geological society of london, special publication. clastic … · 2018. 11. 17. · pindell et al....

Clastic domains of sandstones in central/eastern Venezuela, Trinidad, and Barbados: heavy mineral and tectonic constraints on

provenance and palaeogeography

James Pindell1,2, Lorcan Kennan1, David Wright3, and Johan Erikson4

1. Tectonic Analysis Ltd., Chestnut House, Duncton, West Sussex, GU28 0LH, UK 2. Also at: Dept. Earth Science, Rice University, Houston, TX 77002, USA 3. Department of Geology, University of Leicester, Leicester, LE1 7RH, UK

4. Department of Natural Sciences, St. Joseph’s College, Standish, ME 07084, USA

Corresponding first author: [email protected]

Supplementary material: Location maps and detailed heavy mineral data tables are available at http://www.geolsoc.org.uk/SUP00000

Abstract: Current models for the tectonic evolution of northeastern South America invoke a Palaeogene phase of inter-American convergence, followed by diachronous dextral oblique collision with the Caribbean Plate, becoming strongly transcurrent in the Late Miocene. Heavy mineral analysis of Cretaceous to Pleistocene rocks from Eastern Venezuela, Barbados and Trinidad allow us to define six primary clastic domains, refine our palaeogeographic maps, and relate them to distinct stages of tectonic development: (1) Cretaceous passive margin of northern South America; (2) Palaeogene clastics related to the dynamics of the Proto-Caribbean Inversion Zone before collision with the Caribbean plate; (3) Late Eocene–Oligocene southward-transgressive clastic sediments fringing the Caribbean foredeep during initial collision; (4) Oligocene–Middle Miocene axial fill of the Caribbean foredeep; (5) Late Eocene–Middle Miocene northern proximal sedimentary fringe of the Caribbean thrustfront; and (6) Late Miocene–Recent deltaic sediments flowing parallel to the orogen during its post-collisional, mainly transcurrent stage. Domain 1–3 sediments are highly mature, comprising primary Guayana Shield-derived sediment or recycled sediment of shield origin eroded from regional Palaeogene unconformities. In Trinidad, palinspastic restoration of Neogene deformation indicates that facies changes once interpreted as north to south are in fact west to east, reflecting progradation from the Maturín Basin into central Trinidad across the northwest-southeast trending Bohordal marginal offset, distorted by about 70 km of dextral shear through Trinidad. There is no mineralogical indication of a northern or northwestern erosional sediment source until Oligocene onset of Domain 4 sedimentation. Palaeocene–Middle Eocene rocks of the Scotland Formation sandstones in Barbados do show an immature orogenic signature, in contrast to Venezuela-Trinidad Domain 2 sediments, this requires: (1) at least a bathymetric difference, if not a tectonic barrier, between them; and (2) that the Barbados deep-water depocentre was within turbidite transport distance of the early Palaeogene orogenic source areas of western Venezuela and/or Colombia. Domains 4–6 (from Late Oligocene) show a strong direct or recycled influence of Caribbean Orogen igneous and metamorphic terranes in addition to substantial input from the shield areas to the south. The delay in the appearance of common Caribbean detritus in the east, relative to the Palaeocene and Eocene appearance of Caribbean-influenced sands in the west, reflects the diachronous, eastward migration of Caribbean foredeep subsidence and sedimentation as a response to eastward-younging collision of the Caribbean Plate and the South American margin.

Current kinematically rigorous Cenozoic models for the evolution of northeastern South America invoke a Palaeogene tectonic phase due to inter-American convergence followed by diachronous dextral oblique collision with the Caribbean Plate (Pindell et al. 1991, 2006; Perez de Armas 2005), which became strongly transcurrent in the Late Miocene (Pindell et al. 1998, 2005). In eastern Venezuela and Trinidad, the collision and subsequent shear between the Caribbean Plate and South America (Fig. 1) juxtaposed, imbricated and offset former palaeogeographic elements, hindering

Please do not cite until published. Expected early 2009.In: James, K., Lorente, M. A. & Pindell, J. (eds) The geology and evolution of the region between North and South America,Geological Society of London, Special Publication.

Pindell et al., in press 2009, PREPRINTTrinidad, Venezuela. Barbados heavy minerals and palaeogeography Page 1

Fig. 1. Key tectonic features of the Eastern Caribbean region, including Central and Eastern Venezuela and Trinidad,and key features referred to in the text. The background for the map is the satellite gravity of Smith and Sandwell(1997). Today, Caribbean crust lies east of Tobago and under Barbados. This crust and the Caribbean accretionaryprism have over-ridden much of the proposed Proto-Caribbean Inversion Zone, which is only exposed today in thearea south of Tiburón Rise. The positions shown on this map are based on three-dimensional restoration of featuresmapped on seismic tomography (after Pindell et al. 2007a).

-68° -67° -66° -65° -64° -63° -62° -61° -60° -59° -58° -57° -56° -55° -54°

-68° -67° -66° -65° -64° -63° -62° -61° -60° -59° -58° -57° -56° -55° -54°

8°

9°

10°

11°

12°

13°

14°

15°

16°

8°

9°

10°

11°

12°

13°

14°

15°

16°

Margarita

BARBADOS

Tobago

Guyana ShieldGuarico Basin

VenezuelaBasin

ColumbusBasin

Los Bajos F.

Grenadaintra-arc

Basin

LesserAntilles

Arc

AvesRidge

BohordalFault

Orinoco Delta

Pre-Aptianoceanic crust

Post-Aptianoceanic crust

S. Carib. Foldbelt

V. de Cura Serrania

Oriental

Maturín Basin

Caribbean Prism

Urica F.

Tiburón RiseCaribbeanPlate

Edge ofCarib. crust

Proto-Caribb

ean Inversio

n Zone

“Atlantic” fracturezones (post-95 Ma)

Demerara Fracture ZoneGuyana Transform

GreaterParia

pull-apart

Cret. shelf edge

TRINIDAD

VENEZUELA

Guarico Belt

CariacoBasin

blind Caribunderthrust


reconstruction of former depositional systems. Correct reconstruction of these is important because certain palaeogeographic aspects pertain directly to petroleum exploration. For example, fluvial-depositional systems and turbidite fairways may contain good quality reservoir sandstone packages that can drive hydrocarbon exploration efforts.

Previous work has demonstrated three general principles regarding the provenance of sandstones in northeastern South America (see Figs 2–4 for stratigraphic summaries): (1) South America was the predominant source for most clastic sediments, which are typically quartz prone and mineralogically mature; (2) a less mature Caribbean mineral association began in the Caribbean foredeep basins at the following times: Palaeocene in western Venezuela, Eocene in Central Venezuela, and Oligocene in Eastern Venezuela-Trinidad, indicating the diachronous advance of the Caribbean Plate from the west; and (3) the Palaeogene clastic units of Barbados were derived from relatively high-grade metamorphic (e.g. sillimanite-bearing) rocks, probably from the South American craton or Andes, but also include minerals of probable Caribbean origin such as glaucophane (Senn 1940; Gonzales de Juana et al. 1980; Kasper & Larue 1986; Socas 1991; Kugler 2001). These observations allow the regional stratigraphic units to be understood in the context of the basic Caribbean-South America collisional model (e.g. Dewey & Pindell 1986; Kasper & Larue 1986; Pindell et al. 1988, 1998). However, there has been no systematic attempt to use heavy minerals to test such concepts as the diachroneity of collision, or the possible existence of a Proto-Caribbean prism/thrustbelt (proposed by Pindell et al. 1991, 2006). This study attempts to fill this void, and to define the cause-and-effect relationship between the regional stratigraphic units and tectonic evolution.

We have collected and analysed the heavy mineral content of 118 sandstone and siltstone samples from the Cretaceous and Cenozoic of Eastern Venezuela, Trinidad and Barbados, supported by petrographic examinations of sand grain composition of these and many other samples, to determine sandstone composition variations through the stratigraphic column. In addition, we have studied thin sections and obtained X-ray diffraction data (T. Rieneck & W. Maresch, Universität Bochum, Germany pers. comm. 2007) on field and core samples from the three countries on distinctive red, rounded pebbles and less rounded rip up clasts, informally referred to as “cherries”. In Trinidad, these are particularly characteristic of the Cretaceous (Barremian–Albian) Cuche Formation in the Central Range and probably the similarly aged Toco Formation on the north coast, and are also found in (albeit less-oxidized) coarse intervals of the younger Gautier Formation. They are also found in the (possibly) Late Eocene to earliest Oligocene Plaisance Conglomerate and the basal part of the Mount Harris section of the eastern Central Range in Trinidad, and we have found them in one outcrop of the Oligocene–Early Miocene Nariva Formation sandstone. In Venezuela, they occur in the (possibly) Early Oligocene Lechería beds north of Barcelona. Additionally, we have examined (XRD, thin sections) the dark “clasts” of similar size and shape in the Galera Formation shales that have been previously considered possible precursors for the “cherries” of younger formations (Higgs 2006, 2009).

The new heavy mineral and petrographic analyses augment those previously published, and along with the XRD results and previously published modal point count data are integrated with plate kinematic data and regional structural relationships to constrain Mesozoic–Tertiary clastic distribution patterns and, in turn, palaeogeographic evolutionary models for northern South America.

