ArticlePDF Available

Chicxulub Crater: A possible Cretaceous/Tertiary boundary impact crater on the Yucat??n Peninsula, Mexico

  • Chicxulub Geosciences

Abstract and Figures

We suggest that a buried 180-km-diameter circular structure on the Yucatan Peninsula, Mexico, is an impact crater. Its size and shape are revealed by magnetic and gravity-field anomalies, as well as by oil wells drilled inside and near the structure. The stratigraphy of the crater includes a sequence of andesitic igneous rocks and glass interbedded with, and overlain by, breccias that contain evidence of shock metamorphism. The andesitic rocks have chemical and isotopic compositions similar to those of tektites found in Cretaceous/Tertiary (K/T) ejecta. A 90-m-thick K/T boundary breccia, also containing evidence of shock metamorphism, is present 50 km outside the crater's edge. This breccia probably represents the crater's ejecta blanket. The age of the crater is not precisely known, but a K/T boundary age is indicated. Because the crater is in a thick carbonate sequence, shock-produced CO 2 from the impact may have caused a severe greenhouse warming.
Content may be subject to copyright.
Figure 1. Plate tectonic
reconstruction of Carib-
bean region near K/T
time modified from Pin-
dell and Barrett (1990).
Bold lines—fault zones
between plates; arrows
and triangles indicate
relative motions. Solid
zones; open triangles—
thrusting. V pattern—sub-
duction-related island-
arc volcanism. Dashed
line—paleoshoreline on
North American conti-
nent. Diagonal-rule pat-
tern—areas of possible
impact-wave deposits.
Dots—Deep Sea Drilling
Project sites: impact-
wave deposits are found
at sites 151, 153, and
603B. Stars—positions of -50-cm-thick K/T ejecta layers found at sites in Haiti and Mexico.
Circle—Chicxulub crater on Yucatan platform.
Chicxulub Crater: A possible Cretaceous/Tertiary
boundary impact crater on the
Yucatan Peninsula, Mexico
Alan R Hildebrand*
Department of Planetary Sciences, University of Arizona, Tucson, Arizona 85721
Glen T. Penfield
Aerogravity Division, Carson Services Inc., 32A Blooming Glen Road, Perkasie, Pennsylvania 18944
David A. Kring
Department of Planetary Sciences, University of Arizona, Tucson, Arizona 85721
Mark Pilkington
Geophysics Division, Geological Survey of Canada, 1 Observatory Crescent, Ottawa, Ontario K1A 0Y3, Canada
Antonio Camargo Z.
Gerencia Exploracion, Petroleos Mexicanos, Avenida Marina Nacional 329, Mexico D.F. 11311, Mexico
Stein B. Jacobsen
Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge,
Massachusetts 02138
William V. Boynton
Department of Planetary Sciences, University of Arizona, Tucson, Arizona 85721
We suggest that a buried 180-km-diameter circular structure on the Yucatan Peninsula,
Mexico, is an impact crater. Its size and shape are revealed by magnetic and gravity-field
anomalies, as well as by oil wells drilled inside and near the structure. The stratigraphy of the
crater includes a sequence of andesitic igneous rocks and glass interbedded with, and overlain
by, breccias that contain evidence of shock metamorphism. The andesitic rocks have chemical
and isotopic compositions similar to those of tektites found in Cretaceous/Tertiary (K/T)
ejecta. A 90-m-thick K/T boundary breccia, also containing evidence of shock metamorphism,
is present 50 km outside the crater's edge. This breccia probably represents the crater's ejecta
blanket. The age of the crater is not precisely known, but a K/T boundary age is indicated.
Because the crater is in a thick carbonate sequence, shock-produced CO
from the impact may
have caused a severe greenhouse warming.
The debate concerning the postulated impact
at the Cretaceous/Tertiary (K/T) boundary
(Alvarez et al., 1980) may be resolved by the
discovery of the impact site and/or the thick
proximal deposits of the impact (Hildebrand
and Boynton, 1990a, 1990b). An -50-cm-thick
K/T boundary ejecta layer in Haiti and prox-
imal impact-wave deposits in the Caribbean re-
gion suggest that the K/T boundary impact
occurred between North and South America.
Circular anomalies, -200 km in diameter, in
both magnetic and gravity fields (with asso-
ciated andesitic rocks) on the northwestern mar-
gin of the Yucatan peninsula of Mexico (Fig. 1)
have been interpreted as representing a volcanic
center (Lopez Ramos, 1975) or an impact crater
with associated extrusive material (Penfield and
Camargo, 1981). We describe geophysical, strat-
igraphic, and petrologic evidence indicating that
this structure is a large impact crater of possible
K/T boundary age.
The circular structure is buried in the middle
of the Yucatan carbonate platform in a region of
*Present address: Geological Survey of Canada,
Geophysics Division, Observatory Crescent, Ottawa,
Ontario KIA 0Y3, Canada.
anomaly might be best fit by a center slightly
farther northeast. The gravity-field anomaly is
truncated to the north by an east-northeast-
trending lineament that crosses the Yucatan plat-
form north of the present coastline. A negative
anomaly trails -100 km to the south from the
circular anomaly. Its internal circular structure is
disrupted near both the truncating lineament
and the southward-extending trough.
Total magnetic-field data (Penfield and Ca-
margo, 1981; Lopez Ramos, 1975) show -210-
km-diameter, circular, dipolar anomalies with
large horizontal gradients and some concentric
structure nearly coincident with the gravity
anomaly. Large-amplitude, short-wavelength
anomalies (up to -1000 nT) occur over the cen-
tral gravity high, but extend farther, to a radius
of -35 km. An outer zone of weaker (5 to 20 nT)
short-wavelength anomalies extends to a radius
of -105 km, but has an irregular margin. The
subsequent tectonic quiescence. Bouguer gravity
data show an -180-km-diameter, circular, 30
mgal, negative anomaly (Fig. 2) similar in shape
to those found over large impact craters (Fig. 3).
A center 10 km east of Progreso, near the town
of Chicxulub Puerto, best fits a 20 mgal central
high (20 km radius) and two internal concentric
lows (35 and 60 km radii); the margin of the
GEOLOGY, v. 19, p. 867-871, September 1991
Figure 2. Contour plot (contour interval = 2 mgal) of Bouguer gravity data (Gravity Anomaly Map
Committee, 1988) covering northwest corner of Yucatan Peninsula, Mexico. Outermost heavily
dashed circle—margin of circular negative gravity anomaly; two other circles—concentric lows
within negative anomaly; cross—center of anomaly. Dotted line—east-northeast-trending re-
gional lineament that truncates anomaly. Two light dashed lines indicate positions of profiles
shown in Figure 3. Dark solid line (top) shows approximate position of seismic reflection profile.
