Taphonomic Patterns Research Articles

Taphonomy of Clypeaster fragments: preservation and taphofacies

The preservation of echinoid fragments of the common echinoid genus Clypeaster recovered from bulk sediment samples is used to explore the possibilities of recognizing taphonomic patterns and establishing taphofacies within a shallow water carbonate environment (Northern Bay of Safaga, Red Sea, Egypt). This is accomplished by the comparison and quantification of the taphonomic signatures of numerous fragments of roughly similar size. The main taphonomic processes observed are abrasion and destruction of plate surfaces, including tubercles and plate edges. Encrustation, especially by foraminifera, can be common and intense. Intraplate fracturing and surface features, such as scratch marks, were also quantified. Four different taphofacies with different characteristic signatures were separated using a cluster analysis of cumulative taphonomic grades. The distribution of taphofacies clearly reflects the topographic complexity of the study area and can be explained by ambient environmental parameters that reflect the general picture of wave and current intensities and sedimentation patterns. The potential use of taphofacies analysis as an independent measure of environmental heterogeneity in palaeoecological studies is confirmed in that taphofacies analysis can reveal parameters not immediately obvious when investigating the textural and biotic characteristics of a sediment.

Shell Beds as paleoecological puzzles: A case study from the Upper Permian of the Paraná Basin, Brazil

Microstratigraphic, sedimentological, and taphonomic features of the Ferraz Shell Bed, from the Upper Permian (Kazanian-Tatarian?) Corumbatai Formation of Rio Claro Region (the Parana Basin, Brazil), indicate that the bed consists of four distinct microstratigraphic units. They include, from bottom to top, a lag concentration (Unit 1), a partly reworked storm deposit (Unit 2), a rapidly deposited sandstone unit with three thin horizons recording episodes of reworking (Unit 3), and a shell-rich horizon generated by reworking/winnowing that was subsequently buried by storm-induced obrution deposit (Unit 4). The bioclasts of the Ferraz Shell Bed represent exclusively bivalve mollusks.Pinzonellaillusa andTerraia aequilateralis are the dominant species. Taphonomic analysis indicates that mollusks are heavily time-averaged (except for some parts of Unit 3). Moreover, different species are time-averaged to a different degree (disharmonious time-averaging). The units differ statistically from one another in their taxonomic and ecological composition, in their taphonomic pattern, and in the size-frequency distributions of the two most common species. Other Permian shell beds of the Parana Basin are similar to the Ferraz Shell Bed in their faunal composition (they typically contain similar sets of 5 to 10 bivalve species) and in their taphonomic, sedimentologic, and microstratigraphic characteristics. However, rare shell beds that include 2–3 species only and are dominated by articulated shells preserved in life position also occur. Diversity levels in the Permian benthic associations of the Parana Basin were very low, with the point diversity of 2–3 species and with the within-habitat and basin-wide (alpha and gamma) diversities of 10 species, at most. The Parana Basin benthic communities may have thus been analogous to low-diversity bivalve-dominated associations of the present-day Baltic Sea. The ‘Ferraz-type’ shell beds of the Parana Basin represent genetically complex and highly heterogeneous sources of paleontological data. They are cumulative records of spectra of benthic ecosystems time-averaged over long periods of time (102–104 years judging from actualistic research). Detailed biostratinomic reconstructions of shell beds can not only offer useful insights into their depositional histories, but may also allow paleoecologists to optimize their sampling designs, and consequently, refine paleoecological and paleoenvironmental interpretations.

The Site of Ain Hanech Revisited: New Investigations at this Lower Pleistocene Site in Northern Algeria

New archaeological investigations have been carried out at the Oldowan site of Ain Hanech in northeast Algeria. The archaeological horizons are delineated and positioned relative to the regional stratigraphy. Preliminary palaeomagnetic analysis reveals normal polarity for the Oldowan occurrences that may be correlated with the Olduvai subchron on the indication of the vertebrate faunal biozonation. Broken up bones associated with stone artefacts and contained in a silty deposit mixed with sand and gravels were excavated from two archaeological sites. The bone assemblage includes equids, bovids, elephant, and rhinoceros, and dominated byEquus tabeti. Taphonomic patterns indicate that bones were buried rapidly over a period of years and while the site was occupied. The lithic artefacts are fresh and represent a coherent assemblage, including small debitage. The artefacts, made of limestone and flint, include flaked cobbles, whole flakes, various fragments, and retouched pieces. A microwear study, undertaken on pieces made of flint, indicates the use of two simple flakes and of one denticulate for meat processing. The stone artefact assemblage may be considered as a North African variant of the Oldowan.

