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Available online at http://geology.uaic.ro/auig/ AUI Analele Stiintifice ale Universitatii “Al. I. Cuza” din Iasi GEOLOGIE Seria Geologie 62 (1–2) (2016) 29–46 Oligocene fish fauna and sedimentological particularities of the Bituminous Marls of the Vrancea Nappe, Eastern Carpathians, Romania Dorin Sorin Baciu1, Ionuţ Grădianu2, Anca Seserman1, Tony Cristian Dumitriu1 1 “Alexandru Ioan Cuza” University of Iaşi, Department of Geology, 20A Carol I Blv, 700505 Iaşi, Romania 2 Natural Sciences Museum Piatra Neamţ, 26 Petru Rareș street, Piatra Neamț, Romania Abstract The study was conducted in the Bistriţa Half-Window, Vrancea Nappe, in the Bituminous Marls, which is an intriguing entity, both ichthyological and sedimentological. Formally considered a monotonous lithostratigraphic unit, at a closer look, this organic matter rich formation contains numerous lithofacies such as current and wave ripples, cross-bedding, hummocky and swaley- like cross-stratification, clastic dykes, intraformational slump folds among others. Therefore, the high level of bottom current activity seems somehow in contradiction with previous ideas about the cause for preservation of organic matter. In this study, we present the taxonomy of 13 fish fossils species. The palaeoecology of the fish assemblage is reconstructed based on present-day fish fauna bathymetrical comparisons. Furthermore, some palaeobathimetric observations were made in conjunction with sedimentary features. Keywords: fish fossils, Bituminous Marls, Oligocene, Vrancea Nappe, Eastern Carpathians. 1. Introduction The studied outcrops are located in Vrancea Nappe (Marginal Folds Nappe, The aims of this study are: 1) to sensu Săndulescu, 1984), one of the present the taxonomic composition of fish outermost nappe of the Moldavide, which fossils species discovered in the Bituminous is a geostructural complex unit, consisting Marls studied sections; 2) to reconstruct of several tectonic nappes, namely from the palaeoecology and palaeobathimetry west to est: Teleajen, Macla, Audia, of fish assemblage based on ecology of Tarcău, Vrancea, and Pericarpathian. They recent fish fauna and sedimentological represent the infilling of the Moldavide observations. Basin, that was deformed in Miocene © 2016 Ed. Univ. „Al. I. Cuza” Iași. All rights reserved Corresponding author’s e-mail: [email protected] 30 Baciu D.S. et al. tectogeneses (Săndulescu, 1984). The Miocene isolation of the Paratethys from Vrancea Nappe is cut into the outer margin the Mediterranean Sea after the collision of Tarcău Nappe, in tectonic half- between Africa and Eurasia plates (Rögl, windows, Bistriţa being the second one 1998; Steininger and Wessely, 1999; from north to south of the Eastern Popov et al., 2002), which is described as Carpathians (Băncilă, 1958; Dumitrescu, an anoxic, euxinic, or both event. 1952). The structure of this nappe consists The Bituminous Marls Formation of many faulted folds, which are detached (BM) and their equivalents (Heller along the middle member of the Bisericani Mergelkalk, Dynow Marls) are considered Formation, the grey-greenish mudstones. It to be sedimented during the maximum is structurally interposed between Tarcău isolation of the Parathethys (NP23), being and Pericarpathian Nappes. Close to the a marker level of Oligocene sedimentary nappe front, Doamna-Horaiţa Anticline succession (Rögl, 1998; Steininger and exposes the oldest deposits of this unit. Wessely, 1999; Popov et al., 2002), al- though the age seems to be “not older 2. Stratigraphic setting than late Chattian” (Guerrera et al., 2012). The Oligocene deposits from Vrancea The Moldavide Basin evolved after Nappe are represented by Lower Menilites, the closure of Ceahlău-Severin Ocean, Bituminous Marls, Lower Dyssodilic from Cretaceous to Late Eocene, as part Shales with Kliwa Sandstone, Upper of the Tethys Ocean, and from Oligocene Dyssodilic Shales and Menilites, and on, as part of the Paratethys Sea, its Gura Şoimului Formation (known in the history being presented by Amadori et al. Romanian literature). (2012) and Guerrera et al. (2012), based on existing literature. For Oligocene, 3. Sedimentological observations Miclăuş et al. (2009) proposed a 2D cross section model showing a foreland basin The Bituminous Marls is a source system evolution after Cretaceous rock succession laterally extensive in the tectogeneses during which the Moldavide Basin of Romania, containing easternmost branch of the Alpine Tethys a wide variety of lithofacies, although was (Schmid et al., 2008) was closed. The former described as a monotonous unit of Vrancea Nappe sedimentation area was pelagic origin. It is in fact a heterolithic located on the basinward side of the deposit consisting of simple and com- forebulge