Luis A. Sanchez-Barreda
Consultant
Navasota, Tex.
The Sarstun embayment in southern Belize remains, in effect, unexplored for hydrocarbons. The embayment (Fig. 1) on the southeastern flank of the Yucatan peninsula, forms the eastern extension of the thrust-faulted and folded Guatemala structural foreland basin-part of the larger Chapayal basin (Vinson and Brineman, 1963).
Two giant oil provinces have been discovered bordering the western margin of the Yucatan peninsula in the northern Chapayal basin-the Chiapas-Tabasco Mesozoic province and the Campeche marine platform province.
Prior to 1982, the Chiapas-Tabasco province contained 18% of Mexico's proven oil reserves. Discovery of LaLuna field in 1987, with proved reserves of 20 billion bbl of light oil, has made this area one of Mexico's principal oil producing regions.
The Campeche marine province in 1982 contained 47% of Mexico's total proved oil reserves.
Cantarell, largest of the Campeche producing complexes, has proved reserves estimated at 8 billion bbl of oil. Guatemala's portion of the Chapayal basin, the Rubelsanto area, has considerable oil production from Mesozoic structures, where proved reserves from Cretaceous carbonates have been estimated at 80 million bbl.
BELIZE EXPLORATION
In Belize, oil exploration efforts began in the late 1930s; however, it was not until 1955 that Gulf completed the first exploration well, 1 Yalbac. Most offshore exploration in southern Belize was dominated in the 1950s and 1960s by Phillips Petroleum Co., which drilled eight wells, including the country's deepest, 1 Palmetto Caye (Fig. 2).
Esso followed in the late 1970s, drilling two wells onshore and one offshore. By the early 1980s, two more offshore wells were drilled by Anschutz. Marathon in 1985 drilled the latest of the offshore wells.
Although all wells drilled in southern Belize have encountered encouraging hydrocarbon evidence, failure to establish commercial production may be attributed to insufficient depth to penetrate a sealed reservoir, drilling off structure, or a lack of trapping seals (see table).
Several surface indications of hydrocarbons have been reported in southern Belize (Fig. 2). Possibly the most important is the oil seep near the Temash area. Marathon concluded from analysis of the oil that extensive biodegradation had occurred and a kerogen of dominantly marine origin had been generated. These oil seeps were encountered in Upper Cretaceous limestones on an east-west trending, intensively deformed, surface anticline.
The Esso 1 Temash was drilled on a nose south of this structure but failed to test structural closure at the objective level. During the drilling, steep dips (30-50) were encountered, and slight to good impregnations of viscous, tarry oil were reported throughout the drilled, fractured limestone. Other surface hydrocarbon indicators in southern Belize occur in carbonate rocks of the Late Cretaceous-early Paleocene Toledo formation and consist of oil stained limestones or asphalt veins filling limestone fractures.
REGIONAL SETTING
The Sarstun embayment is on the southeastern flank of the Yucatan peninsula, south of the Maya mountains.
The basin is an eastward extension of a thrust-faulted and folded, foreland, structural province. To the west, this province can be traced through central Guatemala and then northwest in Chiapas, Mexico.
The embayment and Guatemala's foreland basin are bounded to the north by the Maya uplift and subsurface structure of the La Libertad arch. To the south and southeast, these two basins are bounded by the Polochic-Motagua-Jocotan fault system. This wrench fault system also forms the western end of the present day North American and Caribbean plate boundary and is presently associated with development of the Cayman spreading center.
Tectonic evolution of the Sarstun embayment has been affected by several events. The oldest recorded tectonic event involved Laramide age thrust faulting and folding. The consequent Cretaceous structural trend was subjected in early Tertiary, to differential subsidence through block faulting strike slip and wrench faulting occurred during the late Tertiary.
The present day back reef lagoon of southern Belize is the near surface expression of fault movements associated with development of the Cayman trough. A mid-Eocene age for initial rifting of this trough was suggested by Rosencrantz and Sclater (1986).
TECTONO-STRATIGRAPHIC
EVOLUTION
Late Paleozoic In southern Belize, the Paleozoic Santa Rosa series (Fig. 2), considered to be economic basement, outcrops extensively in the Maya mountains.
These rocks consist of sediments. metasediments, and volcanic rocks of Lower Pennsylvanian to Middle Permian age intruded by Triassic granites. Based on lithologies, the Santa Rosa series has been divided into three groups (Dixon, 1957).
