ABSTRACT The deposits of Pleistocene Lake Tecopa include lacustrine, alluvial, eolian, and groundwater discharge deposits of the Tecopa basin in southeastern California. Stratigraphic sections measured in the Tecopa basin and detailed sedimentary facies analysis were used to interpret the depositional settings and track the evolution of sedimentary processes in the basin during the Pleistocene. The early Pleistocene (ca. 2.4–1.0 Ma) deposits of the Lake Tecopa beds record deposition in small saline, alkaline lakes and playas with surrounding mudflats and sandflats and adjacent alluvial fans. Ancestral Amargosa River gravels are first observed in fluvial deposits in the northern part of the basin at ca. 1.0 Ma and correspond with lake expansions (Glass Mountain [GM] lakes) during deposition of the uppermost Glass Mountain ash beds. Several oscillations in lake level followed the post-GM lake decline, culminating in the basin-filling Lava Creek (LC) lake, which reached its acme during deposition of the 0.63 Ma Lava Creek B ash bed. The post–Lava Creek B strata reflect primarily alluvial, fluvial, eolian, and groundwater discharge depositional processes, punctuated in the youngest part of the section by basin-filling lakes (high lake 1 and 2). The Lava Creek B ash bed and older lacustrine strata exhibit extensive zeolitization and clay authigenesis, characteristic of saline, alkaline lake deposits, but the post–Lava Creek B ash bed lacustrine strata have only minor zeolite and clay alteration, suggesting fresher water conditions and a change in the hydrologic state of the basin. Sedimentological observations along with shoreline elevation data provide evidence for intermittent spillover of basin-filling lakes after ca. 0.63 Ma. Subtle tectonic deformation influenced sedimentary processes in the Tecopa basin throughout its history. Episodes of uplift and tilting of Lake Tecopa strata during the middle Pleistocene in the southern part of the basin along the Tecopa Hump likely controlled the sill elevation for spillover of the lake, creating accommodation space for late Pleistocene basin-filling lakes. Ultimately, decreased uplift could not keep pace with increased discharge resulting from high effective moisture during latest middle Pleistocene pluvial periods, and Lake Tecopa drained, most likely during or immediately after marine oxygen isotope stage (MIS) 10 (ca. 0.3 Ma). The deposits of Lake Tecopa provide a detailed record of Pleistocene paleoclimate from ca. 2.4 to 0.3 Ma that demonstrates Milankovitch-scale tuning and clarifies the amplitude of Pleistocene climate change in the southern Great Basin of North America.

Abstract The role of climate change in driving alluvial-fan sedimentation is hard to assess in pre-Quaternary successions, for which detailed chronologies and climate-proxy records cannot be easily established. In the Teruel Basin (Spain), high-resolution (10 4 –10 5 years) chronological and palaeoclimatic information was derived by orbital tuning of Late Miocene mudflat to ephemeral-lake deposits. The semi-arid palaeoclimate made this low-gradient, basinal environment sensitive to thresholds in the local hydrological balance. Basic facies rhythms are attributed to alternating, relatively humid/arid phases controlled by the climatic precession cycle. The lower stratigraphic interval of this reference section interfingers with distal, coarse-clastic beds from a coeval alluvial fan. The consistent interdigitation of debris-flow deposits with distal strata indicative of arid-to-humid climate transitions shows that fan sedimentation was regulated by climate cyclicity. In particular, the largest volumes of terrigenous debris were shed from the fan onto adjacent mudflats during transitions to relatively humid periods with pronounced seasonality, during precession minima. Distal to medial sections within alluvial-fan outcrops also feature prominent, laterally continuous alternations of coarse- and fine-clastic packages. This high degree of architectural organization, uncommon in fan successions, and stratigraphic relationships with the reference section suggest orbitally controlled climate change to have been the forcing mechanism.

Abstract The Chenier Plain of southwestern coastal Louisiana is a Holocene strand plain composed of wooded beach ridges (cheniers) and intervening mudflat grassy wetlands. The mudflats form as prograding tidal flats along the open, but low-energy Gulf of Mexico coast; cheniers form from winnowing of sand and shells from the mudflats by waves during transgression. Mudflats are deposited when a Mississippi River delta lobe is nearby to the east, and cheniers are formed when distributaries switch to a more distant location farther east. All of the cheniers have formed within approximately the past 3000 yr or less and are progressively younger toward the present coastline. Spits are attached to the cheniers at estuaries; they grow westward in response to the dominant longshore currents. Currently, mudflats are prograding in Vermillion Parish to the east, while cheniers form in eastern Cameron Parish along with some regressive beach ridge development in western Cameron Parish. This coast is microtidal with low wave energy. A high rate of subsidence as well as sea-level rise characterizes the Chenier Plain, which is subject to increased wave energy and mud transport every year during many cold-front passages and periodic storm surges associated with tropical cyclones of much lower frequency. Major storm surges can inundate the entire Chenier Plain, wreaking havoc on human settlements.

Abstract Each year from June through November, tropical cyclones are a common potential problem for those living in coastal communities along the southwest Louisiana and southeast Texas coasts. Developing from small tropical disturbances, tropical cyclone strength is determined by many factors: ocean temperature, upper and lower wind circulation, latitudinal position, etc. Ecological, geological, and economic effects of strong-to-devastating tropical cyclones on coastal areas are typically extreme. Since the 1860s, seven strong or greater tropical cyclones have struck the Louisiana-Texas coast. Their impact has made an indelible impression on the coastline as well as on the communities in the area