HEAVY MINERAL STUDY RATIONALE AND LABORATORY METHODS

Background to Heavy Mineral Studies

Heavy mineral analysis allows the efficient reconstruction of source area lithology and provides information on sand provenance and the direction of sand supply, all key to palaeogeographic reconstruction. Diagnostic minerals provide clues to the correlation of sequences linked by a common provenance, and the differentiation of those that were derived from different source lithologies. During the sedimentary cycle, original heavy mineral assemblages may undergo changes controlled by various modifying factors in the sedimentary environment, such as: (1) hydraulic processes during transport, producing preferential sorting according to size, shape and density related to the differing


Fig. 2. Stratigraphic chart for Trinidad showing relationships between key formations both across and along strike,and contrasting our view with more traditional stratigraphic schemes (e.g. Carr-Brown & Frampton, 1979; Saunderset al. 1998). Ages for some of the formations are shown as different to the published literature. The revisions arebased on our own unpublished faunal ages, our observations of field relationships and our interpretations of unpub-lished, proprietary, seismic lines. Ages assigned to most of our samples are based on this framework. Some sampleswere assigned to units different to those in published maps based on distinctive heavy mineral or petrographic char-acteristics. The chart shows the contrasts between the southern Trinidad Platform and the eastern end of the Barce-lona Trough (see Figs 11, 12 for location) to the northwest, which formed during the Palaeogene above the formerpassive margin. The platform overlies less stretched continental basement and lies to the north of the early Creta-ceous shelf edge, probably marked by a reef trend at the palinspastically restored position of the footwall of theCentral Range. The trough lies to the north of the platform, over highly stretched continent, transitional crust, orpossibly oceanic crust of Late Jurassic age and from its inception was significantly deeper. The stratigraphy of thetrough is now found in the highest thrust sheets of the Central Range. Locations for key stratigraphic sections, sam-ple sites and major morphotectonic divisions in Trinidad are shown on Supplementary Figure 1.

Traditional Trinidad (this paper)EW

Southern Shelf Platform Barcelona Trough (deep)

Quaternary

Pliocene

L Miocene

M Miocene

E Miocene

L Oligocene

E Oligocene

L Eocene

M Eocene

E Eocene

E Palaeoc.

Maastricht.

Campanian

Albian

Aptian

Neocomian

M-L Juras.

L Palaeoc.

Ceno.–Sant.

TIME

Cruse

Upper Cipero

Lower Cipero

TamanaBrasso

Navet

ChaudièreLizard Springs

Guayaguayare

Upr Nap Hill

Lr Nap HillGautier

Couva evaporite

San Fernando

HerreraKaramat/Lengua

Angostura

Nariva

NavetCharuma

ChaudièreLizard Springs

GuayaguayareU Nap Hill

Gautier ss

Tarouba

Plaisance

Cruse

Cipero

TalparoSpringvaleManzanilla

Karamat/Lengua

red beds ? marine ?

Barranquín ?

Pt-a-Pierre channels

Mt. Harris

reef talus? (from Laventille LS; not seen)

oceanic crust? or very thinned cont crust

possible Creta-ceous olistoliths

Nariva, shallows up into Cunapo/Brasso

u/c ?

Cun

apo

Herrera

??????

Hospital Hill marlNavet

Nariva

NarivaNESW

SENW

Cipero

S Joseph’s

Lizard Springs

Maridale??

absent

Cuche (shelf)

Cuche (shelf)

Cuche

??

Cuche sands (Mt Harris well)Maridale rubble? (Cuche River)

Trough imbricated and filled tobecome integral with the rest of

Trinidad at this time

??material of this age ishighly condensed orbypassed on a slope

NS

Cuche

Navet

????

M. L’Enfer

Cedros Erin

For.G. Morne GuiacoForest

Morne L’enferErin

Change in orientation

Cret. olistoliths?

Cuche

S Fernando

??

Maridale

Nariva

Pt-a-Pierre

TalparoG. Morne

Manz.Springvale

Cun

apo

Laventille

Soldado

Couva evaporite ?

Tamana

Brasso

Olig. P-a-PSilty Cip.

L Nap HillGautier shale


Fig. 3. Stratigraphic chart for Venezuela showing relationships between key formations both across and along strikefor a NW-SE profile from the Barcelona area to the foreland near Urica, and for a SW-NE from Urica towards thenortheastern Serranía. The approximate location of the profile is shown on Supplementary Figure 2.

Serrania del Interior Oriental, VenezuelaSW NENW SE

La Mesa

Las Piedras

La Pica

Lr Naricual Areo

Caratas

Vidoño

San Juan

San Antonio

QuerecualChimana

red beds

Areo

Guayuta

red beds

Areo

sandy San Antonio

fluvial Barranquín

Carapita

marine

(along Urica Fault) (Urica to El Pilar)

Lecheria?

Upr Naricual

marine Barranquín

San Juan

Los Jabillos

subaerial since end ofMiddle Miocene, due to

Serranían orogeny

Vidoño lst

Querecual

BarranquínGarcia

San Juan

Vidoño

Los Jabillos

Naricual

Paleogene unconformity,due to long-term sealevel fall and Proto-

Caribbean hanging walluplift.

Vidoño lst

Note: Early workers (e.g. Hedberg 1950)suspected Eocene uplift. Most work in

80s–90s presumed all erosion was Mid-dle Miocene and younger. However, Late

Eocene-earliest Oligocene erosion mayhave reached the Albian toward the

northeast, possibly to Barranquín,such that Miocene erosion issuperposed upon the Paleo-

gene unconformity.basal Caribbeanforedceep onlap

E Eocene

E Miocene

L Palaeoc.

TIME

E Palaeoc.

L Oligocene

Maastricht.

L Miocene

Campanian

E Oligocene

Ceno.–Sant.

Quaternary

Albian

L Eocene

Aptian

M Miocene

Neocomian

M Eocene

M-L Juras.

Pliocene

Pre-Late Eoceneprobably present

until LateEocene-earliest

Oligoceneerosion

evaporites?

El Cantil

Tinajitas

Carapita Merecure

evaporites?


Fig. 4. Schematic structural cross-section of Barbados, summarizing possible stratigraphic relationships. Few reli-able ages are available for pre-Miocene strata. According to Senn (1940), the Scotland Group section from top tobottom included the members: Belle Hill/Mount All; Windy Hill/Chalky Mount; Walkers; Murphy‘s and MorganLewis. Speed (2002) aggregated all these into an undifferentiated “Basal Complex”. Further, we suggest that theremay be a juxtaposition of the once-separate Caribbean and Proto-Caribbean accretionary prisms (Basal Complexnorth and south, verging south and north respectively). Locations for key stratigraphic sections and sample sites areshown on Supplementary Figure 3.

Bathsheba Intermediates; other intermediates include Prism Cover,Bissex Hill, Cambridge beds, Kingsley beds, Woodbourne FmOceanic Nappes (note: structurally emplaced in Miocene

Conset Marl (Middle Miocene overlap assemblage)

Mud diapir (Joe’s River Fm)

Basal Complex (Scotland Fm)

Quaternary limestones/alluvium

NNW SSE

Major fault

“Intrusive” contactUnconformity

?

Inter-prism basin floor intermediates? and melange?

Basal Complex northBasal Complex south


densities of the individual species; (2) post-depositional dissolution, due to the low resistance of the majority of heavy minerals to either prolonged acidic or alkaline geochemical conditions either preceding, or following burial. Mineral persistence during diagenesis is directly related to their chemical stability and there is typically a progressive decline in the abundance and diversity of heavy mineral species with increasing depth of burial and increasing age. Ultimately, sediments reach a stage of high mineralogical maturity, where the heavy mineral fraction comprises only ultrastable detrital minerals such as zircon, tourmaline, rutile and apatite. These modifying factors need to be evaluated in any heavy mineral study.

Sample preparation

Analytical work was performed in the geochemical laboratory of the Department of Geology in Leicester University, using the methods described in Mange & Maurer (1992). Sample preparation involved: (1) disaggregation of the consolidated sandstones by rock crushing, using a mortar and pestle; (2) removing drilling mud from the cuttings by wet sieving, using detergent, followed by drying; (3) acid digestion to dissolve carbonates both in cores and cuttings by means of 10% acetic acid which leaves acid-sensitive apatite intact; (4) wet sieving using a sieve of 0.063 mm mesh to remove remaining clay and silt particles; (5) drying, followed by standard sieving, retaining the 0.063–0.210 mm size fractions; (6) oil stained samples and cuttings rich in organic particles were cleaned using chloroform; and (7) heavy mineral separation was performed in bromoform (specific gravity of 2.89) using the centrifuge and partial freezing method.

Microscopy

A split of each heavy mineral sample was mounted in liquid Canada balsam on a glass slide for the microscopic investigation. The viscous consistency of liquid Canada balsam facilitates rolling the grains to obtain the required orientation that helps identification and accurate observation of grain morphology. Grain counting was made along parallel bands on the slide, described as the “ribbon counting” method by Galehouse (1971). Components of the non-opaque heavy mineral suite were counted, excluding micas. However, the presence and abundance of various micas, opaque grains and authigenic phases, together with associated lithic fragments, organic particles etc. was recorded.

The proportion of garnet largely depends on the grain size of the particular deposit, the effects of dissolution processes during diagenesis, mechanical fracture along cleavage planes producing several ‘grains’ from one original, and, to a certain extent, accidental fracturing of the often large grains during rock crushing. It is therefore advantageous to count garnet separately, thereby avoiding the masking effect of varying garnet quantities on the associated minerals. Colourless, and orange to pink varieties were distinguished and their frequencies recorded as a percentage of the total number of grains counted per sample. Anatase, a predominantly authigenic phase, was treated similarly.

During the first stage of grain point-counting the number of individual heavy mineral species was recorded (conventional, species-level analysis) in parallel with the point counting of selected varietal types of zircon, tourmaline and apatite, allocated to relevant categories (high-resolution heavy mineral analysis). When the total of the individual species, excluding garnet, reached 200, counting of the varieties continued until 75–100 grains each of zircon, tourmaline and apatite varietal types were recorded respectively. This permits a reliable estimate of heavy mineral abundance. For recording the grain counting, a specially designed HYPERCARD program was used. Two datasheets were completed for each sample, one for the species-level (overall) mineralogy and one for the varietal study. The raw data were transferred to spreadsheets and recalculated to number percentages.

HEAVY MINERAL DATA

Trinidadian heavy mineral assemblages are summarized in Tables 1 and 2, Venezuelan heavy mineral assemblages are summarized in Tables 3 and 4 and Barbadian heavy mineral assemblages in Table 5. Detailed heavy mineral data and location maps are included in the online supplementary data. We have augmented our data with published sources and the limited older industry data that have been


Table 1. Summary of heavy minerals from Trinidadian formations – this study.

