CLAY MINERALS AND GEOMORPHOLOGY 1N FOUR CARIBBEAN ISLANDS

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1 Clay Mineals (1966) 6, 371. CLAY MINRALS AND GOMORPHOLOGY 1N FOUR CARIBBAN ISLANDS P. J. BAVN AND M. J. DUMBLTON Rad Reseach Labaty, Ministy [ Tanspt, Cwthne, Bekshie (Received 19 Januay 1966) ABSTRACT: Clay mineal analyses f Caibbean sils illustate the diffeences in cmpsitin that can aise fm diffeences in tpgaphy and paent mateial, and emphasize the diffeences between the gups f ppsed new engineeing classificatins f the sils based n these facts. Within ne set f envinmental cnditins the clay mineal assemblage was easnably cnstant. xamples ae given f lcal diffeences in clay type which wee celated with vaiatins in climate and mde f fmatin. In pepaing engineeing sil suveys it has been fund that the gemphlgical units f a egin can be used as a basis f the classificatin and mapping f infmatin equied by the enginee. This is because sil type (including minealgical cmpsitin) is the pduct f the paent mateial and the envinmental cnditins expeienced in the paticula gemphlgical unit in which it ccus, and bth the sil type and envinmental and tpgaphical cnditins influence the engineeing use f the sil. Sil samples have been cllected fm fu Caibbean islands cveing a wide ange f gelgical and tpgaphical cnditins. This pape gives the esult f minealgical analyses dne n these samples. The esults ae guped unde gemphlgical units, which in the tw lage teities, Tinidad and Jamaica, have been used in ppsed engineeing mateials classificatins, and it is shwn that in each gup the clay mineal assemblage is easnably cnstant. MINRALOGICAL XAMINATION Sixty-nine sil samples wee examined by X-ay diffactin analysis. A mm Philips pwde camea with special cllimat and beam tap f lw angle wk was used with CK, adiatin, supplied by a Philips PW 19/3 X-ay diffactin geneat with a fine-fcus table; a 3-h expsue was necessay. The whle sil was examined; the pcedue was pacticable because mst f the sils cntained a

2 372 P. J. Beaven and M. J. Dumbletn substantial amunt f clay, and it had the advantage f giving infmatin n the ttal mineal assemblage. ach sample was examined afte teatment with glycel, and afte the teatments whee necessay. The usual methds wee used t identify the mineals pesent (Bwn, 1961; Dumbletn, 1963); the amunts pesent wee estimated ughly by visual cmpaisn f the intensity f the diffactin lines with thse in standad expsues f pue mineals. The elative quantities indicated in the Tables cespnd t the fllwing appximate anges f cmpsitin: much, 1-4%; cnsideable, 4-15%; sme, 15-5%; tace, 5-%. N accunt is taken in these analyses f mateials amphus t X-ays. A line cespnding t a spacing 14 3, was attibuted t chlite vemiculite (Ch/Ve in the table), and geneally n attempt was made t distinguish between these mineals. In Table 2, vemiculite efes t mateial giving a 14 A line with glycel, which mved fm this psitin n heating t 3 ~ C. Whee pecentages f xides ae quted in the Table, these wee btained by cmpaing the aeas f diffeential themal analysis peaks with thse btained with atificial mixtues f pue mineals (Dumbletn, 1963). RSULTS Tinidad Tinidad can be divided int five maj types f landfm cnsisting f muntains, dissected peneplains, teaces, alluvial aeas, and swamps. These five landfms have been subdivided, mainly n the basis f gelgy, in a suggested classificatin f engineeing mateials (Beaven, 1964). Samples fm the main gups, muntains, peneplains, and alluvial aeas, wee cllected f mineal analysis, the esults f which ae shwn in Tables l(a) and (b). The main diffeence that can be seen hee is that the alluvial sils d nt cntain mntmillnite wheeas in the sils f the Cental Range and Suthen Lwlands, which ae esidual mateials, mntmillnite is usually the maj cnstituent. Within the gup f alluvial sils, which all cme fm the Cani basin, thee is a bad vaiatin in the elative amunts f illite and kalinite. The fu samples fm the Chuchill-Rsevelt Highway cntain nly a tace f kalinite; the mica mineal is muscvite athe than illite and in additin mica flakes can be seen in the sil. The the samples have kalinite in cmpaable quantity t the illite, and hee again mica culd ften be seen in the sil althugh t a lesse extent. This diffeence in clay type may be attibuted t diffeent suces f the alluvium. The samples fm the Chuchill-Rsevelt Highway wee fm the nth f the Cani Rive and pesumably wee deived fm the Nthen Range which cnsists f lw gade metamphsed shales cntibuting t the high pptin f mica in the sils. The the samples, fm suth f the Cani Rive, wee deived fm a wide vaiety f paent cks f the Cental Range, which vay fm clay t shale. The pfiles shwed little n change in minealgy with depth suggesting that diffeences between pfiles ae due t diffeent paent mateial, and ae nt a esult f weatheing in situ.

3 Clay mineals and gemphlgy 373 Cnsideing the esidual sils, tw f the thee pfiles fm the Suthen Lwlands shw changes in clay mineal cntent with depth. These ae f a simila chaacte, ne pfile shws an incease in the amunt f kalinite and decease in the amunt f illite at the suface, and the secnd pfile shws a slight decease f chlite vemiculite at the suface. This suggests that in the tp 3 ft f these sils kalinite is being fmed by weatheing f thee-laye mineals. The changes ae slight, hweve, and suggest that these sils, like the alluvial sils, ae clsely elated in minealgy t the paent ck. Thus the mntmillnite in mst f these sils can be assumed t be an iginal cnstituent f the paent clay shale. An altenative suggestin f appaent lack f weatheing seen in the samples is that they epesent the tp laye f a vey deep weatheing pfile. An example f weatheing f an Oligcene clay/shale in this aea t a depth f 4 ft has been descibed by Rdigues (195), wh fund that the pincipal clay mineal was kalinite, and chlite deceased t a tace in the sil nea the suface. The mntmillnite sils eithe cntain calcium cabnate ae develped ve limestne calcaeus clay. The tw esidual samples which d nt cntain mntmillnite ae develped n paent mateial descibed gelgically meely as clay, which pesumably has a lwe calcium cabnate cntent. Thus it seems that in the paent clay mateial mntmillnite may be assciated with the pesence c.f cnsideable amunts f calcium cabnate. Nn-calcaeus clays ae me usual in the Lwlands f Tinidad and thus mntmillnitic clays may nt be s cmmn as the table suggests. Jamaica Jamaica may be divided int thee egins; the muntains, mainly fmed fm shales and igneus cks; the limestne plateau, cntaining the aea f bauxite sil; and the alluvial aeas. These thee gups ae the basis f a ppsed engineeing classificatin f the sils f Jamaica (Clae & Newill, 1963). Mineal analyses have been made n sils fm eight sites epesenting the main engineeing gups. The elatin between the minealgy and the engineeing ppeties f these sils is discussed elsewhee (Dumbletn, West & Newill, 1966). The minealgical esults ae shwn in Table 2 and it can be seen that each gup has its wn distinctive clay mineal assemblage. Tw f the engineeing gups, the calcaeus shale and alluvium, ae cmpaable t gups fund in Tinidad. The pfile n calcaeus shale which was sampled fm c ne site at a depth anging fm 3 t 6 ft, cnsists essentially f mntmillnite. The cespnding Tinidad sampjes wee fmed n mateials slightly lde gelgically; they als cntained much mntmillnite, but wee fm neae the suface, and shwed sme evidence f weatheing t pduce kalinite in the uppe layes. The ecent alluvium f Jamaica diffes fm that f Tinidad in that it cntains cnsideable amunts f mntmillnite and shws maked minealgical change with depth. In the pfile studied the sample is unifm in minealgical and chemical cmpsitin belw 5 ft, and this pesumably epesents the unweatheed

4 374 P. J. Beaven and M. J. Dumbletn.s _ N ~Y d ~ ~ 7 ~7 7 8 t- 4 ~ ~ ~-~-.~ 2- ~ x C~ -l,~,---,

5 Clay mineals and gemphlgy 375 % N 4- "~ ~.4 e. -6 n >..=_. e~ < q-) s ~ I 7 x3 v~ ~ ;k e., Z

6 376 P. J. Beaven and M. J. Dumbletn paent mateial. It is unusual t find mntmillnite in sils having a ph as lw as 6"-5-5 and it is pssible that the value measued, which was n an ai died sample, is lwe than the field value due t the pesence f sulphate; Wilshaw (194) has shwn that dying f sulphate ich castal alluvium fm Malaya deceases the ph f the sil fllwing xidatin f feus sulphide cmpunds. In the pfile thee is a maked change between the samples at 4 and 5 ft depth. in the uppe f these tw samples the illite has been eplaced by vemiculite and the decease in sulphate cntent shws that sme leaching has taken place. This may be the fist stage f weatheing f the alluvium t the acid sil pesent at 1"3 ft depth cnsisting nly f kalinite, quatz, and gethite. Thus it seems that in this alluvial envinment thee-laye clay mineals weathe t kalinite. Futhe evidence f this is pvided by the sample taken fm ld alluvium, which is pesumably me matue, and cnsists nly f kalinite and quatz. Sils f the limestne aea ae f tw vey distinct types, the bauxite 'tea ssa' sils and the me plastic dake clued clays. The latte type may be mcdeately deep but is ften vey thin and cntains ccnsideable amunts f gavel sand. The paent mateial f the Jamaican bauxite is uncetain but the thee bauxitic sil samples studied appea t epesent stages in the alteatin f kalinite t hydated aluminium xides which takes place unde cnditins f gd dainage and high ainfall. Kalinite, quatz, and in and aluminium xides ae the nly mineals pesent. The nn-bauxite limestne sc.il studied cmes fm a lwe ainfall aea f steep slpes, and as the sil is als well dained, it may be assumed t be in a cmpaatively dy envinment. The sil cntained much quatz, cnsideable mntmillnite and sme hematite and feldspa; its ph was 8'. It is cmpaable t the sample with cnsideable mntmillnite fm the Cental Range f Tinidad, which is als a thin well-dained sil ve limestne. Mcntmillnite is knwn t be chaacteistic f the insluble esidues f limestnes, and has been detected by Lambe & Matin (1954) in a mal fm Kingstn. It seems that in the elatively dy alkaline envinment f these scils mntmillnite emains stable, and pesumably as the sil pfile becmes deepe and acidity inceases, the clay in these sils will be cnveted t kalinite. Genada Genada is a vlcanic island with steep slpes ising t a peak f 275 ft 3 miles fm the nth-west cast. This vaiatin in altitude esults in a lage ange in annual ainfall fm ve 16 in. in the cente f the island t belw 5 in, in pats f the cast. This climatic vaiatin has pduced a egula zning f sil types anging fm shallw heavy clays in the die castal aeas t deeply weatheed fee-daining ed clays n the highe slpes. Ove mst f the island the ck type is hmgeneus, cnsisting f basic vlcanic lavas and tufts, s that the influence f climate n sil fmatin is nt mdified by vaiatins in paent mateial. The main exceptin t this is a small aea f tuffaceus shales in a high ainfall aea

