Paleocene algae in the Dubrovnik Coast ( Adriatic Carbonate Platform )

The presence of Paleocene in the Dubrovnik Coast (Adriatic Carbonate Platform) is documented by algal flora in the locality Plo~ice, Konavli. The algal assemblage includes more than 20 species. Ten taxa present in the Paleocene of the Karst (NE Italy–Slovenia) occur in Plo~ice: Acroporella chiapasensis DELOFFRE, FOURCADE & MICHAUD, Decastroporella tergestina BARATTOLO, Drobnella slovenica BARATTOLO, Dissocladella gracilis RADOI^I], Hamulusella? liburnica (RADOI^I]), Cymopolia elongata (DEFRANCE) MUNIER–CHALMAS, Cymopolia paronai RAINERI, Cymopolia satyavanti (PIA), Cymopolia cf. barberae ELLIOTT and Microsporangiella buseri BARATTOLO. The stratigraphy of the Konavli carbonate belt has been revised in this study.


Introduction
Paleocene sediments on the Dubrovnik Coast (Adriatic Carbonate Platform) have not been documented.The find of the Paleocene algal flora from Plo~ice, Konavli is worthy of the attention although details on the stratigraphic column Plo~ice are missing.A limestone sample with dasycladales and twenty thin sections originating from the bed overlying karstified Upper Cretaceous deposits with bauxite traces were kindly given to me by my colleague MILENKO STOJKOVI].This text -inventory of Plo~ice algal flora -is based on this material alone.

Geological Review
According to the Geological Map, Sheet Dubrovnik 1:100 000 (MARKOVI], 1972;1975), in the Konavli Cre-taceous belt, west of the Zupci fault, sediments of (1) "Maastrichtian" and (2) "Danian" (= Cretaceous Gyropleura beds, and, in the uppermost part, beds with Stomatopsis and Kosinia which "possibly are of Paleocene age") are outcropped.The latter are unconformably overlain by Middle Eocene Alveolina-Nummulites limestone.East of the Zupci Fault, "Danian" is missing -Middle Eocene is lying on the "Maastrichtian" with bauxite at places.Plo~ice is situated west of the Zupci Fault in a succession of "Danian" Gyropleura beds (Fig. 1).To my knowledge, the Konavli carbonate belt consists of ?Turonian, Senonian and Paleocene (?partly) dolomites and limestone (facies of the platform interior) and Lower and Middle Eocene limestone (facies of the marginal area of the platform).Santonian-Campanian sediments bear rich foraminiferal and rudist fauna.Beds with Rhapydionina liburnica and rare Neobalkhania bignoti, with Laffiteina mengaudi and Rotalia trochidiformis, with Gy-ropleura and those with atypic fossils, alternate in the Upper Maastrichtian succession.
Until recently the opinion prevailed that the marine transgression in the given part of the Adriatic Carbonate Platform (= (Dalmatian Zone.auktorum) began only in the Lutetian: BIGNOT & CADET, 1972;CADET, 1978).
Upper Maastrichtian deposits with Rhapydionina liburnica (= Danian sensu MARKOVI], 1972) are also distributed east of the Zupci Fault.On the Dubrovnik Coast and in the Boka Kotorska, these sediments are dolomitized and epigenetically much altered, at places they are more or less karstified.
The information about the Paleocene suggests a need for a more detailed study of the transitional ACP/Cukali Budva Basin area.Dating of stratigraphic gaps would be very important, because they are multiple and of various duration in individual platform blocks.