Exploration wells drilled by PetrOleos Mexicanos: C-1 = Chicxulub-1; S-1 = Sacapuc-1; Y-1, Y-2,
Y-6 = Yucatan-1, 2, and 6; T-1 = Ticul-1.
magnetic-field anomalies extend to the north
without significant disruption across the linea-
ment that truncates the gravity anomaly. The
central anomalous zone is slightly elongated in a
northwest-southeast direction. Modeling of the
magnetic-field anomalies places the top of the
magnetic source bodies at a depth of -1100 m
(Penfield and Camargo, 1981).
The subsurface stratigraphy of the northern
Yucatan peninsula is known primarily from pe-
troleum exploration drillholes (Murray and
Weidie, 1967; Lopez Ramos, 1975, 1983;
Marshall, 1974; A. E. Weidie, Jr., et al., unpub-
lished cross section). A structurally uncompli-
cated platform sequence of nearly horizontal
Lower Cretaceous to Quaternary carbonates
and evaporites overlies a poorly known crystal-
line basement of probable Paleozoic age. In the
northern part of the peninsula the platform se-
quence is at least 3500 m thick. Three deep
exploration wells (1527 to 1631 m total depth)
have been drilled within the margins of the geo-
physical anomalies (Fig. 2). The upper sequence
ranges from Pleistocene to Paleocene in age and
is a flat-lying, conformable sequence with no
known significant stratigraphic breaks (Fig.
The sedimentary facies and fauna reported from
these wells indicate a deeper-water environment
than that found elsewhere on the platform. The
rocks are fossiliferous limestones and marls with
minor shale, bentonite, and chert. The unit
underlying the Tertiary sequence is composed of
fossiliferous limestone, marl, shale, and minor
bentonite, and has been previously dated as Late
The wells penetrated coarse breccias and clas-
tic and andesitic igneous rocks at depth (Fig. 4).
In wells C-1 and S-1, limestone and bentonite
breccias (containing Cretaceous fossils), are in-
terbedded with marlstone, shale, and sometimes-
dolomitic limestones. Thin intercalations of an-
desitic glass are present in the lower part of this
unit. Well Y-6 recorded sandstone interbedded
with shale, marl, and bentonite at this level. Thick
units of andesitic glass underlie the breccias in
wells C-1 (with minor interbedded tuffs) and
S-1. Well Y-6 intersected microcrystalline ande-
sitic rock before bottoming in laminated anhy-
drite. Well C-1 also intersected microcrystalline
andesitic rocks below the andesitic glass unit.
These andesitic igneous rocks occur only in-
side the circular zone of the geophysical anoma-
lies; several other nearby drillholes (Fig. 2) have
not encountered these rocks. Possible analogues
to the limestone and bentonitic breccias com-
pose the uppermost Cretaceous stratigraphy in
other holes. For example, the Yucatan-2 (Y-2)
well, located 135 km southeast of the center of
Figure 3. Two east-northeast Bouguer gravity
profiles (parallel to coastline) across Chic-
xulub structure showing symmetrical negative
anomaly with central high (see Fig. 2 for posi-
tions of profiles). Profiles are drawn through
data points spaced at -6 km intervals. Re-
gional field decreases from east to west, as
shown by dashed line. Bottom profile is lo-
cated -10 km south of upper (central) profile.
Upper profile has been displaced 25 mgal
above its true position to separate the two.
Center of crater, two concentric gravity lows,
and suggested crater rim are indicated along
central profile. Profile from Manicouagan cra-
ter shown for comparison is from Sweeney
(1978); regional background was removed.
Vertical and horizontal scales on Manicoua-
gan profile have been expanded for compari-
son purposes.
the anomalies (Fig. 2), intersected a unit of ben-
tonitic limestone breccia from 240 to 330 m.
To investigate the origin of the andesitic igne-
ous rocks and carbonate breccias within the area
of the circular anomalies, we studied some of the
few remaining samples from petroleum explora-
tion using optical microscopy, X-ray diffraction
(XRD), and electron-microprobe techniques
(Kring et al., 1991).
Sample Y6 N14 (Fig. 5A) came from a depth
of 1208 to 1211 m in the Y-6 well (Fig.
a predominantly sandstone unit. However, this
sample is a partly chloritized, polymict breccia
with angular to subrounded igneous and sedi-
mentary clasts in a fine-grained calcite matrix
(-25%). The sedimentary clasts (-5%) are an-
hydrite and carbonate rocks; there are also trace
amounts of small polycrystalline quartz clasts.
The igneous clasts (-65%) are dominated by a
microcrystalline groundmass consisting of alkali
feldspars (Ab
to Ab
), pla-
gioclase feldspars (An
), and augite
1 1
). About half of the igneous
clasts contain lithic inclusions and/or ropy-
September 1991
swim Limestone
....... ........._ ..........
? -------
inne. la
a Nom...
Figure 4. Stratigraphic columns from three deep interior wells in Chicxulub crater (see Fig. 2).
Vertical exaggeration x10. Drillholes are spaced according to their distance from estimated
center of structure. Arrows show locations of samples from well Y-6, together with sample
numbers. Ages have not
given to units at base of drilled section; these units have pre-
viously been regarded as Upper Cretaceous.
0.7- 0.8
2.4- 3.8
4.7- 5.7
0.1- 0.2
2.4- 3.6
1.0- 1.8
63.1 ±2.1
0.7 ±0.1
15.2 ±0.3
7.3 ±1.7
2.7 ±0.3
5.4 ±0.4
63.2 /60.5
0.4 / 0.4
12.6 /13.6
10.2 /10.5
3.1 / 3.2
4.5 / 5.0
4.0 / 4.7
1.9 / 1.9
0.08/ 0.1
3.6 ±0.3
1.6 ±0.1
0.1 / 0.1
Note: All analyses in weight percent. Sample G6: glass from Haitian ejecta
layer residue (this work); 90G RANGE, 11M: Haitian glasses described by Izett
et al. (1990); BE: average Haitian glass (lo variation; Sigurdsson et al.,
1991); N17: slightly-altered, andesitic, melt-rock sample from the Y-6 well,
Chicxulub crater. All analyses by electron microprobe, except N17 which
analysed by X-ray fluorescence (reported on a sulfur-free basis). No numbers
- not determined.
