|
Introduction
Figure Captions (1-9)
Return to top.
Location
Saba
Bank is a shallow-water submerged carbonate bank in the northeast
Caribbean Sea five kilometers southwest of the northern Lesser Antilles
island of Saba (Figures 1 and
2). It is approximately 140 kilometers
east-southeast of St. Croix, U.S. Virgin Islands. As defined on
published bathymetric charts, Saba Bank is a submerged elliptical
platform, 10 to 100 meters below sea level, that covers approximately
2200 square kilometers (Figure 3). It is about 1000 meters above the sea
floor in the vicinity of Saba Island, the only landmass in the immediate
area, and is separated from the island by a 700-meter deep trough.
The
Saba Bank area is part of the Netherlands Antilles, an autonomous part
of the Kingdom of the Netherlands consisting of the Caribbean islands of
Bonaire, Curacao, Saba, Sint Maarten and Sint Eustatius. Petroleum
activities are administered by Saba Bank Resources N.V., a company
jointly owned by the central government of the Netherlands Antilles
located on Curacao and the island governments of Saba, Sint Maarten, and
Sint Eustatius. For petroleum exploration licensing purposes the Saba
Bank Area is divided into forty-three 7’30” x 3’45” blocks.
Exploration History
The
presence of a relatively large shallow-water area in a geologically
interesting and unexplored region led to at least eleven seismic surveys
being conducted in or near the Saba Bank area by various oil companies,
government agencies, and academic institutions between 1970 and 1999.
Approximately 4300 kilometers of seismic data have been acquired over
the Saba Bank area. They include six seismic surveys conducted on or
near the Saba Bank area between 1970 and 1974 by United Geophysical
(1970 and1971), the USGS (1972 Sparker survey), Weeks Natural Resources
(GSI 1973 and CGG 1974) and Shell (1974 reconnaissance north and east of
Saba), and four subsequent surveys acquired over Saba Bank by Weeks
(1975), Fina Petroleum Sint Maarten N.V. (1980), Aladdin Petroleum
Corporation (1988), and Saba Bank Resources (1999).
In
December, 1974, Weeks signed an agreement with the Netherlands Antilles
Government, which granted Weeks an exclusive seismic option and the
right to select seven contiguous blocks of 3' 45" longitude by 7' 30"
latitude. GSI subsequently shot a 500-kilometer seismic survey for Weeks
in 1975. Weeks then formed an exploration group, which eventually
included Amerada Hess, Anadarko, Hamilton Brothers Petroleum, Marathon,
and Santa Fe Minerals, with Marathon as the operator.
In
December, 1976, the Netherlands Antilles Government enacted a new
petroleum law, which created Saba Bank Resources N.V., with the rights
to explore and produce petroleum on the Saba Bank. A production sharing
agreement between Saba Bank Resources and the Marathon group was signed
on December 15, 1976.
The
Marathon group spudded Saba Bank No. 1 (SB-1) (Figures 4,
5, and
6), the first exploratory  well in the Saba Bank area, on April 6, 1977.
The well was abandoned as a dry hole with minor gas shows on June 21,
1977, after reaching a total depth of 2974.7 meters. No further
exploration was done, and the production sharing contract was terminated
at the end of April, 1978.
On July
1, 1979, Saba Bank Resources N.V. granted Weeks Natural Resources an
exclusive option to acquire nine contiguous blocks with an obligation to
conduct a seismic survey and drill an exploratory well not later than
June, 1982. Weeks formed a group with Fina Petroleum and Cities Service,
and in January, 1980, the group signed a production sharing agreement
with Saba Bank Resources N.V. The contract area was subsequently
increased by an additional five blocks. The group, with Fina Petroleum
Sint Maarten as operator, conducted a detailed 1708-kilometer, 48 fold
seismic survey over the eastern part of Saba Bank (Figure 7), in
September, 1980. Arkla Exploration Company acquired a portion of Cities
Service’s interest in February, 1982. The Fina group spudded the
exploratory well SB-2 (SB-2) (Figure 7), located 15 kilometers
east-northeast of SB-1, on February 22, 1982. It was abandoned as a dry
hole with minor gas shows on May 25, 1982, at a total depth of 4231
meters. The group subsequently dropped the block and withdrew from the
area.
In
January, 1988, Saba Bank Resources N.V. granted Aladdin Petroleum
Corporation an option to acquire 14 contiguous blocks with an obligation
to conduct a detailed seismic survey over the blocks. During February,
1988, Western Geophysical acquired 343 kilometers of 60 fold seismic
data over the western Saba Bank (Figure 8) for Aladdin in fulfillment of
the seismic obligation. On October 22, 1988, Aladdin signed a production
sharing agreement with Saba Resources N.V. covering 14 contiguous blocks
with an obligation to drill one exploration well or re-enter and deepen
the Saba Bank No.1 prior to April 28, 1990. Aladdin withdrew from the
area at the end of 1990 without completing the drilling obligation.
During
December, 1999, Western Geophysical acquired 205 kilometers of 120-fold
infill seismic over the southwestern part of the bank on a large
previously identified prospect for Saba Bank Resources N.V. (Figures 8
and 9).
Database
The
presently available seismic database within the Saba Bank area consists
of field tapes of a1708-kilometer 1980 Fina survey, a 343-kilometer 1988
Aladdin survey, and 205 kilometers acquired for Saba Bank Resource in
late 1999. Tapes and prints of 60 kilometers of Fina data reprocessed
during 1998 and of the entire Aladdin survey reprocessed in 1999 are
also available. This new and reprocessed data is also available as a
project in GeoQuest and Landmark formats. Paper prints of most of the
older vintage seismic lines are also accessible, along with some gravity
and magnetic data acquired by Fina during 1980.
Well data
for SB-1 SB-2 include wireline log suites, mud logs, and operational
reports, as well as various in-house and consulting reports analyzing
and interpreting the biostratigraphy and geochemistry of the sediments
encountered. Several consultants' reports and accompanying maps
describing the prospectivity of the block are also available.
Figure Captions (10-17)
 |
Figure 10. Caribbean Plate in Late Cretaceous, when Saba Bank
lay in a backarc position, east of known Cretaceous basins and
north of the Aves Ridge (after Montgomery and Pessagno, 1999).
|
 |
Figure 11. Caribbean Plate at
present, with the backarc Saba Bank behind a slowly-moving
active-margin-island arc on the eastern edge of the Caribbean
Plate, under which Atlantic oceanic crust is being subducted
(after Babb and Mann, 1999). |
 |
Figure 12. Stratigraphic section, as
shown on dip-oriented seismic line W50 and in well SB-1, with an
Upper Carbonate Unit overlying a Fluvio-delta Sequence that
onlaps, abuts, and overlies a Lower Carbonate Unit, which in
turn overlies andesite. |
 |
|
 |
Figure 14. Well SB-1 on seismic line W-50, with positions of
source-rock samples. The organic matter, considered reworked
Cretaceous material, is oil-mature (Ro=0.8-1.0).
|
 |
Figure 15. Seismic line W-28 and well SB-2, showing four major
units above the andesite—Upper Carbonate Unit, Fluvio-delta
Sequence, Turbidite Sequence, and Lower Carbonate Unit.
|
 |
Figure 16. Seismic line W-28 and well SB-2, showing Fina-designated
ages and positions in the well of reworked Late Cretaceous
marine fauna (calcareous nannofossils).
|
 |
Figure 17. Segments of two seismic
lines and wells SB-1 and SB-2, with correlation of the
stratigraphic sections between the wells and age dates of
andesite encountered at TD in both wells. Above the andesite
there was reefal development on the paleohigh and deposition of
turbidites in the paleolow. |
Regional Setting
Saba
Bank is a backarc basin on the west side of the northern Lesser
Antilles, a slowly moving, active margin island arc on the eastern edge
of the Caribbean plate under which Atlantic oceanic crust is being
subducted at a rate of about 2.2 centimeters per year.
The
present northern Lesser Antilles are formed by a double volcanic arc
that coalesces to the south near Martinique (Figures 1,
10, and 11) to
form a single row of islands in the southern Lesser Antilles. The
islands and islets of the outer arc, often referred to as the "Limestone Caribbees", are composed of middle Eocene to Oligocene volcanics and
questionable Miocene intrusives capped with middle Eocene to Pleistocene
carbonates (Maury et al, 1990). There are no Neogene volcanic centers in
the outer arc. The northern inner arc, often referred to as the
"Volcanic Caribbees", is made up of young volcanic islands, including
Saba Island, in which volcanism was initiated during latest Miocene or
Pliocene and continues today (Figure 11), and by an extinct volcanic
ridge extending 120 kilometers northward from Saba Island to the Anegada
passage (Figure 1). The two arcs are separated by an intra-arc trough,
the Kallinago Depression, which extends from north of Guadeloupe to the
Anegada Passage. It varies in depth from 600 meters to about 2000 meters
at its north end. The forearc complex of the northern Lesser Antilles
near Saba Bank is much narrower than farther south.
Fina's
SB-2 encountered nearly 4000 meters of middle Eocene to Recent sediments
overlying Eocene andesite. The andesite is approximately the same age as
the earliest volcanics identified in the Lesser Antilles outer arc to
the northeast. The Tertiary sediments were deposited in a highly
asymmetric backarc basin resembling a half graben with the eastern steep
basin flank controlled by a large down-to-the-west fault system just
west of St. Eustatius. Seismic data indicate the Tertiary section
thickens to the southeast into the Grenada Trough, the basin that
separates the Antilles Island arc system on the east from the Cretaceous
Aves ridge on the west (Figure 11).
Seismic
and airborne gravity data indicate the Eocene andesites encountered in
both of the Saba Bank wells are underlain by a thick sedimentary section
which appears to thicken to the west. Reworked Paleocene spores and
Cretaceous coaly material identified in SB-1 indicate that the
pre-volcanic section may consist of Paleocene to middle-Eocene-age
sediments overlying an Upper Cretaceous and older sedimentary sequence.
The presence of sediments that predate the middle Eocene outer Lesser
Antilles volcanic arc suggests the Saba Bank area occupied a backarc or
interarc position in an older island arc system which may have included
Avis Ridge, St Croix, Puerto Rico and Hispanola during Cretaceous and
earliest Tertiary time.
