Journal of Paleontology, 92(5), 2018, p. 883–895 Copyright © 2018, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2017.95


Spirolites radwanskii n. igen. n. isp.: vermetid gastropod attachment etching trace from the middle Miocene rocky coast of the Paratethys, Poland


Alfred Uchman, Michał Stachacz, and Klaudiusz Salamon


Institute of Geological Sciences, Jagiellonian University, Gronostajowa 3a; 30-387 Kraków, Poland ⟨alfred.uchman@uj.edu.pl⟩; ⟨michal. stachacz@uj.edu.pl⟩; ⟨klaudiusz.salamon@doctoral.uj.edu.pl⟩


Abstract.—A new ichnogenus and ichnospecies, Spirolites radwanskii, is a spiral boring recognized in large limestone clasts deposited in a Miocene cliff-foot ramp. It is characterized by a semi-circular or inverted Ω-shaped cross section, gradually increasing width, gradual entrenching in the rock from the narrower side, consistent coiling direction, steep margin from the wider side, two-order annuli, and occasional truncation of the narrower side by the wider part. It is interpreted as a boring of vermetid gastropods, similar to the recent Dendropoma. Spirolites co-occurs with the bivalve borings Gastrochaenolites,mostly G. torpedo, sponge borings Entobia, and the spionid polychaete boring Caulostrepsis, which are typical of the Entobia ichnofacies. Spirolites was produced in very shallow, clean and warm sea waters.


Introduction


Etching traces are a characteristic group of borings produced by variable sessile epibiontic organisms colonizing lithic and skeletal hard substrates (see Bromley and Heinberg, 2006, for a review). Often, the etching traces are the only evidence of their producers. Therefore, they carry important information about benthic fossil assemblages, which can be used for paleoenvir- onmental interpretations. Many of the etching traces are ichno- taxonomically classified and well understood, such as Centrichnus (e.g., Neumann et al., 2015) or Podichnus (e.g., Bromley and Surlyk, 1973; Bromley, 2008; Robinson and Lee, 2008), but others are still awaiting closer characterization. In this paper, a new ichnogenus and ichnospecies of a large


and deep spiral etching trace is presented. It occurs in limestone boulders in one locality on the Miocene rocky shore of the Paratethys sea at the northern margin of the Carpathians Fore- deep in southern Poland (Fig. 1), where a similar but partly different etching trace was reported by Radwański (1969, 1970, 1977) and referred by him to serpulid polychaetes. We are not aware of any further studies on this trace fossil in this locality or elsewhere. New findings of well-preserved, similar specimens in the same locality and their good visualization enabled by rubber casts shed new light on their morphology and origin. The aim of this paper is to: (1) describe a new ichnogenus


and ichnospecies of the mentioned trace in the context of its paleoenvironmental conditions and associated borings, and (2) discuss its origin.


Geological setting


The Carpathian Foredeep Basin developed in front of the overthrusting Carpathian orogen during the Miocene


(e.g., Oszczypko, 2001). It was a part of the Paratethys sea and was connected to other foredeep basins of the Alpine orogenic system (e.g., Rögl, 1998). Its northern range is well marked by the Dalmatian type of rocky shore, on which bays, peninsulas, and islands developed on the Paleozoic and Mesozoic carbonate and clastic rocks, which is the southern cover of the Paleozoic massif of the Holy Cross Mountains; this rocky shore displays well-developed bioerosion (Radwański, 1964, 1965, 1969, 1970, 1977; Radwański and Górka, 2008). The southern shore of the basin, which developed on the Carpathian orogeny, is eroded or much more poorly exposed, but bioerosion is also present (Rajchel and Uchman, 1999). The new ichnotaxon was found in an inactive quarry


located on Zajęcza Góra hill at Skotniki, close to the line of the fossil rocky shore (Fig. 1; 50˚25'49.8"N, 20˚48'15.3"E). In the quarry, middle Miocene deposits of the Pińczów Formation lie discordantly on Mesozoic rocks. The lower part of the formation contains indistinctly bedded clast accumulations, which are almost 10m thick and fill a large furrow eroded in soft Cen- omanian sandstones. These deposits are considered a classic example of the transgressive succession of the Miocene (early Badenian) sea encroaching from the south on the southern margin of the Holy Cross Mountains (Radwański, 1969, 1973; Radwański and Górka, 2015). The clasts include gravels, cobbles, and half-meter bould-


ers and blocks (Figs. 1, 2). They are composed of hard Jurassic and Cretaceous limestones, marls, and cherts. Numerous clasts are bored by macro-organisms. Smaller clasts usually occur as matrix between larger clasts. Cementation of these deposits varies from loose rock to a hard-cemented conglomerate. Lat- erally, these deposits transition to sandy limestones and they are replaced at the top by red-algal limestones of the Pińczów


883


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124  |  Page 125  |  Page 126  |  Page 127  |  Page 128  |  Page 129  |  Page 130  |  Page 131  |  Page 132  |  Page 133  |  Page 134  |  Page 135  |  Page 136  |  Page 137  |  Page 138  |  Page 139  |  Page 140  |  Page 141  |  Page 142  |  Page 143  |  Page 144  |  Page 145  |  Page 146  |  Page 147  |  Page 148  |  Page 149  |  Page 150  |  Page 151  |  Page 152  |  Page 153  |  Page 154  |  Page 155  |  Page 156  |  Page 157  |  Page 158  |  Page 159  |  Page 160  |  Page 161  |  Page 162  |  Page 163  |  Page 164  |  Page 165  |  Page 166  |  Page 167  |  Page 168  |  Page 169  |  Page 170  |  Page 171  |  Page 172  |  Page 173  |  Page 174  |  Page 175  |  Page 176  |  Page 177  |  Page 178  |  Page 179  |  Page 180  |  Page 181  |  Page 182  |  Page 183  |  Page 184  |  Page 185  |  Page 186  |  Page 187  |  Page 188  |  Page 189  |  Page 190  |  Page 191  |  Page 192  |  Page 193  |  Page 194  |  Page 195  |  Page 196  |  Page 197  |  Page 198  |  Page 199  |  Page 200  |  Page 201  |  Page 202  |  Page 203  |  Page 204  |  Page 205  |  Page 206  |  Page 207