Browsing by Author "Bally, Albert W."
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Item A petrologic study of Weddell Sea sediments: implications for provenance and glacial history(1984) Andrews, Barbara Ann; Anderson, John B.; Baker, Donald R.; Bally, Albert W.Knowledge of subglacial geology in Antarctica is restricted due to limited outcrop exposure. Investigations of terrestrially derived sediments deposited on the Antarctic continental margin have proved successful for gaining increased understanding of this ice-covered continent. Petrologic analyses conducted on glacial, glacial marine, and sediment gravity flow deposits from the Weddell Sea continental margin provide important evidence concerning subglacial geology and glacial history of land areas contiguous to the Weddell Sea. Petrologic data validates identifications, originally based on sed imen to 1ogic criteria, of basal tills on the Weddell Sea continental shelf. The presence of basal tills indicates a major expansion and coincident grounding of the East or West Antarctic Ice Sheet to the shelf edge. Petrologic evidence suggests that glacial expansion in the area of study was chiefly that of the East Antarctic Ice Sheet. Basal tills and transitional glacial marine sediments form distinct petrologic provinces on the Weddell Sea shelf. Most province boundaries extend inland parallel to ii reconstructed ice paleoflow lines. Till lithologies are dominated by volcanics and quartzose sedimentary rocks, in contrast to metamorphic outcrops of the Weddell Sea region. Comminution does not effectively bias till composition. Till lithologies suggest that mountainous outcrops are not representative of subglacial geology and that sedimentary basins exist beneath the Antarctic Ice Sheet. Four provenance areas for the Weddell Sea basal tills are modeled; correlations between modeled provenance areas and till petrologic provinces are good. Ice-rafted lithologies are limited in number and do not show the expected varied assemblage of Antarctic rock types. Derivation from a limited source area or from lateral moraines is suggested. Sediment gravity flow deposits from the Weddell Sea continental slope and abyssal plain are compositionally very different. Intracanyon slope debris flows and turbidites, composed chiefly of lithic fragments, were generated from basal tills on the adjacent shelf. Abyssal plain turbidites show substantial quartz enrichment and could not have been sourced directly from shelf tills.Item A seismic stratigraphic and structural interpretation of the middle Paleozoic Ikpikpuk-Umiat Basin, National Petroleum Reserve in Alaska(1985) Mauch, Elizabeth A.; Bally, Albert W.; Anderson, John B.; Oldow, John S.The Ikpikpuk-Umiat Basin is located in the eastern NPRA in northern Alaska. The basin overlies the eroded remnants of a Middle Devonian folded belt and contains up to 18, feet of Late Devonian and Mississippian elastics and up to 8 feet of Mississippian and Pennsylvanian carbonates. These sediments were deposited in two depocenters, an older larger depocenter in the southeast primarily composed of the clastic sequence and a younger, smaller depocenter in the northwest predominantly filled with the carbonate sequence. The sediments in the southeastern depocenter were deposited while the basin was undergoing subsidence and extension whereas sediments in the northwest depocenter were deposited during 8n intra-Mississippian compressional event which affected the entire basin. This compressional event is characterized by north vergent thrust faults trending west-northwest across the basin. A number of these thrust faults are reactivated earlier down-to-the-basin normal faults. The Ikpikpuk-Umiat Basin is tentatively interpreted to be part of an A-subduction related backarc region analogous to the Pannonian Basin in Hungary.Item A structural study of the Hukou and Hsinchu areas Northwestern Taiwan(1985) Liu, Chingju; Bally, Albert W.; Oldow, John S.; Anderson, John B.Northwestern Taiwan, which includes the Kuanyin, Hukou and Hsinchu areas, was initially a part of the continental shelf of the mainland China coast. The Neogene sediments were deposited m gently east-dipping basement in a stable shelf type environment. The sedimentary sequence shows a regional tilt as well as a thickening of strata towards the southeast, the location of the former ocean. The structures which make up the Hukou and Hsinchu areas are located in the frontal edge of the western foothills range. The structure is dominated by simple-step thrust faults. Frequently, the upthrown blocks of the faults are folded and form the typical asymmetrical folds with steeper north/northwest limbs (e.g. the Hukou and Chingtsaohu Anticlines). A possible solution to the structure of western Taiwan is a progressive change from a simple-step thrust fault in the north to more imbricated faults in the foothills to the southeast. This is similiar to the type of imbrication found in the Canadian Rocky Mountain. Based on the assumption of the oblique plate convergence in the Taiwan