Applications of Geochemical Data to Modelling Sediment Dispersal Patterns in Distal Turbidites: Late Quaternary of the Madeira Abyssal Plain
Applications of Geochemical Data to Modelling Sediment Dispersal Patterns in Distal Turbidites: Late Quaternary of the Madeira Abyssal Plain
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应用地球化学数据模拟远端浊积岩沉积物扩散模式：马德拉深海平原晚第四纪
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发表时间：
1992
期刊：
影响因子：
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通讯作者：
I. Jarvis
中科院分区：
文献类型：
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作者：
T. Pearce;I. Jarvis
摘要一个广泛的地球化学数据库已被用来约束沉积过程，沉积物分散模式和晚第四纪沉积在马德拉深海平原（MAP）的远源浊积岩的古水流路径。浊积岩是一种以泥质为主的米厚地层单元，具有独特的岩石、生物和化学地层特征，能够对面积超过67，000平方公里的各个地层进行对比。在分布于MAP中部的18个岩心位置，为一个具有代表性的5米厚的床层（浊积岩B）绘制了Si、Ti、Al、Mg、Fe、Ca和Zr的地球化学剖面图。这些剖面与粒度和矿物学数据相结合，表明浊积岩由1-120 cm的层状砂/粉砂基底层组成，富含火山玻璃、玄武岩碎屑、重矿物和有孔虫（1号单元），上覆1-5 m的分级差的粉砂质泥浆。地球化学数据还表明存在一个中心层，该中心层相对富含重矿物和絮凝的粘土-骨料泥浆，并以高Ti、Fe、Mg和Zr含量为代表（单元2）。该单元被沉积物覆盖，其中钙质超微化石和粘土矿物的比例不断增加（单元3），其特征是钙和铝浓度增加。单元1变薄和变细，而单元2和3向盆地最深处和局部凹陷和死胡同变薄和变细。有人认为，大多数浊积岩沉积从不断发展的高度集中的流动，这防止了显着的粒度偏析，并使米厚的差分级泥浆的快速沉积。分选和分级的基底粉砂（1号单元）主要由最初的湍流沉积，该湍流减速并成熟为高度浓缩的流体泥浆浊流。流动底部的剪切力是造成I号机组上部和2号机组粉质泥浆级配的原因。在水流水头下夹带的流体通过水流向上迁移，将轻质碳酸盐和粘土矿物携带至浊积岩顶部，留下覆盖剪切砂/粉砂和粉砂质泥浆的致密泥浆中心塞。Isocon地图（由连接点的化学浓度相等）的基础上平均值的Ca，Ti，Mg和Zr在单元2被用来重建沉积物的分散模式和古水流路径。这些地图证实浊流沉积B的浊流轴向西南流经中部的MAP，这意味着加那利群岛和马德拉提供了一个潜在的源MAP浊流沉积。
ABSTRACT An extensive geochemical database has been used to constrain depositional processes, sediment dispersal patterns and palaeoflow pathways of late Quaternary distal turbidites deposited on the Madeira Abyssal Plain (MAP). Turbidites are meter-thick, mud-dominated units with distinctive litho-, bio- and chemostratigraphic characteristics which have enabled the correlation of individual beds over > 67,000 km2. Geochemical profiles for Si, Ti, Al, Mg, Fe, Ca and Zr have been constructed for a representative 5-meter bed (turbidite b) at 18 core localities distributed across the central part of the MAP. These profiles, combined with grain-size and mineralogical data, demonstrate that turbidites consist of a 1-120 cm, laminated, sand/silt basal layer, rich in volcanic gla s, basalt clasts, heavy minerals and foraminifera (Unit 1), overlain by 1-5 m of poorly graded silty muds. Geochemical data additionally indicate the presence of a central layer which is relatively enriched in heavy mineral and flocculated clay-aggregate muds and is typified by high Ti, Fe, Mg and Zr contents (Unit 2). This unit is overlain by sediments containing increasing proportions of calcareous nannofossils and clay minerals (Unit 3) and characterized by enhanced Ca and Al concentrations. Unit 1 thins and fines, whereas Units 2 and 3 thicken and fine toward the deepest part of the basin and into local depressions and cul-de-sacs. It is argued that the majority of the turbidites were deposited from evolving highly concentrated flows, which prevented significant grain-size segregatio and enabled the rapid deposition of meter-thick poorly graded muds. The sorted and graded basal silts (Unit 1) were deposited primarily by an initially turbulent flow, which decelerated and matured into a highly concentrated fluid mud turbidity current. Shear at the flow base was responsible for the grading in the upper part of Unit I and in the silty muds of Unit 2. Fluid entrained under the current head, which migrated up through the flow, carried light carbonate and clay minerals toward the turbidite top, leaving a central plug of dense muds overlying sheared sands/silts and silty muds. Isocon maps (produced by joining points of equal chemical concentration) based on mean values for Ca, Ti, Mg and Zr in Unit 2 are used to reconstruct sediment dispersal patterns and palaeoflow pathway . These maps confirm that turbidite b was deposited by turbidity currents which flowed axially southwestward across the central part of the MAP, implying that the Canary Islands and Madeira offer a potential source of sediment for MAP turbidites.