Late quaternary paleosealevels and paleoenvironments inferred from foraminifera, Northern Spencer Gulf, South Australia
Late quaternary paleosealevels and paleoenvironments inferred from foraminifera, Northern Spencer Gulf, South Australia
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DOI：
10.2113/0300029
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发表时间：
2000-01-01
影响因子：
1.1
通讯作者：
Murray-Wallace, CV
中科院分区：
文献类型：
--
作者：
Cann, JH;Belperio, AP;Murray-Wallace, CV
斯宾塞湾是一个细长的海上海湾，向北延伸约300公里，进入澳大利亚南部大陆，一直延伸到奥古斯塔港的顶端，向北延伸一条狭窄的河口。自冰后期海平面高峰期以来，通过海草、红树林和蓝藻席的捕获和束缚作用，进积的海岸沉积作用一直是有效的，潮下、潮间和潮上沉积相的明确分带是北湾的特征。软体动物和有孔虫数量丰富，特别是在海草草甸中，它们丰富的完整和粉碎的遗骸形成了生物碎屑碳酸盐沉积。不同的有孔虫组合与各种河口和海洋环境有关。奥古斯塔港口以北的高盐度河口以Textulariids Ammobaculites Barwan ens和TroChammina flata为特征，后者在红树林存在的地方最常见。其中仅有膨胀毛虫和长毛毛藻两种，而轮状线虫则以氨甲藻、节节毛藻和非离子凹陷毛藻为代表。在奥古斯塔港以南的泛盐度潮间带水域，常有膨胀轮藻、贝卡里轮藻和节节轮藻。浅潮下的Posidonia海草草甸支持着丰富的动物群，其中以三种动物为主，即努贝藻(Nubecularia Lucifuga)、平纹盘藻(Peneropis Platatus)和双纹盘藻(Discorbis Dimidiatus)。这些物种继续进入更深的水域，约20m，在那里它们隶属于Ququieloculina lamarckiana，Massilina Milletti，Elphdium crispum和E macelliforme。在斯宾塞湾北部20m水深的振芯中发现了4m的晚第四纪化石沉积物。来自软体动物化石的氨基酸消旋(AAR)和放射性碳测年揭示了四个年代地层包：400-360厘米，倒数第二次间冰期，氧同位素阶段7；360-240厘米，末次间冰期，氧同位素阶段5E；240-180厘米，间冰期，氧同位素阶段3；和180厘米，岩心顶部，冰后，氧同位素阶段1。核心内的有孔虫物种也主要生活在现代海湾，因此保存的组合可以对古环境和古洞穴进行合理的解释。5E亚期大量的拉马克栎属和米勒提栎属表明，澳大利亚南部的末次间冰期海平面仅比今天略高。N.Lucifuga在第三阶段沉积中含量丰富，因此在核心处的古海平面深度小于或等于2m。这一证据进一步支持了先前在圣文森特海湾确定的-30m以上的星际古洞穴。冰后期的基底沉积物保存了一种单一的唇米利奥林氏菌组合，这意味着河口环境具有盐湖的许多特征。全新世的最高海平面以米勒提在90厘米处的顶峰为标志。海平面随后的局部水均衡相对下降既表现为一般有孔虫记录中从90厘米向上的岩心变化，例如米勒蒂有孔虫数量的减少，也表现为与皱纹有孔虫相比，斑点石斑藻的数量减少。
Spencer Gulf is an elongate marine embayment extending northwards ca. 300 km inland into southern continental Australia to the apex at Port Augusta, with a narrow estuarine extension northwards. Since the postglacial sealevel maximum, prograding coastal sedimentation has been effective through the trapping and binding actions of seagrasses, mangroves and cyanobacterial mats, and a well-defined zonation of subtidal, intertidal and supratidal sedimentary facies is characteristic of the northern gulf. Mollusks and foraminifera are prolific, especially within seagrass meadows, and their abundant remains, entire and comminuted, form bioclastic carbonate sediments. Distinctive assemblages of foraminifera are associated with the various estuarine and marine environments. The hypersaline estuary north of Port Augusta is characterized by the textulariids Ammobaculites barwonensis and Trochammina inflata, the latter most common where mangroves are present. Two species of Triloculina, T. inflata and T. oblonga are the only common miliolids, while the rotaliids are represented by Ammonia beccarii, Elphidium articulatum and Nonion depressulus. South of Port Augusta, in euryhaline intertidal waters, Trochammina inflata, A. beccarii and E. articulatum are commonly associated. The shallow subtidal Posidonia seagrass meadows support an abundant fauna which is dominated by three species, Nubecularia lucifuga, Peneroplis planatus and Discorbis dimidiatus. These species continue into the deeper waters, ca. 20 m, where they are subordinate to Quinqueloculina lamarckiana, Massilina milletti, Elphidium crispum and E macelliforme.A vibrocore from 20 m water depth in Northern Spencer Gulf recovered 4 m of late Quaternary fossiliferous sediment. Amino acid racemization (AAR) and radiocarbon ages derived from fossil mollusks revealed four chronostratigraphic packages of sediment: 400-360 cm, penultimate interglacial, oxygen isotope stage 7; 360-240 cm, last interglacial, oxygen isotope substage 5e; 240-180 cm, interstadial, oxygen isotope stage 3; and 180 cm to the top of the core, postglacial, oxygen isotope stage 1. Species of foraminifera within the core are mostly also living in the modern gulf, thus the preserved assemblages permit plausible interpretations of paleoenvironments and paleosealevels. Large numbers of Q. lamarckiana and M. milletti in the substage 5e interval indicate that the last interglacial sealevel in southern Australia was only slightly higher than that of today. N. lucifuga is abundant in the stage 3 sediment, thus paleowaterdepth at the core site was ca. less than or equal to 2 m. This evidence further supports interstadial paleosealevels above -30 m, as previously determined for Gulf St Vincent. Basal sediments of the postglacial interval preserve a monospecific assemblage of Miliolinella labiosa which signifies an estuarine setting having many of the characteristics of a saline lake. Maximum Holocene sealevel is signified by the acme of M. milletti at 90 cm. Subsequent local hydro-isostatic relative fall of sealevel is shown by changes up-core from 90 cm in both the general foraminiferal record, for example by declining numbers of M. milletti, and also by reduced numbers of E. macelliforme compared with those of E. crispum.