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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
PALEOECOLOGY
PALEOECOLOGY
Past, Present and Future
Paleoecology is a discipline that uses evidence from fossils to provide an understanding of ancient environments and the ecological history of life through geological time. This text covers the fundamental approaches that have provided the foundation for present paleoecological understanding, and outlines new research areas in paleoecology for managing future environmental and ecological change. Topics include the use of actualism in paleoecology, development of paleoecological models for paleoenvironmental reconstruction, taphonomy and exceptional fossil preservation, evolutionary paleoecology and ecological change through time, and conservation paleoecology. Data from studies of invertebrates, vertebrates, plants and microfossils, with added emphasis on bioturbation and microbial sedimentary structures, are discussed. Examples from marine and terrestrial environments are covered, with a particular focus on periods of great ecological change, such as the Precambrian-Cambrian transition and intervals of mass extinction.
Readership: This book is designed for advanced undergraduates and beginning graduate students in the earth and biological sciences, as well as researchers and applied scientists in a range of related disciplines.
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Seitenzahl: 450
Veröffentlichungsjahr: 2016
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Table of Contents
Cover
Title Page
Copyright
Preface
Chapter 1: Overview
Introduction
History of study
Paleoecology and the future
Summary
References
Additional reading
Chapter 2: Deep time and actualism in paleoecological reconstruction
Introduction
Perceptions of time
Geological time
Uniformitarianism and actualism
Summary
References
Additional reading
Chapter 3: Ecology, paleoecology, and evolutionary paleoecology
Introduction
Ecology and paleoecology
Functional morphology
Paleoecological models for paleoenvironmental reconstruction
Paleoecology and paleoclimate
Evolutionary paleoecology
Summary
References
Additional reading
Chapter 4: Taphonomy
Introduction
Magnitude of taphonomic processes
Normal preservation
Exceptional preservation
Taphofacies and time averaging
Summary
References
Additional reading
Chapter 5: Bioturbation and trace fossils
Introduction
Trace fossils
Marine environments
Terrestrial environments
Summary
References
Additional reading
Chapter 6: Microbial structures
Introduction
Biofilms
Carbonate environments
Siliciclastic environments
Summary
References
Additional reading
Chapter 7: Across the great divide: Precambrian to Phanerozoic paleoecology
Introduction
Precambrian microbial paleoecology
Early animals
Paleoecology of the Cambrian fauna
Summary
References
Additional reading
Chapter 8: Phanerozoic level-bottom marine environments
Introduction
Data collection and analysis
Nearshore and shelf-depth environments
Low-oxygen environments
Summary
References
Additional reading
Chapter 9: Reefs, shell beds, cold seeps, and hydrothermal vents
Introduction
Reefs
Shell beds
Cold seeps and hydrothermal vents
Summary
References
Additional reading
Chapter 10: Pelagic ecosystems
Introduction
Microfossils
Integrated studies
Macrofossils
Summary
References
Additional reading
Chapter 11: Terrestrial ecosystems
Introduction
Development of ecosystems on land
Post-Paleozoic terrestrial ecosystems
Summary
References
Additional reading
Chapter 12: Ecological change through time
Introduction
Diverse approaches for analyzing Phanerozoic trends from marine environments
Summary
References
Additional reading
Chapter 13: Ecological consequences of mass extinctions
Introduction
End-Permian mass extinction
End-Cretaceous mass extinction
Comparative ecological change of mass extinctions
Summary
References
Additional reading
Chapter 14: Conservation paleoecology
Introduction
Shifting baselines
Nonanalog communities and exotic species
Ancient hyperthermal events
Summary
References
Additional reading
Index
End User License Agreement
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Guide
Cover
Table of Contents
Preface
Begin Reading
List of Illustrations
Chapter 1: Overview
Figure 1.1 The Phanerozoic timescale with distribution of characteristic skeletonized marine fossils. Occurrence of fossils through the stratigraphic record has largely been determined through mapping efforts around the globe to characterize the surface geology of the continents. These fossil distributions have been continuously refined through the use of fossils to build the relative timescale and definition of Eras, Periods, and other time intervals. Key to classes: An, Anthozoa; Bi, Bivalvia; Ce, Cephalopoda; Cr, Crinoidea; De, Demospongiae; Ec, Echinoidea; Ga, Gastropoda; Gy, Gymnolaemata; In, “Inarticulata” (Linguliformea and Craniformea); Ma, Malacostraca; Mo, Monoplacophora; Os, Osteichthyes; Rh, “Articulata” (Rhynchonelliformea); Se, Stenolaemata; St, Stelleroidea; Tr, Trilobita. From McKinney (2007). Reproduced with permission from Columbia University Press.
Figure 1.2 Environmental distribution of selected groups of fossils. This information largely comes from studies on the distribution of these organisms in modern environments, but also includes data on facies associations and functional morphology, particularly for the extinct groups. From Jones (2006). Reproduced with permission from Cambridge University Press.
