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The Cambrian portion of the Potsdam Sandstone contains a suite of scyphomedusae impressions in fine-grained to medium-grained quartz arenites that outcrop on the periphery of the Adirondack Mountains, New York. The fossils are similar taphonomically and morphologically to coeval scyphomedusae from the Elk Mound Group of Wisconsin and were likely stranded on a sand flat. Soft-tissue preservation in such sandstones is rare, except in Ediacaran Konservat-Lagerstätten. Although subtidal facies are abundant and continental facies are present in the Potsdam, soft-bodied fossils are found only in emergent coastal facies. These units are characterized by microbial structures including domal sand buildups, sand shadows, and breached ripples and by such horizontal trace fossils as Climactichnites and Protichnites. Domal sand buildups mantle some medusa carcasses and suggest that carcasses were exposed at the sediment-water or sediment-air interface for significant intervals of time prior to burial. It is unknown if microbial binding mediated preservation of these carcasses, but evidence for rapid flow regime changes in the section suggest stranded medusae were resistant to the upper-flow regime deposition that buried them. In many Laurentian Cambrian sandstones, microbial binding is common, and metazoan bioturbation is minimal in intertidal and emergent facies. The Potsdam Sandstone, thus, exemplifies how the Ediacara-style taphonomic window persisted in emergent Cambrian settings. This preservational regime may persist because bioturbating metazoans did not fully colonize tidal flats until the Middle Ordovician, which allowed soft-bodied animal tracks and carcasses to be preserved without scavenging or disturbance.
Cuttings recovered from two deep exploratory wells in the Lihue Basin, Kauai, Hawaii, include fossiliferous marine deposits that offer an uncommon opportunity to study paleoenvironments from the deep subsurface in Hawaii and interpret the paleogeography and geologic history of Kauai. These deposits indicate that two marine incursions gave rise to protected shallow-water, low-energy embayments in the southern part of the Lihue Basin in the late Pliocene–early Pleistocene. During the first marine incursion, the embayment was initially zoned, with a variable-salinity environment nearshore and a normal-marine reef environment offshore. The offshore reef environment eventually evolved to a nearshore, variable-salinity environment as the outer part of the embayment shallowed. During the second marine incursion, the embayment had normal-marine to hypersaline conditions, which constitute a significant departure from the variable-salinity environment present during the first marine incursion. Large streams draining the southern Lihue Basin are a likely source of the freshwater that caused the salinity fluctuations evident in the fossils from the first marine incursion. Subsequent volcanic eruptions produced lava flows that buried the embayment and probably diverted much of the stream flow in the southern Lihue Basin northward, to its present point of discharge north of Kalepa Ridge. As a result, the embayment that formed during the second marine incursion received less freshwater, and a normal-marine to hypersaline environment developed. The shallow-water marine deposits, currently buried between 86 m and 185 m below present sea level, have implications for regional tectonics and global eustasy.
The early Pliocene locality Galili in the southern Afar depression (Somali Region, Ethiopia) yields fossil suid and elephantoid remains from the Lasdanan, Dhidinley, Godiray, and Shabeley Laag Members in the Mount Galili Formation. The early Pliocene Galili faunal assemblage, including hominid fossils, comes from a crucial time span of early hominid evolution from 3.5 Ma to 4.5 Ma based on biostratigraphic correlation and preliminary radiometric results. Nyanzachoerus pattersoni, Notochoerus jaegeri are found in the Lasdanan, Dhidinley, and younger Shabeley Laag Members, and Anancus kenyensis (advanced morph), Loxodonta cf. exoptata or L. cf. adaurora are recovered from Dhidinley and Shabeley Laag Members, whereas Notochoerus euilus and the genus Elephas were only found in the Shabeley Laag Member. Comparison of pig and elephantoid remains with taxa from radiometrically dated sites in eastern Africa show that the Galili assemblage correlates well with Kenyan fossils from the Kanapoi sequence and the Apak and Kaiyumung Members of Lothagam. Galili further correlates with the Kataboi Member of the Nachukui Formation at West Turkana and the Moiti and Lokochot Members of Koobi Fora at East Turkana. It also correlates well with the Mursi Formation and the Basal Member and Member A of the Omo Shungura Formation and the lower portion of the Hadar and Sangantole Formations in the Middle Awash region in Ethiopia. The paleoecology of the faunal community from the Dhidinley and Shabeley Laag Members suggests open woodland to bushland-woodland and shrubland habitats for Galili.