area, a model with more westerly substructural involvement of pre-Miocene rocks provides a more conservative estimate of the possible amount of the plate shortening in Taiwan than do previously published studies based on the fault-bend folding model.Item Unknown Allochthonous salt, structure and stratigraphy of the northeastern Gulf of Mexico(1989) Wu, Shengyu; Bally, Albert W.The kinematic evolution of allochthonous salt sheets in the northeastern Gulf of Mexico proceeds in three stages. (1) Since its middle Jurassic deposition the Louann Salt was loaded by sediments causing episodic basinward movement and by the end of Lower Cretaceous concentration of salt masses in a slope environment. (2) A regime of starved sedimentation during Late Cretaceous and early Oligocene is responsible for the stabilization of these early salt accumulations. (3) Finally during Neogene-Pliocene, with renewed rapid accumulation of sediments, salt tongues and allochthonous salt sheets formed by gravity spreading within younger sediments on the slope. Autochthonous salt structures, salt tongues and allochthonous salt sheets represent the typical stages for the evolution of allochthonous salt sheets. The down-to-the-basin major growth faults separate allochthonous salt from its feeder stock.Item Unknown Alpine tectonics of the Pannonian Basin(1994) Tari, Gabor Csaba; Bally, Albert W.Allowing for the palinspastic restoration of Tertiary strike-slip and extensional faulting it is concluded that the Pannonian Basin is superposed on a Middle Cretaceous thrust and fold belt which is an integral part of the system of the Alps, the Carpathians and the Dinarides. An upper Cretaceous flexural basin is overlying parts of that fold belt. A Paleogene basin is seen as a retroarc flexural basin with respect to the Paleogene Carpathian arc. The transition from an overall compressional to a transitional setting in the intra-Carpathian area occurred during the Early Miocene when large-scale transcurrent movements segmented the Alpine-Carpathian arc. Major transcurrent faults can be deduced from a study of surface and subsurface geology, but the quality of the seismic data does not permit to image them adequately. The Neogene Pannonian Basin proper shows distinct modes of upper crustal extension. In the deep ($>$8 km) subbasins of the Pannonian Basin system like the Danube Basin the Middle Miocene syn-rift extension was accommodated by low-angle detachment faults overlying metamorphic core complexes. Other intra-Carpathian subbasins such as the Zagyva and Derecske troughs related to a transfer fault system and show moderate or negligible extension. The seismic reflection profiles also suggest that the Pannonian Basin of eastern Central Europe is characterized by broad Quaternary to Recent basement upwarps that may have involved compression of the crust as a whole. These features are responsible for the outcrop distribution of the pre-Neogene "basement" of the basin. They also may suggest the beginning of a large-scale basin inversion process propagating from the W.Item Unknown Cenozoic inversion structures in a back-arc setting, Western Flores Sea, Indonesia(1996) Emmet, Peter Anthony; Bally, Albert W.A geophysical and geological study utilizing high quality seismic and well log data was undertaken of a marginal basin in the Western Flores Sea, Indonesia, to document the evolution of Paleogene extensional basins and their transformation during the Neogene into compressional uplifts. These are referred to as inversion structures because they begin as extensional half-grabens and are transformed by compression into structural highs. The crust underlying the area is transitional between continental crust of the Sunda craton to the west and oceanic crust of the Banda back-arc region to the east. Half-grabens began to form in the middle Eocene by extensional reactivation of thrusts and bedding planes within the deformed and peneplained basement complex which was an accretionary prism during the Cretaceous. Extension and regional subsidence continued until early Miocene time, when compression began to reactivate the extensional bounding faults of the half-grabens as thrusts. Compressional growth of the inversion structures was most dramatic during the late Miocene and Pliocene and continues today. The Paleogene grabens appear to have resulted from essentially orthogonal extension, oriented roughly N-S with respect to present geography. During the Neogene, the axis of compression which caused the inversion of the extensional structures appears to have been essentially the same as that which caused the extensional structures. Seismic interpretation of the Neogene units attempted the resolution of individual depositional sequences related to changes in relative sea level. The sequences were recognized by their constituent lowstand, transgressive and highstand systems tracts, where present, as defined by stratal termination patterns, truncational relationships and incision. The number of Neogene sequences, their ages as constrained by