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A report and a photo-album by Tonći Grgasović

Triassic Dasycladales from Croatia 

 
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Institute of Geology, Zagreb, Croatia

INSTITUTE OF GEOLOGY

CROATIA, Zagreb, Sachsova 2.

In Croatia (cf. Map), for more than a century fossil algae have been found and described in carbonate rocks ranging in age from Upper Carboniferous to Palaeocene. This discussion is a brief review of the associations of Dasycladalean algae from the Middle and Upper Triassic, with emphasis on the stratigraphical ranges of some species or associations (cf. Table). Each species and subspecies is described briefly.

The first association occurs in the lowermost Anisian (?Aegean). It includes Diplopora cellulata, Poncetella helvetica, Poncetella hexaster, and Diplopora proba (Aegean-Pelsonian), as well as Diplopora subtilis (Aegean-Lower Illyrian).

Higher in the succession (?Bithynian) a Physoporella - Oligoporella association appears. It includes: Physoporella pauciforata var. pauciforata, Ph. pauciforata var. sulcata, Ph. pauciforata var. undulata, Oligoporella cornuta (= Ol. pilosa var. varicans), Ol. dissita (= Ph. dissita), Ol. minutula (= Ph. minutula), Ol. pilosa var. intusannulata, Ol. pilosa var. pilosa, Ol. praealpina (= Ph. praealpina), and Ol. varicans (= Ph. varicans) (after GRGASOVIĆ, 1995).

The Oligoporella - Physoporella association, together with Macroporella alpina, has its maximum development in the Pelsonian and Lower Illyrian. Physoporella croatica (Pelsonian) andTeutloporella tabulata (Pelsonian - Lower Illyrian) also occur in this interval, as well as Scinderella scopuliformis and Teutloporella peniculiformis, which is common throughout the whole of the Pelsonian-Fassanian.

Although less abundant than the species listed above, Euteutloporella triasina, Diplopora nodosa and Diplopora annulatissima (in the "classical" form, and in the form of Favoporella annulata) have been found in strata dated Lower Illyrian. Along with Macroporella beneckei these three species have their maximum development in the Upper Illyrian and Fassanian.

The Anisian - Ladinian boundary is marked by the appearance of Diplopora annulata and Kantia dolomitica , both common throughout the Ladinian. During the Fassanian they are associated with the above-mentioned Illyrian species, as well as the rarer Physoporella lotharingica and Clavapora clavaeformis. In the Langobardian (?) they are associated with Teutloporella herculea and the less common Euteutloporella triasina and Diplopora nodosa.

The Carnian is characterised by Clypeina besici, Physoporella jomdaensis, Dissocladella bystrickyi and Griphoporella curvata. Gyroporella vesiculifera appears in the Norian, and along with Gryphoporella curvata is abundant in Rhaetian beds together with the foraminifer Triasina hantkeni.

Simplified geological map of Croatia (by Ivo and Josipa VELIC)
Stratigraphic ranges of Dasyclad algae in the Triassic of Croatia
 
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