We correlate seismic map units identified on industry seismic lines in the Gulf of Chiriquí, southwestern Panama, with onland igneous rocks and sedimentary formations described in this chapter. We propose six principal stages in the stratigraphic development of southwestern Panama based on our results and the results of previous workers in Costa Rica, westernmost Panama, and the western Colombian basin. The first stage in southwestern Panama is represented by basaltic basement rocks of Jurassic?-Late Cretaceous age interbedded with Upper Cretaceous pelagic sedimentary rocks. Following previous workers and data presented here, we suggest that these rocks formed in an intraoceanic, oceanic plateau setting. A second stage is represented by a major stratigraphic hiatus inferred to represent an erosional event that affected the basaltic basement of Panama in Paleocene time. A third stage is represented by a widespread basal transgressive section of coarse clastic rocks and reefal carbonate rocks of early to middle Eocene age. This section records initiation of clastic sedimentation over much of southern Central America. A fourth stage is represented by a thick section of mainly marine turbidites that appears to represent continued erosion of the land areas in southern Central America and upward deepening of adjacent marine environments. A fifth stage is represented by a stratigraphic hiatus in middle Miocene to late Miocene time that may represent the “breakup” unconformity associated with initiation of strike-slip faulting and rifting in the Gulf of Chiriquí. A sixth stage is represented by early Pliocene to Pleistocene rifting and syn-rift sedimentation in the Gulf of Chiriqu&iacute. Thick sedimentary fill of rift basins may reflect accelerated uplift of southern Central America and increased activity of the Middle America arc. The regional extent of the stratigraphic record of several of these stages across large areas of southern Central America and the western Colombian basin supports the previously proposed hypothesis that the crust of southern Central America represents the western upturned edge of a Late Cretaceous Caribbean oceanic plateau known from deep-sea drilling and seismic stratigraphic studies in the Colombian and Venezuelan basins of the Caribbean Sea.

The structure and the tectonic development of the southern Panama plate boundary have been derived from an interpretation of marine geophysical data, including GLORIA (Geological LOng Range Inclined Asdic) long-range side-scan sonar and seismic reflection profiles, most of which were acquired in 1989 from a cruise of the RRS Charles Darwin. The northern boundary of the Nazca plate runs within the continental margin of southern Panama. South of the Gulf of Panama this boundary, the Southern Panama fault zone, is predominantly left-lateral strike-slip and occupies an elongate sedimentary basin. South and southwest of the Azuero Peninsula the boundary becomes one of oblique subduction, with active formation of an accretionary complex. The eastern part of this accretionary complex slips around the bend in the overriding Panama block to the purely strike-slip portion of the plate boundary, where it ceases to accrete sediment. South of the Gulf of Panama, the fault zone is flanked on its southern side by a bathymetrie ridge, containing rocks of a high density, that was once a part of the Panamanian continental margin. The ridge has been displaced 140 km eastward by the motion between the Panama block and the Nazca plate. The eastern end of this ridge is being subducted beneath South America, and at the ridge crest, the deformation front of the Colombian accretionary complex meets the Southern Panama fault zone. The inactive trench, filled with sediment, that lies at the foot of the Southern Panama continental margin owes its existence, in the west, to the downward flexure of the Nazca plate beneath the overriding Panama block at the oblique subduction boundary, and in the east, where the lithosphere of the Nazca plate is “broken” along its transform boundary, to the flexural load of the displaced basement ridge. A continuation of the Southern Panama fault zone runs southeastward behind the Colombian accretionary complex, separating it from forearc basin sediments deposited on the “continental” basement of northernmost Colombia. Deformed mud diapirs indicate a component of left-lateral strike-slip motion on the fault zone. This pattern of tectonics around this northernmost corner of the Nazca plate has probably been active since the collision of Panama and South America about 3.5 Ma.

Abstract Thick sedimentary cover (≤16 km), vintage seismic and disparate crustal terranes have hindered understanding of the basement underlying the Caribbean plate. The plate formed by Early Cretaceous to Miocene amalgamation of four crustal types: the Caribbean Large Igneous Province oceanic plateau; the Chortis continental block; the related Great Arc of the Caribbean and Siuna/Mesquito Composite Oceanic Terranes island arc blocks; and the Colombian and Venezuelan basin oceanic crust. We characterize each terrane through interpretation of surface geology, 62 000-line-km of 2D seismic reflection data, 366 seismic refraction stations, 47 wells, 74 basement samples, 2D forward modelling, magnetic and gravity anomaly grids, and integration of previous studies. Basins overlying island arc crust are small, fault-bounded and deep, while on continental crust, they are broader and shallower. Strongly flexed oceanic and oceanic plateau crust along amagmatic subduction zones on the southern and northeastern edges of the Caribbean plate produce the largest and deepest sediment-filled basins. Areas of proven hydrocarbon source rocks and mapped seeps are associated with continental and island arc terranes in the western Caribbean plate, while organically-rich, but immature, Late Cretaceous source rocks occur across the more elevated areas of the central and eastern Caribbean plate interior.

Abstract The Colombian Caribbean Margin, offshore the Guajira Peninsula, results from the complex interaction of the Caribbean oceanic, South American, and Nazca tectonic plates through geologic time. The Chichibacoa–Rancherias Basin (CRB) is located at the boundary of the Caribbean and South American tectonic plates, and extends from the shelf northward into deepwater. The basement of the CRB is characterized by lateral terrane accretion within a major transpressional province, involving the Caribbean plate arc, accreted terranes of transitional crust, and continental crust. The tectono-stratigraphic framework of the CRB is made up of 10 Paleogene and Neogene depositional sequences we define as SQ 1 to SQ 10 and an earlier Cretaceous (Maastrichtian to Campanian) sequence we define as SQ 0. Each of these sequences records an average time span of 5–10 My, representing major second- to third-order sequences. The definition and classification of the basin involved the application of high-resolution biostratigraphy from exploratory wells, U–Pb zircon isotopes (core), and a systematic calibration of seismic profiles using wells and biostratigraphic data. U–Pb zircon geochronology is used to constrain the age and nature of the basement in the CRB, which consists of Cretaceous meta-sedimentary rocks ranging in age from 67 My to 82 My (SQ 0). Analysis and interpretation of the data reveals that the CRB displays different structural styles of deformation, distinctive basement types, and sedimentary basin fills. The CRB is bounded by normal faults with strike-slip component. Locally, the strike-slip faults are inverted during the deformation of the accretionary prism of the Southern Caribbean Deformed Belt (SCDB). According to the structural reconstructions, gravimetric and magnetics modeling and basement sample analysis, the CRB lays over continental crust. Along the northern edge of the CRB, the SCDB shows two styles of deformation. The landward segment is characterized by structural inversion of pre-Eocene and probably Oligocene depocenters. Gravity and magnetic data indicate that this zone has a Cretaceous meta-sedimentary basement, which differs from the CRB, which is underlain by continental crust basement. The seaward structural segment (younger) exhibits well-developed thrust faults and duplexes associated with the Miocene and Pliocene deformation.