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Phosphorite Deposits on the Sea Floor Off Southern California R BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA PHOSPHORITE DEPOSITS ON THE SEA FLOOR OFF SOUTHERN CALIFORNIA R. S. DIETZ, K. O. EMERY, AND F. P. SHEPARD CONTENTS Page Abstract.................................................................................................................................. 816 Introduction........................................................................................................................... 816 Acknowledgments................................................................................................................. 817 Description of the phosphorite........................................................................................... 817 General........................................................................................................................... 817 External character........................................................................................................ 817 Internal character......................................................................................................... 818 Phosphate minerals.............................................................................................. 818 Structure................................................................................................................ 819 Enclosed material................................................................................................. 819 Insoluble residues................................................................................................. 820 Associated sediments.................................................................................................... 820 Chemical and X-ray investigations of the phosphorite................................................. 821 Chemical analyses......................................................................................................... 821 X-ray data..................................................................................................................... 822 Paleontological data............................................................................................................. 823 Vertebrate remains....................................................................................................... 823 Foraminifera.................................................................................................................. 823 General................................................................................................................... 823 Fauna of the associated sediment...................................................................... 823 Fauna of the associated nonphosphatic rocks................................................. 823 Fauna of the phosphorite.................................................................................... 824 Distribution of phosphorite................................................................................................ 828 World distribution........................................................................................................ 828 Continental distribution...................................................................................... 828 General oceanic distribution............................................................................... 828 Submarine distribution off southern California...................................................... 828 General................................................................................................................... 828 Physiographic distribution.................................................................................. 829 Depth and relation to shore............................................................................... 830 Distribution in adjacent regions........................................................................ 830 Occurrence on land in southern California.............................................................. 830 Origin of the phosphorite.................................................................................................... 831 Previous views............................................................................................................... 831 Chemistry of phosphate in the ocean....................................................................... 833 General................................................................................................................... 833 Solubility data for Ca3(P04)2............................................................................. 833 Sources of error..................................................................................................... 835 Application of the solubility data..................................................................... 836 (815) Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/53/6/815/3431076/BUL53_6-0815.pdf by guest on 29 September 2021 816 DIETZ, et al.----PHOSPHORITE DEPOSITS OFF SOUTHERN CALIFORNIA Page Deposition essentially in situ...................................................................................... 836 Origin of nodules......................................................... ................................................. 837 Origin of oolites............................................................................................................. 838 Time of phosphorite deposition........................................................................................... 839 General considerations................................................................................................. 839 Possible Miocene age of phosphorite........................................................................ 840 General................................................................................................................... 840 Formed in nondepositional areas persisting since Miocene......................... 840 Formed by residual concentration of Miocene phosphorite nodules........... 841 Possible Quaternary (or Pliocene) age of phosphorite........................................... 842 General................................................................................................................... 842 Formed by infiltration and replacement of Miocene limestone.................... 843 Formed in reworked Miocene deposits............................................................. 843 Summary and conclusions................................................................................................... 844 References cited.................................................................................................................... 846 ILLUSTRATIONS Figure Page 1. Relationship between ionic strength (ju) and solubility of Ca3(PO.i)2............... 834 Plate Facing page 1. Phosphorite nodules and phosphatized bone.......................................................... 818 2. Internal characteristics of phosphorite.................................................................... 819 3. Phosphorite localities off southern California......................................................... 848 ABSTRACT Dredging operations on banks, on escarpments, and on walls of submarine canyons off southern California have shown that nodular phosphorite is the most abundant type of rock in these nondepositional environments. Approximately one-third of all the rock recovered is phosphorite. Petrographic and megascopic examination reveals that the nodules are largely formed by direct precipitation, but that they enclose some replaced material. Examination also shows that the phosphorite was probably deposited essentially in situ. Miocene Foraminifera have been identified in the nodules from many of the stations, but Recent or Pleistocene faunas have also been found in some of the phosphorite. Whereas the enclosed Miocene fauna suggests a Miocene age for most of the nodules, significant nonpaleontological data indicate that this fauna has probably been reworked into more recent deposits before enclosure in the nodules. INTRODUCTION During the series of geological cruises of the E. W. S c r ipps in 1938, rock was dredged from a large number of stations off the southern Cali­ fornia coast and from a few stations farther north. This rock will be described in a future paper by Emery and Shepard, but it was thought that special treatment should be given to the phosphorite because of its surprising abundance and because of the special problems which it raised. Phosphorite was recovered in greater abundance and was found in more localities than any other type of rock. Its abundance on the submarine surfaces in contrast to its. scarcity in outcrops over any area of the same size on land, and the possibility that the present environment is Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/53/6/815/3431076/BUL53_6-0815.pdf by guest on 29 September 2021 INTRODUCTION 817 that in which the nodules were formed gave special interest to the in­ vestigation. The large nodules were collected in bucket dredges (Shepard and Emery, 1940, PI. 5, fig. 2). Many of the smaller ones were found in snapper samples and in cores of unconsolidated sediment. Dietz made the principal laboratory study of the phosphorite samples but was assisted by Emery especially in the chemical investigation. Shepard conducted the marine investigation of the deposits. All of the writers have
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