Environmental and depositional controls on laminated freshwater carbonates: An example from the Roman aqueduct of Patara, Turkey Gül Sürmelihindi a , Cees W. Passchier a, ⁎, Orhan N. Baykan b , Christoph Spötl c , Paul Kessener d a Institut für Geowissenschaften, Universität Mainz, Becherweg 21, Mainz, Germany b İnşaat Mühendisliği Bölümü, Mühendislik Fakültesi, Pamukkale Üniversitesi, Denizli, Turkey c Institut für Geologie und Paläontologie, Universität Innsbruck, Innrain 52, Innsbruck, Austria d Department of Classical Archaeology, Radboud University, P.O. Box 9103, 6500 HD Nijmegen, Netherlands abstract article info Article history: Received 17 November 2012 Received in revised form 17 May 2013 Accepted 3 June 2013 Available online 11 June 2013 Keywords: Turkey Roman aqueduct Carbonate deposits Calcareous sinter Palaeoclimate Stable isotopes Archaeoseismology Patara Carbonate deposits in aqueducts are a new high-resolution data source for environmental changes during the time of the Roman Empire, notably in the fields of palaeoclimate and spring hydrology. In order to distinguish environmental effects from those related to depositional setting, laminated carbonate deposits were com- pared along the entire length of an ancient aqueduct channel at Patara, Turkey. The carbonate deposits, up to 80 mm in thickness, are composed of lamina couplets up to 1 mm thick of alternating porous microspar and dense, columnar sparite. The former formed in the dry, warm season and the latter in the wet, cool sea- son. The presence of biofilms seems to play a role in the development of the porous laminae. The relative im- portance of both lamina types depends also on the location within the aqueduct: dense, coarse-crystalline laminae dominate in steep sections of the aqueduct, while porous, fine-crystalline laminae are mostly found on gentle slopes. This is attributed to the flow velocity of the water, since fast flow on steep slopes hampers the development of biofilms. Carbonate microstructures can vary considerably down the line of a specific aqueduct; hence multiple sampling is needed along the channel in order to collect specimens suitable for detailed research. δ 18 O profiles show oscillations with increasing amplitude downstream reflecting rising water temperatures in the channel, while evaporation plays a minor, damping role on these oscillations. The periodicity of the δ 18 O values can be used to recognise annual layering in order to establish the number of years an aqueduct was operating. δ 13 C values are higher in open masonry channel sections than in ceramic pipes, probably due to stronger degassing of CO 2 in the open channel. Carbonate deposits in Roman aque- ducts hold high promises as seasonally resolved archives of hydrology and climate and, possibly, of earthquakes. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Laminated freshwater carbonate deposits such as tufa, travertine and speleothems have been the focus of many studies in recent years (Pentecost, 2005; Alonso-Zarza and Tanner, 2010; Pedley and Rogerson, 2010; Fairchild and Baker, 2012). These carbonate deposits are thought to form in flowing water, recording changes in climate, aquifer charac- teristics, vegetation cover and other environmental factors. An analysis of the structure, trace element and stable isotope composition of such deposits, in combination with dating, can therefore yield relevant data on long-term environmental and ecological changes over periods of 10 2 to 10 6 years (e.g. Sasowsky and Mylroie, 2004; Pentecost, 2005; Pedley and Rogerson, 2010). As such, freshwater carbonate deposits are of great importance to understand natural changes on a variety of timescales, which may be distinguished from anthropogenic effects. Some freshwater carbonates show layering defined by variations in colour, microstructure and/or composition. This layering is usually interpreted as an effect of changes in water composition, temperature and/or biological activity (Pentecost, 2005; Pedley and Rogerson, 2010). In many deposits, part of this layering is highly regular and com- monly interpreted as annual (Matsuoka et al., 2001; Ihlenfeld et al., 2003; Kano et al., 2003, 2004; O'Brien et al., 2006; Brasier et al., 2011). Many other types and frequencies of laminae and layers occur on shorter or longer time scales. The main difficulty in unravelling the na- ture and origin of layering in freshwater carbonates is the complex en- vironment in which they form, and the many competing factors that can influence the microstructure and chemistry of these deposits. Recently, carbonate deposits in Roman aqueducts have been sug- gested as a potential high-resolution palaeo-environmental archive for the Mediterranean region and Western Europe (Carlut et al., 2009; Sbeinati et al., 2010; Carlut, 2011; Sürmelihindi et al., 2013). Aqueducts are one of the most impressive legacies of the Roman Empire. Typically built as long roofed masonry channels, these gravity-driven water transport systems brought water from springs, rivers and lakes to cities, Palaeogeography, Palaeoclimatology, Palaeoecology 386 (2013) 321–335 ⁎ Corresponding author. Tel.: +49 61313923217; fax: +49 61313923863. E-mail address: cees.passchier@uni-mainz.de (C.W. Passchier). 0031-0182/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.palaeo.2013.06.002 Contents lists available at SciVerse ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo