EXPLANATORY NOTES
FOR
1997 GEOLOGICAL MAP OF TRINIDAD
General Explanatory notes & changes from H.G. Kugler' 5 1959 Map
By J.B. Saunders (pages 2-12)
Notes on the Northern Range & changes from H.G. Kugler's 1959 Map
By H.C. Potter (pages 13-21)
Reference List & Acknowledgements (pages 22-25)
EXPLANATORY NOTES TO 1997 GEOLOGICAL MAP
J.B. Saunders
CHANGES FROM KUGLER'S 1959 GEOLOGICAL MAP
The first reaction to the revised 1997 edition may be that the outlines of the formations look much as they did
in the earlier map. Because a geological map indicates units that are mappable on the surface, the fact that the
areas attributable to the various formations have not changed greatly is to be expected and is a measure of the
success in choosing the mappable units in the first instance. This is not so for the Northern Range where complete
new appraisals have been undertaken in the intervening years.
The stratigraphy of Trinidad has been slowly pieced together beginning in the middle of the last century when Wall
& Sawkins published their memoir with its accompanying coloured map and cross sections in 1860.
Hundreds of wells drilled over the intervening years have allowed a three dimensional picture to be built up with
a good understanding of the nature of the contacts between the stratigraphic units. The order of deposition could
be checked and stratigraphic columns created. Next it was necessary to put an age to the rocks. With no 'absolute'
dating methods available until recently, the method was largely to use the fossils found in the rocks and to compare
them with similar forms already known from other areas.
Before the study of microscopic organisms, larger fossils were used including molluscs, corals, echinoids and even
plant leaves. The resulting stratigraphy covers a time interval from the Jurassic to the present day, a span of
150 million years.
Much of the driving force behind this work came from Dr. Hans G. Kugler who worked as an oil geologist in Trinidad
and Venezuela from 1920 until 1959 when he retired to the Natural History Museum in Basel, Switzerland to continue
his work until his death in 1986. There were many outstanding geologists working in Trinidad during those years
but it is to Hans Kugler's foresight and drive that we owe the outstanding geological map of 1959. Hans Kugler
was actively involved in the work towards a revised version and it is with pleasure that we can acknowledge his
contribution along with the many geologists who now work in Trinidad or study its geology from abroad.
It is in the dating of the younger formations from the Late Miocene to the Present Day that we see the greatest
differences from the earlier map. Originally, the subdivision of these rocks relied on megafossils, particularly
molluscs, for its subdivision into Epochs. Even with the advent of micropaleontological studies, the lack of age
diagnostic species has made correlation within the thick, very young deltaic sequences across the island uncertain.
Advances in correlation in the last few years using sequence stratigraphy have led to a new understanding when
comparing the young sediments outcropping from Moruga to Guayaguayare with the 'classical' Forest/Cruse nomenclature
and this is reflected in colour changes on the revised map.
The map is best used in conjunction with the Stratigraphic Table printed alongside as this illustrates the correlations
as we believe them to be today.
NORTHERN RANGE
The changes since the publication of Kugler's 1959 map are very considerable. During these years, Hans Kugler himself
was involved in new mapping and new stratigraphic and structural interpretations.
The basis for the main changes came from the work of H.C. Potter who mapped the western half of the Range for his
Ph.D. thesis and who published a series of papers while the work was in progress (e.g. Potter, 1973). Dr. Potter's
Notes are placed in this explanatory text.
Structural and lithostratigraphic work by S.T. Algar has been most important in the eastern half of the Range and
along the El Pilar Fault zone. This led to publications by him and also in conjunction with J.C. Pindell.
The Sans Souci volcanics were restudied by G. Wadge and R. MacDonald.
J.B. Saunders and G.E. Higgins collected widely leading to a review of palaeontological results for the Range (Saunders,
1972).
Dating of the metamorphism has added a new dimension as recorded in abstracts by R.C. Speed & Foland (1991)
and J.C. Weber & colleagues (1995).
Structural studies in the El Pilar Fault zone include those by Speed & colleagues (1991) and P. Robertson and
colleagues (1986).
The changes are documented in a preliminary way in the notes to accompany the 1997 revised map, mostly under the
formations involved. Fuller text is being prepared for an updated stratigraphic lexicon that is planned to follow
the map. There it will be possible to show the contributions made by individual geologists in the field and in
publications. There follows a preliminary list of scientists who have contributed publications directly concerned
with Northern Range studies since the publication of Kugler's map:
R. Ahmad & colleagues; S.T. Algar; K.W. Barr; H.M. Bolli; P. Bower; J.C. Burke & colleagues; M. Frey &
colleagues; K.A. Foland; M. Furrer; T.A. Jackson & colleagues; H.G. Kugler; R. Macdonald; K. Persad; J.C. Pindell;
H.C. Potter; K. Rodrigues; J.B. Saunders; J. Scott; R.C. Speed; G. Wadge; J.C. Weber & colleagues.
NORTHEAST OF THE GRANDE RIVIERE FAULT
The stratigraphic table produced with the 1997 map shows the following formations grouped north of the Grande Riviere
Fault and its continuation westwards from Grande Riviere to Chupara Point:
Galera Fm, Tompire Fm, Toco Fm and Sans Souci Fm.
Additionally, the Toco and Sans Souci formations are separated from the Galera and Tompire formations by Algar's
Grande Riviere Fault Zone which is thought by him to be the front of an allochthonous package. Its eastern limit,
to the east of Reefs point, constitutes a high angle right lateral shear zone more than one km wide.
The northern boundary of the Guayamara Fm. between Grande Riviere and Chupara Point is thought to be structural,
though this has not been proved satisfactorily to date.
This grouping is something of a compromise linking the views of Algar and Pindell with the work of Barr, Kugler,
Saunders, Higgins and Potter. We consider, from field relations and a study of air photographs (HCP) that the Grande
Riviere Fault does extend to the east coast as originally mapped by Barr.
The majority of the Galera Fm remains as depicted on the 1959 map which was taken from Barr's thesis work (published
in 1962/63), though the fault pattern near Galera Point at the eastern end of the outcrop area has been omitted
because we can find no satisfactory evidence for it.
Barr erected the Tompire Fm. for slates exposed on the east coast that carried a distinctive fauna of small ammonites.
We later combined this unit with the Toco Fm. as a member (Stratigraphic chart of 1975). Algar placed these beds
within his Rampanalgas Fm which was predominantly erected to replace the earlier Rio Seco Fm.
