Bear Lake sediments were predominantly aragonite for most of the Holocene, reflecting a hydrologically closed lake fed by groundwater and small streams. During the late Pleistocene, the Bear River flowed into Bear Lake and the lake waters spilled back into the Bear River drainage. At that time, sediment deposition was dominated by siliciclastic sediment and calcite. Lake-level fluctuation during the Holocene and late Pleistocene produced three types of aragonite deposits in the central lake area that are differentiated primarily by grain size, sorting, and diatom assemblage. Lake- margin deposits during this period consisted of sandy deposits including well-developed shoreface deposits on margins adjacent to relatively steep gradient lake floors and thin, graded shell gravel on margins adjacent to very low gradient lakefloor areas. Throughout the period of aragonite deposition, episodic drops in lake level resulted in erosion of shallow-water deposits, which were redeposited into the deeper lake. These sediment-focusing episodes are recognized by mixing of different mineralogies and crystal habits and mixing of a range of diatom fauna into poorly sorted mud layers. Lake-level drops are also indicated by erosional gaps in the shallow-water records and the occurrence of shoreline deposits in areas now covered by as much as 30 m of water. Calcite precipitation occurred for a short interval of time during the Holocene in response to an influx of Bear River water ca. 8 ka. The Pleistocene sedimentary record of Bear Lake until ca. 18 ka is dominated by siliciclastic glacial flour derived from glaciers in the Uinta Mountains. The Bear Lake deep-water siliciclastic deposits are thoroughly bioturbated, whereas shallow-water deposits transitional to deltas in the northern part of the basin are upward-coarsening sequences of laminated mud, silt, and sand. A major drop in lake level occurred ca. 18 ka, resulting in subaerial exposure of the lake floor in areas now covered by over 40 m of water. The subaerial surfaces are indicated by root casts and gypsum-rich soil features. Bear Lake remained at this low state with a minor transgression until ca. 15 ka. A new influx of Bear River water produced a major lake transgression and deposited a thin calcite deposit. Bear Lake quickly dropped to a shallow-water state, accumulating a mixture of calcite and siliciclastic sediment that contains at least two intervals of root-disrupted horizons indicating lake-level drops to more than 40 m below the modern highstand. About 11,500 yr B.P., the lake level rose again through an influx of Bear River water producing another thin calcite layer. The Bear River ceased to flow into the basin and the lake salinity increased, resulting in the aragonite deposition that persisted until modern human activity. The climatic record of Bear Lake sediment is difficult to ascertain by using standard chemical and biological techniques because of variations in the inflow hydrology and the significant amount of erosion and redeposition of chemical and biological sediment components.

A variety of sedimentological evidence was used to construct the lake-level history for Bear Lake, Utah and Idaho, for the past ~25,000 years. Shorelines provide evidence of precise lake levels, but they are infrequently preserved and are poorly dated. For cored sediment similar to that in the modern lake, grain-size distributions provide estimates of past lake depths. Sedimentary textures provide a highly sensitive, continuous record of lake-level changes, but the modern distribution of fabrics is poorly constrained, and many ancient features have no modern analog. Combining the three types of data yields a more robust lake-level history than can be obtained from any one type alone. When smooth age-depth models are used, lake-level curves from multiple cores contain inconsistent intervals (i.e., one record indicates a rising lake level while another record indicates a falling lake level). These discrepancies were removed and the multiple records were combined into a single lake-level curve by developing age-depth relations that contain changes in deposition rate (i.e., gaps) where indicated by sedimentological evidence. The resultant curve shows that, prior to 18 ka, lake level was stable near the modern level, probably because the lake was overflowing. Between ca. 17.5 and 15.5 ka, lake level was ~40 m below the modern level, then fluctuated rapidly throughout the post-glacial interval. Following a brief rise centered ca. 15 ka (= Raspberry Square phase), lake level lowered again to 15–20 m below modern from ca. 14.8–11.8 ka. This regression culminated in a lowstand to 40 m below modern ca. 12.5 ka, before a rapid rise to levels above modern ca. 11.5 ka. Lake level was typically lower than present throughout the Holocene, with pronounced lowstands 15–20 m below the modern level ca. 10–9, 7.0, 6.5–4.5, 3.5, 3.0–2.5, 2.0, and 1.5 ka. High lake levels near or above the modern lake occurred ca. 8.5–8.0, 7.0–6.5, 4.5–3.5, 2.5, and 0.7 ka. This lake-level history is more similar to records from Pyramid Lake, Nevada, and Owens Lake, California, than to those from Lake Bonneville, Utah.

