Holocene calcrete crust deposits on the moraine of Batura Glacier, northern Pakistan
Article first published online: 21 DEC 2005
Volume 14, Issue 4, pages 368–377, December 2005
How to Cite
Waragai, T. (2005), Holocene calcrete crust deposits on the moraine of Batura Glacier, northern Pakistan. Island Arc, 14: 368–377. doi: 10.1111/j.1440-1738.2005.00492.x
- Issue published online: 21 DEC 2005
- Article first published online: 21 DEC 2005
- Received 4 January 2005; accepted for publication 29 August 2005.
- accelerator mass spectrometry 14C age;
- glacial stage;
- Karakoram Mountains
Abstract Calcretes can be observed on the surface of old moraines around Batura Glacier in the upper Hunza Valley, Karakoram Mountains, Pakistan. They develop as a calcareous crust cementing small gravels under boulders. In order to understand the genesis of the calcrete crust, a variety of methods were employed: (i) study of mineralogy and geochemistry of a calcrete crust precipitated on the lateral moraine using X-ray diffractometer and electron probe microanalysis; (ii) analysis of solute chemistry of surface water and ice bodies around the Batura Glacier; and (iii) accelerator mass spectrometry 14C dating of the crust itself. The results indicate that the calcrete crust has definite laminated layers composed of a fine-grain and compact calcite layer, and a mineral fragment layer. The chemical composition of the calcite layer is approximately 60% CaO and 1% MgO. The mineral fragment layer consists of rounded grain materials up to 0.2 mm in diameter. It shows a graded bedding structure with fine grains of quartz, albite and muscovite. Meanwhile, as the Paleozoic Pasu limestone is distributed around the terminal of Batura Glacier, Ca cations dissolve in the melt water of the glacier. Accordingly, the calcrete crust is precipitated by decreases in CO2 partial pressure from glacier ice and evaporation of the melt water, including high concentration of Ca2+ at ephemeral streams and small ponds stagnating between the moraine and glacial ice. On the basis of the AMS 14C age, the calcrete is considered to have formed approximately 8200 calibrated years bp under the Batura glacial stage.