Pleistocene “muddy” forced-regression deposits on the Adriatic shelf: A comparison with prodelta deposits of the late Holocene highstand mud wedge
Pleistocene “muddy” forced-regression deposits on the Adriatic shelf: A comparison with prodelta deposits of the late Holocene highstand mud wedge
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DOI：
10.1016/j.margeo.2005.06.042
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发表时间：
2005-11
期刊：
影响因子：
2.9
通讯作者：
D. Ridente;F. Trincardi
中科院分区：
文献类型：
--
作者：
D. Ridente;F. Trincardi
亚得里亚海边缘的上更新世-全新世地层学由一系列由陆架不整合面分隔的沉积层序组成。这些沉积序列中最近的一次包括近25 kyr，由末次冰期最高低潮、随后的海平面上升和现代高潮分别形成的低潮、海侵和高潮单元组成。较老的沉积被分为4个沉积层序，每个层序记录了大约100 kyr的冰川-隆起旋回，时间间隔在大约450 - 25 kyr BP之间。这些更新世层序主要由长时间海平面下降阶段沉积的泥质前积单元组成；因此，这些层序代表了保存完好的泥质强迫后退沉积的独特例子。详细的地震地层分析表明，构成这四个层序的强迫退积沉积与近岸和（或）河流三角洲环境没有直接联系。相比之下，在露头中定义并在文献中报道的典型强迫退缩沉积物由富含沙子的近岸/三角洲相组成，这些相作为古代海岸线的斑块残余物保存下来。我们认为亚得里亚海陆架上的泥质强迫退积体代表了在露头中被认为是典型强迫退积产物的滨面沉积的海上对应物。有趣的是，亚得里亚海陆架上的泥质强迫退积与全新世晚期高地泥楔有明显的相似之处，表明它们通过细粒沉积物的横向平流形成了共同的沉积机制。在这种观点中，泥质沉积物的水下进积发生在风暴波基底以下，在海平面继续下降期间，水下翻滚点可能位于与时间等效海岸线的距离逐渐减小的位置。
The upper Pleistocene–Holocene stratigraphy of the Adriatic margin consists of a succession of depositional sequences separated by shelf-wide unconformities. The most recent of these depositional sequences encompasses the last ca. 25 kyr, and consists of lowstand, transgressive and highstand units formed, respectively, during the Last Glacial Maximum lowstand, the subsequent sea level rise and the modern highstand. Older deposits are grouped into four depositional sequences, each recording ca. 100 kyr glacio-eustatic cycles during an interval between ca. 450 and 25 kyr BP. Each of these Pleistocene sequences is composed dominantly by muddy progradational units deposited during prolonged phases of sea level fall; therefore, these sequences represent a unique example of well-preserved muddy forced-regression deposits. Detailed seismic–stratigraphic analyses show that forced-regression deposits composing the four sequences are not directly connected to nearshore and/or fluvio-deltaic environments. In contrast, typical forced-regression deposits defined in outcrop and reported in the literature consist of sand-rich, nearshore/deltaic facies preserved as patchy remnants of ancient shorelines. We suggest that muddy forced-regression deposits on the Adriatic shelf represent the offshore counterpart of shoreface deposits recognised in outcrop as the product of typical forced regressions. Interestingly, muddy forced-regression deposits on the Adriatic shelf bear clear similarities with the late Holocene highstand mud wedge, suggesting a common depositional mechanism through lateral advection of fine-grained sediment. In this view, subaqueous progradation of muddy deposits occurs below storm wave base, with a subaqueous roll-over point that, during proceeding sea level fall, likely positioned at decreasing distance from the time-equivalent shoreline.