Ichnofossils from Cretaceous-Paleogene flysch of Mide locality (Budva Zone, southern Montenegro)

Cretaceous-Paleogene flysch represents the youngest formation in the Budva Zone. Although the Maastrichtian-Lower Eocene age of these rocks has been well documented in the literature, trace fossils are only mentioned as abundant and not described. In the present paper, only a small number of ichnotaxa from Mide locality has been described, including Lorenzinia carpathica (ZUBER), Nereites irregularis (SCHAFHÄUT), Scolicia plana KSIĄŻKIEWICZ and Paleodictyon latum VIALOV & GOLEV. They confirm deepsea environment.


Introduction
Cretaceous-Paleogene flysch formation of the Budva Zone stretches along the Montenegrian coastal region from the cities of Herceg-Novi towards Budva and Bar, from where it passes along the southern side of Rumija mountain into Albania.At present state of knowledge, the Budva Zone is interpreted as an intraplatform deep-water basin (SCHMID et al., 2008), developed between two shallow-water units, i.e. the South Adriatic and the High Karst zones.It is characterized by deep-water sedimentary rocks of Triassic, Jurassic, Cretaceous and Paleogene age, developed in several thrust units.Cretaceous-Paleogene flysch formation represents the youngest formation within the Budva Zone.In general, it is characterized by the repeated cycles of calcareous sandstones and marls, with rare intercalations of limestone.Sedimentological features, as well as the determined age (Maastrichtian-Lower Eocene), have been described in ma-ny publications (MILADINOVIĆ, 1960(MILADINOVIĆ, , 1964;;PAVIĆ, 1970;ANTONIJEVIĆ et al., 1973;KALEZIĆ et al., 1976;MIRKOVIĆ et al., 1978).This formation has also been found in deep boreholes for oil exploration in Buljarica (ČANOVIĆ, 1958).However, trace fossils from this formation have not been described so far, but are mentioned as abundant.GRUBIĆ (1961) described Lorenzinia carpathica (ZUBER) from a locality near Mide.VJALOV & GOLEV (1963)

Geological setting
Sediments of Cretaceous-Paleogene flysch formation have an avarage thickness of 120 m and are the youngest rocks of the Budva Zone (KALEZIĆ et al., 1976).In general, they are represented by carbonate breccias, sandstones, sandy limestones and marls.Underlying this formation are the Globotruncana limestone facies with chert nodules and interlayers of Maastrichtian age.The Cretaceous-Paleogene flysch is capped by Triassic rocks of High Karst Unit.

Description of the studied section
The Mide locality is situated in the southern Montenegro, ca. 15 km ESE from the town of Bar (Fig. 1).The Budva Zone deposits in this area are represented by Cretaceous-Paleogene flysch and Cretaceous Globotruncana limestones, which are in inverted position to each other due to tectonic deformations caused by rock masses of the Southern Adriatic and High Karst zones.
The Cretaceous-Paleogene flysch formation in the Mide locality is 67 m thick (Fig. 2).Based on fossil content, only Paleocene and Lower Eocene have been determined in this locality.Lower part of the section, 48 m thick, is comprised of grey and greenish-grey sandstones and marls, that are 2-15 cm thick, with rare intercalations of limestones.Sandstones are made of quartz, rock fragments and feldspar, with rare mica fragments.In the limestone intercalations, only Chilo-Geol.an.Balk.poluos., 2018, 79 (2), 11-18.guembelina cf.midwayensis (CUSHMAN) (Fig. 3A) has been determined.Ichnofossils described in this paper occure in the lowermost part of this interval and are found mostly on the lower bed-surface of sandstone layers.Only Nereites irregularis (SCHAFHÄUT) is found on the upper surface of the layer.Next interval, 15 m thick, is composed of red sandstones (Fig. 3B) intercalated with green marls, where the sandstone layers are 5-8 cm thick.In them, the pelagic foraminifera Morozovella angulata (WHITE) (Fig. 3C

Trace fossils
Up to the present day, there is no unified systematics for ichnofossils.BERTLING et al. (2006) propose that morphology of trace fossils is the most important criterion for their evaluation, and not size, producer, age, facies or preservation, but they don't introduce a new systematic scheme.In the present paper, description of ichotaxa follows the ones given by KSIĄŻKIEWICZ (1977) and UCHMAN (1998), which are based on morphological features of ichnospecies.
The collection is kept in the Geological Survey of Montenegro.Each specimen has an inventory number, which consists of abbreviations for the locality, number of the specimen and the abbreviation for the year when the specimen was found (e.g.MID 1/15).
Description.The star and the areola have an elliptical shape.Maximum width of the diameter of the star is 41 mm and maximum diameter of the areola is 23.4 mm.There are 22 riblets that have rounded outer and inner ends and are all of similar size.Their length and width haven't been measured because of the poor preservation of the specimen.Dimensions of the specimen and the relation between the star and areola (D:d is 1.75) as well as the number of riblets fit into the description of the ichnospecies as described by KSIĄŻKIEWICZ (1977).
Remarks.GRUBIĆ (1961) described two specimens of Lorenzinia carpathica (ZUBER) from the Eocene flysch of Montenegro, one of which was found between the locations of V. Kaliman and Mide.However, the exact locality is not shown in the paper.In this area, both Eocene flysch of the South Adriatic Zone and the Cretaceous-Paleogene flysch of the Budva Zone are developed, so it is not clear in which layers was this specimen found, but it is more likely that it originates from Paleocene sediments of the Budva Zone.UCHMAN (1998) revised the ichnogenus Lorenzinia, including part of the material described by KSIĄŻKIE-WICZ (1977) as different ichnospecies, into ichnospecies Lorenzinia carpathica (ZUBER).In the literature, Lorenzinia was interpreted as a trace of holothurians, crabs or annelids (UCHMAN, 1998, and references therein).

