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Journal of Paleontology

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FIRST HEXACTINELLID SPONGE REPORTED FROM THE UPPER TRIASSIC NAYBAND FORMATION OF CENTRAL IRAN

¹ Department of Geology, Brigham Young University, Provo, Utah 84604, USA, rigbyjkeith@qwest.net
² Institute of Paleontology, University of Erlangen-Nürnberg, Loewenichstrasse 28, D-91054 Erlangen, Germany, basendera@pal.uni-erlangen.de

The first 20% of the full text of this article appears below.

	INTRODUCTION

 
SPONGES, ALONG with scleractinian corals, are among the main reef-building organisms in Triassic reefs. Hypercalcified groups, including the chambered sphinctozoans, and the unchambered inozoans, chaetetids, and spongiomorphids, represent the most abundant Triassic reef-building sponges. Earlier workers have described elements of the latter group as "hydrozoans." Hexactinellid sponges, abundant in some Permian reefs (e.g., in Texas, Finks, 1960), are rarely known from similar Triassic deposits, in general (Tichy, 1975), and particularly from Upper Triassic stratigraphic units. Hexactinellid sponges have been sporadically reported from well-investigated Upper Triassic reefs in the western Tethyan region (e.g., Keupp et al., 1989). However, a variety of hexactinellid sponges have been reported from Upper Triassic deposits and reefal limestones of the northern and central Tethyan realm (Boiko, 1990; Wu, 1989; Wu and Xiao, 1989; Rigby et al., 1998).

Hypercalcified sponges are abundant in Upper Triassic reefs that occur within the Nayband Formation in central and northeastern Iran, along the southwestern Tethys margin. Sponges of these reefs have been described by Senowbari-Daryan et al. (1997), Senowbari-Daryan and Hamedani (1999), and Senowbari-Daryan (2003, 2005a, 2005b). In addition to the hypercalcified sponges, both chambered and unchambered hexactinellid sponges also occur, but are less abundant in these Upper Triassic reefs in Iran. Here, we report the first, and the largest known hexactinellid sponge from the Nayband Formation. It was collected from exposures approximately 50 km south of the town of Delijan, in central Iran.

The Upper Triassic (Norian-Rhaetian) siliciclastic-carbonate deposits of the Nayband Formation reach a thickness of about 3,000 m at the type locality at Kuh-e Naybandan, south of Tabas (see Fürsich et al., 2005). The formation is an important stratigraphic unit exposed in several localities in central and northeastern Iran. General information . . . [Full Text of this Article]