Chapter 18 Structural and sedimentary development of a neogene transpressional plate boundary between the caribbean and South America plates in Trinidad and the Gulf of paria
1999; Elsevier BV; Linguagem: Inglês
10.1016/s1874-5997(99)80052-5
ISSN1874-5997
Autores Tópico(s)Geological and Geophysical Studies Worldwide
ResumoTrinidad, the Gulf of Paria, and Eastern Venezuela lie in a diffuse and complex zone of Cenozoic tectonic interaction between the Caribbean and South America plates. Numerous models have being proposed to explain the complex tectono-stratigraphie evolution of the area. In this paper, we interpret an integrated data base consisting of well logs and seismic reflection profiles to document five sequences of the Gulf of Paria-Northern basin of Trinidad. Sequences 1 and 2 consist of a Late Jurassic-early Valanginian carbonate megaplatform with overlying carbonate bank buildups that together form the basement to overlying siliciclastic sedimentary sequences 3 through 5 of mainly Neogene age. Sequence 3 is a Late Miocene-Early Pliocene shallow marine to brackish-water conglomerate and sandstone that represents a southward-fining and thinning and eastward-thickening siliciclastic wedge derived from the Late Miocene uplift and erosion of Trinidad's Northern Range and records early activity along the El Pilar strike-slip fault at the mountain front of that range. Sequence 3 and overlying sequences 4 and 5 fill in topographic relief created by the growth of the carbonate banks of sequences 1 and 2 and by space created by tectonic extension in the Gulf of Paria and Northern basin. Sequence 4 is an Early to Middle Pliocene inner neritic to shallow marine conglomerate, sandstone, silt, and clay that represents a northward-fining and thinning siliciclastic wedge derived primarily from the Late Miocene-Early Pliocene uplift and erosion of the Central Range with some input from the northwest and north. Sequence 5 is a Late Pliocene to Pleistocene marine to brackish-water sand, silt, clay and minor conglomerate that represents continued siliciclastic deposition in an increasingly restricted basin between the uplifted Northern and Central Ranges. Comparison of two-way travel time structural contour maps of each boundary between sequences 3-5 (totaling 2-3 km in thickness) with two-way travel time isochron maps of the seismic sequence immediately overlying each structural surface allows a better visualization of the space available at tectonically significant times in the history of the Gulf of Paria-Northern basin and the subsequent sedimentary infill onto that structural surface and sequence stratigraphic boundary. This comparison allows the identification of three Neogene deformational phases that have affected the area and closely control the proposed sequence strati- graphic boundaries: Phase one, Late Miocene-Early Pliocene strike-slip motion along the El Pilar fault and north-to-south filling of the Gulf of Paria and Northern basins; Phase two, Middle to Late Pliocene strike-slip motion along the Warm Springs-Central Range fault zone and south-to-north filling of the Gulf of Paria and Northern basins; and Phase three, Late Pliocene to Pleistocene strike-slip motion along the Warm Springs-Central Range fault zone and continued filling of the Gulf of Paria and Northern basins. Paleocurrents and environments of deposition of the Gulf of Paria and Northern basins have been closely controlled by structural events during the three deformational phases. Paleocurrents for deformational phase one (deposition of sequence 3) are oriented orthogonal (north-south) and parallel (east-west) to the axis of the basins and reflect strong control of the bounding El Pilar fault zone along the northern edge of the basin. Paleocurrents for deformational phases two (sequence 4) and three (sequence 5) become increasingly dominated by a west-to-east paleoflow along with a southeast-to-northwest flow in the area of the Goodrich sub-basin (southern Gulf of Paria basin). Environments of deposition reflect the Late Miocene (10 Ma) uplift and erosion of the Northern Range during phase one followed by subsequent uplift and erosion of the Central Range and the gradual decrease in the importance of the Northern Range siliciclastic source area during phases two and three. Environments generally remain proximal, shallow, and brackish along the El Pilar fault zone on the northern edge of the basin and distal, deeper, and less restricted along the central and southern edges of the basin. Through time the basin has become increasingly brackish and more restricted. Seismic lines are used to illustrate the variation in the structural style and geomorphic expression of the El Pilar fault zone along the northern edges of the Gulf of Paria-Northern basin. In the western Gulf of Paria, the fault exhibits a transpressional structure consistent with its east-northeast strike. A slight change in strike to a more east-southeast strike in the eastern Gulf of Paria is consistent with the more transtensional structure of the fault and its association with the Puerto Grande sub-basin in the northern Gulf of Paria basin. The trace of the El Pilar fault zone is poorly expressed onland in Trinidad and may reflect its waning activity in recent time in an eastward direction and/or cultural obliteration of its tectonic geomorphology in this highly urbanized part of Trinidad. Seismic lines are used to illustrate the structural style of previously undescribed oblique-slip faults in the Gulf of Paria. These styles include: (1) gravity-related detachment faults possibly localized along the unconformity between Cretaceous carbonate and overlying siliciclastic rocks; and (2) transtensional faults formed in the stepover area between the El Pilar fault to the north and the Warm Springs fault to the south. Seismic