The Maya group consists of graywackes, quartzites, slates, phyllites, and shales with some schists. Degree of metamorphism in the Maya group decreases away from the core of the Maya mountains.
The Macal group is mainly a shale sequence with minor sandstone interbeds. To the west of the Maya mountains, the Shell 1 Laguna Blanca reported Macal section containing traces of asphalt and good cut and fluorescence. Macal crinoidal limestones described by Dixon (1957) are time equivalent to early Permian limestones and shales of Guatemala's Chochal formation.
Finally, the Bladen group consists of acid lava flows, tuffs, and volcano-clastics with highly magnetic affinities. Intrusion of the Cockscomb granites into these igneous and sedimentary rocks occurred during Triassic.
The uplifted basement block of the Maya mountains is cut by numerous faults trending east-west and northeast-southwest. The block is bounded both to the north and south by regional faults.
The northern fault is more obvious since Paleozoic rocks are juxtaposed next to Cretaceous carbonates. Faulting and uplift of the basement block at the end of the Paleozoic prevented deposition of Triassic and Jurassic sediments (Bishop, 1980).
LATE JURASSIC-EARLY CRETACEOUS
The Yucatan shield area, including the Maya mountains uplift, appears to have been emergent from late Paleozoic well into the Jurassic.
Mesozoic sedimentation over the region began with accumulation of Todos Santos formation red beds. These beds consist of reddish, lithoclast-conglomerates, sandstones, and mudstones.
In western Guatemala and Chiapas, Mexico, the Todos Santos grades laterally into nearshore, marine sandstones and vertically into marine carbonates of the San Ricardo formation. Fossils from San Ricardo carbonates range from Oxfordian (late Jurassic) to Hauterivian (early Cretaceous) age (Blair, 1988).
On the western flank of the Yucatan Peninsula along the Campeche-Reforma trend, more than 3,000 ft of Upper Jurassic marine carbonates are present.
Todos Santos and San Ricardo equivalents are missing along the outcrop belt on the south and southeastern flank of the Maya mountains; Cretaceous carbonates rest directly on Paleozoic basement rocks.
In the Dangriga area (Fig. 2) east of the Maya uplift, the Anschutz 1 Spanish Lookout penetrated a Todos Santos, quartzite-clast conglomerate at the base of the Mesozoic sequence. This conglomerate unit grades upward into red sandstones and mudstones interbedded with anhydrite.
In southern Belize, the onshore well Phillips 1 San Jose penetrated 24 ft of interbedded gray and sandy shales of the Todos Santos formation. Locally, Todos Santos is unconformably overlain by dolomites of the Coban formation.
Offshore, the Todos Santos was penetrated by the Esso 1 Seal Caye. More than 150 ft of varigated conglomerates of carbonate clasts in a red, argillaceous matrix were described overlain by 300 ft of red to reddish-brown shale with thin interbeds of nearshore, marine limestones.
Above the Todos Santos red beds, a late Jurassic transgressive cycle is represented by 617 ft of dark, open-marine, fossiliferous limestones interbedded with dark, limey shales, equivalent to the San Ricardo formation of western Guatemala and southern Mexico.
Outcrop samples recently collected by the author from southern Belize near the drill site of Phillips 1 Punta Gorda (Fig. 2) yielded an age ranging from late Jurassic Tithonian to early Cretaceous Valanginian (IES-Marinex, 1989).
This is the first time that Upper Jurassic-Lower Cretaceous rocks have been described in southern Belize outcrops. These rocks are probably equivalent in age to late Jurassic-early Cretaceous limestones that were penetrated at 8,609-9,226 ft in the off shore 1 Seal Caye 25 miles east of the outcrop.
The limestone samples consist of organic rich, dark brown to gray, pelletoidal, fossiliferous mudstones occasionally interbedded with fossil fragments and pelletoidal wackestones deposited in a low energy, open shelf environment.
While these muddy carbonates offer little in the way of potential reservoir, the interbedded, organic-rich, argillaceous limestone and shale units offer substantial source rock potential.
CRETACEOUS
After a short period of subaerial exposure at the end of Neocomian, a major marine transgression during Middle and early Upper Cretaceous initiated establishment of the great Yucatan carbonate bank.
Even the Maya mountains, a topographic high at this time, were progressively onlapped and partially covered by Cretaceous seas.
An evaporate lagoon 150-200 miles wide formed the interior of the Yucatan bank. The southern half of the lagoon, a gentle basement depression known as the Peten basin, received more than 15,000 ft of evaporates, limestones and dolomites of the Coban formation (Fig. 2).
