Foraminifera from Onotoa Atoll Gilbert Islands
Total Page:16
File Type:pdf, Size:1020Kb
US. Foraminifera From \m Onotoa Atoll Gilbert Islands GEOLOGICAL SURVEY PROFESSIONAL PAPER 354-H I ft Foraminifera From Onotoa Atoll Gilbert Islands By RUTH TODD SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 354-H Ecologic study of Recent assemblages from beaches , reefs, and shallow lagoon floor UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1961 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington 25, D.C. CONTENTS Page Page Abstract_________________________________________ 171 Examination of fish contents.________________________ 182 Introduction._ _____________________________________ 171 Foraminifera from pits._______ ______________----__ 184 Material studied____________________________________ 171 Local distribution of Calcarina and Baculogypsina _ _____ 186 Locality data_._________________________________ 173 Notes on selected species.- ________________________ 186 Fauna___________________________________________ 176 References cited-___________________________________ 188 Wet samples_______________________________________ 181 Index.____________________________________________ 189 ILLUSTRATIONS [Plates 22-25 follow index] PLATE 22. Recent benthonic Foraminifera from Onotoa Atoll. 23. Recent benthonic Foraminifera from Onotoa Atoll. 24. Recent planktonic Foraminifera from Onotoa AtolL 25. Foraminifera sands from Onotoa Atoll. FIGURE 40. Map of Onotoa showing locations of samples studied and major occurrences and relative abundance of Calcarina and Baculogypsina. _-_________________________________--__-____-__-_-__-------------------_------- 172 41. Diagrammatic sections of 7 dug pits on the northern main island of Onotoa Atoll-__---_-----_-------------- 185 TABLES TABLE 1. Distribution of Recent Foraminifera of Onotoa Atoll______________.________________________-_-_--__.-----_ 177 2. Occurrence of Foraminifera in stomach and gut contents of fish from the lagoon at Onotoa Atoll- _ .____..-___-_ 183 in SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY FORAMINIFERA FROM ONOTOA ATOLL, GILBERT ISLANDS Bv RUTH TODD ABSTRACT coral reefs on the southwest side (fig. 40). Its dimen The distribution of 168 species and varieties of smaller Fo- sions are roughly 12 miles long and 4 to 5 miles wide. raminifera is recorded within the lagoon and on the reefs and Latitude and longitude at its northwestern end are beaches of Onotoa Atoll as represented by 33 surface samples and 23 pit samples. Nearly all the species are well known in 1°46' S. and 175°30' E. Its physical description may shallow-water sediments of the tropical Pacific; 7 are indetermi be found in a preliminary report by Preston E. Cloud, nate; none are described as new. The lagoon collecting localities Jr. (1952), who in 1951 made the collections upon were all but one from depths no greater than 20 feet, and mostly which this study is based. from areas protected from the open ocean. Preservation in Acknowledgments. I am indebted to Preston E. alcohol of 24 samples permitted a staining process to be used and an estimate to be made of the very small live-dead ratio, and Cloud, Jr., for making available the well-documented determination of the living places of certain of the species. material and to John E. Randall for the identifications Recognition of two major distinctive habitats- (a) reef sur of the fishes studied. For helpful suggestions and dis faces and their adjacent slopes and (b) limesand bottom of the cussions I am grateful to Preston E. Cloud, Jr., and to lagoon is based in part on the relative abundance of species Richard Cifelli. Invaluable help in preparation of and in part on the presence of live (stained) specimens. Four species Calcarina spengleri, Baculogypsina sphaerulata, material and tabulation of results was received from Amphistegina madagascariensis, and Marginopora vertebralis Doris Low. The illustrations of the individual speci make up quantitatively most of the foraminiferal material in mens of Foraminifera were made by Elinor Stromberg. the reef sediments. Major foraminiferal constituents of the lagoon sediments are, in quantitative order: Amphistegina MATERIAL STUDIED madagascariensis, Heterostegina suborbicularis, Marginopora vertebralis, and Elphidium striato-punctatum. Quantitatively Samples were studied from the following areas of insignificant because of their smaller size, but common or abun Onotoa Atoll: dant in most samples, are many species of miliolids and several (1) Area open to ocean on west (leeward) side of atoll species in each of the following families: Textulariidae, Penero- plidae, Buliminidae, Discorbidae, Cyinbaloporidae, Anomalini- (7 samples from depths between 3 and 18 feet); dae, and Planorbulinidae. Globigerinids are present, but only (2) Lagoon: rarely, and appear to have come in from the open ocean through (a) Southern part (8 samples from depths be breaks in the reef. Seventeen other families are represented tween 6 and 17 feet, with 1 exception, mostly by rare or scattered