area (Miclăuş et al., 2009). posite bed-sets with different sedimentary The deposits accumulation, in the structures from small scale fine lami- Moldavide Basin, lasted from Early Creta- nation, hummocky and swaley-like cross ceous to Middle-Late Miocene (Băncilă, stratification, wavy and lenticular bedding 1958; Dumitrescu, 1952; Ionesi, 1971; to large scale low angle cross strati- Săndulescu, 1984, 1988; Grasu et al., 1988; fication (Miclăuş et al., 2009; Miclăuş and Ștefănescu, 1995). The background black Schieber, 2014). These structures are the shale-type sedimentation was inprinted by results of different processes with low or two main events: Early Cretaceous Oceanic high energy, from hemipelagic to tractive, Anoxia Events (OAE) and Oligocene-Early and even debris flows. The full suite of AUI–G, 62, 1–2, (2016) 29–46 Oligocene fish fauna and sedimentological features of the Bituminous Marls, Vrancea Nappe 31 Fig. 1 Geological map of the Piatra Neamţ area with the locations of the fish outcrops (based on Baciu, 2017). traction-produces muddy bedforms with deformational meta-depositional struc- cm-scale ripples and dm-scale megaripples tures such as convolute lamination, both led to the idea of reworking and bedload in bituminous marls and sandstone transport of sediment arrived at the interlayers, load casts and flames, and seafloor via pelagic settling (Miclăuş and post-depositional structures such as Schieber, 2014). The authors mentioned clastic dykes and intraformational slump that the bottom current activity is incom- folds. Some facies are consistent with a patible with previous scenarios of anoxic slope and deeper water depositional bottom waters as the cause for preser- setting, but others suggest that the vation of lamination and organic matter. seabed was from time to time within the Aside from primary sedimentary reach of storm waves (Miclăuş and structures, there were also observed Schieber, 2014). AUI–G, 62, 1–2, (2016) 29–46 32 Baciu D.S. et al. A significant Oligocene fish fauna has sharksuckers (Echeneidae), jaks and pom- been collected from the Bituminous Marls panos (Carangidae), pomfrets (Bramidae), of the Vrancea Nappe in Bistriţa Half- snake mackerels (Gempylidae), cutlass- Window (Piatra Neamţ area) (Fig. 1). fish (Trichiuridae), mackerels, and tunas Most of the type specimens as well as (Scombridae), driftfish (Nomeidae), left- numerous additional materials from this eye fluoders (Bothidae), triplespines area have been collected from the Lower (Triacanthidae) (Baciu, 2010). Dysodilic Shales and are deposited in the During the geological investigations paleontological collection of the Museum between 2003 and 2010, three outcrops of Natural Sciences, Piatra Neamț were discovered. Two of them were (MNSPN-PC). situated in the main level of the The collection contains more than bituminous marls, on the top of Cozla 1000 specimens which belong to about 50 Mountain (46º 56' 56.19" N, 26º 22' species, representing about 20 families. 08.52" E, 640 m.) and Văleni Village (46º The most important species include 54' 51.49" N, 26º 22' 39.11" E, 304 m.) sardinas (Clupeidae), bristlemouth and the third one, on the Pietricica (Gonostomatidae), hachetfish (Sternoptychidae), Mountain, Piatra Neamț (46º 55' 47.72" N, lightfish (Photichthyidae), lanternfish 26º 22' 51.80" E, 519 m.); the latter is (Myctophidae), codlets (Bregmacerotidae), situated in the second level of the squirrelfish (Holocentridae), dories Bituminous Marls, considered by Ionesi (Zeidae), boarfishes (Caproidae), shrimp- and Grasu (1993) to be an olistolith fish (Centriscidae), bigeyes (Priacanthidae), (Fig. 1). 4. Systematic Paleontology Class CHONDRICHTHYES Huxley, 1880 Order LAMNIFORMES Berg, 1958 Family ODONTASPIDIDAE J.P. Müller & Henle 1839 Genus Carcharias Rafinesque, 1810 Carcharias acutissima (Agassiz, 1844) Fig. 2 1977 Odontaspis cuspidata Agassiz, 1844, Ciobanu M., p. 43, pl. VI, fig. 5; 1991 Carcharias acutissima (Agassiz, 1844), Pharisat A., p. 21, figs 4 and 5. Because of the taphonomical context, waters from Atlantic, Indian and Pacific Carcharias acutissima teeths are actually Oceans (Nelson, 2006). Mostly an inshore rare in the Oligocene formations of the species, found in shallow waters. Vrancea Nappe. In the recent fauna the However, this species was also recorded sand tiger sharks (Carcharias taurus down to 191 m, close to the bottom, at the Rafinesque, 1810) are worldwide distrib- surface, or midwater (Grzimek’s Animal uted in tropical to temperate continental Life Encyclopedia 2003). AUI–G, 62, 1–2, (2016) 29–46 Oligocene fish fauna and sedimentological features of the Bituminous Marls, Vrancea Nappe 33 Family CETORHINIDAE Gill, 1862 Genus Keasius Welton, 2013 Keasius parvus (Leriche, 1908) Fig. 3 1977 Cetorhinus parvus Leriche, 1908,