We now feel that the Tompire Fm should again be retained as a stratigraphic entity for reasons of lithology, fossil
content and because the Rio Seco may well be of a different age to anything in the Range (see notes for Rio Seco
Fm.). We believe that the Tompire Fm at its type locality should be linked with rocks exposed in Anglais Road inland
from the coast as had been done by Barr. On rather sparse faunal evidence we would continue to use the term Tompire
Fm westwards in an outcrop belt south of the coastal Galera belt almost as far west as Filette point. We had previously
linked this belt with the Toco Fm. though it shows no signs of the varied lithologic and faunistic variety shown
by that formation. Now, also, we have the probability that the two formations are separated by a major structural
break as advocated by Algar & Pindell (1991).
The volcanic rocks of the Sans Souci Fm have been studied again by Wadge & Macdonald (1985). They consider
the contact between this formation and the Toco Fm to be conformable. There are undated dark shales very similar
to those within the Toco Fm caught up within the tholeiites of the Sans Souci Fm and there are minor ash beds within
the Toco Fm. lending credence to this view.
On Kugler's 1959 map there is a small outcrop of diorite 1.7 km south of Toco Bay. This had been found by Barr
and placed by him in his Toco Fm. We have restudied the diorite in the field and find the outcrop to be almost
certainly fault bounded. As it occurs very close to Algar's right lateral shear zone it is shown as within the
fault complex on the revised map (no.39 on the key).
RIO SECO FM
The Rio Seco Fm was named by Barr (1963) in his work on the eastern end of the Northern Range. This work was already
available to Hans Kugler during his compilation of the 1959 map. The result was that this unit was expanded enormously
to include the limestones of the Maraval Formation (a name not then in use). In fact, ml 959, all the units named
within the Rio Seco Fm are now those of the Maraval Fm while nothing is designated for the east coast outcrops
of Barr's original formation.
Some of these problems were alluded to by Saunders (1972) where he dated the Rio Seco beds as being most likely
of mid Cretaceous age on sparse foraminiferal faunas. This contrasts with the age of the Cuare Limestone within
the Maraval Fm where Tithonian (latest Jurassic) ammonites had been published as early as 1939 by Hutchinson. This
anomaly was corrected in the stratigraphic chart compiled by Saunders in 1975 and widely used since.
In 1991 Algar & Pindell use the term Rio Seco in the same sense but in a later paper in the same year, they
erect the term Rampanalgas Fm in which they include the type beds of the Rio Seco Fm. On the revised map we have
retained the name Rio Seco Fm.
However, there is yet a further problem with this unit that still has to be resolved. A limestone sampled for thin
section analysis (JS 2948 in the Siras River) contains at least one section of an Orbitocyclina that is restricted
to the Campanian or Maastrichtian stages at the top of the Cretaceous. The limestone was, in fact, a flattened
boulder among many similar limestone
masses most of which were embedded in the contorted shales. We have so far not been able to duplicate this find.
This is a prime location for further field and laboratory work.
LOPINOT FM.
Between Arima and Port of Spain, within the El Pilar Fault trend, occur phyllites that, in Hans Kugler's 1959 map,
were included with the limestones of Laventille Hill in the formation of that name.
It might be wiser to use the term 'Southern Northern Range Zone' as pointed out by Algar & Pindell (1991) rather
than the El Pilar Fault Zone as the bounding fault to the North is the Arima Fault which may not be particularly
linked with the El Pilar system.
In 1972, J.B. Saunders linked these rocks with the Tompire Member of the Toco Fm because a small proportion of
the new samples collected had a sparse micro fauna that showed similarities to those found in the Toco and Tompire
formations.
The most distinctive microfaunas were obtained by Saunders in the Turure River and on the Lopinot Road so, in line
with the description of the same rocks as the Lopinot Fm by Algar, we now use this name on the revised map.
ARIMA FM
This stratigraphic unit is being named for the 1997 map as it is felt that the rocks that are grouped here are
sufficiently different to warrant a separate name at this time. It is hoped that later work will clarify some of
the relationships that are still not clear.
The major outcrops are on the western side of Arima and on the northern side of the town in the Arima River and
along Calvary Trace. A few isolated outcrops further east along the El Pillar fault trend have also been tentatively
grouped here. The formation is best displaced in outcrops along the river but, even here, the section is not continuous.
Away from the river itself, outcrops are concealed below terrace gravel and alluvium.
The range of rock types and ages is briefly discussed in Saunders (1972, pp.4.58-459). The mixture of ages involved
spans a time interval from mid Cretaceous to the topmost Cretaceous Maastrichtian) with the youngest sediments
being closest in micro fauna and lithology to the Guayaguayare Fm. Also in the river and in Calvary Trace occur
non-calcareous silty phyllites carrying agglutinated foraminiferal faunas similar to those found in the Galera
Fm.
On the 1959 map, the late cretaceous agglutinated foraminiferal faunas of the Calvary Trace phyllites were already
known but the complexities in the river were not discovered until later, when R. Young and H.C. Potter sent samples
to J.B. Saunders. With G.E. Higgins, Saunders later worked the river with the results summarized above. At the
time of this field work, he wrote that "the matrix" is considered to be composed of dark shales with
inter bedded, indurated marls and, somewhat separated from the latter, indurated grits, conglomerates and quartzites".
There is evidence for limestones and a polygenetic breccia as boulders within crumpled shales.
The non-Continuous nature of the outcrops in the river makes it difficult to say how much faulting is involved
in juxtaposing the various ages and rock types.
Though the beds were originally included with the Galera Fm that outcrops extensively along the north coast, newer
views on the structure of the Northern Range make the present writer conclude that, at this stage, a new name should
be used to allow flexibility when future studies are carried out.
CRETACEOUS south of the Northern Range
The Upper Cretaceous occurs very rarely in outcrop, apart from the argillite of Naparima Hill in San Fernando.
Most of our knowledge comes from well sections.
The upper part of the Lower Cretaceous is much better represented at the surface by small outcrops of Gautier Fm
and much larger areas of Cuche Fm.
Field work carried out by K.W. Barr (1952) and later by C.J. Campbell and the author shows that the difference
between the Maridale Marl and the Cuche Shale is lithologic and the Maridale should be considered as a member within
the top of the Cuche Formation. The Maridale microfaunas have been shown by Bartenstein, Bettenstaedt & Bolli
(1966) to be younger than the datable levels within the Cuche Fm, but the outcrop of Cuche type shales in the critical
area of the Cuche River cannot be precisely dated causing the two units to be figured as shown on the Stratigraphic
Table.
The Stratigraphic Table shows a number of missing intervals within the Upper Cretaceous in Trinidad. The one between
the Guayaguayare Fm and the underlying Naparima Hill Fm is better documented than that between the Naparima Hill
Fm and the underlying Gautier Fm where drilling now suggests the existence of a continuous sequence. This has certainly
suggested lithologically but could not originally be proven biostratigraphically.