Figure 1.3 Tiering history among marine soft-substrata suspension-feeding communities from the late Precambrian through the Phanerozoic. Zero on the vertical axis indicates the sediment–water interface; the heaviest lines indicate maximum levels of epifaunal or infaunal tiering; other lines are tier subdivisions. Solid lines represent data, and dotted lines are inferred levels. These characteristic tiering levels were determined for infaunal tiers by examination of the trace fossil record, particularly the characteristic depth of penetration below the seafloor of individual trace fossils. Data on shallow infaunal tiers also came from functional morphology studies of skeletonized body fossils. Paleocommunity and functional morphology studies of epifaunal body fossils comprise the data for epifaunal tiering trends. Tiering data from the late Precambrian is from studies of the Ediacara biota. This tiering history has been updated as more data have become available. From Ausich and Bottjer (2001). Reproduced with permission from John Wiley & Sons.
Figure 1.4 Schematic of modern carbon cycle including anthropogenic influence. Combustion of lithospheric carbon such as coal and oil is the modern cause of global warming, and a similar mechanism involving igneous intrusions through sedimentary rocks rich in carbon has been the cause of rapid global warming episodes, or hyperthermals, in the past. From the New York State Department of Environmental Conservation website: http://www.dec.ny.gov/energy/76572.html.
Figure 1.5 Increase in ocean heat content since 1955 shown as a time series of yearly ocean heat content in joules (J) for the 0–700 m layer. Each yearly estimate is plotted at the midpoint of the year, with the reference period from 1957 to 1990. From Levitus et al. (2009). Reproduced with permission from John Wiley & Sons.
Figure 1.6 Location of hypoxic system coastal “dead zones.” Their distribution matches the global human footprint, where the normalized human influence is expressed as a percent, in the Northern Hemisphere. For the Southern Hemisphere, the occurrence of dead zones is only recently being reported. From Diaz and Rosenberg (2008). Reproduced with permission from the American Association for the Advancement of Science.
Figure 1.7 Increase in atmospheric carbon dioxide and its influence on ocean acidification and the resultant affect on development of coral reefs in the past, present, and future. (a) Increased carbon dioxide concentration in the oceans leads to decreased availability of carbonate ions, which are needed by corals to secrete their skeletons made of calcium carbonate. (b) Plot of temperature, atmospheric carbon dioxide content, and ocean carbonate ion concentration showing the predicted trend in the future of reefs not dominated by corals with increased levels of acidification. From Hoegh-Gulberg et al. (2007). Reproduced with permission from the American Association for the Advancement of Science.
Figure 1.8 The effects of human overfishing on coastal ecosystems. Simplified food webs showing changes in some of the important top–down trophic interactions before and after fishing in kelp forests, coral reefs, and estuaries. Bold font represents abundant, normal font represents rare, “crossed out” represents extinct, thick arrows represent strong interactions, and thin arrows represent weak interactions. From Jackson et al. (2001). Reproduced with permission from the American Association for the Advancement of Science.
Figure 1.9 The net radiative forcing due to changes in atmospheric carbon dioxide concentration and total solar irradiance from 5 to 45 million years ago. The three curves represent the range in carbon dioxide concentration using three different proxies for ancient atmospheric carbon dioxide. The shaded area denotes the range in radiative forcing projected to occur by 2100 according to the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (2007). Net radiative forcing is in watts per square meter. From Kiehl (2011). Reproduced with permission from the American Association for the Advancement of Science.
Chapter 2: Deep time and actualism in paleoecological reconstruction
Figure 2.1 Steps in construction of a geological timescale. The chronostratigraphic scale is a relative timescale and includes (from left to right) formalized definitions of geologic stages (here with examples of Triassic stages), magnetic polarity zones, and biostratigraphic zonation units, with examples here indicated by fossil symbols (from top to bottom, conodont, ammonoid, echinoderm, foraminifera, bivalve). The chronometric scale is measured in years and includes absolute ages measured from radiogenic isotope systems such as argon/argon and uranium/lead and astronomical cycles exemplified by the sedimentary expression of Earth's orbital cycles. These orbital cycles, termed Milankovitch cycles, have specific time implications and can be detected from measurements on sedimentary bed thickness, composition, and geochemistry. Other chronostratigraphic approaches not illustrated here include stable isotope stratigraphy (strontium, osmium, sulfur, oxygen, carbon). Commonly, when determining the age of a sedimentary section, fossils can be collected for biostratigraphic determinations. Fossils, along with sedimentary samples, can be analyzed for geochemical data, and other sedimentary observations can be made for determination of astronomical cycles (if this evidence is available). Oriented sedimentary samples can also be collected for analysis in a magnetometer to detect reversed and normal polarity zones. If volcanic rocks, such as tuffs, exist, these can be sampled for radiogenic isotope measurements to determine an absolute age in years. If some or all of this chronometric and chronostratigraphic information is available, it can then be merged to produce an age calibration that allows linkage into a formal geologic timescale, here indicated as that found in Gradstein et al. (2012). From Gradstein et al. (2012). Reproduced with permission from Elsevier.
