Two New Species of Acritarchs From the Ordovician of Iraq

Abstract

Two new distinctive species of acritarchs belonging to genus Fractoricoronula are described from strata of Late Ordovician Epoch in borehole Khleisia–1 in Iraq. These are Fractoricoronula densa sp.nov. and Fractoricoronula khabouri sp.nov. ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ ـــــــــــــــــــــــــــ فصو ن كراتيركلأا نم نيديدج نيعو ا نم قا رعلا يف يشيفودرولأ رماع ردان دؤاد دبع را زن ىلوملا دحاولا ضرلأا مومع مسق مومعلا ةيمك لصوملا ةعماج صخلملا طممم و ممم ار ةوممم لأ ر ممماوعت لممم للأسممملأس لوحطممم عمممجنن عونممموو فمممترةسار لا مممش ممماإ نمممجار Fractoricoronula هو واخ ئب ف اح ر شوفن ةنلار ةطخج ل – 1 ر ار ف ق و هن : sp.nov. Fractoricoronula densa ن Fractoricoronula khabouri sp.nov. ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ ـــــــــــــــــــــــــــ INTRODUTION The oldest rock unit exposed in northern Iraq is the Ordovician Khabour Formation which crops out in narrow limited zone in the core of Ora, Chalki and Kaista anticlines in north and northwestern Amadia district (Bellen et al., 1959). In the western side of Iraq the oldest rock unit exposed is the Ga'ara Formation (Late Carboniferous – Permian) in the Ga'ara depression. Due to the limited outcrops exposure the information about the Paleozoic Formations were obtained from the deep wells, which drilled in the area between Khleisia and Mosul city and the studied well is one of these (Fig. 1). The studied Amer D. Nader and Nazar A. Al-Mola 99 samples were collected from borehole Khleisia–1, which is located at 35° 21.3 ̋N,41° 18 ̋E at Khleisia anticline northwestern Iraq, the total depth of the well is (3791.4m.) and the studied section is between depths (3400.0 2543.5m) penetrating Khabour Formation (Fig. 2). The Paleozoic sedimentary strata fall into three characteristic major sedimentary cycles, separated by relatively major breaks, indicating the effects of the Caledonian and Hercynian orogeneses. One of these cycles is the Cambrian – Ordovician – (?Silurian) cycle represented in Iraq mainly by the Khabour Formation (Buday, 1980). Bellen et al., 1959 and other earlier authors included the Pirispiki Red Beds and Chalki Volcanics in this cycle (Buday, 1980). Seilacher, 1963 in Buday, 1980 proved that Pirispiki Red Beds and Chalki Volcanics belong to the next cycle (Devonian – Lower Carboniferous) cycle and were deposited after the Caledonian uplifted. Fig. 1. Locality Map Showing the Location of the Studied borehole Khleisia – 1. Two new species of acritarchs from the Ordovician of Iraq 99 Fig. 2: The Studied Stratigraphic Succession of Borehole Khleisia –1. Amer D. Nader and Nazar A. Al-Mola 99 STRATIGRAPHY The Khabour Formation was first defined by Wetzel, 1950 in van Bellen et al., 1959 in the northern thrust zone, which named after the Khabour river in the vicinity of Amadia district, north of Iraq. The exposed part of the type section is (800m) thick (base not reached). The outcrop portion of the Formation is purly clastic composed of thin bedded, fine grained sandstone and silty micaceous shale (Buday, 1980) (Fig. 2). According to the palynological study the Khabour Formation was deposited in the inner-middle shelf, under low energy water (Al-Mola, 2009). MATERIAL AND METHODS Eleven samples were taken from Iraqi Exploration Oil Company representing depths (3400.0–2543.5m), these samples have been treated with the standard method in preparing palynological samples by adding HCl to dissolve carbonates, HF to dissolve silicates and with HNO3 to oxidize organic matters from the samples. SYSTEMATIC PALYNOLOGY INCERTAE SEDIS Informal Group ACRITARCHA Evitt, 1963 Genus Fractoricoronula Colbath, 1979 emend. Turner, 1984 Type species: Fractoricoronula cubitalia Colbath, 1979, p.15, pl. 5, Figs.1-5, (by original designation) Fractoricoronula densa sp. nov. Pl.1, Figs.1-9 2009 Genus A Al-Mola p.109-110, pl. 21, Figs.11–16, pl.22, Figs.1-4. DESCRIPTION Vesicle triangular, sides straight to convex, angles rounded, three processes arise from the vesicle, one process at each angle in the plain of vesicle, processes conical, flexible, the proximal side of the process is closed by inner wall or plug (2-3μm) Two new species of acritarchs from the Ordovician of Iraq 99 length and (2.5-5μm) wide, the processes terminated with acuminated tip. The vesicle wall is (3μm) thick while the processes wall (1μm) in thickness, both walls are laevigate. Excystement structure is observed in some specimens as epityche between any two processes. Holotype: Depth (2766.0 m.), slide number (N6), Fig.1, R 1.5/128.7, size 45 μm. COMPARISON This species is differed from F. cubitalia Colbath, 1979 by it is thicker vesicle wall and smooth ornament for both vesicle and processes wall and from F. trirbetica Turner, 1984 by the process length (which is less than the vesicle length), conical shape and thicker vesicle wall. MEASURMENTS Vesicle size in (μm) Process length in (μm) Width of process base in (μm) Specimens measured 28 49 16 45 2.5 5 27 Name Derivation: Greek densa, thick. Fractoricoronula khabouri sp. nov. Pl.1 Figs.7-9 2009 Genus A Al-Mola, p.110, pl.22, Figs. 5-7. DESCRIPTION Vesicle triangular, sides straight, angles rounded, three processes arise from the triangular angles in the plain of vesicle, the forth process arises from the vesicle face near one of the angles, processes conical and flexible, the proximal side of the process is closed by inner wall or plug (2-3μm) length and (2.5-5μm) wide, the processes terminated with acuminated slender tip. The vesicle wall is (2-3μm) and the processes wall (1μm) in thickness, both walls are laevigate. No excystement structure is observed. Holotype: Depth (2810.30m.), slide number (N5), Fig.7, R 6.0/133.8, size 43 μm. Amer D. Nader and Nazar A. Al-Mola 99 COMPARISON This species is distinguished from Fractoricoronula densa sp. nov. in having fourth process arising from the vesicle surface. MEASURMENTS Vesicle size in (μm) Process length in (μm) Width of process base in (μm) Specimens measured 43 47 21 45 3 4 5 Name Derivation: Khabouri after the Khabour river.