The work of Koutsoukos & Merrick (1985) has shown that less is missing between the Maridale level of the Cuche
Fm and the Gautier Fm. Where new wells produce palaeontological results, the missing intervals shrink as Koutsoukos
and Merrick show.
The situation in the Northern Basin and in wells drilled in the northern part of the Gulf of Paria provides a different
picture, with early to middle Cretaceous rocks uplifted, eroded and often steeply folded, overlain by Cenozoic
sediments mainly of Neogene age.
The evaporite deposits found in the Gulf of Paria are discussed separately under a new unit: the Couva Marine Fm.
COUVA MARINE FM
The evaporite deposits here grouped as the Couva Marine Formation are shown on the key to the map and are placed
on the stratigraphic table where they are considered by the present writer to be best placed on the age evidence
so far available. The dating relies on a potassium-argon date on micas of 124+-5 Ma as made available from oil
company sources and quoted in Eva (Caribbean Geological Conference, Cartagena, 1983).
The stratigraphic relationship of the evaporites of the Couva Marine Formation will be explained more fully in
the Stratigraphic Lexicon now in preparation. The present writer's view is that the evaporites equate with those
of the Patao Member of the Cariaquito Fm outcropping on the Venezuelan Paria Peninsula. Above these follow the
limestones and shales of the Guinimita Fm which are believed to equate with the Laventille and Lopinot formations
in Trinidad.
The writer believes that the gypsum of St. Joseph occurs as blocks in the El Pilar Fault Zone and is therefore
not necessarily in place. Minor gypsum occurrences in the Laventille Limestone still need clarification but could
represent somewhat later evaporite production than the Couva marine beds, though there is also the possibility
that they, too, have been structurally emplaced.
The Couva Marine Formation is named for the sections in marine wells, particularly in Couva Marine #2 where open
file information was reported by A. Eva.
CUNAPO FORMATION
In the 1956 Stratigraphic Lexicon, Hans Kugler declared the Cunapo Conglomerate an obsolete term as the original
horizons were considered to be conglomerates within the Brasso Fm.
In 1965, the stratigraphic chart of Barr & Saunders showed the Cunapo conglomerates as including great sweeps
of coarse material within the Northern Basin spanning a wide age range. This was refined in a stratigraphic chart
produced by Saunders in 1975 incorporating the work of Kugler, Saunders and others, and now widely circulated.
The stratigraphic range at that time was given as Subrecent to approximately base Miocene. The conglomerates penetrated
within the Northern Basin can rarely be directly dated but they interfinger southwards with other named formations.
They have a predominantly northern source though with influxes coming in from the south from time to time.
The conglomerates outcropping in the Cunapo area of the eastern Central Range and the southern flank of the Northern
Basin constitute a distinctive unit that was well studied by Hans Kugler.
The conglomerates from this area have been named as the Cunapo Conglomerate Member of the formation on the 1997
map and stratigraphic table.
Another unit separately named within the formation is the Puerto Grande Conglomerate
Member with its type section in the well of the same name where there is a long section of coarse beds, often strongly
conglomeratic, from Pleistocene probably to within the Miocene.
The fission track dating of the time of metamorphism of the rocks constituting the main part of the Northern Range
as Miocene means that there has been even greater very recent uplift of the Range than had previously been imagined.
This would explain the enormous shedding of conglomerates southwards into the present Northern Basin (Puerto Grande
Member) and northwards into the offshore area where equivalent thicknesses of conglomerate exist.
MIOCENE LIMESTONES
On the 1959 map a series of limestones is grouped together carrying the same colour as the Lengua Fm. They were
placed within the Tamana Fm., a unit first used by Wall and Sawkins and redefined by Kugler using Tamana Hill as
the type area where 300ft. of limestone are found resting unconformably on Brasso Fm.
On the 1959 map the Tamana Fm includes a series of limestones occurring from the east coast at Brigand Hill, through
Tamana Hill, Chimborazo, Tabaquite and Mayo to Guaracara in the west.
We continued to adopt the terminology in later stratigraphic charts. However, recent field and laboratory work
by Erlich, Farfan & Hallock (1993) and others shows strong evidence for the differing ages of the conformable
bases of many of the limestone placing them within the Brasso Fm. They are shown within the Brasso Fm on the revised
map.
What does still seem likely is that there are a few limestone levels, including the Concorde limestone and calcareous
silts in Pointe-a-Pierre and the Chimborazo limestone 13km further east that do reflect the original age of the
Tamana Fm. Because of the likelihood of confusion and because the Tamana Hill outcrops remain, as yet, poorly dated,
the Concord and Chimborazo beds are grouped together as the Concord Formation on the present map.
The discrete limestone masses such as St.Croix, Morne Diablo, Biche, Kapur and Meijas that were already placed
within the Brasso Fm on the 1959 map remain as units within that formation.
The present state of knowledge is indicated on the Stratigraphic Table presented with the 1997
THE RIO CLARO BOULDER BED
In the Stratigraphic Lexicon of 1956, Hans Kugler has an entry for the "Rio Claro clay pebble and bounder
bed" as a member of the Lengua Fm. On his 1959 map, parts of the upper Lengua carry a pattern of small circles
denoting out crops of the bounder bed unit widely spaced across south Trinidad from east of Rio Claro in the east
to Princes Town in the west. The nature of this unit is under review at the present time. There is a tendency to
view some or all of this heterogeneous layer as a fault breccia or a tectonic melange. Some examples may be, but
heterogeneous levels do occur at about the Lengua level in the subsurface in the south west of the Island.
RD. Liska (1998) studied new outcrops in the Rio Claro area and, at least there, could find nothing to suggest
a boulder bed but rather, the presence of tightly folded beds of Cipero age that could have been misinterpreted
earlier due to poorer outcrops.
For the present, the pattern for a boulder bed has been left off the revised map and the outcrop area 2km northwest
of Rio Claro studied by Liska has been shown as Late Cipero in age.
SPRINGVALE FM
There is a difference between the representation of the Springvale Fm in the 1959 map and in the 1997 map. In the
new revision, the lowest member - the Gransaull Clay Member - has been given a different colour, being now green
in contrast to the blue colour of the upper two members which are the Savaneta Glauconitic Sandstone Member and
Chickland Clay Member.
The new colours for the members have been chosen to reflect new information on age correlations across the island.
The best interpretation now is that the Gransaull Clay is likely to equate with the Forest Fm and the higher parts
of the Springvale Fm with the Morne L'Enfer Fm.