Formation Age Heavy minerals Cuche sandstone Cretaceous ZTR only

Gautier sandstone Cretaceous ZTR, garnet, apatite, possible spinel

Toco Cretaceous ZTR, garnet, apatite

Naparima Hill sandstone Cretaceous ZTR only

Chaudière Palaeocene–Eocene ZTR, possible rare apatite

Pointe-a-Pierre Palaeocene–Eocene ZTR only

Charuma phacoids Palaeocene–Eocene (?) ZTR, apatite, garnet, chloritoid

Plaisance Conglomerate Early Oligocene ZTR, rare epidote

Mt. Harris sandstone Early Oligocene ZTR, rare epidote

Nariva Late Oligocene ZTR, garnet, chloritoid, staurolite, kyanite, glaucophane, apatite, epidote, corundum, monazite

Cunapo Miocene ZT only (extremely low recovery of heavy minerals)

Brasso Miocene ZTR and chloritoid. Characteristic blue tourmaline

Herrera Miocene ZTR, staurolite, epidote, garnet, apatite, sphene, monazite, anatase. Rare hornblende, kyanite

Basal Manzanilla* Miocene ZTR only

Lower Manzanilla Miocene ZTR only

Upper Manzanilla Miocene ZTR, apatite, epidote, clinozoisite, kyanite, chloritoid, chlorite

Cruse Miocene–Pliocene ZTR, apatite, staurolite, garnet, kyanite, chloritoid

Talparo Pleistocene ZTR, staurolite, sphene, kyanite, glaucophane, epidote, sillimanite, xenotime

* Appears to have been mismapped by Kugler (1996) as Cunapo Conglomerate.

Table 2. Summary of heavy minerals from Trinidadian formations – other sources.

Formation* Age Heavy minerals Reference

Naparima Hill Argilite Cretaceous ZTR, trace garnet, staurolite, kyanite, epidote Edelman & Doeglas 1934

Lr. Lizards Springs Palaeocene ZTR, trace garnet, staurolite, kyanite, epidote Edelman & Doeglas, 1934

San Fernando Early Oligocene ZTR, garnet in some samples, trace staurolite, kyanite, epidote Edelman & Doeglas 1934

Bamboo or Flat Rock Silt Early Oligocene ZTR, trace garnet, staurolite, epidote, glaucophane in one sample Edelman & Doeglas 1934

Moruga Miocene ZTR, apatite, staurolite, garnet, blue topaz Kugler 2000

Forest Pliocene ZTR, apatite, garnet, chloritoid, epidote, staurolite, kyanite, andalusite, glaucophane, spinel.

Kugler 2000

Morne L’Enfer Pliocene ZTR, epidote, garnet, chloritoid, staurolite, kyanite, andalusite, topaz, anatase, glaucophane

Kugler 2000

Erin Pliestocene ZTR, epidote, staurolite, kyanite, andalusite, amphibole, topaz, anatase. Rare glaucophane

Kugler 2000

* There appears to be no public-domain heavy mineral data from the Mayaro or Springvale Formations or from the Angostura sandstones.

Table 3. Summary of heavy minerals from Venezuelan formations – this study.

Formation Age Heavy minerals Barranquín Cretaceous Zircon, tourmaline, rutile (hereafter ZTR). Minor staurolite, epidote

San Juan Cretaceous ZT only

Caratas Eocene ZT only

Lechería Early Oligocene ZT only

Los Jabillos Early Oligocene ZT only

Lr. Naricual Early Oligocene ZT, rare kyanite

Areo Late Oligocene ZT, minor garnet

Quebradón Miocene ZTR, apatite, staurolite, garnet


Table 4. Summary of heavy minerals from Venezuelan formations – other sources.

Formation* Age Heavy minerals Reference Pre-Cretaceous Palaeozoic,

Jurassic ZTR, hornblende, tremolite, glaucophane (or non-HP/LT

blue-grn amph?). One report of chloritoid Escalona 1985

Canoa Cretaceous ZT, epidote, zoisite, magnetite, ilmenite. Minor kyanite, staurolite, other amphiboles

Escalona 1985

Tigre Cretaceous ZT, epidote, kyanite, staurolite, glaucophane (or non-HP/LT blue-grn amph?). Minor magnetite, ilmenite, other

amphiboles

Escalona 1985

Mito Juan Cretaceous ZTR, garnet, chloritoid, ilmenite, leucoxene PDVSA 2005

Garrapata Eocene (?) Amphiboles, pyroxenes in association with volcanic rock fragments

PDVSA 2005

Los Cajones Palaeocene–Eocene (?) ZTR, epidote, apatite, magnetite, leucoxene, in association with volcanic and schist fragments

PDVSA 2005

Guárico

Palaeocene–Eocene ZTR, garnet, trace chloritoid, anatase. (Guarumen-Ortiz sandstone)

Kamen-Kaye 1942

Misoa (El Mene) Eocene ZTR, staurolite (upper member only), rare garnet Feo-Codecido 1955

Cobre Eocene ZTR, garnet, staurolite PDVSA 2005

La Pascua Early Oligocene ZTR. Minor or trace staurolite, kyanite, hornblende, other amphiboles

Escalona 1985

Lr. Roblecito Late Oligocene ZTR. Minor staurolite, kyanite Escalona 1985

Upr. Roblecito Late Oligocene ZTR, staurolite, kyanite, glaucophane Escalona 1985

Merecure Late Oligocene–Miocene ZTR, minor garnet, minor chloritoid PDVSA 2005; Feo-Codecido 1955

Carapita Late Oligocene–Miocene ZTR, epidote, glaucophane Feo-Codecido 1955

Capaya Miocene ZTR, staurolite, glaucophane PDVSA 2005

Chaguaramas Miocene ZTR, staurolite, kyanite, andalusite, sillimanite, glaucophane, chloritoid

PDVSA 2005

Oficina Miocene ZTR, staurolite, kyanite, garnet, chloritoid PDVSA 2005 Hedberg et al. 1947

Freites Miocene ZTR, some garnet, chloritoid, staurolite, kyanite, glaucophane

Feo-Codecido 1955

La Pica Miocene ZTR, epidote, some garnet, chloritoid, staurolite, kyanite, glaucophane

Feo-Codecido 1955

Las Piedras Pliocene ZTR, kyanite, chloritoid, corundum, hornblende. Minor sillimanite, staurolite, epidote, garnet, kyanite,

glaucophane

PDVSA 2005 Hedberg et al. 1947

La Mesa Pleistocene ZTR, staurolite, kyanite, andalusite, sillimanite, magnetite Hedberg et al. 1947

Rio Caroni Holocene ZTR, ilmenite, staurolite Wynn 1993

* We recovered no heavy minerals, nor are there reports in the literature of heavy minerals from the Palaeocene-Eocene Vidoño Formation.

Table 5. Summary of heavy minerals from Scotland Group members – this study.

Member Heavy minerals

Morgan Lewis ZTR, epidote, clinozoisite, apatite, garnet (abundant), chloritoid, kyanite, staurolite

Walkers ZTR, clinozoisite (very abundant), epidote, apatite, garnet, chloritoid, kyanite (abundant), staurolite, sphene; rare tremolite, chrome spinel, lawsonite

Chalky Mount ZTR, epidote (minor), clinozoisite, apatite, garnet (abundant), chloritoid (abundant), kyanite (abundant), staurolite

Windy Hill ZTR, epidote, clinozosite (abundant), garnet, chloritoid, staurolite

Mount All ZTR, epidote (rare), clinozosite (abundant), garnet, chloritoid, kyanite, staurolite

Belle Hill ZTR, epidote (rare), clinozosite, garnet, kyanite, staurolite

Bathsheba ZTR, epidote, clinozoisite


released. Both sources are generally non-quantitative. A limited number of modern quantitative studies remain proprietary. Where sediment ages are well-constrained, the results are discussed by age, from oldest to youngest. Figures 2, 3 and 4 summarize the stratigraphy of Trinidad, Venezuela and Barbados, respectively.

Trinidad

Trinidadian samples were collected from numerous outcrops and from several well cores. Although exposure is generally poor, there is good palaeontological age control at many outcrops, and field data from past industry mapping and augering (down to 20 m) was made available to us. Where possible (usually), samples were collected from active stream cuts, or from recent quarries, in order to get below the worst of the tropical weathering. The Trinidad data (Tables 1 and 2) appear to be immediately separable into two age dependent assemblages, with only three possible exceptions as noted below. The large number of samples and the availability of absolute and relative age control allow the data to be displayed as a synthetic stratigraphic column (Fig. 5) that accentuates the contrasts between the two assemblages. Early Rupelian (Early Oligocene) and older rocks are characterized by mature zircon, tourmaline and rutile (ZTR) assemblages. Some garnet and apatite was also found in core samples from the Late Albian–Cenomanian Gautier Formation and in one sample of the similar-aged Toco Formation on the north coast. In contrast, probably Late Rupelian and definitely Late Oligocene, and younger rocks are consistently dominated by an immature assemblage of labile minerals, including staurolite, aluminium silicates and glaucophane, in addition to some apatite. Abundant garnet and chloritoid are particularly characteristic. Tropical weathering of outcrops cannot explain this apparent abrupt maturity contrast. Within a given formation, similarities between borehole and field samples, notwithstanding weathering and/or diagenesis, indicate there is a primary compositional difference, and therefore a difference in provenance, between Early and Late Oligocene sediment source rocks. In addition, we sampled both younger and older formations with identical weathering effects, some from immediately adjacent outcrops, and always found dramatic contrasts in heavy mineral assemblages. In some formations for which we have many samples from both outcrop and wells (e.g. Late Oligocene–Early Miocene Nariva Formation), it is clear that there is a geographical grouping of samples in which there seems to be a correlation between increasing tropical weathering and decreased content of certain unstable heavy minerals (Fig. 6). There may also be an element of subtle variation in original heavy mineral content within the Nariva. However, the primary contrast between mature and immature sands is still clear.