occurrences. f 11683 [GOC-55] collected from 48 feet) Stomach and gut contents of 22 fish were found to contain Foraminifera tests nearly as varied as the naturally occurring (b) Central and northern part (7 samples from fauna. The fact that most of the individual fish did not contain depths down to 20 feet); as great a variety as the composite of all the fish suggests a (3) Reef areas (3 samples from leeward side of atoll rather localized feeding area for each fish. and 2 from windward); Seven pits provide short sections a maximum of 10 feet into (4) Southern part of atoll (4 samples of fine sediment the sediments that make up the northern main island. These sediments are interpreted as beach sands overlying and transi and incipient beachrock); tional to reef flat deposits. (5) Islands along the east (windward) side of atoll (a) Beach sands (4 samples) INTRODUCTION (b) Material from pits having depths from 20 Onotoa Atoll is a "dry" atoll (referring to its rainfall inches to 11% feet. The pits start in beach [Cloud, 1952, p. 10-15]) in the southern part of the sands, in which many of the specimens are Gilbert Islands. It is elongate northwest-southeast severely corroded (13 samples), and pene and bordered nearly continuously on the northeast trate through progressively richer transi (windward) and south sides by narrow islands but either tional sediments (7 samples) into sedi open to the ocean or protected by discontinuous living ments of a reef-flat horizon (3 samples). 171 172 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY EXPLANATION O Foraminifera locality, showing per centage of occurrence of Calcarina and Baculogypsina t Church Maneaba ge meetinghouse FtGUEE 40. Map of Onotoa showing locations of samples studied and major occurrences and relative abundance of Calcarina and Baculogypsina. FORAMINIFERA FROM ONOTOA ATOLL, GILBERT ISLANDS 173 LOCALITY DATA u.s.o.s. loc. No. Field localities and descriptions The following locality and sample descriptions, taken shore) end of lagoon-side jetty at Govern from P. E. Cloud's field notes, are arranged in order of ment Station and 660 ft inshore from sea beach along line bearing S. 87° W. at Pacific their U.S. Geological Survey Foraminifera locality Science Board campsite. Pit similar to numbers. They include pertinent details of the various GOC-1. Pit section in descending order, environments from which the Foraminifera from Onotoa with unit thicknesses, is: Atoll, Gilbert Islands, were derived. f11644. GOC-2A. Medium- to fine-grained limesand, dark brownish gray from organic matter. U.S.G.S. loc. No. Field localities and descriptions Worn Calcarina about 60 percent; remainder of detrital fines. Roots uncommon. Some fl!639-fll643. GOC-1. Southern part of northern main island, about 1,100 ft S. 41° E. from east stones as much as three-fourths of an inch in (inshore) end of lagoon-side jetty at Govern diameter. Top 5 in. GOC-2B. Medium-grained limesand. Worn ment Station and 325 ft inshore from sea beach f11645. Calcarina about 70 percent with occasional along line bearing S. 87° W. at Pacific Science pebbles as much as three-eighths of an inch Board campsite. Pit in which water level in upper 7 in. Up to 95+ percent worn fluctuated with tide. Pit section in descend Calcarina below. Remainder is detrital ing order, with unit thicknesses, is: fl!639. GOC-1 A. 99+ percent medium-grained Cal- CaC03. Tan to flesh colored; darker above than below. Roots abundant, as much as carina sand, dark brownish gray from organic three-eighths of an inch in diameter. Thick matter. Roots very abundant, up to seven- eighths of an inch in diameter. Foraminifera ness, 19 in. worn or eroded by organic acids. Subaerial f 11646. GOC-2C. Loose CaC03 gravel composed of 50 percent CaCOs pebbles as much as 2J4 in. accumulation?. Top 9-10 in. long and 50 percent worn Calcarina and f 11640. GOC-1B. 99+ percent medium-grained dark- tan Calcarina sand, abruptly gradational to detrital CaCOs. Roots abundant, as much as one-fourth of an inch in diameter. Thick f 11639 (GOC-1 A). Sample f 11640 differs only in organic content, abundance of roots, ness, 11 in. and good preservation of Calcarina, suggest f11647. GOC-2D. Strongly indurated flesh-colored ing only slight transportation. Roots mod granule sandstone, of varied detrital CaCOs. erately abundant, as much as one-half of an One loose sand layer 2-4 in. from base. Roots inch in diameter, cutting off abruptly at very rare. Thickness, 15 in. base. Subaerial accumulation?. Thickness, f 11648. GOC-2E. Very fine grained flesh-colored 16-17 in. detrital limesand. No roots. Thickness, fl!641. GOC-1C. Similar to fl!642 (GOC-1D), which 6 in. follows, but has alternating layers of semi- f11649. GOC-2F. Zone of Heliopora. Essentially indurated to indurated material. Basal 1-4 same as fl 1643 (GOC-1E). No roots. Reef in. indurated. Roots rarely extend into unit flat horizon? Thickness, 51 in. C. Probably deposited along beach near fl!650-fll653. GOC-3. Southern part of northern main reef flat. Thickness, 7-10 in. island, about 870 ft S.