Origin of Ball and Pillow-like Structures in Tanjero and Kolosh Formations

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

 

Abstract

 Tanjero and Kolosh Formations as   clastic dominated units consist 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. The outcrops of the formations, in   Sulaimaniya area, contain many ball and pillow-like structures These structures are studied in the field in several localities and concluded that they are formed during   burial after deposition by differential load pressure and tectonic   stresses. Different stages of the development are found in the field and all combined to show their   paragenesis. The author used, on the basis of field data, suitable sketch and field photos for establishing a conceptual (deterministic) model of development. The model    includes jointing and possibly fracturing (as starting point during burial stage) and converting to spheroidal or pillow-like bodies at the final stages of developments by tectonic deformation and load pressure. No evidence is found to relate   the recorded ball-and- pillow to the   deposition or early diagenetic process.

    Keywords: ball and pillow, sedimentary structure, deformation, Tanjero Formation, Kolosh Formation, geology of Kurdistan, deformation.

Introduction

Pettijohn (1975)[1], Potter and Pettijohn (1977)[2] 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)[3] 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 [4] and Buday and Jassim, 1987[5]). According to Karim (2004)[6], 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.

Fig.(1) Geological map of the studied area ellipsoidal, or pillow like sandstone and limestone bodies. These structures are observed, by the author, in different types of rocks supposed to be deposited in different environments such deep and shallow. These bodies range in size both  formations, from 4cm to more than 20 cm in diameters   (Plate1).
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) [8] showed similar structures photographically and attributed them to slump structures. Recently Lawa( 2004, p.226) [9]    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

    Through fieldworks the two end members (jointed blocks) and intermediate stages of ball-and-pillow structures are indicated. All the stages are photographed and are illustrated by suitable diagrams, which combined as a conceptual model (natural model) for development of these structures. The model includes and      passes through the    following steps:

   1. The initial stage starts with jointing   and fracturing of thin or medium bedded sandstone or limestone during burial by differential pressure. The beds are must be stiff (competent) and intercalated between thick beds of soft marl or shale (Fig.2A and Plates 1.1 and 2.1). These form angular (rectangular and rhombic joints and fractures) blocks of sandstone.

 2.When the tectonic pressure increase the soft marl is injected into the spaces between the blocks through fractures. The same process may occur by differential load pressure but of less effect than tectonic. This flowage is due to plastic flow of soft enveloping soft layers.  This     leads to smoothing of edges of the blocks. This strongly analogous to the flow of plastic salt inside country rocks shown by Warren, (1999)[10]. The sketches showed by him include   smoothing of that part of country rocks directly in contact with the moving salt materials. Hyndman, (1979) [11] discussed similar processes by forceful injection. It is  possible that blocks are dislocated from their position in all direction. This stage of ball and pillow is similar to the development of boudin (sausage) which discussed by Davis and Rhynolds (1996) [12]. Potter and Pettijohn (1977, p.201)[2] found these structures in highly deformed shale which   wrapped the pillows by squeezing.  In this stage an edgeless polygonal structure is formed which is transitional between the original joints and the ball-and-pillow structures (Plates 1.2, 2.2, 2.3 and   Fig.2B). This stage includes further possible dislocation of the blocks so that each one is isolated from the adjacent   ones. This stage is similar to development of boudinage structures in highly deformed competent beds.

3. Further increase of the pressure and flowage of marl causes removal of all edges with possible rotation of blocks.   The rolling is   attributed to flow of soft material in the different direction due to tectonic stresses. Rotation is not impossible in rocks as Carey (1998, 1001) [13] mentioned and illustrated by diagram rotation of resistant grain in metamorphic rocks during syn-tectonism. Finally the ball-and-pillow structure is developed   (Plate 1.3, 1.4, 2.6 and fig.2C and D). Davis and Rhynolds (1996) [12] mentioned rotation of boudins during development and deformation. Karim (2003b, p12) [14] showed the rotation of competent inclusions by flowage of soft material in the black marble of Penjween area. Van Den and Brun (1987)[15] studied rotation of competent bodies (inclusions) in an incompetent matrix by high strain shear zones. Rosas et al. (2001)[16] showed by experiment rotation of rigid inclusion by simple shear in a viscous matrix. The blocks and matrix, in this stage were deformed more or less plastically while they underwent brittle deformation in first stage. We must not ignore the role of weathering in modification of final shape of the structures and magnifying the miner difference in composition and hardness. But the original shape is due to the effect of stress and diagenetic processes.

  4-The ions-bearing   solution   migrates from the compressed soft materials into block    precipitating cementing materials and converting them to coherent bodies.  Mcbridge et al. (2003)[17] found large spheroidal calcite concretion (20-200cm) in sandstone of Wyoming and Utah, U.S.A. which grown displacively  from solution bearing  Ca  ions. Pettijohn et al, (1987, p.122) [18] showed large balls of cross bedded sandstone.   They classified them under the concretion and  attributed their development to transport of solution and   cementation.  The evidences for the late diagenetic origin of these ball and pillows-like   structures are cited   as following:

Fig.(3) Different field photos showing stages  of ball and pillow development In the Tanjero FormationFig.(4) Different field photos showing stages  of ball and pillow development in  the Kolosh Formation

 

 

Ball and pillow in other rocks rock

 Conclusions

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.