Plate Tectonic History
In
order to develop a coherent geologic model for Saba Bank it is necessary
to examine the geologic history of the northern Lesser Antilles within
the framework of the tectonic development of the Caribbean Plate. Within
the last decade a number of syntheses for the plate tectonic history of
the Caribbean have been published. While there remain numerous
unresolved details, there appears to be general agreement among the
leading researchers for a plate history involving a single Great
Caribbean island arc system (Burke, 1988), also referred to as a
continuous Mesozoic Arc (Bouysse, 1988), which was initiated in the
Pacific during Cretaceous time and migrated into the Atlantic.
The
Caribbean did not exist prior to the Late Triassic-Jurassic breakup of
the Pangean supercontinent. By Early Cretaceous time a Proto-Caribbean
Ocean had developed with oceanic crust being created along
northeast-trending spreading axes as North America, South America and
Africa drifted apart. A Proto-Greater Antilles island arc formed in the
Pacific Ocean at the eastern edge of the Farallon plate subduction zone
in the widening gap between North and South America. The polarity of the
subduction zone beneath the Proto-Greater Antilles island arc changed
from east-dipping to west-dipping as the Farallon Plate began to intrude
between North and South America. The Proto-Caribbean oceanic crust was
subducted beneath the Greater Antilles island arc as the plate moved
eastward. By Late Cretaceous (Campanian) time Cuba, Puerto Rico, and
Aves Ridge (including the Saba Bank area) formed the eastward advancing
active island arc (Figure10). The Caribbean Plate continued to advance
to the northeast during the Paleocene. The Grenada Basin began to form
at this time, probably by backarc spreading. By middle Eocene time it
was probably fully opened, and the Aves Ridge was no longer part of the
active island arc. During the remainder of the Cenozoic, the Lesser
Antilles formed the eastward-migrating volcanic island arc along which
the Atlantic oceanic crust was being subducted.
Today
the Lesser Antilles remains a slowly moving active margin island arc on
the eastern edge of the Caribbean plate (Figure
11). Because of the low
rate of convergence, volcanism and seismic activity are presently
relatively subdued (Bouysse, 1984).
Within
the framework of the overall plate tectonic history, the Lesser Antilles
have experienced a complex history which is not well understood, but
they have probably been part of an active volcanic arc since Early
Cretaceous time (Bouysse, 1988). Their pre-middle Eocene history is not
well known because of lack of outcrops. The oldest known rocks are
uppermost Jurassic to Lower Cretaceous volcanics reported from La
Desirade Island; they may represent early stages in the development of
the Great Arc. Upper Cretaceous volcanics have been dredged from the
midslope of the Anguilla and Antigua platforms and Cretaceous
granodiorite and volcanic fragments have been dredged from the Aves
Swell. Other pre-middle Eocene data are limited, but the Lesser Antilles
were probably part of an arc system that included what is now the Aves
Swell as well as the Greater Antilles until mid-Eocene time when the
Grenada basin formed and left the Aves Swell as an inactive remnant arc
west of the Cenozoic Lesser Antilles volcanic island arc. At about the
same time the Lesser Antilles volcanic arc was separated from the
Greater Antilles arc.
As
noted earlier, the present northern Lesser Antilles are a double
volcanic arc composed of an inactive Eocene-Oligocene outer arc formed
by the islands and islets of Marie-Galante, Grande-Terre of Guadeloupe,
Antigua, St. Barthelemy, St. Maarten, Tintamarre, Anguilla, Dog and
Sombrero, and an active Neogene inner arc consisting of the islands of
Dominica, les Saintes, Basse-Terre of Guadeloupe, Montserrat, Redonda,
Nevis, St. Kitts, St. Eustatius, and Saba. It has been suggested that
this westward shift of magmatism to the northern Volcanic Caribbees
during the latest Miocene or Pliocene was induced by the subduction of
ridges that flank old transform faults in the Atlantic oceanic crust (Bouysse,
1984; Westbrook and McCann, 1986). This may have produced a flattening
of the angle of subduction of the lithosphere because of the buoyant
effect of the ridges, or a narrowing of the forearc by
displacement/erosion of part of the forearc by the ridges.
Paleogeographic Evolution
Saba
Bank presently is a backarc basin on the west side of the active
northern Volcanic Caribbes island arc platform. Data from SB-1 and SB-2
along with records from several seismic acquisition programs give the
most complete record of the post-Late Eocene geology in the northern
Lesser Antilles from which to interpret the local paleogeography.
Seismic records over the Bank show that there is a significant pre-late
Eocene stratigraphic sequence present, which, on regional
considerations, may include Upper Cretaceous to middle Eocene sediments,
but there is little direct evidence to describe the pre-late Eocene
paleogeography of Saba Bank.
Late Cretaceous
As
noted in the section of plate tectonic history, Jurassic to Lower
Cretaceous volcanic units have been identified on La Deseride Island,
and Upper Cretaceous volcanic rocks have been dredged from steep
escarpments located east of Antigua, Barbuda and Anguilla, and from the
Aves Swell. They strongly suggest that both the northern Lesser Antilles
and the Aves Swell were part of a Mesozoic volcanic island arc that was
initiated in the Pacific and was intruding into the Caribbean by Late
Cretaceous time (Figure 10). The southern Lesser Antilles volcanic arc
may not have existed prior to the Eocene so that by Late Cretaceous time
the northern Lesser Antilles-Aves Ridge volcanic arc was impinging on
the northwest margin of South America (Figure 10).
While
the stratigraphic evidence necessary to define the paleogeography of
Saba Bank during Late Cretaceous time is sparse, scattered dredge hauls
suggest extensive shallow-water platform areas were present within the
volcanic island arc. Dredging along the northern slope of the Anguilla
platform during the French Arcante 3 cruise recovered volcanic tuffs and
marls from depths between 4100 and 2500 meters containing radiolarians
and also planktonic foraminifera and nannofossils with a Late Cretaceous
age range of 86 to 65 Ma. Some reworking of neritic biogenic components
appears to have occurred, indicating the existence of a shallow platform
at that time. An Arcante 3 dredge haul from the northern part of the
Aves Swell (Loro Seamount) recovered Upper Cretaceous shallow-water
tuffaceous limestones. Bouysse et al (1985) conclude from dredging
results, bathymetric mapping, and seismic surveys that the numerous
seamounts and ridges present on the Aves Swell are the remnants of
volcanic islands in the Cretaceous volcanic island arc. Pindell's (1991)
model for the formation of the Grenada Basin (Figure 11) places Saba
Bank in a backarc position.
St.
Croix Island, 150 kilometers to the west-northwest of Saba Bank, has
over 10,000 meters of strongly deformed Upper Cretaceous deepwater
calcareous turbidites and volcaniclastics. They were deposited in a
deep-water basin from a northerly volcanic arc source and appear to be
unrelated to Upper Cretaceous sediments of the Aves Swell/Lesser
Antilles island arc.
Analyses of kerogens in SB-1 by Marathon revealed considerable reworked
Cretaceous coaly material in the upper Eocene-middle Miocene
volcaniclastic sequence. The character of the material indicates it was
sourced from an exposed Cretaceous deltaic source that had undergone
considerably less deformation than the St. Croix section. Robertson
Research reported reworked Cretaceous calcareous nannofossils from the
equivalent, but deeper water section in SB-2. The relationship of Saba
Bank -1 and SB-2 suggests the Late Cretaceous sediment source was to the
west or northwest of the wells.
Paleocene
The
only known outcrop of Paleocene rocks in the Lesser Antilles is on
Anguilla island where uppermost Danian to Thanetian pelagic marly
limestones and black shales completely devoid of volcanic elements crop
out at Crocus Bay. They indicate that a pause in volcanic activity
occurred approximately between 65 and 58 Ma; i.e., during most of
Paleocene time. The lack of volcanism is probably related to the opening
of the Grenada Basin during the Paleocene by backarc spreading. Some
authors, in studies of backarc spreading in the western Pacific arc-backarc
complex, have suggested that periods of backarc spreading are
accompanied by a marked weakening or by quiescence of arc volcanism.
Dredge
hauls east of Grande-Terre de Guadeloupe and west of Sombrero Island
recovered Paleocene to Eocene platform limestones and shallow-marine
limestone and greywacke, respectively. DSDP holes 30 and 148 drilled on
the Aves Swell recovered reworked Paleocene microfauna. Reworked
Paleocene spores were also found in a sidewall sample from 2795 meters
in SB-1.
With no
apparent volcanic activity during the Paleocene and only the very
limited geologic data described above we can only speculate that the
Aves Swell/Lesser Antilles area was a dormant island arc magmatic
platform with eroding island landmasses surrounded by inter-island
carbonate platforms and deeper basins. Plate II is a representation of
what the paleogeography of Saba Bank and the northern Lesser Antilles
may have been like during the late Paleocene
.
Middle-Late Eocene
Outcrops on the islands of the Limestone Caribbees, extensive dredge
hauls, and the results of SB-1 and SB-2 provide considerably more data
from middle Eocene and younger rocks than is available for the older
section. During middle and late Eocene time most of Saba Bank area was
located on a backarc carbonate platform. The southeastern part of the
bank was in deeper water of the northern end of the backarc Grenada
Basin. Dredge hauls from the Aves Swell indicate Saba Bank formed part
of what was a much more extensive shallow-marine backarc platform or
series of inter-island platforms developed on the flanks of and over the
tops of the extinct Cretaceous volcanic islands, perhaps similarly to
those presently surrounding the Limestone Caribbees. By early Eocene
time volcanic activity had been initiated in the Lesser Antilles outer
volcanic island arc well to the east of Saba Bank at St. Maarten Island,
and by the middle Eocene, St. Barthelemy Island was also the site of
shallow submarine volcanism. Volcanic activity appears to have increased
during the late Eocene with Anguilla, Dog, and Sombrero Islands probably
also sites of active volcanism.
SB-1
encountered a thick mid- to late Eocene reefal carbonate unit that grew
on a shallow-marine carbonate shelf. SB-2, drilled to the east-northeast
off the shelf edge, encountered neritic to bathyal slope submarine
sands, pelagic shales, and fine-grained turbidites in the equivalent
section. They were deposited in the northernmost part of the Grenada
Basin. The carbonate and clastic sections can be correlated to the
middle part of the Point-Blanche Formation on St. Maarten.