Plo~ice algal flora
The sampled Paleocene bed (subtidal bioclastic packstone-wackestone, partly removed) contains rich algal flora which were a transported component and sorted in part of the bed (Pl.6, Fig. 5).Numerous altered specimens have lost primary features, in such a way that even their generic characters could not be recognized.The fauna consists of rare gastropods, corals and numerous foraminifera (prevailing frequently discorbids, Bangiana, Gyroidinella, Rotalia, Miliolidae).Disaggregated and resedimented Paronipora elements are dispersed or concentrated in laminae.Vugs with speleothem fabric in this Paleocene limestone indicate subaerial exposure as well as karstification.
BARATTOLO (1998) presented rich and well preserved assemblages of Dasycladales and microproblermatica from Maastrichtian and Paleocene in Karst, Slovenia-Italy boundary area.Ten taxa of this algal flora, including two new genera, were found in the Plo~ice Paleocene.The abundant transported algae in the Plo~ice limestone originate from shallow-water littoral areas which were inhabited by diverse algal populations.
The algal assemblage from Plo~ice includes the following species: Acroporella chiapasensis DELOFFRE, FOURCADE & MICHAUD, 1985 Pl. 1, Figs. 1-11, 13 This species is described in rich but poorly preserved material from the Maastrichtian of the Chiapas region in Mexico: small-sized cylindrical thallus (D 0.375-1.05mm) with "un axe principal particulierment large" (0.225-0.6 mm), inclined primary, bearing tufts of 5-8 secondary laterals and a d/D of 60%.In the illustrated sections, the secondary laterals are not clearly visible.
In the Karst area, the species is found in beds "from uppermost Maastrichtian to lower Danian (Sopada section) or only in Danian beds (Cole de Medea) (BARAT-TOLO, 1998).
The specimens of Acroporella chiapassenis in Plo~ice are much better preserved than those in type localities.The thin dark microcrystalline layer around the axis and those around some pores is calcified membrane of primary organic origin.Short secondary laterals are rarely observed (Pl. 1, Fig. 1).The thallus is smaller in size (0.336-0.640 mm) and, compared with type material, has a narrower axis (0.160-0.320 mm) and, consequently, a different d/D value (34-45%).
It seems that specimens of smaller dimension prevail in the population of Acroporella chiapasensis from the Karst area (BARATTOLO, 1998;pl. 1, figs. 1, 2, 4), but that rare specimens have a larger axis diameter similar to the Mexican material (Pl. 1, Fig. 3) Most probably, individuals with a small sized thallus and a narrower axis prevail in populations of this alga in Dinaridic domains.
It should be mentioned at this point that Acroporella chiapasensis is also present in the Maastrichtian of the same belt, east of the Zupci Fault.The only specimen, shown in Pl. 1, Fig. 13, was found in a bed with Rhapydionina liburnica.
Clypeina sp.aff.Clypeina occidentalis (JOHNSON & KASKA, 1965) Pl. 6, Fig. 2 Rare, poorly preserved, narrow cylindrical tubes with whorls of bowl-like inclined primary laterals are Clypeina, which are similar to Clypeina occidentalis in terms of the form of the laterals.
Genus Cymopolia LAMOUROUX is represented by rare specimens of different species:

Cymopolia paronai RAINERI, 1930
Pl. 2, Fig. 12 Only two fragments of this species (which are very frequent in the Karst area) are recognized in the examined thin sections.(PIA in RAMA RAO & PIA, 1936) Pl. 1, Fig. 12 The oblique section of a cylindrical tube ascribed to this taxon represents a sterile article (see sterile articles illustrated by PIA in RAMA RAO and PIA, 1936;pl. 1).Whorls of sterile articles consist of inclined laterals: a short primary bearing two funnel-like secondaries gradually enlarged, swollen at the distal end.The latter are arranged in pairs, one above the other in a vertical plane, which is clearly visible in the illustrated section (arrows).
Cymopolia sp. 1 Pl.2, Fig. 7 The article with oblique primary laterals and large sporangia is Cymopolia, presented by BARATTOLO as Cymopolia cf.barberae ELLIOTT, 1968.BARATTOLO, 1998 Pl. 3, Figs. 8-13 Genus Decastroporella -type species Decastroporella tergestina is introduced on the rich, well preserved material from the Karst area.The main characteristics of the species are a peculiar thallus structure (lower cylindrical portion and well differentiated head), the presence of sterile and fertile laterals and, possibly, double location of the reproductive organs.

