Abstract Unusual dike-like bodies and lenses of paralava, up to 1–5 m long and 10 cm thick, are found in the “olive” unit of the combustion metamorphic complex in the Hatrurim Basin, Israel. High-temperature rocks of the “olive” unit are composed of anorthite and clinopyroxene (diopside-hedenbergite-esseneite) and are connected with pipe-like explosion structures. The paralavas are cryptocrystalline rocks that exhibit vesicular and fluidal textures. The main mineral assemblage in these rocks, identified by electron-microprobe analysis and X-ray diffraction, consists of basic plagioclase + Fe-Ti oxides + clinopyroxene + K-feldspar + tridymite ± apatite. The silica content of the paralavas is similar to that of basalt, whereas the high calcium content suggests similarity to anorthosite. The occurrence of glass in the paralava is evidence for melting. The glasses are compositionally similar to rhyolites and more acidic melts. Melting temperatures were at least 1100 °C. The presence of pipe-like explosion structures, the occurrence of melted rocks, and various geological relationships throughout the Hatrurim Basin provide evidence for a new hypothesis about the genesis of this pyrometamorphic complex. The combustion metamorphic rocks in the Hatrurim Basin in Israel formed as a result of repeated ignition of hydrocarbon gases. The setting we envisage has many geological features typical of mud-volcano provinces. The occurrence of paralavas is restricted to the areas of gas ignition.

Abstract The northern Andes in Colombia form three great ranges, the Cordilleras Oriental, Central, and Occidental (Fig. 1). Other ranges include the Sierra Nevada de Santa Marta, Guajira Peninsular ranges, and physiographic extensions of the Cordillera Oriental northeast into Venezuela, including the Sierra de Perijá and the Cordillera de Mérida (Venezuelan Andes). The present physiographic expression is the result of Tertiary (Neogene) uplift. The Cordillera Occidental is underlain by deformed oceanic crust, perhaps allochthonous as judged from the low metamorphic grade of Mesozoic rocks in the north (see chapter by Escalante, this volume; Duque-Caro, 1990); most of the Cordillera Central, Cordillera Oriental, Sierra de Perijá, and Cordillera de Mérida are underlain by continental crust. The Sierra Nevada de Santa Marta and ranges on the Guajira Peninsula are probably underlain by both types of crust, and oceanic segments on the north sides are probably allochthonous. In the following summary of the regional geology, the main mountain ranges will be described from east to west. The Sierra Nevada de Santa Marta, Guajira ranges, and sedimentary basins will be discussed last. Some of the generalized descriptions are modified from Case and others (1984). Geologic maps by Bellizzia and others (1976), Arango C. and others (1976), Mart×n F. (1978), Case and Holcombe (1980), Etayo-Serna and others (1983, 1986), and Case and others (1984) provide a regional framework for this summary. Bürgl (1961,1973), Irving (1975), Etayo-Serna and others (1983, 1986) and González and others (1988) provided very useful syntheses of the pre-1960 to 1970 literature for

The greater Caribbean region has been divided into more than 100 geologic provinces, some of which are tectonostratigraphic terranes or suspect terranes as defined by Coney, Jones, and Monger (1980). The principal criteria for distinguishing provinces are groups of rocks that differ from their immediate neighbors with respect to: (1) rock lithology, thickness, and age, (2) structural style, (3) presence or absence of outcropping igneous rocks, (4) degree of metamorphism, (5) physiographic expression, (6) nature of crust, and other characteristics. Many of the provinces thus identified are bordered by known major faults, including suture and transform zones; other provinces are bordered by unexposed or cryptic faults; and still other boundaries are drawn on the basis of major changes in rock facies, and so are not boundaries of tectonostratigraphic terranes. Paleomagnetic data, far from complete in the region, indicate that many of the provinces have experienced large tectonic translations and rotations. Colors and patterns have been used on the map in an attempt to portray provinces that appear to be geologically similar in rock type and age, and style and age of principal deformation. For example, Neogene accretionary prisms of the Lesser Antilles, North Caribbean, South Caribbean, North Panama, and Pacific margin deformed belts are shown by the same color, with slight variations in pattern to indicate apparent structural differences between the deformed belts. Many provinces defined here can be further subdivided on the basis of existing information, and many changes will be required as new data accumulate.