Figure 2.2 Methods used to construct the geological timescale for the Phanerozoic in Gradstein et al. (2012), which depend on the quality of data available for different time intervals. Cyclostratigraphic analyses of Milankovitch orbital cycles are used in orbital tuning approaches. Seafloor spreading rates are calculated from the distribution of ocean seafloor magnetic anomalies. Direct dating involves use of high-precision radiogenic isotope ages, usually determined from zircons collected from volcanic rock. Proportional zone scaling and scaled composite standard analyses involve scaling using biostratigraphic data. Cubic spline curve fitting geomathematically relates observed ages to their stratigraphic position. From Gradstein et al. (2012). Reproduced with permission from Elsevier.
Figure 2.3 Geological timescale From Gradstein et al. (2012). Reproduced with permission from Elsevier.
Figure 2.4 Estimates of Phanerozoic atmospheric O
2
concentrations from two different models, showing Paleozoic O
2
peak in the Carboniferous. These O
2
curves are produced using biogeochemical models, the Carbon-Oxygen-Phosphorus-Sulfur-Evolution (COPSE) model by Bergman et al. (2004) and the GEOCARBSULF model by Berner (2006). Model inputs include carbon and sulfur weathering and burial rates, and different model assumptions lead to different oxygen concentrations and the different O
2
curves shown here for the Mesozoic and Cenozoic. From Kasting and Canfield (2012). Reproduced with permission from John Wiley & Sons.
Figure 2.5 Atmospheric CO
2
through the Phanerozoic, reconstructed using proxies for CO
2
and GEOCARB III, a biogeochemical carbon cycle model developed by Berner and Kothavala (2001). Proxies for CO
2
include stomatal densities and indices in plants, the δ C13 of soil minerals, and the δ B11 of marine carbonates. Smoothed proxy data is plotted using a locally weighted regression (LOESS). The best-guess predictions of GEOCARB III are plotted as a dashed line, and the range of reasonable predictions of this model are shown as a gray-shaded region. From Royer (2006). Reproduced with permission from Elsevier.
Figure 2.6 Reconstruction of a Carboniferous forest including a dragonfly with a wingspan of 60 cm. Correlation of large insect size with atmospheric oxygen content assumes insect size limitation is related to the surface area of the respiratory system versus organism size, so that all other things being equal an increase in atmospheric oxygen content allows a larger body size. Other size limitations such as the lack of predators like birds or pterosaurs which had not yet evolved during this time have also been suggested as contributing to the large size of Carboniferous dragonflies. From Kump et al. (2009).
Chapter 3: Ecology, paleoecology, and evolutionary paleoecology
Figure 3.1 Categorization of Earth's environments. Marine environments, as shown in this schematic, are defined in a variety of ways with an emphasis on water depth. These include benthic (or seafloor) environments and pelagic environments in the water column. The littoral zone is the mosaic of shoreline environments. The continental shelf divides the benthic sublittoral and pelagic neritic from oceanic benthic (bathyal, abyssal, hadal) and pelagic (epipelagic, mesopelagic, bathypelagic, abyssopelagic) environments. Terrestrial environments differ according to variations in temperature, humidity, and elevation, and include freshwater environments such as wetlands, ponds, lakes, and streams, and subaerial environments such as deserts, grasslands, shrub lands, and forests. From Brenchley and Harper (1998).
Figure 3.2 Marine food web schematic. Producers which capture energy from sunlight through photosynthesis include phytoplankton and seafloor plants on the continental shelf. Zooplankton consume the phytoplankton. Baleen whales and small fish consume the zooplankton, and the small fish are in turn consumed by squid and larger fish. Squid are consumed by sperm whales and the larger fish are consumed by sharks and porpoises. In the deep sea well below the photic zone the abundance of life is diminished with only a few seafloor consumers such as sponges and crinoids filtering plankton suspended in the seawater. A more common strategy for deep seafloor animals is to extract their food from sediment which they ingest while burrowing, known as deposit-feeding. In the deep sea larger fish such as anglerfish attract and consume smaller fish. Remains of organisms from above settle to the seafloor, to be decomposed by bacteria, and the nutrients left from this process are returned to the surface by upwelling for use again by photosynthetic life. From Stanley (2008). Macmillan Higher Education.
Figure 3.3 Morphologic features of byssally attached and free-swimming scallops. The characteristic shape of a scallop is a relatively flat pair of teardrop to ovate shells which articulate along a hinge line that is accentuated by a more pointed structure called the umbo. At each side of the umbo are triangularly shaped projections of the shell called the auricles. The pointed intersection of the shell that forms the umbo can be measured as the umbonal angle; a smaller umbonal angle produces a more teardrop-shaped shell, and a larger umbonal angle produces a more ovate shell. In a scallop species the size of the auricles can be equal or unequal. The degree to which they are unequal can be expressed by measuring the dimensions of the two auricles along the straight edge to the intersection with the umbo, and calculating their ratio. As shown, scallops with a relatively low umbonal angle and teardrop shape also have asymmetrical auricles, with the larger auricle acting as an outrigger for these byssally attached organisms, where the byssus is located at the intersection of the auricle with the main part of the shell away from the point of the umbo. Scallops with equal auricles typically have large umbonal angles and more ovate shapes which allows for better hydrodynamic behavior of the shells during swimming. From Stanley (1970). Reproduced with permission from the Geological Society of America.
