Content uploaded by Keith H James
Author content
All content in this area was uploaded by Keith H James on May 31, 2016
Content may be subject to copyright.
The Caribbean – overlooked hydrocarbon potential on N America’s doorstep
Keith H. James, Consultant Geologist, Plaza de la Cebada, 3, Covarrubias, 09346
Burgos, Spain, tel. (34) 947 406481, khj@kjgeology.com
Recent huge discoveries below salt in the Gulf of Mexico and Brazil show that
much remains to be learned about deepwater areas. They also disprove the notion that
the elephants have all been found. Another paradigm that needs to fall is the 40 year-
old idea that the Caribbean Plate formed in the Pacific and migrated between the
Americas. This understanding implies that the plate consists mostly of oceanic crust
and volcanic arc rocks -- not many think about hunting for oil in deep water here.
However, there is much evidence (continental rocks, continental gravity densities,
seismic velocities and crustal thicknesses, abundant high silica rocks and regional
tectonic fabric) that continental crust is abundant (Figs. 1, 2).
NORTH AMERICA
shelf edge
plate boundary
5°
20°
35°
-55°
Gulf of
Mexico
Lesser
Antilles
Leeward
Antilles
Greater Antilles
Chortis
-100°
C
SOUTH AMERICA
CENTRAL
AMERICA
ATLANTIC
PACIFIC
"plateau"
.
evidence of continental
crust
J
PR
CR
B
BB
N
G
H
P
Maya
HO
FB
T
NR
Figure 1. Middle America. On the Caribbean Plate (heavy dashed line) only
Chortis is supposed to carry continental crust. Red asterisks locate indications of
other continental fragments. B – Belize; BB – Barbados; C – Cuba; CR – Costa Rica;
FB – Florida-Bahamas; G – Guatemala; H – Hispaniola; HO – Honduras; J – Jamaica;
N – Nicaragua; NR – Nicaragua Rise; P – Panamá; PR – Puerto Rico; T -
Tehuantepec.
Middle America, including the Caribbean Plate, exhibits a regional NE and
NW structural pattern (Fig. 2). The former reflects Triassic-Jurassic rift/drift
reactivation of Palaeozoic sutures and is well known in N and S America. The latter
is the trend of ocean fractures and major intra-continental faults active during
northwestward separation of N America from Gondwana. Major Jurassic faults
crossing the Maya and Chortis blocks in the west (Fig.1) remain parallel to the
regional NE trend (Fig. 2) and show that they have not rotated, as commonly
believed. Continental rocks are exposed on mainland Chortis but this block extends
to Jamaica via the Nicaragua Rise and forms a large part of the western Caribbean.
Its presence there precludes migration of a Pacific plate both geometrically and
geologically.
Carolina
Trough
"Caribbean Plateau"
magnetic lineations
Bahamas FZ
Blake Spur FZ
Carolina FZ
YB
CT
Gravity outline
"oceanic "crust
5°
35°
-100°
Cuba FZ
BRR
RGR
MR
Seismic
Line
MAT
"oceanic"
crust
BR
AR
Figure 2 Middle America NE and NW structural fabric. Red lines highlight
known Triassic-Jurassic rifts. Green lines indicate mapped structural trends indicated
by magnetic anomalies. The blue line marks the SE limit of the Caribbean “Plateau” –
the Central Venezuela FZ (Fig. 3). The NE trend over the "plateau" area (Fig. 1)
reflects basement structures and shows that it shared regional geological history. AR
– Aves Ridge; BR - Beata Ridge, BRR – Blue Ridge Rift; CT – Cayman Trough; FZ
– fracture zone; MAT – Middle America Trench; MR - Mississippi Rift, OR –
Ouachita Rift, RGR - Río Grande Rift, YB - Yucatán Basin.
