudooneotodus beckmanni (Bischolf & Sannemann, 1958) occur near ehe top. This interval comprises me Klonk Event.
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(3) Tue appearance of the early Lochkovian species lcriodus postwoschmidti Mashkova, 1968, marks ehe base of ehe third unic, which lies near where coarser skeletal carbonaces appear. Carbon isotope (o 13C) values fluccuace irregularly below conodonr faunal unit 1 and show a small shift near me base of faunal unic 2. Through faunal unit 2, carbon isotope values remain remarkably consistent, varying less than 0.5 per mil. Near ehe base of faunal unit 3, carbon isotope values show more distincc shifr of + 1 per mil that forms a shorr-lived peak in faunal unit 3. Graphie correlation shows that ehe base of ehe Devonian lies within conodonc faunal unit 2, within ehe Klonk Evenc, near ehe extinccion level of Dapsil.odus and below thac of Oulodus elegans detorta. Without graphic correlation precise placemenc is not possible because comparable biostratigraphic derail for conodoncs from other boundary sections, such as Klonk, does not exist. Tue small shifcs in carbon isotopes recorded here do not compare weil wich carbon isotope excursions reporred near ehe Silurian/Devonian boundary at sections in Europe, Nevada, and ehe Appalachians, and cannot be used to correlace eo those secrions. Tue major turnover in coniform conodonc species ac ehe Klonk Evenc, however, could provide me most reliable means by which to recognize ehe base of ehe Devonian in carbonate sections lacking graptolites.
PALEOENVIRONMENTAL AND EUSTATIC CONTEXT OF MIDDLE DEVONIAN BIOEVENTS IN EASTERN NORTH AMERICA, GERMANY, AND MOROCCO Alex Bartholomew 1 & Carlton Brecc2 Geology Department, 1 Hawk Drive, State Universicy of New York at New Paltz, New Palcz, New York 12561, USA, barchola@ newpaltz.edu; 2Room 500 Geology/Physics Building, Geology Department, Universicy ofCincinnati, Cincinnati, Ohio 45221-0013, USA 1
Although, much attention has been focused on ehe cyclicicy and bioevents ofthe Late Devonian, it is becoming increasingly evident char ehe Middle Devonian was also a critical interval in physical and life hiscory, characterized by both intervals of strong local stabilicy as weil as episodes of abrupt change. Recent decailed comparative studies ofstratigraphic and faunal patterns in eastern Laurentia, Avalonia, northern Gondwana, and elsewhere, have documented comparable patterns chat point eo ehe global nature of climatic, eustatic, and biotic events wichin this interval. A refined, high-resolution record of sea-level changes has been elucidated in recenc years, providing evidence for high-order cycles wich probable Milankovi~ch periodicicies, despite ehe fact that ehe Middle D evonian lies solidly within a "greenhouse" phase of global climatic histocy. Tue present review considers the paleoecologica l and paleoenvironmencal contexts of three major Middle Devonian bioevenrs: ehe early Eifelian Chocek, ilie late Eifelian Kacak, and ehe lace G ivetian Taghanic events, in eastern Norch America, Germany, and Morocco. Within rhe generally warm mid-D evonian interval, there is also accumulating evidence for periods of abrupt temperature change, especially in ehe late Eifelian and even more markedly in ehe lare Giverian. These thermal events are associaced wich episodes of cransgression eo highscand, and expansion of dysoxic to anoxic environ-
