Carbon isotope stratigraphy of Upper Cambrian (Steptoean Stage) sequences of the eastern Great Basin: Record of a global oceanographic event
Carbon isotope stratigraphy of Upper Cambrian (Steptoean Stage) sequences of the eastern Great Basin: Record of a global oceanographic event
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DOI：
10.1130/0016-7606(1998)110
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发表时间：
1998-03
影响因子：
4.9
通讯作者：
M. Saltzman;B. Runnegar;K. C. Lohmann
中科院分区：
文献类型：
--
作者：
M. Saltzman;B. Runnegar;K. C. Lohmann
在大盆地东部三个剖面的高分辨率地层中，记录了晚寒武世翼头生物阶段/斯特普托阶段(Aphelaspis-Elvinia带)δ13 C的大规模全球正漂移(从∼0.5到4.5‰)。这次漂移，我们称之为斯特普托正碳同位素漂移，或香料漂移，开始与一次世界范围的物种灭绝事件重合。来自大盆地的δ13C数据反映了全球范围内各种岩性的海水价值，包括橄榄砂砾岩、怪石、血栓岩边界岩和平卵石砾岩。我们使用伊根山脉南部Shingle Pass的一个剖面将翼头类生物群划分为8个同位素阶梯，代表了δ13C上升和下降(±4‰)的相等划分。这为认识翼头类生物群/斯特普林阶段的修订年代地层格架提供了基础。在香料漂移开始时沉积的地层记录了大盆地东部沉积模式的重大变化。这反映在内华达州Shingle Pass的硅质碎屑-碳酸盐转变，以及犹他州House Range和Lawson Cove段的碳酸盐-硅质碎屑转变。在整个大盆地中公认的区域性硅质碎屑流入发生在香料漂移的顶峰附近。来自怀俄明州克拉通剖面的碳同位素分析提供了独立的证据，表明在香料漂移期间克拉通发生了重大的沉积间断。δ13C、相对海平面和海洋生物群在SPICE漂移过程中的相关变化为一次重大的古海洋事件提供了非常详细的记录。我们推测，海平面、气候或构造的变化可能触发了香料漂移和同时代灭绝事件。随后有机碳的埋藏导致了δ13C的增加，并可能导致了一段时间的全球降温。这一研究结果为前中生代岩石的碳同位素研究提供了信心。
A large, global positive excursion in δ 13 C (from ∼0.5 to 4.5‰) during the Late Cambrian Pterocephaliid biomere/Steptoean Stage (Aphelaspis-Elvinia zones) is documented at high stratigraphic resolution in three sections in the eastern Great Basin. The excursion, which we refer to as the Steptoean Positive Carbon Isotope Excursion, or SPICE excursion, began coincident with a world-wide extinction event. The δ 13 C data from the Great Basin reflect global seawater values in a wide range of lithologies, including oolitic grainstones, wackestones, thrombolitic boundstones, and flat-pebble conglomerates. We use a section at Shingle Pass in the southern Egan Range to divide the Pterocephaliid biomere into eight isotope steps that represent equal divisions of the δ 13 C rise and fall (±4‰). This provides a basis for recognition of a revised chronostratigraphic framework for the Pterocephaliid biomere/Steptoean Stage. Strata deposited during the beginning of the SPICE excursion record a major change in the pattern of sedimentation in the eastern Great Basin. This is reflected in a siliciclastic-carbonate transition at Shingle Pass, Nevada, and a carbonate-siliciclastic transition at the House Range and Lawson Cove sections in Utah. A regional siliciclastic influx recognized throughout the Great Basin occurs near the peak of the SPICE excursion. Carbon isotope analyses from cratonal sections in Wyoming provide independent evidence that a major sedimentary hiatus took place on the craton during the time of the SPICE excursion. The correlated changes in δ 13 C, relative sea level, and the marine biota during the SPICE excursion provide remarkably detailed records of a major paleoceanographic event. We speculate that changes in sea level, climate, or tectonics may have triggered the SPICE excursion and coeval extinction event. Subsequent burial of organic carbon caused the increase in δ 13 C and may have led to an interval of global cooling. The results of this study lend confidence to carbon-isotopic studies of pre-Mesozoic rocks.