Oligocene
Volcanic activity continued in the Lesser Antilles outer arc during
early Oligocene time. St. Maarten, St. Barthelemy, and Antigua were all
sites of volcanism in the northern Lesser Antilles, and Martinique and
the Grenadines were active in the southern Lesser Antilles. Volcanism
ceased in the northern Lesser Antilles in mid-Oligocene time (30 Ma) and
did not resume until the late Miocene (10 Ma) when it shifted to the
Inner Arc. A volcaniclastic section was deposited in the eastern Saba
Bank area in an inner shelf to upper slope environment. The sands and
silts encountered in both SB-1 and SB-2 form an eastward prograding
fluvial deltaic sequence containing significant quantities of
volcanoclastic material. At SB-2, turbidites were initially deposited in
a fore-reef trough which the fluvial deltaic system eventually prograded
across. The previously noted reworked Cretaceous coaly material in both
SB-1 and SB-2, and reworked Paleocene spores in SB-1 indicate erosion of
exposed older rocks to the west or northwest of the wells, possibly from
the western part of Saba Bank and adjacent areas.
Other
than Oligocene corals and limestones recovered in a dredge haul
southeast of Aves Island, there are very little Oligocene data available
for Aves Swell. It was the site of extensive late Eocene and early
Miocene shallow-marine carbonate platform deposition, and there is no
reason to believe that conditions were any different during the
intervening Oligocene.
Early Miocene
There
is no evidence of volcanic activity in the northern Lesser Antilles
outer arc during early Miocene time, but volcanism continued in
Martinique and other islands in the southern part of the arc. Dredging
results on the northern outer arc magmatic platform indicate deeper
water conditions, with pelagic marls and tuffs being widely deposited.
Shallow-water carbonates may have been developed on the platforms of the
dormant volcanoes.
Deposition of the fluvial deltaic volcaniclastic sequence continued on
the eastern Saba Bank, while erosion of older sediments probably
continued on the western part of the bank and adjoining areas to the
west or northwest. Dredging results indicate shallow to open marine
carbonate deposition continued on the Aves Swell.
Late Miocene-Pliocene
The
inner volcanic arc of the northern Lesser Antilles developed during late
Miocene-Pliocene, and parts of it have remained active during historic
time. An intra-arc basin, the Kallinago Depression, developed to the
east of the northern volcanic arc, between it and the now inactive outer
arc. Westward tilting of the northern Lesser Antilles magmatic arc
complex occurred during mid-Miocene, resulting in major subsidence on
the Aves Swell.
The
westward tilting was also responsible for subsidence of the Saba Bank
and adjacent areas that had been a source of clastic sediments during
the Oligocene and early Miocene. Saba Bank became the site of carbonate
deposition that kept pace with the rate of subsidence so that it
remained a shallow-water carbonate platform while deeper water pelagic
clays, mudstones and calcareous oozes were deposited on the Aves Swell.
Large
shallow-marine carbonate platforms developed on the northern Lesser
Antilles magmatic arc around the extinct volcanoes, which probably
provided limited sources for volcaniclastic sediments. Deeper water
pelagic marls and tuffaceous marls were deposited in the interplatform
area and between the volcanic islands of the active inner arc.
Structure
Saba
Bank is a highly asymmetric backarc basin on the west side of the slowly
moving Lesser Antilles island arc. It is essentially a half graben with
the eastern steep basin flank controlled by a large down-to-the-west
normal fault system just west of St Eustatius (Figure 1).
A
major northeast-trending, down-to-the-southeast fault divides Saba Bank
into a western platform area characterized by a thin Tertiary section
unconformably overlying a thick pre-Eocene (Cretaceous?) sequence and an
eastern area with a thick Tertiary sedimentary section overlying Eocene
volcanics and an older (Cretaceous?) sequence (see
Figure 24). The
Tertiary section in the eastern area thickens to the southeast into the Genada Trough. Reworked Late Cretaceous kerogen in SB-1 indicates the
down-to-the southeast fault has been active since at least late Eocene
time. Interpretation of the seismic data reprocessed during 1999 clearly
shows a complexly faulted flower structure indicating that at least the
latest movement on the fault has been wrenching and that significant
lateral movement may have occurred.
Angular unconformities seen on the reprocessed seismic data show that
the area west of the flower structure (the “western block”) was uplifted
and eroded at least twice prior to deposition of the middle
Miocene-upper Pliocene Upper Carbonate Unit. The detailed pre-Eocene
structural history is obscure, but it is apparent that a large fault
block developed in the southwestern corner of the Bank. That corner of
the fault block was tilted upward and was eroded to form an almost flat
surface. The western and southwestern edges of the western block are
controlled by a large down-to-the-west fault.
The
structure of the eastern Tertiary basin fill is typical of a subsiding
shelf-shelf edge trough with numerous down-to-the-basin and antithetic
normal faults. The structure of the pre-Eocene is obscured by its
greater depth and the presence of a volcanic section, but the
reprocessed data indicate extensive half grabens and tilted fault blocks
are present in what appears to be a continuation of the thick pre-Eocene
section to the west.
Stratigraphy
SB-1
and SB-2 encountered a thick Tertiary sedimentary section composed of
carbonate and clastic sequences with some pyroclastic intercalations
resting on porphyritic andesite. In each of the wells the section
overlying the andesites has been divided into three major stratigraphic
units (Figures 12, 13,
14, 15,
16, and 17). They are: an Upper Carbonate
Unit, a Fluvio-Deltaic (Fina) or Volcaniclastic Unit (Marathon), and a
Lower Carbonate Unit in SB-1 and its Channel-Turbidite Unit equivalent
in SB-2.
Analyses of seismic data after the drilling of the two wells indicate a
thick sedimentary section is present beneath the andesites. A number of
seismic lines have fair to good quality reflections below the volcanics
with dips that are unconformable with the overlying sequences (see
Figure 26). According to Warner et al. (1989), a depth interpretation of
airborne magnetic data flown by Aladdin Petroleum Corporation over the
SB-2 location during 1982 indicates basement is between 6100 and 6700
meters below sea bottom; correspondingly, there is a 1500- to 2400-meter
sedimentary section below the andesite at that location. Seismic data
indicate the pre-volcanic sediments may thicken to the west.
The
stratigraphy of the post-volcanic units has been summarized by Robertson
Research (1984), a summary of which is presented below.
Upper Carbonate Unit (e.g., Figures 14,
16)
The
uppermost unit encountered in SB-1 is an 1110-meter carbonate sequence
composed of translucent to pale yellow, crystalline to micro-
crystalline limestones with sugary texture, and white bioclatic
limestone with micritic cement. The lower portion of the unit is more
argillaceous and contains cryptocrystalline light green limestones and
light brown, hard, brittle microcrystalline sucrosic dolomites. Fossils
are abundant throughout the unit with numerous shell and coral
fragments, algae, and foraminifera. Porosity generally varies from 10 -
25 percent.
SB-2
well encountered a thicker Upper Carbonate Unit (1429 meters) with
similar lithology. Lost circulation was common while drilling the Upper
Carbonate Unit. As a consequence, no samples were recovered from the
lowermost part of the unit in either well, and its lower boundary is
placed from wireline log and seismic data.
Planktonic foraminifera give a middle Miocene to early Pliocene age for
the Upper Carbonate Unit. The fossil data indicate deposition at shallow
depths within a reef complex that was dominated by lithothaminoid algae
throughout most of its development.
The
Upper Carbonate Unit is at least in part equivalent to the Kingshill
Limestone that crops out on St. Croix Island and is similar to
limestones of the same age exposed on St. Maarten, St. Barthelemy, and
Anguilla Islands.
Fluvial-Deltaic Unit (Volcaniclastic Middle Series) (e.g.,
Figures
14, 16)
SB-1
encountered a 755-meter clastic sequence immediately beneath the Upper
Carbonate Unit. It consists primarily of interbedded siltstones,
claystones, and tuffaceous, very fine grained to silty sandstones with
conglomerates and rare thin marine limestones. Marathon referred to this
sequence as the Volcaniclastic Series. The sandstones and some
conglomerates have fair to excellent porosity. Foraminiferal assemblages
indicate an inner shelf environment down to a depth of 1554 meters.
The
interval between 1554 meters and 1920 meters is mostly mudstone with
interbedded siltstone, some fine-grained sandstones, and rare thin
limestones. The mudstones contain foraminiferal assemblages indicating
initial deposition in an upper slope environment that shallowed with
time to outer, and then inner shelf environments. The volcaniclastic
series has been age-dated as late Eocene to middle Miocene.
SB-2
encountered a 1486-meter sequence of fluvial-deltaic sediments beneath
the Upper Carbonate Unit, which Fina named the Fluvial-Delta Sequence.
Robertson Research (1984) has divided the unit into two sections as
follows:
The
Upper Section (1480-2256 meters) is mainly composed of dark green, firm
claystones grading to pale green, slightly calcareous siltstones, with
some beds of white silty limestones and red to brown claystones, in the
upper part. The unit becomes increasingly sandy with depth.
Microfossils are rare at the top of the interval where very poor
assemblages of benthonic rotalid foraminifera occur. Below 1770 meters
Miogypsina, Elphidium,and a few ostracods are recognized.
The unit ranges in age from late Oligocene to early Miocene. The
sediments were deposited in an inner neritic environment.
On the
basis of log correlation, seismic reflections,and age control, this
upper section in SB-2 has been correlated with a series of tuffaceous
claystones containing thin calcareous intercalations, sandstones, and
sandy conglomerates encountered from 1167 to 1562 meters in SB-1; it was
also deposited in an inner neritic environment.
In the
Lower Section (2256-2967 meters), the lithology from the top down to
2930 meters is quite similar to the overlying section, except that it is
less sandy and siltstones become more abundant. Some patches of black
organic matter are also present. Seismically, the Lower Section is
characterized by southeasterly prograding sequences.
A
middle to late Oligocene age has been assigned to this section based
mainly on good calcareous nannofossil assemblages. Benthonic
foraminifera indicate an open marine, probably middle neritic
environment was predominant, but the intermittent occurrence of
nannofossils also suggests fluctuating conditions. This sequence in SB-2
is tentatively correlated with the section of interbedded claystones and
tuffaceous, very fine grained to silty sandstones encountered in SB-1
from 1556-1685 meters, where slightly shallower inner to middle neritic
conditions are indicated.
Lower Carbonate Unit (Figure 14)
SB-1
encountered a thick carbonate unit beneath the Volcaniclastic Series (at
1922 meters), which Marathon referred to as the Lower Carbonate Unit.
