Reciprocal Changes In Foreset To Bottomset Facies In A Gilbert-Type Delta: Response To Short-Term Changes In Base Level
Reciprocal Changes In Foreset To Bottomset Facies In A Gilbert-Type Delta: Response To Short-Term Changes In Base Level
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吉尔伯特型三角洲前积层到底积相的相互变化：对基准面短期变化的响应
DOI：
10.2110/jsr.2014.83
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发表时间：
2014
影响因子：
2
通讯作者：
W. Nemec
中科院分区：
文献类型：
--
作者：
Katarina Gobo;M. Ghinassi;W. Nemec
摘要 报道了希腊科林斯裂谷南海岸更新世中期吉尔伯特型伊利亚斯三角洲的详细沉积学研究结果。研究表明，三角洲前积沉积物以浊积岩为主的相组合（TFA）的发育与倾斜的三角洲边缘几何形状有关，这意味着由于基准面下降或稳定而导致三角洲前缘可容纳性的不足。当基准面上升且三角洲边缘几何形状变为 S 形时，就会形成以碎屑为主的前积物组合 (DFA)，这意味着三角洲前缘可容纳性的增加。同期前积和前积与三角洲底积沉积的比较表明，相组合呈现相反的相互变化模式，前积TFA沉积对应于三角洲英尺DFA沉积，前积DFA沉积对应于三角洲英尺TFA沉积。 TFA和DFA相组合的这种相互交替归因于短期基准面变化驱动的三角洲前缘适应性变化，由于系统自生变异和区域气候波动，相记录中存在一定程度的“噪音”。这项研究为吉尔伯特型三角洲系统中水下沉积物扩散随基准面变化而变化的模式提供了新的线索。这也为在其他类似的古代三角洲的详细相分析的基础上识别此类变化的隐藏记录提供了新的可能性。
Abstract Results of a detailed sedimentological study of the mid-Pleistocene Gilbert-type Ilias delta at the southern coast of the Corinth Rift, Greece, are reported. The study indicates that the development of a turbidite-dominated facies assemblage (TFA) of delta foreset deposits is associated with an oblique delta-brink geometry, which signifies a deficit of delta-front accommodation due to the falling or stable base level. A debrite-dominated assemblage (DFA) of foreset deposits forms when the base level is rising and the delta-brink geometry becomes sigmoidal, signifying an increase in delta-front accommodation. The comparison of coeval foreset and toeset to bottomset deposits in the delta indicates a reverse pattern of reciprocal changes in facies assemblages, with the foreset TFA deposits corresponding to delta-foot DFA deposits, and with the foreset DFA deposits corresponding to delta-foot TFA deposits. This reciprocal alternation of TFA and DFA facies assemblages is attributed to changes in the delta-front accommodation driven by short-term base-level changes, with a degree of “noise” in the facies record due to the system autogenic variability and regional climatic fluctuations. The study sheds a new light on the changing pattern of subaqueous sediment dispersal in Gilbert-type deltaic systems in response to base-level changes. It also indicates a new possibility for the recognition of a hidden record of such changes in other similar ancient deltas on the basis of their detailed facies analysis.