biostratigraphic data, relative amounts of incision and truncation at specific sequence boundaries, and the stacking patterns of the sequences were compared to those predicted by the published, reputedly globally-correlative, sea level chart of Haq and others (1987). The comparison is generally favorable, with the greatest variances noted in the ages of individual sequences, and the greatest similarity noted in the long-term stacking patterns of the sequences, especially for tectonically quiescent parts of the basin.Item Unknown Foredeep and thrust belt interpretation of the Maturin Sub-Basin, Eastern Venezuela Basin(1998) Hung, Enrique J.; Bally, Albert W.The nature of the basement underneath the Monagas foothills and the Serrania del Interior of the Eastern Venezuela Basin is unknown. It could consist of crystalline Precambrian, Paleozoic sedimentary rocks and/or Jurassic rocks deposited in half grabens. Alternative structural interpretations across the Monagas foothills range from basement-involved to non-basement-involved decollement tectonics. These hypotheses imply varying amounts of shortening along the Serrania to Foreland transect ranging from 15 to 115 km oblique component of the El Pilar fault. The foreland-verging thrust system appears to be "in sequence". In the Monagas foothills earlier decollements at the base of the Miocene are responsible for the formation of a complex accretionary wedge. The deeper structures of the Monagas foothills involve the Mesozoic which was thrusted following the emplacement of the Carapita accretionary wedge. Apparent "out of sequence" are due to the interference of late deeper structures with the earlier structures of the accretionary wedge.Item Unknown Geologic evolution of the Burgos Basin, northeastern Mexico(1993) Perez Cruz, Guillermo A.; Bally, Albert W.The Burgos Basin in northeastern Mexico has been the site of interaction of the Cordilleran thrust and fold belt of western North America with the passive margin of the Gulf of Mexico. The primary tectonic episodes in this region include: (1) Middle-Upper Eocene compression associated with foreland deformation of the Sierra Madre Oriental and Coahuila fold and thrust belts, (2) Upper Oligocene regional uplift and the emplacement of granodioritic plutons, and (3) Miocene-Pleistocene regional uplift and volcanism. Compressional deformation extended from the Sierra Madre Oriental and Coahuila fold and thrust belts approximately 100 km east into the Burgos basin, interacting with the passive margin of the western Gulf of Mexico. Eocene compression created (1) large-scale, southwest-vergent thrusts and folds involving basement, (2) salt-cored, complex folds developed in strata overlying thick Upper Jurassic salt, (3) partially inverted structures, and (4) tight folds with multiple decoupling levels. Upper Oligocene regional uplift and erosion west of the basin margin caused deposition of a thick package of conglomerates in the western areas of the basin. Rapid subsidence, siliclastic deposition, and growth faulting occurred further the east. Regional uplift was contemporaneous with emplacement of granodioritic plutons, now exposed in the cores of some of the basement-involved anticlines in the western portion of the basin. Regional western uplift and erosion continued in the Miocene to Pleistocene, producing increasing amounts of siliciclastic influx into the basin. Sediments were accommodated within the downthrown blocks of expanded growth fault systems. The Cenozoic normal fault trends of coastal Texas extend southward into the Burgos Basin, but their amount of expansion and orientation has been modified by periods of thrusting, folding, regional uplift, and plutonism.Item Unknown Late Paleozoic and Early Mesozoic geologic evolution of the Arklatex Area(1988) Milliken, Jeffrey Van; Bally, Albert W.A structural and sedimentological history for the Late Paleozoic and Early Mesozoic is formulated from subsurface and seismic reflection data for the Arklatex Area. The Ouachita structural belt is the product of Pennsylvanian folding and thrusting of an Early Paleozoic passive margin wedge. An Atokan thin-skinned thrust complex (Ti Valley) was deformed during the DesMoinesian by basement-involved duplexing, which carried with it Early Paleozoic foreland carbonates. These carbonates and the underlying Precambrian basement may be mapped about 80 km south of the outcrop areas of the Ouachita Mountains. Following regional post-Atokan peneplanation, post- to synorogenic deposition commenced in the continental backarc (Paleozoic Arklatex) basin which formed on the hinterland side of the Ouachita arc. This successor basin contains over 8000 feet (2400 meters) of Pennsylvanian and Permian shelf carbonates and clastics. Following another regional unconformity, over 7000 feet (2100 meters) of discontinuous Triassic redbeds were deposited in structural troughs formed during a poorly-documented rifting event. Finally, Jurassic Werner clastics and anhydrite buried most remaining Triassic topography during the initial