The new interpretation reflects palynological studies by D.T. Pocknall and the regional lithologic and paleontological
work of B. Carr-Brown, J. Frampton and A. King.
The history of the erection of the Springvale as a formation, beginning with Maury's work in
1925, was compiled by Hans Kugler and is being edited by H.M. Bolli for a new addition of the
Stratigraphic Lexicon for Trinidad.
The shell bed of the Savaneta Glauconitic Sandstone Member is well developed in the west of the island where it
lies unconformably directly on the underlying Manzanilla Fm. Towards the east coast, in contrast, the Gransaull
Member has been mapped as representing the whole formation. Though the members have significance where they are
typically developed, it may be that their inclusion together in one formation may be less secure.
Also, on the east coast, inland from Pt. Salou, the 1959 map shows a syncline of the Springvale Fm. S-1 surrounded
by Manzanilla Fm. The beds are synclinal but whether this is Springvale Fm is uncertain. The surface samples are
inconclusive so, at this time, the Springvale colour has been removed, though the outline of the outcrop has been
left on the map.
SOUTH EAST TRINIDAD
One of the major problems of geological mapping in Trinidad has always been the difficulty within the Miocene and
younger beds of correlation between the western end of the southern basin, where the classic nomenclature of Forest
and Cruse was developed, and the southeastern area from Moruga east of Guayaguayare.
The stratigraphic table issued with the 1997 map shows the present state of knowledge regarding the correlation
of various members of the Moruga Fm outcropping in the Moruga Hills and Trinity Hills in relation to the formations
named in the Guayaguayare area, the south eastern coastal strip, the Pilote syncline and the Ortoire Syncline.
The colours chosen for the 1997 revised map also attempt to show, wherever possible, the age equivalents for these
formation and their relationship to the Cruse/Forest/Morne L'Enfer formations in the southwest and the Manzanilla
and Springvale formations north of the Central Range.
The revision leans heavily on the work of B. Carr Brown, J. Frampton and A. King who have used a mixture of dating
on microfossil evidence linked to a comparison of lithologic sections creating a sequence stratigraphy. Useful
correlation lines have also come from the palynological work of D. Pocknall.
The relationship between the classic Moruga sequence outcropping in the hills west of Moruga to subdivisions used
further east still needs verification. The same goes for the extent of sediments at present grouped as equivalent
to the Trinity Hill Sandstone and the St. Hilaire silt.
The new map retains most of the old boundary lines, but adjacent blocks may carry the same name if it now seems
wise to combine them.
It is difficult to use the term Gros Morne Fm widely and perhaps it will eventually be replaced.
The change to the use of the name 'Cruse' is somewhat arbitrary north of the Ortoire Syncline and also going westwards
into the Siparia Syncline where the introduction of the term 'Forest' is also difficult to define.
The differences between the eastern and western facies is better defined by the time of deposition of the Morne
L'Enfer Fm that is largely equivalent to the offshore levels above the Palmiste Clay which occurs at the base of
that formation. The top of the Palmiste Fm has yet to be defined. This will have to be done using eastern offshore
well sections.
Subdivision within the Cruse Fm, especially between Middle and Lower Cruse is not particularly satisfactory. This
was already becoming apparent on palynological evidence as far back as 1968 when D. Batjes erected the Roseau Fm
for Lower Cruse type clays in the Rio Seco area that were known to extend higher in the section than the typical'
Lower Cruse of the west.
The area going westwards from Goudron Field to Moruga and north from the Moruga-Canari coast to the Singineau uplift
needs closer attention before the surface map can be considered at all safe. It is hoped that seismic information
and shot hole samples already taken can be used in a revision of the area.
The present designation of stratigraphic names in parts of the south east of Trinidad cannot be considered final
but it represents an attempt to take into account the excellent work that is being done in the oilfields, in seismic
interpretation and by modem analysis of surface Sections. The advantage of the present map is that it is held in
a digital database so that updates can he made. However, one would hope that any significant changes would be clearly
dated and signed at the time that they are done.
Structural Lines
The fault pattern in the centre and south of Trinidad is largely taken from the 1959 map, though the interpretation
of fault types is controversial.
The nature of formational boundaries at the western end of Goudron is a case in point. The break is now known to
be a major fault on seismic evidence provided by R. Bierley. It is hoped that the exact position can be verified
so that it can be added to the map at a later date.
NOTES ON THE NORTHERN RANGE & changes from H.G. KUGLER'S MAP
H.C. Potter
INTRODUCTION
The geological map of Trinidad of l959 compiled by H.G. Kugler and associates has long been accepted as the definitive
map of the Northern Range. However it will be seen that the new map of this area differs from the 1959 man in a
number of significant stratigraphic, structural and outcrop details.
Some of the chances stem from detailed mapping at 1: 10000 scale by H.C. Potter from 1963 to 1971 in the range
west of Grande Rivere. This was undertaken at the suggestion of H.G. Kugler. Changes in the mapping caused by this
work were discussed with H.C. Kugler and K.W. Barr in the field and the changes were agreed upon.
As well as having preliminary contoured D.O.S. plotted sheets provided by the Trinidad Government. Potter was able
to use new air photographs which had not been available when most or the fieldwork for the1959 map was being carried
out.
Work by S.T. Algar and J.L. Pindell in 1989 to 1991 introduced stratigraphic and structural changes both on a regional
basis and locally in the Toco area.
STRUCTURE OF THE NORTHERN RAINGE
The structure of the Northern Range varies along its length but on the whole the oldest rocks, Maraval and Maracas
formations, occupy the central spine of the range, while younger rocks outcrop along the north and south flanks.
In the western peninsula from Port of Spain to Chacachacare the structure that of a single north vergent overturned
anticline trending East-West (Potter 1963), The fold appears to plunge gently westward as shown by the narrowing
and then disappearance of the Maraval limestone core. There is a well developed overturned north flank at the longitude
of Pont of Spain with Chancellor Fm. on both flanks of the structure but this narrows westwards. Finally, only
the gently dipping upright south flank is exposed above sea level. The axis of the structure appears to be displaced
by the Morris Bay Fault on Monos island and is assumed to lie at depth north of Huevos and Chacachacare.
Eastwards from the Santa Cruz River the structure changes from a single overturned anticline to become two major
lines and one minor line of Maraval Limestone outcrops associated with thrusting to the north in a series of nappes.
Various small folds occur in the Maraval outcrops of the Brasso Seco area.
