Biogenic Sedimentary Structures Research Articles

Paleoenvironments of Mowry Shale (Lower Cretaceous), Western and Central Wyoming: GEOLOGIC NOTES

The Lower Cretaceous Mowry Shale of western and central Wyoming contains three distinct facies, each of which is characterized by a unique suite of physical and biogenic sedimentary structures: (1) laminated mudstone, (2) bioturbated mudstone, and (3) bioturbated sandstone. We interpret the facies to represent the following marine biotopes (Schafer's terminology): (1) lethal isostrate--quiet, anaerobic, >150 m deep; (2) vital isostrate--quiet, marginally aerobic, 15 to 150 m deep; and (3) vital heterostrate--agitated, fully aerobic, <15 m deep. Bentonite datum planes show that the boundaries between facies are time transgressive, and indicate a west-to-east progradation of the shoreline and lateral filling of the Mowry sea. An east-dipping paleoslope inclined at 0 76;13^prime has been estimated. The depositional topography of the Mowry basin as reconstructed from the facies pattern shows that the thickest accumulation of sediment occurred along the western margin where water was shallowest, whereas in the deeper water basin center a much thinner section was deposited. Thus, isopach patterns of the Mowry in no way reflect the original depositional topography. The significance of this study for petroleum geology is threefold: (1) a facies sequence is used to reconstruct the depositional basin configuration of a known source rock; (2) the facies correlate with previously published regional variations in organic carbon concentration in the Mowry; and (3) the facies also correspond approximately to facies based on electrical resistivity.

Retrogradational Shelf Sequence--Upper Cretaceous (Campanian-Maestrichtian) Cape Sebastian Sandstone, Southwestern Oregon: ABSTRACT

In the tectonically active Circum-Pacific belt, thick retrogradational (transgressive) sequences are not uncommon, in contrast with the Cretaceous of the Western Interior. Retrogradational sediment packages reflect rapid sedimentation rates but even more rapid rates of relative sea-level rise. A well-exposed and convincingly documented example is the Cape Sebastian Sandstone, a 250-m-thick, fining-upward sequence representing foreshore to offshore accumulation. Progressively increasing depth of deposition is reflected in both physical and biogenic sedimentary structures in the Cape Sebastian Sandstone. The basal, shelly boulder conglomerate is overlain by trough-cross-bedded pebbly sandstones, plane-laminated coarse-grained sandstones, and graded conglomerates. A single, subvertical trace-fossil type is locally abundant. These sediments represent foreshore to nearshore depositional environments. The middle and bulk of the formation comprises hummocky cross-stratified sandstones. Grain size, frequency of pebble lenses, and thickness of hummocky laminae decrease upward. Burrowed zones, diversity of burrows, plane-laminated zones, plant debris, and oscillation-ripple preservation increase upward. These sediments reflect storm-influenced, inner-shelf sedimentation. The uppermost part of the formation consists of alternating laminated, fine-grained sandstones and progressively thicker, burrowed sandy siltstones. Increased trace-fossil size and diversity, as well as abundant plant debris, characterize these sediments, which represent an outer-shelf sedimentary environment. Modern examples of the described structures have been observed off the Oregon and California coasts, corroborating the hypothesis that the Cape Sebastian Sandstone represents a retrogradational shelf sequence. Also, evidence for Late Cretaceous faulting in southwestern Oregon supports the proposition that thick, retrogradational sequences may be deposited in tectonically active regions. End_of_Article - Last_Page 422------------

Videotapes of Active Primary Physical and Biogenic Sedimentary Structures of Epicontinental Shelf, Northern Bering Sea: ABSTRACT

