A Middle Pleistocene palaeovalley-fill west of the Malvern Hills
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New sections and detailed mapping of the Pleistocene deposits on the west side of the Malvern Hills show that the area occupied by ice during a pre-Devensian glaciation was greater than previously envisaged. The deposits associated with the glaciation occur in a palaeovalley and comprise lacustrine silts and clays and till. They are considered to be of Anglian age as they are locally overlain non-sequentially by newly described silts of probable late Anglian to early Hoxnian age, the most westerly record of such deposits in southern Britain. Gravels underlying the glacigenic deposits are thought to have been laid down by a southward-flowing river either earlier in the Anglian or during a preceding stage. Deposits formed during two post-Hoxnian episodes of gelifluction are correlated with similar deposits on the east side of the Malvern Hills. The younger gelifluctate is probably late Devensian in age and the older, much dissected deposit is attributable to periglacial processes during an earlier Devensian or Wolstonian cold period.Protolith
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Banded iron formation
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Abstract Four types of Pleistocene clastic dykes are present in a variety of sediments in the King Valley. They include till dykes injected into bedrock fractures produced by overriding ice; gravel dykes in bedrock openings that appear to be eroded and stream‐filled bedding planes; gravel dykes in weathered limestone formed as fillings of dolines and solution tunnels; and gravel dykes in unconsolidated Pleistocene deposits. Gravel‐filled, wedge‐shaped structures in Pleistocene tills and outwash gravels are the most numerous dykes and most occur in three distinct swarms. The dykes of one swarm have along‐slope strikes and are formed on laminated glacial lake sediments that have been subjected to landsliding; the dyke structures apparently formed as tensions cracks caused by the landslides. The other two swarms have downslope strikes and are associated with sediments deposited in ice contact environments. Although these dykes resemble ice wedge casts, they probably formed syndepositionally by the collapse and deformation of the sediments as buried ice melted. Key Words: clastic dykesgravel dykesPleistocenetension crackstill dykeswedge structureswestern Tasmania Notes Present address: University College, The Australian Defence Force Academy, Campbell, ACT 2600, Australia.
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During the last 10 m.y., the Nanga Parbat Haramosh Massif in the northwestern Himalaya has been intruded by granitic magmas, has undergone high‐grade metamorphism and anatexis, and has been rapidly uplifted and denuded. As part of an ongoing project to understand the relationship between tectonism and petrologic processes, we have undertaken an isotopic study of the massif to determine the importance of hydrothermal activity during this recent metamorphism. Our studies show that both meteoric and magmatic hydrothermal systems have been active over the last 10 m.y. We suggest that the rapid uplift of the massif created a dual hydrothermal system, consisting of a near‐surface flow system dominated by meteoric water and a flow regime at deeper levels dominated by magmatic/metamorphic volatiles. Meteoric fluids derived from glaciers near the summit of Nanga Parbat were driven deep into the massif along the transpressional faults causing δ 18 O and δD depletions in the gneisses and marked oxygen isotopic disequilibrium between mineral pairs from the fault zones. The discharge of these meteoric fluids occurs in active hot springs that are found along the steep faults that border the massif. At deeper levels within the massif, infiltration of low δ 18 O magmatic fluids caused δ 18 O depletions in the gneisses within the migmatite zone. These low δ 18 O fluids were derived from the young (<4 Ma), relatively low δ 18 O granites (∼8‰c) that are found within the core of the massif. Geochronological evidence in the form of fission track and 40 Ar/ 39 Ar cooling ages and U/Pb ages on accessory minerals from the granites and gneisses provide a constraint on the timing of fluid flow in the surface outcrops we examined. Fluid infiltration in the migmatite zone rocks located along the Tato traverse was coeval with metamorphism, granite emplacement, and rapid denudation, in the interval 0.8–3.3 Ma. Finally, we infer from the presence of active hot springs that significant flow systems continue to be active at depth within the central portion of the Nanga Parbat‐Haramosh Massif.
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The eastern flank of Mt. Etna volcano rests on Pleistocene marine sediments, which unconformably cover the Apenninic–Maghrebian Chain units. A quantitative biostratigraphic analysis was carried out based on the calcareous nannofossil content of the Pleistocene deposits outcropping along the S and NE periphery of the volcano. Sediments were constrained to the MNN19e and MNN19f biozones, deposited from 1.2 to 0.589 Ma. According to the depth of deposition and the present altitude of the Pleistocene succession, uplift rates are estimated between 1.1 and 1.7 mm yr −1 for the northeastern sector of the Etna edifice, and between 0.36 and 0.61 mm yr −1 for the southern one. This inhomogeneous long‐term uplift rate affecting the Etna region, probably results from a buried thrust below the northern flank of Etna, which is related to the post‐Tortonian geodynamic evolution of NE Sicily.
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