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Stratigraphic Lexicon of Iraq
Lexique Stratigraphique International, Asie (Iraq)

Tertiary by R.C. van Bellen;
Mesozoic and Palaeozoic by H.V. Dunnington, R. Wetzel and D.M. Morton
Under the direction of Louis Dubertret

FOREWORD

In 1959, the Centre Nationale de Recherches Scientifique (CNRS) published the Stratigraphic Lexicon of Iraq by R.C. van Bellen, H.V. Dunnington, R. Wetzel and D.M. Morton. This publication was part of an international series of lexicons that covered many countries worldwide. Besides Iraq, the CNRS published several other Middle East lexicons in the 1960s and 1970s; these include Iran, Jordan, Lebanon, Qatar, Saudi Arabia, Syria, Turkey and Yemen.

The lexicon of Iraq was the first compilation of the names and descriptions of all the strata and rock units in Iraq that were known up to that time. Since the publication of this book 46 years ago, many new studies on the geology of Iraq have been written in Arabic and other languages, by academics, geological surveyors and industry professionals. Also since 1959 more oil fields have been discovered and studied using more modern subsurface tools. This additional information has substantially increased our knowledge and understanding of the geology of Iraq. Naturally, because of its fundamental nature, the original 1959 lexicon is referred to either directly or indirectly in most of these newer studies.

But many interested readers do not have access to the lexicon as it is now rarely found in libraries or on the bookshelves in the offices of professionals and academics. It is because of this shortcoming that the Ministry of Oil of Iraq, Chevron and GeoArabia have undertaken to reprint the original lexicon. By providing this book to all interested readers, both in hardcopy and electronically, we believe that the geoscience community will be in a better position to understand various important aspects of the geology of Iraq.

Firstly, from an historical perspective, the original lexicon reviews, in an authoritative manner, the origins of the names assigned to each rock unit in terms of geographic localities. It also provides the geographic coordinates of the outcrop sites and wells where they are found (see Plates I and V). This allows geologists to review and restudy the rock units in outcrop and to identify the wells where the rock unit was encountered in the subsurface.

Secondly, the lexicon of Iraq presents the first formal definitions of the rock units in terms of groups, formations and members – most of which continue to be used today. The formally defined rock units in 1959 are identified in this reprint by capitalizing the first letters of the words Group, Formation and Member when they succeed the name of the unit (see Plates I to IV and VI). This modern and international practice renders communication regarding stratigraphic conventions clearer and more precise. Conversely, informal and obsolete rock units are identified by not capitalizing their rank and similar descriptors. From this framework it becomes possible to maintain or update, where necessary, the nomenclature and status of the rock units to reflect their current standing.

Thirdly, the 1959 lexicon provides the names of the original authors and the titles of the studies in which they wrote about the rock units, whether in journals, books or unpublished reports. Accordingly the results of studies that were written since 1959 can be more readily related to those of the original authors. This insures greater continuity between the original stratigraphic framework of Iraq and subsequent scientific and technological developments.

The original lexicon of Iraq should therefore neither be forgotten nor considered to be the only and final authoritative source of information on the stratigraphy of the country. Instead it should serve as the source for further studies or even a second edition that would update the rock units in a systematic manner. Indeed a second edition could contain modern data such as electrical logs and seismic images. It could recast the stratigraphic column of Iraq in terms of the modern international Geological Time Scale and provide correlations to other rock units in the Middle East.

With the revolution in information technology, the data and interpretations of the rock units in Iraq could be maintained in an electronic format and updated on a regular basis. This would make it easier for all interested parties to follow the latest scientific developments and interpretations.

But aside from serving as a source for further studies, the 1959 lexicon in its own right, can serve as a good introduction for petroleum development and exploration experts who are not familiar with Iraq’s geology, and of course for students. For petroleum development, it names and describes the main reservoir zones in each formation and their characteristics. It compares many of these zones to ones of the same age, but having different names, in nearby countries.