Decastroporella tergestina
Decastroporella tergestina is characterized by an articulated cylindrical portion.Relatively more or less long articles bear numerous sterile laterals (hair type) and, at the top, a whorl of phloiophoreous fertile primary laterals.The head of the thallus is also covered by numerous sterile laterals.Due to its dismembered thallus, the head occurs separately from the cylindrical portion.
In the Plo~ice limestone, the thallus of this species is dismembered; separate articles are dispersed in the rock, fragments with two or three articles rarely occur.The recrystallized wall of the articles is often thicker without preserved pores corresponding to sterile laterals (Pl. 3,Figs. 2,3,9).One large circular section with a thin microcrystalline wall is the only specimen of a thallus head.(Pl.6, Fig. 6).

Dissocladella gracilis RADOI^I], 1991
Pl . 4, This small Dissocladella decribed from Paleocene of Mt.Majevica, Bosnia, was recognized by Barattolo in Danian beds of the Cole de Medea section.Specimens from Plo~ice are somewhat larger than those in the type locality (Table 1).
Calcareous tubes of Dissocladela gracilis in the Plo-~ice limestone are differently preserved, in some of them pores are rare or unpreserved, especially the pores of secondary laterals.Some specimens have more or less enlarged pores.
Hamulusella? liburnica (RADOI^I] in BUSER & RADOI^I], 1987) Pl. 5, Figs. 6, 7 Only some sections are ascribed to this species, which is widely distributed and well preserved in Paleocene of the Karst area.BARATTOLO, 1998 Pl. 5, Fig. 8 This taxon is represented by a few specimens only.

Microsporangiella buseri
Dasycladalean DS2 (gen.nov.?, sp.nov.)Pl. 5, Figs.1-5 In the Paleocene of Materija, Slovenia, dasycladalean DS2 occurs, as in Plo~ice, associated with Decastroporella tergestina and Drobnella slovenica (BUSER & RA-DOI^I], 1987, pl.3, figs. 3, 4).Some sections of this species appear to have a thallus of a simple structure, as is the case with some Clypeina.In fact its structure is more complex, the fertile ampullae location is not quite clear.At the moment, the available material does not provide sufficient data for the introduction of a new genus and species .

Microproblematica, Alga
Drobnella slovenica BARATTOLO, 1998 Pl. 4, Figs. 1-6 Although Drobnella slovenica is described on the rich relatively well preserved material (numerous large thallus fragments), their systematic position is at the moment uncertain: Chlorophyta or Charophyta?The species is characterized by a peculiar thallus structure and, especially, by an exceptional calcareous skeleton, which "does not seem to have been recorded before in more or less similar fossil algae" (BARATTOLO, 1998: 89).
In the Plo~ice Paleocene, as in Materia, Slovenia, Drobnella slovenica is presented only by small skeletal fragments and different sections of elongated pores -"main pores".The unusual tangential-oblique section of the main pore, illustrated in Pl. 4, Fig. 6, has a very long pointed distal end, much longer than observed in the Karst material.

Age of Plo~ice limestone
Decastroporella tergestina, Drobnella slovenica, and Acroporella chiapasensis are the dominant species in the Plo~ice assemblage.In the Karst area, Decastroporella tergestina and Drobnella slovenica appear "very close to the K/T boundary" and were distributed in SBZ1.Acroporella chiapasensis appears in Maastrichtian; in the Danian SBZ1, it is associated with Decastroporella tergestina and Drobnella slovenica.These taxa appear before the appearance of the Cymopolia assemblage in the lowest part of SBZ1 (BARATTOLO, 1998: 93).Consequently, the algal flora in the Plo~ice limestone can be asscribed to the Late Danian.Valuable data on the development and the distribution of Paleocene in this domain of the Adriatic Carbonate Platform is to be expected through further and more detailed studies of the Konavli Paleocene.