An integrated sequence stratigraphic, palaeoenvironmental, and chronostratigraphic analysis of the Tangahoe Formation, southern Taranaki coast, with implications for mid‐Pliocene (c. 3.4–3.0 Ma) glacio‐eustatic sea‐level changes
An integrated sequence stratigraphic, palaeoenvironmental, and chronostratigraphic analysis of the Tangahoe Formation, southern Taranaki coast, with implications for mid‐Pliocene (c. 3.4–3.0 Ma) glacio‐eustatic sea‐level changes
复制标题
对塔拉纳基海岸南部 Tangahoe 组进行的综合层序地层、古环境和年代地层分析，对上新世中期（约 3.4-3.0 Ma）冰川海平面变化的影响
DOI：
10.1080/03014223.2005.9517780
复制
发表时间：
2005
影响因子：
2.2
通讯作者：
B. Ricketts
中科院分区：
文献类型：
--
作者：
T. Naish;Florian Wehland;G. Wilson;G. Browne;R. Cook;H. Morgans;M. Rosenberg;P. King;D. Smale;C. Nelson;P. Kamp;B. Ricketts
上新世中期的抽象沉积物（c。新西兰塔拉纳基南部海岸线沿着暴露在悬崖中的Tangahoe组包括一个270 m厚的循环浅海相序列，该序列已轻微弯曲成一个由北向南的低角度背斜。本研究考察了暴露于背斜西翼的10个米兰科维奇规模（6级）浅海沉积层序的沉积学、动物群和岩相学特征。这些层序是根据其组成岩相的周期性垂直叠加来识别的，这些岩相是由海侵滨面侵蚀过程中产生的尖波切割面所限定的。每个层序由三部分组成：（1）一套0.2-2 m厚的、向上加深的基底改造生物碎屑岩滞后沉积（上覆壳层）和/或上覆基质支持的近海大陆架亲和性软体动物壳层（2）厚5-20 m，逐渐变浅的加积粉砂岩序列;（3）5-10 m厚的强反褶积、分选良好的“强制海退”海岸线砂岩。三重细分分别对应于海进、高位和海退体系域（TST、HST和RST），代表了冰川-海平面变化周期中的沉积。低位体系域沉积物没有记录，因为露头位于c。在现代大陆架边缘以东100公里处，当时暴露于空气下。发育良好的、尖锐的和渐变的强制海退砂岩包含各种风暴就位的沉积结构，代表了海平面升降期间海岸线向风暴主导的浅陆棚的快速和突然的盆地内平移。砂岩重矿物学的岩相分析表明，在“强制海退”期间，南岛西北部的沉积物供应增加。基于生物地层学的年代学和一个新的磁性地层学与磁极性时间尺度的对比允许：（1）识别猛犸（C2 An. 2 r）和Kaena（C2 An.（1）亚时;（2）海岸剖面与怀皮皮阶的对比;（3）海岸剖面的年龄估计为3.36-3.06 Ma。有孔虫普查数据和软体动物古生态学的定性评估揭示了每个层序沉积期间从陆架到海岸线环境水深的周期性变化。在海洋氧同位素时间尺度上，水深在20 - 50 m之间的7个主要周期与40 ka冰川-海平面升降周期相关联。沿海的Tangahoe地层提供了在北方大陆上重要冰盖形成之前全球冰川-地球运动的浅海记录，并支持海洋δ 18 O档案的证据，即南极冰量的变化发生在上新世。
Abstract Sediments of the mid‐Pliocene (c. 3.4–3.0 Ma) Tangahoe Formation exposed in cliffs along the South Taranaki coastline of New Zealand comprise a 270 m thick, cyclothemic shallow‐marine succession that has been gently warped into a north to south trending, low angle anticline. This study examines the sedimentologic, faunal, and petrographic characteristics of 10 Milankovitch‐scale (6th order), shallow‐marine depositional sequences exposed on the western limb of the anticline. The sequences are recognised on the basis of the cyclic vertical stacking of their constituent lithofacies, which are bound by sharp wave cut surfaces produced during transgressive shoreface erosion. Each sequence comprises three parts: (1) a 0.2–2 m thick, deepening upwards, basal suite of reworked bioclastic lag deposits (onlap shellbed) and/or an overlying matrix supported, molluscan shellbed of offshore shelf affinity (backlap shellbed); (2) a 5–20 m thick, gradually shoaling, aggradational siltstone succession; and (3) a 5–10 m thick, strongly progradational, well sorted “forced regressive” shoreline sandstone. The three‐fold subdivision corresponds to transgressive, highstand, and regressive systems tracts (TSTs, HSTs, and RSTs) respectively, and represents deposition during a glacio‐eustatic sea‐level cycle. Lowstand systems tract sediments are not recorded because the outcrop is situated c. 100 km east of the contemporary shelf edge and was subaerially exposed at that time. Well developed, sharp‐ and gradational‐based forced regressive sandstones contain a variety of storm‐emplaced sedimentary structures, and represent the rapid and abrupt basinward translation of the shoreline on to a storm dominated, shallow shelf during eustatic sea‐level fall. Increased supply of sediment from north‐west South Island during “forced regression” is indicated from petrographic analyses of the heavy mineralogy of the sandstones. A chronology based on biostratigraphy and the correlation of a new magnetostratigraphy to the magnetic polarity timescale allows: (1) identification of the Mammoth (C2An.2r) and Kaena (C2An. 1r) subchrons; (2) correlation of the coastal section to the Waipipian Stage; and (3) estimation of the age of the coastal section as 3.36–3.06 Ma. Qualitative assessment of foraminiferal census data and molluscan palaeoecology reveals cyclic changes in water depth from shelf to shoreline environments during the deposition of each sequence. Seven major cycles in water depth of between 20 and 50 m have been correlated to individual 40 ka glacio‐eustatic sea‐level cycles on the marine oxygen isotope timescale. The coastal Tangahoe Formation provides a shallow‐marine record of global glacio‐eustasy prior to the development of significant ice sheets on Northern Hemisphere continents, and supports evidence from marine δ18O archives that changes in Antarctic ice volume were occurring during the Pliocene.