Figure 3.4 Model of the Late Cretaceous pterosaur
Quetzalcoatlus northropi
in flight. This halfscale working model was designed and built by a team at Aerovironment, Inc., led by Paul MacCready, an aeronautical engineer. When alive this pterosaur had a wingspan of 11 m. The design of this robot addressed questions on how this pterosaur flew without an aerodynamic tail structure, and therefore how it achieved pitch stability and yaw control, conditions that allow controlled directed flight by a flying animal. AeroVironment, Inc. website: http://www.avinc.com/uas/adc/quetzalcoatlus/. Reproduced with permission.
Figure 3.5 Skeleton (a) and interpretive drawing (b) of a fetus preserved within a pregnant adult Late Cretaceous plesiosaur
Polycotylus latippinus
. This is the first definitive evidence that plesiosaurs were viviparous. This evidence includes skeletal features showing that the smaller individual is a juvenile, taphonomic evidence that the juvenile was not consumed by the adult, articulation features of the juvenile skeleton indicating that it was within the adult at the time of burial, and skeletal features showing that both skeletons are
P. latippinus
. This relatively large single fetus indicates that plesiosaurs reproduced differently from other marine reptiles but does resemble the K-selected strategy of all modern marine mammals. The r-selected reproduction of other marine reptiles involves giving birth to several relatively small young, where parental investment is spread across these several young. The likely K-selected strategy of
P. latippinus
with parental investment concentrated in a small brood with large birth size may indicate that like modern marine mammals plesiosaurs were social and invested heavily in parental care. Labelled bones are listed in O'Keefe and Chiappe (2011). From O'Keefe and Chiappe (2011). Reproduced with permission from the American Association for the Advancement of Science.
Figure 3.6 Specimen of the Early Cretaceous bird
Yanornis
(a) with ingested whole fish in the crop (b) and macerated fish bones in the ventriculus (c). This specimen of
Yanornis
is from the Lower Cretaceous Jehol Group (China) and is an early representative of the Ornithuromorpha, the lineage in which living birds are included. This and other specimens of
Yanornis
indicate that this taxon was a fish-eater, that it did not use its teeth to macerate fish before they entered the crop, and that fish were subsequently macerated in the ventriculus (gizzard or muscular stomach). Scale bars are 5 cm for (a), 1 cm for (b) and 1 mm for (c). From Zheng et al. (2014). Used under CC-BY-3.0 https://creativecommons.org/licenses/by/3.0/.
Figure 3.7 The conceptual framework of morphodynamics represented as a tetrahedron. The specific research fields for determining function include bioarchitecture, biomechanics, functional morphology, and ethology. The research fields utilized in determining phylogenetic tradition include cladistics and molecular approaches. The fields of theoretical morphology, developmental mechanics and developmental genetics provide information on fabrication. The effective environment is determined through facies analysis and ecological studies. From Briggs (2005). Reproduced with permission from the author.
Figure 3.8 Cross-section of a typical Tepee Butte within the Pierre Shale. These are fossilized Cretaceous methane-seep ecosystems, and numerous examples of these mounds which may be as high as 20 m (hence the name “butte”) preferentially weather-out near Pueblo, Colorado. The vuggy limestone (VL) marks the central vent. A coquina of the lucinid bivalve
Nymphalucina
typically surrounds the vent (NC). A thrombolitic micrite (TM) then drapes these central facies. In the process of metabolizing the venting methane as well as associated sulfates microbes increase the carbon dioxide concentration leading to precipitation of carbonate minerals. Chemosymbiotic bacteria are inferred to have lived within the tissues of
Nympholucina
as well as tube worms found in these deposits. From Shapiro and Fricke (2002). Reproduced with permission from the Geological Society of America.
Figure 3.9 Relationship between leaf margin morphology and temperature as a paleothermometer. These analyses are made from assemblages of leaves collected from a single sample horizon, and have provided significant information on temperatures for the last 100 million years. Smooth-margined leaves are more characteristic of warmer temperatures. From Stanley (2008). Reproduced with permission from W.H. Freeman.
Figure 3.10 Cenozoic paleotemperatures determined from stable oxygen isotope variations in foraminifera shells. Before 34 million years ago the data is a record of deep ocean temperatures. After 34 million years ago, continental ice sheets developed, so that the signal is a mixture of temperature and the effects of ice volume. Note the late Paleocene and early Eocene warm intervals as well as the late Oligocene warming and mid-Miocene climatic optimum which overlie a broad temperature decline as the Earth has progressed from a Greenhouse state in the Eocene to its current Icehouse state (see also Figure 1.9). From Beerling (2008). Reproduced with permission from Oxford University Press.