7 Clay mineals and gemphlgy 377 i ~ e'~ N (7 O i ~ :Z d 9 i k; 9, _L' ~ e := O~ ~. Z~ '- 2~ Y,=,.., 2= 5

8 378 P. J. Beaven and M. J. Dumbletn which, pesumably due t the pesence f mntmillnite in the iginal ck, give ise t heavy, ply-dained clays. Sil samples epesentative f the main types ecgnized in the agicultual suvey (Venn, Payne & Spect, 1959) wee cllected f mineal analyses, and the esults ae given in Table 3 tgethe with the estimated annual ainfall and elevatin f each site. Fm this table thee gups f sils can be distinguished. Whee the annual ainfall is geate than 8 in. nly kalinite mineals ae pesent. The ne exceptin is a sample f sil fm the aea mentined abve (fm Mile 12, West Cast Rad), which is fmed n shales and cntains mntmillnite. The next gup, whee the annual ainfall is between 6 and 8 in., cntains sils with diffeent pptins f kalinite and mntmillnite. This gup epesents a tansitin t the final gup whee annual ainfall is less than 6 in. and the sil cntains mntmillnite withut any kalinite. In the sils studied maghemite and hematite ae cmmn, and cistbalite was ften nted which fm micscpical examinatin f ne sample appeaed t be f inganic igin, as might be expected in a mateial deived fm vlcanic cks, in which this mineal is nt uncmmn. The kalinite mineal was f a vey disdeed type, smetimes being metahallysite. At the sites with the highest ainfall the sils cntaining less kalinite mineals wee vey ich in gibbsite, indicating vey high leaching. Field suveys f these sils had suggested the pesence f allphane. Hay (196) has descibed the ccuence f allphane in a vlcanic ash in the neighbuing island f St Vincent, but ntes that the lde depsits, which ae buied by ecent ash, cnsist chiefly f hydated hallysite. The samples examined fm Genada wee pbably taken fm belw the hizn whee allphane might be expected t be cmmn; nne was detected by X-ays, but the mineal gives a vey indistinct X-ay patten, and the methds might have detected it. Babads Babads is mainly a cal island cnsisting f a seies f teaces ising t appximately 1 ft. These teaces mak stages in the emegence f the island fm the sea and it has been suggested that the sils ae pbably fmed fm vlcanic dust falling n the island. A vey maked cliff sepaates the Upland Plateau and its eddish and bwnish sils fm the Lwlands with thei dak clued sils. Within the cal aea the St Jhns and St Geges Valleys ae fled with deep clay depsits and ae pbably the sites f ld lagnal aeas within the cal eef system. It has been bseved that these diffeent gemphlgical units have pedlgically diffeent sil types, and the pedlgical classificatin has been simplified t distinguish sils having distinctive engineeing ppeties (Call, 1964). Ten sites epesenting the ange f pedlgical cnditins wee sampled f mineal analysis, and the esults ae shwn in Table 4. It can be seen that the tw exteme gups, the Upland Plateau and St Geges Valley, ae quite distinct. The clay mineal f the sils f the St Geges Valley is essentially mntmillnite. In cntast the clay mineal f the sils n the Upland Plateau, which ae well dained and pesumably have been expsed t weatheing f the lngest peid

9 Clay mineals and gemphlgy 379 OQ ~' O' c, ~ O' O' A ~3 nz ~J A. OA 2.,-, "3 -fi 7- e- A L -?,< I'--- ~ ~ " 4 I m N = ~ = m - ~ = " ~ ~ ~.. e-. ~~ xg d

10 38 P. J. Beaven and M. J. Dumbletn 4- ~ c- q- 4-,< ~ < < v t- O v~ '~ ~ < ~ ~ -5.~< e'~ >-, ~z, J >