Disarticulation patterns in Ordovician crinoids: Implications for the evolutionary history of connective tissue in the Crinoidea

Taphonomic information is examined to evaluate the early history of connective tissues in the Crinoidea. The pattern of stalk segmentation of Middle and Late Ordovician crinoids is consistent with the two-ligament (intercolumnal and through-going ligaments) pattern present in living isocrinid crinoids and interpreted for fossil isocrinids, holocrinids, and Lower Mississippian crinoids. A single rhombiferan was also examined; its taphonomic pattern is also indicative of this style of tissue organization. Furthermore, the taphonomy of all Middle and Late Ordovician crinoids may reflect that they lacked discretely organized muscles between arm brachials, which is consistent with the hypothesis that muscles evolved as a connective tissue between plates only once within the Crinoidea, during the Early Devonian. These data indicate that the two-ligament organization of the stalk is a primitive feature among the Crinoidea and perhaps even among stalked echinoderms. Therefore, the autotomy function of this column-tissue organization among living crinoids is an exaptation. On the other hand, discretely organized muscles as connective tissue in crinoid arms is a derived trait that first appeared during the middle Paleozoic; this adaptation proved very successful for the advanced cladid crinoids.

Biological basis for taphonomic patterns in the trilobite fossil record

Appreciating the biological component of taphonomic patterns is necessary for accurately interpreting the mode of formation of fossiliferous assemblages. This study documents taphonomic patterns in three Late Ordovician trilobite genera (Flexicalymene, Isotelus, Ceraurus) and identifies four biological factors that affect incorporation of trilobite exoskeletal elements into the fossil record:1) Exoskeletal architecture. Recurring patterns of displaced tergites and points of disartiuclation indicate differential susceptibility of the exoskeleton during ecdysis, and presumably also during decay of a carcass. Disolcations are most common at articulation points, e.g., between cephalon and thorax, among thoracic segments, and between the thorax and pygidium. There is no evidence that facial sutures were lines of weakness except during ecdysis.2) Exoskeletal thickness. Thickness is a better predictor of preservation potential than the position, shape, function, or size of a tergite. For example, Ceraurus and Flexicalymene have hypostomata of similar shape and size, but the thicker Ceraurus hypostoma is more frequently preserved (or at least identified) than the thin ventral plate of Flexicalymene.3) Ecdysis. Molting potentially releases the greatest number of trilobite tergites to the fossil record. Molt ensembles are recognized by recurring assemblages of tergites (e.g., thoracopygidia, cephalothorax, multiple thoracic segments) although individual elements (e.g., hypostomata and librigenae) are shed as well. Distinguishing individual molt elements from tergites disarticulated via scavenging or post-mortem transport of carcass or exuvia is problematic. Ecdysis often releases intact exoskeletal elements: most breakage probably occurs later. during post-ecdysial transport or scavenging of the exuvia.4) Predation/scavenging. These effects are characterized by broken (vs. disarticulated) exoskeletal elements. The impact of these processes on the trilobite fossil record is difficult to assess: sublethal wounds are easiest to recognize, the product of successful predation/scavenging is most often unidentifiable comminuted trilobite debris. The products of successful predation/scavenging are identified as such indirectly by their association with the remains of possible predators or by their presence in coprolites.

