Depositional Patterns in the Late Holocene Po Delta System
Depositional Patterns in the Late Holocene Po Delta System
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DOI：
10.2110/pec.05.83.0365
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
A. Correggiari;A. Cattaneo;F. Trincardi
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文献类型：
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作者：
A. Correggiari;A. Cattaneo;F. Trincardi
摘要：晚全新世波河三角洲系统由波河注入，波河流经东西向波河平原（汇水面积74，500 km 2），进入亚得里亚海陆表海。Po三角洲体系包括广泛的三角洲平原、受波浪影响的三角洲前缘和广泛的不对称前三角洲存款。前三角洲向北呈现较陡较短的斜坡，向南呈现非常平缓的斜坡，在此，厚的Po前三角洲与晚全新世亚得里亚海泥楔融合。晚全新世Po三角洲的增长开始于5.5 kyr BP，在现在的海平面高水位达到之后。Po三角洲的特点是交替阶段的快速推进和放弃其多个三角洲叶。这种三角洲的历史反映了高频率的气候变化，autocyclicavulsions，和人为因素，作用于变量，但通常很短的时间尺度上的强迫。通过以下方式对Po系统进行了研究：（1）回顾了几个世纪以来的历史制图;（2）综合调查了现代三角洲近海记录的VHR地震剖面，从水深5米到前三角洲趾部约30米;（3）来自精确定位的沉积物岩心的沉积学和地质年代学数据。历史记载和制图表明，在高位剥蚀期间，撕脱作用是Po三角洲建设的一个重要过程;参考现今Po三角洲的位置，较老的元素向南北发展。在青铜时代晚期（约。公元前3 kyr），波河发展了两条主要支流：位于北方的Po di Adria和位于南方的Po di Spina。在罗马时代（CA。2.5-1.5 Po前三角洲地层的重建以及与三角洲平原地貌和历史资料的对比表明：（a）三角洲-前三角洲系统的显著不对称性，每个三角洲河口南部有显著的下漂沉积物散布，前三角洲叶不对称;（B）三角洲叶从供给主导向波浪主导的短期转变;和（c）在前三角洲中存在两种明显不同的沉积元素。两种主要的前三角洲沉积物是：（1）以横向连续地震反射体为特征的瓦状沉积前三角洲瓣，显示岩心中保存洪水沉积物的证据，以及（2）伴随着“切割-充填”特征的沉积前三角洲瓣，通常在短寿命、非常活跃的分流河道的近海检测到，其特征是岩心中的大量淤泥。在第一种前三角洲存款中，各个叶在横向上相互重叠，反映了它们的供给系统在短时间内相对重要性的变化。在第二种情况下，地震剖面表明，渠道状的形式有尖锐的基地和记录重复的情节切割和填充，而整个瓣建设。水道状地貌通常成群出现，个别宽度从100米到300米不等，深度可达4-5米，充满大量淤泥到极细砂。短寿命的情节切割和填充假设归因于突发性洪水事件的灾难性复活独特的波河分支驱动的河流排放的自然起源或人为干预的突然增加。河流三角洲-概念、模型和实例
A BSTRACT : The late Holocene Po delta system is fed by the Po river, which drains the E–W-trending Po plain (catchment area 74,500 km 2 ) and enters the Adriatic epicontinental sea. The Po delta system includes an extensive delta plain, a wave-influenced delta front, and a broad asymmetric prodelta deposit. The prodelta shows a steeper and shorter slope to the north and a very gentle slope to the south, where the thick Po prodelta merges into the late Holocene Adriatic mud wedge. The growth of the late Holocene Po delta started 5.5 kyr BP, after the present sea-level highstand was attained. The Po delta was characterized by alternating phases of rapid advance and abandonment of its multiple deltaic lobes. This delta history reflects the forcing of high-frequency climate change, autocyclic avulsions, and anthropogenic factors, acting on variable, but typically short, time scales. The Po system has been investigated through: (1) a review of historical cartography extending back several centuries; (2) integrated surveys of VHR seismic profiles recorded offshore of the modern delta from water depths as shallow as 5 m to the toe of the prodelta in about 30 m; and (3) sedimentological and geochronological data from precisely positioned sediment cores. Historical accounts and cartography show that avulsion was an important process in Po delta building, during highstand progradation; with reference to the position of the present-day Po delta, older elements developed both to the north and to the south. During the late Bronze Age (ca. 3 kyr BP), the Po river developed two main branches: the Po di Adria , in the northern sector, and the Po di Spina , to the south. During the Roman Age (ca. 2.5–1.5 The reconstruction of the stratigraphy of the Po prodelta and the correlation to geomorphologic and historical data in the delta plain show: (a) a marked asymmetry of the delta–prodelta system with significant down-drift sediment dispersal to the south of each individual delta mouth and asymmetric prodelta lobes; (b) short-term shifts from supply-dominated to wave-dominated delta lobes; and (c) the presence of two markedly distinct depositional elements in the prodelta. The two main kinds of prodelta deposits are: (1) shingled depositional prodelta lobes characterized by laterally continuous seismic reflectors showing evidence of variably preserved flood deposits in core, and (2) depositional prodelta lobes accompanied by “cut-and-fill” features typically detected offshore of short-lived, very active distributary channels characterized by massive silt in core. In the first kind of prodelta deposit, individual lobes onlap each other laterally, reflecting changes in the relative importance of their feeding systems over short intervals. In the second case, seismic profiles indicate that the channel-like forms have sharp bases and record repeated episodes of cut and fill while the entire lobe is building. The channel-like features typically occur in clusters, with individual widths ranging from 100 to 300 m and depths up to 4–5 m, filled with massive silt to very fine sand. The short-lived episodes of cut and fill are hypothetically attributed to episodic flood events of catastrophic reactivation of distinctive Po river branches driven by sudden increases in river discharge of natural origin or by human intervention. River Deltas—Concepts, Models, and Examples