11 Clay mineals and gemphlgy 381 f time, is a kalinite mineal, which in ne case can be identified as metahallysite. The sils f the lwlands which ae pedlgically intemediate between these tw cntain eithe kalinite mntmillnite. The seies f samples fm the Paish f St James, which csses the bunday f the Upland Plateau and the Lwlands, shws little minealgical vaiatin, all samples cntaining kalinite mineals. Despite this similaity in mineal cmpsitin, these sils have diffeent ppeties in the field, pesumably due t diffeences in sil stuctue the pptin f clay pesent. Thus it appeas that in Babads the lde me matue sils ae kalinitic, the yunge sils may be mntmillnitic, and the yungest sils, fund at the lwest level in ply dained aeas, ae mntmillnite sils. CONCLUSIONS In fu Caibbean islands classificatins f engineeing mateials have been ppsed, based n the gemphlgical units pesent. Results f clay mineal analyses shw that in each engineeeing gup the clay mineal assemblage is easnably cnstant. Whee changes ccu within the sils f a gup, these ae usually assciated eithe with vaiatins in paent mateial, with diffeences in weatheing cnditins. Cnsideable diffeences in clay mineal assemblage ccu amng the sils n the same island. These diffeences have been elated t engineeing gups based n land fm analysis. Amng the many facts that have cntibuted t these diffeences the mst imptant f these islands ae: (1) In gelgical paent mateials in Tinidad and Jamaica, mntmillnite is assciated with a high pptin f calcium cabnate. (2) These mateials, calcaeus clay/shales and limestnes, weathe t mntmillnitic sils. (3) On the vlcanic island f Genada thee is an assciatin between climate and the clay mineal assemblage; kalinitic sils ae fund in the high ainfall aea, mntmillnitic sils in the dy aeas, and mixtues f mntmillnite and kalinite ccu as an intemediate zne. (4) On the cal island f Babads whee the sils ae als pbably fmed fm vlcanic dust, a simila sequence can be seen, but the intemediate zne is nt develped. (5) The bauxite sils f the limestne aea f Jamaica ange fm kalinite with sme sesquixides, t sesquixides (mainly gibbsite) withut kalinite, accding t the extent f leaching. (6) In alluvial sils the minealgy f the suce aea influences the cmpsitin f the sediment. ACKNOWLDGMNTS The auths wuld like t thank the Public Wks Depatments in the teities visited f assistance in cllecting samples. The sil suveys f the Agicultual Depatments f Babads and Genada als helped in lcating the sil seies in the field, and the staff f K

12 382 P. J. Beaven and M. J. Dumbletn the Reginal Reseach Cente, Univesity f the West Indies, pvided valuable discussin n Caibbean sils. Many f the samples wee c llected by M D. Newill, and M G. West and M L. W. Tubey assisted in the minealgical analyses. This pape is cntibuted by pemissin f the Diect f Rad Reseach. Cwn cpyight. Repduced by pemissin f the Cntlle f He Majesty's Statiney Office, RFRNCS BAVN P.J. (1964) Dep. Scient. ind. Res., Rd Res. Lab. Nte N. LN/518/PJB. BROWN G. (dit) (1961) The X~ay Identificatin and Cystal Stuctue f Clay Mineals. Minealgical Sciety, Lndn. CARROLL D.M. (1964) Dep. ScienL ind, Res., Rd Res. Lab. Nte N. LN/524/DMC. CLAR K.. & NWILL D. (1963) Dep. Scien: ind. Res., Rd Res. Lab. Nte N. LN/318/KC.DN. DUMBLTON M.J. (1963) Dep. Scient. ind. Res., Rd Res. Lab. Nte N. LN/282/MJD. DUMBLTON M.J., WST G. & NWILL D. 966) ngng Gel. 1, 235. HAY R.L. (196) Am. J. Sci, 258, 354. LAMB T.W. & MARTIN R. TORRNC (1954) Pc. Highw. Res. Bd, 33, 515. RODRIGUS G, (195) Caib. Cmm. Rept~. Sils Cnf. 195 (Puet Ric), p, 19. VRNON K.C., PAYN H. SPCTOR J~ (1959) Sil and Land-Use Suveys, N. 9. Genada. Impeial Cllege f Tpical Agicultue, Tinidad. Wf.SHAW R.G.H. (194) Malayan agic. J. 27, 352.