* Values given are averages of multiple analyses.
textured phyllosilicates. Quartz grains in two of
these xenoliths exhibit multiple sets of planar
elements that are indicative of shock metamor-
phism. Quartz crystals (up to 1.25 mm long)
with up to eight sets of planar elements are also
present in grain residues of three breccia splits
(Fig. 5B). Debye-Scherrer XRD studies of single
grains confirm the visual identification of shock
deformation (Florz and Quaide, 1973) and indi-
cate that the quartz grains have been subjected
to shock pressures ranging from --10 to 20 GPa.
Sample Y6 N17 came from between 1295.5
and 1299 m in the Y-6 well (Fig. 4) and is
compositionally similar to andesites (Table
1). It
consists predominantly of a microcrystalline
groundmass of plagioclase feldspars (An30Ab64
to An
), alkali feldspars (Ab
to Ab
), and augite
to Wo
)• Minor
amounts of magnetite, ulvospinel, and apatite
occur interstitially. Large quartz grains or aggre-
gates of
grains are scattered throughout
the rock, each surrounded by coronas of
medium-grained augite and feldspar that appar-
ently nucleated on the preexisting quartz. Sim-
ilar coronas are common in impact-melt rocks
(e.g., Grieve, 1975), although they have also
been observed around xenoliths and quartz xe-
nocrysts in volcanic andesites and basalts (Sato,
1975). This rock lacks plagioclase phenocrysts,
but does contain pods of microcrystalline feld-
spar. Small pockets of secondary anhydrite and
calcite and quartz veins pervade the sample, in-
dicating that the unit has been altered.
Sample Y2 N6 is a series of core fragments
taken from 301 to 303 m in well Y-2 (Fig. 2).
The sample is from a 90-m-thick bentonitic
breccia, which is the uppermost Cretaceous unit
in the well (A. E. Weidie, Jr. et al., unpublished
cross section). The rock is a poorly sorted poly-
mict breccia with angular to rounded fragments
of calcareous and dolomitic limestones (some-
Figure 5. A: Polished slab showing polymict
breccia sample Y6 N14. Specimen is 4 cm
Shocked quartz grain (0.32 mm
across) from polymict breccia Y6 N14. Grain
shows eight sets of lamellae when rotated: two
sets are visible
ejecta clast in
polymict breccia sample Y2 N6. Note con-
torted internal fabric and crosscutting gypsum
veins. Scale shows centimetre divisions.
times fossiliferous), anhydrite, and marl; there is
also one 5-cm-diameter, crudely laminated, disc-
shaped clast of very poorly ordered smectite
(Fig. 5C). Grain residues from two different
samples of the breccia contain quartz grains with
rare grains (up to 1.1 mm long) containing sin-
gle and multiple planar lamellae typical of shock
deformation. The large smectitic clast contains
-2% quartz and feldspar grains that also have
single and multiple planar lamellae typical of
shock deformation. Debye-Scherrer XRD stud-
ies on individual quartz and feldspar grains
confirm the visual identification of shock
Because the rocks that cause the geophysical
anomalies are deeply buried, the shape of the
GEOLOGY, September 1991
presumed circular structure is not well known.
The K/T boundary within the structure is de-
pressed —600 to 1100 m relative to its —500 m
depth in the Ticul-1 (T-1) well (Lopez Ramos,
1975), located 5 km outside the suggested
margin of the structure. A multichannel seismic
reflection line —45 km north of Progreso (Fig. 2)
shows that a rough acoustic reflector, which
probably corresponds to the K/T boundary, oc-
curs at a depth of —1500 m (PetrOleos Mexica-
nos, unpublished data). These indicators of a
depressed K/T boundary in the area of the cir-
cular anomalies, together with the presence of
relatively deep water facies, suggest that a basin
existed there in early Tertiary time. No obvious
topographic or bathymetric expression of the
circular structure exists now, although the struc-
ture may influence the near-surface ground-
water regime (Pope et al., 1991).
We believe that the geophysical, stratigraphic,
and petrologic evidence described here strongly
indicates the presence of a buried impact crater.
The circular negative Bouguer-gravity anomaly,
with a central high and two concentric lows, is
consistent with an —180-km-diameter peak-ring
crater. The andesitic glasses and microcrystalline
rocks interbedded with polymict breccias are
probably a sequence of interbedded impact-melt
rocks and impact breccias. Assuming a specific
gravity contrast of 0.3 g/cm
(based on values
determined for breccia sample Y6 N14 vs. the
overlying sediments), an —2 km breccia thick-
ness would be required to produce the observed
—25 mgal negative gravity-field anomaly.
Therefore, the 200-450-m-thick breccias overly-
ing the andesitic rocks may produce the rever-
sals in the gravity profiles by forming two peak
rings, but most of the anomaly must be the result
of some other mass deficiency, such as fractured
basement beneath the crater. The breccias and
the andesitic rocks may be the cause of the
magnetic-field anomalies. Samples Y6 N14 and
N17 have magnetic susceptibilities of 2.5 x 10
and 1 x 10
(cgs units), respectively, which is in
contrast to the 10
to <10
(cgs units) suscep-
tibilities of the overlying sediments. Therefore,
the andesitic rocks may produce, at least in part,
the central high-amplitude anomalies, whereas
the intracrater breccias and proximal ejecta may
produce the small-amplitude anomalies that ex-
tend —15 km past the margin of the gravity
anomaly (and suggested crater rim). The depres-
sion of the K/T boundary by —600 m indicates
the presence of a basin with a depth consistent
with the strength-limited depth of —500 m ex-
pected for terrestrial impact craters (Melosh,
The Y6 N14 and Y2 N6 polymict breccias
contain shocked quartz, indicating production
by impact. The presence of both shocked and
unshocked material in the Y6 N14 breccia and
the absence of a glassy matrix (although a glass
matrix could have been altered) suggests that the
unit is a sedimentary breccia, which is consistent
with a marine impact. The underlying Y6 N17
rock does not contain unambiguous evidence of
shock-induced melting, but the presence of
quartz and quartz-aggregate xenoliths, and the
absence of plagioclase phenocrysts and ortho-
pyroxene, are unusual for volcanic andesites.
