STUDIES EST FORAMINIFERA 



103 



given by several of the authors, the present writer 

 tentatively places the Oligocene-Miocene boundary 

 between the Globorotalia kugleri and Catapsydrax dis- 

 similis zones of the Cipero formation. This level 

 approximately coincides with a marked increase in 

 planktonic species and with the first occurrence of the 

 genus Globigerinoides. This alone may not be sufficient 

 reason for placement of the Oligocene-Miocene bound- 

 ary, and further careful studies of the faunas of the 

 classical localities and comparison with their equivalents 

 in the Caribbean region will have to be made before a 

 more conclusive correlation can be offered. 



Type Section of Cipero Formation 



The first detailed description of the Cipero formation 

 was published by Stainforth (1948b). He used the 

 same three zones as proposed earlier by Cushman and 

 Stainforth (1945). In addition he distinguished a 

 "Flat Rock tongue" of different lithological aspect 

 separating Zones I and II. This "Flat Rock tongue" 

 was formerly also known as "Bamboo silt." 



In order to obtain an up-to-date interpretation of the 

 Cipero type area, based on the present subdivision of 

 the formation, a complete revision became necessary. 

 In addition to the reidentification of existing augerhole 

 samples from the area east and northeast of the type 

 section, 110 new sui-face samples were collected from 

 the type section along the coastline and several addi- 

 tional auger lines were run further inland. The 

 reassessment of the coastal section is siunmarized below 

 and the interpretation of the complete survey is shown 

 on the map and section in text-figure 19. 



In this connection it is imperative to note that marine 

 erosion along the Cipero coast amounts to at least 2 

 feet per year. This ingress leads to a changing picture 

 at least as far as the northern part of the section is 

 concerned. 



The fixed point from which all measurements were 

 taken is the southernmost of a number of iron rails 

 driven into the marls along the beach. This iron rail 

 is 140 feet south southeast from the present south end 

 of the sea wall. The coast hne along which the type 

 section is exposed runs approximately in a northeast- 

 southwest direction, the fixed point being 60 feet south- 

 west of the northernmost exposure. From the fixed 

 point a chain was run along the coastline in a south- 

 west direction to the "Cipero Nose" (a distance of 823 

 feet); from there 87 feet to the east and then again 

 2293 feet to the southwest. The composition of the 

 type section is as follows : 



From 60 ft. NE. to 2 ft. SW.: M.a,Tl; Globigerina ciperoensis 

 ciperoensis zone. 



From 28 to 235 ft. SW.: Marl; Globigertna opima opima 

 zone. 



From 250 to 368 ft. SW.: Clay, silty clay, marl lenses; 

 Globigertna ampliapertura zone, upper part ("Flat Rock 

 tongue"). 



At 406 ft. SW. : Pebble bed with whitish marl pebbles. Diag- 

 nostic Foraminifera of the bed are Globorotalia fohsi 

 barisanensis Le Roy, Globorotalia fohsi fohsi Cushman 



and EUisor, Globigerinoides triloba (Reuss) group, 

 tOrbulina sp., Globigerinoides rubra (d'Orbigny). The 

 youngest components are of Globorotalia fohsi fohsi 

 zone age. This pebble bed appears to belong to the 

 large slump-mass which occurs further to the south. 



From 433 to 536 ft. SW.: Marl and dark brown silty clay, 

 with rounded, iron-rich mudstone pebbles and thin 

 pebble beds. Globigerina ampliapertura zone, occasion- 

 ally with ?younger faunas ("Flat Rock tongue"). 



From 536 to 758 ft. SW. : Strongly heterogeneous interval; 

 predominantly dark, silty clay with marl lenses and 

 pebble beds. Samples taken here represent either mixed 

 faunas of Globigerina ampliapertura zone to Globoro- 

 talia fohsi fohsi zone age or, if taken from larger slip- 

 masses or pebbles, may be pure faunas from any zone 

 within the above named interval. Between 613 and 

 679 feet is a lens of Upper Eocene Hospital Hill marl. 



From 759 to 845 ft. SW.: Large slip-mass of indurated marl 

 forming the prominent "Cipero Nose" promontorj', 

 Globigerinalella insueta zone. 



From 848 to 913 ft. SW.: Pebble bed. Oldest component, 

 Globorotalia opima opima zone; youngest, Globorotalia 

 fohsi robusta zone. This pebble bed may be regarded 

 as the base of a large slump-mass resting unconform- 

 ably on the Globorotalia fohsi robusta zone. 



From 937 to 1483 ft. SW.: Marl; Globorotalia fohsi robusta 

 zone. 



From 1583 to 1774 ft. SW.: Marl; Globorotalia fohsi lobata 

 zone. 



From 1780 to 1794 ft. SW.: Marl; Globorotalia fohsi fohsi 

 zone, lower part. 



From 1815 to 1835 ft. SW.: Pebble bed. Oldest compo- 

 nents — Globigerinatella insueta zone, youngest — Globo- 

 rotalia fohsi fohsi zone. 



From 1845 to 2052 ft. SW.: Marl; Globigerinatella insueta 

 zone. 



From 2154 to 3203 ft. SW.: Marl; Catapsydrax stainforthi 

 zone. 



The type section can best be divided into the three 

 major units described below: 



1. The southern part of the section beginning in the 

 south with the Catapsydrax stainforthi zone and ending 

 with the Globorotalia fohsi robusta zone. This is a 

 normal sequence except that the Globorotalia fohsi 

 barisanensis zone is missing. A reduced Globorotalia 

 fohsi fohsi zone rests with a basal pebble bed directly on 

 the Globigerinatella insueta zone. 



2. The large slump-mass beginning with a pebble bed 

 lying on the Globorotalia fohsi robusta zone immediately 

 south of the "Cipero Nose" promontory and extending 

 to the northernmost pebble bed 406 feet south of the 

 fLxed point. Pebbles or larger slump-masses represent- 

 ing upper Eocene Hospital Hill marl and almost every 

 zone of the Cipero formation are found in this complex 

 unit. These pebble beds and slump-masses were ap- 

 parently deposited late in Globorotalia fohsi robusta 

 time (late Cipero), or at the beginning of Lengua time 

 and thus may well be an equivalent of the Rio Claro 

 boulder bed which occurs in the Globorotalia mayeri 

 zone of the Lengua formation in the eastern part of the 

 island. 



No planktonic Foraminifera younger than Globoro- 

 talia fohsi fohsi zone age have been found thus far in 

 the slump-mass and pebble bed complex north of the 

 "Cipero Nose," which itself is a large slumped unit of 

 the Globigerinatella insueta zone. It is thus possible 