These rocks have been subdivided into a series labeled from A through D. It is the C member of this series that has provided oil production in the Rubelsanto area of Guatemala.
The Coban formation and its equivalent in Belize thin considerably to the east and southeast. Evaporites are gradually replaced by dolomites and limestones, indicating more normal marine conditions. On the northern side of the Maya mountains, Coban equivalents are known as the Hillbank and Yalbac formations.
An incomplete section of more than 5,500 ft of Coban was penetrated in Esso 1 Temash. Based on foraminiferal age dating and lithology, the formation can be divided into upper and lower members, Esso's well completion report shows.
The upper member, some 5,420 ft thick, contains light brown, skeletal, micritic limestones and dolomites with chalky, sucrosic textures, white to light gray, massive to well bedded anhydrides, and light gray to dark brown dolomites.
Alternations of these lithologies suggest that deposition occurred in a relatively shallow, low energy restricted marine environment. Porous intervals are related mostly to fractures caused by complex faulting, and traces to good impregnations of oil and asphalt are very common.
In Esso 1 Temash, more than 60 ft of live oil, good fluorescence, and C1-C5 were reported. The lower Coban member in the Temash well consists of more than 95 ft of dark brown, highly fractured carbonate. No oil shows and no favorable porosities were reported.
In general, intercrystalline and fracture porosities are better developed in the Upper Coban, providing the upper unit with consequently greater reservoir potential than the lower unit.
Well data from the onshore 1 Temash and the offshore 1 Snake Caye and 1 Seal Caye indicate that the Coban formation equivalent was deposited in a restricted, peritidal, platform lagoon at those sites. The shelf edge, reef facies found in 1 Coco Plum (Fig. 2), with its Reforma type exploration potential, most likely occurs south of the Temash area and east of the 1 Seal Caye.
Three formational concepts were employed to subdivide the post-Coban Cretaceous section in southern Belize:
- Campur formation-tectonically, relatively stable, platform carbonates ranging in age from Turonian to Campanian;
- La Cumbre formation-a carbonate lithoclast, talus apron formed from collapse of the carbonate platform margin from middle Campanian to early Paleocene; and 3. Toledo formations foredeep facies beginning deposition from Campanian throughout Paleocene and possibly into the Eocene (IES, 1989).
Regionally, the evaporates, limestones and dolomites of the Coban formation and its equivalents appear to grade upward into late Cretaceous, shallow platform limestones of the Campur formation. But local unconformities exist, such as reported dips in the 1 Seal Caye of 60-75 for the Lower Cretaceous immediately beneath Upper Cretaceous rocks with dips of 30 or less.
The transition from evaporitic to open shelf environment seems to coincide with a regional, onlap pattern related to Middle Cretaceous eustatic sea-level rise.
The Campur formation is typically composed of shallow, subtidal, muddy carbonates, rich in benthic foraminifera and mollusks.
Tracing the Campur formation from its type locality in Guatemala eastward into southern Belize, an increase in rudist pelecypod density occurs and actual rudist bioherms are interpreted as present. Bioherms suggest the proximity of a carbonate platform margin to the east.
Potential reservoir rocks in the Campur formation would include mainly the bioherms, skeletal buildup deposits, and a forereef, skeletal, talus apron containing primary porosity and fracture porosity and permeability as well as secondary leached porosity in all carbonate facies exposed or subjected to prolonged meteoric water contact.
A core taken in this formation from the onshore 1 Punta Gorda was reported by Phillips to have bled oil.
During the middle to late Cretaceous, an initial pulse of crustal deformation occurred when the northeastbound proto-Caribbean plate collided with the Yucatan block. In central Guatemala, folding of the Coban B and older units occurred and locally, up to 5,000 ft of pre-Coban A section were eroded off the open fold structures.
As a result, the Coban A lies unconformably over subunits of the Coban B and C (Bishop, 1980). In southern Belize and around the Maya uplift, the former carbonate platform was uplifted and subaerially exposed.
Continuous movement of the Antilles volcanic chain initiated onset of a major Laramide thrusting event at the end of the Cretaceous. Increasingly intensive, compressive stresses developed a foreland basin between the advancing thrust sheets and crustal block.
Substantial depositional relief characterized the region. Shallow water carbonates developed on the upthrown side of the imbricate thrust blocks. Accumulations of carbonate turbidites of the La Cumbre formation and open-marine, hemipelagic shales of the Toledo formation were also deposited between the structural lows and along the hinge area of the basin.