Ichnogenus Nereites MACLEAY, 1839
Nereites irregularis (SCHAFHÄUTL, 1851) Fig. 5 central string is about 2 mm wide, while the width with two lobes goes to about 5 mm.Meanders are closely packed and the distance between them is less than 1 mm.They are developed in only one level.The central string and the side lobes are of the same colour.
Remarks.The specimen from the Mide locality mostly resembles the ones described by KSIĄŻKIEWICZ (1977) as Helminthoida labyrinthica HEER.UCHMAN (1995UCHMAN ( , 1998) ) revised the material of previous author and concluded that it represents a junior synonym of the ichnospecies Nereites irregularis (SCHAFHÄUTL), based on the morphological features of the specimens.
The origin of the tracemaker is still unknown.Material.Two partial traces, probably of the same trace (inventory number MID 2A/15).
Description.The specimen represents the hypi-chnial form of this ichospecies.It is a convex, arcuate ridge, with two sediment strings and a small crest in the middle, on which faecal pellets are visible.The width of the ridge varies from 18.6 to 24.3 mm.The crest is 11.5 to 12.8 mm wide and the strings are from 1.4 to 2.6 mm wide.
Remarks.Scolicia plana KSIĄŻKIEWICZ from Mide locality was found on the lower bed-surface of sandstone layer.It was previously described as Subphyllochorda striata KSIĄŻKIEWICZ.UCHMAN (1998) has described the link between this form and Scolicia plana KSIĄŻKIEWICZ, that is described from an upper surface of layers and considers them the same ichospecies.Both forms represent traces made by irregular echinoids.

Material. One specimen (inventory number MID 2B/15).
Description.Hexagonal network of small size.The string is 0.6 mm wide, while the maximum mesh   width varies from 1.9 to 2.4 mm.The meshes are mostly uniform in shape, although some are more elongated.
Remarks.KSIĄŻKIEWICZ (1977) and UCHMAN (1998)  New finding of Lorenzinia carpathica (ZUBER) in the Cretaceous-Paleogene flysch formation of the Mide locality indicates that the specimen described by GRUBIĆ (1961) found between the the locations of V. Kaliman and Mide also probably originates from these deposits.

Conclusion
The
mention that VIALOV & GOLEV described this ichnospecies as sp.nov. in 1965, when they designated a holotype from the Carpathians.For this reason, the use of the name Paleodictyon latum in the paper from 1963 represents a nomen nudum.Even though incipient Paleodictyon has been found in recent sediments on the deep-sea floor (RONA et al., 2009), it is still unknown what kind of organism produce this trace fossil.Discussion UCHMAN & WETZEL (2012, and references therein) describe a large number of examples of Nereites ichnofacies, that is characteristic for deep-sea turbidite-dominated environments.Based on the dominance of specific trace fossils (meandering forms, rosette and network traces etc.), authors distinguish proximal and distal facies in the turbidites.Since there are only four ichnotaxa described from the Mide locality, it is not possible to argue what are the dominant forms, but all of them are characteristic for Nereites ichnofacies as described by UCHMAN & WETZEL (2012), i.e. they indicate a deep-sea environment.In the area near the Mide locality, both Cretaceous-Paleogene flysch formation of the Budva Zone and Adriatic flysch formation (Upper Eocene-Oligocene, ČAĐENOVIĆ et al., 2010) of the South Adriatic Zone are developed.These formations do not differ only in age and tectonic units they belong to, but also contain different ichospecies.In Adriatic flysch formation of this area Scolicia strozzi (SAVI & MENEGHINI), Paleodictyon hexagonum MARCK and Paleodictyon praedictum VIALOV & GOLEV trace fossil have been determined (ĐAKOVIĆ et al., 2018).Trace fossils of the Cretaceous-Paleogene flysch formation are represented by ichnospecies described in the present paper.However, all ichnotaxa indicate a deep-sea environment of the Nereites ichofacies (UCHMAN & WETZEL, 2012).
present paper represents a contribution to the knowledge of ichnofossils in Cretaceous-Paleogene flysch of the Budva Zone.Trace fossils are very important tools for interpretation of the environments.The trace fossils from Mide locality, even though they are represented by four ichnotaxa, clearly indicate a deep-water environment, of the Nereites ichnofacies (UCHMAN & WETZEL, 2012).Geol.an.Balk.poluos., 2018, 79 (2), 11-18.
also describe representatives of ichnogenus Paleodictyon from the Eocene flysch of Montenegro.Since Eocene flysch sediments are more common in the South Adriatic Zone of the Montenegro coastal region, which is underlying the Budva Zone, it is more likely that these ichnofossils originate from these sediments.Four ichnotaxa: Lorenzinia carpathica (ZUBER), Nereites irregularis (SCHAFHÄUT), Scolicia plana KSIĄŻKIEWICZ and Paleodictyon latum VIALOV & GO-LEV have been identified from the Cretaceous-Paleogene flysch of the Budva Zone.Nereites irregularis (SCHAFHÄUT) is found on the upper bed-surface of the sandstone layer, while other ichnospecies originate from the lower surface of the layers.Even though there are only four ichnospecies found, they all indicate deep-water environment, of the Nereites ichnofacies (UCHMAN & WETZEL, 2012).