Burial Experiments with Marine Turtle Carcasses and Their Paleoecological Significance

Two carapaces of the hawksbill turtle (Eretmochelys imbricata) were buried in intertidal calcareous sands in a lagoonal setting of the Seychelles Islands (Indian Ocean). The taphonomic patterns are compared to similar ones from Upper Jurassic deposits of Central Europe

From plants to coal: peat taphonomy of upper carboniferous coals

Quantitative analyses of the botanical composition in coal-ball concretions provide a basis for assessing stratigraphic and regional patterns of peat taphonomy in relation to swamp paleoecology and, in turn, to coal origins. The categories of plant organ and tissues we discuss are lycopod outer trunk bark, lycopod cortical and twig litter, stigmarian roots, wood (all sources), fern roots, medullosan cortisal tissues, foliage and fructifications. Data are drawn from 20 coals from 34 mines, ranging from lower Westphalian A of England and Belgium to lower Stephanian (Missourian) of Illinois, U.S.A. The 53 data sets represent 8115 coal balls and 388,872 cm 2 of surface area of peels with contents identified by taxa, tissue-organs and preservational states or as an unidentified fraction of organic detritus and non-botanical components. Lycopod trees contributed 26–86% of biovolume in Westphalian coal-ball deposits with important exceptions in Iowa (cordaites = 48–60%). Relative abundances of lycopod peat generally are 75–84% (Westphalian A), 44–74% (Westphalian B—C), to 55–75% (Westphalian D). Shoot/root (S/R) ratios increase during the Westphalian from 0.5–1.0 in Westphalian A, 0.5–1.4 in Westphalian B—C to mostly > 1.4 in Westphalian D. S/R values reflect, in part, changes in abundance of outer decay-resistant bark, 10–29% in Westphalian A—C and up to 45% in Westphalian D. Lycopod litter patterns differ in the main tree genera, so that all litter abundances vary according to the mixes of taxa and diversity of other plants occurring in the Westphalian D (Desmoinesian). Wood from all sources is usually < 10% of deposits, reaching 13–32% in cordaitean-rich deposits, mostly occurring in the Westphalian C—D transition. Evidence of detritivore destruction of wood (cordaitean and calamitean) is most extensive in Westphalian B—C (upper Pottsville) coal-ball deposits. Psaronius tree ferns (mostly roots) contributed 6–27% in the Westphalian D and 33–76% in the Stephanian; seed ferns (mostly medullosan) formed up to 22% of coal-ball contents in these deposits. Stratigraphic trends of principal taphonomic patterns reflect, in large part, changes in the taxonomic makeup of peat-swamp floras. Westphalian deposits exhibit shifts from stigmarian root-rich peats in the Westphalian A, to mixed stigmarian-cordaitean root peats in Westphalian B—C, to an increase in diversity and sizes of litter types in the Westphalian D. Abundances of lycopod bark, total foliage and fructifications reach maxima in the Westphalian D. Stephanian peats are rich in tree-fern roots with variable distribution in the tissues of other tree types (expecially wood and lycopod bark); sizes of trunk litter suggest larger trees than earlier deposits. Taphonomic patterns are closely linked both to taxonomic composition of the vegetation and prevailing environmental conditions. Stratigraphic changes in the qualitative and quantitative aspects of peat formation reflect shifts in both composition of peat-swamp floras and in climatic and physical factors attendant to peat accumulation. Dominant plant groups in the lowland habitats of the Late Carboniferous were very distinctive taxonomically (representing at least four classes of vascular plants) and thus differed enormously in the kind of tissues they produced in their rooting patterns, and in their life histories. This contrasts sharply with woody seed-plant dominance of most post-Paleozoic landscapes. Consequently, extinctions or changes in dominance-diversity patterns lead to major changes in litter accumulation patterns. The Westphalian D (Desmoinesian) exhibits the greatest diversity and shared dominance and, thus, the most diverse litter and root patterns. Average litter size markedly increased in the middle Westphalian D. Lycopod stem tissues, in particular Lepidophloios and Diaphorodendron bark, suggest an increase in physical stability of the environment (reduction in disturbance frequency) that permitted lycopod trees to attain large size. Stephanian deposits are consistent with an even more stable swamp environment with still larger trees (tree ferns, medullosans, calamites and the lycopod Sigillaria) but generally more severely degraded litter. The relative importance of subsidence regimes versus paleoclimate is discussed as a major factor that may have distinct stratigraphic and regional patterns. Origins of carbonate-to-pyritic coal balls are briefly reviewed as they pertain to taphonomic data and their biases.