Microcrystalline melt rocks, apparently resulting
from impact-melt bodies of sufficient size to re-
crystallize, are known at much smaller impact
craters, such as the 28-km-diameter Mistastin
Lake crater (Grieve, 1975). The required vol-
umes of melt could easily be produced at a
crater of this size; using a melt-volume scaling
relation (Melosh, 1989) and a transient crater
diameter of 110 km, we calculate a lower limit
to the ratio of melt volume to the displaced-mass
volume of 0.3. The 6 to 8 m of anhydrite inter-
sected at the base of 380 m of andesitic rocks in
well Y-6, located —50 km from the crater cen-
ter, may indicate that this is the outer and
thinner part of the melt sheet.
We suggest that the breccias recorded at the
K/T boundary exterior to the crater, such as the
90-m-thick breccia in well Y-2, represent the
proximal ejecta blanket, because the Y2 N6
breccia contains evidence of shock metamor-
phism. The large smectitic clast is probably al-
tered impact-melt ejecta, which may be analo-
gous to Muong Nong tektites or to the Ries
crater suevite bombs. The ejecta was probably
mixed with locally derived sediment when it
was deposited and/or was disturbed by impact
waves. The back surge filling the crater may also
have extensively modified parts of the ejecta
Although the available stratigraphic informa-
tion provides some bounds, the age of the crater
is not precisely known. Former work suggested
a Late Cretaceous age for the 60 to 170 m of
limestone and marl overlying the presumed im-
pact breccias and melt rocks (Lopez Ramos,
1975). However, G. Keller and W. Sliter inde-
pendently determined a late Paleocene (P3) age
(based on foraminifera) for sample Y6 N12
(Fig. 4) from the limestone-marl unit (from
1000 to 1003 m depth), although the preserva-
tion is not good. Therefore, the earlier age as-
signment is probably invalid, and the top of the
breccias could be of K/T boundary age. In addi-
tion, the 90-m-thick boundary breccia in well
Y-2 probably corresponds to the crater's prox-
imal ejecta blanket, thus indicating that the
crater formed at the KIT boundary.
The size and location of the Chicxulub struc-
ture come close to satisfying the characteristics
necessary for the KIT crater (Hildebrand and
Boynton, 1990b). Because its calculated maxi-
mum excavation depth is —15 km (Melosh,
1989) and the crust under the Yucatan platform
is at least 30 km thick (Ewing et al., 1960), the
crater could have excavated only continental
crust. It is an attractive candidate for supplying
the shocked quartz and alkali-feldspar grains
found in the boundary layers (Izett, 1990), and it
is well located to produce the observed size dis-
tribution and fluence of shocked grains, which
are largest at Caribbean K/T sites (Hildebrand
and Boynton, 1990a). The proportion of the
shocked grains in the mineral residue from the
Y6 N14 breccia and the Y2 N6 ejecta clast are
27% and 31%, respectively, within the range of
12% to 47% reported for 12 K/T sites (Izett,
The Chicxulub crater is also an attractive
source for the K/T boundary tektites (Izett et al.,
1990; Sigurdsson et al., 1991), particularly be-
cause the Haitian K/T tektites are deficient in
silica relative to most tektites (Koeberl, 1986),
and the Chicxulub crater has melt rocks of the
necessary intermediate composition (Table 1).
The composition of the Chicxulub andesitic
rock is within the range observed for the K/T
tektites, except for its lower Al
03 and TiO
content. In addition, the carbonate rocks of the
Yucatan platform are a good candidate source
for the high-Ca tektites reported from the Hai-
tian K/T sites (Sigurdsson et al., 1991).
However, the Chicxulub crater may not be
the sole source of the boundary layers, because
isotopic data (Shaw and Wasserburg, 1982)
suggest that a mantle component occurs in the
boundary layers, and the presence of unaltered
pyroxene spherules (Smit, 1990) establishes that
there is at least a small ultramafic component.
Another potential difficulty is that the Chic-
xulub andesitic rock Y6 N17 yields an
Ma) of —5.0, which is lower than values of —2.9
(65 Ma) found in altered boundary clays
(Hildebrand and Boynton, 1988) or —2.8
(66 Ma) found in tektite glass (Promo and lzett,
1991). If the Chicxulub crater were the source of
the boundary ejecta, some Nd isotopic hetero-
geneity would be required in the andesitic melt
rocks. However, the
(65 Ma) of the andesitic
rock (+55) is similar to that of the Haitian tek-
tites (+62).
The Chicxulub crater is well located to pro-
duce the known K/T boundary ejecta. This
crater is approximately equidistant between the
two thickest known deposits, the 0.5-1.2-m-
thick K/T ejecta found on Haiti (Hildebrand
and Boynton, 1990b), which was to the south-
east at K/T time, and the 0-1.0-m-thick ejecta
layer found in northeastern Mexico by
A. Montanari, N. Swinburne, and W. Alvarez
(W. Alvarez, personal commun.). The Chic-
xulub crater might not have produced the
observed suite of impact-wave deposits (Fig. 1),
GEOLOGY, September 1991
because it formed on a shallow-water platform a
minimum of -200 km from the deep sea, and
the size of impact-induced waves is limited by
the water depth at the impact site. Nevertheless,
because the Chicxulub impact would be seismi-
cally equivalent to a magnitude 10 to 11 earth-
quake (McKinnon, 1982), it may have triggered
the formation of the deep-water slump and
turbidity-current deposits (which may be over-
lain by crater ejecta) observed at the K/T
boundary at Deep Sea Drilling Project (DSDP)
Sites 94, 95, 536, and 540, adjacent to the
Campeche bank (Fig. 1; Buffler et al., 1984).
The coarse boundary deposits in the trough
present at KIT time between Cuba and the Ba-
hamas may be seismically triggered slumps, as
suggested by Pszczolkowski (1986). However, it
might have been difficult for this impact to pro-
duce the distant impact-wave deposits, such as at
Brazos River, Texas, or DSDP Sites 603B, 151,
and 153, if the ocean on the Yucatan platform
was too shallow at K/T time; therefore, a
nearby, deep-water impact may have occurred
at the same time.
The Chicxulub impact, having presumably
produced the largest impact crater on Earth,
must have caused a mass extinction, assuming
that any impact can do so. In addition to prompt
lethal effects, it should have produced a dra-
matic greenhouse warming by the shock produc-
tion of CO
from the >3-km-thick carbonate
target rocks, as suggested by O'Keefe and
Ahrens (1989). Crater scaling relations (Melosh,
1989) and the size of the Chicxulub crater sug-
gest that an order of magnitude increase in CO
above the current atmospheric inventory would
have occurred. A temperature increase of -10
°C for 10
to 10
years could have resulted
(O'Keefe and Ahrens, 1989), causing an ex-
tended period of extinctions. The period of
warmer climate could also allow for increased
continental erosion to produce the K/T bound-
Sr spike (Hess et al., 1986).