This pattern continues some kilometers east of the Arima River where another change occurs towards the Aripo, Cumaca,
Platanal area, the core of the Range and the largest outcrop Maraval Limestone. A number of north vergent folds
have been mapped in this area. North of the main limestone block appears to be an E-W graben in the headwaters
of the Rio Grande and Platanal rivers. Bubbling hydrogen sulphide springs in the upper course of the Rio Grande
may be connected with this fault system. The eastern extension of this feature, however, becomes a pericline with
good exposures of limestone in the headwaters of the Salybia and Rio Seco. Another Maraval Limestone outcrop occurs
further east but does not reach the East Coast. More detailed mapping would be worthwhile north of this general
area.
The southern edge of the Northern Range is dominated by the Arima Fault (Kugler 1959 map) and associated faults
of this system. Algar & Pindell (1991) believe that the main outcropping fault, which marks the northern boundary
of their 'Southern Northern Range Zone' shows thrusting of less metamorphosed rocks from the south over the more
metamorphosed rocks of the main range - a backthrust.
Seismic and gravity work by Dominion Oil disclosed a number of parallel faults south of the main Arima Fault and
the inclination of these faults appeared to be nearly vertical. Drilling of two wells to the south of the Laventille
area showed downthrow of thousands of feet across one, and probably both, of these faults which have so far been
considered to be an extension of the El Pilar Fault system. The relationship of the Arima Fault to the El Pilar
fault system is as yet unclear.
The structure of the western end of the range has been described already. However on the north flank there is a
major change of structure between Chupara Point and Filette Point where the Filette Fault, a NW-SE wrench brings
overturned, nearly horizontal Guayamara Fm against nearly vertical, folded Galera Fm. The fault continues for some
7km before it swings to an E-W trend across the Marianne River and continues eastward as a slide forming the northern
boundary of the Guayamara Fm. The nature of the slide is not clear due to the lack of good outcrops, nor is it
clear whether it continues all the way to the Grande Riviere valley.
Along the coast, folded Galera quartzite sandstones form high ground through which the main rivers cut gorges and
narrow valleys. Further inland the calcareous shales of what is now mapped as Tompire Fm form low ground in which
large subsequent tributaries have developed.
On Kugler's 1959 map there are several large NW-SE dextral wrenches shown cutting across the range from the north
coast to the southern boundary of the range. Detailed mapping together with air photo analysis dose not confirm
the presence of all these large faults. However, there are both dextral and sinistral wrenches on a smaller scale.
Even the Grande Riviere Fault seems to be a system made up of several smaller faults.
The Toco area has recently been re-mapped by Algar (1990). The boundary between the Toco and Galera formations
has been shown to be a major zone, and the boundary between the Toco and Sans Souci formations is suggested as
another fault zone.
Additional Notes
The geology of the Northern Range from the western end to a line between Grande Riviere and Matura Point was mapped
at a scale of 1:10,000 by H.C. Potter between 1963 and 1971. Much of this work was supported by a NTRC grant. Additional
help was provided by the Trinidad Government who provided accommodation in Government Rest Houses, copies of topographic
maps, access to areas not open to the public, the boat transport. Additional help was provided by a number of oil
companies and by many friends.
NORTHERN RANGE STRATIGRAPHY
Almost all the rocks of the Northern Range consist of the low grade metamorphic series of the Caribbean Group,
more than 2500m thick. The oldest known fossils in the group are Upper Jurassic and the youngest are Upper Cretaceous.
Throughout the Northern Range there is alluvium at surface in the main valleys and south of the range itself. The
valleys are wider and deeper in the west. Presumed quaternary terraces lie along the south flank especially in
the east. Below the surface of the wider valleys and the plain south of the Northern Range there are gravel beds
and fans which are also probably Quaternary. These fans provide an important water supply at St. Joseph.
MARAVAL FORMATION
These are the oldest rocks in the Northern Range. The base of the formation is not exposed. A thickness of 500m
has been measured in the western part or the range. Recrystallised limestones seems to be the most common rock
type. In the lower part of the formation massive recrystallised limestones are common, sometimes resembling former
reefal mounds and sometimes platforms separated by recrystallised, phyllitic limestones.
Higher in the formation more thinly bedded phyllitic limestones predominate together with interbedded phyllites,
often calcareous,
Fossils are rare in the Maraval Fm but Jurassic Tithonian ammonites were recovered at the Hollis damsite near the
top of the formation (Hutchison, 1938); Echinoid and algal fossil material was found in that general area suggesting
shallow marine deposition not older than Upper Jurassic (Furrer, 1968). In thin sections sericite is common even
in the massive rock as well as on bedding planes of the bedded limestones. There is a noticeable association of
sparite and quartz in clusters of larger crystals and layers, which suggests that the quartz was developed during
metamorphism. Field observations and study of thin sections show that there is some dolomitisation of the limestones
in the Brasso Seco area, where one pyroclastic fragment was also found (Furrer, 1968).
The outcrops of Maraval Fm form rounded ridges along the E-W strike in the western part of the Northern Range.
They are neither as high nor as angular as the overlying quartzites of the Maracas Fm. The boundary between the
two formations is generally clear. In the area east of the Diego Martin River there is well developed karst topography
in the outcrop of the Maraval Fm. Another striking topographic feature along the length of the Northern Range concerns
the fact that where the N-S rivers cut through the Maraval outcrops broad alluvial valley plains occur, presumably
formed by solution of the limestones.
The visitor can examine exposures of Maraval Fm by driving north along the North Coast Road from the Saddle (643849)
to Milepost 1½ (647867), crossing the upright and the overturned limbs of the Maraval Fm outcrop in 2 kms.
Better exposures lie on the two minor roads that lead to Paramin village (620857) north of the Morne Coco Road
approximately 2.5 kms to the west.
Further East good exposures of Maraval limestones can be seen in the Verdant Vale area north of Arima, in the heights
north of the Hollis Reservoir, in the headwaters of the Oropouche River, the Platanal area, and the northwestern
headwaters of the Rio Seco.
Previously, as in Kugler's 1959 map, the Maraval Fm had been shown as individual limestones (Maraval, Hollis, Cuare)
all lying in the Rio Seco Fm the Maraval Fm is now recognised as a unit throughout the length of the Northern Range,
while the Rio Seco Fm is mapped as a younger formation of Lower Cretaceous age confined to the eastern half of
the Northern Range (Saunders, 1972), and separated from the Maraval Fm by the whole of the Maracas/Guayamara formations.
Interesting exposures of tightly folded Maraval limestone occur in the Turure Quarries off the Cumaca road and
in a tributary of the Turure River where the valley bottom is Maraval limestone while the slopes are in Maracas
quartzites.