Videotapes from 23 camera stations in the northern Bering Sea provide a unique view of the formation and modification of primary sedimentary structures in the marine environment. The study area is a shallow-water ( 25 cm/sec) bottom currents. Swales between sand ridges are covered predominantly with mud, generally devoid of bed forms, and contain local patches of shell accumulations. Current speeds are reduced (<15 cm/sec) and strongly asymmetric in the swale areas. The videotapes show the transport of fine-grained sediment and organic material in suspension and the formation of burrows, trackways, and trails by benthic organisms (crabs, worms, and shrimp). The information conveyed by these videotapes is useful for interpreting primary sedimentary structures in adjacent lithofacies of ancient epicontinental-shelf deposits. End_of_Article - Last_Page 450------------

Formation and paleontologic recognition of structures caused by marine annelids

Laboratory and field collected sediments were x-rayed to document the array of biogenic sedimentary structures produced by the burrowing and feeding behavior of six species of marine intertidal annelid (Glycera robusta, Nephtys caecoides, Pectinaria californiensis, Notomastus magnus, Eupolymnia crescentis, and Cirriformia spirabrancha). Polychaete burrows were found to vary greatly in structural complexity with both errant (N. magnus) and relatively sessile forms (C. spirabrancha) producing a variety of biogenic structures. Sediment mixing by the tentacle-feeding polychaete C. spirabrancha was observed by sequentially x-raying an experimental field enclosure stratified with an opaque substance. The experiment demonstrates that tentacle-feeding polychaetes can influence the topography of the sediment-water interface and transport substantial amounts of near surface material downward.Criteria by which fossil biogenic sedimentary structures, presumably produced by soft-bodied organisms, can be assigned a feeding function have been advanced by Walker (1972). Some of the assumptions inherent in feeding function analysis were applied, with varying degrees of success, to the biogenic structures of modern soft-sediment polychaetes.

An Electro-Osmotic Knife for Slicing Large Box Cores

ABSTRACT Large box cores can be sliced vertically or horizontally on board ship with a knife that has an electrified metal blade. The knife operates on the principle of electro-osmosis, which reduces drag along the blade during slicing and minimizes distortion of the sediment. The slices are useful for subsampling the core and for studying physical and biogenic sedimentary structures. Making slices helps solve the problems of handling, storing, and shipping the large volumes of sediment recovered in box cores.

Biogenic Sedimentary Structures Formed By Rays

ABSTRACT Excavations made by the feeding activity of rays (elasmobranchs) are extremely abundant in tidal flats and in estuarine sand bars and channels of the Georgia coast. Rays make excavations by flapping their wings in order to erode the substrate hydraulically and thereby obtain benthic organisms for food. Subsequently, the hole is refilled with new sediment. The structure that results from this feeding activity is composed of two parts: a broad, shallow, surface depression that is dish-shaped and a lower, roughly circular hole as much as 30 cm deep. Feeding depressions formed by rays are distinctive sedimentary structures that are easily recognized in cores from Holocene sediments. Recently they have also been found in Pleistocene and Cretaceous outcrops.

Distribution and Relation of Physical and Biogenic Sedimentary Structures, Shallow Continental Shelf Off Northwestern Florida and Alabama: ABSTRACT

Distribution and Relation of Physical and Biogenic Sedimentary Structures, Shallow Continental Shelf Off Northwestern Florida and Alabama: ABSTRACT

Biogenic Sedimentary Structures of South Texas Outer Continental Shelf: ABSTRACT

Biogenic Sedimentary Structures of South Texas Outer Continental Shelf: ABSTRACT

Biogenic Sedimentary Structures Produced by Crabs in Lagoon Margin and Salt Marsh Environments Near Beaufort, North Carolina

