Large-Scale Seismogenic Deformation of A Carbonate Platform Straddling the Precambrian–Cambrian Boundary, Karatau Range, Kazakhstan
Large-Scale Seismogenic Deformation of A Carbonate Platform Straddling the Precambrian–Cambrian Boundary, Karatau Range, Kazakhstan
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DOI：
10.2110/jsr.2013.76
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发表时间：
2013-11
影响因子：
2
通讯作者：
C. Heubeck;G. Ergaliev;S. Evseev
中科院分区：
文献类型：
--
作者：
C. Heubeck;G. Ergaliev;S. Evseev
位于哈萨克斯坦南部Malyi Karatau山脉的Ediacaran Kyrshabakty组Berkuty成员位于世界上最大的早寒武纪沉积磷酸盐矿床之下。该单元厚5 ~ 30 m，展露走长约40 km，是由半固化碳酸盐岩区域地震变形形成的复杂碳酸盐岩单元。有三个细分。下部单元（单元1）厚约3-5 m，局部被米尺度的弯曲褶皱缩短，显示下伏硅质单元的逆冲和叠瓦作用；局部延伸由软沉积边界调节。中间单元（单元2）厚约2 - 5米，主要由直径达1米的角状到次圆形白云岩碎屑组成的巨角砾岩。上部单元（单元3）由同沉积低角度正断层切割而成的微生物层状白云岩、白云岩、平卵石砾岩组成，厚度可达3 m。第3单元顶部的水道化和岸缘滑坡之后是岩溶作用，之后形成了高能量、浅水、碳酸盐-磷酸盐海岸环境。我们将Berkuty段解释为至少一次大地震事件（Mb大于约8）变形的不完全和不均匀碳酸盐岩岩化台地的例子。下部单元的变形包括局部滑动、瓦叠和褶皱，而中部单元的变形是由于广泛的震动造成的原位崩解。区域性同震或震后早期软沉积物抬升（可能在海平面以上）导致了大面积的重力塌陷、快速的水系切割以及河岸塌陷和砾岩楔体对水系的充填。虽然在这个单元中观察到的每一个变形特征和地层元素都不能诊断出一个孕震起源，但露头的显著横向程度、与软沉积变形有关的广泛结构、它们的系统横向变动性以及与内部过程有关的地层，以一种示范的方式表明，单个软沉积变形事件可以在一个广阔的地区产生大量的特征。主要是由于微小的流变差异。
Abstract The Berkuty Member of the Ediacaran Kyrshabakty Formation in the Malyi Karatau Mountains of southern Kazakhstan immediately underlies some of the world's largest sedimentary phosphate deposits of earliest Cambrian age. This 5–30 m thick unit, exposed over > 40 km strike length, is a complex carbonate unit that was formed by regional seismic deformation of semiconsolidated carbonate. Three subdivisions are recognized. The lower unit (Unit 1), ∼ 3–5 m thick, is regionally shortened by meter-scale flexural folds, and shows thrusting and imbrication of underlying siliciclastic units; local extension is accommodated by soft-sediment boudinage. The middle unit (Unit 2), ∼ 2–5 m thick, consists largely of a megabreccia of angular to subrounded dolomite clasts up to a meter across. The upper unit (Unit 3), up to 3 m thick, consists of microbially laminated dolobindstone, dolorudstone, and flat-pebble conglomerate, cut by syndepositional, low-angle normal faults. Channelization and bank-margin slumping at the top of Unit 3 was followed by karsting, prior to the formation of a high-energy, shallow-water, carbonate–phosphatic coastal environment. We interpret the Berkuty Member as an example of an incompletely and unevenly lithified carbonate platform deformed by at least one large seismic event (Mb greater than approximately 8). Deformation of the lower unit included local sliding, imbrication, and folding, whereas the middle unit was deformed by in-situ disaggregation due to extensive shaking. Regional coseismic or early postseismic uplift of soft sediment, possibly above sea level, led to widespread gravitational collapse, rapid drainage incision, and drainage fill by bank collapse and conglomeratic wedges. While each of the deformational features and stratigraphic elements observed in this unit is not diagnostic of a seismogenic origin, the remarkable lateral extent in outcrop, the wide range of structures related to soft-sediment deformation, their systematic lateral variability, and the internal process-related stratigraphy demonstrates in an exemplary way the manner in which single soft-sediment deformation events can produce a large array of features over a broad area, largely due to minor rheological differences.