MARACAS FM
These rocks lie apparently conformably above the Maraval Fm. Measurements of a number of sections suggest surprisingly
uniform thicknesses of approximately 1500m without there being any good correlations between the sections.
There seems to be a tendency for the lowest part of the formation to contain more slates and sericitic phyllites
than average, with some thin interbedded sericitic quartzites. Higher in the formation are beds of massive orthoquartzites.
Individual beds may reach 100m in thickness, but their lateral extent is limited. These rocks form high cliffs
and deep gorges and they underlie the highest peaks in the western part of the Northern Range.
A considerable part of the Maracas Fm consists of interbedded quartzites and phyllites. In the laminated material
a number of sedimentary structures can still be seen, such as scarce graded bedding, convolute bedding, slump folds
and poor ripple flow marks. The strange thing about these features is that, considering the nature of the original
sediments, we would have expected the current direction in these submarine fans to have been northwards off the
South American Plate; but in fact most of the current indications seems to be southwards.
A few thin recrystallised limestones looking like Maraval limestone occur, interbedded with phyllites and slates
in the lower part of the Maracas Fm and appear to be in place. In addition there are small isolated outcrops of
more massive recrystallised limestones or marbles which look like Maraval limestone; some may be klippen and some
may be exotic blocks of Maraval Fm.
On the North Coast road (647868) about 100m north of Milepost 1.5 there is an epidote greenschist about 6m thick,
occurring about 60m above the base of the formation. Other similar by thinner exposures were mapped in the area
which is now overgrown and in an exposure 9km to the west (553874) north of Green Hill. All these metavolcanics
appear to have been tholeiitic volcanic ash though they have been described as tholitic metabasites by Jackson,
Smith and Duke (1991). Convolute bedding on the overturned base of the tuff now the upper surface, suggests palaeocurrence
flow from north to south, as in much of the Maracas Fm.
In the northern part of the Maracas River, about 250 m south of Loango, a thin bed of magnetite/haematite bedded
with Maracas quartzites occurs in the river (723854). In a side road to the west there are boulders of magnetite
with some haematite as they had fallen from the La Vigies ridge above. Extensive investigation has been carried
out, but it does not appear extensive investigation has been carried out, but it does not appear that economic
exploitation of the iron occurrence is likely.
In Kugler's 1959 map the Maracas Fm was confined to the northern flank of the range in the west and the central
part further east, with outcrops of the younger Grande Riviere Fm flanking the Maracas to both north and south.
The Grande Riviere Fm is no longer recognised and the southern and western outcrops are mapped as Maracas Fm. Following
the work of Algar and Pindell (1991) the northern and eastern outcrops of Grande Riviere Fm have been remapped
as Guayamara Fm, a relatively fine grained equivalent of the Maracas Fm. The Guayamara Fm is described separately.
The present map shows the Maracas Fm on the south flank of the range extending eastward nearly to the Oropouche
River, and then occurring as a separate outcrop on the Salybia River and Rio Seco. It is not clear how far eastward
this outcrop extends before being properly regarded as Guayamara Fm.
Detailed stratigraphic study and mapping of the north and south flanks of the western and central parts of the
range confirm the presence of Maracas Fm along a large part of the south flank.
Mapping of the Maracas Fm eastwards along the cliffs of the north coast leads to a change in lithology from the
quartzites of Abercromby Point to the interbedded dark coloured phyllites of Chupara Bay. The boundary between
the two lithologies trends southeastwards to the Blanchisseuse Road and then eastwards towards the east coast.
GUAYAMARA FM
S.T. Algar introduced a new unit - the Guayamara Fm into the geology of the Toco area, based on very good exposures
along the east coast. The lithology appears very like the Grande Riviere Fm of Kugler (1959) as described by Barr
(1963).
The Guayamara Fm also seems similar to the phyllitic facies of the Maracas Fm east of Chupara Bay and on the Yarra
River. The revised map has extended the Guayamara outcrop from the east coast to Chupara Bay, as Algar (1991) did
in one of his maps.
In addition, the new map has extended the Guayamara Fm into the Platanal Graben, an area of poor exposure except
for the folded and faulted structures in the surrounding Maraval limestone. An east-west trending limestone pericline
in the upper reaches of the Salybia River and the Rio Seco is noteworthy.
The formation was formally established by Algar & Pindell (1991). It replaces the northern outcrop of the Grande
Riviere Fm as shown by Kugler (1959) and stretches from Guayamara Bay on the East Coast, westward to Chupara Bay
in the middle of the Range, where there appears to be facies change and the Guayamara is replaced to the west by
the Maracas Fm. The Guayamara Fm is confined to the north flank of the range except in the headwaters of the Oropouche
and Platanal rivers where it seems to extend southwards into part of the core of the range.
There is doubt about the two most southeasterly outcrops of the range in the Matura Point area and the Fronton
de Saline area, mapped by Kugler (1959) as Grande Rivere Fm and by Algar and Pindell as Rio Seco Fm. With some
hesitation they are now mapped as Guayamara Fm based on detailed mapping in the Primera Pria River area.
The formation consists predominantly of interbedded slates, siltstones and sandstones with occasional quaitzitic
grits and areas of slates. Algar & Pindell (1991) suggests an approximate thickness of 800m.
CHANCELLOR FM
Although the Chancellor Fm (formerly Chancellor Beds) is confined to the western end of the Northern Range, extending
36 km eastwards, it does outcrop on the north coast as well as on the south coast of the peninsula and islands.
The formation occurs overturned on Maravaca Island, Medine Point and Les Boquets Islands lying under the overturned
Maracas Fm. It therefore provides important additional evidence on details of the main north-vergent ant form.
There appear to be four members in the Chancellor Fm - a lower limestone member lying apparently conformably on
the Maracas Fm, succeeded by a phyllite member which is followed in turn by an upper limestone sequence; then finally
by upper phyllitic beds. The Morvant beds may lie unconformably on the Chancellor Fm, although evidence for the
nature of the unconformity is not everywhere clear. The thickness of the Chancellor Fm. varies and seems to average
about 400m.
The Chancellor limestones are usually dark grey, recrystallised and thinly bedded (1cm to 1 m) with interbedded
dark grey slates, phyllites and occasional schistose quartzites. The lower limestone has a number of sedimentary
structures in the interbedded phyllites. In this section the Chancellor limestones appear less pure than Maraval
limestones, and are finer grained. Quartz is present in almost every Chancellor limestone and sericite is common
in irregular bands. Pyrite is also common. Recrystallisation has not been carried as far as in the Maraval limestones,
possibly because of the thinner bedding and the higher pelitic content.