For exploration geologists and geophysicists, the lexicon shows the distribution of the various rock units in space and geological time. It also interprets the ancient settings in which these rock units were deposited. In the case of Iraq’s strata, the lexicon reaches back in time to the oldest known rocks in the country, namely the Khabour Quartzite Formation that was deposited in the Ordovician Period – some 450 million years ago. Besides a special section for this formation (and all the other formal formations and members), the section General Outline of Stratigraphy narrates how this and younger formations were successively deposited during repeated advances and retreats of the sea. These cycles of transgression and regression are also illustrated in the plates that are reprinted in an enlarged scale and in color.

For each formal rock unit the lexicon includes a dedicated section that describes its characteristic lithology, as well as the depth at which it is encountered and its thickness range. It reviews the relationship between each rock unit and other strata that lie above and below it, and how the unit passes laterally to other units. It identifies important stratigraphic breaks and unconformities that resulted from the erosion of the underlying strata during episodes of tectonism or exposure. The ages of the rock units are interpreted based on extensive collections of fossils that are listed in detail.

The geology of Iraq records a fascinating story that goes back in time to more than 450 million years ago, and covers an area of some 500,000 square kilometers from the margins of the ancient Tethyan Oceans to the north and east, to near the Arabian Shield in the southwest. Unraveling this story will undoubtedly continue to provide not only important scientific achievements but also enhance our understanding of the petroleum geosciences and engineering disciplines of our country. The reprinting of this lexicon represents a small contribution to this important endeavor.

Dr. Ibrahim Bahr al-Ùlum
Minister of Oil of Iraq

Dr. Ibrahim Bahr al-Ùlum was appointed as Iraq’s oil minister on 8 May 2005. Previously he held the position of Oil Minister as a member of the Iraqi Governing Council from September 2003 to mid-2004. After graduating from Baghdad University in 1976 with a BSc degree in Petroleum Engineering he worked for five years as a Reservoir Engineer focused on reservoir stimulation studies for the Ministry of Oil in Kuwait. He then commenced his postgraduate work towards his MSc and PhD studies at the New Mexico Institute of Mining and Technology. From 1993 to 1996, Dr. al-Ùlum was employed by Energy Trade International in the UK to provide consulting services on the private sector of the Kuwaiti oil industry. From early 1997 until 2003, he was employed initially by Duke Engineering & Service in the UK which eventually became part of ECL, a broad-based E&P consulting company with offices in the UK, US, Canada and Australia.


GEOARABIA PREFACE

The Stratigraphic Lexicon of Iraq by R.C. van Bellen, H.V. Dunnington, R. Wetzel and D.M. Morton was published in 1959. Today, this book continues to serve as one of the foremost sources of information on the Mesozoic and Cenozoic geology of Iraq and the Arabian Peninsula. The long life of this book is due to many factors.

Firstly, the authors wrote the comprehensive descriptions of all the known rock units and biostratigraphic zones in Iraq (as of 1959) mostly based on direct examination of the data. Therefore the descriptions continue to be applicable today. Secondly, they documented and correlated these units from outcrop to the subsurface across a vast region of some 500 by 1,000 square kilometers. This region forms a major part of the petroleum habitat in the Middle East.

Thirdly, and perhaps most surprisingly, they placed all of these rock units into a regional tectono-stratigraphic framework that predates Earth Science breakthroughs such as Plate Tectonics and Sequence Stratigraphy. Geologists who are familiar with the tectono-stratigraphic evolution of Arabia will immediately recognize in Plates II to IV and VI (redesigned here as large colored posters) that these authors had already recognized most of the Mesozoic and Cenozoic second- and many third-order sea level cycles and main tectonic unconformities from the Tethyan realm near the Zagros Mountains, to the stable shelf in western Iraq, Kuwait and Saudi Arabia.