lines are used to illustrate the previously undescribed structural styles and geomorphic expression of the Warm Springs-Central Range-Caigual fault zone. In the Gulf of Paria, the Warm Springs fault zone exhibits a transtensional structure consistent with its east-southeast strike. An abrupt change in strike to a more east-northwest strike near the western shoreline of Trinidad is consistent with the more transpressional structure of the continuation of the Warm Springs fault zone in the Central Range (Central Range-Caigual fault zones). We reinterpret the overall structure of the Central Range as a transpressional uplift bounded by inwardly dipping reverse faults and bisected by the Central Range-Caigual strike-slip fault system rather than as the southeast-verging fold-thrust belt proposed by previous workers. Integration of data by previous workers in the Southern basin of Trinidad allows us to make a comparison between the style and age of deformation in the Southern basin and that described by us in the Gulf of Paria-Northern basin. The style of deformation in the Southern basin is predominantly south-vergent and older than the deformation in the Gulf of Paria and Northern basins because Middle Miocene (~11.4 m.y. horizon) units onlap folded and faulted older Middle Miocene units. The unconformity between the Late Miocene-Early Pliocene sequence 3 and the middle to Late Pliocene sequence 4 in the Northern-Gulf of Paria basins correlates with a less prominent unconformity between the Upper Cruse and Lower Forest Formations of southern Trinidad. The deformation in the Southern basin is therefore older than observed in the Gulf of Paria-Northern basin. Compilation of regional geologic data and integration of the Southern basin data with our results from the Gulf of Paria- Northern basins allows the following events to be constrained in the Middle Miocene through recent evolution of the Trinidad region. Middle Miocene (10 Ma): high-angle faulting affects the Southern basin; we do not regard this event as a regional fold and thrusting event because we do not observe widespread fold-thrust sturctures in the pre-Late Miocene rocks of the Gulf of Paria-Northern basin. Late Middle Miocene: uplift of the Central Range at this time may be related to the Middle Miocene thrusting observed in the Southern basin. Early Late Miocene: during this period a lobe of conglomeratic sediment was shed from the Northern Range into the Gulf of Paria-Northern basin and is interpreted to reflect the first significant lateral movement along the right-lateral El Pilar fault zone. We propose that the fault was propagating from west to east during this time as the accretionary wedge and forearc of the Lesser Antilles arc moved past the South American passive margin. The Los Bajos fault is thought to have propagated southeastward at this time. Termination of that strike-slip fault on the Southern Range may have led to a widening of the Neogene belt of transpressional thrusting during this time. Late Miocene-Early Pliocene: during this time, there was a rapid spread of strike-slip and oblique-slip faulting to the south of the El Pilar fault zone along the Warm Springs fault zone and within the Goodrich sub-basin. This southward shift is interpreted as recording the development of a pull-apart basin at the stepover area between the El Pilar and Warm Springs fault zones. Formation of the stepover may have deactivated slip along the eastern continuation of the El Pilar fault zone at the northern margin of the Northern basin. Early to middle Pliocene: this period saw continued development of the subsidence and faults of the previous period in the stepover area between the El Pilar and Warm Springs faults. Late Pliocene to Pleistocene: a major wedge of sediment derived from erosion of the Central Range and sources to the north and northwest filled the Goodrich sub-basin and continued southeastward propagation of the Los Bajos fault offset fold axes in the Southern basin by 10.5 km. The El Pilar fault zone appeared to undergo transpressional reactivation in the Northern basin but most offset seems to have shifted to the Warm Springs-Central Range-Caigual fault zone in the Central Range. We compare this sequence of events and the structural development of Trinidad with the events and structure of the Eastern Venezuelan basin in order to infer large-scale tectonic controls on the broad zone of deformation between the South America and Caribbean plates. The Eastern Venezuelan basin to the west and along-strike of Trinidad is a classic foreland basin associated with an adjacent, southeast-verging fold-thrust belt (Serranfa del Interior) formed by ~45-90 km of shortening. Trinidad exhibits a slightly younger record of fault-related sedimentation, lacks evidence for significant shortening of the Cretaceous-Pleistocene sequences 1-5 documented in this paper, and exhibits transpressional-type structures with no uniform sense of vergence in the Northern Range, Gulf of Paria-Northern basin and Central Range. In order to explain these differences between the pattern of deformation in the Eastern Venezuelan basin and Trinidad, we propose that Precambrian crust of the Guyana shield adjacent to the Eastern Venezuelan basin acted as an effective backstop and did not allow continued southeastward migration of the obliquely colliding Caribbean crust. In contrast, Trinidad appears to occupy the site of a rifted passive margin whose thinner crust acted as less of a backstop than the Precambrian crust underlying the Eastern Venezuelan basin. This less confined 'free face' to the southeast of Trinidad allowed strike-slip movement of Caribbean and passive margin crust to the southeast in a direction roughly parallel to the trend of the former passive margin.
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