Labofina S.A. describes the 934-meter Lower Carbonate Unit as
alternations of micritic to microsparitic limestone, dense to slightly
porous, containing bioclasts; biomicrites and biosparites to
biomicrosparites, locally recrystallized, having very good vuggy and
intergranular porosity; and thin clayey laminations. Poorly sorted,
bioclastic fractions composed mainly of very abundant debris of
encrusting coralline algae do not exceed 50%. Large sized bioclastic
debris is mainly coral encrusted by coralline algae, which are abundant
and present everywhere in this unit. Less numerous are echinoderm
debris, echinoid spines, pelecypods, microgastropods, ostracods, and
foraminifera.
Study
of conventional core material, sidewall cores and wireline logs indicate
substantial intervals of porous and permeable rock with porosities from
11 to 25%.
The
Lower Carbonate unit is separated from the underlying volcanic sequence
by a 12-meter weathered zone of undetermined age. Based on the
predominant larger benthonic foraminifera assemblages, the age of the
Lower Carbonate Unit was determined to be middle to late Eocene and is
partially time-equivalent to a silty section drilled in SB-2 from 3367
to 4032 meters.
A
shallow, shelf marine environment is indicated for the Lower Carbonate
Unit. The presence of reef building organisms such as coralline algae
and corals, associated with large benthic foraminifera, indicates a reef
facies. However, the common presence in cores of algal grains rather
than large crusting or branching colonies may suggest a back reef shelf
environment.
Channel-Turbidite Unit (Figure 16)
SB-2
did not encounter the Lower Carbonate Unit beneath the Fluvial-Delta
unit as expected, but instead penetrated a 1065-meter clastic unit which
Fina termed the Turbidite Sequence and which Robertson Research has
named the Channel-Turbidite Unit. They divided it into two sections as
follows:
The
Upper Section (2967-3367 meters) of the Channel-Turbidite Unit is a
thick series of siltstones, claystones, and clayey siltstones. An age
from late Eocene to early Oligocene has been assigned this section even
though the position of the Oligocene/Eocene boundary cannot be precisely
defined.
In
SB-1, a late Eocene to early Oligocene age has also been assigned to the
interval between 1685 meters and the top of the Lower Carbonate Unit.
This interval consists mostly of claystones with some interbedded, very
fine-grained sandstones. The sequence has also been interpreted as
having been deposited in a shallowing-upward, middle neritic to upper
bathyal environment. As in SB-2, the section is characterized by an
increase of planktonic foraminifera with depth. It is considered the
equivalent of the Upper Channel-Turbidite Unit in SB-2 (see
Figure 24).
The
Lower Section (3367-4032 meters) is primarily a sequence of silty
claystones and argillaceous siltstones. Several sandstones with low to
moderate porosity were reported between 3829 and 3840 meters and between
3937 and 3969 meters. They represent the only significant reservoir
development in this unit.
Sedimentological evidence from cores at 3421-3428 and 3786-3795 meters
strongly suggests the presence of an outer submarine fan sequence with
pelagic shales and fine-grained turbidites. The sandstones and
siltstones are usually graded.
Planktonic foraminifera and calcareous nannofossils date the unit as not
older than late Eocene. Foraminiferal faunas indicate deposition in an
outer neritic to bathyal slope environment. The top of this section in
SB-2 is considered the time equivalent of the top of the Lower Carbonate
sequence in SB-1. The base of the unit is separated from the volcanic
unit by a 57-meter interval of either weathered volcanic rock or
sedimentary rocks containing abundant volcanic fragments. According to
Robertson Research, the lower section of the Channel-Turbidite Unit and
the SB-1 Lower Carbonate Unit can be correlated with the upper Eocene
Point-Blanche Formation that is exposed on St. Maarten Island.
SB-1
encountered a volcanic unit from 2856 to 2975 meters (T.D.). As
described from a conventional core at the base of the drilled section,
the rock is a gray-green andesite porphyritic unit with dark green
millimetric phenocrysts, euhedral to subhedral hornblende and indistinct
white battens of plagioclases, coated in a microlitic goundmass composed
primarily of plagioclases. Streaks of hematite and small millimetric
accumulations of pyrite are scattered in the rock. Potassium/Argon
radiometric dating of hornblende by Geochron USA for Marathon dated the
andesite encountered at 2865 meters in SB-1 as 64.5 Ma, or earliest
Paleocene.
SB-2
also penetrated an andesite. The top of the unit is somewhat ambiguous,
but Fina picked it at 4032 meters on a velocity increase on the sonic
log. However, gamma ray readings increase sharply at 3974 meters and
remain high to 4032 meters. The lithology of the 3975-4032-meter
interval could be either weathered volcanic rocks or sedimentary rocks
containing frequent to abundant volcanic fragments. The volcanic
section continues to 4231 meters (T.D.). According to Robertson Research
(1984), the andesites in the two wells are probably equivalent even
though some macroscopic differences are evident in cores as well as in
microscopic studies and laboratory analyses. Whole rock Potassium /Argon
dating by Robertson Research determined the age of the andesite
encountered at 3927 meters in SB-2 to be 38.4 Ma. The Universite Libre
de Bruxelles dated samples supplied by Fina of the SB-2 andesite as 34.4
Ma and the SB-1 andesite as 37.3 Ma using the Potassium/Argon whole rock
method. With a margin of error of 3.7 to 1.4 m.y., the dates are all
late Eocene.
Marathon interpreted the andesite in SB-1 as a near surface intrusion
and/or part of a volcanic feeder system. Neither well penetrated the
base of the andesite, but seismic data strongly suggest the presence of
a thick sedimentary section beneath the volcanic unit. Thus it is
unlikely the andesite originated as oceanic crust. It is more likely
related to a regional magmatic pulse. Igneous rocks outcropping on St.
Maarten Island have been dated from 28 to 32 Ma.
Pre-Volcanic Sequence (Figures 14,
16,
and 17)
The age
of the pre-volcanic sequence is uncertain. Marathon dated the andesite
encountered at 2865 meters in SB-1 as earliest Paleocene. The
radiometric analyses Fina had done on both the SB-1 and SB-2 andesites
dates both rock units as late Eocene. If the age dating done for Fina
is correct, the pre-volcanic section could consist of Paleocene to
middle Eocene age sediments overlying Upper Cretaceous and older
sediments.
During
the Late Cretaceous, Saba Bank is thought to have occupied a backarc
position on the Aves Swell volcanic arc that was part of the Greater
Antilles volcanic arc that also included Cuba, Hispanola, Puerto Rico,
and St. Croix Island. As noted earlier, scattered dredge hauls over the
Aves Swell suggest extensive shallow-water platform areas were present
during the Late Cretaceous. St. Croix Island has over 10,000 meters of
strongly deformed Upper Cretaceous calcareous turbidites and
volcaniclastics that were deposited in a deep-water basin and appear to
be unrelated to the Upper Cretaceous sediments of the Aves Swell. Puerto
Rico also has thick sequences of Cretaceous and Early Tertiary volcanic,
volcaniclastic and calcareous rocks. The strata include shales,
sandstones, and rare limestones deposited as turbidites, shelf
sediments, and reefs, suggesting the magmatic arc platform was
topographically complex.
Analyses of kerogens in SB-1 by Marathon revealed considerable reworked
Cretaceous coaly material in the upper Eocene-middle Miocene
volcaniclasitic sequence. The character of the material indicates it was
sourced from exposed deltaic sediments. Thermal maturation indices
within the oil window indicate the deltaic rocks have undergone
considerably less deformation than the St. Croix sequence. Marathon
biostratigraphic studies also report the presence of reworked Cretaceous
fossils in the Tertiary volcaniclastic section, and Robertson Research
found similar reworked Cretaceous fossils in SB-2. The relationship of
the two wells along with dipmeter data from SB-2 indicate the exposed
Cretaceous deltaic sequence supplying sediments to the volcaniclastic
sequence was located to the west or northwest of the wells, possibly in
the western Saba Bank platform area.
The
sediment source for the indicated Cretaceous deltaic sediments may have
been the southern Yucatan block with which the Greater Antilles arc
collided during Late Cretaceous time (Figure 10).
It is
possible that the Saba Bank pre-volcanic sequence also contains
Paleocene sediments. Reworked Paleocene spores were found in a sidewall
sample from 2795 meters in SB-1. Bouysse (1988) reports the presence of
Paleocene (uppermost Danian to Thantian) pelagic marly limestones and
black shales completely devoid of volcanics on Anguilla Island. As noted
in the section on paleogeography, dredge hauls in the Lesser Antilles
have recovered Paleocene shallow-marine limestone and greywacke while
DSDP holes 30 and 148 drilled on the Aves Swell recovered reworked
Paleocene microfauna. Because of the probable exposure of Cretaceous
sediments to the west, Paleocene sediments, if present, would probably
be limited to the eastern part of Saba Bank.
Well
Results
SB-1
was drilled by Marathon and partners on the southeast part of the Saba
Bank to test the hydrocarbon potential of a well defined seismic anomaly
thought to be a mid-Tertiary reef (Figures 13
and 14). The well was spudded on April 16, 1977, and was plugged and abandoned June 21, 1997,
as a dry hole at a total depth of 2974.7 meters in andesite. The well
penetrated a series of carbonate and clastic sediments dated Pliocene to
Eocene overlying the andesite. The objective reef carbonate section,
which was encountered at 1922 meters, was 934 meters thick.
The
reef section contains several intervals of porous and permeable
carbonates with porosities in the 20-25% range, but the only indications
of hydrocarbons are minor gas shows between 2140 and 2380 meters. No
other oil or gas shows were encountered in the well. Electric log
interpretation indicates all potential reservoir rocks are wet. No drill
stem tests were made.
Kerogen
analyses indicate the thermal maturity of the penetrated section is low.
Data indicate that samples near the bottom of the well are approaching
the oil generation zone, but are not thermally mature enough for
generation.
The
presence of what were thought to be good, but immature source rocks in
SB-1, along with good reservoir intervals within the Lower Carbonate
Unit suggested that a carbonate buildup located deeper in the basin
within the oil window would likely contain producible hydrocarbons. This
led the Fina group to drill SB-2 on a relatively well defined seismic
anomaly located on a basement high deeper in the basin (Figures 17 and
18). It was expected that the well would encounter a carbonate buildup
with associated reservoir facies.
SB-2
was spudded on February 22, 1982, and was plugged and abandoned as a dry
hole on May 25, 1982, at a total depth of 4231 meters. As expected, the
well did penetrate a sequence of Pliocene to Eocene age sediments
overlying what has been dated as late Eocene andesite; however the
objective carbonate facies were not present. The Lower Carbonate Unit
facies equivalent penetrated by SB-2 is a series of claystones,
argillaceous siltstones to silty claystones with subordinate sandstones
having low to moderate log porosity. The unit has been interpreted by
Robertson Research as a turbidite/deep sea fan sequence.
