Late Quaternary vadose carbonate diagenesis in coastal and desert dune and beach sands: is there a palaeoclimatic signal?

Abstract

A study of the variation in cement amounts in aeolianite and sandy beach calcarenites that range in age from Holocene to Last Interglacial is used to assess whether a palaeoclimatic control on vadose diagenesis can be identified. Examples are taken from modern-day arid to subhumid settings and represent a geographical distribution ranging from Libya and Oman, to the Mediterranean, the Caribbean and Mexico. The results indicate that a palaeoclimatic signal can be identified in some deposits. However, in other sediments there is substantial variability in mean cement abundance within deposits as well as between these sand bodies. Moreover, many of the better cemented sediments are located in areas where there is accelerated diagenesis, such as in the sea spray zone, close to the groundwater table or near to a palaeosurface, rather than in climatically wet regions. The inference is that palaeoclimatic interpretations are substantially complicated by other factors that affect diagenetic processes and change. Therefore caution is needed when studying the role of climate in vadose diagenesis in the light of the effects of other intrinsic and extrinsic controls. This paper does not aim to provide a definitive comparison of sites from different climatic zones. The approach taken here is: (a) to see if there is an overall palaeoclimatic signal in the samples studied; (b) to use examples to illustrate how explanations/controls other than those relating to climate can account for the variabilities observed; and (c) if there is a climatic effect, to see if it is the main over-riding control on vadose diagenesis. The conclusions drawn from this research highlight that it is possible to misinterpret evidence if the study is approached with preconceived notions of simplistic relationships between diagenesis and climate.

Polygenic Red Calcic Soils in Coastal Middle Palaeolithic Environments, Israel: Taxonomy and Pedosedimentary Reconstructions

“…He also attempted to distinguish between phreatic and vadose meteoric type of digenesis. However, calcareous cement in aeolianites is strongly variable at a local level (McLaren and Gardner 2004), depending on texture, plant cover, exposure to sea spray, etc.…”

Introduction: Geochemical Sediments in Landscapes

“…Calcium carbonate, gypsum or halite cementation of near-coastal and desert dune sands may, for example, signifi cantly enhance their preservation potential once they are transformed to aeolianite (e.g. McKee, 1966;Gardner, 1998;McLaren and Gardner, 2004;see McLaren, Chapter 5). Similarly, the induration of fl uvial terrace sediments through the development of pedogenic or groundwater calcretes may increase their resistance to erosion and reworking and hence preserve key palaeohydrological evidence (e.g.…”

Aeolianite

“…Dravis (1996) studied subaerially exposed oolitic sands that had become case-hardened in the upper 10-20 cm in less than 10 years as a result of 'fabric selective dissolution and associated low-Mg calcite cementation in the freshwater vadose zone ' (p. Magaritz et al, 1979;Gardner, 1988;McLaren and Gardner, 2004). This indicated that the cements were derived locally from the dissolution of the aragonitic clasts making up the sands.…”

“…McLaren and Gardner (2004) attempted to assess whether a macroscale palaeoclimatic control on vadose diagenesis can be identifi ed. McLaren and Gardner (2004) found that a palaeoclimatic signal could be recognised in some deposits. McLaren and Gardner (2004) found that a palaeoclimatic signal could be recognised in some deposits.…”

“…As a consequence, meteoric diagenesis on Joulters Cay, northern Bahamas, is fast and widespread (Halley and Harris, 1979), whereas on Hogsty reef, southern Bahamas, it is negligible (Pierson and Shinn, 1985). However, McLaren and Gardner (2004) found that sandy deposits from climatically wet regions did not always contain the most cement; instead it was those sediments that were located in zones of accelerated diagenesis, such as the sea-spray zone, close to the groundwater table or near to a palaeosurface. Hussein (2002), working in the arid Gulf Coastal Province in eastern Saudi Arabia, studied Quaternary coastal aeolianites that were weakly cemented and still in their original depositional framework.…”