Alternative fits of the continents around the future site of the Caribbean about 200 Ma ago and alternative relative motions since then of North and South America and of Africa with respect to each other allow a wealth of information, including data tabulated here on the distribution of rift systems; early ocean floor; obducted ocean floor fragments and dated plutons to be assessed in relation to a history of Caribbean development. After an early rift phase, the Gulf of Mexico formed by divergence mainly before the Caribbean itself. Convergence on what are now the northern and southern Caribbean margins during the Cretaceous produced arc-systems and carried the present Caribbean ocean floor, which represents an oceanic plateau, out of the Pacific. Cenozoic convergence in the Lesser Antilles and Central America has been contemporary with more than 1000 km of roughly eastward motion, distributed in wide plate boundary zones, of the Caribbean with respect to both North and South America. Moderate internal deformation of the Caribbean plate is perhaps attributable to its oceanic plateau character because it behaves mechanically in a way that is intermediate between that of normal ocean floor and continent. Although numerous problems remain in Caribbean geology, a framework into which many of them can be accommodated is beginning to emerge.

A compilation of existing magnetic data clearly demonstrates the presence of extensive, NE-SW trending, linear anomalies over the central Venezuelan Basin. These long wavelength, small amplitude anomalies are truncated in the east by a series of N-S linear anomalies over the Aves Ridge, and in the south by E-W trending anomalies over the Aruba Basin, Curacao Ridge, and Los Roques Basin. In the southeastern corner of the basin, there is a magnetic quiet zone similar to that observed in the North Atlantic and Pacific Oceans. Analysis of the NE-SW anomalies reveals an axis of symmetry which crosses the basin from north of the Guajira Peninsula to near the Muertos Trough at 68° W. Modelling indicates that the linear anomalies are the result of a phase of seafloor spreading between 153 and 127 m.y. at a half rate of 0.4 to 0.5 cm y −1 . The quiet zone is therefore believed to correspond to a period in the Middle Jurassic which may be characterized by frequent short reversals. The magnetic study together with other geologic and geophysical evidence suggests that the Venezuelan Basin formed in the Pacific region as a western extension of the N. Atlantic in Middle-Late Jurassic. Spreading appears to have ceased when, in the early Cretaceous, the South Atlantic began to open. As a result of these changes in plate motion, the Venezuelan Basin became trapped behind the juvenile Antilles arc-trench system. The Venezuelan Basin was then gradually inserted into the Caribbean region as this system migrated eastward with respect to North and South America.

The mantle reference frame defined by stationary hotspots has been used to determine the positions and motions of continental and oceanic plates surrounding the Caribbean region from late Jurassic time (140 m.y.) to the present. First, the position of the Pacific plate and the Pacific-Farallon spreading ridge has been reconstructed using the ages and geometry of island and seamount chains emanating from Pacific hotspots. Then, by assuming symmetric spreading across the Pacific-Farallon ridge, the motion of the Farallon plate relative to the mantle has been calculated. This shows that the postulated oceanic plateau which may form the core of the present Caribbean plate could have been erupted onto late Jurassic to early Cretaceous oceanic lithosphere as the Farallon plate passed over the Galapagos hotspot, hypothesized to have been initiated in mid- to l ate Cretaceous time (100 to 75 m.y. B.P.). The thickened volcanic plateau collided with the Greater Antilles Arc, then filling the gap between South America and nuclear Central America, in late Cretaceous time (80 to 70 m.y. B.P.) and was not subducted; instead, subduction of the Farallon plate commenced behind the plateau. This buoyant, indigestible piece of oceanic lithosphere drove the Greater Antilles Arc northeastwards, accompanied by subduction of proto-Caribbean crust, until it collided with the Bahama platform in late Eocene time. Concomitantly, the trench and island arc which developed behind (southwest of) the plateau generated what is now a part of Central America. Subsequent westward subduction of Atlantic lithosphere beneath the Lesser Antilles Arc and continuing eastward subduction of oceanic lithosphere beneath Central America, together with transform faulting (left-lateral Cayman transform fault in the north, right-lateral strike-slip motion in and off Venezuela in the south) defined the present boundaries of the Caribbean plate.

