Palaeosols as indicators of geomorphic stability in two Old Red Sandstone alluvial suites, South Wales
Palaeosols as indicators of geomorphic stability in two Old Red Sandstone alluvial suites, South Wales
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DOI：
10.1144/gsjgs.150.6.1109
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发表时间：
1993-11
影响因子：
2.7
通讯作者：
S. Marriott;V. Wright
中科院分区：
文献类型：
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作者：
S. Marriott;V. Wright
在南威尔士南部的迪费德，晚志留世-早泥盆世的冲积层摩尔悬崖组和鼠岛泥岩（淡水西组）中有丰富的古土壤（化石土壤）。古土壤出现在季节性半干旱气候下洪泛平原上沉积的厚泥岩中，代表了变性土型土壤。简单、单一的剖面很少，大多数泥岩间隔显示出复杂的叠印剖面。然而，在所研究的两个单元中，古变性土之间存在着重大差异。摩尔悬崖组包含较厚的洪泛平原间隔，有频繁侵蚀和早期土壤层再活化的证据。相关的粗河道沉积物主要代表短暂的河流。冲积系统是不稳定的，闪光的，易于广泛剥离存储洪泛区沉积物。Arroyos（不稳定的短暂流通道）可能在此期间开发。任何海洋对土壤发育的影响的证据是失踪和以前的猜测，形成可能代表沉积在一个上潮间带或潮上系统不支持。鼠岛泥岩代表了一个完整的对比，因为很少或根本没有剥离河漫滩沉积物。河道沉积物通常为向上变细型，代表更稳定、低弯曲度的河道，并伴有短暂的河流洪水。通过整合古土壤，可以更详细地描述这些单元的地貌历史。与当代流域的比较表明，气候的变化是两个单位之间的差异，更频繁和更严重的风暴发生在老鼠岛泥岩沉积的可能原因。
Palaeosols (fossil soils) are abundant in the alluvial late Silurian–early Devonian Moor Cliffs Formation and Rat Island Mudstone (Freshwater West Formation) of south Dyfed, South Wales. The palaeosols occur in thick mudstones deposited on floodplains under a seasonal, semi-arid climate, and represent Vertisol-type soils. Simple, single profiles are rare and most of the mudstone intervals exhibit complex overprinted profiles. However, a major difference exists between the palaeo-Vertisols in each of the two units studied. The Moor Cliffs Formation contains thick floodplain intervals with evidence of frequent erosion and reactivation of earlier soil horizons. The associated coarser channel deposits mainly represent ephemeral streams. The alluvial system was unstable, flashy and prone to extensive stripping of stored floodplain sediment. Arroyos (unstable ephemeral stream channels) probably developed during this interval. Evidence for any marine influence on soil development is missing and previous speculations that the formation may represent deposition in an upper-intertidal or supratidal system are not supported. The Rat Island Mudstone represents a complete contrast in that there was little or no stripping of floodplain sediments. The channel deposits are typically of the fining-upwards type representing more stable, low sinuosity channels and with ephemeral-stream floods. By integrating the palaeosols, a more detailed picture of the geomorphic history of these units can be formulated. Comparison with contemporary drainage basins indicates that a change in climate was a possible cause for the differences between the two units, less frequent and more severe storms occurring during the deposition of the Rat Island Mudstone.