Higgs (2006, 2009), reported that previous authors had identified staurolite and other non-ZTR minerals throughout the Palaeogene strata in Trinidad (relying heavily on the synthesis of Suter 1960) and proposed a northern, rather than Guayana Shield, source for both Palaeogene and Neogene strata. However, our examination of unpublished industry heavy mineral studies (Petrotrin archive files mostly from the 1930s–1950s) show the same mature-immature contrast that we have found, as also reported by Kugler (1996, but based on a 1950s synthesis) and Illing (1928). Trace to low abundance staurolite, kyanite, chloritoid and very rare glaucophane have been found in a few samples (and many were exotic blocks associated with mud volcanoes; their origins and age were thus poorly known), and there is little justification for considering these minerals as characteristic of the Palaeogene as a whole.

There are three potential exceptions in our data to the apparent Oligocene character change for Trinidad. First, the samples from the Middle Eocene “Charuma Silt Member” of the Pointe-a-Pierre Formation at its type locality yield an immature heavy mineral signature (Table 1). Although this is the type locality of this stratigraphic unit, exceptional recently cleared exposure on the day of our collection showed that the Charuma section comprised sheared, sandstone phacoids within a scaly clay gouge zone, with sections and rafts of silty clay. There is no undisrupted bedding in the outcrop and the silty clay carries a Middle Eocene “Gaudryina” fauna. There are no fresh outcrops of this formation and attempts to separate heavy minerals from other sites where stratigraphy and field relationships are clear (e.g. from Piparo Gorge, where adjacent beds are mapped as typical Pointe-a-Pierre sandstone and show zircon and tourmaline only) failed to yield any, much less immature, heavy minerals. Although this unit has been drilled in several wells, there are no longer any cuttings available and the drilled section rarely if ever included sandstones (John Keens-Dumas pers. comm.).


0 20 40 60 80 100LK06-07LK5-09LK5-41LK5-70

LK06-08LK5-16LK5-13

LK Sun 2CLK5-53

BP 347/3BP 347/2BP 347/1

BC 1/4BP 362/3BP 362/2BP 344/2

BC 1/3BP 362/1

BC 1/2BP 344/1CA 40/1CA 40/2

BC 1/1BR1

AUG03/01LK5-18LK5-07LK5-06

LK5-11cLK5-12LK5-01LK5-55

LK06-02LK06-03LK06-04

AUG03/06LK7-02

LK Sun2

LK5-44LK5-43LK5-37LK5-32LK5-14

LK06-06LK06-16LK06-19LK7-20LK5-33LK5-20

T45-1TTM2

LK5-45LK5-29

LK5-24CLK5-52LK5-54LK5-68LK5-65LK5-63

LK06-26LK06-24LK06-22LK5-51LK5-50

LK ANT 1

CU

CH

ETO

CO

/G.

PAP

MT.

H.

CH

AU

D/P

AP

PL

CH

AR

NA

RIV

AB

RH

ER

RE

RA

MA

NZ

UK

CR

TOP CRETACEOUS

PROVENANCE BREAK

SVT

PERCENTAGE

ME15 GAUTIERSNAKE R

TOCO ANDRE PT

3x CUCHE RIVER

2x MT. HARRIS 1

MD34 LR. NAP. HILLGALERA

SAN FABIEN RDBRAKE FACTORY

NAVET DAMPIPARO GORGE

EAST MT. HARRISWEST MT. HARRIS

NORTH MT. HARRISMT. HARRIS

3x CHAUDIÈRE RIVERMT. HARRIS PICNIC SITE

2X WEST MT. HARRIS

2x PLAISANCE QUARRY

3x CHARUMA

PLUM MITAN

3x CHAUD. R. “NARIVA”

ABM54 WELLCORBEAU HILLWILLIAMSVILLE

COLDAN QUARRY

2x SANDSTONE TRACE

PIPARO MUD VOLCANOCUNAPO S. ROAD

NESTOR MAMON ROADBALATA CENTRAL

2x CATSHILL

PENAL BARRACKPOREBALATA CENTRAL

PENAL BARRACKPOREBALATA CENTRAL

3x PENAL BARRACKPORE

BALATA CENTRAL

3X PENAL BARRACKPORE

MD34

2x CUNAPO S. ROAD

CITRUS GROVEMAMORAL

2x GALFA PT.

MAMORALCAROLINA

GarnetEpidote GpStauroliteOthersRutileApatiteTourmalineZircon

KEY:

Fig. 5. Heavy mineral varieties from Trinidad samples, sorted by relative age. Note the very mature assemblages inCretaceous through Early Oligocene rocks; trace staurolite and kyanite has also previously been reported from a fewsamples of this age. Regional facies patterns and provenance data both indicate a broadly “southern provenance”.There is a very pronounced provenance break in late Early Oligocene and younger samples, marked by the appear-ance of immature mineral assemblages derived from in part from the Caribbean Orogen. The orogen was to the westat the time but sediment of this age was transported down the axis of an orogen-parallel drainage system, much likethe present-day Orinoco. In both wells and outcrops it is possible to find adjacent examples of these two assemblagesin rocks which appear to have similar weathering or diagenetic characteristics, indicating that they are primary dif-ferences. Late Middle Miocene and younger strata show a more mixed provenance, with Caribbean detritus dilutedeither by new south-derived input into the basin or recycled Palaeogene rock which had been incorporated into theedge of the Caribbean orogen. Sediment recycling may also contribute to the cleaner signature. Our few Late Plio-cene and Pleistocene samples (Mamoral sample from Springvale Formation and Carolina sample from TalparoFormation), are strikingly more immature than slightly older Herrera and Cruse samples. Abbreviations: UK UpperCretaceous, PAP type Pointe-a-Pierre, MT. H. Mount Harris sandstone, CHAUD/PAP mapped as Chaudière/Pt.-a-Pierre but probably equivalent to or younger than MT. H., PL Plaisance Conglomerate (possibly equivalent to basalMT. H.), CHAR Charuma “Silt”, BR Brasso, MANZ Manzanilla Formation in Caroni Basin, CR Cruse Formation inSouthern Basin, SVT undifferentiated Springvale-Talparo.


Outside in:LK05/6LK05/7

Nariva FormationOther outcrops

Outside in:LK05/1, Corbeau HillLK05/11, Guaracara

Nariva FormationSandstone Trace

Outside in:LK06/4LK06/3LK06/2All Chaud. River

Nariva Formation“Striped” sands

Outside in:LK05/55, ABM54LK05/12, WilliamsvilleLK05/18, Piparo MV

Nariva Formation“Sealed” sands


KEY:

Fig. 6. Variations in heavy mineral abundance in the Nariva Formation. Significant changes in relative abundanceof key mineral in Nariva samples probably reflect post-depositional leaching by acidic fluids (basinal or tropicalsoil origin) superimposed on some original, unquantifiable, but probably limited compositional variation. Fairlyfresh “striped” sandstones from the Chaudière River show intermediate amounts of garnet and some chloritoid andkyanite, but “sealed” samples from outcrops, core or mud volcanoes where intense surface weathering has not hap-pened show very high levels of garnet, with some apatite and staurolite also preserved. The Williamsville Quarrysample is the only one with preserved glaucophane (very unstable). Weathered outcrop samples in the Piparo areashow moderate preservation of chloritoid but no garnet and only trace apatite. The Sandstone Trace samples showintense feldspar breakdown and pervasive clay cement but otherwise do not show deep weathering. Chloritoid isparticularly abundant but garnet is rare and apatite and staurolite are absent. The relative ages of these samples arenot clear. All are associated with earliest Miocene shales in adjacent outcrops.


Faults juxtaposed the sampled outcrops with the Navet marls and Nariva sandstones, the latter with the same complex mineral signature and similar textural characteristics in thin-section. We suspect contamination is possible in our Charuma sample due to the shearing; the sample could be Oligocene Nariva contaminated by Eocene Charuma or Navet fauna, or it could be true Charuma (Eocene) contaminated by Nariva minerals. If this were not the type section of the Charuma beds, we would consider the outcrop as structurally disrupted enough to pay it little attention. Alternatively, the chloritoid, kyanite and garnet present in the samples could represent a rare flush of first cycle labile minerals from the shield into the Trinidad area. Trace kyanite and garnet are both reported from Palaeogene sections close to top Cretaceous and Late Eocene unconformities in Trinidad (Edelman & Doeglas 1934) and all these minerals are present on the shield to the south (see below).

The second exception is a lignite-bearing sandstone collected from an isolated fault-bounded outcrop in the Chaudière River (on the north flank of Mount Harris), which also has a characteristic Nariva heavy mineral signature. Although mapped as Palaeocene Chaudière Formation by Kugler (1996), bedding in the outcrop dips in the opposite direction to proven Palaeocene beds nearby, and is closely associated with poorly exposed breccias, suggesting it may be fault-bounded. Abundant lignite is not found in formations older than Nariva. “Chaff-like plant remains and wisps of carbonaceous matter” (Kugler 1996) are described from the well-cemented sandstones at the Pointe-a-Pierre type locality, but heavy minerals from this site were extremely mature (other than one unpublished report of a single kyanite grain in one of several samples). In hand specimen, these samples are friable compared to adjacent Chaudière sandstones, and in thin section, these samples are texturally identical to Nariva sandstones collected elsewhere, being fine-grained, well-sorted, with poorly rounded grains. Nariva is mapped along strike several hundred metres west of this outcrop and we suspect it continues unmapped along the north flank of Mount Harris.

The third exception is a sample from some 200 m south of the Mount Harris picnic site of the eastern Central Range, also mapped as Chaudière or Pointe-a-Pierre Formation (Algar 1993; Kugler 1996). We have identified chloritoid and blue tourmaline here, both characteristic of the younger Brasso Formation. Thin sections are texturally indistinguishable from Nariva or Brasso Formation sandstones collected elsewhere, and quite unlike nearby sandstones mapped as Pointe-a-Pierre Formation. Furthermore, a sample of interbedded claystone yielded a single foraminifer no older than earliest Miocene (J. Frampton pers. comm. 2006). We provisionally interpret this sample as Brasso sandstone in the footwall of a thrust carrying Early Oligocene Mount Harris sandstone in its hanging wall. There are mapped Brasso outcrops within a few hundred metres of this site.

