Origin of Ball and Pillow-like Structures in Tanjero and Kolosh Formations in Sulaimaniya area, NE-Iraq
By: Kamal Haji Karim, 1Department of Geology, University of Sulaimani, Sulaimani City
Published in: (KAJ) Kurdistan Academicians Journal, 2005, 4(1) part A
Keywords: ball and pillow, sedimentary structure, deformation, Tanjero Formation, Kolosh Formation, geology of Kurdistan, deformation.
Pettijohn (1975), Potter and Pettijohn (1977) found Ball and pillow structures in both sandstone and limestone. The former author ascribed these structures to foundering of unconsolidated sand into quasiliquid substrate. He added that they are post depostional structures before deposition of overlaying strata “penecontemporaneous deformation”. The latter authors argued in detail all aspects of these structures they attributed them to different origins such as foundering of sand beds and slump. Ball and pillow structures are defined by Bate and Jackson (1980) as: primary sedimentary structure found in sandstones and some limestones, characterized by hemispherical or kidney-shaped mass resembling ball and pillows and commonly attributed to foundering: e.g. a flow roll or pseudonodules Tanjero and Kolosh Formation belong to Maastrichtian and Paleoceneages respectively. They are identified as clastic dominated units, consisting mainly of alternation of medium-bedded sandstone and calcareous shale. The formations crop out as a northwest-southeast belt in northeastern Iraq near the border with Iran in the High Folded and Imbricated Zones (Buday 1980  and Buday and Jassim, 1987). According to Karim (2004), both formations were deposited in an early foreland basin in front of an advancing positive land of the Iranian plate. The outcrops of both formations, in Sulaimaniya area, contain many ball and pillow structures which consist of The bodies of the structures are composed of fine or medium sized clayey or clean sandstones and in some case they are composed of limestones (Plate 2.6). The pillows or balls may be connected by necks or completely isolated and floating freely in marly or shally matrix (Plate 1.4, 2.4, 2.5 and Fig. 2.4D). Those which are exist in the thick beds of marl or shale is well developed and closed to sphere (Plate1.3, 1.4 and 2.5) while those found in the sandstone-dominated intervals are badly developed (Fig.2). Most structures show concentric lamination while others are structureless.
Origin of the structuresAl-Shammary and Yahya (1997) studied similar structures in the Kolosh Formation and concluded that they were developed bymovement of unconsolidated sand sediments due to specific gravity. Al-Rawi (1981, p.45)  showed similar structures photographically and attributed them to slump structures. Recently Lawa( 2004, p.226)  found also ball and pillow structures in Kolosh Formation and included them in the sedimentary structures which regarded them as evidence for criteria of synsedimentary tectonic activity in the basin of the formation. Ball-and-pillow structures in the present study are interpreted to be late diagenetic structures (deformational and post depostional sedimentary structures) developed after lithification during burial and subsequent uplifting.Fig.(2) Different stages of ball and pillow development
B. They are seen inside soft massive beds of marl or shale without sedimentary bedding and lamination, which show clear disturbance flowage of materials in different direction. Originally the marl or shale possibly contained many laminations and few sandstone beds (Fig.2A). But later they changed to massive ones by deformation.
Ball and pillow in other rocks rock
The paper has the following conclusions:
1. Many deformational structures are found during fieldwork, which are related to the end members of a proposed process of development of ball-and-pillow-like structures in Tanjero and Kolosh Formations. 2. The field evidences showed that these structures started with jointing of the competent sandstone beds (as one end member and completed with well developed ball and pillow structures (as other end member).3. The two end members and transition structure are all combined together and showed by field photographs and discussed with sketches to illustrate field-based conceptual model (deterministic model) of paragenesis of these structures.4-The ball-and-pillows are well developed in fine grain intervals while in coarse grain intervals not so.5. These structures are studied in the field in several localities and concluded they are formed during deep burial after deposition by differential load pressure and subsequent tectonic horizontal stresses.5- Same structure, in large scale, are found also in diorite and shale of Jurassic rocks in the studied area. Therefore the model of development of ball and pillow structures is valid for igneous and metamorphic rocks also.
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