ABSTRACT Barbados is actively rising in the latest phase of a long history of emergence that began as far back as 15 Ma. The current phase began at or before ca. 700 ka, is highly nonuniform, and at least locally, has been nonsteady. The uplift rate field in SE Barbados ranges between near-zero and 0.47 m/k.y. and is harmonic to active structures of NNW-SSE contraction. Emergence markers include limestone strata, coral, and shoreline angles, but we used only shoreline angles in calculations. We divided the capping limestone of windward Barbados into 10 units using physical criteria and dated them with over 40 230 Th ages as oxygen isotope stages 5a, 5e, late 7 and early 7, and old (older than 300 ka). The oldest unit is a relic of an earlier phase of emergence. Younger units, probably as old as 700 ka, downlap the eroded flank of the oldest unit and sublimestone foundation. Younger units comprise landward clastic facies deposited on abrasion platforms during eustatic highstand and seaward-coalescent fringe reef blankets deposited on preexisting slopes, mainly in transgression. Earlier models of ridged reefs of catch-up growth origin are not supported in windward Barbados. Shoreline angles, the updip tips of terrace floors and of younger limestone units, are isochronous markers of maximum highstand levels. Despite the lack of direct determination of their ages, shoreline angles provide the truest measures and highest values of emergence. Coral thought to indicate highstand growth gives moderately lower uplift rates due to depths of growth and collapse. Coral grown during transgression gives a marked error in emergence.

ABSTRACT The geomorphic evolution of southeastern windward Barbados is embodied in the development of a terraced seaward island slope on a tectonically rising scarp. The island slope is wholly erosional and a product of marine and subaerial processes. Modulation of the slope by terraces has occurred fundamentally by marine erosion at eustatic stillstands but includes morphologic additions by limestone deposition. The ongoing phase of morphologic development and island emergence began at or before ca. 700 ka. Emergence has proceeded at an increasing rate northwestward along the island’s southeastern coastline. The terraced island slope is markedly affected by post-terrace denudation. As many as eight marine terraces are preserved on the windward island slope below the planed surface of the Central Highlands, which is counted as terrace 1. Relics of an upper set of terraces are perched on the face of Second High Cliff, the ancient erosional margin of the oldest limestone capping Barbados. Second High Cliff developed by successive marine incisions over a probably long duration preceding oxygen isotope stage 9. A lower terrace set was excised in stages 9 through 5a in the siliciclastic island foundation or (and) in limestone cover of preceding terraces. Marine terrace floors extend seaward from an erosional backcliff and shoreline angle to a younger erosional cutoff. The most broadly preserved terrace floors indicate the following systematic succession of seaward profile elements: narrow upper ramp; broad upper flat; lower ramp; and on one, a lower flat. Carbonate cover is chiefly clastic on the upper ramp and flat, and chiefly reefal on the lower ramp. Most shoal-water reefal facies appear to be in fringe reef blankets. Terrace profile geometries are explained by a simple theory of wave abrasion in proportion to duration of sea level at a shoreline. At stillstands, the wave impact caused large shoreline recession and development of flats, whereas in transgression and regression, rapid sea-level change permitted only minor recession. Corresponding differences in cover facies are explained as functions of duration of breaking waves and seabed stability. Widespread post-terrace denudation is attributed to floods of upland provenance, local overland flow, and marine flooding. Riverine processes have produced channelization and a high degree of terrace preservation on the interfluves in the steeper, foundation-based northern windward region. This differs markedly from the more diffuse, shallow gullying and stripping of the limestone-covered shallow slopes of the southern region. An intensely stormy spell is suggested between stages 5e and 5c.