episode of evaporite deposition.Item Unknown Late Tertiary tectonic evolution of the central Walker Lane, west-central Nevada and California(1998) Keller, Richard Paul; Bally, Albert W.An integrated model is derived for the sequential development of tectonic events in time among different evolving component structural domains comprising the central Walker Lane, west-central Nevada, based on constraints from data compiled from multiple disciplines. Evidence indicates four major tectonic episodes: (1) between 27 and 22 Ma; (2) 22 to 17, 15 Ma; (3) 17, 15 to 11, 10 Ma, and; (4) post-11, 10 Ma. These can be consistently tied to a temporal clockwise reorientation of the regional extension (from northerly to NW-SE) within the central Walker Lane, and also correspond in time with the occurrence of four distinctive litho-compositional assemblages that are confined within major chrono-stratigraphic boundaries defined by regional unconformities within the Tertiary volcano-sedimentary section representing the last 30 m.y. Incorporation of the many isolated Tertiary sections into a regional chrono-stratigraphic framework based on abundant isotopic age data, provides the universal reference frame in time with which to correlate tectonic events among the component structural domains. In this model, the tectonic evolution of the component structural domains results from decomposition of the regional crustal relative displacement field into normal and trace-parallel components along major faults, within the upper brittle crustal layer. Conservation of net relative displacement fields is provided by the mechanical lamination along one or more mid-crustal low-angle to near-horizontal dislocation surfaces (detachment zones) above which decomposition of the changing displacement field is resolved along structures within adjacent developing structural domains. These changing displacement field decompositions and related extension occur E of a major coherent crustal boundary structure, the Sierra Nevada block, and are considered in terms of its motion relative to stable North America, for the evolution of the Walker Lane as a boundary region between it and the expanding Basin and Range to the east.Item Unknown Marine geology of the northwestern Weddell Sea and adjacent coastal fjords and bays: implications for glacial history(1985) Smith, Michael John; Anderson, John B.; Bally, Albert W.; Dunbar, Robert B.Sedimentologic, compositional, and cleat shape analyses reveal that piston cores obtained on the northwest Weddell See continental shelf penetrated residual glacial marine sediments adjacent to Seymour Island, compound glacial marine sediments north of 64Item Unknown Melville Island's salt-based fold belt (Arctic Canada)(1991) Harrison, John Christopher; Bally, Albert W.Melville Island lies astride the Cambrian through Devonian Arctic Platform, correlative rocks of the Franklinian Mobile Belt and, unconformable post-Devonian cover of the Sverdrup Basin. Seismic profiles and a revised geology map provide insight into Melville Island bedrock structure spanning a billion years of earth history to depths exceeding 20 km. Structures at the deepest levels include possible ?Precambrian crystalline basement and three ?Proterozoic seismic successions deformed and eroded prior to unconformable overlap by ?Lower Cambrian strata. Over a south to north distance of 300 km, the ?Cambrian through Devonian shelf-marginal wedge increases from 1200 m to at least 12500 m in thickness. The overlying Devonian clastic wedge (3000 to 4600 m) represents the depositional record of the ancestral Ellesmerian Orogeny. deformation that eventually terminated lower Paleozoic sedimentation. This southerly-directed deformation produced large contractional features on the island, and a salt-based fold belt that dominates surface structure. The fold belt is continuous downwards with: a seismically-imaged, folded and thrust faulted interval with up to 28 km (15%) horizontal shortening; a basal detachment at 5 km, and; an array of southerly- and northerly-transported thrusts most of which fail to appear at surface. Elements of a younger Ellesmerian deformation phase, recognized in surface cross-fold axes, are also mapped within the folded sub-salt succession below 5 km. Ellesmerian deformation continues to the west where style is related to slip on a ?mid-Cambrian detachment. Thrusts that ramp up to the sub-salt decollement have produced large anticlinoria near the present margin of the Sverdrup Basin. These faults have been repeatedly reactivated since the ?Precambrian. Recognized phases include: a N40-10$\sp\circ$W-directed Late ?Proterozoic extension; mid-?Cambrian growth faulting; two phase sinistral transpressive inversion of these extensional structures during the Ellesmerian Orogeny; northerly-directed rifting of Sverdrup Basin in the Carboniferous; inversion of the rift zone during the mid-Permian; evaporite diapirism and magmatic activity in the Jurassic and pre-Albian Cretaceous; southwesterly-directed sinistral transpressive adjustments coeval