Figure 3.11 Familial biodiversity of the three Phanerozoic marine evolutionary faunas, as determined by Sepkoski through factor analysis of his marine Phanerozoic biodiversity data base. Each consists of broad sets of taxa that were globally dominant through long periods of geological time, with characteristic taxa for each fauna schematically displayed. The Cambrian Fauna includes many organisms characteristic of the Cambrian Explosion. The Paleozoic Fauna consists of organisms that characterize the Great Ordovician Biodiversification Event (GOBE). The Paleozoic Fauna was significantly affected by the end-Permian mass extinction, which led to dominance by the Modern Fauna in the post-Paleozoic. From Foote and Miller (2007). Reproduced with permission from W.H. Freeman.
Figure 3.12 Biodiversity trends for Phanerozoic vertebrate orders and plant species since the Devonian. (a) Trends for both marine and terrestrial vertebrate orders, including fish (lower blank pattern), amphibians, reptiles, mammals, and birds. (b) Trends for terrestrial plants, including pteridophytes (vascular plants that reproduce by spores), gymnosperms, and angiosperms (more recent studies show an earlier angiosperm history beginning in the Late Jurassic). From Foote and Miller (2007). Reproduced with permission from W.H. Freeman.
Figure 3.13 Phanerozoic biodiversity curve showing the three Phanerozoic marine evolutionary faunas, as determined by Alroy from a sampling standardized diversity curve generated from generic data in the Paleobiology Data base. The unlabeled area represents groups not assigned to one of the evolutionary faunas; Cm is Cambrian Fauna. From Alroy (2010). Reproduced with permission from the American Association for the Advancement of Science.
Figure 3.14 Theoretical ecospace use cube. Tiering indicates where the organism lives above and below the seafloor, and includes pelagic (in the water column), erect (benthic, extending into the overlying seawater), surficial (benthic, not extending significantly upward), semi-infaunal (partly infaunal and partly exposed), shallow (infaunal, living in the top ∼5 cm of sediment), and deep (infaunal, living more than ∼5 cm deep in the sediment). Motility level includes fully, fast (regularly moving, unencumbered); fully, slow (regularly moving but with a strong bond to the seafloor); facultative, unattached (moving only when necessary, free-lying); facultative, attached (moving only when necessary, attached); nonmotile, unattached (not capable of movement, free lying), nonmotile, attached (not capable of movement, attached). Feeding mechanisms include suspension (capturing food particles from the water), surface deposit (capturing loose particles from a substrate), mining (recovering buried food), grazing (scraping or nibbling food from a substrate), predatory (capturing prey capable of resistance), and other (e.g., photo-or chemosymbiosis, parasites). From Bush et al. (2007). Reproduced with permission from Cambridge University Press.
Chapter 4: Taphonomy
Figure 4.1 Flow diagram of organic remains as they progress from death to becoming a fossil to collection by the paleontologist. The effectiveness of the various filters in taphonomic processes allows different degrees of paleobiological and paleoecological reconstruction from each paleontological sample. In paleoecological studies that involve statistical comparisons of numerous samples, it is important that the samples are taphonomically comparable.
Figure 4.2 Progression for benthic organisms of taphonomic processes from living to dead to buried remains to final incorporation into the fossil record. Organic remains may experience multiple episodes of reworking through processes of bioturbation and biostratinomy.
Figure 4.3 Progression of taphonomic processes for benthic organisms with calcium carbonate skeletons emphasizing environments of dissolution. Shells can be destroyed on the seafloor surface by bioerosion, physical processes, and dissolution. In the TAZ, increased acidity produced by decay of organic material and reoxidation, producing H
2
S, can cause dissolution of high-Mg and aragonitic shells. Under these conditions, only minor amounts of aragonitic shells, such as deep-burrowing bivalves, would survive into the sub-TAZ diagenetic zone. Carbonate from dissolution of shells contributes to preferential early cementation of limestones allowing better three-dimensional preservation of shells than in shale beds, where fossils are more compacted.
Figure 4.4 Variations in the Phanerozoic frequency of occurrence for major taxonomic groups of marine macrofauna. Data is from the Paleobiology Database that was downloaded 9/4/2007. Li, Lingulida; Gr, Graptolithina; Cr, Crinoidea; An, Anthozoa; Ec, Echinoidea.
Figure 4.5 A Permian assemblage exhibiting parts of a variety of plants. This preserves an autochthonous Late Permian forest-floor litter in which leaves of the gymnosperm
Glossopteris
(fossil at top of lower right quadrant) are preserved with horsetail (sphenopsid) ground cover which includes
Trizygia
(leaves in upper center and upper right quadrant; a cone in left center of lower left quadrant) and
Phyllotheca
(two foliar whorls showing long, narrow leaves that fit into a funnel-shaped sheath in left center of upper left quadrant). Such litter horizons, from the Upper Permian Balfour Formation, are an uncommon feature of the sequence transitioning the Permian–Triassic boundary, as defined by vertebrate biostratigraphy, in the Karoo Basin, South Africa. Locality and additional paleoenvironmental information can be found in Prevec et al. (2010) and Gastaldo et al. (2014). Photograph by Robert A. Gastaldo. Reproduced with permission.