Part of the Caribbean Plate is up to 20 km thick. DSDP drilling encountered
Turonian basalts at the top of this Caribbean "oceanic plateau" (Fig. 1), which is
generally seen to be the result of Cretaceous oceanic plate thickening over a hot spot
or mantle plume in the Pacific. If this were true, the plateau would exhibit a radial
structural pattern. Instead, it shares the regional NE trend of Middle America – an
unlikely coincidence if it had formed in the Pacific
Seismic data over the plateau (Fig. 3) reveal a deep architecture that repeats
the form of distal basins along the eastern seaboard of N America from Baltimore
Canyon to the Blake Plateau. These asymmetric basins contain wedges of Triassic
red beds and Jurassic – Cretaceous sediments, source rocks and salt. They share the
Gulf of Mexico history of Mesozoic extension. The Caribbean "plateau" is probably
their southern continuation. Instead of blocks of vertical igneous dykes flanked by
wedges of volcanic flows and volcaniclastic sediments, with seamounts locally at the
seafloor (current understanding) it probably consists of 40 km wide continental blocks
flanked by 100 km wide wedges of Triassic- Jurassic clastic sediments, including
source rocks and salt, overlain by Jurassic - Cretaceous carbonates. Smoothness and
great lateral extent of seismic Horizon B” (Fig. 3) and vesicularity of cored Turonian
basalts suggest they were shallow/sub-aerial, perhaps causing restriction that
produced prolific source rocks known along northern S America. Supposed
seamounts push up through overlying upper Cretaceous – Recent sediments are very
similar in appearance to Sigsbee salt knolls of the Gulf of Mexico. At least some are
salt diapers, with indications of adjacent rim synclines,
Other parts of the Caribbean Plate, west and southeast of the plateau, resemble
oceanic crust (Fig. 3, Rough Horizon B"). However, they are abnormally thin (3- 4
km) and do not manifest spreading magnetic anomalies. They are likely to be areas of
extremely attenuated continental crust or serpentinized upper mantle (serpentinite is
remarkably abundant around the plate margins). The only spreading anomalies
(Miocene – Recent) in the whole of Middle America occur in the central 300 km of
the Cayman Trough.
NW SE
?Salt diapir
Triassic-
Pz basement
oceanized crust
M-U
Jur
U-Jur -
L - Cret
M - U Cret
Upper Eocene - Recent
Moho
?
?
SB" A"
RB"
Sea floor
?
CVFZ
50 km
7
8
9
Sec twt
Figure 3. Interpretation of seismic line over the Caribbean Plateau (located on Fig. 2).
The interpretation suggests that Caribbean, Gulf of Mexico and eastern N America
basin histories were similar. Triassic-Jurassic rifting accommodated continental –
shallow marine sediments and salt. Drifting introduced open marine Jurassic –
Cretaceous sediments. Late Cretaceous extension resulted in shallow marine -
subaerial flows over the Caribbean plateau, forming smooth Horizon B" (SB") and
serpentinization of adjacent mantle, forming rough Horizon B" (RB"). Horizon A" is
the Middle Eocene contact between chert and unconsolidated sediments. CVFZ –
Central Venezuelan Fault Zone (Fig. 2).
Instead of bearing a “foreign” Caribbean Plate, Middle America shows an
internal geological integrity that reflects ancient basement structures extended by drift
of North America away from and South America. Proximal margins subsided
gradually, accommodating carbonate platforms many kilometres thick (Florida-
Bahamas, Tehuantepec, Campeche-Maya). More distal areas foundered below the
deeper Gulf of Mexico and the Caribbean. Areas of greatest extension suffered
“oceanization”.
Caribbean geology is related to that of the Gulf of Mexico and marginal basins
along the eastern flanks of the Americas. The area lies between the giant oil
provinces of the Gulf of Mexico and northern S America. It probably carries a wide
variety of hydrocarbon plays involving Jurassic and Cretaceous source rocks. The
risk is that igneous activity over-matured these in some areas. However, live oil stain
occurs in fractured rocks on Puerto Rico, oil is present on Hispaniola, Jamaica,
Belize, Guatemala, Honduras, Nicaragua, Costa Rica, Panamá and Barbados. Some is
thought to come from Tertiary sources, but oils of Guatemala, Belize, Jamaica, Costa
Rica and Barbados have Jurassic or Cretaceous chemical signatures. This 2.5 million
square kilometre, virtually unexplored area lies close to N America and is governed
by friendly nations.