ABSTRACT Intertidal burrowing crabs produce distinctive biogenic sedimentary structures in protected lagoon margin and salt marsh environments in the vicinity of Beaufort, North Carolina. Distribution of crabs is determined primarily by substrate characteristics, salinity, and vegetation cover in the intertidal zone. Protected sand beaches and flats are heavily burrowed by the sand fiddler, Uca pugilator, which produces gently curved J-shaped and sharply curved L-shaped burrows 1 to 2 cm in diameter. Larger Y- and U-shaped burrows are formed by the ghost crab, Ocypode quadrata, in the backshore and foredune ridge zones above the high tide line. Salt marshes influenced by normal to near normal marine salinities are burrowed by U. pugilator, U. pugnax, and Sesarma reticulatum. U. pugnax and S. reticulatum burrow in muddy substrates, particularly along tidal creek banks, whereas U. pugilator is restricted to sandy substrate areas. U. pugnax burrows are 1 to 2 cm in diameter and have complex twisting and turning forms. The larger communal burrows of S. reticulatum consist of a complex of interconnected shafts with several oval-shaped surface openings. Panopeus herbstii is often found inhabiting these burrows. In salt marshes where the influence of fresh water is great, U. minax and U. pugnax are the dominant crabs. U. minax forms burrows 2 to 5 cm in diameter with ho ded entrances and long vertical shafts. Intertidal crabs are important agents of bioturbation in the environments that they inhabit. Their burrows have excellent potential for preservation in the sedimentary record. Recognition of the record of biogenic sedimentary structures produced by intertidal crabs would be of significant value in identifying paleoenvironments, fixing ancient lagoon margin and estuarine shorelines, and determining paleosalinities.

Trace Fossils and Bathymetry of the Upper Cretaceous Point Loma Formation, San Diego, California

Distinctive biogenic sedimentary structures (trace fossils) in sedimentary rocks reflect the burrowing behavior of the animals that made them. Because the distribution of these animals is influenced by environmental factors such as water depth and substrate type, trace fossils have been used widely as paleoenvironmental guides. The massive, ungraded sandstones in the Point Loma Formation have sharp upper and lower contacts, thick lenses of mudstone clasts, and common load-deformation structures, suggesting deposition largely by grain-flow processes. Foraminifers and most of the trace fossils suggest deposition in a deep, probably bathyal environment. However, two abundant trace fossils, Qphiomorpha and Thalassinoides , are widely held to represent very shallow-water to intertidal paleoenvironments, and they usually occur in such facies. Two morphologic forms of a third trace fossil, Zoophycos , have been thought to reflect different environmental conditions, but they occur here in the same strata. These occurrences emphasize the point that paleoenvironmental interpretations should not be based on individual trace-fossil taxa, but that such traces should be considered only in conjunction with other available evidence.

Characteristic Physical and Biogenic Sedimentary Structures in Georgia Estuaries

Estuaries of the Georgia coast possess a wide variety of sedimentary textures and physical and biogenic sedimentary structures. Sediment grain sizes range from fine mud to pebbles. Physical sedimentary structures include small- to large-scale sets of parallel-, ripple-, and cross-laminae. Biogenic structures include abundant burrows and bioturbations by many marine invertebrate organisms. Our studies of animals, sediments, and sedimentary structures in these estuaries indicate that (1) very fine-grained sediments tend to accumulate near the ocean, regardless of substantial sand sources far upstream; (2) Pleistocene sand outcrops are very important locally, especially near the ocean; (3) tests and shells generally are scarce; (4) ebb-current flow structures predominate over flood-current flow structures; (5) diversity and abundance of biogenic sedimentary structures decrease both landward and toward the deeper parts of estuarine channels; and (6) muds generally contain distinct burrows, whereas sands may contain both discrete burrows and more general bioturbation.

Abyssal Sediment Burrowers--Trace Fossils in Caribbean Chalks and Marls, Deep-Sea Drilling Project Cores: ABSTRACT