The Chicxulub crater is the largest probable
impact crater on Earth. Its position and target-
rock composition satisfy many of the character-
istics required for the K/T crater, and it may
have a K/T boundary age. This impact may
have caused the K/T extinctions.
Alvarez, L.W., Alvarez, W., Asaro, F., and Michel,
H.V., 1980, Extraterrestrial cause for the Creta-
ceous/Tertiary extinction: Science, v. 208,
p. 1095-1108.
Buffler, R.T., Schlager, W., and others, 1984, Initial
reports of the Deep Sea Drilling Project, Volume
77: Washington, D.C., U.S. Government Print-
ing Office, 747 p.
Ewing, J., Antoine, J., and Ewing, M., 1960, Geo-
physical measurements in the western Caribbean
Sea and in the Gulf of Mexico: Journal of Geo-
physical Research, v. 65, p. 4087-4126.
Gravity Anomaly Map Committee, compilers, 1988,
Gravity anomaly map of North America:
Boulder, Colorado, Geological Society of Amer-
ica, Continent-Scale Map no. 2,4 sheets.
Grieve, R.A.F., 1975, Petrology and chemistry of the
impact melt at Mistastin Lake crater, Labrador:
Geological Society of America Bulletin, v. 86,
p. 1617-1629.
Hess, J., Bender, M.L., and Schilling, J-G., 1986, Evo-
lution of the ratio of strontium-87 to strontium-
86 in seawater from Cretaceous to present:
Science, v. 231, p. 979-984.
Hildebrand, A.R., and Boynton, W.V., 1988, Proven-
ance of the K/T boundary layers,
Global ca-
tastrophes in Earth history: An interdisciplinary
conference on impacts, volcanism, and mass
mortality [abs.]: Lunar and Planetary Institute
Contribution 673, p. 78-79.
1990a, Locating the Cretaceous/Tertiary bound-
ary impact crater(s): Eos (Transactions, Ameri-
can Geophysical Union), v. 71, p. 1424-1425.
1990b, Proximal Cretaceous-Tertiary boundary
impact deposits in the Caribbean: Science,
v. 248, p. 843-847.
Harz, F., and Quaide, W.L., 1973, Debye-Scherrer
investigations of experimentally shocked silicates:
The Moon, v. 6, p. 45-82.
Izett, G.A., 1990, The Cretaceous/Tertiary boundary
interval, Raton Basin, Colorado and New Mex-
ico, and its content of shock-metamorphosed
minerals; evidence relevant to the K-T boundary
impact-extinction theory: Geological Society of
America Special Paper 249,100 p.
Izett, G.A., Maurrasse, F.J-M.R., Lichte, F.E.,
Meeker, G.P., and Bates, R., 1990, Tektites in
Cretaceous-Tertiary boundary rocks on Haiti:
U.S. Geological Survey Open-File Report OF-
90-635, 31 p.
Koeberl, C., 1986, Chemistry of tektites and impact
glasses: Annual Review of Earth and Planetary
Sciences, v. 14, p. 323-350.
Kring, D.A., Hildebrand, A.R., and Boynton, W.V.,
1991, The petrology of an andesitic melt-rock
and a polymict breccia from the interior of the
Chicxulub structure, Yucatan, Mexico, in XXII
Lunar and Planetary Science Conference ab-
stracts: Houston, Texas, Lunar and Planetary
Science Institute, p. 755-756.
Lopez Ramos, E., 1975, Geological summary of the
Yucatan Peninsula,
Nairn, A.E.M., and Stehli,
F.G., eds., The ocean basins and margins, Vol-
ume 3-The Gulf of Mexico and the Caribbean:
New York, Plenum, p. 257-282.
-1983, Geologia de Mexico (third edition): Mex-
ico City, Universidad Nacional Autonoma de
Mexico, p. 269-301.
Marshall, R.H., 1974, Petrology of the subsurface
Mesozoic rocks of the Yucatan platform, Mexico
[MS. thesis]: New Orleans, Louisiana, University
of New Orleans, 97 p.
McKinnon, W.B., 1982, Impact into the Earth's ocean
floor: Preliminary experiments, a planetary mod-
el, and possibilities for detection,
Silver, L.T.,
and Schultz, P.H., eds., Geological implications
of impacts of large asteroids and comets on the
Earth: Geological Society of America Special
Paper 190, p. 129-142.
Melosh, H.J., 1989, Impact cratering: A geologic
process: Oxford, Clarendon Press, 245 p.
Murray, G.E., and Weidie, A.E., Jr., 1967, Regional
geologic summary of Yucatan Peninsula,
Weidie, A.E., ed., Field trip to peninsula of
Yucatan, guide book (second edition): New
Orleans, Louisiana, New Orleans Geological
Society, p. 5-51.
O'Keefe, J.D., and Ahrens, T.J., 1989, Impact pro-
duction of CO
by the Cretaceous/Tertiary ex-
tinction bolide and the resultant heating of the
Earth: Nature, v. 338, p. 247-249.
Penfield, G.T., and Camargo Z., A., 1981, Definition
of a major igneous zone in the central Yucatan
platform with aeromagnetics and gravity,
Technical program, abstracts and biographies
(Society of Exploration Geophysicists 51st an-
nual international meeting): Los Angeles, Society
of Exploration Geophysicists, p. 37.
Pindell, J.L., and Barrett, S.F., 1990, Geological evo-
lution of the Caribbean region: A plate-tectonic
Case, J.E., and Dengo, G., eds.,
Caribbean region: Boulder, Colorado, Geological
Society of America, The Geology of North
America, v. H, p. 405-432.
Pope, K.O., Ocampo, A.C., and Duller, C.E., 1991,
Mexican site for K/T crater?: Nature, v. 351,
p. 105.
Premo, W.R., and Izett, G.A., 1991, Nd-Sr isotopic
signature of tektites from the K-T boundary on
XXII Lunar and Planetary Science Con-
ference abstracts: Houston, Texas, Lunar and
Planetary Science Institute, p. 1091-1092.
Pszczolkowski, Andrzej, 1986, Megacapas del Maes-
trichtiano en Cuba occidental y central: Polish
Academy of Sciences, Earth Sciences, Bulletin,
v. 34, p. 81-94.
