A composite reference section for terminal Proterozoic strata of southern Namibia

被引:205
作者
Saylor, BZ
Kaufman, AJ
Grotzinger, JP
Urban, F
机构
[1] Harvard Univ, Bot Museum, Cambridge, MA 02138 USA
[2] Hobart Coll, Dept Geol, Geneva, NY USA
[3] MIT, Dept Earth Atmospher & Planetary Sci, Cambridge, MA 02139 USA
来源
JOURNAL OF SEDIMENTARY RESEARCH | 1998年 / 68卷 / 06期
关键词
D O I
10.2110/jsr.68.1223
中图分类号
P5 [地质学];
学科分类号
0709 ; 081803 ;
摘要
Integrated sequence stratigraphic and chemostratigraphic data yield a framework for correlations of stratigraphic units in the terminal Proterozoic to Cambrian Witvlei and Nama Groups of Namibia. Coupled with precise U-Pb zircon age constraints, these correlations make it possible to construct a composite reference section for use in calibrating terminal Proterozoic chronostratigraphy, The Namibian reference section starts with two distinct glacial horizons and extends up to within 1 million years of the Proterozoic-Cambrian boundary. The two glacial horizons may represent each of two distinct Varanger-age glaciations better known from the North Atlantic region. From the higher of the two glacial horizons up, the composite stratigraphy preserves one of the thickest and most complete available records of carbon-isotope variability in post-Varanger terminal Proterozoic seawater. Four carbon-isotope chemostratigraphic intervals are recognized: (1) a postglacial negative delta(13)C excursion (Npg interval); (2) a rising interval (Pr interval) of increasing positive delta(13)C values; (3) a falling interval (Pf interval) characterized by decreasing positive delta(13)C and culminating in near zero or negative values; and (4) an interval of moderately positive, relatively invariant delta(13)C values (I interval) that extends up to the unconformity that contains the Proterozoic-Cambrian boundary. Each of these chemostratigraphic intervals can be recognized in widely separated correlative sections around the world. By comparing sediment accumulation rate in the radiometrically calibrated Namibian stratigraphy with sediment accumulation rates in correlative sections in Arctic Canada and Oman, a maximum age of 564 Ma is estimated for the end of the younger Varanger glaciation, 25 m.y. younger than previous estimates.
引用
收藏
页码:1223 / 1235
页数:13
相关论文
共 62 条
  • [1] AITKEN JD, 1991, GEOLOGY, V19, P445, DOI 10.1130/0091-7613(1991)019<0445:TLPGMM>2.3.CO
  • [2] 2
  • [3] ALLEN PA, 1986, INT ASS SEDIMENTOLOG, V8
  • [4] [Anonymous], 1995, MILANKOVITCH SEA LEV
  • [5] Arthur M.A., 1987, GEOL SOC SPEC PUBL, V26, P401, DOI DOI 10.1144/GSL.SP.1987.026.01.25
  • [6] CALIBRATING RATES OF EARLY CAMBRIAN EVOLUTION
    BOWRING, SA
    GROTZINGER, JP
    ISACHSEN, CE
    KNOLL, AH
    PELECHATY, SM
    KOLOSOV, P
    [J]. SCIENCE, 1993, 261 (5126) : 1293 - 1298
  • [7] BURNS SJ, 1993, ECLOGAE GEOL HELV, V86, P595
  • [8] CHEEL RJ, 1992, J SEDIMENT PETROL, V62, P933
  • [9] CRIMES TP, 1982, J PALEONTOL, V56, P890
  • [10] SEDIMENTARY CYCLING AND ENVIRONMENTAL-CHANGE IN THE LATE PROTEROZOIC - EVIDENCE FROM STABLE AND RADIOGENIC ISOTOPES
    DERRY, LA
    KAUFMAN, AJ
    JACOBSEN, SB
    [J]. GEOCHIMICA ET COSMOCHIMICA ACTA, 1992, 56 (03) : 1317 - 1329