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.

ABSTRACT Montecito, California, has a complicated Quaternary history of debris flows, the most recent being the Montecito debris flows of 9 January 2018, which were wildfire-debris flow–linked events that took 23 lives and damaged or destroyed several hundred homes. Relative flow chronology, based on boulder weathering, incision rates, and soil dates with limited numerical (radiocarbon and exposure) dating, is used to identify paths of prehistoric debris flows. Topography of debris flow fans on the piedmont is significantly affected by the south-side-up reverse Mission Ridge fault system. Examination of weathering rinds from Pleistocene debris flows confirms that the Rattlesnake Creek–Mission ridge debris flows are folded over the ridge, and that lateral propagation linked to uplift of marine terraces (uplift rate of ~0.5–1 m/k.y.) significantly altered debris flow paths. As communities continue to rebuild and live in these hazard-prone areas, disaster risk reduction measures must take into account both spatial and temporal components of vulnerability. This field guide includes four stops from Montecito to Santa Barbara. The first stop will be to observe debris flow stratigraphy over the past ~30 ka beneath an earthquake terrace and a prehistoric Chumash site on the beach near the Biltmore Hotel in Montecito. The second stop will be at San Ysidro Creek in San Ysidro Canyon, the site of the largest Montecito debris flow that occurred on 9 January 2018. We will discuss source area and processes of the debris flow, and take a short hike up the canyon to visit the debris flow basin and a ring net designed to reduce the future hazard. The final two stops will explore the debris flow chronology of Santa Barbara over the past ~100 ka. Figure 1 shows the location of the field-trip stops. There is no road log as field sites can be found with a search on a smartphone.