Sedimentology, stratigraphic context, and implications of Miocene intrashelf bottomset deposits, offshore New Jersey
Sedimentology, stratigraphic context, and implications of Miocene intrashelf bottomset deposits, offshore New Jersey
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DOI：
10.1130/ges01530.1
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发表时间：
2017-12
期刊：
影响因子：
2.5
通讯作者：
D. Hodgson;J. Browning;K. Miller;S. Hesselbo;M. Poyatos‐Moré;G. Mountain;J. Proust
中科院分区：
文献类型：
--
作者：
D. Hodgson;J. Browning;K. Miller;S. Hesselbo;M. Poyatos‐Moré;G. Mountain;J. Proust
新泽西陆上和海上中新世斜坡层内的钻探提供了对其顶积层和前积层的更好理解，但其底积层的沉积学和地层学尚未详细记录。在综合大洋钻探计划（IODP）313考察期间收集的三个岩心孔（M27-M29）与多个底积层相交，其分析有助于完善层序地层解释和陆内斜坡的过程响应模型。在站点M29，最下倾的位置，年代地层学良好约束的底积层遵循重复的地层基序。粗粒的灰石英砂包裹体突然覆盖在深挖洞的表面。通常，这些包裹体先变粗，然后向上变细，并向上进入生物扰动粉砂岩。这些粗砂层是混合的，分选不良，含有薄壁壳，底栖有孔虫，和盆外碎屑，符合碎屑的解释。这些包的沉积学和丘状地震特征支持解释为碎屑为主的波瓣复合体。进一步向上倾，在站点M28，相同的年代地层单元合并，没有生物扰动粉砂，表明近端位置的侵蚀更多。M28站较年轻层序中的分级砂岩和沙丘级交错层理表明浊流和河道化作用的沉积作用。每个包的尖锐的基地被解释为层序边界，与一个时期的侵蚀和沉积物旁路证明了挖表面，粗粒碎屑和浊流沉积物代表低位体系域。上覆细粒沉积物被解释为海侵和高位体系域沉积物的组合，并包含最大洪水面的深水等效物。在粗粒底置包的厚度和粒度的趋势的变化指向一个自生控制，通过补偿叠加的叶片和叶片复合体。然而，大规模的地层组织的底置存款和粗粒的未成熟的盆外和改造reworked reconconititic碎屑指向外部控制，可能相结合的相对海平面下降和沉积物供应的盈亏周期。该研究表明，在横跨深大陆架的相对浅（~100-200 m深）和低梯度（~1°-4 °）的斜坡层中，可以产生大量的沉积物重力流沉积。这种自然地理可能导致泥石流沉积物的优势，由于短的运输距离限制转换为低浓度的浊流。
Drilling of intrashelf Miocene clinothems onshore and offshore New Jersey has provided better understanding of their topset and foreset deposits, but the sedimentology and stratigraphy of their bottomset deposits have not been documented in detail. Three coreholes (Sites M27–M29), collected during Integrated Ocean Drilling Program (IODP) Expedition 313, intersect multiple bottomset deposits, and their analysis helps to refine sequence stratigraphic interpretations and process response models for intrashelf clinothems. At Site M29, the most downdip location, chronostratigraphically well-constrained bottomset deposits follow a repeated stratigraphic motif. Coarse-grained glauconitic quartz sand packages abruptly overlie deeply burrowed surfaces. Typically, these packages coarsen then fine upwards and pass upward into bioturbated siltstones. These coarse sand beds are amalgamated and poorly sorted and contain thin-walled shells, benthic foraminifera, and extrabasinal clasts, consistent with an interpretation of debrites. The sedimentology and mounded seismic character of these packages support interpretation as debrite-dominated lobe complexes. Farther updip, at Site M28, the same chrono strati graphic units are amalgamated, with the absence of bioturbated silts pointing to more erosion in proximal locations. Graded sandstones and dune-scale cross-bedding in the younger sequences in Site M28 indicate deposition from turbidity currents and channelization. The sharp base of each package is interpreted as a sequence boundary, with a period of erosion and sediment bypass evidenced by the burrowed surface, and the coarse-grained debritic and turbiditic deposits representing the lowstand systems tract. The overlying fine-grained deposits are interpreted as the combined transgressive and highstand systems tract deposits and contain the deepwater equivalent of the maximum flooding surface. The variety in thickness and grain-size trends in the coarse-grained bottomset packages point to an autogenic control , through compensational stacking of lobes and lobe complexes. However, the large-scale stratigraphic organization of the bottomset deposits and the coarse-grained immature extrabasinal and reworked glauconitic detritus point to external controls, likely a combination of relative sea-level fall and waxing and waning cycles of sediment supply. This study demonstrates that large amounts of sediment gravity-flow deposits can be generated in relatively shallow (~100–200 m deep) and low-gradient (~1°–4°) clinothems that prograded across a deep continental shelf. This physiography likely led to the dominance of debris flow deposits due to the short transport distance limiting transformation to low-concentration turbidity currents.