No
significant hydrocarbon shows were encountered while drilling. Minor gas
shows were encountered in sandstones and siltstones between 3800 and
3975 meters and log interpretation indicated the presence of possible
gas-bearing reservoirs that were subsequently evaluated by testing
through a 7-inch liner. Two intervals were tested: 3936.7-3946.8 meters
and 3961.4-3970 meters. No liquid hydrocarbons were recovered, but a
small amount of gas with a C1-C5 composition was
recovered from the drill collars. Fina has suggested that severe mud
losses while drilling the section may have resulted in extensive
formation damage and that the test is inconclusive.
Source Rock Potential and Geochemistry (Figures 19-22)
Geochemistry of SB-1
In 1977
Marathon Oil's Denver Research Center made geochemical analyses on nine
composite samples from SB-1 between 387 meters and 2837 meters. The
analyses include total organic carbon (TOC), percent carbonate carbon,
qualitative analysis of extracts, and kerogen maturity based on organic
matter coloration.
Although TOC values were generally low, bitumen extracts yielded total
hydrocarbons of 239-593 ppm. As no evidence for contamination by mud
additives such as crude or diesel oil was found, Marathon interpreted
these data as indicating that good, but immature oil source rocks occur
in both mudstones and carbonates in a sequence at around 2840 meters
(composite sample 8) on the basis of higher total organic carbon (1.3%)
and 593 ppm hydrocarbons. They note that the hydrocarbons appear to be
immature, based on hydrocarbon distributions seen in gas chromatographs
of the saturate hydrocarbon fractions. Shallower samples were also
reported as potentially good source rocks on the basis of total
hydrocarbons although TOC values were low.
Robertson Research's interpretation of these data (1984) is that not
enough analyses were done to give an accurate assessment of the
hydrocarbon-generating potential of the penetrated section. On the basis
of the data that are available, they believe that most, if not all, of
the extractable hydrocarbons in the samples represent migrated
hydrocarbons and not indigenous material. Yields and composition of
source rock extracts from Robertson Research's 1984 report are given in
Table 1. Organic richness is very low in most samples and conventional
assessment of source bed quality based on organic richness (TOC) would
classify most of the samples as nonsource (<0.5% TOC) to marginal
(0.5-1.0% TOC) sources. They rate one interval (2453-2600 meters) with
1.3% organic carbon as good source. Rock-Eval pyrolysis data presented
by Robertson Research have very low hydrogen indices for the tested
samples and suggest they are gas prone.
Kerogen
maturation studies by Marathon based on spore and cuticle coloration
indicate the thermal maturity of the penetrated section is low. The data
indicate that the samples near the bottom of the well are approaching
the oil generation zone, but are not thermally mature enough for
generation to have occurred.
During
the course of the kerogen maturation evaluations, Marathon noted older
reworked organic material in several samples. A sidewall core at 1679
meters contained much fungal material and many pieces of light brown
cuticle with a color indicating thermal maturity (Ro=0.8%), as well as
fusinite and wood fragments. G. K. Guennel, who conducted the study,
stated that he considered this material to be reworked from older, more
mature rocks, probably from a Cretaceous coal seam. He noted similar,
but not as abundant, material in a sidewall core at 1538 meters. A ditch
sample from 2390-2399 meters also contained abundant fungal material,
wood, and fusinite along with a suite of medium brown Mesozoic spores
(Ro=1.0%), probably associated with the fungal material. Guennel again
suggested a Cretaceous coal or lignite might have been one of the
sources for some of the organic material in this sample. Ditch samples
from 2582-2591 and 2737-2246 meters also contain similar reworked fungal
and coaly material.
In
summary, the geochemical data from SB-1 indicate that significant
quantities of extractable hydrocarbons are present in the samples
throughout the entire sedimentary section. However, the low TOC values
and low maturity (<0.6% Ro equivalent) of these samples strongly suggest
that the hydrocarbons present are migrated rather than indigenous. The
implication is that, although SB-1 probably does not contain good,
mature source rocks, there is a good possibility of more deeply buried,
thermally mature petroleum source rock facies in the area.
Geochemistry of SB-2
Geochemical studies on cuttings, sidewall, and conventional cores from
SB-2 were conducted by both Labofina in Brussels (82 samples) and
Robertson Research in Houston (12 samples) in order to determine TOC,
thermal maturity, and source rock quality.
Vitrinite reflectance values indicate that SB-2 reached the mature zone
for oil generation. The top of the oil window is located between 2760
meters (Ro=0.55%) and 3100 meters (Ro=0.62%). Most of the samples
analyzed are low in organic carbon (<0.5% TOC) and are rated as
non-sources, with the exception of a few intervals between 2899 to 3423
meters and in core material at 2788 meters, where some samples rated as
marginal source rocks. The organic matter that is present is primarily
humic Type III, which is generally gas-prone. Data from Rock-Eval
Pyrolysis give low Hydrogen Indices and high Oxygen Indices, also
indicative of gas-prone organic material. Some sapropelic organic
material was also recognized, but the concentrations are minimal.
Bottom
hole temperatures derived from wireline logs give a geothermal gradient
of 3.3oC/100 meters from 1520-4185 meters. This gradient is
lower than the SB-1 geothermal gradient, which is 3.8oC/100
meters.
The
lack of significant source rocks in the generally deeper water sediments
encountered in SB-2, along with the presence of abundant thermally
mature, reworked Upper Cretaceous organic material in SB-1 and reworked
Upper Cretaceous marine fauna in SB-2, strongly suggest the possibility
that the migrated hydrocarbons in SB-1 were sourced from the underlying
Upper Cretaceous rocks.
Regional Geochemical Considerations
A
review of Caribbean hydrocarbon source rock data strongly suggests that
early Late Cretaceous rocks are the most likely source for hydrocarbons
on Saba Bank. The Tertiary basin in the east, where SB-1 and SB-2 are
present, shows immature source and/or unlikely sourcing (Figure 19).
According to Pindell (1991, 1995), rocks of this age, which he terms
"medial" Cretaceous, are the most significant hydrocarbon source rocks
for the two primary suites of rock that occur in the Caribbean region.
These source rocks for the highly prolific Proto-Caribbean autochthonous
suite of Jurassic, Cretaceous, and Cenozoic passive margin sediments
deposited along the rifted margins of North and South America are well
documented while their role as source rocks of the allochthonous suite
of the Caribbean Plate are less well known and their hydrocarbon
potential has yet to be realized. Pindell postulates the Caribbean Plate
medial Cretaceous source rocks were deposited in the eastern Pacific
realm during an oceanic anoxic event, similar to roughly contemporaneous
events in the Atlantic and Proto-Caribbean, prior to the relative
eastward migration of the plate into the present Caribbean region.
Supporting evidence are reported TOC concentrations of up to 4.2% from
Upper Cretaceous anoxic shales interbedded with limestone from D.S.D.P.
site 146 in the deepwater Venezuelan Basin (Edgar et al., 1973), and the
occurrence of Upper Cretaceous source rocks with reported TOC values of
up to 7% in Puerto Rico.
Robertson Research (1984) performed geochemical analyses on a limited
number of outcropping sediments from St. Martin and St. Barthelemy
Islands on the Anguilla Platform, St. Croix, and Puerto Rico, and on
several samples from three wells in Puerto Rico. Saba Bank Resources had
samples from Anguilla Island analyzed for source rock potential. In
addition, nearly 100 outcrop samples from Puerto Rico were collected and
analyzed for source rock potential by J. A. Hayes for an M.S. thesis
(1985) at Stanford University; the study was subsequently published
(Hayes et al., 1986).
The
four outcrop samples Robertson Research analyzed for source-rock
potential from the Eocene St. Bartholomew Formation on St. Barthelemy
Island were found to have very low organic carbon content, ranging from
0.03 to 0.09% TOC. Maturity data from vitrinite reflectance analysis
performed on one sample indicates that it is overmature with a Ro of
1.86%. Only one sample from the upper Eocene Pointe Blanche Formation on
St. Martin Island was analyzed. It contained 0.17% TOC and was
classified as a nonsource.
Saba
Bank Resources had eight outcrop samples from the Paleocene section at
Crocus Bay on Anguilla Island analyzed by DGSI in 1996. The total
organic content was very low (0.04-0.21%); correspondingly, no
additional work was done.
Thirteen Cretaceous outcrop samples from the Late Cretaceous Caledonia
Formation of St. Croix were analyzed by Robertson Research to determine
their hydrocarbon-generating potential. All of the samples, except one,
were too organically lean to be considered potential hydrocarbon source
rocks. The exception contains 0.56% TOC, but maturity data determined by
pyrolysis and vitrinite reflectance indicate it is well beyond the
oil-generating stage with an Ro>3.2%. Kerogen typing indicates that
large quantities of oil-generating components are present and that this
rock probably represents a marginal spent source bed.
There
are two confirmed reports of minor oil occurrences in the rocks of the
Older Series in the south-central part of Puerto Rico. Robertson
Research analyzed four samples from pre-middle Tertiary outcrops and
three probable pre-middle Tertiary samples from Kewanee Oil company
CPR-1 for source-rock potential. Three of the outcrop samples rated as
non-source rocks on the basis of organic richness (0.06-0.16% TOC) as
did the CPR-1 samples (0.14-0.28% TOC). The fourth outcrop sample, from
an Upper Cretaceous mudstone, had 1.29% TOC but was thermally overmature
for oil generation (Ro=2.05%). Visual kerogen examination indicates that
a large quantity of oil-generating amorphous kerogen is present in the
sample. Robertson also analyzed a limited number of middle to Upper
Tertiary age samples from the Kewanee CPR-1, 2, 3 and 4 wells for
source-rock potential. Some samples have over 1% TOC, but all contained
primarily terrestrial dry-gas generating organic matter and were
generally thermally immature.
Nearly
100 samples were collected by J. A. Hayes (Hayes et al., 1986) from
outcrops located throughout Puerto Rico of the Cretaceous-Early Tertiary
volcanic, volcaniclastic, and calcareous strata composing the sediments
deposited on the Late Jurassic-Early Cretaceous magmatic arc platform
and from the Kewanee CPR-1 and 3 wells. Sampling concentrated on
organic-rich Cretaceous strata, but some Lower Tertiary units were also
sampled. Rock types analyzed included chert, calcareous and
non-calcareous shale, and limestone. The samples were analyzed for total
organic content, thermal maturity (vitrinite reflectance), and visual
kerogen identification with reflected light. If the samples displayed
Ro<2.0%, thermal alteration index (TAI) was measured and kerogen types
were identified. Rock-Eval pyrolysis was conducted on samples with
sufficient kerogens and Ro<2.0%.