with the mid-Tertiary Eurekan Orogeny, and; a final phase of uplift and continuing seismicity.Item Unknown Pleistocene seismic stratigraphy of the Galveston South addition, offshore Texas(1984) Lewis, Dana Lynn; Clark, Howard C.; Bally, Albert W.; Anderson, John B.Seven seismic sequences were identified on the outer shelf and upper slope of the northwestern Gulf of Mexico from a grid of high resolution seismic sections. The sequences were deposited during eustatic fluctuations of sea level during Wisconsin glacial and interglacial stages. The sequences include deposits of an early Wisconsin low stand, middle Wisconsin high stand, and late Wisconsin low stand of sea level. Growth faults trending parallel to the shelf break expanded the secton from 6% to 6%. The faults resulted from salt flowage at depth in response to loading by thick deltaic deposits, which prograded to the shelf edge during low stands of sea level. Smaller, local fault systems are associated with diapiric intrusions. Diapirs exerted little control over Wisconsin sedimentation in the study area. Diapirs on the inner shelf are stock-like in appearance while those on the outer shelf and upper slope are broad swells and ridges.Item Unknown Potassium-argon age and petrography of the Sierra Blanca Peak igneous intrusives Hudspeth County, Texas(1983) Matthews, William K.; Adams, John A. S.; Baker, Donald R.; Bally, Albert W.Rhyolite and diorite intrusives are exposed six miles west of Sierra Blanca (Hudspeth County) in West Texas. StructuraUy, they lie between the relatively undeformed Diablo Platform and the folded and faulted Chihuahua Tectonic Belt (Laramide). In thin sections the rhyolite was homogeneous and the diorite proved more variable in mineralogy. Detailed field mapping (1:24) confirmed the general outlines of the five rhyolite laccoliths described by earlier workers. New details of rhyolite dikes, autobrecciation, and flow banding were recognized. A rhyolite age of 36.1 m.y. was reported by earlier workers. The new mapping documented over fifty previously unreported diorite dikes and sills with a concentrated swarm near Sierra Blanca Peak. A potassium-4/argon-4 age of 88 +4 m.y. from a single hornblende phenocryst from a 3 foot dike in the diorite swarm is the oldest Mesozoic age reported to date in this region. Mineralogical differences between the rhyolite and diorite and the 5 m.y. interval between emplacements increase the probability that they are from unrelated magma sources and different tectonic regimes.Item Unknown Salt and slope tectonics offshore Louisiana(1993) Wu, Shengyu; Bally, Albert W.Various stages of mid-Jurassic salt deformation resulted in post-salt extensional and contractional systems on the continental slope offshore Louisiana. Pre-mid-Cretaceous salt deformation resulted in salt massifs, small allochthonous salt bodies, pseudo-clinoforms and turtle structures. During a significant period of sediment starvation between mid-Cretaceous and mid-Oligocene time, previously formed salt and related structures remained stable. Following the reactivation of salt structures from mid-Oligocene to early-Miocene, rapid sedimentation during middle Miocene resulted in the development of large diapiric salt walls and stocks fed from the pre-mid-Cretaceous salt massifs. The rising diapiric salt structures displaced the downslope section of the rapidly deposited overburden seaward to form the Mississippi Fan Fold Belt focused near the frictional boundary along the basinward limit of the mother salt. The shortening in the fold belt ceased when the allochthonous salt began to spread near sea floor within sediments during Late Miocene. Since late Miocene, up-dip from the fold belt, large scale primary allochthonous salt sheets continued to form and spread down-slope. As massive salt withdrew from the mother salt, large primary withdrawal basins, regional, counter-regional growth fault systems, tension faults, primary and secondary welds and turtle structures formed. With increased sediment loads, the primary allochthonous salt was deformed. Consequently, supra allochthonous structures such as the secondary allochthonous salt, secondary and tertiary withdrawal basins, tertiary, quaternary and quintic welds and large extensional growth faults and occasionally contractional faults developed.Item Unknown Seismic stratigraphy of the Northwest Gulf of Mexico(1985) Archer, Robert E.; Bally, Albert W.; Anderson, John B.; Clark, H.C.Pleistocene sedimentation at the outer continental shelf of the northwest Gulf of Mexico was related to eustatic fluctuations of sea level during the Wisconsin period. Four seismic sequences interpreted from high resolution records corresponded to deposition during a Recent high sea level stand, a late Wisconsin low sea level stand, a middle Wisconsin interglacial high stand, and the forth sequence was evidenced by the record of deposition during an early Wisconsin low sea level stand. Growth faulting, seen as expansion of section, and a more prevalent faulting due to salt diapirism were present