From the above, the three apparent exceptions to the Oligocene heavy mineral character change appear to be explicable by faulting and mis-mapping of fault-bounded Neogene rocks as Palaeogene. This is not surprising, as up to 150 km of dextral shear must have passed through Trinidad since 10 Ma (Pindell & Kennan 2007a).

Venezuela

Signature minerals such as kyanite, staurolite and glaucophane appear, at first glance, more common in Venezuelan samples (Tables 3 and 4). However, our samples show a fundamental difference between Eastern Venezuela versus Central and Western Venezuela: in the east, as in Trinidad, Late Maastrichtian through Early Oligocene sandstones (i.e. San Juan, Caratas, and Los Jabillos Formations) are highly mature (ZTR-dominated, Fig. 7). There is an apparent break in sandstone provenance along the Palaeogene South American margin at the Gulf of Barcelona/Urica Fault. East of this break, the South American shelf and slope section did not know about the impending arrival of the Caribbean Plate until at least the latest Early Oligocene. This accords with the concept of eastward younging oblique collision between the two plates that was first identified by the eastward migration of Caribbean foredeep subsidence along the margin (Pindell 1985; Pindell & Barrett 1990).

Only trace glaucophane and staurolite have been reported from pre-Cretaceous and Late Cretaceous samples from wells in the foreland south of Caracas. Even in Central Venezuela, where orogenesis has commonly been thought to have begun in the Cretaceous, signature minerals are in much higher abundance in Late Oligocene and younger strata, such as the Upper Roblecito and Quebradón Formations, than they are in earlier autochthonous and para-autochthonous Caribbean


V05-19

10/05-10F

10/05-10D

V05-08

10/05-5B

10/05-5A

10/5-12A

10/05-4A

V05-15

V05-03

10/05-2B

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V05-24A

V05-18

V05-13

V05-32

V05-30

V05-28

V05-14

V05-04

20% 40% 60% 80% 1000% %

PROVENANCE BREAK

4 x Barranquin

El Cantil

4 x San Juan

4 x Caratas

Peñas Blancas

2x Los Jabillos

Lecherias

Areo-Lr. Naricual

2x Naricual

Quebradón

TOP CRETACEOUS

BASE EOCENE

Domain 1

Domain 2

Domain 3

Domain 4

Domain 5

PERCENTAGE


KEY:

Fig. 7. Heavy mineral varieties from East Venezuela samples, sorted by apparent relative age. Trace kyanite andstaurolite are seen in the Barranquín Formation, but all other Cretaceous to Early Oligocene samples are highlymature. Kyanite reappears in the Areo, and garnet and staurolite in Naricual and younger samples.


foredeep strata such as the Guárico Formation. The Early Oligocene La Pascua and Lower Roblecito Formations, which onlap an earlier Palaeogene hiatus, are characterized by a mature ZTR assemblage with only trace kyanite and staurolite suggesting, as in Trinidad, an important provenance break of intra-Oligocene age.

In Central Venezuela, the volcanic, serpentinitic, and metamorphic content of the Garrapata and Los Cajones Formations (Early Eocene; Macsotay et al. 1995) indicate that Caribbean uplift, erosion and redeposition of clastic materials in a trough between the two plates was underway at that time, but these units are entirely allochthonous by an uncertain distance as there is uplift, rather than subsidence, of that age in the foreland. Table 4 appears to suggest that the Guárico Formation was receiving northern/Caribbean-derived detritus as well. However, Peirson’s (1965) original mapping of the Los Cajones and Garrapata as members of the Guárico is invalid, based on more recent field studies. Vivas & Macsotay (1997) propose the Los Cajones and Garrapata units as distinct formations, with no syn-sedimentary intercalation. Further, Perez de Armas (2005) states that the contact between the internal (Los Cajones/Garrapata) and external (Mucaria/Guárico) zones of the Guárico Fold-Thrust Belt is always a fault. Our own field studies support this view entirely, and suggest that the three isolated mapped occurrences of Los Cajones strata within the Guárico Belt south of the Don Alonso and Guárico faults (as shown by Bellizzia & González 1971) are not Los Cajones Formation, but rather sections of Guárico that have been intensely deformed with two intersecting cleavages, giving the false appearance of sedimentary rubble in shaly matrix. Thus, the Guárico and the Los Cajones/Garrapata Formations appear to have been initially deposited in different depocentres that merged over time as the Caribbean thrustbelt advanced upon South America. To our knowledge, it is not permissible with current data to consider the Garrapata and Los Cajones strata as members of the Guárico Formation, nor to claim that the volcanic, serpentinite, and metamorphic clasts and minerals of the Los Cajones/Garrapata units have anything to do with the Guárico Formation south of the Don Alonso-Guárico Fault. Our thin sections from Guárico samples show no such contamination, and we find nothing in the literature to counter this mature characterization of the Guárico. However, with the approach of the Leeward Antilles Arc in the Palaeogene, it would not be surprising if the Guárico were eventually shown to contain crystals of airfall tuff, as is the case with the Oligocene in Trinidad (Algar et al. 1998).

We also highlight the occurrence of chloritoid in the Maastrichtian–(possibly) Palaeocene Mito Juan Formation of the southwest Maracaibo area, which we believe is the only known occurrence of this mineral in Cretaceous through Early Oligocene strata in Venezuela (PDVSA 2005). However, it is characteristic of Late Oligocene and younger sandstones in Eastern Venezuela-Trinidad, with rare exceptions.

Barbados

In Barbados, Palaeogene terrigenous turbidites of South American affinity (bearing mainly quartz with high-grade metamorphic clasts and minerals) occur in the Scotland District (stratigraphic and structural relations are summarized in Fig. 4). Senn (1940) and Poole & Barker (1982) subdivided the “Scotland Beds” into Lower and Upper Scotland units. Senn further considered the Lower Scotland to comprise the Morgan Lewis and the Walkers sections, and the Upper Scotland to comprise the Murphy’s, Chalky Mount, and Mount All sections. Speed (2002) considered all these Scotland beds as packets of accretionary prism material in his “Basal Complex”. The age range of the Scotland beds is Late Palaeocene through Middle Eocene, based on foraminifera and radiolaria (Speed 2002) and pollen (Pindell & Frampton 2007, citing D. Shaw 2007).

Senn (1940) listed the following heavy minerals (citing an unpublished report by Hollis Hedberg) from 113 samples of the Scotland Formation: black opaque minerals, leucoxene, zircon, tourmaline, garnet, staurolite, sillimanite, kyanite, andalusite, topaz, glaucophane (in 5 of the samples only), epidote, zoisite-clinozoisite, rutile, anatase, brookite, chloritoid, hypersthene, augite, titanite, and corundum. Unfortunately, the locations of the samples were not specified and thus the data, as reported by Senn at least, cannot be used to attribute certain heavy mineral signatures to specific Scotland sections.

In our data (Table 5 and Fig. 8), characteristic metamorphic minerals are found in all but the Bathsheba sample, which was considered as the “Intermediate Unit” (possible Early Miocene) by


20% 40% 60% 80% 1000% %

E1

E2

JP 12/06-03

JP 12/06-05

E4

JP 12/06-04

D1

D2

D5

D6

A1

A2

A3

B1

B2

C2

C4

JP 12/06-06

JP 12/06-01

JP 12/06-08a

JP 12/06-08b

G2

H1

JP 12/06-02

JP 12/06-07

2x MORGAN LEWIS BEDS

2x MORGAN LEWIS BEDS

THE CHASE

WINDMILL

4x OIL QUARRY

3x CAMBRIDGE

2x BARCLAYS PARK

2x CHALKY MT. POTTERIES

WINDY HILL

3x MOUNT ALL

BELLE HILL

RAGGED POINT

BELLE HILL EAST

BATHSHEBA


KEY:

PERCENTAGE

Fig. 8. Heavy mineral varieties from Barbados samples, sorted by apparent relative age. All but the youngest sam-ple, from Bathsheba, show mixed South America and Caribbean provenance. The Bathsheba sample is swamped byepidote group minerals but is otherwise mineralogically mature, with only zircon, tourmaline and rutile.


Barker et al. (1986) rather than true Scotland. Apatite is absent in Mount All, Belle Hill and Bathsheba samples, and chloritoid is only absent in the Belle Hill and Bathsheba samples. The various Barbados lithostratigraphic units do not appear to be characterized by very distinct heavy mineral signatures. However, there is tremendous diversity in relative proportions within and between units that suggests the mixing, during transportation, of two end member sediment sources, one mineralogically and texturally mature and one immature. This would be expected if the Scotland Formation (Basal Complex) were fed by a foreland trunk river system flowing between the developing Caribbean Orogen and the Guayana Shield (Kasper & Larue 1986). As will be seen, given the Late Palaeocene–Middle Eocene age of the Scotland beds, the source area was probably situated in Colombia and/or Western and possibly Central Venezuela. The almost ubiquitous chloritoid, common staurolite, kyanite and glaucophane are in striking contrast to strata of the same age in east Venezuela and Trinidad, which show none of the mixed provenance seen in Barbados. If the Basal Complex of Barbados is not very far travelled (i.e. < 300 km), then its depocentre must have been deeper than, if not isolated from, the deep-water deposits of Eastern Venezuela and Trinidad, and also been depositionally downstream of Western or Central Venezuela, where Caribbean allochthons were being unroofed. However, the Basal Complex may be farther travelled than 300 km and the mature south-derived component of the sands may derive from Colombia or Western Venezuela, where, for example, sillimanite-bearing basement was exposed between the times of Guaduas (Early Palaeocene) and La Paz (Late Eocene) Formation deposition (Pindell et al. 1998), coeval with Scotland deposition.