The phyllite members are frequently poorly exposed and the uppermost phyllites have been much eroded along the
south coasts of the islands. At widely scattered localities these beds weather lilac to purple in colour. On Fort
George Road the lilac to purple colouring has spread to other parts of the formation, as it has on Lady Young Road.
In Dumas Bay at the southwest end of the island on Monos, the uppermost bedded limestones are interbedded with
conglomerates. In the conglomerates are rounded quartzite pebbles and limestone pebbles resembling Chancellor rocks.
The pebbles are up to 150 mm diameter.
As well as interbedded conglomerates there are also what appear to be channels cut into the bedded limestones and
now filled with conglomerates. There is also one example of a channel in the conglomerate which appears to have
been filled with normal bedded Chancellor limestone.
In Kugler's1959 map the Chancellor Formation is shown as the Chancellor beds, the uppermost member of the Grande
Riviere Formation, which itself is no longer recognised. However, these beds were not shown on the islands of Monos
or Huevos, although they were shown on Chacachacare on the 1959 map.
RIO SECO FM
In the Kugler 1959 map, Rio Seco Fm is shown as entirely Jurassic with four members - Caure limestone, Hollis conglomeratic
limestone, Maraval beds and Aripo limestone, in order of increasing age. These members would all fit into the Maraval
Formation as shown on the new map. However, on the 1959 map the Rio Seco Fm also included Barr's 1963 original
type locality in the Rio Seco and Sena Bay on the East Coast. Partly based on the misnamed Balandra Anticline,
Barr suggested a Jurassic age. J.B. Saunders (1972) suggested a Lower Cretaceous age for Rio Seco samples from
the east coast and the Turure River.
As now mapped, the Rio Seco Fm extends eastward from the Aripo River along the southern boundary of the Northern
Range. At the western end of the outcrops it is faulted against Maracas Fm by the eastern extension of the Arima
Fault, then from the Oropouche River to the Matura River it is thrust in a somewhat unclear manner against Maraval
limestones, then successively outcrops against Maracas and Guayamara formations until it reaches the East Coast.
Most of the formation consists of grey to dark grey shales and slates, often calcareous with bedded limestones
and occasional quartzitic sandstones.
The thick sandstones of the Balandra Grit mapped by Kugler and Barr as in the Grande Riviere Fm, but which Algar
(1991) assigned to the Rio Seco Fm, have been returned, as it were, by now mapping them as part of the Guayamara
Fm.
The Formation is much folded especially in the western part of the outcrop and it is difficult to measure the thickness
accurately. Algar & Pindell (1991) suggest an approximate thickness of 2000m but this may be excessive.
LAVENTILLE FM
The name Laventille is here restricted to the massive limestones with interbedded slates and shales that form the
isolated hill in the eastern suburbs of Port of Spain, and then outcrop to the West in Five Islands, Carrera, Cronstadt
and Point Gourde. They are considered to be equivalent to the conglomeratic limestones of Patos Island in Venezuela.
The eastern boundary of the Laventille limestone in the Laventille Hills appears to be a stratigraphic feature
- the edge of a platform limestone development which covers the whole of the Laventille hills area. However, in
this area there are upper and lower limestone member separated by shales and slates of variable thickness. There
appears to be an unconformity in the middle of the sequence during which the Lower Limestones are faulted, while
neither the Middle slates nor the Upper Limestone are faulted. In the Lower Limestones there are also what appear
to be pinnacle reefs over which the Middle slates are draped (Potter, 1974).
In addition, the limestones are underlain by phyllityic slates and overlain by similar rocks. These phyllites,
slates and shales are now assigned to the Lopinot Fm which now extends eastwards to the Arima area.
Formerly, as in Kugler's 1959 Geological map, the Laventille Fm included both the limestone and the shales and
slates that continue in outcrop almost as far east as Arima. This practice was followed by Potter in 1974. These
beds now fall within Algar & Pindell's Lopinot Fm (1991).
However, the shales and slates between the limestones in the Laventille Hills are mapped within the Laventille
Fm.
Minor ore deposits of fluorite and haematite occur in the Laventille Limestone on Gaspar Grande. Rare evaporites
occur. Kugler observed lenses of gypsum at the foot of Gonzalez Quarry, and Gonzalez & Scott reported gypsum
northeast of Fort Picton associated with graphitic shales. It is not clear what is the tectonic position of these
isolated evaporites.
LOPINOT FM
Apart from the area around the Laventille Hills and certain small exposures of slates on the western islands which
may belong to the Lopinot Fm, these rocks are confined to a narrow outcrop running eastwards from the Laventille
Hills along the southern margin of the Northern Range as far as Arima - about 22 km.
The formation largely consists of slates, occasionally calcareous, with some interbedded siltstones and sandstones.
Limestone beds are also present as at Champ Fleurs.
Slightly to the west of St Joseph some meters of bedded anhydrite and gypsum lay vertically in contorted shales
and slates and were quarried. A similar exposure occurred at Trotman Street schoolyard at Laventille just southeast
of the main Laventille Limestone outcrop.
These rocks were formerly mapped as part of the Laventille Fm by Kugler (1959) and followed by Potter (1974). However,
palaeontological variations observed by Saunders led him to follow Algar & Pindell (1991) in using the term
Lopinot Fm rather than equating them with the Tompire Member of the Toco Fm as he did in 1972, although they are
still seen as equivalent in age -most probably Barremian to Aptian.
MORVANT BEDS
These beds occur in the area between Laventille and San Juan lying on the Lopinot Fm in a number of small synclines.
Road building and housing development have reduced the areas of outcrop. The relationship with the underlying Lopinot
Fm is not now easy to see, but when the Lady Young Road was being cut, and the exposures were fresh, Lopinot clasts
and sedimentary features strongly suggested an unconformity between the two formations. At a road junction near
the summit of the Lady Young Road there originally appeared to be an exposure of Morvant
Beds north of the road, lying unconformably on Chancellor Fm phyllites.
Outcrops of possible Morvant Beds also occur further west at the southern tip of the Lady Chancellor road where
these beds appear to lie on the Chancellor Fm. However, similar exposures on the shore of Cocorite Bay, west of
the House of Refuge seem to be faulted against the Chancellor Fm.
The Morvant beds consist of coarse yellow to buff quartzitic sandstones, often in thick massive beds, and slates
and shales that resemble similar rocks in the Galera Fm. Along the North coast between Blanchisseuse and Grande
Rivere. It may very well be that the Morvant Beds are the southwest equivalent of the Galera Fm.