Sato, H., 1975, Diffusion coronas around quartz xeno-
crysts in andesite and basalt from Tertiary vol-
canic region in northeastern Shikoku, Japan:
Contributions to Mineralogy and Petrology,
v. 50, p. 49-64.
Shaw, H.F., and Wasserburg, G.J., 1982, Age and
provenance of the target materials for tektites and
possible impactites as inferred from Sm-Nd and
Rb-Sr systematics: Earth and Planetary Science
Letters, v. 60, p. 155-177.
Sigurdsson, H., D'Hondt, S., Arthur, M.A., Bralower,
T.J., Zachos, J.C., van Fossen, M., and Channell,
J.E.T., 1991, Glass from the Cretaceous/Tertiary
boundary in Haiti: Nature, v. 349, p. 482-487.
Smit, J., 1990, Meteorite impact, extinctions and the
Cretaceous-Tertiary boundary: Geologie en Mijn-
bouw, v. 69, p. 187-204.
Sweeney, J.F., 1978, Gravity study of great im-
pact: Journal of Geophysical Research, v. 83,
p. 2809-2815.
Supported in part by NASA Grant NAG9-37. We
thank G. Keller and W. Sliter for paleontological stud-
ies. A. Weidie provided access to samples and unpub-
lished stratigraphic information. Petroleos Mexicans
allowed discussion of proprietary seismic reflection
data. X-ray fluorescence data are courtesy of A. Hein-
rich, R. Rousseau, and the Geological Survey of Can-
ada. Magnetic susceptibility data are courtesy of
G. Calderone and the U.S. Geological Survey.
Manuscript received February 26,1991
Revised manuscript received May 22,1991
Manuscript accepted May 30,1991
Reviewer's comment
Proposes the long-sought K/T crater-the "smoking gun."
GEOLOGY, September 1991
Printed in U.S.A.
... The Alvarez theory, published in Science (Alvarez et al. 1980), followed by a search for evidence and the discovery of the Chicxulub crater a decade later (Hildebrand et al. 1991), blended cosmic, terrestrial, biological, and anthropological history into a single narrative. ...
... That all changed in 1991 when satellite photography with ground-penetrating radar located a 110-milewide impact crater centered at Chicxulub, an ancient Mayan village near the northwest coast of the Yucatan Peninsula (Hildebrand 1991). Half the crater was situated on land; the other half lay under sea bottom sediment in the Gulf of Mexico, but the impact had occurred at a time when both the Yucatan Peninsula and the adjacent gulf were part of the same shallow Figure 2. In 1979 Walter Alvarez and his father discovered an iridium-rich layer at the K-Pg Boundary in the Apennines dated at 65 million years BP. ...
In 1979 geologists Luis and Walter Alvarez discovered a layer of iridium-rich rock in the Apennine Mountains dating from 66 to 65 million years BP, the time when dinosaurs went extinct. Their theory that an asteroid strike had caused this massive extinction remained speculative and controversial until the 1991 discovery of a telltale crater from a synchronous asteroid impact. The effects of this impact, centered at Chicxulub on the Yucatan Peninsula, were worldwide. Over the years, impact spherules were found at numerous sites, along with evidence of a massive tsunami throughout the Gulf of Mexico and adjacent coasts. From accumulating evidence, the theory was ratified in 2012, though many details remained unknown. However, a series of dramatic discoveries reported from 2019 to 2022 have led to a chronology of events both during and subsequent to the impact. Evidence for the rapid recovery and development of mammals has been found in the fossil record and, thus, the biological foundations of our own emergence. The final 2019 issue of Science (20 December) named this a “superyear” for studies of the Cretaceous-Paleogene (K-Pg) extinction as the runner-up science “breakthrough of the year.” Through these separate discoveries, a coherent hour-by-hour narrative has emerged, marking the onset of the Cenozoic era and providing a foundation for the emergence of Homo sapiens.
... Eventually this process resulted in present distribution of the land masses: an east-west alignment in the Northern Hemisphere (Eurasia-North America) and three north-south alignments in the Southern Hemisphere (South America, Africa, Australasia) with Antarctica isolated at the South Pole (see Figure 2, maps). When Mesozoic life was devastated by the Cretaceous-Paleogene (K-Pg, formerly K-T) extinction 66 million years ago (Hildebrand et al., 1991), all the continents were isolated within oceans (Figure 2, bottom right map). Furthermore, all the low-lying continental areas had been extensively flooded by marine waters due to high sea levels caused by fast spreading mid-oceanic ridges (Seton et al., 2009). ...
Full-text available
Our understanding of global diversity patterns relies overwhelmingly on ecological and evolutionary correlates of latitude, and largely ignores longitude. However, the two major explanations of biodiversity patterns – energy and stability – are confounded across latitudes, and longitude offers potential solutions. Recent literature shows that the global biogeography of the Cenozoic world is structured by longitudinal barriers. In a few well-studied regions, such as South Africa’s Cape, the Himalayas and the Amazon-Andes continuum, there are strong longitudinal gradients in biodiversity. Often, such gradients occur where high and low past climatic velocities are juxtaposed, and there is clear evidence of higher biodiversity at the climatically-stable end. Understanding longitudinal biodiversity variations more widely can offer new insights towards biodiversity conservation in the face of anthropogenic climatic change.
... Starting in 1980, with the proposal by Alvarez et al. [20] of the large asteroid impact event as the cause of the most recent mass extinction marking the end of the Cretaceous ("66 Myr ago), the extra-terrestrial origin of mass extinction events was considered. The hypothesis was confirmed in 1991 by the discovery [29] of a crater 180 km in diameter in the Yucatan Peninsula, which is now considered the impact site of the asteroid or comet proposed by Alvarez et al. [20]. Although still debated (e.g., [30]), the 1991 discovery confirmed the possibility that astrophysical events can affect the evolution of life on Earth. ...
Full-text available
Can high-energy transient events affect life on a planet? We provide a review of the works that have tried to answer this question. It is argued that that gamma ray bursts, specifically those of the long class, are among the most dangerous astrophysical sources for biotic life and may exert evolutionary pressure on possible life forms in the universe. Their radiation can be directly lethal for biota or induce extinction by removing most of the protective atmospheric ozone layer on terrestrial planets. Since the rate of long gamma ray bursts is proportional to the birth rate of stars but is reduced in metal rich regions, the evolution of the “safest place” to live in our galaxy depended on the past 12 billion years of evolution of the star formation rate and relative metal pollution of the interstellar medium. Until 6 billion years ago, the outskirts of the galaxy were the safest places to live, despite the relatively low density of terrestrial planets. In the last 5 billion years, regions between 2 and 8 kiloparsecs from the center, featuring a higher density of terrestrial planets, gradually became the best places for safe biotic life growth.
