Kugler, H. G.

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348 CorrespondenceMay I finally add that, in the study of mineralogical equilibria, the practiceof adding ferric iron and manganese to ferrous iron has no justification andcan only bring confusion?I am indebted to Dr. G. M. Brown for a stimulating discussion on pyroxenetie-lines.PAUL BARTHOLOME.UNIVERSITE LOVANIUM,LEOPOLD VILLE,REPUBLIQUE DU CONGO.Mth February, 1961.REFERENCEMUELLER, R. F., 1960. Compositional characteristics and equilibrium rela-tions in mineral assemblages of a metamorphosed iron formation.Amer. J. Sci., 258, 449^97.TERTIARY OF BARBADOS, W. I.SIR,—In a recent paper on exploration results in Barbados, P. H.Baadsgaard (1960) introduced several insufficiently defined stratigraphicterms that appear to offer no improvement on the definitions of A. Senn(1940, 1948).Scotland Formation. Senn's Lower Scotland Formation includes theMorgan Lewis and the Walkers beds. Baadsgaard places his " P-unit"below the Walkers beds, and suggests the term " River Formation " for thethree members. He describes his " P-unit" as " a new subsurface unit ofblack, sometimes fossiliferous silty shales and mudstones with few thin finesandstones ". Senn (1940, p. 1553) gave a thickness of 240 metres for theexposed type-section of the Walkers beds. In a bore-hole 650 metres of thesebeds were penetrated without having reached the bottom. The " P-unit"appears to form part of the lower, unexposed Walkers beds, hence the term" River Formation " appears to be unnecessary. If Baadsgaard wants tointroduce a new subdivision he should bring out the lithological andpalaeontological differences, and discuss the boundaries as seen in theFriendship well.Senn's Upper Scotland Formation consists of Mount AH, Chalky Mount,and Murphy s beds. The "Bruce Vale Formation " of Baadsgaard embraces thesame three members, and for this reason appears to be synonymous withSenn's Upper Scotland Formation.Baadsgaard's " T-unit" is " a new subsurface stratigraphic elementbeneath the superficial Oceanic section in Friendship-1, Springyale-1, andInce-1 ". This unit " consists of blue or purple claystones with thin siltstonesand, locally, bedded sandstones and septarian limestones ". In Text-fig. 2 the" T-unit" crosses the time lines from Middle Eocene to Upper Oligoceneanalogous to the older " P-unit ". The " T-unit " of bore-hole Ince-1 iscovered by beds of Baadsgaard's " Oceanic Group ", for which no age isgiven. Baadsgaard shows in his Text-fig. 3 at least " three superimposedmajor structural plates " which he assumes to be " sheet-like displacementswith extensive overturned sections ". In none of the seven exploration wellsis the " T-unit " involved in these tectonic complexities. It always rests on topof Senn's Scotland Formation, and below Baadsgaard's " Oceanic Group ".Where palaeontologically identified in Ince-1, the "T-unit", Bruce Vale andRiver formations yielded faunas compared by Bronnimann with the Herreramember of the Cipero Formation of Trinidad. This makes them not olderthan Aquitanian and not " good Oligocene " as stated by Baardsgaard.Oceanic type marls are known from lower horizons of the Miocene, fromOligocene and from Eocene below which follows the Scotland Formation.Unless Baadsgaard can give strong proof of the highly diachronous natureof all these units it seems wiser to consider the younger, Miocene parts of thehttps://doi.org/10.1017/S0016756800060696Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 11 Jul 2017 at 07:13:51, subject to theCorrespondence 349Bruce Vale and River formations, together with the " T-unit", as a flyschfades within younger formations and not as part of the Scotland Formation.An analogy could be drawn with Trinidad where the muddy flysch fades of theNariva Formation interflngers with the Cipero marls.Baadsgaard's term " Scotland Group " is premature as long as there are nowell-defined formations to compose such a group.Joes River Formation. Baadsgaard believes the Joes River Formation to bea kind of shear-zone breccia locally mobilized by gas, oil, and water, andoccurring at different levels in his " Scotland Group ". He is, therefore, notprepared to give the Joes River beds the rank of a formation. Senn consideredthe Joes River Formation to be the product of mud volcanoes, partly inter-bedded with normally deposited silts. To Hess (1937, p. 73 and 1938, p. 89)these rocks appeared " to be of the nature of a submarine landslide " whichtook place during the downward movement of the West Indian tectogene.The Joes River Formation of Senn is stratigraphically defined. Though shearzones may have given rise to the formation of " pebbly silts ", and are possiblyresponsible for the presence of large blocks of Paleocene Discocyclina lime-stone and other rocks, we must look upon the pebbly silt as representingmudflows separated one from the other by layers of normally bedded silt andclay. Senn (1940, p. 1576) considered the massive silt breccia and boulderbeds to be resting with apparent unconformity on the Scotland beds.Baadsgaard found rocks of a lithology comparable to that of the Joes RiverFormation in Springvale-1 from 2,000 to 9,650 feet in the highly disturbedScotland Formation. Senn (1940, p. 1574) already considered the Joes Riverpebbly silt to have been derived from various parts of the Scotland Formation,and to have ascended in vents that could now be