As the foredeep basin developed to the north, carbonate talus conglomerates and turbidites of the La Cumbre formation were deposited along the basin axis. La Cumbre formation deposits are widely distributed throughout Belize and Guatemala forming a lithologically mappable unit.
This unit can be traced along sporadic outcrops from the San Antonio anticline in Belize as far west as the vicinity of the Chinaja anticline in Guatemala. In the subsurface, distal portions of La Cumbre were reported as far north as the Pecten 1 Dangriga.
Most of the La Cumbre formation near the shelf edge consists of a limestone megabreccia (clasts up to 1 km long) and conglomerates of skeletal and micritic limestone blocks in a calcareous to dolomitic matrix. In the upper part of the formation, the breccia and conglomerates interfinger with and grade into clastic turbidite sequences.
This talus wedge developed from collapse of a Campur carbonate platform margin as the margin oversteepened during Laramide compression. Relative age of the talus emplacements has been determined from occurrence of foraminiferal assemblages (IES, 1989).
The first emplacement occurred during the middle to late Campanian, a second event during the Maastrictian, and a third in the early Paleocene. Structural lows between fault blocks were occupied by deep marine, open basinal conditions where thick, hemipelagic facies of the Toledo formation were deposited.
Major differences in depositional environments, existing from late Cretaceous to early Eocene, are reflected by rocks of equivalent age penetrated in the 1 Monkey River and 1 Palmetto Caye.
The sequence in the 1 Monkey River consists of hemipelagic shales, claystones and marls interbedded with turbidites of carbonate clasts and quartzitic sandstones. Both lithofacies and associated pelagic fossils indicate an open basin, bathyal, depositional environment perhaps 1,000-2,000 ft deep.
On the other hand, equivalent age rocks penetrated by the 1 Palmetto Caye were deposited on a reef-shoal or evaporitic carbonate platform essentially at sea level. Subsequent tectonic movements and block subsidence affected the offshore considerably. Top of the Toledo is 14,500 ft deeper in the 1 Palmetto Caye than in the 1 Monkey River (IES, 1989)
Further south in 1 Punta Gorda, more than 350 ft of salt were penetrated at a depth of 1,200 ft. Five miles to the west in 1 Machaca, the same evaporitic interval was penetrated but contained only 100 ft of interbedded anhydrides and dark shales at a depth of 500 ft.
In Guatemala east of the Santa Cruz mountains, a sequence of red mudstones, shales, light colored limestones and some gypsum occurs that is reported from microfossils to be Eocene.
The Eocene section drilled in the 1 Livingston contained considerable anhydrite. The Toledo formation evaporitic intervals in the Punta Gorda-Machaca area and in eastern Guatemala appear to represent development of small, localized, evaporitic basins and to be equivalent to Vinson's (1962) Buena Vista formation of northern Guatemala.
Hydrocarbon source rock potential is present in the Toledo basinal facies. In 1 Palmetto Caye, 10,195 ft of Toledo was penetrated. In this interval, thin, organic-rich laminae, each only a few millimeters thick, constitute great thicknesses of this hemipelagic, lime mudstone and shale sequence.
A potential reservoir for the hydrocarbon source is found in La Cumbre talus deposits in a stratigraphic position similar to the collapsed, carbonate bank, margin apron on the western slope of the giant Cantarell complex in the Bay of Campeche where Paleocene dolomitic breccia is the main reservoir. For instance, the 2 Akal produces more than 5,000 b/d without stimulation from this breccia (Santiago, 1980).
By the end of the early Paleocene, compressional stresses of the Laramide had diminished, and the folded and thrusted foreland terrain was subjected to differential subsidence through block faulting.
This faulting created a complex mosaic of highs and deep, interlock-basin lows. The deeper lows were slowly covered with Toledo open basin sediments, while shallower lows developed restricted depositional conditions.
TERTIARY
Regional uplift of the Yucatan block and its margins resulted from interaction between Caribbean and North American plates.
This prolonged period of uplift and subaerial exposure lasted well into the Miocene and led to development of a mid-Tertiary unconformity. Subsequent marine transgression over the unconformity surface occurred during the latter part of the early Miocene.
Mid to late Miocene reef carbonates, equivalent to Guatemala's Rio Dulce formation, onlapped the high-relief surface of the mid-Tertiary unconformity. Fringing reef and lagoonal complexes formed on the flanks of structural highs, while hemipelagic shales accumulated in the lows.