In carbonate depositional environments, sediment is mostly produced by different groups of organisms. Ecological parameters, thus, play a major role controlling carbonate production. In the present work, carbonate-producing biota, especially foraminifers, are studied to construct a depositional model and paleoecological interpretation of the lower Tortonian distally steepened ramp of Menorca (Balearic Islands, Spain). This carbonate platform corresponds to a highstand systems track prograding and aggrading over a Paleozoic, Mesozoic, and, locally, lower Tertiary basement. Outcrops are excellently exposed in the southern part of the island. Five facies associations are observed, which, in downdip direction, correspond to inner ramp, middle ramp, ramp slope, toe of the slope, and outer ramp. Samples have been studied using point counting of 102 thin sections. Six foraminiferal assemblages have been distinguished. Eight microfacies are identified (IR.1, IR.2, MR, URS, LRS, TS.1, TS.2, and OR), based on the abundance and ecological significance of the foraminifers (large benthic foraminifers, epiphytics, low-oxygen indicators, and planktonics) and other carbonate-producing organisms (echinoids, mollusks, barnacles, bryozoans, serpulids, coral genus Porites, and green and red algae). Seagrass meadows in the inner ramp correspond to the euphotic carbonate factory, whereas red algae and large benthic foraminifers dominate the oligophotic carbonate factory in the middle ramp and upper ramp slope. Microfacies composition verified intense sediment-transport processes from inner and middle ramp down to lower ramp slope, toe of the slope, and outer ramp. Finally, microfacies analysis also indicates that carbonate-production took place in warm-water conditions, in oligotrophic-to-mesotrophic waters.
Taphonomic analysis of Lenticulina from the Upper Jurassic foraminiferal assemblages of midshelf environments was carried out in a marl-limestone rhythmite of the Prebetic. Size, fragmentation-corrasion, microboring, encrustations, recrystallization, mineralization, sedimentary infillings, and cementation of tests were analyzed by thin section. Encrustations, microborings, and dominance of micritic infillings in the tests are indicative of long exposure on the sea bottom related to low-sedimentation rates. In contrast, the frequency of sparitic cements and reelaborated tests is indicative of higher-sedimentation rates, which are also increased by the input of sediment winnowed from shallower areas. The stratigraphic distribution of these taphonomic features reveals trends in sedimentation rates and sediment input that may be interpreted according to the sequence stratigraphy proposals for the Prebetic. During transgression, increasing relative distance from shore produces a lower-sedimentation rate and prolonged exposure of the fossil remains. This results in increased amounts of microborings, encrustations, and micritic infillings, while fragmentation and the proportion of the reelaborated tests of Lenticulina decrease. Rapid burial is related to increasing sediment input and sedimentation rates and can be associated with aggradation and progradation during the development of a highstand systems tract and a shelf margin wedge. A higher-sedimentation rate explains the scarcity of encrustations and microborings and the abundance of sparitic cements. A higher allochthony of Lenticulina is indicated by the locally high values of fragmentation and reelaborated tests. This taphonomic analysis is useful in monotonous epicontinental lithofacies as marl-limestone rhythmites can reveal features indicative of depositional developments that can be fitted to sequence stratigraphic models.
Phosphatic concretions containing mineralized three-dimensional plant and invertebrate tissues occur in a mid-Cenozoic terrestrial freshwater carbonate deposit at the Riversleigh World Heritage area in northwestern Queensland, Australia. Mineralogical composition and microstructure of the concretions show that this fossil assemblage was preserved by rapid, early diagenetic phosphatization. Preserved material includes tissues typically considered to have a poor potential for phosphatization, such as internal plant structure and arthropod exoskeletal components. Phosphatization may have been mediated by the presence of microbial films. Study of this rich assemblage has the potential to make significant contributions to both the Australian Cenozoic terrestrial invertebrate fossil record and the Cenozoic plant megafossil record of northern Australia.