Algar S.T. (1995)
Interaction of the Caribbean and South American Plates as revealed in the Northern Range of Trinidad
Third Geological Conference of the Geological Society of Trinidad and Tobago: Field Trip Guide
Algar. S.T. & J.L. Pindell (1991)
Structural development of the Northern Range of Trinidad, and implications for the tectonic evolution of the Southeastern
Caribbean
Transactions of the Second Geological Conference of the Geological Societv of Trinidad and Tobago, pp.6-22
Algar ST. & J.L. Pindell (1991)
Stratighraphy and Sedimentology of the Toco Region of the Northern Range, N.E. Trinidad
Transactions of the Second Geological Conference of the Geological Society of Trinidad and Tobago. pp.55-69
Barr. K.W. (1963)
The Geology of the Toco District Trinidad, West Indies
Her Majesty's Stationary Office, 1963. 65 pp
Barr. W.K. & JB. Saunders (1965)
An outline of the Geology of Trinidad
Transactions of the Fourth Caribbean Geological Conference, pp.1-10
Bartenstein. H.Benenstaedt. F&H.M. Bolli (1957)
Die Foraminiferen der Unterkreide von Trinidad B.W.I. Erster Teil: Cuche-und Toco-Formation
Eclog.Geol.Helv.v.50,pp.5-07
Baties. D.A.J.(1968)
Palcoecology: of foraminiferal assemblages in the Late Miocene Cruse and Forest Formations of Trinidad, Antilles
Transactions or the Fourth Caribbean Geological Conference, pp.141-150
Erlich. R.N.. Farfan. P.F.&P. Hallock (1993)
Biostratigraphy, depositional environments, and diagenesis of the Tamana Formation. Trinidad: a tectonic marker
horizon
Sedimentology. v.40,pp.743-702
Eva. A. 1983)
Stratigraphy and Tectonic Significance of the Couva Marine Evaporite, Offshore Trinidad
Transactions of the Tenth Caribbean Geological Conference Cartagena, 1983
Furrer M.A. (1968)
Palaeontology of some Limestones and Calcphyllites of the Northern Range of Trinidad, West Indies
Transactions of the Fourth Caribbean Geological Conference, pp.21-24
Hutchinson A.G. (1939)
A Note upon the Jurassic in Trinidad, B.W.I.
Bull. Amer. Assoc. Petrol.Geol., vol.3, no.8
Jackson T.A. Smith. T.E.&M.J.M. Duke (1991)
The Geochemistry of a Metavolcanic Horizon in the Maracas Formation, Northern Range, Trinidad: evidence of Ocean
Floor Basalt activity
Transaction of the Second Geological Conference of the Geological Society of Trinidad and Tobago, pp.42-47
Koutsoukos E.A. & K.A. Merrick (1986)
Foraminiferal Paleoenvironments from the Barremian to Maestrichtian of Trinidad. West Indies
Transaction of the First Geological Conference of the Geological Society of Trinidad and Tobago, pp.85-101
Kugler. H.G. (1956)
Trinidad
Lexique Stratigraphique International, Fasc. 2b (Antilles), pp.42-116
Liska. RD. (1988)
The Rio Claro Boulder Bed of Central Trinidad, a sedimentary or Tectonic Event
Transactions of the Eleventh Caribbean Geological Conference, pp.12-i to 12-7
Maurv. C.J. (1925)
A further contribution to the paleontology of Trinidad. (Miocene horizons).
Bull. Amer. Pal., vol. 10,no.42,pp. 153-402
Potter H.C. (1973)
The overturned anticline of the Northern Range of Trinidad near Port of Spain
Journ. Geol. Soc. London, vol.129,pp.133-138
Potter, H.C. (1974)
Observations on the Laventille Formation. Trinidad
Verhandi. Naturf. Ges.Basel, band 84, no.1
Potter. H.C. (1976)
Type sections of the Maraval, Maracas and Chancellor formations in the Caribbean Group of the Northern Range of
Trinidad
Transactions of the Seventh Caribbean Geological Conference, pp.505-527
Robertson. P. Burke. K.&.G. Wadge (1986)
Structure of the Melajo Clay near Arima, Trinidad, and Strike-Slip Motion in the El Pilar Fault Zone
Transactions of the First Geological Conference of the Geological Society of Trinidad and Tobago, pp.
Saunders. J.B. (192)
Recent Paleontological results from the Northern Range of Trinidad
Transactions of the Sixth Caribbean Geological Conference, pp.455-459
Speed. R. Russo R. Weber J&K.C. Rowley (1991)
Evolution of Southern Caribbean Plate Boundary, Vicinity of Trinidad and Tobago: Discussion
Bull. Amer. Assoc. Petrol. Geol. Vol.75, pp.1789-1793
Wadge, G.& R. Macdonald (1985)
Cretaceous Tholleites of the Northern Continental Margin of South America: the Sans Souci Formation of Trinidad
(Preprint)
Wall, G&J.G. Sawkins (1860)
Report on the Geology of Trinidad
Geol. Surv. Mem. London, 211 pp.
Weber. J.C. Ferrill. D.& M. Roden-Tice (1995)
Northern Range, Trinidad: Burial and exhumation history from fission-tracks, microstructures, and fault kinematic
indicators
Preprint presented to Geol. Soc. America meeting New Orleans 1995
For the Northern Range, H.C. Potter and J.B. Saunders have combined Potter's mapping extending over 30 years with
input from others including H.G. Kugler, K.W. Barr, J.B. Saunders, C.J. Campbell, G.E. Higgins and, for the Sans
Souci area, G. Wadge. Recent mapping and, in particular, structural measurements by S.T. Algar, are important in
the revised interpretation.
Another area of readjustment of mapped units is the Southeast of Trinidad to the south of Radix Point and to the
east of Negra Point. Here the ongoing work of B. Carr Brown, J. Frampton and A. King has produced new age correlations
between stratigraphic units, and these may still need further refinement.
The work of R.N. Erlich, P.F. Farfan and colleagues on the Miocene limestones has resulted in changes clearly evident
on both the map and the stratigraphic chart. Additional complexities at the Middle to Late Miocene level are being
studied. These studies include the work of R.D. Liska.
A list of Foraminiferal Zones is included as part of the Stratigraphic Table. It is recognised that other microfossil
groups are equally important today but, as an accident of history, it was the foraminifera that were instrumental
in relative dating and in the positioning of many of the lithologic units. In that respect it is good to acknowledge
the vital part played by Hans Bolli in this work.
While the work was in progress we had great help from the Ministry of Energy and Energy Industries and also from
geologists in Amoco (E.B. Eggertson) Petrotrin (including, particularly, Winston Ali), Exxon (R.E. Bierley) and
British Gas (Derek Hudson).
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