Continued sea level rise drowned many of these reef complexes and effected their burial by basinal shales. During this period, continual activity of the Cayman spreading center placed the southern Belize margin under shearing stress leading to development of roughly north-south, left-lateral, strike-slip faults superimposed on the older Laramide structural grain.
An abrupt shallowing over the southern Belize margin led to deposition of a heavily dolomitized, porous, shallow marine limestone, which is equivalent stratigraphically to the Barrios formation of southeastern Guatemala.
This medium to coarse-grained, crystalline dolomite (more than 1,400 ft thick in the 1 Palmetto Caye) is responsible for the distinct acoustic velocity contrast between the underlying shales and marls and the competent unit.
This prominent seismic event and mid-Tertiary unconformity have been used to map the Neogene section over a large area of the present day Belize shelf and coastal area. Several wells drilled in east-central and southern Belize have recorded strong hydrocarbon shows from this dolomitic unit.
PLIOCENE-RECENT
The Neogene stratigraphic interval overlying the dolomitic seismic marker consists of cyclic, reefal carbonates interbedded with open-shelf maris and marly limestones. Pleistocene rocks contain interbedded limestones, shaley limestones, and siliciclastic horizons.
These complex horizontal and vertical facies changes reflect the interplay between sea level fluctuations and recent regional structural deformation. The present day barrier reef is estimated to be 200-2,500 ft thick and may have occupied the fault-line, shelf margin since sometime in Pliocene.
CHEMICAL EXPLORATION
Belize has many reported oil and gas "shows" in exploratory wells and a number of surface "seeps."
Therefore, in addition to the surface and subsurface geological exploration, the hydrocarbon potential of southern Belize has also been investigated through surface geochemical techniques. These techniques have in their initial phase indicated promising hydrocarbon potential for several locations in southern Belize.
Surface geochemical exploration relies on detection in near surface sediments of upward migrated hydrocarbons such as methane through pentane from deep gas or crude accumulations, These compounds are useful since they are petroleum's most mobile phases and are easily detected by an extremely sensitive, fluorescence spectrophotometer.
Sensitivity for the fluorescence spectrophotometer ranges in the parts per trillion, which enables detection of hydrocarbons and their possible linkage to oil reservoirs.
Results from the total scanning fluorescence procedure are plotted on three perpendicular axes: intensity (1) of the emitted light is plotted on one axis, and excitation (Ex) and emission (Em) wave-lengths are plotted on the other two axes, respectively.
This 3D fluorescence analysis is helpful in determining content of the reservoir by providing semiquantitative estimates of total high molecular weight aromatic compounds and ring number distribution of fluorescent aromatic compounds (Horvitz, 1989).
It has been observed that samples with an emission wavelength (Em) of 320 nm are commonly related to gas and-or condensate prone deposits, while samples with emission wavelengths (Em) of 365 nm indicate the presence of heavier hydrocarbons (oil). in addition, if the ratio (R) of intensities of emissions 320-360 is greater than 1.0, there is an increasing presence of oil. R values below 1.0 indicate oils in the condensate range (Miller, 1988; 1989).
Results from 3D fluorescence analysis for two samples collected along the Temash river in southern Belize indicate the presence of condensate and oil-condensate reservoirs (Miller, 1988).
In Fig. 4, at the 270 nm excitation wavelength value, a high intensity 320 nm emission wavelength is produced in contrast to the considerably lower intensity 365 nm emission. In this sample, an R value of .6249 suggests an area with gas-condensate affinities. The sample shown in Fig. 5, collected about one half mile west of the previous sample, possesses an R value of 2.796, suggesting the presence of heavier hydrocarbons in the oil range.
SEISMIC
Evaluations by various exploration companies of several vintages of seismic data from onshore and offshore Belize have delineated a number of drillable prospects (Williams, 1982).
However, only a few of these prospects have been drilled. Some of the wells did not reach their objective, and those wells that did reach the anticipated reservoir section were off-structure or were not able to properly test the interval.
Generally, seismic data interpretation below the mid-Cretaceous unconformity is poor and unreliable.
Some factors contributing to the scarcity of seismic reflectors in Lower Cretaceous and older units are steep structural dips, dissipation of energy throughout intensely fractured carbonates, and a lack of strong acoustical impedance contrasts in the fairly homogeneous, dense carbonate section.
The mid-Tertiary unconformity (Fig. 3) has been used for correlating and mapping the base of the Neogene section over a large portion of the Belize shelf and coast. Although this surface formed during a major erosional period, it reflects structural relief and major closures present in the older section.