The contact relationships between metabasalts (eclogites, glaucophanites, prasinites, etc.) and the enclosing mica schists in the Venezuelan Coast Ranges favour a common petrological history for both. Mineralogical disequilibria, such as replacement textures and mineral zoning in the metabasic assemblages, can all be related to a single metamorphic cycle. Relict deuteric/late magmatic hornblende epitaxially overgrown by the barroisitic amphibole of this metamorphic event shows that the latter has been the only regional metamorphic episode to have affected these rocks. The high-pressure character of the metamorphism is a logical consequence of overthrusting related to collision of the Aruba-Blanquilla island arc with the South American continental margin. The well-defined stratigraphy and detailed radiometric dating of intrusive rocks in the Netherlands Antilles indicate that this collision took place in the Coniacian/Campanian interval. The igneous rocks of the Netherlands Antilles, which are considered to form part of the colliding arc, consist largely of submarine volcanics, as well as a tonalite/gabbro batholith. These rocks range in age from middle Albian to Coniacian. The volcanics of Curaçao and Aruba are composed of basalts with a MORB chemistry and are oceanic in origin. Nevertheless, these sequences differ from "normal" oceanic crust by their thickness, chemical homogeneity and the non-depleted nature of the source, thus suggesting that they were fed by a prolific chondritic mantle plume. The volcanics of Bonaire range from basalt to rhyolite in composition and are chemically related to the primitive island arc series. An important characteristic is the high initial water content of these magmas, as shown by the geometry and mineralogy of the flows. The tonalite/gabbro batholith on Aruba is of calc-alkaline composition. The similarity in chemistry between the volcanics of Bonaire and the Villa de Cura Group of the Venezuelan mainland supports the view that the latter is an overthrust remnant of the colliding arc. Comparison with the metabasalts of the La Rinconada Group of Margarita Island is equivocal. Existing paleomagnetic evidence indicates that the arc underwent a 90° north-south to east-west rotation shortly before collision, and that the colliding arc extended via the Aves Ridge into the Greater Antilles. The age of the oldest volcanics of this arc, and thus the age of its origin, is uncertain. Most data favour formation in the Early Cretaceous, but a Late Jurassic age is also possible. Consequently, two alternative models for the evolution of the arc are proposed: one in which the arc forms as a lengthening Central American "isthmus" in response to opening of the Caribbean in the Late Jurassic, and a second in which the arc originates in the Pacific in the Early Cretaceous. In order to collide with the northern as well as southern margin of the Caribbean, the arc must have lengthened to more than twice the width of the gap. Lengthening probably occurred at a trench-trench-ridge triple junction, thus explaining the large volume of MORB-volcanics in the arc. The high water content of the primitive island arc series is attributed to a high rate of subduction due to the worldwide surge in spreading rates in the mid-Cretaceous. In the second model, a strong causal connection between the mid-Cretaceous thermal event in the Pacific as well as the origin and evolution of the arc/trench system is postulated.

The Caribbean Plate was created as the North and South American Plates began to separate about 140 m.y. ago, allowing the Phoenix/Farallon spreading ridge to extend eastward. The Caribbean Plate was separated from the Phoenix/Farallon spreading ridge, about 110-100 m.y. ago, by a subduction zone near present-day Central America, connected by transform faults to the older Greater Antilles subduction zone. Geologic data from the margins of the Caribbean Plate indicate six important discontinuities in the history of the plate. Near the beginning of the Albian (110 m.y. B.P.), northeast-dipping subduction in the Greater Antilles zone may have been blocked by underthrusting of part of the Chortis Block of Central America, causing subduction to flip to southwest-dipping, perhaps followed by the beginning of subduction beneath Central America. A Santonian (85 m.y. B.P.) discontinuity may be the result of thickened oceanic crust formed at the Galapagos hot spot reaching the Central American subduction zone and blocking or modifying subduction. At the beginning of the Tertiary (66 m.y. B.P.), the Caribbean Plate changed its relative motion from northeastward to eastward and began to underthrust northern South America. In the Late Oligocene (27 m.y. B.P.), the Farallon/Phoenix Plate separated into the Nazca and Cocos Plates. The present-day emergence (5-0 m.y. B.P.) has not yet been correlated with plate motion changes. Major changes in plate arrangement and motion are thus reflected in the Caribbean Plate by major geologic discontinuities such as unconformities. Geologic structures along the plate margins are the resultants of the direction of relative plate motion, and of the type of lithosphere. Oblique plate motion produced horizontal slip accompanied by slow subduction without volcanism, by uplift and erosion, or by a combination of processes. Oceanic lithosphere forms relatively simple plate boundaries, as in the Greater Antilles, but continental lithosphere forms complex border zones composed of old structural blocks moving along ancient zones of weakness, as in northern South America.

