Depositional styles of Early Ediacaran terrestrial volcanosedimentary succession in Gebel El Urf area, North Eastern Desert, Egypt
Depositional styles of Early Ediacaran terrestrial volcanosedimentary succession in Gebel El Urf area, North Eastern Desert, Egypt
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DOI：
10.1016/j.jafrearsci.2009.11.002
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发表时间：
2010-06-01
影响因子：
2.3
通讯作者：
El Gameel, Khaled
中科院分区：
文献类型：
--
作者：
Eliwa, Hassan;Breitkreuz, Christoph;El Gameel, Khaled
位于乌尔加达西北100公里处的Gebel El Urf火山-沉积岩系暴露在北纬27度45' 30 "和27度51' 00“之间，东经32度49' 00”和32度59' 00”之间。Gebel El Urf的火山沉积序列出现在一个由不同的晚元古代深成岩复合体主导的地区。与不同花岗岩类单元的侵蚀和侵入接触已被确定。从富含晶体和贫岩屑的熔结凝灰岩中获得了两个SHRIMP年龄，分别为615 +/- 4 Ma和616.0 +/-5.4Ma，将这里描述的山间盆地的演化置于Ediacaran早期。在Gebel El Urf地区，一个东南向的倾斜序列（Gebel El Urf序列，GUS）约。厚2000米，位于带有侵蚀不整合的粗粒花岗岩上。该地区存在的另一个层序（Wadi Kefri层序，WKS）代表火山成因沉积物，其表现出一定程度的变质叠印。在古近系中，划分出14种岩相类型，划分为7个岩相组合。GUS可细分为四个沉积阶段，始于冲积扇相厚的块状碎屑支撑砾岩（圆形碎屑高达100 cm）。GUS继续以泥质到砂质浊积岩湖泊和桑迪辫状河沉积，偶尔有火山玻璃碎片（现为伊利石）（第2阶段）。GUS的上半部分主要是火山沉积物，从50米厚的交替熔结凝灰岩和同火山沉积物质流沉积物开始，后者与蒸汽岩浆喷口有关（第3期）。随后是一系列较厚的焊接至非焊接熔结凝灰岩，其中有一个20 m厚的粗圆形砾岩夹层（第4阶段）。在湿润的气候条件下，GUS的发育表现出从高能沉积到低能沉积再到低能沉积的循环。第二阶段以盆肩伸展和断陷为特征。据推测，构造活动也导致了河流的筑坝，形成了一个汗水湖。火山活动在第二阶段以小的喷口开始，在第四阶段以大量的喷发结束。(C)2009爱思唯尔有限公司版权所有。
Located 100 km northwest of Hurghada, the volcanosedimentary successions of Gebel El Urf is exposed between latitude 27 degrees 45' 30 '' and 27 degrees 51' 00 '' N and longitude 32 degrees 49' 00 '' and 32 59' 00" E. The volcanosedimentary successions of Gebel El Urf crop out in an area dominated by different Late Proterozoic plutonic complexes. Both, erosional and intrusive contacts with different granitoid units have been identified. Two SHRIMP ages have been obtained from crystal-rich and lithic-poor ignimbrites yielding 615 +/- 4 and 616.0 +/- 5.4 Ma placing the evolution of the inter-montane basins, described here, into the Early Ediacaran. In the Gebel El Urf area, a southeastward dipping succession (Gebel El Urf Succession, GUS) of ca. 2000 in thickness rests on coarse-grained granite with an erosional unconformity. Another succession present in the area (Wadi Kefri Succession, WKS) represents volcanogenic sediments which exhibit degrees of metamorphic overprint. In places, it is presumed to be older than GUS.For the GUS, 14 lithofacies types have been differentiated and grouped to seven lithofacies associations. Subdivided into four depositional phases, GUS starts with a thick, massive and clast-supported conglomerate of alluvial fan facies (well-rounded clasts up to 100 cm). GUS continues with pelitic to sandy-turbiditic lacustrine and sandy braided river deposits with occasional volcanic glassy fragments (now illite) (Phase 2). The upper half of the GUS is dominated by volcanic deposits, starting with a 50 m thick package of alternating ignimbrites and synvolcanic sedimentary mass flow deposits, the latter related to phreatomagmatic vents (Phase 3). A thick succession of welded to non-welded ignimbrites follows, with one 20 m intercalation of coarse well-rounded conglomerates (Phase 4). Numerous SiO2-rich and - poor dykes and sills emplaced into GUS.The GUS development displays a cycle from high to low energy sedimentation and back, under humid climatic conditions. Phase 2 was characterized by extension and down faulting of basin shoulders. Tectonic activity presumably also led to damming of the river creating a sweat water lake. Volcanism commenced with small vents during Phase 2 and terminated with voluminous eruptions in Phase 4. (C) 2009 Elsevier Ltd. All rights reserved.