Identifying glacial influences on sedimentation in tectonically-active, mass flow dominated arc basins with reference to the Neoproterozoic Gaskiers glaciation (c. 580 Ma) of the Avalonian-Cadomian Orogenic Belt
- 作者：Shannon L. Carto ; scarto@utsc.utoronto.ca ; Nick Eyles
- 关键词：Neoproterozoic glaciations ; Avalonian-Cadomian Terranes ; Diamictites ; Snowball Earth ; Gaskiers glaciation ; Remobilized till
- 刊名：Sedimentary Geology
- 出版年：2012
- 期刊代码：81_00370738
- 类别：ear
- 出版时间：15 June, 2012
- 卷：261-262
- 期：Complete
- 页码：1-14
- 文件大小：3877 K
摘要
Neoproterozoic 鈥楢valonian-Cadomian鈥?volcanic arc basins once lay peripheral to Gondwana and are now found around the North Atlantic Ocean in New England, Atlantic Canada and northwestern Europe as 鈥榩eri-Gondwanan terranes.鈥?Their thick (up to 9 km) marine fills are dominated by turbidites, debrites (diamictites and variably graded conglomerates), slumps and olistostromes recording the dominance of mass flow processes in arc basins oversupplied with volcaniclastic sediment. Several diamictite horizons in these basins were identified as glacial tillites more than one hundred years ago on the basis of poor textural sorting, and the lack of any understanding of mass flow processes. An association with thin-bedded turbidite facies, then interpreted as glaciolacustrine varvites, was seen as evidence for widespread glacial conditions which is still the basis today of a near global 鈥楪askiers glaciation鈥?at c. 580 Ma, despite classic sedimentological work which shows that the 鈥榯illites鈥?and 鈥榲arvites鈥?of these basins are deep marine sediment gravity flow deposits. Only in two basins (Gaskiers Formation, Avalon Peninsula in Newfoundland, and the Konnarock Formation of Virginia) is a distal and regionally-restricted glacial influence on marine sedimentation identified from ice-rafted, striated dropstones in turbidites but terrestrial 鈥榠ce-contact鈥?facies are absent. As revealed in this study, terrestrial glacial facies may not have survived frequent volcanic activity such as seen today on glaciated active plate margin volcanoes such as Mount Rainier in Washington USA, and Cotopaxi Volcano in Ecuador where primary glacial sediment is frequently reworked by lahars, pyroclastic flows, debris avalanches and outburst floods. The weight of evidence presented in this study indicates that ice covers during the Gaskiers glaciation were not widespread across the Avalonian-Cadomian back arc basins; the deep marine Grenada Basin (Caribbean Sea) filled with turbidites, debrites (lahars) and debris avalanches from the adjacent Lesser Antilles Arc is identified here as a modern analogue for these ancient basins.