Figure 4.6 Silicification of fossil forests buried by volcanic eruptions. On the western side of the island of Lesvos, Greece, volcanogenic debris flows and lahars preserve autochthonous Miocene forests, where erect, silicified trunks of
Taxodioxylon
(
Sequoia
) are preserved to a height of 7.1 m. The 350 m-thick Miocene volcaniclastic sequence, known as the Sigri Pyroclastic Formation, erupted from the Barossa stratovolcano and buried at least two major forest horizons. From Mpali Alonia Park in the Lesvos Petrified Forest GeoPark, Robert A. Gastaldo for scale. Photograph by Robert A. Gastaldo. Reproduced with permission.
Figure 4.7 Block diagram showing a fluvial sedimentary environment with a superimposed vegetational mosaic and resulting composition of fossil leaf assemblages from different environments. This fluvial landscape of moderate relief has a meandering river crossing that includes numerous oxbow ponds. A small lake exists just downstream of the highland portion of the river. In the lowlands, the river feeds into a basin that includes a lake that fluctuates with swamp conditions. The flora includes a mostly swamp flora (including water's edge and mire communities that form deposits of peat), a dry lowland flora (including river margin or riparian components and an interfluvial forest), as well as a highland forest flora. The hypothetical composition of leaf assemblages in several sedimentary facies from these environments is shown in the pie charts. A swamp-coal facies (1) includes mostly flora from wetland environments as well as a component of lowland vegetation. Alternating with the swamp-coal facies are lake deposits (2) which contain a much greater component of lowland vegetation, due to fluvial transport. The highland lake (3) includes highland vegetation as well as components of lowland vegetation. The oxbow pond facies (4) is dominated by lowland flora including a large riparian component. Thus, the overall floristic composition of each facies is strongly affected by selective taphonomic processes.
Figure 4.8 The hierarchy of terrestrial taphonomic processes and controls on the vertebrate fossil record. (a) Macroscale features include distribution of continental plates, sea-level variations, ocean circulation variations, differences in atmospheric composition and circulation, variability of intensity and distribution of solar radiation on the surface, and biome distribution. (b) Mesoscale landscape characteristics include variations in local weather patterns as well as differences in species population dynamics, biogeochemical cycles, predation/death, and scavenging of remains. (c) Microscale features include variations in soft tissue decay, bone exposure, desiccation and cracking from solar radiation, as well as invertebrate utilization, bioturbation, nutrient use and organic acid release by plant roots, leaching of bone mineral (B) and collagen (C), incorporation of exogenous ions (I) and humics (H) into bone matrix, bacterial and fungal degradation (inset), diagenesis, and hydraulic flow of groundwater.
Figure 4.9 Some major marine conservation lagerstätten and the relative role in their preservation of obrution, stagnation, and bacterial sealing processes. The Ediacara biota from South Australia (but also of global extent) is of late Precambrian Ediacaran age and includes the oldest macroscopic animal fossils; the Burgess Shale, from British Columbia in Canada, is of Middle Cambrian age and exemplifies the faunas of the Cambrian explosion; the Ordovician Beecher's Trilobite Bed, from New York state in the United States, is well known for including pyritized trilobite soft tissues; the Hunsrück-Schiefer of Germany is of Devonian age and also includes extensive pyritized soft tissues; the Lower Jurassic Posidonienschiefer (Posidonia Shale; see also Figure 8.13 and 8.14) from Germany includes spectacular specimens of marine reptiles and marine invertebrates; and the Upper Jurassic Solnhofen of Germany includes broad preservation of marine and terrestrial organisms with soft tissues including the bird
Archaeopteryx
.
Figure 4.10 Crinoid assemblage from the Lower Mississippian Maynes Creek Formation, Le Grand, Iowa. Burial by storm deposition led to the instantaneous preservation of complete crinoid crowns, thus providing an “ecological snapshot” of this assemblage. Such preservation provides unparalleled resolution of morphological variability within specimens. Width of the darkest, common crinoid is 1 cm. Photograph by William I. Ausich. Reproduced with permission.
Figure 4.11 Depositional model for the early Cambrian Chengjiang biota in Yunnan, China. Onshore–offshore transect shows the distribution of important depositional processes for exceptional preservation of fossils, including storm-generated currents and presence of bioturbation and microbial mats. Facies with interbedded background mudstones and event mudstones are where the best specimens with soft tissue preservation are found, at localities in the Chengjiang, Haikou, and Anning areas. Schematic representations of organisms emblematic of the Chengjiang biota, and their interpreted ecology in this Early Cambrian marine environment, are displayed on right. SL is sea level, NWB is normal wave base, SWB is storm wave base, and MSWB is maximum storm wave base.
Figure 4.12 Microbial mats and preservation of the Ediacara biota. (a) A typical nearshore Ediacaran sandy seafloor covered by a microbial mat on which rests an individual of the Ediacaran animal
Dickinsonia
. (b) An event such as a storm has covered the seafloor with a layer of sand, and the
Dickinsonia
as well as the microbial mat on which it lived begins to decay, leading, in the presence of seawater sulfate, to the production of hydrogen sulfide which combines with the iron in the sediment to produce iron sulfide and, ultimately, with the inclusion of organic compounds, pyrite. (c) A microbial mat forms on the event bed, limiting sulfate and oxygen diffusion into the overlying seawater, while the pyrite forms a sole veneer or “death mask” which casts the
Dickinsonia
from below.