Besides these important achievements, the lexicon contains a vast array of primary data and insightful interpretations that are of considerable value today. It is for these reasons that GeoArabia has located a rare copy of the book and reprinted it with the sponsorship of the Ministry of Oil of Iraq and Chevron. This reprint makes every effort to represent the original work without modifying its technical contents. To the contrary, it adopts several editing conventions that emphasize the original meaning. The following discussion identifies the key editing conventions that were applied to the original book.

Authors: In the present reprint, for each rock unit, two categories of names are listed under the heading “Authors”. The first category provides the names of the primary authors who wrote about the rock unit in reports, journals and books. They are credited with, for example, first naming the unit, or first defining it, etc. The names of these primary authors are repeated here from the original lexicon with minor reformatting (e.g. parenthesis, punctuation). The second category consists of the names of one or more of the lexicon’s authors who compiled the description for the rock unit from the works of the primary authors. In this reprint the names of the second category of authors are shown in brackets at the end of the list of primary authors. In the original lexicon the names of these authors were identified by their initials at the end of the description of each rock unit: H.V.D [H.V. Dunnington], D.M.M. [D.M. Morton], R.C.V.B. [R.C. van Bellen] and R.W. [R. Wetzel].

References: In the main text of the lexicon the title of some papers is given in full although they are repeated in the section entitled “References”. In this reprint, only the author and year is given in the text. Throughout this reprint, references cited in the main text and in the reference list are restyled to be consistent with GeoArabia’s format (e.g. parenthesis, punctuation). Several references are made in the text to manuscripts that were in preparation (sometimes indicated as MS) and these are shown as “manuscript, then in preparation” in the Reference list. Where MS followed the names of fossils, the MS was left in place.

Formal Rock Units: In the original lexicon, the authors stated which rock units are formal (Tables 1 to 6 and Plates I to IV and VI); however, they did not capitalize the word “group”, “formation” and “member” where these terms followed the names of formal rock units. The formal names of some rock units also carry a lithological description “Limestone”, “Shale”, etc. In this reprint all formal units (including formal lithological descriptions) are capitalised wherever they appear.

For example, the original lexicon shows the formal “CHIA ZAIRI LIMESTONE FORMATION” as the title for this rock unit and “Chia Zairi limestone formation”, “Chia Zairi limestone” or “Chia Zairi formation” in the text, tables and plates. In this reprint, the name of this rock unit is written as “Chia Zairi Limestone Formation”, or “Chia Zairi Limestone” or “Chia Zairi Formation”. Where the authors refer to the “Chia Zairi limestones” the term limestones is not capitalized.

Informal Rock Units: All rock units that are indicated as informal are not capitalized except for the name of localities; for example, Mosul marble, etc. The authors noted that: “In order to stress the informality of the beds, distinguished in certain formations (e.g. Dammam Formation, Lower Fars Formation) the unit term bed has been capitalized as Bed. Article 1, Remark (c) of the rules in Ashley et al. (1939) prohi­bits capitals for the initial letters of terms designating units.” In the present edition this convention was reversed so that all units, beds, etc. are not capitalized.

Moreover, each formal unit contains a subsection listing its informal or obsolete synonyms that are again not capitalized. For the cited synonyms the encompassing quotations were not consistently applied in the original and these were removed where appropriate. This was possible because the formal rock units are capitalized here. Also the word “part” is here positioned immediately after the relevant rock unit (instead of in parenthesis after it) to emphasize that the authors meant that the correlation is partial to the formal rock unit that is being described.

