Some Ammonites From Central Saudi Arabia

GEOLOGICAL SURVEY PROFESSIONAL PAPER 643-D

Prepared in cooperation with the Saudi Arabia Ministry of Petroleum and Mineral Resources and the U.S. National Museum^ under the sponsorship of the Kingdom of Saudi Arabia and the U.S. Department of State

Some Jurassic Ammonites From Central Saudi Arabia By RALPH W. IMLAY CONTRIBUTIONS TO PALEONTOLOGY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 643-D

Prepared in cooperation with the Saudi Arabia Ministry of Petroleum and Mineral Resources and the U.S. National Museum, under the sponsorship of the Kingdom of Saudi Arabia and the U.S. Department of State

Descriptions and illustrations of some stratigraphically useful ammonites from Saudi Arabia

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1970 UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HIGKEL, Secretary

GEOLOGICAL SURVEY William T. Pecora, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 55 cents (paper cover) CONTENTS

Page Abstract. ______Dl Introduction ______1 Biological relationships.______---_--___-__-_-_- 1 Stratigraphic comments.______--____-____--_- 3 Faunal sequences and correlations-______3 Geographic and stratigraphic distribution.______8 Systematic descriptions.------.------10 References cited-_-___-__-______--___-__-__--____- 14 Index.______17

ILLUSTRATIONS

[Plates 1-4 follow index]

PLATE 1. Spiroceras, Normannitest, Dhrumaites, Rollieritesl, and Pachyceras. 2. Erymnoceras, E. (Pachyerymnoceras), and E. (Erymnocerites). 3. Grossouvria and Dhrumaites. 4. Dhrumaites. Page FIGURE 1. Generalized geologic map of part of the Northern Tuwayq quadrangle, Saudi Arabia, showing the distribution of Jurassic localities where collections were made in 1962______D2 2. Chart showing stratigraphic distribution of ammonites collected in central Saudi Arabia in 1962______3 3. Chart showing correlation of some Jurassic ammonite faunas in central Saudi Arabia.______5

TABLES

Page TABLE 1. Ammonite genera and subgenera of to ages in central Saudi Arabia, showing biological relationships and relative numbers available for this and Arkell's (1952) studies______-___-__--_ D4 2. Geographic distribution of some Toarcian to Callovian ammonites from central Saudi Arabia______-_-_--__--__--_-----_--_--_-- 6 3. Some Jurassic fossil localities in central Saudi Arabia.______8 HI

CONTRIBUTIONS TO PALEONTOLOGY

SOME JURASSIC AMMONITES FROM CENTRAL SAUDI ARABIA

By EALPH W. IMLAT

ABSTRACT and Mineral Eesources, and the U.S. Department of Jurassic ammonites collected stratigraphically in central State. It is based mainly on collections made by geolo­ Saudi Arabia show that the ammonite sequence and the ages gists of the Arabian-American Oil Co. and the U.S. of the formations as determined by Arkell in 1952 are essen­ National Museum since 1952, when W. J. Arkell de­ tially correct and need modification only for parts of the Dhru- ma Formation. In particular, the middle Bajocian age of the scribed all the available Jurassic ammonite collections lower part of the Dhrurna Formation is extended upward nearly from central Saudi Arabia and evaluated their age sig­ to the Ermoceras beds by an occurrence of Dorsetensia just nificance in terms of the standard European stages (Ar­ below the Dhibi Member. A late Bajocian age for the upper kell, 1952). A new evaluation of the age significance of part of the Ertnoceras beds is proved by the association of the ammonites at this time is opportune because o^her Spiroceras Mfnrcatiim (Quenstedt) with Ermoceras and Tliattir bocera-s throughout 5.5 meters of beds just above the Dhibi paleontologists are now describing the associated eehi- Member. noids and pelecypods, which, although much more The