Figure 4.13 Schematic illustration of hypothetical sequence of events in the formation of the biogenic sedimentary structure “mop” from the Ediacara Member of the Rawnsley Quartzite in South Australia. (a)
Charniodiscus
-like organisms with circular holdfasts attached within or beneath a nearshore microbially bound sandy substrate with stalks and fronds oriented vertically in the water column (three sizes depicted to illustrate the effect of size on mop formation). (b) An event including unidirectional currents flowing from right to left produces stress resulting in bunching, compression, and puckering of the holdfasts, including dragging, stretching, and shearing of the substrate by the smaller holdfasts. (c) The stress of the event current results in severing of the stalks, leaving some or none of the stalk. (d) The event causes deposition of a sand bed and compression of the remaining holdfast tissue and associated microbial and sedimentary structures, with subsequent lithification of the beds. (e) In the modern, a paleontologist separates the beds to reveal preservation of a puckered disk (right) and two smaller morphological variants of mop.
Figure 4.14 Ediacara biota fossils on the “E” surface from the Mistaken Point Formation, showing the stalked suspension feeder
Charniodiscus spinosus
(disk with attached frond below coin), and various rangeomorphs. This surface was preserved by volcanic ash that covered a living community after falling into the ocean. Opinions on the phylogenetic affinities of
Charniodiscus
are varied, and rangeomorphs are considered to be an extinct group that did not survive into the Phanerozoic. The fossils from Mistaken Point, Newfoundland, Canada, are considered to be part of the Avalon assemblage of the Ediacara biota, which make them the oldest Ediacara fossils, dated at 575–560 million years ago (see also Figure 7.8). Coin is 24 mm. Additional information can be found in Narbonne et al. (2007). From Photograph by David J. Bottjer.
Figure 4.15 Two different cycles of sedimentation were largely involved in preservation of the Eocene Florissant fossils. An irregular volcanic cycle deposited ash and pumice from volcanic eruptions preserving fossil forests on land and depositing thick tuff layers in lakes. In the lakes, deposition typically produced paper shales, consisting of alternating layers of freshwater diatoms that settled to the bottom as part of mucilaginous mats and microlayers of clay formed by the weathering of volcanic clay as it washed into the lake. Plants and insects were trapped in the diatom mats and show exquisite preservation of soft tissues as sediment impressions or as compressions of the original organism, with a darkened color due to the organism's residual carbon content. Many of the compressed fossils retain some of the original three-dimensional nature of the organism.
Figure 4.16 Estimated limits on time averaging of selected types of continental plant tissues and vertebrate and marine invertebrate assemblages. The different categories (tissues vs. deposits) reflect the fact that those studying fossil plants regard tissue type as playing the most important role in time averaging for plant remains, while those studying fossil animals regard depositional environments or process as more important. Attritional (attrit.) assemblages involve the accumulation of discarded organic products and input from normal mortality over periods of years to millennia. Microvertebrate fossil assemblages (Micro.) are also called microsites. Composite (compos.) beds reflect more than one sedimentary event during deposition. Hiatal concentrations (conc.) are fossil assemblages deposited during a long-term period of slow sediment accumulation.
Figure 4.17 Spatial and temporal representation in fossil assemblages for different major groups of organisms in continental and benthic marine depositional settings. (a) Continental settings: dotted lines show areas of the time/space plot occupied by vertebrate remains, and dashed lines plant remains; estimate for pollen excludes trees because certain morphotypes can be transported hundreds of miles by water or thousands of miles by wind prior to settling from the water or air column, respectively. (b) Benthic marine settings include shelly macroinvertebrates and exclude nektonic and planktonic contributions to the fossil assemblage, because spatial resolution of these components can depend upon current drift.
Chapter 5: Bioturbation and trace fossils
Figure 5.1 Trace fossils made by invertebrates represent a suite of behaviors that may combine or grade with each other. In this schematic, the ethological patterns reflected as typical trace fossils are grouped so that the families of feeding behaviors are evident. Behaviors and typical trace fossils associated with higher-energy environmental settings are depicted on the left, while those typical of lower-energy environments are found on the right. This association of behaviors and resulting trace fossils with depositional processes forms the basis for the ichnofacies classification.
Figure 5.2 Sediment accumulation and preservation of trace fossils in marine pelagic/hemipelagic mud. Under typical depositional conditions, mixed layer structures are not preserved. Structures formed in the transition layer dominate the historical layer, although visibility of these structures can be limited by poor contrast between trace fossils and host sediments (A, C). In contrast, these transition-layer structures may have enhanced visibility due to a variety of processes including changes in sediment type and downward transport of contrasting sediments, such as at bed junctions (B, D); textural or compositional segregation by tracemakers (E); diagenetic mineralization (F); and differential weathering/erosion (G) of burrows or host sediments. Trace fossils preserved at bed-junction preservation show particularly good preservation if they crosscut previously unbioturbated sediments such as dark, laminated shales (D).