POTENTIAL SOURCE AREAS FOR CHARACTERISTIC HEAVY MINERALS

Our approach to the heavy mineral data has been to identify the signature minerals that characterize particular formations or groups of formations. Our sampling is too sparse to look in detail at the ratios of particular minerals, or to more than qualitatively interpret the relative abundances of particular mineral varieties or grain shapes (typical of detailed studies on a particular well or formation). Instead, we attempt to tie these minerals to well-described possible sediment source regions in Colombia, Venezuela and Trinidad (Fig. 9 and Table 6). Identification of sediment source regions would be greatly aided by modern fission track studies of both potential source areas and of detrital grain populations in foreland sediments (an approach used in, for example, Ecuador by Ruiz 2004, 2007). Modelled unroofing history of detrital grains could then be compared to that of sediment source areas and combined with heavy mineral data could lead to less ambiguous identification of sediment sources, where there is more than one possible source for particular minerals, but where those source regions have different unroofing histories.

The heavy minerals present in the Late Cretaceous to Palaeogene Venezuelan, Trinidadian and Barbadian sediments can derive from old metamorphic or igneous source areas, or may be eroded and recycled from Cretaceous or Tertiary strata. Sufficient information is available to constrain potential sediment sources, especially when combined with additional information such as sedimentary, structural or radiometric constraints on age of uplift, cooling and development of associated unconformities. Potential source areas for selected key heavy minerals are readily identified (Table 6). Some minerals, such as sphene, epidote and apatite are so ubiquitous in greenschist or amphibolite facies terranes or widespread plutons and associated aureoles as to be non-diagnostic of sediment source. Others, such as garnet, chloritoid, staurolite and kyanite, are geographically widespread but absent in a few critical localities of significance for palaeogeographic reconstruction. They may be present in small quantities in sediments of Palaeogene and older age, but dramatic changes in their abundance also correlate with the appearance of distinctive larger clasts, such as circum-Caribbean volcanic rocks, which suggest they are palaeogeographically diagnostic. Some minerals, such as glaucophane, appear to be very strongly associated with Caribbean provenance. Other useful indicators include the presence of rare but distinctive species (e.g. chrome spinel and lawsonite) and mineral associations indicative of a particular paragenesis (e.g. clinozoisite with glaucophane, epidote and chrome spinel is indicative of a metabasic blueschist source lithology).

The major possible sediment source areas can be classified based on distinctive mineralogies and discrete tectonic origins. Four of these classes are unambiguously associated with terranes at the leading edge of the allochthonous Caribbean Plate and four appear to belong to autochthonous or


Fig. 9. Maps showing location of sediment source areas classified in the text. Caribbean allochthons (cross-hatchpattern) comprise: (1) Palaeozoic-Mesozoic igneous and sedimentary protoliths with greenschist to amphibolitefacies metamorphism; (2) Precambrian-Palaeozoic protoliths, HP/LT metamorphism; (3) Mesozoic mixed protoliths,HP/LT metamorphism; and (4) Mesozoic mixed protoliths, greenschist-facies or lower grade metamorphism. Ande-an Para-autochthons, shield areas (grey) comprise: (5) Precambrian-Palaeozoic protoliths, greenschist-amphibolitefacies, locally granulite; (6) Mesozoic mixed protoliths, greenschist-facies or lower grade metamorphism; (7)Mesozoic sediments, unmetamorphosed, Cenozoic uplift and unroofing; and (8) Precambrian meta-igneous andmeta-sedimentary rocks.

2/3

51/4

5

5

1-4

5

5

6

5

8

7

7

-80°

-80°

-75°

-75°

-70°

-70°

-65°

-65°

-60°

-60°

-55°

-55°

-50°

-50°

-5° -5°

0° 0°

5° 5°

10° 10°

GUAYANA SHIELD

5

5/6

1/4

8

15/61,4

Panama and W.Colombia werenot sedimentsources for E.Venezuela andTrinidad

6

7

5

6

6

6

6

77

5

65

Caribbean allochthons

South Americanpara-autochthonousthrust sheets

MMV

Marañon-Oriente

MAR

Putumayo

Llanos

BarinasGuárico

Maturín

Solimões

Amazonas

BRAZILIAN SHIELD

InteriorCaribbean Plate

LMV

UMV


Table 6. Possible source areas for selected characteristic heavy minerals.

Mineral Sediment source area Reference

Yaritagua complex (Lara) PDVSA 2005

Cordillera de la Costa HP/LT belt Sisson et al. 1997

Antimano Formation PDVSA 2005

Villa de Cura Group Smith et al. 1999

El Copey Formation, Araya Peninsula PDVSA 2005

Glaucophane

Guayana Shield (very doubtful, location not specified) Kamen-Kaye 1937

Pastora, Botanamo Proterozoic greenschists and metavolcanics, Guayana Shield

Sidder & Mendoza 1995

Margarita Island HP/LT belt Stöckhert et al. 1995

Manicuare Formation, Araya Peninsula Schubert 1971


Santa Marta Metamorphic Belt (Colombia) Maya-Sánchez 2001*

Cordillera Central, Colombia (west of Palestina Fault) Maya-Sánchez 2001

Chloritoid

Amaime-Cauca blueschist belt (Colombia) Maya-Sánchez 2001

Villa de Cura Group Smith et al. 1999 Lawsonite

Bocas Complex (offshore Venezuela) PDVSA 2005

Margarita Island HP/LT belt (Juan Griego) Stöckhert et al. 1995


Los Torres Association, Merida Andes PDVSA 2005

El Aguila Formation, Merida Andes PDVSA 2005

Iglesias Complex, Merida Andes PDVSA 2005

Macuira Formation gneisses, southeast Guajira (Colombia) Maya-Sánchez 2001

Santa Marta Metamorphic Belt (Colombia) Maya-Sánchez 2001

Silgara Formation, Santander Massif (Colombia) Maya-Sánchez 2001

Cordillera Central Colombia (west of Palestina Fault) Maya-Sánchez 2001

Bakhuis granulite belt, Suriname Delor et al. 2003a

Greenschist belts, French Guiana Delor et al. 2003b

Staurolite

Rio Caroní sediment (Guayana Shield) Wynn 1993

Eastern Guayana Shield PDVSA 2005

Manicuare Formation, Araya Peninsula Schubert 1971

Margarita Island Stöckhert et al. 1995

Cordillera de la Costa (Central Venezuela) Sisson et al. 1997

Iglesias Complex, Merida Andes PDVSA 2005


Kyanite

Caldas Gneiss (Central Cordillera, Colombia) Maya-Sánchez 2001

Imataca Archaean granulite gneisses, Pastora, Botanamo Proterozoic greenschists, overlying Roraima sediments, Guayana Shield


Cabriales Gneiss (Central Venezuela) PDVSA 2005



Guaicaramo, Garzón Massifs (Eastern Cordillera, Colombia) Maya-Sánchez 2001

Cordillera Central Colombia (west of Palestina Fault) Maya-Sánchez 2001

Sillimanite

Guiana Shield (southeast Colombia) Maya-Sánchez 2001


Cerrajón Schist, El Baúl Uplift PDVSA 2005

Cerro Azul, El Aguila Formations, Mérida Andes PDVSA 2005

Iglesias Complex, Mérida Andes PDVSA 2005

Pastora, Botanamo Proterozoic greenschists and metavolcanics, Guayana Shield


Roraima and Mapare Guayana Shield quartzites PDVSA 2005; Sidder & Mendoza 1995

Northwest Guajira schists (Colombia) Maya-Sánchez 2001


Cordillera Central, Colombia (west of Palestina Fault) Maya-Sánchez 2001

Andalusite

Guayana (or Guiana) Shield (southeast Colombia) Maya-Sánchez 2001

Shield amphibolite facies terranes PDVSA 2005

Hato Viejo Formation (Cambrian, Guárico wells) PDVSA 2005

Mérida Andes amphibolite facies terranes PDVSA 2005


El Tinaco Allochthon Oxburgh 1966†

Garnet

Las Brisas, Formation, Caracas Group PDVSA 2005

Sphene Ubiquitous in metagranites and schists from Araya-Paria and west, not source specific

PDVSA 2005; Bellizzia 1985

Apatite Ubiquitous, not source specific PDVSA 2005

El Baúl Arch “cornbunianites” (or tourmalinites) PDVSA 2005 Blue tourmaline

Guayana Shield “cornubianites” (or tourmalinites) PDVSA 2005

* Text to accompany Maya-Sánchez and Vásquez-Arroyave, 2001. † This area originally interpreted as Las Mercedes Formation, Caracas Group but now mapped as part of the El Tinaco “basement” complex (e.g. Bellizzia, 1985).


parautochthonous South America (Fig. 9). There are important mineralogical contrasts (the reader is referred to the references in Table 6 for mineral-specific data sources) between these two groups of potential sediment source areas that support the palaeogeographic models we discuss later. The regional plate tectonic context and detailed local geological evolution of many of the Andean source areas discussed below is discussed in more detail in companion papers (Kennan & Pindell 2009; Pindell et al. 2009).

Class 1: Far-travelled Caribbean greenschist and amphibolite-grade metamorphic terranes with mostly Palaeozoic or older sedimentary (primary), and plutonic or volcanic (secondary), protoliths

These terranes all lie outboard, north or west, of accreted Caribbean oceanic or arc terranes. Where dated, they typically have a Palaeozoic initial age of metamorphism related to the final assembly of Pangaea. Initial cooling from a subduction zone-related orogenic event is Albian to early Late Cretaceous (Stöckhert et al. 1994; Sisson et al. 2005), indicating an origin to the west of Colombia because only passive margin conditions existed at that time along northern South America (Villamil & Pindell 1998). Class 1 rocks were rifted from South America and then incorporated into the leading edge of the Caribbean Plate west of Colombia in the Early Cretaceous and comprise the basement to the “Great Arc of the Caribbean”. Examples include the schists and gneisses of the northwest Guajíra Peninsula, parts of the Santa Marta Massif, and the Arquia Complex of western Colombia. We also interpret the El Tinaco Complex as a far-travelled Palaeozoic basement fragment (an idea proposed by Bellizzia 1985), because its geological history is typical of circum-Caribbean terranes and unlike that of the South American autochthon in Central Venezuela. The associated Tucutunemo Formation includes Permian limestones that are not local to Central Venezuela (Benjamini et al. 1986, 1987). These rocks are the westernmost potential sediment source area for sillimanite and andalusite, prior to eastward migration with other Caribbean terranes.