Total
Organic Carbon in the majority of the Puerto Rico samples is less than
3.0%, but ranges to 7%, with Upper Cretaceous limestones having the
highest values (Figure 20). Kerogen identification by reflected light
was successful on 62 of the samples. Of these, 24 (39%) contained enough
amorphous organic matter and exinite to plot in the oil and gas
producing field (Figure 21), 12 (19%) of the samples plot in the wet gas
and condensate field and 26 (42%) plot in the dry gas field. Rocks
younger than Eocene are in general immature to marginally mature. Rocks
of Eocene age (limited sampling) are mature to overmature; Upper
Cretaceous rocks are slightly less mature, and Middle Cretaceous rocks
are mature to greatly overmature. A plot of Rock-Eval pyrolysis derived
Hydrogen Index vs. Oxygen Index data on a modified van Krevelen diagram
(Figure 22) shows that the majority of the samples are in the fields of
types II and III kerogen; i.e., those that are oil- and gas-prone or
gas-prone.
In
summary, a significant percentage of the Cretaceous rocks sampled on
Puerto Rico have moderate to fair source rock potential based on their
TOC content, maturity, and kerogen type. The majority contain kerogen
that is prone to gas generation; however, a few formations, particularly
limestones, contain good amounts of oil- and gas-generative kerogen.
Summary of Geochemical Studies
In the
limited areas of the northeast Caribbean where geochemical data are
available, the Tertiary sedimentary section generally contains poor
petroleum source rocks. In samples from the Saba Bank wells, outcrop
samples on Anguilla, St. Maarten, and St. Barthelemy Islands on the
Anguilla Platform, and outcrop and well samples on Puerto Rico, total
organic carbon values are universally low; the kerogens that are present
are generally gas-prone; and the post-Eocene section is immature for oil
generation. Eocene sediments reach maturity in SB-1, and they are
overmature on St. Maarten and St. Barthelemy Islands. On Puerto Rico the
limited number of Eocene age rocks analyzed were mature to overmature.
The only Paleocene rocks analyzed for source rock potential are on
Anguilla, where they have very low TOC values and are rated as
non-source rock.
The
high bitumen extract yields in SB-1 are believed to be migrated
hydrocarbons generated from deeper, more mature source rocks. The
occurrence of abundant reworked mature Cretaceous organic material in
that well suggests the source of the migrated hydrocarbons is the
underlying Cretaceous source rocks. Saba Bank was part of the Greater
Antilles Magmatic Arc until early or mid-Eocene time and shared a common
Cretaceous history with Puerto Rico. The studies of source rocks on
Puerto Rico described by Hayes et al (1986) demonstrate that fair to
moderate quality source rocks capable of generating both oil and gas are
present in the Cretaceous sediments deposited on the magmatic arc
platform. There is no reason to believe that similar source rocks are
not present in the thick pre-volcanic sequence underlying Saba Bank.
Reservoir Geology
The
results from SB-1 and SB-2 confirm the presence of good to excellent
reservoirs throughout the post-andesite Tertiary section. The Upper
Limestone Unit is reported by Fina to have good porosity with visual
estimates of 10-25%. No permeability data are available, but the
extensive lost circulation that occurred in SB-1 and to a lesser extent
in the No. 2 well indicates high permeability zones.
Marathon reported that sandstones and some conglomerates in the
Volcaniclastic Middle Series (Fluvio-Deltaic Unit) in SB-1 include
intervals with fair to excellent porosity and adequate permeability. The
equivalent section in SB-2 is less sandy, and most of the sands that are
present have a high clay content and low porosity. Occasional thin
sands in the lower part of the sequence have 10-25% computed log
porosity.
The
934-meter Lower Carbonate Unit in SB-1 is composed of dense to slightly
porous micritic to microsparitic limestone, biomicrites and biosparites
to biomicrosparites having very good vuggy and intergranular porosity,
and thin clayey laminations. Study of conventional core material,
sidewall cores, and wireline logs indicate substantial intervals of
porous and permeable rock, with porosities from 11 to 25%. Marathon's
Denver Research Center described scattered occurrences of
solution-enlarged primary interparticle porosity, supplemented by moldic
porosity, which ranges up to 35-40%.
The
Channel-Turbidite Unit encountered in SB-2 contains a basin-plain outer
submarine fan sequence deposited by turbidity currents. Porosities in
the fine-grained sand units are low, however, and are generally less
than 10%.
The
most promising remaining prospects are in the pre-andesite sequence with
Cretaceous reservoirs as the primary target. There are no data on the
type or quality of Cretaceous reservoirs. The reworked Cretaceous coaly
material encountered in both Saba Bank wells suggests the presence of
marginal marine deltaic sediments that would be expected to have
significant sand bodies with good reservoir quality.
Seismic Programs and Interpretation
Figure Captions (23-35)
 |
Figure 23. Location map for east-west
seismic line E-12, through well SB-1. |
 |
Figure 24. E-12 geoseismic section,
showing the units described from SB-1and an interpreted major
wrench fault. |
 |
Figure 25. Uninterpreted seismic line
E-12. |
 |
|
 |
|
 |
Figure 28. Interpreted seismic lines
SBR-3 and E-12, corresponding to the
geoseismic section
(Figure 27). Cende
Prospect on the left at a time of <1 second. |
 |
|
 |
Figure 30. Interpreted seismic line SBR-2. Note that the fault
seems to control the edge of Saba Bank. |
 |
Figure 31. Interpreted seismic line
SBR-3, across the heart of Cende prospect. |
 |
Figure 32. Interpreted seismic line
SBR-4, across part of prospect for proposed test. |
 |
Figure 33. Interpreted seismic line
NE-9, from the Aladdin 1988 survey, across Cende prospect,
illustrating quite well the amount of dip closure and the
unconformity. The thickness of the section has been confirmed by
gravity and magnetic data. |
 |
Figure 34. Interpreted seismic line
SBR-11 across Cende prospect, with
some shallow multiples.
|
 |
Figure 35. Reprocessed seismic line
NE-8 across Cende prospect; showing the location of the fault,
which controls the bank edge,
and the strong dip reversal over Cende Prospect. |
Focus
The
overall focus of the Saba Bank evaluation has been on the potential of
the untested pre-Eocene (Upper Cretaceous?) sediments. The major
geophysical emphasis has involved the reprocessing and interpretation of
selected Petrofina seismic lines and all of the Aladdin lines, and the
acquisition, processing, and interpretation of 205 kilometers of infill
data acquired in late 1999. The input data and results of these projects
follow.
Petrofina commissioned Western Geophysical to acquire a seismic grid
over the eastern half of Saba Bank in September of 1980. Acquisition
parameters for this survey included firing 8 Aquapulse source guns at
intervals of 25 meters into 96 receiver groups spread over a 2400-meter
streamer cable and recording data at 2-millisecond intervals on DFS V
instruments. These parameters resulted in 48-fold stack. The effort was
the state of the art at the time, but it was designed for an objective
shallower than 2500 meters. Subsequent drilling and seismic
interpretation have proved the effort to be inadequate for the currently
understood target; but much of the problem can be overcome with a longer
cable.
Western
also recorded the data shot for Aladdin in February 1988. Better
acquisition tools were available by that time, and a conventional
recording system and survey design were employed. Western used 18
airguns popping at 26.7-meter intervals into a 3300-meter cable with 120
receiver groups, resulting in 60- fold stack. A more advanced Litton
LRS-16 system recorded the data at 2-millisecond intervals. The longer
cable, higher fold, additional groups, and more powerful source allowed
better records from greater depths and subsequent better evaluation of
normal moveout velocities.
Every tool in the processor's kit has been improved significantly since
the original processing was performed. Some improvements are due simply
to more powerful computers, and others are a result of new and better
algorithms. The key steps in the reprocessing that differentiated it
from earlier efforts included deterministic designature, FK filtering,
tau-p deconvolution, automated velocity analysis, and radon transform
demultiple. However, the two most important are post-stack procedures:
migration and the FK demultiple program.
The lack of migration on the original Petrofina data combines with
inadequate multiple attenuation to make it uninterpretable in many
places. Recognizing the problem, Petrofina later used various multiple
elimination schemes without success. While the newer Aladdin data set is
better, the original attempt at processing was so poor as to be almost
totally useless to the interpreter. Understanding the source of the
problems, plus using great care in each step of the pre-stack
processing, allowed the migration and FK demultiple algorithms to make
the data interpretable.
Petrofina
Data Reprocessing
In the first phase of reprocessing,
Western Geophysical of Denver worked on three of the seismic
profiles (60 kilometers) acquired for Petrofina in 1980. The principal
objectives were to determine if the data could be improved enough to
warrant further reprocessing, and to obtain more information about the
local geology. Western was successful in improving the interpretability
of the data, but many multiples remain on the sections and they continue
to hinder geological understanding. Based upon what was learned in the
subsequent reprocessing of the Aladdin data, it should be possible to
improve the Petrofina data more. However, it will be impossible to equal
the quality of the newer Aladdin data due to the deeper geological
target in the Petrofina area and to certain limitations in the recording
parameters of the older data.
The
improved multiple attenuation allowed better resolution of the
pre-Eocene (Upper Cretaceous?) reflectors. This targeted zone, which on
most original seismic lines appeared to be crystalline basement, is now
seen to be composed of probable clastic sediments. After reprocessing of
the three lines in this initial effort, it was apparent that there was a
change in dip between these deeper events and the overlying sediments.
The newly visible deep area was originally interpreted as half-grabens
which could act as important hydrocarbon source areas for the known
Tertiary reservoirs.
Aladdin
Data Reprocessing
Sterling Seismic and Western
Geophysical both attempted reprocessing of five of the lines acquired
for Aladdin Petroleum (134 kilometers). Sterling made remarkable
improvements in the data; after considerable assistance and time,
Western improved the data somewhat. While the old sections showed little
more than flat reflectors and seemed to indicate shallow basement and
little petroleum potential, the results from both processors show
geology that is consistent with the expectations for the area.
The
presence of a very thick sedimentary sequence of apparent Cretaceous age
is quite encouraging. Therefore, the field tapes for the remaining seven
Aladdin seismic lines were requested and obtained (209 kilometers).
