Original Research Dynamics and genesis of calcic accumulations in soils and sediments of the Argentinean Pampa Alsu Kuznetsova a,n , Olga Khokhlova b a Department of Renewable resources, University of Alberta Edmonton, Canada, T6G 2E3 b Institute of Physicochemical and Biological Problems of Soil Science RAS Puschino, Moscow region, 142290, Russia article info Article history: Received 6 December 2013 Received in revised form 18 September 2014 Accepted 19 November 2014 Available online 6 July 2015 Keywords: Carbonate accumulations Gypsum accumulations Pedogenic rhizoliths Tosca abstract Micromorphology of calcic accumulations (calcite, whewellite and gypsum) and geochemical indices were considered as indicators of genesis and evolution of pedogenic accumulations in soils and paleosediments of the Argentinean Pampa. Two groups of separate and independent calcic accumula- tions were studied using scanning electron microscopy: (i) in situ Argiudolls, reflecting the current soil formation; (ii) in the layers of calcrete (locally named tosca), reflecting the past environments and conditions of these layers sedimentation. New pedogenic gypsum accumulations in Argiudolls were described and possible ways of their formation were suggested. Combined analyses of morphology of carbonate accumulations and geochemical indices in different horizons of Argiudolls and layers of tosca showed that the tosca is paleopedocomplex with complicated formation history. Influence of current environment on tosca morphology is absent, so it is possible to use these pedofeatures for paleor- econstructions in further studying. & 2015 International Research and Training Centre on Erosion and Sedimentation/the World Association for Sedimentation and Erosion Research. Published by Elsevier B.V. All rights reserved. 1. Introduction Argiudolls of the Argentinean Pampa are forming on a complex pedosedimentary sequences of paleosols and sediments of diverse origins (Amiotti et al., 2001; Zarate et al., 2009; Kemp et al., 2006). Marine sediments, usually calcareous, were deposited on fine paludal silts 128ka ago (Kemp et al., 2006). These marine sediments were then overlain by fine silt deposits of fluvial/paludal genesis (before 23ka ago), after that, the eolian loess deposits were formed during several sedimentary pulses since the Late Pleistocene (Pye, 1987). In the Early Holocene in an arid climatic conditions, active eoline and fluvial erosion processes dominated in the region (Amiotto et al., 2001; Blanco & Stoops, 2007) and the carbonate paleosurface was exhumed. In the Middle Holocene, a loess deposit buried the carbonate paleosur- face again (Amiotti et al., 2001) and with stabilization of loess mantle, pedogenesis and sedimentation processes (pulses eolian accretion) occurred simultaneously (Kemp et al., 2006). Because of this, the parent material for the surface soils (Argiudolls) is carbonate free loess (a mixture of eolian and fluvially or colluvially reworked material), but underlain by the carbonate layers which may have an influence on soil formation (Paez & Prieto, 1990; Zarate & Blassi, 1991; Rabassa, 1990; Amiotti et al., 2001). The underlying layer for the majority of soils in the Argentinean Pampa is an almost continuous calcrete, locally termed tosca (2Ckm- petrocalcic horizon), that has great variability in depth, structure, degree of indurations, hardness and CaCO 3 content (Blanco & Stoops, 2007). Because of its high variability it is difficult to give an average characteristic of the tosca (Pazos & Mestelan, 2002). Macromorpholo- gical structure of this horizon varies with depth and from site to site: tosca can be massive, layered or laminar; silica materials may also be embeded in a calcareous matrix (Buschiazzo, 1986, 1988; Pazos, 1990; Bedogni, 1996; Blanco & Stoops, 2007). High variability in CaCO 3 content of the tosca layers was shown previously (Pazos, 1990; Bedogni, 1996; Amiotti et al., 2001) with CaCO 3 contents ranging from 7.5 to 52.4% for different sites. Sometimes the weathered tosca can be very friable, with a very fine blocky structure and strong evidence of modern processes such as clay illuviation and CaCO 3 dissolution and recrystallization. In these cases, roots can freely develop through the tosca. But strongly indurated layers occur which cannot be penetrated by roots and a dense root mat forms on top of the tosca. Genesis of tosca is still not well understood; most probably it is a thick Plio-Pleistocene layer formed by different cycles of sedimentation and with upper part was transformed during Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ijsrc International Journal of Sediment Research http://dx.doi.org/10.1016/j.ijsrc.2014.11.002 1001-6279/& 2015 International Research and Training Centre on Erosion and Sedimentation/the World Association for Sedimentation and Erosion Research. Published by Elsevier B.V. All rights reserved. n Corresponding author at: Soil Chemistry and Environmental icrobiology Research Laboratory, Department of Renewable Resources, University of Alberta, 4-53 South Academic Building Edmonton, Alberta, Canada, T6G 2G7. Tel.:+1 780 492 4422. E-mail addresses: alsu@ualberta.ca (A. Kuznetsova), alexkh1@sares-net.ru (O. Khokhlova). International Journal of Sediment Research 30 (2015) 179–189