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Holothurian Sclerites from the Middle Jurassic of Wadi Huni, Northwest Jordan

1990; Micropaleontology Press; Volume: 36; Issue: 4 Linguagem: Inglês

10.2307/1485475

1937-2795

Heinz W. Kozur, Walid Sadeddın,

Geological and Geophysical Studies

Six genera and 13 species of holothurian sclerites were found in the Middle Jurassic of Wadi Huni, northwest Jordan. Of these, 4 genera and 9 species are new. Like the Middle and Late Triassic holothurian sclerites, the Jurassic ones are also stratigraphically important. In spite of the fact that most of the species described here are new, the fauna clearly indicates Middle Jurassic, most probably Bathonian age. INTRODUCTION Middle and Late Triassic holothurian sclerites are well known and stratigraphically important (Mostler 1973; Kozur and Mock 1974). Jurassic holothurian sclerites are not as well investigated and are seemingly not so diverse as the Triassic ones. But without any doubt the Jurassic holothurian sclerites are of equal stratigraphical importance, especially for ammonoid-free limestones in marginal shallow water seas. No holothurian sclerites have been previously described from Jordan. Middle Jurassic limestones from Wadi Huni (NW Jordan) yielded well-preserved holothurian faunas, which are described in this paper. GEOLOGICAL SETTING Jurassic rock sequences in Jordan are exposed along the river Zarqa, NW of Amman, from the old Zarqa river bridge to the town of Deir-Alla, as well as in side wadis near Arda (see text-fig. 1). These Jurassic sequences have been studied and described by several authors, but their exact age is not yet well established. A short historical review of investigations of the Jurassic in Jordan is given by Bender (1968). According to this author the first Jurassic fossils from the river Zarqa were reported in the middle of the last century by Wetzstein (1859), but detailed paleontological investigations only began with Cox (1925) and Muir-Wood (1925), who identified fossils collected by Wyllie, Campbell and Lees along the river Zarqa. On the basis of bivalve studies, Cox (1925) placed the collected material into the Bajocian -Bathonian, whereas Muir-Wood (1925) recognized Upper Bajocian and Bathonian ages on the basis of brachiopods. Wetzel and Morton (1959) assigned plant-bearing sandstones found in the lower part of the Jurassic sequence along the Zarqa River 10km west of King Talal Dam (Wadi Huni area) to the Rhaetian ?Liassic, and the higher part of the sequence to the Bajocian, Bathonian and Callovian, while Jordan (in Bender 1968) placed the limestones just below the plant-bearing sandstones in the Aalenian/Bajocian -Lower Bathonian interval. Bender (1968) placed the entire Jurassic sequence of the river Zarqa into the ?Aalenian/Bajocian, Bathonian and ?Callovian stages. Basha (1979), who investigated the ostracod fauna of the Zarqa Jurassic, recognized 4 associations of Aalenian, Bajocian, Bathonian and Callovian Kimmeridgean ages. The Aalenian and Callovian to Kimmeridgean ages however, are not well established. Well documented estimates on bivalves, brachiopods and ostracods indicate a Bathonian (or Late Bajocian and Bathonian) age for the Jurassic beds along Zarqa River. This age is also supported by the holothurian sclerites reported here, which indicate Bathonian age for at least most of the Jurassic in this area. We have investigated holothurian sclerites in these beds from the Wadi Huni area, near the confluence of Wadi Huni and Zarqa rivers and about 17km north of the town of Salt. The exposed sequence begins here with about 60m of Triassic sediments (sandstones, claystones, dolomites, marly limestones, limestones, gypsum) which belong, according to their conodont faunas (Sadeddin in press) to the Late Ladinian and Camian. The Jurassic, which rests with a major erosional unconformity on Camian rocks is about 200m thick, and consists of sandstones; blue-gray to purple, partly pisolitic claystones; marls; marly and sandy limestones; creamish-gray to pink limestones; and dolomites. The holothurian-bearing samples were taken from the limestone beds. The richest associations of holothurian sclerites were found in the samples WH7, HU3 and HU4 (see text-fig. 2). Sample WH7 was taken from bedded, sandy limestones about 20m thick in the lower part of the Jurassic sequence. Sample HU3, from the middle part of the sequence about 110m above sample WH7, was taken from biomicritic compact pink limestones. Sample HU4, from the upper part of the Jurassic sequence about 30m above sample HU3, was taken from a micritic gray limestone intercalated between marls. In each of these three stratigraphic levels, typical Middle Jurassic holothurian sclerites were found. Sample WH7 appears to be already in the Bathonian, and a Bathonian age for the youngest sample HU4 is probable, although a Callovian age cannot be excluded because Callovian holothurian sclerites are not yet well known. Late Jurasssic age, however, can be ruled out because of the presence of Spinopriscopedatus aegyptiacus (Said and Barakat) and the absence of Priscopedatus s. str. Our biostratigraphic assignment based on holothurian sclerites is in agreement with the data by Bender (1968), who as noted above micropaleontology, vol. 36, no. 4, pp. 353-366, pls. 1-4, 1990 353 This content downloaded from 207.46.13.172 on Tue, 23 Aug 2016 05:55:26 UTC All use subject to http://about.jstor.org/terms H. Kozur and W. Sadeddin: Holothurian sclerites from the middle Jurassic of Wadi Huni, Northwest Jordan