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Palaeogeographic and lake‐level reconstructions provide powerful tools for evaluating competing scenarios of biotic, climatic and geological evolution within a lake basin. Here we present new reconstructions for the northern Lake Tanganyika subbasins, based on reflection seismic, core and outcrop data. Reflection seismic radiocarbon method (RSRM) age estimates provide a chronological model for these reconstructions, against which yet to be obtained age dates based on core samples can be compared. A complex history of hydrological connections and changes in shoreline configuration in northern Lake Tanganyika has resulted from a combination of volcanic doming, border fault evolution and climatically induced lake‐level fluctuations. The stratigraphic expression of lake‐level highstands and lowstands in Lake Tanganyika is predictable and cyclic (referred to here as Capart Cycles), but in a pattern that differs profoundly from the classic Van Houten cycles of some Newark Supergroup rift basins. This difference results from the extraordinary topographic relief of the Western Rift lakes, coupled with the rapidity of large‐scale lake‐level fluctuations. Major unconformity surfaces associated with Lake Tanganyika lowstands may have corresponded with high‐latitude glacial maxima throughout much of the mid‐ to late Pleistocene. Rocky shorelines along the eastern side of the present‐day Ubwari Peninsula (Zaire) appear to have had a much more continuous existence as littoral rock habitats than similar areas along the north‐western coastline of the lake (adjacent to the Uvira Border Fault System), which in turn are older than the rocky shorelines of the north‐east coast of Burundi. This model of palaeogeographic history will be of great help to biologists trying to clarify the evolution of endemic invertebrates and fish in the northern basin of Lake Tanganyika.

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Although much is known about the interaction of faulting and sedimentation within the basins of active segmented continental rift systems, little is known about these processes within the interaction zones of varying geometries that separate the young interacting segments. We address this problem by exploring the non-volcanic rift interaction zones (RIZ) along the humid, magma-poor juvenile western branch of EAGE KOLAWOLE Et AL. F I G U R E 1Cartoon illustrating the growth of propagating rift segments along active continental rift systems (updated and modified after Nelson et al., 1992). Note that this cartoon only features collinear and underlapping parallel rift segments. For each zone of rift segment interaction, the cartoon illustrates the pre-and post-linkage geometries of the rift segments. Also, note that cartoon represents rift segmentation and interaction at the early stages (stretching stage) of continental rifting F I G U R E 4 Eastern Africa rift basins and the major rift interaction zones. (a) Map of eastern Africa showing the different segments of the Cenozoic Western Branch (WBEARS) of the East African Rift System (and some of the Eastern branch segments). Also shown are the Mesozoic rift segments that are reactivated (e.g. LR, RR, SRZ) and unreactivated (e.g. LmR, MnR, RuR, ZR) during the current phase of Cenozoic extension.

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Watershed deforestation, road building, and other anthropogenic activities result in sediment inundation of lacustrine habitats. In Lake Tanganyika, this threatens the survival of many rock‐dwelling species by altering the structure and quality of rocky habitats. We investigated the relationship between habitat quality, as related to watershed disturbance intensity, and the biodiversity of faunal communities at three rocky littoral sites of low, moderate, and high disturbance. Turbidity measurements and other environmental observations confirmed that our lake sites represented a gradient of disturbance conditions. We documented differences in species density (number of species per constant area or time), species richness, abundance, and trophic ecology for fishes, molluscs, and ostracods. Fish censuses were performed by scuba divers at 1–20 m and by remotely operated vehicle (ROV) at 40–80 m. In the fish surveys, abundance, species density and richness, and herbivory reached their maxima at intermediate water depths. The depth range of herbivores, however, was restricted at higher‐disturbance sites. The ROV fish surveys at the high‐disturbance site showed high species richness despite low species density and abundance, and piscivores were proportionally more prevalent than in all other surveys. Molluscs censused by diver quadrats and sieve samples showed decreasing species richness and species density (sieve samples only) with increasing disturbance and no significant abundance trend. Ostracod species richness was similar between low‐ and moderate‐disturbance sites but was markedly lower at the high‐disturbance site (species density and abundance data were not available). Our faunal analyses suggest that all three taxonomic groups are negatively affected by sediment inundation but may have varying response thresholds to disturbance. Further, this study emphasized the utility of using complementary survey techniques to monitor and ultimately manage biodiversity in complex freshwater ecosystems.

Atmospheric CO 2 exerts a robust and well-documented control on Earth's climate, but the timing of glaciation during the late Paleozoic Ice Age (LPIA; ca. 360-260 Ma) is inconsistent with pCO 2 reconstructions, hinting at another factor. Stratospheric volcanic aerosols produce a large but temporary negative radiative forcing under modern conditions. Here we examine explosive volcanism over 200 m.y. of Earth history to show that the LPIA corresponded with a sustained increase in volcanism in both tropical and extratropical latitudes. A major peak in explosive volcanism at ca. 300 Ma likely corresponded to stratospheric sulfur-injecting eruptions at least three to eight times more frequent than at present. This level of volcanism created a steady, negative radiative forcing potentially sufficient to initiate and, most critically, sustain icehouse conditions, even under increasing levels of pCO 2 , and helps resolve discrepancies between glacial timing and CO 2 records. Accounting for the radiative forcing effects of CO 2 and sulfate indicates that both are required to explain the LPIA, with sulfate producing an especially strong effect at peak icehouse ca. 298-295 Ma. Frequent explosive volcanism would have increased atmospheric acidity, enhancing the reactivity of iron in abundant volcanic ash and glacially generated mineral dust, thus strengthening the climate impact of volcanism through a marine biological pump further primed by feedback with glaciation.

A B S T R A C TLandscapes are thought to be youthful, particularly those of active orogenic belts. Unaweep Canyon in the Colorado Rocky Mountains, a large gorge drained by two opposite-flowing creeks, is an exception. Its origin has long been enigmatic, but new data indicate that it is an exhumed late Paleozoic landform. Its survival within a region of profound late Paleozoic orogenesis demands a reassessment of tectonic models for the Ancestral Rocky Mountains, and its form and genesis have significant implications for understanding late Paleozoic equatorial climate. This discovery highlights the utility of paleogeomorphology as a tectonic and climatic indicator.