Seismic sections across the southern margin of the Caribbean reveal structures related to the convergence of the Caribbean and South American plates. The South Caribbean Deformed Belt and its eastward extension, the Curacao Ridge, is a zone of intensely deformed Cretaceous and Tertiary sediments that lies along the southern edge of the Colombia and Venezuela Basins. Undeformed sediments of the Caribbean basins abut the deformed belt abruptly to the north. To the south, the South Caribbean Deformed Belt gives way to older deformed belts of the Netherlands and Venezuelan Antilles Ridge and to the continental margin of Colombia and Venezuela containing pre-Tertiary structures. Along most of the South Caribbean Deformed Belt an apron of sediments progrades northward across the deformed belt suggesting active deformation at the northern edge of the belt and progressively older Tertiary deformation to the south. Caribbean oceanic crust extends southward beneath the deformed belt and southward-dipping reflections occur within the deformed belt possibly indicating slices of oceanic crust incorporated within it. Bottom simulating reflectors along parts of the deformed belt indicate the presence of gas hydrates. The chemical phase relationships of gas hydrates and the depth of the bottom simulating reflections indicate a thermal gradient of approximately 0.04 degrees/meter.

Magnetic provinces, recognized by trend geometry and anomaly character, are delineated in western Venezuela utilizing aeromagnetic data from the 1950s oil company surveys. In northwestern Venezuela, the Guajira-Paraguaná province (east-west anomalies) lies north of a proposed east-west fault zone extending from the southern Para-guaná Peninsula across the Gulf of Venezuela and south of the pre-Tertiary outcrops on the Guajira Peninsula. South of this fault zone and on the west is the Perijá province (northeasterly trends) and on the east the Coro province (northwesterly trends). The Oca zone province (east-west trends) separates the northern and southern parts of the Perijá province. Geologic features which can result in these magnetic anomalies are fault blocks, east-west faults, some in sets, faults oblique to east-west shear, and probably intrusions into the crust parallel to these features. These have been produced by differential motion between the major zones of dislocation resulting from right-lateral offsets on east-west transcurrent faults during extension in the Tertiary. Thus, the magnetic anomalies locate a complex zone of Cenozoic interaction on this margin of the Caribbean-South American plate boundary. South of the Oca fault, the Perijá province trends are related to the geologic trends of the Sierra de Perijá, and the Jurassic La Quinta graben complex and the Central Lake Graben. There are only modest, trendless anomalies in the eastern Maracaibo Basin, the Falcón Basin, and the area to the south. Magnetic basement rocks here are probably igneous and metamorphic Paleozoic units, similar to those exposed in the Venezuelan Andes. Southeast of the Andes, a major lineation between the Barinas and Río Meta provinces is correlated with the projection of the Altamira fault. Unmetamorphosed lower Paleozoic sedimentary rocks are preserved in a block dropped down to the north. This is possibly an extension of the Espino Graben complex, which is 300 km to the northeast and in which Jurassic basalt is preserved. Strong magnetic anomalies west and south of the El Baúl Uplift are probably associated with Jurassic volcanics, similar to those exposed in the uplift, perhaps preserved in the same graben complex. These appear as major features of the interior plains (llanos) north of the Guayana Shield. The primary subdivision of the magnetic provinces is two-fold. North of and including the Oca fault-Coro area, magnetic anomalies document the complex zone of interaction related to east-west shear in Cenozoic time. South of this, magnetic anomalies are related to the distribution of pre-Cretaceous rocks, some of which were involved in the plate boundary interactions, but others to the south are related to the development of the pre-Cretaceous terrane north of the Guayana Shield.