A structural seismic map of southern Belize (Fig. 6) near the top of the Cretaceous unconformity indicates the presence of more than 15 structural leads (Geology and Petroleum Office of Belize, 1986); however, only three of these structures have been drilled.
Results of two tests near the shelf margin (1 Seal Caye and 1 Snake Caye) indicate a lack of sealing facies in either the Middle Cretaceous or the Toledo. The structural lead drilled by the lagoonal 1 Palmetto Caye encountered more than 10,000 ft of potential Toledo seal facies.
Seismic interpretation and well data indicate that the shelf and lagoonal locations experienced different Tertiary depositional histories since the Seal Caye and Snake Caye areas remained structurally higher than the Palmetto Caye area.
Southwest of 1 Palmetto Caye, four major untested structures are situated in a structural and depositional trend similar to that of the Palmetto Caye well. Onshore, Tertiary sediment is restricted to structural lows and to anticlines with moderate relief.
Where Cretaceous rocks are exposed on the larger surface anticlines, Lower Cretaceous anhydrite beds similar to those anhydrides encountered by the 1 Temash could provide efficient intraformational seals.
More than a dozen offshore and onshore structures in the Sarstun embayment of southern Belize have the potential for containing large quantities of hydrocarbons.
Source rock exists in Upper Jurassic-Lower Cretaceous limestones and shales equivalent to the San Ricardo formation, in interbedded limestones and shale of the Coban formation, and in basinal shales of the Toledo formation.
Good reservoir characteristics exist in fluvial facies of the Todos Santos formation, the fractured limestones of the Coban formation, and forereef facies of the La Cumbre formation. Seals can be effectively provided onshore by Coban anhydrides and offshore by basinal Toledo shales.
Future success of Belize as an oil province will depend upon the use of innovative technologies and advanced interpretative techniques. Similarities in stratigraphy and structural development between Mexico and southern Belize have been established.
Correct assumptions and applied experiences from Mexican analog petroleum plays could also prove propitious for future oil discoveries in Belize's Sarstun embayment.
BIBLIOGRAPHY
Blair. T.C., 1988. Mixed siliciclastic-carbonate marine and continental syn-rift sedimentation, Upper Jurassic-lowermost Cretaceous Todos Santos and San Ricardo formations, Western Chiapas, Mexico. Jour. of Sedimentary Petrology, Vol. 58, No. 4, pp. 623-636.
Bishop, W.F., 1980. Petroleum geology of northern Central America. Journal of Petroleum Geology, 3, 1, pp. 3-59.
Dixon, C.G., 1987. Geology of southern British Honduras, with notes on adjacent areas: Gov't. printer, Belize, British Honduras, 85 p.
Geology and Petroleum Office. 1986. Petroleum prospect and potential of Belize Basin, Belize. Ministry of Natural Resources, Belmopan, Belize, 66 p.
Horvitz, E.P., 1989. Geochemical soil sampling: advanced surface exploration. A Short Course. Society of Independent Professional Earth Scientists, Houston, Tex.
IES, 1989. Hydrocarbon exploration potential of Caribe Natural Gas, Ltd., license, southern Belize. Internal report prepared by Integrated Exploration Services, 23 p.
IES-Marinex, 1989. Petrographic analysis of outcrop samples from southern Belize by Integrated Exploration Services, Inc. Marinex Petroleum Iberia, internal report, 4 p.
Miller, N. Lee, 1988. Geochemical exploration in Belize. Internal report for exploration contractors, 18 P.
Miller. N. Lee, 1989. Exploration with fluorescence, 1 p. Internal report for exploration contractors, 1 p.
Rosencrantz, E. and Sclater J.G., 1986. Depth and age in the Cayman trough. Earth and Planetary Science Letters, Vol. 79. pp. 133-144.
Santiago, J., 1980. Giant fields of the southern zone-Mexico, in: M.T. Halbouty, editor. Giant Oil and Gas Fields of the Decade 1968-1978. AAPG Memoir 30, pp. 339-385.
Vinson, G.L., 1962. Upper Cretaceous and Tertiary stratigraphy of Guatemala. AAPG Bull. Vol. 46, No. 4, pp. 425-456.
Vinson, G.L. and Brineman J.H., 1963. Nuclear Central America, hub of Antillean Transverse Belt, in: Backbone of the Americas, a symposium. Childs, O.E. and Warren Beebe, B., editors. AAPG Memoir 2, pp. 101-112.
Williams, D.W., 1982. Belize, Central America, petroleum prospects. Internal report for Marinex Petroleum, 6 p.
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