... Map base adapted from Reguero and Goin (2021). bolide impact and sustained increased volcanism from a large igneous province (Hildebrand et al., 1981;Archibald et al., 2010;Schulte et al., 2010;Petersen et al., 2016;Schoene et al., 2019;Chiarenza et al., 2020;Morgan et al., 2022). These triggers would have resulted in numerous changes to the environment, including short-term cooling and a period of darkness, reduction in precipitation, and ocean acidification (Schulte et al., 2010;Morgan et al., 2022). ...
... 22 km. A hypothetical 10 -15 km large asteroid vaporised while striking the Earth surface emitting huge pressure clouds of dust (Hildebrand et al. 1991;Schulte et al. 2010). ...
... The exact cause of this mass extinction is intensely debated. In the last decades, numerous theories have been proposed to explain the mass extinction including an asteroid impact (Alvarez et al., 1980;Hildebrand et al., 1991;Alvarez et al., 1995), and widespread volcanism eruption (McLean, 1985;Courtillot et al., 1986;Vandamme et al., 1991). Timing and which one was most effective from these two catastrophic event remain debated (Schulte et al., 2010;Keller, 2014). ...
Full-text available
The Cretaceous/Paleogene (K/Pg) boundary marks the global extinction of many life forms, this boundary around Sulaimani city coincides with the boundary between Tanjero and Kolosh formations. These two units are flysch deposits of the Zagros Foreland Basin. This study focuses on petrography and clay mineralogy variations between these two units. Petrographic study, X-Ray Diffraction analysis, and Scanning Electron Microscope analysis were conducted on samples from different lithologies. The petrographic study of fine-grain lithologies shows that they are mainly wackestone without variation across the boundary. Sandstone petrography shows variation in framework components by increasing quartz, feldspar, and igneous fragments while argillaceous, carbonates, chert, and chalcedony fragments are decreased from Tanjero to Kolosh formations. Obtained results from XRD and SEM show that the clay mineral assemblage is dominated by corrensite (regularly interstratified chlorite/smectite) with discrete chlorite, smectite and traces of illite. The existence of these clay assemblage suggests that corrensite is the diagenetic product of smectite as it is an intermediate stage of smectite chloritization. Enrichment of precursor smectite and high content of unstable grains in sandstones across the K/Pg boundary is the result of low-intensity weathering in arid and seasonal climates of the source area. The smaller size of detrital smectite than other clay minerals is behind its enrichment in the deep marine basin for both Tanjero and Kolosh formations. Sandstone enrichment with sedimentary fragments in both formations related to uplifted sedimentary terrain in its hinterland, while variation across the boundary indicates gradual uplift of Zagros ophiolite zone in the early Paleogene.
Full-text available
The suevite (polymict melt rock-bearing breccia) composing the upper peak ring of the Chicxulub impact crater is extremely heterogeneous, containing a combination of relict clasts and secondary minerals. Using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS) and electron probe microanalysis (EPMA), we investigated the nature and occurrence of primary and secondary Fe-oxide and Fe-sulfide minerals to better understand hydrothermal trends such as mineral precipitation and dissolution, and to document the remobilization of Fe and associated siderophile elements within suevites. Large primary Fe-oxides (~20–100 µm) reveal decomposition and dissolution patterns, forming sub-micrometer to micrometer Fe-oxide phases. Secondary sub-micrometer Fe-oxide crystals are also visibly concentrated within clay. The occurrence of Fe-oxide crystals within clay suggests that these likely formed at temperatures ≤100 °C, near the formation temperature of smectite. The formation of Fe-oxide minerals on clay surfaces is of interest as it may form a micro-setting, where free electrons (from the oxidation of Fe2+) and the adsorption of simple organic molecules on the surface of clay could generate reactive conditions favorable to microbial communities. Primary and secondary Fe-sulfide minerals exhibiting a variety of morphologies are present within samples, representing different formation mechanisms. Secondary Fe-sulfide minerals occur within rims of clasts and vesicles and in fractures and voids. Some secondary Fe-sulfide grains are associated with Ni- and Co-rich phases, potentially reflecting the post-impact migration of siderophile elements within the suevite of the Chicxulub crater.
This is the first high-resolution seismic study showing how the Chicxulub impact shaped the eastern slope of the Campeche Bank in the south-eastern Gulf of Mexico. The induced shock wave fractured Cretaceous strata causing the collapse of the upper slope and shelf over a length of ca. 200 km. Failed material was either transported downslope or remained in parts on the accommodation space created by the collapsed. In the Cenozoic, the East Campeche Plastered Drift developed within the created accommodation space, controlled by the inflowing surface current from the Caribbean, which forms the Loop Current. The internal reflection configuration of the drift shows that the closure of the Suwannee Strait in the Late Oligocene and the closure of the CAS in the Mid to Late Miocene controlled the variability of the southern Loop Current in time. Since the Loop Current transports heat and moisture from the western Atlantic warm water pool into the North Atlantic and further to NW Europe by the Gulf Stream, the drift represents an archive for controlling factors that influenced climate of the northern hemisphere. This first high-resolution seismic reflection study from the eastern Campeche Bank expands the understanding of destructive processes that a meteorite impact induces into the earth system. Furthermore, these data document that the East Campeche Plastered Drift bears the potential to understand the link between the climate variability of the northern hemisphere and oceanic processes in the equatorial western Atlantic.
The present Cretaceous/Tertiary extinction debate started with findings by Alvarez et al. (1980) of enhanced levels of iridium at K/T sections in Italy, Denmark and New Zealand. They postulated that the iridium was extraterrestrial in origin and related to a 10 km diameter asteroid impact which would have produced a crater some 200 km in diameter. They further suggested that a giant dust cloud would have been injected into the stratosphere from the impact with a residence time of several years and that the resulting darkness would have suppressed photosynthesis with a consequent elimination of succeeding members in the biological food chain — ergo, a mass extinction event.