The igneous and metamorphic rocks of Venezuela may be classified in three geographic units: a southern Precambrian Shield, an intermediate belt of Paleozoic age and a northern border of Mesozoic to Tertiary age. The shield is exposed in the south; it extends northward under a sedimentary cover to an inferred contact with the metamorphosed Paleozoic or Mesozoic-Tertiary rocks. South of this contact, in the eastern states of Anzoátegui and Monagas, the shield's oldest known sedimentary cover is of Cretaceous age; to the west, it is of Cambrian age. A graben is identified in the State of Guarico, located approximately along the contact of the Paleozoic basement with the Precambrian Shield. It contains a 2,390 m (7,840 ft) column of sedimentary rocks of Carboniferous and Jurassic age, not previously identified in the Barinas-Apure and Eastern Venezuela basins. Preliminary interpretation of recently acquired aeromagnetic data indicates that this feature forms part of a much longer graben, hitherto not known, which may extend westward from near Barcelona, Anzoátegui, to the Colombian border at approximately 70° 00' West Longitude, 7° 10' North Latitude, a distance of 600 km (375 mi).

The right-lateral El Pilar fault system extends from the Gulf of Cariaco in northeastern Venezuela to the east coast of Trinidad. The fault is seismically active, deforms Quaternary strata, and is the boundary between two very different geological provinces. North of the fault is the eastern Cordillera de la Costa, which is composed of Lower Cretaceous metasediments and igneous rocks that accumulated in a tectonically and volcanically active environment, probably a fore-arc setting. These rocks were metamorphosed to greenschist facies during the Late Cretaceous, and deformed by imbricate fold and thrust faults during the Cretaceous and Tertiary. South of the fault is the Serrania del Interior, a fold and thrust belt composed of Cretaceous and Paleogene sediments that were deposited, at least during the Early Cretaceous, in a comparatively stable tectonic environment, probably a passive continental margin, and deformed during post-Middle Eocene time. In northeastern Venezuela the El Pilar fault consists of two major branches, one of which was not recognized in previous studies. Geologic mapping demonstrates a cumulative dextral displacement that must exceed 20 km. A steep gravity gradient across the fault system suggests that the fault plane is a nearly vertical density discontinuity to a depth of at least 5 to 10 km. Gravity models imply that a relatively dense mafic crust is present north of the fault, and regional geology demonstrates that a similar crust does not exist south of the fault anywhere east of the Gulf of Cariaco. It follows that a total right-lateral displacement of 150 to 300 km may be necessary to account for the steep gravity gradient at the fault.

The Urica fault zone is viewed as a major transpressive geosuture in the tectonic evolution of northeastern Venezuela. It can be traced for 350 km from the Coche fault zone on the northwest and, with less certainty, to the area of Tucupita on the southeast, right-lateral displacement being about 35 km. Interpretation of new seismic reflection data shows it as a broad zone of dislocation, 10 km or more in width, the "flower" pattern geometry being characteristic of transpressive strike-slip faults. It separates the Maturin sub-basin into a zone of compression, characterized by imbricate thrusting to the north, from one of tension, distinguished by normal fault sets to the south.

The Falcón Basin in northwestern Venezuela and adjacent offshore basins developed within a zone of extensional tectonics during Oligocene and Miocene times. Extension resulted from right-lateral motion along offset, east-west-trending, transcurrent faults, including the Oca fault in western Venezuela, the Cuiza fault in northern Colombia, and the San Sebastián fault along the coastal areas of central Venezuela. On both local and regional scales, transcurrent and normal faults were active during the early evolution of the basins. These faults define rhomb-shaped pullapart basins in map plan. Extension occurred in a northeast direction causing normal faulting along north-west trends. Basin subsidence was accompanied by crustal thinning and injection of basaltic magmas. Evidence of Oligocene magmatic activity is found in the central part of the Falcón Basin where volcanic rocks and hypabyssal intrusions are exposed. These rocks are similar to other suites of continental igneous rocks typically associated with rifting environments. Basaltic rocks of both alkalic and subalkalic affinities are present. Xenoliths of the underlying crust and mantle are abundant. Felsic igneous rocks are relatively rare. Other structures within the Falcón and Bonaire basins formed during later stages of basin development. These include folds and reverse faults of northeast trend and conjugate sets of small transcurrent faults. These structures were amplified by greater compressional stresses during late Miocene and Pliocene time. A similar Tertiary tectonic regime is postulated for the larger area of the Bonaire Crustal Block, a block that includes the Falcón and Bonaire basins. This block is a broad region of extensional pullapart structures which developed during the Oligocene to Miocene, right-lateral motion between the Caribbean and South American crustal plates. Minimum extension within the northern part of the block, along the Venezuelan and Netherlands Antilles and the Paraguaná and Guajira peninsulas, is estimated at 35 to 45 km in an east-west direction. The extension within this nonrigid block should be considered when determining Tertiary movements between the Caribbean and South American plates.