Figure 5.3 Schematic of common marine ichnofacies, which vary from shallow to deepwater environments and substrate type. Sketches of typical trace fossils for each ichnofacies are shown; the name of each ichnofacies (e.g.,
Trypanites
) reflects a characteristic trace fossil for that ichnofacies. To identify a particular ichnofacies, the trace fossil which gives that ichnofacies its name does not need to be present. From MacEachern et al. (2010), where data sources are indicated. Reproduced with permission from the Geological Association of Canada.
Figure 5.4 Ichnofabric indices exemplified by flashcards according to the method proposed by Droser and Bottjer (1989). These show the amount of sediment reworked for different marine sedimentary environments as observed in vertical cross section. Percent of reworking for ichnofabric indices (I.I.) 1–5 shown on left. Ichnofabric index 1 is a fabric that is all physical sedimentary structures (lacking bioturbation), and ichnofabric index 6 is complete homogenization by bioturbation.
Skolithos
and
Ophiomorpha
ichnofabrics are for sandy nearshore sedimentary environments. From McIlroy (2004). Reproduced with permission from the Geological Society.
Figure 5.5 Thorough bioturbation resulting in ichnofabric index (ii) 5 developed at a marly chalk–chalk transition (mid- to outer shelf) in the Upper Cretaceous (Campanian) Demopolis Chalk (Selma Group) exposed in western Alabama (eastern Gulf coastal plain), United States. Distinct lighter-filled trace fossils include
Thalassinoides
(wide vertical structure on left side and probably highest long horizontal structure near top),
Zoophycos
(horizontal structure with faint meniscate backfill below left side of horizontal
Thalassinoides
?), and
Chondrites
(lightest structures including dots to short branching segments). Additional information can be found in Locklair and Savrda (1998). Scale is in centimeters.
Figure 5.6 Measurement of ichnofabric indices (ii). (a) Schematic diagram of hypothetical stratigraphic section logged for ichnofabric indices during vertical sequence analysis. (b) Ichnogram computed from this hypothetical data. Logging is based on a 50 cm-wide field of view. Of 5 m measured, ii1 was recorded from 15 cm, ii2 from 200 cm, ii3 from 255 cm, and ii4 from 30 cm.
Figure 5.7 The bedding plane bioturbation index, with different indices showing the proportion of bedding planes covered by trace fossils. Column A represents example bedding planes covered by trace fossils of even size and shape with even distributions. Column B represents example bedding planes covered by trace fossils of different sizes and shapes and with uneven distributions.
Figure 5.8 Ichnofacies distribution in terrestrial environments, including lacustrine and fluvial settings. These are largely based on the occurrence of trace fossils made by invertebrates. The
Mermia
ichnofacies characterizes subaqueous oxygenated lacustrine environments and includes grazing and feeding traces as well as locomotion traces. The
Scoyenia
ichnofacies is found in environments that are periodically covered in water, such as the margins of fluvial and lacustrine systems. This ichnofacies is characterized by traces of mobile organisms including tracks, trails, and meniscate-backfilled burrows. The
Skolithos
ichnofacies, with simple vertical as well as U-shaped burrows, is found in high-energy lacustrine and fluvial environments. The
Coprinisphaera
ichnofacies is present in paleosols.
Figure 5.9 Trackways made by saurischian dinosaurs. The Saurischia, one of the two major groups of dinosaurs, comprises the herbivorous sauropodomorphs, which include the sauropods such as
Diplodocus
and their ancestral relatives, as well as the carnivorous theropods such as
Tyrannosaurus
. Trackway configurations in the center for these main groups of saurischian dinosaurs (top), with an inset showing a theropod footprint with metatarsal impressions (MT). From left to right, trackways are
Grallator
,
Megalosauripus
,
Otozoum
narrow-gauge,
Otozoum
wide-gauge,
Parabrontopodus
, and
Brontopodus
, all based on type material. All scale bars 1 m except for
Grallator
. Note that all footprints are longer than wide and that footprint axes (arrows) point forward or outward (bottom rows). Characteristic step and foot length (SL and FL) ratios are also shown, and stippled rectangles correspond to track length and width.
Figure 5.10 Trackways made by ornithischian dinosaurs. The Ornithischia, one of the two major groups of dinosaurs, are all herbivores and include such familiar animals as
Stegosaurus
,
Triceratops
, and
Edmontosaurus
. Trackway configurations in the center for main groups of ornithischian dinosaurs (top), with an inset showing an ornithopod footprint with metatarsal impressions (MT). From left to right, trackways are unnamed stegosaur trackway,
Tetrapodosaurus
,
Anomoepus
,
Caririchnium
, and
Ceratopsipes
, all based on type material. All at same scale except for
Anomoepus
. ? = no trackways known for scutellosaurids and pachycephalosaurids. Note that all footprints are as wide as or wider than long and that footprint axes (arrows) point inward and forward (bottom rows). Characteristic step and foot length (SL and FL) ratios are also shown, and stippled rectangles correspond to track length and width.