Class 2: Far-travelled Caribbean high-pressure, low-temperature (HP/LT) metamorphic terranes with mostly Palaeozoic or older major sedimentary (primary), and plutonic or igneous (secondary), protoliths

Class 2 rocks are situated in the same areas as Class 1. Well-known examples include the Juan Griego high-pressure rocks of Margarita, some Cordillera de la Costa metasedimentary protoliths and possibly much of the Manicuare Formation (Schubert 1972) of the Araya Peninsula. The garnet and glaucophane schists of the Yaritagua Complex of Lara, Venezuela (protolith age unknown) may also belong in this grouping (since pre-Caribbean HP/LT rocks are unknown in northern South America). All are intimately associated with HP/LT meta-igneous rocks and are often near ophiolite remnants inferred to be part of the Caribbean suture zone. By 100–120 Ma they were juxtaposed with younger igneous rocks (Class 3, below) and share the same metamorphic, structural and exhumation history (Stöckhert et al. 1995; Pindell et al. 2005). On the north side of the Venezuela and Trinidad foredeep basin, Margarita and the Cordillera de la Costa are the easternmost identified potential sources for staurolite and the Manicuare Formation is the easternmost identified source for garnet and kyanite. The limited drainage from these areas into the Orinoco suggests that they are secondary sources for foredeep staurolite, kyanite and garnet, at least for the last few million years, compared to the Mérida Andes (Class 5 below), which drains directly into the headwaters of the Orinoco.

Class 3: Far-travelled Caribbean HP/LT metamorphic terranes with Cretaceous volcanic and volcano-sedimentary protoliths and initial age of metamorphism

Class 3 rocks include the Rinconada metabasic rocks (Margarita), the Villa de Cura blueschist belt, and the Jambaló, Barragán and Pijao blueschists of Colombia. The Cretaceous protolith age is constrained by the oldest U-Pb zircon ages from Margarita (for a very detailed review of the geological evolution of Margarita, see Maresch et al. 2009). Detailed metamorphic and geochronological studies indicate protolith eruption followed rapidly by juxtaposition with continental-affinity rocks, high-pressure blueschist-eclogite metamorphism at 100–120 Ma, onset of


exhumation and cooling in the mid-Cretaceous, and intrusion at mid-crustal levels by granitoids by 85–90 Ma. These two HP/LT rock types are the only identified sources of the glaucophane that characterizes Late Oligocene and younger sediments in the study area and are also likely sources of kyanite and chloritoid. The easternmost glaucophane source is found at Tres Puntas on the Araya Peninsula, mapped as part of the El Copey Formation. The Villa de Cura, Cordillera de la Costa and Manicuare Formation are the easternmost identified chloritoid sources. There is a report of possible lawsonite in the Bocas-1 well (Escalona 1985), just north of the Paria Peninsula.

Class 4: Far-travelled Caribbean lower grade metamorphic terranes with Cretaceous volcanic and volcano-sedimentary protoliths and initial age of metamorphism

Class 4 rocks include the schists of the Quebradagrande Complex and northwest Guajíra Peninsula, both in Colombia, and the schists and meta-igneous rocks of Tobago (Snoke et al. 2001). The Cretaceous rocks which unconformably overlie the allochthonous El Tinaco “basement” of Central Venezuela also belong in this grouping. The Cojedes (with a basal conglomerate on El Tinaco Complex basement), Pilancones and Araguita Formations comprise Aptian–Albian clastic sediments and carbonates, with intercalated Albian and younger volcaniclastic and extrusive rocks (Bellizzia 1985). In the offshore Bocas-1 well along the northern Paria Peninsula, limestones thought to be Albian overlie metavolcanic schists (Ysaccis 1997), and the well may also contain a thin section of Mejillones Formation arc volcanic rocks. The association of low-grade metasedimentary rocks unconformably overlain by limestones and pillow basalts is typical of many Aptian–Albian circum-Caribbean arc terranes (e.g. Lebron & Perfit 1993; Pindell et al. 2005, 2006) and indicates a far-travelled Caribbean origin for the El Tinaco and the Bocas rocks. Low-grade metavolcanic rocks mapped as El Copey Formation on the Araya Peninsula may also belong in this class. They are spatially associated with fragments of mid-Cretaceous basalt that structurally overlie low-grade continental-affinity Mesozoic metasedimentary rocks (Class 6 below) and may be the remnants of the sole thrust of the Caribbean accretionary prism. The Sans Souci basalts of northern Trinidad may also be of this origin (Algar & Pindell 1993). Metamorphism is typically prehnite-pumpellyite, greenschist or lower amphibolite facies and fossils are sometimes well-preserved. The terranes are potential sources of pyroxene, hornblende, apatite, chlorite and apatite. There are few metapelites in these terranes, and no reports of chloritoid, garnet, staurolite or aluminum-silicates.

Class 5: Parautochthonous and authochthonous greenschist to amphibolite facies metamorphic terranes with Precambrian to Palaeozoic protoliths and typically Late Palaeozoic (Carboniferous–Permian) initial metamorphism

Rocks sharing the same Pangaea-assembly origin as Class 1 are common inboard of the Caribbean allochthons. They are found within thrust sheets driven ahead of accreted Caribbean rocks or uplifted during Late Oligocene and younger “Andean orogeny”, as “basement” slices beneath Mesozoic metasedimentary rocks, and as basement arches in the foreland. As such, they typically have significantly younger cooling ages than similar rocks associated more closely with the Caribbean Arc, and those ages become younger from west to east. Examples include:

• Metamorphic belts intimately associated with the accretion of Caribbean terranes, such as parts of the Central Cordillera, Santa Marta Massif and Guajíra Peninsula of Colombia in the west. Garnet, sillimanite and kyanite-bearing schists are common in these belts. In the west, these terranes started to exhume following Late Cretaceous onset of subduction of Caribbean lithosphere beneath Colombia and accretion of Caribbean allochthons, while in the east Caribbean-associated unroofing is of Miocene or younger age.

• Greenschist and amphibolite facies belts which started to unroof at the Late Oligocene onset of regional Andean orogeny in western South America, which include parts of the Central Cordillera, the Eastern Cordillera of Colombia, the Santander Massif and the Mérida Andes. With the exception of the Colombian Central Cordillera, which was unroofed in the Middle Eocene and then mostly re-buried in Late Eocene–Oligocene time (Pindell et al. 1998), there is no evidence for earlier Palaeogene unroofing of these belts. Andalusite is commonly associated with low-


pressure contact metamorphism adjacent to Late Palaeozoic plutons. A large area of the Mérida Andes drains directly into the upper Orinoco and this may have been the primary source for Late Oligocene and younger staurolite and Al-silicates. In contrast, these minerals are restricted to the Cordillera de la Costa of Central Venezuela and, at least at the present day, this area does not drain into the Orinoco. In the past, the Caribbean Mountains source areas may have been larger and may have drained south into a palaeo-Orinoco.

• Sheared granitoids and metasedimentary rocks such as the Sebastopol Gneiss (Central Venezuela) and the Dragon Gneiss of the Paria Peninsula (Eastern Venezuela) are inferred to be the basement of Caracas Group and to structurally underlie far-travelled Caribbean rocks. Mega-feldspar augengneisses are associated with greenschist facies (chlorite, biotite, muscovite bearing) schists and phyllites, some granites and associated hornfels contact metamorphic rocks. Reported protolith ages (mostly Rb/Sr) range from c. 450–166 Ma and K-Ar and fission track cooling ages are as young as Miocene. There are no reported occurrences of garnet or staurolite within these “basement” gneisses and sillimanite is only reported in one place, adjacent to the Cordillera de la Costa. There is no evidence that Palaeogene unroofing was sufficient to fully exhume these rocks and their mineralogy indicates they are not a source for higher grade metamorphic minerals (in contrast to the model of Higgs 2006, 2009).

• Poorly dated Palaeozoic rocks are also known from the foreland El Baúl Arch, where low-pressure metavolcanic and metasedimentary rocks, intruded by Carboniferous or Permian granitoids, crop out within the foreland basin. Andalusite is typical of contact metamorphic aureoles. The age of uplift of this arch is uncertain and it seems likely to be only a secondary source of andalusite, possibly only in the Late Neogene.

• On the north side of the Guayana Shield there is an abrupt transition from Precambrian and Palaeozoic rock. Within the Palaeozoic terranes there may be one or more sutures related to Pangaea assembly which could be the source of some blue amphibole (identified in probable error as glaucophane) and chloritoid, found in small quantities in both pre-Cretaceous (possibly Jurassic) and Late Cretaceous passive margin strata. Such rocks have not been identified in the relatatively few deep wells and, thus, this idea remains unproven. Low-grade or non-metamorphic Palaeozoic clastic rocks are also reported from the Guárico Basin subsurface (Cambrian Hato Viejo and Carrizal Formations, PDVSA 2005). Heavy mineral assemblages in these rocks are mature, with some garnet. The strata are notably micaceous. These Palaeozoic rocks appear to be absent from the basement of the Maturín Basin, east of 65°W.

