Present address: Center for Coastal and Ocean Mapping/Joint Hydrographic Center, University of New Hampshire, 24 Colovos Road, Durham, NH 03824, USA.
Microstratigraphy of a Miocene layered phosphatic pebble from the western margin of South Africa
Article first published online: 22 OCT 2012
© 2012 The Authors. Journal compilation © 2012 International Association of Sedimentologists
Volume 60, Issue 3, pages 666–678, April 2013
How to Cite
Wigley, R. A. and Compton, J. S. (2013), Microstratigraphy of a Miocene layered phosphatic pebble from the western margin of South Africa. Sedimentology, 60: 666–678. doi: 10.1111/j.1365-3091.2012.01355.x
- Issue published online: 18 MAR 2013
- Article first published online: 22 OCT 2012
- Manuscript received 23 January 2012; revision accepted 17 July 2012
- Continental shelf;
- Sr isotopes
Detailed microstratigraphy and geochemistry of a single-layered phosphatic pebble from the Southern Rocky Plateau at the Head of the Cape Canyon on the western margin of South Africa are utilized to reveal a complex interplay between deposition, erosion and authigenesis in the Miocene. The phosphatic pebble has three micrite and carbonate fluorapatite cemented layers separated by Fe-rich hardground surfaces. The layers contain a diverse grain assemblage of reworked glauconite, phosphorite, detrital quartz and biogenic carbonate. Overlapping Sr-isotope derived ages of point-drilled samples from the three layers range from 19·1 to 17·6 Ma, although a single point near the outer edge of the uppermost layer has a Sr age of 12·8 to 10·4 Ma, and a reworked bivalve shell fragment from the middle layer has a Sr age of 26·3 to 24·6 Ma. The microstratigraphy of the phosphatic pebble provides evidence of multiple Baturin cycles, where periods of deposition and carbonate fluorapatite authigenesis are followed by reworking, erosion and precipitation of iron oxide hardground surfaces. The condensed microstratigraphy of the pebble is consistent with the regional depositional history of the area and indicates significant fluctuations in the depositional environment related to changes in sea-level, sediment supply and upwelling along the western margin of southern Africa during the early to middle Miocene.