Palaeobiogeography of the Late Carboniferous brachiopoda from Velebit Mt. (Croatia)

An abundant and diverse Late Carboniferous brachiopod fauna from Velebit Mt. (Croatia) comprises 63 brachiopod taxa dominated by Productida and Spiriferida. The Spiriferinida, Athyridida, Orthotethida and Rhynchonellata are less common, while the Orthida, Dictyonellida and Terebratulida occur in very small numbers. Brachiopods are mostly preserved as casts and moulds in shales, limestones and sandstones. Associated fusulinid foraminifera and calcareous algae indicate a Kasimovian to Gzhelian age for the brachiopod–bearing deposits. The global biogeographic distribution of brachiopod taxa indicates the probable seaways and brachiopod migration routes, along the Euramerican shelves. to 6 km wide, representing the core of an anticline, with a NW– SE strike (Fig. 1). They exhibit a variety of ancient environments varying from shoreline forests and swamps, through coastal and shallow shelf biomes (SREMAC, 2012; CLEAL et al., 2015). Carboniferous shelves were densely populated with foraminifera (mostly fusulinids), calcareous algae, brachiopods, crinoids, bryArticle history: Manuscript received September 30, 2015 Revised manuscript accepted June 21, 2016 Available online June 29, 2016


INTRODUCTION
Brachiopods are common marine macrofossils in the Late Carboniferous sedimentary rocks of Velebit Mt. They have been collected since the beginning of the 19 th century and stored in the Croatian Natural History Museum.
Upper Carboniferous (Pennsylvanian) sedimentary rocks from Velebit Mt. crop out in an elongate belt, 40 km long and up The Carboniferous palaeogeographic map chosen to present the Carboniferous brachiopod localities is based upon Blakey's (2015) reconstruction.

BRACHIOPOD TAXA
Brachiopods were discovered in Carboniferous sedimentary rocks forming the core of the anticline on the continental slopes of Velebit Mt. (SIMIĆ, 1935;SALOPEK, 1942SALOPEK, , 1948. Brachiopods are in most cases preserved as casts and moulds (Fig. 2), and it is not always possible to determine them to species level.

MATERIALS AND METHODS
Carboniferous brachiopods from this study were collected by SALOPEK (1942SALOPEK ( , 1948 and by the present authors between 2012-2014. The brachiopod collection is stored in the Croatian Natural History Museum (under 96 inventory numbers).

Palaeoecology and the local distribution of brachiopod genera
Brachiopod finds are clearly grouped into three areas with different fossil assemblages (Tabs. 1., 2., Fig. 3). Palaeobiodiversity evidently increases towards the East (Tab. 2., Fig. 8). It is important to note that these three areas very rarely comprise the same taxa (Tab. 1). The exceptions are several tolerant taxa, capable of adapting to a variety of marine environments, such as Linoproductus lineatus (present in all three areas and in all lithological units -shales and siltstones, greywackes and limestones), or Transennatia gratiosa, present in the central and eastern areas, and in two of the three lithological units (shales and siltstones; limestones) (Tab. 1.).
The western area (A, Fig. 1) is characterized by several small productid taxa, with the exception of the larger Linoproductus The presence of Neochonetes variolata (Fig. 4 a) indicates a most probable deep subtidal depositional area (KALASHNIKOV, 1993). Rhynchonella confinensis seems to be endemic, occurring only in Velebit Mt. and in the Permian deposits in neighbouring Slovenia (SCHELLWIEN, 1892).
Well sorted conglomerates and the aligned orientation of fusulinids in some sandstone layers indicate a the coastal environment. Partial or complete dissolution of fusulinid tests (SALOPEK, 1948;KOCHANSKY, 1955) indicate a probable fresh-water influence (SREMAC, 2012). Brachiopods, although numerous and highly diverse, are also mostly present as casts or moulds (Figs. 1-6). All these features indicate a variety of environments, from beaches to the more favourable subtidal niches.
Erosion of the uplifted Variscan Mountains provided nutrients and enabled the significant diversification of marine biota.

Palaeobiogeographic studies
The Late Carboniferous was a time of a slight increase in brachiopod diversity (SHU-ZHONG et al., 2006) and these organisms were present in all seas and oceans. Their geographic distribution was closely related to the position of continental shelves and possible sea-ways and climate gradients, recently studied by several authors (ANGIOLINI et al., 2007;BERRA & ANGIOLINI, 2014). During the Late Carboniferous, the study area was a part of NE Gondwana, situated near the equator (VO-ZAROVA et al., 2009;SREMAC, 2012;CLEAL et al., 2015)  In order to identify possible migration routes, some of the common Carboniferous brachiopod genera from Velebit Mt. were selected for further palaeobiogeographic studies.
pearance near the equator is interesting (Fig. 10). Alternatively, the genus Transenatia is rather endemic, appearing on the eastern continental shelves of Euramerica, near the equator (Fig. 10).

CONCLUSIONS
The Carboniferous brachiopod fauna from Velebit Mt. is very rich and diverse. but in most cases not well preserved. All together 63 taxa were determined, belonging to nine brachiopod groups, with a predominance of productids and spiriferids.
Brachiopods were observed in the form of moulds and casts in shales and siltstones, limestones and graywackes, with the highest abundance in fine-grained clastic deposits. Three different areas with diverse brachiopod associations can be clearly recognized. The highest brachiopod diversity was observed in coastal fine-grained clastic deposits at the eastern part of the outcropping Carboniferous rock belt.
A Kasimovian to Gzhelian age was proposed on the basis of the associated fusulinid fauna.
During the Late Carboniferous, brachiopods were common along the continental shelves of Euroamerica. Southern hemisphere records are less common and represented by tolerant gene ra, e.g. the cosmopolitan Neospirifer and Derbya.