throughout the study area. The growth faults were consistent through the sections. Faults related to diapirism were local and many were not traceable from section to section. Both growth faulting and diapirism, as well as eustatic sea level changes, seem to have exerted an influence on sedimentation in the study area.Item Unknown Structural evolution of SE Mexico (Chiapas-Tabasco-Campeche) offshore and onshore(1995) Garcia-Molina, Gorgonio; Bally, Albert W.The Yucatan Platform bisects the NW-SE Sierra de Chiapas fold belt of SE Mexico at right angles. The outcropping Sierra de Chiapas involves Mesozoic platform carbonates, but its northwestern subsurface continuation involves mostly Mesozoic basinal and slope facies sediments in the Villahermosa folds and their offshore continuation, the Sonda de Campeche folds. The main decollement level for the folds is a middle Jurassic evaporite sequence. The pre-salt "basement" of the area is poorly defined but estimated to dip from about a depth of 6 km to the north (Campeche offshore) to 13 km in the south (Sierra de Chiapas). The fold belt was formed during upper Miocene time and is characterized by bivergent NW-SE striking folds. The amount of shortening is estimated to be in the order of 45 km to 65 km. In the onshore and offshore subsurface the folded belt is orthogonally superposed by a late Neogene growth fault system which soles out near the base of the Neogene. This growth fault system developed on the continental slope and intercepted salt diapirs that probably emanated from the core of deep-seated folds. Much of the salt accumulated farther north in the large allochthonous mass of the Campeche salt domes.Item Unknown Structural evolution of the central External Betic Cordillera, southern Spain(1990) Blankenship, Cynthia Lee; Bally, Albert W.A new tectonic subdivision of the central External Betic Cordillera is proposed based on previous stratigraphic studies, interpretation of seismic reflection profiles and balanced cross-sections. All available surface and subsurface data are used to constrain a balanced cross-section in the central part of the Betic folded belt, and reconstructions are presented to illustrate three optional evolutionary sequences for this folded belt. In the favored option, the outermost allochthonous unit is interpreted to be bounded to the south by a backthrust. In the reconstruction this unit is located immediately south of the undeformed foreland. Furthermore, the dominant structure in the main part of the folded belt is postulated to be a large, elongate klippe emplaced by a north-directed overthrust. Based upon stratigraphic correlations across and along the thrust belt, the paleogeography that results from this structural reconstruction is that of a single basin.Item Unknown Structural evolution of the Neogene Adana and Iskenderun basins, South Turkey(1994) Pralle, Norbert; Bally, Albert W.The structural styles of the Neogene basins in Southern Turkey formed in two stages. (1) Early to Middle Miocene transtension in a NNW-SSE direction disrupting the Paleozoic--Mesozoic substratum in the Adana Basin and the allochthonous ophiolite basement in the Iskenderun Basin. (2) Late Messinian-Pliocene transpression in a NW-SE direction which yielded structures on two levels. Inversions of former extensional faults sole in the substratum. The compression also shows advancing thrusts which utilize the Messinian evaporites as a decollement surface. Synchronously with regional shortening gravitational tectonics sloping towards the deeper parts of the Iskenderun Basin accompany the overall deformation. The study area and the Amik Basin to the southeast is a strain transfer system between two major sinistral transform faults; the Ecemis fault to the northwest of the Adana Basin and the Dead Sea fault to the southeast of the Iskenderun Basin, where it loses its transcurrent character into the graben zone of the Amik Basin.Item Unknown Structural evolution of the offshore forearc basins of Peru, including the Salaverry, Trujillo, Lima, West Pisco and East Pisco basins(1994) Azalgara, Carlos; Bally, Albert W.The basins of the study area were filled with the following sequences: E$\sb0$ (lower? to middle Eocene); E1 E2 and E3 (fill middle Eocene half grabens); E-O (uppermost middle Eocene-Oligocene); M1, M2 and M3 (lower-upper Miocene); P (uppermost Miocene-Pliocene); and, Q (Quaternary). Four compressive events occurred during Paleocene?, middle Eocene?, upper-middle to late Miocene and middle Pliocene?; and two extensional episodes took place during middle Eocene and late Pliocene. Pre-Tertiary substratum was involved in all tectonic events. The Salaverry-Trujillo High which formed during the third compressive event and the Pliocene consists of a trench-parallel open flexure and a belt of middle Eocene to upper Miocene inverted wedges. The continuous uplifting of the Salaverry-Trujillo High produced a sustained shallowing of the sea floor at the slope break zone on the western side of the high and the incision of submarine canyons.