Class 6: Parautochthonous greenschist-facies or lower grade metamorphic terranes with mostly Mesozoic protoliths

In the Caribbean Mountains of Central Venezuela (66°–68°W, Fig. 1), the Caracas Group comprises greenschist facies schists in an anticlinal structural window beneath the Villa de Cura HP/LT allochthons. Limited K-Ar and fission track data indicate that peak metamorphism pre-dates the arrival of Caribbean allochthons dated by nearby foredeep subsidence (Pindell et al. 1991). Similar rocks are found in the Araya and Paria Peninsulas north of the Serranía Oriental and in the Northern Range of Trinidad, where cooling appears to be Late Oligocene and younger. Quartzites and marbles are common. Greenschist facies phyllites and schists are characterized by muscovite, epidote, chlorite and graphite. There are no reports of staurolite and chloritoid or Al-silicates. Garnet is not known east of the westernmost Araya Peninsula. Thus, as with the “basement” gneisses above, they are not a viable northern source region for sediments with higher-grade metamorphic minerals.

Class 7: Mesozoic sediments, unmetamorphosed, Cenozoic uplift and unroofing ages

Unmetamorphosed Cretaceous strata of the Colombian Eastern Cordillera and the Subandean fold-thrust belts of Ecuador and Colombia unconformably overlie metamorphic and plutonic rocks of Jurassic and older age. They uplifted significantly for the first time during the Neogene (e.g. Villamil 1999) and may have contributed significantly to Early Miocene and younger rocks in the study area. There are no published heavy mineral data on these rocks, but we expect they are broadly similar to rocks of the same age (i.e. mineralogically mature) examined in the course of this study.


Class 8: Heterogeneous Precambrian metamorphosed sedimentary and igneous rocks in the Guayana Shield

A wide variety of minerals are reported from the amphibolite and granulite facies rocks of the Guayana Shield in Venezuela (alternatively spelled Guyana or Guiana in neighbouring countries), and from associated granitoids and their metamorphic aureoles, including all three Al-silicates, garnet, cordierite and chloritoid (Sidder & Mendoza 1995; Schruben et al. 1997). Glaucophane is reported, but no locality given, by Kamen-Kaye (1937) but is otherwise unknown anywhere in the shield (Salomon Kroonenberg pers. comm. 2008). Riebeckite and other blue-green amphiboles, not characteristic of HP/LT metamorphism, are present (Schruben et al. 1997) and we suspect that these may have been mistaken for glaucophane. Tropical weathering and laterite formation results in a low diversity heavy mineral assemblage in river sediment regardless of rock type in the drainage basin. We expect garnet to be more stable than staurolite, chloritoid (in acid water conditions), Al-silicates and, especially, glaucophane. None of these minerals are likely to survive more than two cycles of sedimentation. There appears to be only one published report on recent river sediment on the shield. The Río Caroní, which flows north from the Guayana Shield at c. 63°W, crosses a wide variety of metasedimentary and metavolcanic terranes. Heavy mineral residues comprise ZTR, ilmenite and, notably, staurolite (Wynn 1993). Staurolite is not reported in situ from the Venezuelan portion of the shield, but is present to the southeast in contact aureoles around granitoids within the greenstone belts of French Guiana (Delor et al. 2003a), continuous with those of Guyana (Cole & Heesterman 2002) and southeastern Venezuela, and in the high-temperature rocks of the Bakhuis Metamorphic Complex of Suriname (Delor et al. 2003b). Chloritoid is widespread, and appears to be a product of staurolite breakdown during near isobaric cooling. Although the shield must have been an important sediment source on the Cretaceous passive margin (below), we suspect that it only made a relatively small contribution to the characteristic unstable heavy minerals found in the Neogene basins because of the effects of tropical weathering. Although areas of low elevation have much lower denudation rates than areas of higher elevation (e.g. Wilkinson & McElroy 2007), the enormous area of the shield resulted in a large volume of sand, deposited in southwest to northeast-flowing fluvial-deltaic systems fringing the foreland basin in Venezuela and Trinidad up to the present day, and these sediments constantly dilute the heavy minerals derived from more exotic peri-Caribbean terranes.

PALINSPASTIC RECONSTRUCTION, TECTONIC ELEMENTS, AND PLATE BOUNDARY/THRUSTBELT EVOLUTION

In order to understand original facies distributions and the relationships of sediments to possible sediment source areas, it is essential to palinspastically restore plate movements and structural deformations back in time, and to portray former sedimentation patterns on appropriate palinspastic basemaps. Post-depositional deformation can juxtapose sediments and facies of very different origins, rotate palaeoflow indicators, and change the orientation of sandstone fairways. In northeast South America, there have been three superimposed deformation phases since the Jurassic creation of the passive margin, from youngest to oldest: (1) east-west-oriented Caribbean-South American dextral strike-slip since about 10 Ma; (2) Early and Middle Miocene southeastward dextral oblique collision between the Caribbean and South American crusts; and (3) the Palaeogene development of the Proto-Caribbean Inversion Zone (Pindell et al. 1991, 1998). A map restoring phase 1 deformation should be used to show late Middle Miocene facies belts, and a map restoring phases 1 and 2 deformations should be used to show Oligocene facies belts, and so on.

From 2001 to 2007, Petrotrin provided the opportunity for us to work with much of the relevant seismic and well data in and around Trinidad and Tobago in conjunction with our field studies in Eastern Venezuela, Trinidad, and Barbados. We have critically examined most structures in the region to assign them to the correct phase of deformation, and have tested and refined estimates of shortening and strike-slip offset. This is important because most workers have previously combined the structures of phases 1 and 2 into a single model of ongoing transpressive collision between the Caribbean and South America, thus blurring the superposition of distinct structural styles.


Our palinspastic maps address the stratal level at which deposition was occurring for the indicated age of the map. We account for the depth to fault detachment and only apply the restoration to strata within fault hanging walls or to terranes that are allochthonous relative to South America. This principle has some important consequences for understanding geological development, particularly in southern Trinidad where Late Miocene through Pliocene eastward extension soled into a detachment above previously deformed Middle Miocene and older strata, while a similar magnitude of dextral shear soling into an intra-Cretaceous or base-Cretaceous detachment was occurring on the Point Radix-Darien Ridge fault zone through central Trinidad. Thus, palinspastic grids appropriate for Cretaceous levels show large magnitude offset across the Point Radix Fault, while grids for late Neogene strata show much smaller offset, although the deformation is of late Neogene age.

The methods of palinspastic map construction in northern South America have been described elsewhere (e.g. Pindell et al. 1998, 2000), and the detailed strain estimates used to construct the maps shown here are discussed in Pindell & Kennan (2007a). We have constructed palinspastic latitude-longitude grids for c. 12 Ma (Fig. 10), at the transition to phase 1 strike-slip-dominated plate boundary movements and for c. 25 Ma (Fig. 11), restoring the effects of transcurrent motions and oblique collision of the Caribbean Plate in eastern Venezuela and Trinidad. The estimated position of the crystalline leading edge of the Caribbean Plate is shown in both maps. These reconstructions are based on careful assessment of shortening, extension and strike-slip offsets, but reconstructions for times before 25 Ma are subject to greater uncertainty, as are strain estimates in central and western Venezuela. However, south of the deformation front shown for 25 Ma (Fig. 11) the basemap for older reconstructions remains the same.

A general tectonic elements map of the Caribbean-South America collision zone (Fig. 12), using the 25 Ma palinspastic restoration, includes the migrating Caribbean trench and arc, the migrating Caribbean foredeep on the South American margin, and the Proto-Caribbean Inversion Zone of northern South America. The concepts of arc-passive margin collision (Speed 1985) and of a migrating Cenozoic arc-passive margin collision (Dewey & Pindell 1986; Pindell et al. 1988) have been well accepted, but the existence of a Proto-Caribbean Inversion Zone ahead of the Caribbean Plate remains more speculative, and is one of the features on which this paper may shed some light. The Proto-Caribbean Inversion Zone was probably initiated in the latest Maastrichtian, and certainly by the Palaeocene, by which time motion between North and South America had become convergent (Pindell et al. 1988; Müller et al. 1999). Based on seismic tomographic images (Van der Hilst 1990) of subducted Atlantic/Proto-Caribbean lithosphere below the eastern and southern Caribbean Plate, we have previously suggested (Pindell et al. 1991, 2006; Pindell & Kennan 2001, 2007a) that the convergence was accommodated, prior to the arrival of the Caribbean Plate from the west, at a newly formed south-dipping “Proto-Caribbean Inversion Zone” beneath northern South America. Today, only the eastern end of this inversion zone has not yet been subducted beneath the Caribbean Plate and remains visible at the earth’s surface, projecting east from the Lesser Antilles trench. There, an ENE-trending ridge (south) and trough (north) pair with some 3 km of buried basement relief is situated between the Caribbean crystalline limit and the Late Maastrichtian western Atlantic magnetic anomaly 30, and cuts across the previously formed regional pattern of Atlantic fracture zones (Speed et al. 1984). The linearity, basement relief, and cross cutting relationship of this structure are suggestive of a north-vergent thrust/inversion zone plate boundary. Beneath the Caribbean Plate, the seismic tomography suggests that this plate boundary once continued west-southwest to at least the Golfo de Triste along Venezuela, at the northeast end of the Mérida Andes. From there, the plate boundary may have continued along the limit of the continental crust to the north of Maracaibo and northern Colombia. It is not yet clear if deformation in the Mérida Andes of possibly Palaeogene age tied into this structure as well. Accepting our projection of the Proto-Caribbean Inversion Zone below the present day Caribbean Plate (Fig. 12), we suggest that the Proto-Caribbean hanging wall would have had positive but submarine bathymetric expression created by basement uplift about 2–3 km, as basement does today in the not-yet-subducted area south of Tiburón Rise (see basement structure map in Speed et al. 1984; Pindell & Kennan 2007a).

We propose the existence of the “Barcelona Trough”, situated north of the South American margin and south of the Proto-Caribbean Inversion Zone and accretionary prism, that formed during the Palaeocene (Fig. 12). The trough was the site of significant Palaeogene clastic deposition, initially deep water but shallowing upward by Late Oligocene time. It was also the site of initial Oligocene

Pindell et al., in press 2009, PREPRINTTrinidad, Venezuela. Barbados heavy m

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