interpreted as " mobilizedshear zones ". The product of these shear zones could have been extruded,spread, and normally deposited as now found in the basal part of the OceanicFormation. The pebbly silt is incompetent. Under orogenic pressure it waseven injected into cracks of the Oceanic marls. Drilling in Trinidad hasproved that Miocene pebbly clays with large blocks and slip-masses ofpre-Miocene rocks form diapiroid bodies comparable to salt plugs. Thewriter saw no difference between the Joes River Formation and his " marine-slope clay-breccias " (Kugler, 1953, p. 51) which he described from Trinidad.Marchant (1960), who described the Ancon " Clay Pebble-beds " of Ecuador,also studied those of Trinidad. He found both to be very similar sedimentarydeposits, formed by submarine sliding. Baadsgaard (p. 24) states" . . . transitions can be traced from structureless Joes River to normalcountry rock " ; such transitions appear to exclude the presence of mobilizedshear zones.Oceanic Formation. Already Senn, and later Beckmann, have shown thatthe Oceanic Formation represents an uninterrupted sequence of foraminiferalmarls with planktonic assemblages ranging in age from the middle EocenePorticulasphaera mexicana zone to the top of the Codrington College marl,which belongs to the base of the Catapsydrax dissimilis zone of the CiperoFormation of Trinidad (Beckmann, 1956, p. 131). It is difficult to conceivehow this uniformly widespread formation should be replaced by the ScotlandFormation, or a facies of it, as is shown in Baadsgaard figure 2. The resultsof the bore-holes do not support his interpretation. No interdigitation ofOceanic type sediments with Scotland type sediments is known from surfaceexposures.Bissex Hill Formation. This formation with its shallow water fauna overlapsthe Oceanic Formation at Bissex Hill. It belongs to the Globigerinatellainsueta zone and, in facies and age, is to be correlated with the Ste. Croix bedsof Trinidad (Beckmann, 1956, p. 130). The Ste. Croix limestone is a memberof the Cipero Formation with its calcareous clays and marls. In Trinidaddeeper water Cipero marls were laid down contemporaneously with theSte. Croix member, while in Barbados the lower part of the " Upper OligoceneGlobigerina Marl " of Senn seems to be an age equivalent of the Bissex HillFormation (according to Beckmann, 1956, p. 140).https://doi.org/10.1017/S0016756800060696Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 11 Jul 2017 at 07:13:51, subject to the350 CorrespondenceUpper Oligocene Globigerina Marl. Senn (1948, p. 214) described this marlin detail. He knew it only from water wells, but Beckmann (1956, p. 140)states : " The Upper Globigerina marls of Senn are now known from surfaceoutcrops (e.g., at St. Mark's near Conset Bay). They represent the Globorotaliafohsi and Globigerinatella insueta zones. Therefore, they are not older than theBissex Hill Formation, as Senn (1948) assumed, but younger." FinallyBeckmann states : " The sedimentary fades of the ' Upper OligoceneGlobigerina marls' is closely related to that of the Codrington Collegemember of the Oceanic formation." Baadsgaard gives no description of his" Water-well Marls ". There is little doubt, however, that they are the sameas Senn's " Upper Oligocene Globigerina Marl ". It is here suggested that thismarl be given the name " Conset Marl". Senn (1948, p. 215) believed thatthere are indications of an unconformity between his Upper OligoceneGlobigerina Marl and his Oceanic Formation. According to Baadsgaard,exploration-well Adams Castle-1 penetrated 5093 feet of " an unbrokensequence from upper Eocene to upper Oligocene ". Apparently no " T-unit "or Bissex Hill Formation ws observed. The bore-hole proved the presence ofa deep, post-middle Eocene trough that existed in the S.W. corner of Barbados.Should detailed palaeontological studies of the bore-hole samples corroborateBaadsgaard's claim, one would be justified in extending the term OceanicFormation to include also marls of Miocene age. In such case one couldtreat the Bissex Hill Formation and the Conset Marl as members of theOceanic Formation.Acknowledgment. I am obliged to Mr. J. B. Saunders of Texaco TrinidadInc., for contributions to this note.H. G. KUGLER.NATURAL HISTORY MUSEUM,AUGUSTINERGASSE,BASEL, SWITZERLAND.22nd April, 1961.REFERENCESBAADSGAARD, P. H., 1960. Barbados, W. I. Exploration results, 1950-1958.Int. Geol. Congr. Report of 21st Session, xviii, 21-27.BECKMANN, J. P., 1956. Barbados. Lexique stratigraphic international.(Amerique latine). Fasc. 2b. Antilles.HESS, H. H., 1937. Geological interpretation of data collected on cruise ofU.S.S. " Baracuda " in the West Indies. Trans. Am. Geoph. Union., 1938. Gravity anomalies and island arc structure with particularreference to the West Indies. Proc. Amer. Phil. Soc, 79, No. 1.KUGLER, H. G., 1953. Jurassic to recent sedimentary environments inTrinidad. Bull. Ass. Suisse Geol. et Ing. Pet., 20, 27-60.SENN, A., 1940. Paleogene of Barbados and its bearing on history andstructure of Antillean-Caribbean Region. Bull. A.A.P.G., 24, No. 9., 1948. Die Geologie der Insel Barbados B.W.I, (kleine Antillen) und dieMorphogenese der umliegenden Grossformen. Eclog. Geol. Helv.40, No. 2.https://doi.org/10.1017/S0016756800060696Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 11 Jul 2017 at 07:13:51, subject to the

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