ABSTRACT This chapter presents geological documentation of Quaternary (and perhaps older) event histories of southeastern Barbados. The Barbados Limestone is herein formally defined. A time-stratigraphic division of the Barbados Limestone in southeastern Barbados and the properties of the stratigraphic units are presented. A major finding of this study is that the marine terraces originated wholly by marine erosion, not by reef construction, and evolved in stages over a long duration. The hydrology and thickness data of the Barbados Limestone are discussed, and hypotheses on causes of thickness variations are given. The study domain is divided into seven areas that contain a continuous flight of nine marine terraces preserved in various partial sequences. Discussions of these key seven areas in southeastern Barbados are supported by geologic maps at large scale and cross sections. Sections with VE > 1 display limestone stratigraphy and facies over relatively large lengths. Sections with VE = 1 show true structural configurations over short lengths. Detailed observations and radio isotopic dating of the limestone units permit differentiation and correlation among them.

Emergence and Evolution of Barbados is a three-part analysis of the Quaternary geologic and geomorphologic evolution of the island of Barbados in the southeastern Caribbean. “Geology of Southeastern Barbados” assembles and integrates detailed observations into a complex 700 k.y. history of marine sculpting and riverine flooding processes. “Marine Terrace Evolution of Windward Barbados” revises the Quaternary stratigraphy of the island, describes the tectonics of emergence, and demonstrates that uplift rates vary by location. “Active Emergence, Chronology, and Limestone Facies in Southeastern Windward Barbados” is the first comprehensive study to integrate marine erosion and deposition with tectonic uplift rates. Major findings of this work are that Barbados’ Central Highlands are an erosional remnant, and that terraces originated principally by marine erosion rather than by reef construction.

This text accompanies a set of twelve 1:10,000 geological maps of Barbados, West Indies; four associated cross sections that transect the island; and a three-part appendix. Basement rocks on Barbados are assigned to two Paleogene tectonic complexes that formed within or above an active subduction complex. The nature and origin of these rocks were the subject of many publications by Robert C. Speed and his students and colleagues, and are briefly recapitulated in this Special Paper. The basement rocks are overlain by Quaternary rocks and sediments, and Speed's studies of these younger materials are the focus of this volume. The island's marine terraces, modern shore zone, modern marine seacliffs, stream networks, and landslides are analyzed in detail. Uplift rates that were calculated at 71 sites, and dozens of 230 Th dates of Pleistocene limestone are presented here for the first time. The accompanying CD-ROM has advanced drafts of two manuscripts—one relating emergence episodes and stratigraphy to tectonic and eustatic sea-level changes, and the other documenting the history of terrace development—as well as an appendix that supplements both of those manuscripts. The materials in this contribution are components of a multidisciplinary, comprehensive analysis of the geology and geomorphology of Barbados by Robert Speed, who passed away in 2003 shortly before finalizing this work.

Abstract This chapter presents a synthesis of the structure and Phanerozoic tectonic evolution of continent-ocean transitions around nearly the entire North American continent. Its objectives are to compare and contrast the modern transitions and Phanerozoic histories of specific margins of North America discussed in other chapters of this book and in the Transect displays (see Foreword) and to present ideas on processes in the evolution of continent-ocean transitions. A word about the focus on the continent’s margins and their place in the global scheme of tectonics may be warranted. The modern transitions between the North American continent and adjoining oceanic basins are where plate tectonics has most recently affected the continent aside from rigid translation. At active margins, where oceanic lithosphere underrides or slides along the continent, the development of the margin is ongoing and may have been continuous over a long time. In contrast, at passive margins where the continent has split and sea-floor spreading has occurred, the continent-ocean transition was developed in a discrete event and was discontinuous in time. At passive margins, the most recent North American transitions range from Holocene to mid-Mesozoic. At collisional margins, where the North American continent is or was on the underriding plate, the development of the margin was also discrete and discontinuous. As with passive margins, an existing collisional margin is generally the product of an ancient event. During the development of all margin types, the motions between the North American plate and adjacent plates have commonly been broadly distributed and nonuniform