Sterling reprocessed this data, again with promising results.
It is
important to note that Western Geophysical was not content with the
results they achieved in reprocessing the first five lines. On their own
initiative, they tested a new post-stack multiple attenuation technique
on line E-12. This is the key line in the data set; it is the only one
of the newer profiles that connects the eastern area of Saba Bank to the
western area. That is important because the wells were drilled in the
eastern area, and the Aladdin data was shot in the western area, where
the pre-Eocene reflections are much shallower and the data quality is
much higher. Line E-12 crosses the poorly understood boundary between
these areas, which had never been satisfactorily imaged by any
processing flow. Western's reprocessing cleared the picture sufficiently
to allow a new geological theory: the boundary zone is probably a
wrench fault.
When Western Geophysical was shown the importance of their successful
independent trial on E-12, they agreed to perform additional processing
on two more lines at no cost and with additional interpreter input. This
work, which came at the very end of the project, confirmed the existing
deep interpretation and added more detail to the visible structures.
There was little doubt that performing the same multiple attenuation
technique on the other twelve reprocessed profiles would be similarly
successful.
Western's poststack F-K demultiple program is used to attenuate specific
residual multiple energy, either water bottom or interbed, having
constant and uniform dip. This is precisely the problem in the Saba Bank
area: the shallow Kingshill carbonate material is flat and it generates
flat multiples from within and from its contact with the dipping clastic
sediments below. Western employed the F-K technique as a supplement to
the conventional pre-stack demultiple routines, Parabolic Radon
transform and Tau-P deconvolution. The F-K technique requires accurate
knowledge and identification of the multiple energy; in this case the
interpreter worked with the analyst to digitize the base Kingshill
event. While the resulting improvement was sometimes dramatic, the reprocessing was still able only to transform uninterpretable data
into fair quality data. Structural "ties" were impossible, so it was
feasible only to make a formline structure map within the pre-Eocene
(Figure 9).
Acquisition of New Seismic
Because
of the potential that became visible on the seismic reprocessing, Saba
Bank Resources N.V. decided in late 1999 to acquire new seismic. Ten
lines were planned to detail a large rollover prospect in the
southwestern portion of Saba Bank and to evaluate further a lead
immediately to the east. A total of twelve lines totaling approximately
205 kilometers were recorded, including two new lines added when rapid
processing indicated that the eastern lead was valid (Figure 23).
The
MV Western Inlet acquired the new 2-D seismic data with a
6000-meter cable and a 25-meter shot interval, resulting in 120 fold.
Acquisition began on December 28 and was completed on January 1, 2000.
The field data were improved from the older vintages, largely because of
the longer offsets used. The processing flow at Western for the new data
was similar to that for the Aladdin data.
When
the processing of the new seismic data was completed, the Saba Bank
interpretation project was converted to digital format. This involved
digitizing the old base maps, adding the new seismic base locations, and
loading the final seismic processing and reprocessing. Some of the 1970s
vintage seismic data is also marginally useful, and it could be scanned
and added to the database in the future.
Previous interpretations of the Saba Bank area had shown no faults with
other than normal displacement. Such a picture is unlikely in the
regional setting of the Northeast Caribbean. Once the complex faulting
of the flower structure could be seen on one seismic line, it was
possible to interpret it on even the original Fina processing from more
than twenty years ago. The current interpretation shows this line of
demarcation trending almost north-south, dividing Saba Bank into two
equal-sized but economically different geological regimes.
The character of the reworked material found in the two Saba Bank wells
suggests that it was sourced from an exposed Cretaceous deltaic sequence
located on what is now the platform area of western Saba Bank, or from a
landmass farther to the west. The reprocessed seismic corroborates this
interpretation, as it shows that the area west of the flower structure
was uplifted and eroded at least twice. The angular unconformities
marking these times are visible on several seismic lines (e.g.,
Figures
24, 25, 26,
27, and 28).
The western half of Saba Bank is
the more tantalizing because of depth: not only is the bank itself
shallow enough for drilling by a jackup rig, but the objective section
is much shallower than in the eastern portion. The probable Cretaceous
sediments are only about 1000 meters from the surface, and the section
is at least 6000 meters thick.
During the complex structural history of the pre-Eocene, a large fault
block developed in the southwestern corner of the Bank. That corner of
the fault block was tilted and eroded to almost a flat surface; it
apparently served as the provenance of the reworked sediments to the
east. Structure maps (e.g., Figure 9) indicate that this prospect has
about 28 square kilometers of four-way dip structural closure and at
least 157 square kilometers of three-way dip closure against a bank edge
down-to-the-southwest normal fault.
Although the eastern half of the
Bank also is characterized by shallow water, the depth to base Eocene
increases rapidly to the east and south before the dip becomes gentle.
The two Saba Bank wells are located in a moderately thick Tertiary
basin. Because the Cretaceous lies below the andesite penetrated in the
wells, the drilling depth east of the wells would be greater than 4000
meters. With the benefit of the Aladdin reprocessing, it can now be seen
that the deeper areas, which were initially interpreted as small
half-grabens, are actually much more extensive. It would appear that
these are continuations of the thick pre-Eocene section in the west, so
they should be similarly prospective geologically. Economic adjustments
should be made for drilling depth and increased potential for gas.
The
prospects and leads on Saba Bank can be divided into two groups:
prospects and leads in the eastern Tertiary basin and pre-Eocene
(Cretaceous?) prospects in the western platform area. The focus of the
seismic reprocessing and interpretation made for the current assessment
of the petroleum prospects of the Saba Bank area has been on the
pre-Eocene section. Because of limitations in the recording parameters,
it has not been possible to enhance the Petrofina data sufficiently to
allow mapping of prospects beneath the thick Tertiary section in the
eastern part of the Bank, although it is apparent that a thick
pre-Eocene section is present. Reprocessing of the Aladdin data over the
western platform area, however, has resulted in significant improvement
in imaging of the pre-Eocene section and the recognition of a major
wrench-fault separating the platform and Tertiary basin areas as well as
the presence of large tilted fault blocks on the platform. Acquisition
of 205 kilometers of new seismic allowed confirmation of these large
prospects.
Eastern Tertiary Basin
Petrofina mapped a number of untested prospects and leads in the
Tertiary section of the eastern basin after reinterpretation of their
seismic data following the drilling of SB-2. They recognized both
carbonate and channel/turbidite/deep sea fan prospects.
Carbonate Buildups
In
addition to the carbonate buildup tested by SB-1, Petrofina identified
carbonate buildups and associated reef facies in two other areas,
designated by the Greek letters d
and m in
Figure
18. The mapped boundaries of these features do not represent the true
limits of the carbonate developments but indicate the tentative limits
of the geophysical event associated with the reef buildups.
The
d prospect is a
structural and stratigraphic trap. The prospective reservoirs are likely
to be carbonate reservoirs similar to that encountered in the Lower
Carbonate Unit in SB-1, as well as Cretaceous clastic reservoirs similar
to those in the western Saba Bank. Marine mudstones at the top and
inter-reef facies should provide a good seal.
The
Tertiary reef appears to have grown on a local high developed on a
tilted, north-dipping pre-Eocene fault block. The hydrocarbon source is
thought to be in the underlying pre-Eocene section that is believed to
have generated the migrated hydrocarbons encountered in SB-1. According
to Fina, the d
prospect has 15,600 acres of areal closure and could reservoir from 450
to 700 million barrels of recoverable reserves.
Petrofina estimated possible recoverable reserves of 87 to 130 million
barrels of oil for the m
prospect. It is located in a faulted area, however, and the presence of
an effective seal is questionable making it a higher risk prospect than
d.
Channel/Turbidite/Deep Sea Fan Prospects
Analysis of cores in the lower section of SB-2 indicate that the shales,
siltstones, and sandstones were deposited in the outer fan environment
of a basin plain and that the sands were deposited by turbidity flow.
Petrofina’s post-drilling seismic review shows that SB-2 was drilled on
a paleo-ridge to the east of a north-south trending trough located
between it and the d
prospect (Figure 18). Hummocky, chaotic, discontinuous seismic
reflections indicative of channels, mounds, and associated turbidite
facies occur in the trough (Figure 15). The paleo-ridge acted as a
barrier partially preventing eastward turbidite flow, resulting in
north-south oriented assemblages of stacked sands. The distal facies
encountered in SB-2 had poor reservoir quality, but a drill stem test in
the interval did recover minor quantities of C1 to C5+
gas components, indicating migration
of liquid hydrocarbons has taken place and suggesting that the trough is
prospective for hydrocarbon accumulations in the turbidite sequence. The
prospect area is 10 to 15 kilometers long and 3 to 4 kilometers wide.
Petrofina estimated potential minimum recoverable oil reserves in this
area to be 300 to 400 million barrels.
Several seismic lines suggest
similar leads may also be present between SB-1 and the
d
prospect.
The
untested Western Platform area presents the best opportunity on the Saba
Bank for a major hydrocarbon discovery. The Tertiary section is thin and
unconformably overlies a very thick pre-Eocene section which, based on
the reworked material in SB-1 and SB-2, is probably Cretaceous in age.
The pre-Eocene section contains at least one prospect capable of
containing a giant oil or gas field.
As
noted above, a very large pre-Eocene fault block has been mapped in the
southwestern corner of the Bank (Figures 9,
29, 30,
31, 32,
33, 34, and
35). The prospect has approximately 28 square kilometers (approximately
7,000 acres) of four-way dip closure with 1200 meters of vertical
closure, and 157 kilometers (approximately 38,800 acres) of three-way
dip closure with 3700 meters of vertical closure against a
down-to-the-southwest normal fault. The crest of the pre-Eocene section
is at a depth of about 1000 meters and the section is at least 6000
meters thick. Water depth is approximately 40 meters.
There
is no direct evidence to indicate the nature and quality of prospective
reservoirs in the pre-Eocene section. However, the character of the
reworked Cretaceous age materials recovered from SB-1 and SB-2 indicates
they were derived from an unmetamorphosed deltaic sequence, probably
located in the platform area. The nature of the pre-Eocene seismic
reflectors also suggests a clastic sequence is present.
Significant quantities of migrated hydrocarbons occur in SB-1 and C1
to C5+ gas components were recovered in a SB-2 DST. The lack
of significant Tertiary source rocks in either of the wells, along with
the general lack of good Tertiary petroleum source rocks in the
northeast Caribbean, strongly suggest migration from a pre-Eocene
source. Regional considerations indicate Upper Cretaceous sediments are
the most likely source rocks.