Mass extinctions shape the history of life and can be used to inform understanding of the current biodiversity crisis. In this paper, a general introduction is provided to the methods used to investigate the ecosystem effects of mass extinctions (Part I) and to explore major patterns and outstanding research questions in the field (Part II). The five largest mass extinctions of the Phanerozoic had profoundly different effects on the structure and function of ecosystems, although the causes of these differences are currently unclear. Outstanding questions and knowledge gaps are identified that need to be addressed if the fossil record is to be used as a means of informing the dynamics of future biodiversity loss and ecosystem change.
Full-text available
A detailed record of the strontium-87 to strontium-86 ratio in seawater during the last 100 million years was determined by measuring this ratio in 137 well-preserved and well-dated fossil foraminifera samples. Sample preservation was evaluated from scanning electron microscopy studies, measured strontium-calcium ratios, and pore water strontium isotope ratios. The evolution of the strontium isotopic ratio in seawater offers a means to evaluate long-term changes in the global strontium isotope mass balance. Results show that the marine strontium isotope composition can be used for correlating and dating well-preserved authigenic marine sediments throughout much of the Cenozoic to a precision of ±1 million years. The strontium-87 to strontium-86 ratio in seawater increased sharply across the Cretaceous/Tertiary boundary, but this feature is not readily explained as strontium input from a bolide impact on land.
Full-text available
Coronas around quartz xenocrysts in andesite and basalt from Tertiary volcanics in northeastern Shikoku, Japan, have been described. The coronas are composed mainly of Ca-rich clinopyroxene and glass. Compositional profiles across the corona glass show monotonous variation of major elements except for alkalis. Preliminary experiment on the reaction between basaltic melt and quartz has shown that alkalis diffused against their concentration gradients. This particular feature of alkali enrichment in corona glass is explained by a diffusion model, in which non-ideality of alkalis in silicate melt is assumed. Preferred crystallization of Ca-rich clinopyroxene in coronas of orthopyroxene andesite is discussed using a chemical potential diagram in the system SiO2-CaO-RO (RO=MgO+FeO), and it is suggested that higher (Na+K)/Al ratio of the corona glass, which increases the effective CaO concentration and thus increases the CaO/ RO, is responsible for the preferred crystallization of Ca-rich clinopyroxene.
Most workers in the field already favour a terrestrial origin; presented here are several additional aspects invalidating the lunar hypothesis and giving further clues to the view of tektites as terrestrial impact glasses.-from Author
At the Mistastin Lake structure, Labrador, igneous rocks overlying shock-metamorphosed and brecciated Precambrian anorthosite, mangerite, and granodiorite have a preserved thickness of 80 m and have characteristics believed compatible with an origin by impact melting. At the base, the impact melt is glassy and very fine grained with abundant shocked and unshocked country-rock inclusions. At higher levels, it becomes medium-grained poikilitic to subophitic with relatively few recognizable inclusions. Plagioclase, pigeonite-ferroaugite, and interstitial glass are the principal melt phases. The volumetric bulk of the melt shows a small compositional range, 53.4 to 58.4 percent SiO2 and 1.1 to 2.3 percent K2O; however, a rare microporphyritic variety occurs locally at the base and contains 65.3 percent SiO2 and 4.6 percent K2O. Minor partial melt with a granitic composition occurs in mangerite inclusions; glass globules with an equivalent composition are found in the immediately surrounding impact melt. Calculations indicate that the melt can be generated from a compositional mix of the country rocks; the calculations are consistent with a presented impact model for the origin of the Mistastin Lake structure and the formation of the melt as a total melt of the country rocks near the point of impact. The observed compositional range may be the result of the differential assimilation of inclusions and (or) a reflection of original variations in the proportions of the country rocks within the melted volume. Textural similarities between the Mistastin Lake melt and lunar impact melts lead the writer to infer that the lunar melts may have formed in a similar manner - that is, as total melts of portions of their respective targets and not as partial melts in hot ejecta blankets.
The residual Bouguer gravity field associated with the 65-km-diameter Manicouagan circular structure in eastern Quebec consists of a peripheral -4 to -10-mGal ring that grades gently upward to a central high of 0 mGal. This pattern of gravity anomalies is consistent with the distribution of upper crustal density contrasts predicted by a hypervelocity meteorite impact origin for the structure. Excavation of a transient cavity produced by meteorite impact is limited to crustal depths between 2 and 8 km and is most likely between 3 and 5 km at Manicouagan on the basis of gravity model calculations of the vertical component of cavity infilling.
The data from 48 seismic refraction profiles in the western Caribbean Sea and in the Gulf of Mexico are presented in the form of structure sections crossing the Colombian basin, Nicaraguan rise, Cayman trough, Cayman ridge, Beata ridge, Yucatan basin, Campeche bank, and Sigsbee deep. The Cayman trough has a remarkably thin crust, which suggests that it is a tensional feature. Although parts of the basins have a relatively thin crust, similar to the oceanic type, the shallower areas are intermediate or almost continental in structure. In the Gulf of Mexico the main basin is similar to typical ocean basins in structure except that the high-velocity crust is overlain by very thick sediments. The depth to the mantle is appreciably greater in the Gulf than in an ocean basin. This may be partly the result of loading by the sediments, but large scale tectonic activity is a more likely cause. The Sigsbee escarpment, the northern boundary of the main basin, appears to be the surface expression of a fault or sharp flexure in the layers beneath the unconsolidated sediments.
The Caribbean plate is allochtonous to its neighbors. Possibly a Pacific origin. South America: (1) migrated from N. America during later Triassic-early Campanian (2) remained fixed to N. America from early Campanian-mid Eocene (3) converged with N. America since mid Eocene. Magmatic arcs are used to identify subduction processes. Ophiolites are also used as indicatores of subduction. Summary: (1) Middle to late Jurassic rifting betweeen N. America, the Bahamas, the Yucatan block, and northern. America. (2) Late jurassic-late Cretaceous passive margins in Bahams, Yucatan, and northern S. America during rift between Americas and widening of the proto-Caribbean Basin. (3) Late Cretaceous to Recent eastward progressing, time-transgressive orogeny aroung the Caribbean. (4) Eocene to Recent development of complex strike-slip boundary zones in the northern and southern Caribbean, associated with eastward migration of Caribbean plate. (5) Miocene to Recent period of devormation across entire Caribbean. Results from interaction between Caribbean and the American plates (a) compression caused by convergence between North and South America (b) northeastward migration of the Andean Terranes of northwest South America (c) convergence at the Hispaniolan Restraining Bend along the ORiente-Puerto Rico Trench transform fault.