Abstract The continental margin transect program evolved through a desire to define the specific characteristics of North America’s modern continental margins and to compare the modern margins with Paleozoic examples, now found within the continent. Thus, the features of modern margins can be used to locate and elucidate the structures of ancient analogues. Conversely, the exposed rocks of ancient margins provide an insight into the evolution and deep structures of modern examples. Ocean-continental transitions, rifting mechanisms, development of sedimentary basins, processes of continental breakup, and ancestral controls are all features that warrant comparison between modern and ancient examples. The Atlantic coast has the best-known passive margin of North America. Inboard of it is the Appalachian Mountain chain, which records a clear history of late Precambrian rifting and the passive development of a Paleozoic continental margin. Transects across both these modern and ancient examples provide information on scale and detail that is useful for comparisons. The modern continental margin of eastern Canada (Fig. 1a, 1b) has a wider variety of ages and styles than that of its eastern United States counterpart. Segments of the margin southeast of Nova Scotia and east of Labrador are typical of rifted margins, though of different ages. Between them lies the tortuous segments of the northern and eastern Grand Banks where rifting and subsidence occurred over a broad area of the continental shelf. In contrast, the southern boundary of the Grand Banks is a transform segment. Rocks of the Appalachian Paleozoic margin are best preserved and exposed

Abstract The continental margin of eastern North America has been studied as part of the North American Continent-Ocean Transect Program by synthesizing existing data along six corridors, each at least 100 km wide, between Newfoundland and Georgia that extend from the Phanerozoic craton to the oceanic crust. The term Phanerozoic craton is used here for a cratonal area that has not undergone significant deformation since the beginning of Phanerozoic time. One of these corridors is in Canada (Dl; Haworth and others, 1985), and two additional Canadian transects (D2 and D3; Keen and Haworth, 1985a, 1985b) cross the present continental margin, but do not extend westward to the craton. Herein I analyze the evolution of the eastern continental margin as depicted by the five corridors or transects, El through E5, prepared or in preparation for the United States. The five transects in eastern United States are outlined in Figure 1 and are as follows. E1, Adirondacks to Georges Bank (Thompson and others, 1993). The corridor length is 1000 km. E2, New York Appalachian basin to the Baltimore Canyon trough (Drake and others, unpublished). The corridor length is 860 km. E3, Pittsburgh to Baltimore Canyon trough (Glover, 1989; Glover and others, unpublished). The corridor length is approximately 850 km. E4, Central Kentucky to the Carolina trough (Rankin and others, 1991). The corridor length is 1100 km. E5, Cumberland Plateau to Blake Plateau (Hatcher and others, 1994). The corridor length is approximately 1280 km. Because of the time constraints, E2 and E3 will not

Abstract The Gulf of Mexico basin on the southeastern margin of North America is one of the most extensively studied basins in the world. Most of this work, however, has been concentrated on the shallower parts of the thick sedimentary section around the periphery of the basin, primarily related to the search for oil and gas and other minerals. Although comparatively little is known about the details of the more deeply buried parts of the sedimentary section and the crust below, enough geological and geophysical data exist now to enable compilation of a reasonable framework for the entire basin and document the evolution of the crust in general terms. The crust in the region contains the record of three successive phases of plate motion: 1. Divergent motion. Late Precambrian to early Paleozoic rifted margin and early Paleozoic south-facing passive margin along the southeastern edge of the North American craton. 2. Convergent motion. Late Paleozoic diachronous Appalachian-Ouachita orogenic belt, including foreland thrust belts, interior belts, and accreted terranes. 3. Divergent motion. Early to middle Mesozoic rifted margin and middle Mesozoic to present passive margin centered around a small ocean basin (present Gulf of Mexico basin). Mesozoic rifting introduced a new set of extensional faults, including a northeast-trending rift set and a northwest-trending transform set. Some faults used planes of weakness related to late Paleozoic compressional structures, and the Mesozoic transform system essentially duplicated an early Paleozoic transform system. Mesozoic extension resulted in a broad area of stretched or attenuated continental crust (transitional

