Carboniferous and Triassic conodonts from Syrian boreholes

A sparse but important collection of conodonts recovered from four boreholes in north-eastern and central Syria contains Neogondolella mombergensis, which is the first record of Triassic conodonts from Syria. The Carboniferous rocks are characterised by species of Gnathodus which indicate the presence of late Tournaisian to late Viséan strata.

become thinner towards the central part, being about 338 m in the Dalaa Borehole and 310 m in the Doubayat Borehole. Lower Carboniferous deposits are absent from the extreme southern portion of the country. The deposits show regional variations in facies. In the southern and central part of Syria (in the Tenf and Swab Boreholes), they are represented by sandstones, intercalated with grey argillites and cream coloured dolomites with fragments of coal and fossil wood. These rest unconformably on Silurian rocks at Tenf and on Ordovician rocks at Swab. They are overlain unconformably by carbonates of Upper Cretaceous age. In the northeast of Syria (in the Markada -101 and El-Bowab Boreholes) the Lower Carboniferous is represented by massive, black, schistose, argillites with intercations of dolomite, which rest unconformably on Silurian rocks at Markada and on Ordovician rocks at El-Bowab. They are overlain unconformably by Triassic deposits. Wolfart (1 967) found spores in the boreholes at El-Bowab and Al-Barde, which indicated that the Lower Carboniferous is conformably overlain by rocks of Upper Carboniferous (Stephanian -Westphalian and Namurian) age.

THE LOCATION OF THE BOREHOLES AND SAMPLES PROCESSED FOR CONODONTS
Samples from boreholes at four selected localities in north-eastern and central Syria (Fig. 1) were studied in an attempt to establish a biostratigraphic zonation utilising conodonts.
The boreholes studied were those of Swab-1, Markada -101, Jbissa-207 and Roumylan-6. The numbering system follows that employed by the Syrian Petroleum Company.
I -THE SWAB BOREHOLE Swab is located to the south of the city of Dier-Al-Zor. Four cores were taken from different horizons at the depths indicated. The samples studied were as follows:- A sample was taken from the interval 3602 -3604m. It was a dark grey limestone with shale.
Samples of black limestone and laminated shale were collected from the interval 3618 -3629m. They contained brachiopods.
Dark grey, compact, highly argillaceous limestone with some veins of quartz.

THE CONODONT FAUNA
The present study is based upon 55 rock samples, each approximately one kilogram in weight, which were collected from the mainly Lower Carboniferous deposits present in four boreholes in north-eastern and central Syria. Eleven samples contained conodonts. The conodonts were not very abundant and generally occurred as fragments. The Carboniferous fauna is dominated by the genus Gnathodus. The numerical distribution of the conodont elements recovered is illustrated (Figs. 2-4). (Fig. 2) Samples from Cores 5, 7 and 8 failed to yield any conodonts. Samples from Core 6 yielded elements representing 16 species and 7 genera.  indices for late VisCan and early Namurian age strata (Rhodes et al. 1969, Higgins 1975and Meischner 1970. The presence of Gnathodus homopunctatus indicates a VisCan age at least to a depth of 1297.60m Gnathodus texanus and Gnathodus pseudosemiglaber which are present below the first appearance of Gnathodus homopunctatus have their oldest stratigraphic occurrence in the Scaliognathus anchoralis Zone, which is of late Tournaisian age (Lane, Sandberg & Ziegler, 1980). Despite the low yield of conodonts we suspect the Tournaisian-Vistan boundary to fall within the interval of Core 6.

THE SWAB BOREHOLE:
THE MARKADA BOREHOLE: (Fig. 3) Samples from Core 21 contained no conodonts. Only one horizon in Core 18 contained conodonts. Samples from the Markada Borehole at a depth of 3120.30m contained two broken specimens of Neogondolella mombergensis. The specimens clearly exhibit the fairly broad platform features, which are rounded posteriorly. The platform forms a point at the anterior end and the carina is low. The presence of this species in Core 18 is indicative of a Middle Triassic age (Mosher, 1968). The genus was not recovered from any other sample. It represents the first record of Triassic conodonts from Syria.
Samples from the interval 3363.80111 -3436.40111 of Cores 19 and 20 are characterised by the presence of Gnathodus pseudosemiglaber. At depth 3362.60m, a single specimen of G. cuneiformis occurs together with a specimen of G . texanus. The sample from depth 3435.90 m produced two specimens of Apatognathus geminus together with Spathognathodus scitulus. This association indicates that at this level there is a shallow water facies (Austin, 1976). Gnathodus texanus occurs again at depths of 3436.40m and 3429.85 m.
The presence of Gnathods texanus, Gnathodus cuneiformis and Gnathodus pseudosemiglaber implies that the rocks present in Cores 19 and 20 of the Markada Borehole are of late Tournaisian-early VisCan age. THE JBISSA BOREHOLE: (Fig. 4) Only three samples from the Jbissa borehole at depths of 3869.40m, 4147.80m and 4178.90m in Cores 1, 3 and 4 yielded conodonts. Cores 2 and 5 did not yield any conodonts. The specimens recovered are mostly frag- Fig. 4. Conodont species, Jbissa Borehole.
mentary, but a few are sufficiently well preserved for generic and specific identifications to be made. The species Gnathodus pseudosemiglaber and Gnathodus cuneiformis are recognised in Core 4 and Gnathodus pseudosemiglaber in Core 3, which implies an age close to the Tournaisian-VisCan boundary.

REPOSITORY OF SPECIMENS
The conodont specimens of this study are deposited at the Department of Geology, The University, Damascus.