Petrographic features of tills as a tool in solving stratigraphical and palaeogeographical problems e A case study from Central-Eastern Poland Piotr Czubla a, * ,Slawomir Terpilowski b , Anna Orlowska b , Pawel Zieli  nski b , Tomasz Zieli  nski c , Irena Agnieszka Pidek b a Laboratory of Geology, Faculty of Geographical Sciences, L od z University, Narutowicza 88, PL-90-139 L od z, Poland b Department of Geoecology and Palaeogeography, Maria Curie-Sklodowska University, Kra snicka 2 d, PL-20-718 Lublin, Poland c Institute of Geology, Adam Mickiewicz University, Mak ow Polnych 16, PL-61-606 Pozna n, Poland article info Article history: Received 30 March 2017 Received in revised form 8 August 2017 Accepted 9 August 2017 Available online xxx Keywords: Lithostratigraphy Petrographic analysis Tills Indicator erratics Middle Pleistocene Poland abstract Lithostratigraphical correlation of tills in Poland is most often carried out on the basis of petrographic analysis of fine gravel fraction (<10 mm). The authors have undertaken the methodically more advanced studies of indicator erratics in the fraction >20 mm of tills from Central-Eastern Poland. Samples were taken in the sites, the stratigraphy of which was previously well recognized. Based on the proportions between erratics derived from different regions of Fennoscandia, and their calculated theoretical boulder centres, two main lithotypes of tills of Middle Pleistocene age are distinguished: A and B. Lithotype A is assigned to Elsterian (the South Polish Complex e Sanian 2 e MIS 12), lithotype B is considered to be characteristic of Saalian (the Middle Polish Complex). Within litothype B there are distinguished two sublithotypes B-1 and B-2, which can be linked to the advances of Fennoscandian Ice Sheet during MIS 8 (Older Saalian) and MIS 6 (Younger Saalian). The results of the research reveal that the changes of erratics assamblages in tills, deposited during the successive ice-sheet advances in Central-Eastern Poland, reproduce a trend that has been ascertained earlier in the sites located approx. 200 km further west in Central Poland and 600 km in Northern Germany, where their stratigraphic position is not so clear-cut. The general trend of changes in all three areas is the same, but the petrographic composition of tills of the same age varies along the former glacier front. The results indicate the advisability of using a modified, more appropriate methodology in the analysis of indicator erratics occurring in tills. We recommend that the calculation of Theoretical Boulder Centres (TBC) should be based only on crystalline (igneous and metamorphic) erratics. They are strongly resistant ones, therefore the lithostratigraphic correlation of tills of various weathering degree is more reliable. © 2017 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction Correct interpretation of the stratigraphy of tills is a key research problem in Quaternary geology. Absolute dating of tills is impos- sible due to the lack of appropriate methodology. The attempts to use luminescence analyses (TL, OSL, IRSL) for till dating proved to be completely ineffective and have been abandoned (cf. Aitken, 1985; Bluszcz, 2000; Fuchs and Owen, 2008; Munyikwa, 2014). At the most, absolute or relative (e.g. palynological) dating of the deposits underlying and/or overlaying a glacial series may be useful to bracket the time of till deposition. It is also difficult to correlate the isolated patches of glacial tills occurring at very similar heights above sea level in scattered and generally small, shallow exposures. It is worth noting that the conditions of subglacial and termino- glacial deposition permit synchronous formation of deposits in very different hypsometric positions. Even if a vast, horizontal and continuous till layer has been deposited in a region, it is unlikely that it has been preserved due to intensive fluvial erosion and redeposition occurring after ice-sheet retreat. Due to limited possibilities of determining the relative age, and all the more absolute age of tills, attempts are made to find the methods for their correlation. For this purpose, lithostratigraphic * Corresponding author. E-mail address: piotr.czubla@geo.uni.lodz.pl (P. Czubla). Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint http://dx.doi.org/10.1016/j.quaint.2017.08.028 1040-6182/© 2017 Elsevier Ltd and INQUA. All rights reserved. Quaternary International xxx (2017) 1e14 Please cite this article in press as: Czubla, P., et al., Petrographic features of tills as a tool in solving stratigraphical and palaeogeographical problems e A case study from Central-Eastern Poland, Quaternary International (2017), http://dx.doi.org/10.1016/j.quaint.2017.08.028