Qualifiers of Stages: In the reprint the use (or suppression) of capitalization of the qualifiers “upper, late, middle, lower, and early”, where they appear before the name of a stage (age) or period (system) was not modified. Accordingly the apparent inconsistency of using, for example, “Upper Aptian” and “late Aptian” (sometimes late-Aptian”) was not modified. Nor were these terms switched to reflect time (late, mid, early) or stratigraphic position (upper, middle, lower). Thus phrases that mix time and position like, for example, “late Upper Campanian” or sometimes “uppermost Campanian” remain as in the original. In the reprint the respective position of units and ages occurring at contacts is written “Upper Unit/Lower Unit” or “Younger Age/Older Age”. Also the informal “Middle” Cretaceous (capitalized “Middle” in the original lexicon) was not decapitalized. Finally the term “Maestrichtian” is spelled here as “Maastrichtian”.

Combining Paragraphs: The page size of the original lexicon is about half that of this edition’s page size and, in places, it consists of many short paragraphs or single sentences. In this reprint, for the benefit of conciseness, related short paragraphs are combined. Also some sentences have been repositioned to sections where they retain their context.

Combining “Location and Thickness” Sections: For the formally defined rock units this edition combines the sections entitled “Location” and “Thickness”, into a “Location and Thickness” section. This is because the thickness of a rock unit is usually a single numeric entry and derived from the depths cited in the well or outcrop under “Location”. The phrase “Brief description of type section” was deleted as in all cases it now refers to the indented discussions under the sections on lithology, fossils, age, underlying and overlying formations and detail of contact. Furthermore, where appropriate, this reprint provides all thicknesses in both meters and feet (1.0 m = 3.28 ft).

Tables 1–7: Tables 1–6 (pages 15-22) were not numbered in the original lexicon. They are here positioned close to where they appeared in the original text. In the original lexicon the names of wells are cited by operating company (B.O.D., B.P.C., I.P.C., M.O.D., etc.) followed by the well name (e.g. Kirkuk Well No. 109). In the present reprint the names of wells are shortened to just well name and number (e.g. Kirkuk-109). The new Table 7 (pages 238-239) consists of a list of all the wells cited in the text, operating company of that time, and coordinates (where known). Also, where possible, phrases with several named wells and name places are listed alphabetically. Where coordinates are cited the word “lat.” and “long.” were removed as the numeric coordinates are followed by E (east) and N (north).

Capitalization and Nameplaces: Where geographic features are considered well known then their descriptor was capitalized; for example, Shield (as in Arabian Shield). Other examples are Depression, Mountain, River, Valley, Village, etc. The words foraminifera, ostracoda, etc. were decapitalized and not italicized. Throughout the text the Arabian Gulf was substituted for the Persian Gulf.

Dr. Moujahed Al-Husseini
Editor-in-Chief, GeoArabia


 

TABLE OF CONTENTS

Page

4 Foreword
6 GeoArabia Preface
9 Introduction
13 Acknowledgements
15 General Outline of Stratigraphy
15 Paleozoic
15 Triassic
16 Jurassic
17 Cretaceous
23 Tertiary
29 Stratigraphic Units
225 References
229 Unpublished Reports and Correspondence
230 Stratigraphic Index

Tables

15 Table 1: Palaeozoic Formations
16 Table 2: Triassic Formations
16 Table 3: Jurassic Formations
19 Table 4: Early Cretaceous, Berriasian-Albian Formations
21 Table 5: Middle Cretaceous, Albian-Turonian Formations
22 Table 6: Late Cretaceous,Turonian-Maastrichtian Formations
238 Table 7: Wells cited in Text and Plates

Plates

Plate I: Locations of Type Sections of named Mesozoic and Palaeozoic Rock Units in Iraq

Plate II: Age Relationships of named Mesozoic and Palaeozoic Rock Units in Northern Iraq (Mosul Liwa)

Plate III: Age Relationships of named Mesozoic and Palaeozoic Rock Units in Northern Iraq

Plate IV: Age Relationships of named Mesozoic and Palaeozoic Rock Units in Northern Iraq (with projection to Kuwait and Saudi Arabia)

Plate V: Index of Place Names including Type Localities of Tertiary Rock Units

Plate VI: Age Relationships of named Tertiary Rock Units in Iraq

 

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