Paleomagnetic data for basaltic intrusions in the central Falcón Basin document a secondary magnetization associated with alteration during Miocene time. The rocks are extensively altered; however, most of this alteration probably accompanied cooling soon after intrusion. Comparing these secondary magnetic signatures to those of other Cenozoic sites in South America, we conclude that magnetization occurred before the late Miocene folding in the basin and soon after intrusion. A later stable partial overprinting of this secondary magnetization occurred in which the present geomagnetic field was superimposed on the stable Miocene remanence. At many sites it is difficult to remove this overprinting during demagnetization. The resultant magnetic signature has a steep positive inclination, which in the past has been difficult to interpret.

The four major Cenozoic tectonic phases in the Sierra de Perijá and adjacent basins are the early Eocene tectonic phase, the middle Eocene Caribbean orogeny, the late Oligocene phase, and the late Miocene to present Andean orogeny. Ages of unconformities associated with particularly rapid regional uplift during these phases are early Eocene (53 m.y.), middle Eocene (45 m.y.), late Oligocene (25 m.y.), and Pliocene (3 m.y.). Northwest-southeast compression may have commenced in the Perijá and the Maracaibo Basin as early as the early Eocene. By the middle Eocene the Macoa-Totumo arch had begun to form during intense alpine-type folding and thrusting to the east in Falcón and Lara. During the late Oligocene phase, the Palmar area was uplifted and the most important structural features for hydrocarbon accumulation in the Maracaibo Basin developed. The late Oligocene phase initiated a basement block tectonic style that culminated during the Pliocene in the northwest thrusting of the Santa Marta massif, Sierra de Perijá, and Venezuelan Andes over the adjacent basins. The main uplift of the Sierra de Perijá occurred during the late Miocene-Pliocene Andean orogeny. Right-lateral oblique-slip movement of 90 to 100 km on the Oca fault and left-lateral oblique-slip movement of 100 km on the Santa Marta fault were caused by late Tertiary overthrusting in the Sierra de Perijá and Santa Marta massif. The northwest-southeast shortening that uplifted the Santa Marta massif, Sierra de Perijá, and Venezuelan Andes is related to Caribbean-North Andean convergence along the South Caribbean marginal fault. During the Pliocene the Panama volcanic arc collided with South America. The North Andean block became detached from the South American plate and is being wedged slowly to the north between the rapidly converging Nazca, Caribbean, and South American plates. The convergence of the three plates has produced rapid subduction at the Colombia trench (6.4 ± 0.7 cm/yr; 088° ± 7°), slow subduction at the South Caribbean marginal fault (1.7 ± 0.7 cm/yr; 128° ± 24°), and right-lateral shear (1.0 ± 0.2 cm/yr; 235° ± 5°) on the Boconó and East Andean fault systems.

The Jurassic age La Quinta Formation in the Sierra de Perijá of northwestern Venezuela consists of red continental sedimentary rocks, interbedded volcanic rocks, and associated hypabyssal intrusives. These strata were deposited in a series of graben that parallel the present Sierra de Perijá and the Venezuelan (Mérida) Andes. Trace element and isotopic data indicate that crustal contamination and/or anatexis were important factors in the petrogenesis of the igneous rocks. Red beds, some with volcanic rocks, of similar type, age, and tectonic setting are found from Mexico to Chile, suggesting that the depositional environment was related to convergent plate margin processes. Tension related to opening of the Caribbean and/or separation of Central America and North America may also have been a factor in Jurassic time. However, paleomagnetic data indicate a differential rotation between the Sierra de Perijá and the Venezuelan Andes that cannot be reconciled with simple models of tension and separation. This suggests that the Sierra de Perijá is an allochthonous terrane emplaced during Jurassic time. Its current setting is the result of a composite of subduction, rifting associated with opening of the Caribbean, and transcurrent motion.

Whole-rock K-Ar ages of 155 ± 5 m.y. and 146 ± 7 m.y. were obtained from two hornblende-andesite flows associated with the Jurassic La Quinta Formation of northwestern Venezuela and are in agreement with others reported for this formation. These data provide age control on stratigraphic relationships and paleomagnetic measurements.