Potential reserves are very high. A 100-foot
net oil pay section could easily result in a recoverable reserve greater
than 500 million barrels.
Selected Bibliography
Andreief, P., Bonneton. J.R., Vila. L.M., and Westercamp.
D., 1984. Decouverte de Paleocene superieur a Anguilla, a l'extremite
nord de l'arc des Petites Antilles (abs.), 10e Reunion Annuelle des
Sciences de la Terre: Societe Geologique de France, p.15.
Andreieff, P., Bouysse, P., and Westercamp, D., 1979,
Reconnaissance geologique de l'arc insulaire des Petites Antilles;
Resultats d'une campagne a la mer de prelevements de roches entre
Sainte-Lucie et Anguilla (ARCANTE 1): Bulletin du Bureau de Recherches
Geologiques et Minieres, ser. IV, no. 3/4, p. 227-270.
Babb, S., and Mann, P., 1999, Structural and sedimentary
development of a Neogene transpressional plate boundary between the
Caribbean and South America plates in Trinidad and the Gulf of Paria,
in Sedimentary Basins of the World, v. 4: Elsevier, p. 495-557.
Bouysse, P., 1979, Caracteres morphostructuraux et
evolution geodynamique de l'arc insulaire des Petites Antilles (Campagne
ARCANTE 1): Bulletin du Bureau de Recherches Geologiques et Minieres,
ser. IV, no. 3/4-1979, p. 185-210.
Bouysse, P., 1984, The Lesser Antilles island arc:
structure and geodynamic evolution, in Biju-Duval, B., and Moore,
J.C., Initial reports of the Deep Sea Drilling Project, Volume 78a:
Washington, D.c., US. Government Printing Office, p. 83-103.
Bouysse, P., 1988, Opening of the Grenada back-arc
Basin and evolution of the Caribbean plate during the Mesozoic and Early
Paleogene: Tectonophysics, v. 149, p.121-143.
Bouysse, P., and Guennoc, P., 1983, Donnees sur la
structure de l'arc insulaire des Petites Antilles, entre Ste. Lucie
etAnguilla: Marine Geology, v. 53, p. 131-166.
Bouysse, P., and Mascle, A., 1994, Sedimentry basins and
petroleum plays around the French Antilles, in Mascle, A., ed.,
Hydrocarbon and petroleum geology of France: Special Publication of the
European Association of Petroleum Geoscientists, v. 4, p.431-443.
Bouysse, P., and Westercamp, D., 1990, Subduction of
Atlantic aseismic ridges and late Cenozoic evolution of the Lesser
Antilles island arc: Tectonophysics, v. 175, p. 349-380.
Bouysse, P., Andreieff, P., and Westercamp, D., 1980,
Evolution of the Lesser Antilles island arc, new data from the submarine
geology: Transactions, 9th Caribbean Geological Conference, Santo
Domingo, 1980, p. 75-88.
Bouysse, P., Andreieff, P., Richard, M., Baubron, J.,
Mascle, A., Maury, R.C., and Westercamp, D., 1985, Aves Swell and
northern Lesser Antilles ridge: Rock-dredging results from Arcante 3
cruise, in Mascle, A., ed., Symposium Geodynamique des Caraibes:
Paris, Technip, p. 65- 76.
Burke, K., 1988, Tectonic evolution of the Caribbean:
Annual Reviews, Earth and Planetary Science, v. 16, p. 201-230.
Case, J.E., and Holcombe, T.L., 1980, Geologic-tectonic
map of the Caribbean region: U.S. Geological Survey Miscellaneous
Investigations Map 1-1100, scale 1:2,500,000.
Christman, R.A., 1953, Geology of St. Bartholomew, St.
Martin, and Angui1la, Lesser Antilles: Geological Society of America
Bulletin, v. 64, p.65-96.
Daly, T.E., 1995, The Petroleum potential of the
Netherlands Antilles, in Miller, R.L., Escalante, G., Reinemund,
J.A., and Bergin, M.J., eds., Energy and Mineral Potential of the
Central American-Caribbean Regions: Circum-Pacific Council for Energy
and Mineral Resources Earth Science Series, v. 16, Springer-Verlag,
Berlin-Heidelberg, p. 123- 130.
Dengo, G., and Case, J.E., 1990, eds, The Caribbean
Region: Geological Society of America, The Geology of North America, v.
H.
Edgar, N.T., et al., 1973, Initial reports of the Deep
Sea Drilling Project, Leg 15: Washington, U. S. Government Printing
Office.
Fina, 1983, Saba Bank Permit Farmout Proposal:
Unpublished Report, 23p.
Fox, P.I., Schreiber, E, and Heezen, B.C., 1971, The
geology of the Caribbean crust: Tertiary sediments, granitic and basic
rocks from Aves Ridge: 'tectonophysics, v. 12, p.89-109.
Hayes, J.A., Larue, D.K., Joyce. G, and Schellekens, J.,
1986, Puerto Rico: reconnaissance study of the maturation and source
rock potential of an oceanic arc involved in a collision: Journal of
Marine and Petroleum Geology, v. 3, p. 126-138.
Larue, D.K., and Warner, A.J., 1991, Sedimentary basins
of the NE Caribbean plate boundary zone and their petroleum potential:
Journal of Petroleum Geology, v. 14 (3), p. 275-290.
Lewis, J.F., and Draper, G., 1990, Geology and tectonic
evolution of the northern Caribbean margin, in Dengo, G., and
Case, J.E., eds., The Caribbean region: Geological Society of America.,
The Geology of North America, v. H., p. 11-133.
Lewis, J., and Robinson, E., 1976, A revised stratigraphy
and geological history of the Lesser Antilles: Transactions, 7th
Caribbean Geological Conference, Guadeloupe, 1974, p.339-344.
Lidz, B., 1988, Upper Cretaceous (Campanian) and Cenozoic
stratigraphic sequence , northeast Caribbean (St. Croix, U.S. Virgin
Islands): Geological Society of America Bulletin, v. 100, p. 282-298.
Maury, R.C., Westbrook, G.K., Baker, P.E., Bouysse, P.,
and Westercamp, D., 1990, Geology of the Lesser Antilles, in
Dengo, G., and Case, J. E., eds., The Caribbean Region: Geological
Society of America, The Geology of North America, v. H, p. 141-166.
Montgomery, H., and Pessagno, E.A., Jr., 1999, Cretaceous
microfaunas of the Blue Mountains, Jamaica, and of the northern and
central basement complexes of Hispaniola, in Sedimentary Basins
of the World, v. 4: Elsevier, p. 237-246.
Nagle, F., 1972, Rocks from the seamounts and escarpments
of the Aves Ridge: Transactions, 6th Caribbean Geological Conference,
Margarita, 1971, p. 409-413.
Nemec, M.C., 1980, A two-phase model for the tectonic
evolution of the Caribbean: Transactions, 9th Caribbean Conference,
Santo-Domingo, 1980, p. 23-34.
Pindell, J.L., 1991; Geologic rationale for hydrocarbon
exploration in the Caribbean and adjacent regions: Journal of Petroleum
Geology, v. 14 (3), p. 237-257.
Pindell, J.L., 1995, Circum-Caribbean sedimentary
basin development and timing of hydrocarbon migration as a function of
Caribbean plate tectonic evolution, in Mi1ler, R. L., Escalante,
G., Reinemund, J.A., and Bergin, M.J., eds., Energy and Mineral
Potential of the Central American-Caribbean Regions: Circum-Pacific
Council for Energy and Mineral Resources Earth Science Series, v.
16.,Springer-Verlag, Berlin Heidelberg, p. 47-56.
Pindell, J. L., and Barrett, S. F., 1990, Geologic
evolution of the Caribbean region; a plate-tectonic perspective, in
Dengo, G., and Case,.J.E., eds., The Caribbean Region: Geologic Society
of America, The Geology of North America, v. H, p. 405-432.
Pindell, J.L., Cande, S.C., Pitman, III, W.C., Rowley,
D.B., Dewey, J.F., Labrecque, J., and Haxby, W., 1988, A plate-kinematic
framework for models of Caribbean evolution: Tectonophysics, v. 155, p.
121-138.
Pinet, B., Lajat, D., LeQueIlec, P., and Bouysse, P.,
1985, Structure of the Aves Ridge and Grenada basin from multi-channel
seismic data, in Mascle, A., ed., Symposium Geodynamic des
Caraibes: Paris, Technip, p. 53-64.
REM, 1989, Petroleum potential, Saba Bank area,
Netherlands Antilles: Unpublished Consulting Report prepared for Saba
Bank Resources, N.V., 16p.
Robertson Research, 1984, Geology and hydrocarbon
potential of the Caribbean with emphasis on the Tertiary carbonates,
Phase 3: The north and northeast Caribbean: Proprietary consulting
report.
Ross, M.I., and Scotese, C.R., 1988, A hierarchical
tectonic model of the Gulf of Mexico and Caribbean region:
Tectonophysics, v. 155, p. 139-168.
Speed, R.C., Smith-Horowitz, P.L., Perch-Nielsen, K.v.S.,
Saunders, J.B., and Sanfilippo, A.B., 1993, Southern Lesser Antilles arc
platform: Pre-Late Miocene stratigraphy, structure and. tectonic
evolution: Geological Society of America Special Paper 277, p. 1-98.
Speed, R.C., et al., 1984, Lesser Antilles arc and
adjacent terranes, in Atlas 10, Ocean Margin Drilling Program,
Regional Atlas Series 28: Woods Hole, Massachusetts, Marine Science
International, 28 p.
Warner. A.J., Jr., 1991. Regional aspects of Cretaceous
and Tertiary evolution. Depositional history, and relation to the
occurrence of petroleum of the Saba Bank, northeastern Caribbean:
Unpublished.M:S. thesis, Wichita State University, 118 p.
Warner, A.J., Jr., and Kubena, Reed, 1989, The petroleum
potential of the Saba Bank, an interpretation: Unpublished Consulting
Report, 36 p.
Whetten, J.T.,
1966, Geology of St. Croix, U.S. Virgin Islands, in Hess, H.H.,
Bowin, C.O., Donnelly, T.W., Whetten, J.T., and Oxburgh, W.R., eds.,
Caribbean Geological Investigations: Geological Society of America
Memoir 98, p. 177-239.
Return to top.
|
Print this page
Click
to view article in PDF format.