Abstract We present a tectonic evolution of Mexico over the past 600 m.y., with focus on the position of southern margin of Proterozoic North America in Mexico, the Phanerozoic events that shaped this margin, and the accretion of terranes that built Mexico out from that margin to its present configuration. The evolution of Mexico is a peculiar and difficult problem in tectonics. Whereas the kinematic history of the region of Mexico, for example, the end of Proterozoic continental breakup, the collision of North and South America in the late Paleozoic, the drifting apart of those two continents in the Mesozoic, and the motions of plates in the Pacific basin relative to North America in Cretaceous and Cenozoic time, is reasonably well known, the kinematics of terranes now in the region is poorly understood. In large part, this disparity is due to the extraordinary extent and volume of Cenozoic volcanism. Although such volcanism informs us about Cenozoic convergence, it cautions that the crust of Mexico has probably undergone major modification in Cenozoic time. Moreover, the volcanic cover limits greatly the direct access to older rocks and structures necessary to develop the story of an evolution that is well resolved in space and time. A tectonic synthesis of Mexico thus requires more assumptions than for most mountainous regions. Our model of tectonic evolution of Mexico attempts to satisfy both far-field and sparse near-field kinematic histories and existing geologic and geophysical data. This chapter is a companion to an in-depth synthesis of data, identification

Abstract Corridor C-3 (Fig. 1) traverses the transition from oceanic crust to cratonal rocks of North America along a 1,500-km transect from offshore southern California to central New Mexico (Howell and others, 1985; Gibson and others, 1985). The western end of the transect is offshore in an oceanic seamount province of the Pacific plate. Eastward, it crosses the southern California borderland and emerges onshore in the batholith-dominated Peninsular Ranges. C-3 spans the Salton trough, a transform rift floored by nascent oceanic crust, and the Basin and Range structural province, formed by extension and disruption of cratonal rocks. The eastern end of C-3 is on the stable craton. Neogene tectonism has severely disrupted the older structural grain between the oceanic lithosphere and the craton. Much of this young tectonism is attributed to interactions along the plate edges after the spreading ridge system separating the Pacific and Farallon plates inpinged upon the North American plate in late Oligocene time. Two triple junctions—one migrating northward, the other southward relative to the Pacific plate—formed as the spreading system moved eastward relative to the North American plate. The San Andreas fault system began to develop within a broad zone of right shear as the triple junctions moved apart. The main strand of the San Andreas is but one of many northwest-trending right-lateral faults in the system. The boundary between the Pacific and North American plates is best perceived as a broad zone of right shear rather than a specific fault trace. The continental crust of the

Abstract The evolution of the North American continent and adjacent ocean basins in the central Cordillera of the western United States in Phanerozoic time was governed by three sequential tectonic regimes. The first included the creation of a passive margin during the latest Proterozoic to Early Cambrian (Stewart, 1976) and the removal of an unknown amount of sialic crust from the western margin of the continent. The second regime maintained a passive continental margin of western North America from Middle Cambrian to Triassic time, but permitted collisions of outboard terranes with the sialic margin in Mississippian and Permian-Triassic time (Speed, 1982; Dickinson and others, 1983). Since Triassic time, western North America, adjacent oceanic plates, and intervening microplates and other tectonic packets have existed in a regime of active margin tectonics (Hamilton, 1969; Coney and others, 1980; Saleeby, 1983; Saleeby and Busby-Spera, 1992) driven mainly by eastward subduction of oceanic lithosphere. This third and currently operating regime has been marked by diverse phenomena including subduction of oceanic lithosphere below the continent and phases of highly oblique convergence and suture-zone or intra-arc spreading, ridge-trench collision, growth of a continental arc, major foreland contraction and extension, and the accretion of displaced terranes to the sialic edge. Corridors C1 and C2 of the Ocean-Continent Transect Program traverse all essential elements of the transition from Pacific plate oceanic crust to cratonal North America that have resulted from these three tectonic regimes. Figure 1 shows the locations of the corridors in relation to the major tectonic elements