Abstract A siliceous permineralized peat block recovered from Hopen in the Svalbard archipelago hosts a low-diversity Late Triassic flora dominated by autochthonous roots and stems of bennettitaleans and lycophytes, and parautochthonous leaves, sporangia, spores and pollen from a small range of pteridophytes and gymnosperms. Some parenchymatous bennettitalean root cells show interactions with chytrid fungi and bacteria; the remains of other fungi and fungi-like organisms are dispersed within the peat’s detrital matrix. Cavities excavated through some roots and compacted detritus contain abundant coprolites probably derived from sapro-xylophagous oribatid mites, although no body fossils have yet been identified. Sparse larger coprolites containing leaf fragments attest to the presence of invertebrate folivores in the ancient ecosystem. The low-diversity flora, relatively few trophic levels and simple nutritional web, together with sedimentological aspects of the host formation and the peat structure, collectively favour accumulation of the organic mass as a fibric (root-dominated) peat within a temperate (high middle-latitude), well-aerated mire.

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.

Subaerial exposure surfaces in the Middle and Upper Mississippian Slade Formation of northeastern Kentucky are largely composed of cutanic concentrations of micritic calcite within the former Ccam horizons of caliche soils. The association of this material with soil horizons and structures, as well as with abundant root traces, strongly indicates a pedogenic origin. In fact, the contribution of plants and small soil organisms was far greater than has been previously recognized. The caliches occur as “interformational” profiles on disconformities separating lower Slade members and as “intraformational” profiles within three lower Slade units. Paleoexposure was related to position on a structurally active margin of the Appalachian Basin and to episodes of regional and local regression. The caliches resulted from soil and ground-water conditions in a semi-arid climate characterized by seasonal rain and drought and an overall net moisture deficit. Growth of roots, desiccation, and displacive crystallization broke up parent limestones, allowing access of vadose waters and creating framework (skeleton) grains that were easily transformed into a mobile plasma fraction by solution. Solution of carbonate grains and eluviation of carbonate-bearing solutions primarily occurred during the moist rainy season, whereas illuviation rapidly followed the onset of drought. The calcium carbonate was deposited largely as internal, laminar plasma concentrations called cutans, which have been incorrectly referred to as “crusts” in previous work on the Slade. Accumulation of these cutanic laminae formed indurated laminar calcrete deposits near the bases of the caliche profiles. These calcretes may be of physicochemical or rhizocretionary origin, depending on conditions of exposure. More diffuse, irregular calcretes apparently developed along avenues of porosity and were formed by plasma separation, the in situ micritization of other limestone textures. Although climate in the Meramecian and earliest Chesterian epochs was the major factor responsible for caliche formation, the length of exposure and the type of carbonate lithology controlled the nature and thickness of caliche profiles. “Intraformational” profiles are always thin and immature, representing short-lived exposure on porous lithologies like calcarenite. Conversely, “interformational” profiles are always mature or composite and represent longer periods of exposure on more impermeable lithologies such as calcilutite. Impermeable lithologies were important, because they prevented migration of soil waters and plasma below the soil profile. By late Early Chesterian time, the climate had become more humid, and the latest formed caliches were partially destroyed by solution, creating a leached, clayey residual soil on top of earlier caliche soils. On structurally elevated areas, where exposure was long and drainage was good, this period of humid pedogenesis resulted in composite terra rossa paleosols produced from the humid weathering of older caliche profiles.

Nodular calcareous paleosols are common in the upper member of the Upper Triassic Dolores Formation in the San Juan Mountains of southwestern Colorado. These soils are developed in reddish brown, very fine-grained sandstone and siltstone of a sand-sheet facies that was deposited by eolian and aqueous processes on the margins of a large Triassic erg. Characteristics of these paleosols include nearly complete destruction of physical sedimentary structures, extensive mottling associated with burrows and root trace fossils, poorly sorted textures, and abundant carbonate nodules. Vegetative stabilization of the sand sheet is recorded by trace fossils of long, monopodial root systems, and fine networks of rootlets. Distinctive purple pigmentation of the large root mottles appears to have been produced by more coarsely crystalline hematite, which precipitated in the presence of root-derived organic compounds. Faunal bioturbation in these soils takes the form of meniscate and structureless burrows of the Scoyenia ichnofacies. The meniscate burrows are common in recent soils and pre-Holocene paleosols, and probably represent sediment reworking by arthropods. Carbonate nodules in these soils are composed of micrite and microspar, and they contain sparry calcite crystallaria and septaria. These glaebules occur as individual “floating” entities and as stacked columns. Burrows cross-cut some nodules, indicating that at least some of the pedogenic carbonate accumulations were relatively unlithified at the time of deposition.

Paleosols are well preserved beneath Upper Cretaceous continental sediments from the eastern Gulf Coastal Plain to the northern Mississippi Embayment. These buried soils are remnants of land surfaces that weathered during Cretaceous time and formed on several rock types, including Precambrian(?) metamorphic rocks and Paleozoic limestone and sandstone. Most soil profiles have distinctive morphologic features and exhibit pedogenic horizon zonation with ferruginous and clay-rich B horizons grading downward to saprolite and parent material within 7 m. Organic matter is not preserved, but pedotubules, which we interpret as fossil roots or burrows, are present in many paleosols. Illuvial and residual concentrations of Al 2 O 3 and Fe 2 O 3 occur in upper soil horizons where kaolinite and halloysite are the principal clay minerals. A variety of precursor minerals, including 2:1 lattice clays, muscovite, feldspar, and biotite, are present in the lower part of the soil profiles. Variations in pedogenesis were caused by differences in parent material and by local geomorphic factors such as paleoslope and drainage. The rates of paleosol development and the residence times of the various land surfaces are uncertain, but the times of burial and preservation range from Cenomanian to early Maestrichtian. Chemical and mineralogic characteristics of these paleosols are similar to those of modern soils of tropical to subtropical climates; however, the fossil soils may be polycyclic, and their pedogenic characteristics could have been modified by postburial diagenesis. Climatic reconstructions based on paleobotanical, lithostratigraphic, and paleotemperature data from Cretaceous sediments support our interpretation that these paleosols formed in a warm, humid environment on well-vegetated piedmont surfaces.