Abstract The Newark Basin Coring Project (NBCP) has recovered over 6730 m of continuous core from 7 coring sites. Cores spanning the 4800 m of Lockatong and Passaic formations are characterized by cyclic lacustrine mudstone and shale, which reflect rise and fall of lake level in response to climatic fluctuations at intervals of 20,000 years and larger patterns of 100,000- and 400,000-year intervals. Sedimentary structures in the mudstones include: 1. Organic-rich laminites with thin, flat, continuous lamination; thick lamination with diffuse or irregular boundaries; silty or sandy laminae; or crystal-rich lamination. 2. Mudcracked, thin-bedded mudstone with lenticular sandstone layers; graded sandstone layers; mudstone layers with sharp contacts; muddy siltstone curls; or crystal-rich layers. 3. Massive mudstones with angular breccia fabric; vesicular fabric; rounded breccia fabric; root-disrupted fabric; or crystal-rich fabrics. These structures define five types of cycles: 1. Cycles dominated by thick, organic-rich laminites deposited in deep lakes and rounded breccias, reflecting deflated, salt-encrusted mudflats. 2. Cycles similar to the previous, but with more thin-bedded mudstone and massive mudstone with upward-fining crystal sequences reflecting saline mudflats. 3. Cycles with mudcracked thin beds grading to brecciated mudstone, then vesicular fabric reflecting shallow lakes drying up to dry playa mudflats. 4. Cycles similar to the previous, but with more organic-rich laminites or thin beds and root-disrupted mudstone at top, indicating wetter conditions and vegetation growth before lake transgressions. 5. Cycles dominated by root-disrupted mudstone and thin, organic-poor laminites or thin beds reflecting thick soils superimposed on shallow lake deposits. The abundance of each cycle type changes through the stratigraphic section, reflecting the change from arid conditions in a narrow basin upward to semi-arid to subhumid conditions in a broad basin. The use of climatic patterns and tectonic setting can provide important information toward modeling source and reservoir rocks in rift basin lacustrine deposits.

Abstract: Efflorescent salt crusts composed primarily of halite dominate the saline mudflats of Saline Valley and Death Valley, California. These crusts form by the complete evaporation of saline groundwater at the sediment-air interface. Efflorescent crusts also form where halite dust is introduced by wind, then dissolved by rain and reprecipitated as the rainwater is evaporated. Wind-blown silt and clay adhere to thin hydroscopic water films coating crystals in the efflorescent crusts, and coarser sediment is trapped in surface depressions. The sediment is left as a lag deposit when the halite dissolves at the base of the crust in the undersaturated waters below the surface. Efflorescent crust deposits slowly aggrade producing irregular sand and silt lenses in poorly sorted porous mud. The sand and silt lenses have distinctive cuspate contacts, ragged edges, and irregular layering and grain-size distributions. Efflorescent crusts growing on sandy sediment distort the upper surface into polygonal bowl shapes, or deform ripples into hump-shaped lenses. Deposition during flooding over an efflorescent crust commonly produces local areas of solution collapse, which are filled with the sediment as it accumulates. The latter resemble load casts but do not have associated flame structures. Efflorescent crust fabrics similar to those in Saline Valley and Death Valley are documented in the lacustrine Blomidon Formation (Fundy basin, Nova Scotia, Canada) and Bigoudine Formation (Argana basin, Morocco). Efflorescent crusts composed of less soluble minerals, such as gypsum or borates, may leave humpy layers of broken crystals and plates. Powdery efflorescence of minerals, such as thenardite or thermonatrite, generally only disturbs the internal layering of sandy deposits. Puffy ground in dry mudflats, formed by powdery efflorescence growth in mudcracks, produces a distinctive granular fabric.

Abstract The Newark Supergroup consists of continental sedimentary and igneous rocks of Late Triassic to Early Jurassic age that fill a series of exposed half-graben basins along the eastern coast of North America. The rift basins formed along reactivated Paleozoic faults during extension that later led to the opening of the Atlantic Ocean. The basins had internal drainage systems, with base level largely independent of sea level. In general, each basin exhibits a similar vertical succession of sedimentary environments, although the ages of the deposits may differ from basin to basin: 1) Thin (<200 m), discontinuous immature fluvial conglomerates unconformably overlie Paleozoic or Precambrian rocks; these deposits reflect local provenance and small drainages. 2) Moderately thick sequence (500-1000 m) of conglomerate, crossbedded sandstone, and siltstone reflecting braided-river deposition with greater maturity than the basal conglomerates which they abruptly, and possibly unconformably, overlie. 3) Thick sequence (500-2000 m) of medium to fine sandstone and siltstone reflecting deposits of meandering streams and vegetated muddy plains. 4) Very thick sequence (1000-6000 m) of lacustrine mudstone and siltstone, in moist basins forming cyclic patterns of deep-water to subaerial deposits. In addition to this succession, alluvial-fan deposits intertongue with lacustrine and fluvial deposits along the faulted basin margins. The vertical succession of depositional environments reflects: 1) the initial erosion surface prior to rifting; 2) basin subsidence and the localization and capture of regional drainages; 3) progressive loss of stream power as fault-related uplift constricted outlets and sediment aggradation lowered gradients; 4) partial or complete hydrographic closure of the basins, as faulting restricted outlets. Fault-related uplift created highlands producing alluvial fans sometime before the end of the third episode of deposition. The timing of these events for each basin probably depends on the relationship of the regional extensional field with the orientation and distribution of Paleozoic faults and preexisting drainages. A progressive vertical decrease in the abundance and thickness of deep-lake laminites within cyclic lacustrine strata may reflect an increase in basin area during subsidence. Three volcanic events extruding large volumes of flood basalt occurred apparently simultaneously in at least three basins and may have been associated with periods of increased subsidence. In several basins, the final stage of sedimentation is fluvial, suggesting a decrease in subsidence or a lowering of the outlet. Tectonic activity may also be reflected by decimeter-scale sequences of grain-size changes in alluvial-fan deposits and by radical shifts in the locations of marginal fluvial deposits. Climatic fluctuation, however, is the most important contributor to development of lake cycles and may also account for some fluvial variability.