Cores recovered in the Caribbean Sea on JOIDES Leg 15 exhibit a superb assemblage of biogenic sedimentary structures. They are identified as distinctive trace fossils (ichnogenera) similar to those well-known from land-based stratigraphic sections. They represent the burrowing behavior of benthic animals living contemporaneously with sedimentation. Some of the best examples are at sites 146 and 149 in the Venezuelan basin. These adjoining sites were drilled in abyssal depths of 3,949 and 3,472 m, respectively, and provide a complete section from Coniacian to Pleistocene. Faunal and sedimentologic evidence from the cores suggests that deposition was abyssal. The most distinctive biogenic structures are Zoophycus (a spiral web), Teichichnus (a laminated trough), and Chondrites (a regularly branched system). These represent the deep-water trace fossil assemblage of Seilacher, which has been documented in rocks of various ages deposited in bathyal and abyssal frameworks from widespread geographic areas. Because similar trace fossils are present throughout the Phanerozoic, it is disappointing that they are not recognized in modern deep-sea sediments, and the animals responsible for them have not been identified. One reason is that the traces are accentuated only with time. Our material shows a progressive enhancement of biogenic structures, from vague outlines in the softer Tertiary sediments to increasingly marked contrast and detail downward in the cores. Furthermore, little knowledge exists about modern abyssal burrowers and their burrows, and few cores have been taken for the identification of potential fossil traces. End_of_Article - Last_Page 811------------

Physical and Biogenic Characteristics of Sediments from Outer Georgia Continental Shelf: ABSTRACT

Eighty-eight box cores were taken on the outer Georgia continental shelf, in water depths from 15 to 200 m. Textural analysis indicates that the midshelf area is covered by medium to coarse sand, evenly distributed, with no north-south linear trends. Areas of fine sand are present on the inner and outer shelf edges, and in 2 distinct lobes extending seaward from the Georgia coast. Parts of the lobes suggest that the finer material forming them was supplied by the Savannah and Altamaha Rivers. Local patches of semiconsolidated mud indicate the location of remnant marsh or estuary deposits. Offshore shell assemblages indicate a mixing of faunas in terms of both environment and age. Pleistocene regressions and transgressions across the shelf resulted in alternate oceanward and landward migrations of nearshore and estuarine faunas, reworked subsequently with open-ocean faunas. Live animals offshore are adding their shells to the already mixed assemblages. Biogenic sedimentary structures significantly exceed those of primary physical structures. All box cores show some degree of biogenic reworking, and most were more than 60% bioturbated. Physical sedimentary structures include crossbedding, ripple lamination, interbedded sand and mud, wavy bedding, and graded bedding. Physical and biogenic reworking of the outer Georgia continental shelf sediments has removed or greatly modified most of their original depositional characteristics. Thus, reference to these sediments as relict is misleading. End_of_Article - Last_Page 784------------

Concepts in the Study of Biogenic Sedimentary Structures

ABSTRACT Ichnology--the study of fossil and recent traces of organisms--has yielded considerable information that is valuable in such fields as paleontology, sedimentology, and environmental reconstruction. Many of the basic concepts and definitions in ichnology are misused or misunderstood in current literature, however, which stresses the need for more stability or uniformity within the subdiscipline. With that goal in mind, a meaningful synthesis and evaluation of these basic concepts has been attempted in this paper; the views presented represent a consensus among 33 competent specialists from 12 countries, who criticized the original manuscript.

Burrows of the Ghost Crab Ocypode Quadrata (Fabricius) on the Barrier Islands, South-Central Texas Coast

ABSTRACT Burrows of the grapsoid crab Ocypode quadrata (Fabricius) are important biogenic sedimentary structures on Texas barrier islands. Variation in the shape, diameter, length, orientation, and areal density of the burrows can be used to define subenvironments of the beach and foredune ridge. An increase in diameter, length, and morphological complexity of the burrows together with a decrease in burrow abundance from the upper foreshore to the back edge of the beach differentiate beach subzones. Greater burrow size and abundance and a simpler shape distinguish O. quadrata burrows in the dune mounds from burrows in the interdune flats of the foredune ridge. A preferred burrow orientation descending to the northwest in the backshore contrasts with a random orientation of burrow in the foredune ridge. Although the preferred orientation is away from the shoreline, factors not directly related to shoreline trend may be responsible.

Usable Beach-to-Offshore Model for Tide-Dominated Shoreline; Sapelo Island, Georgia: ABSTRACT

This study represents a cooperative effort by sedimentologists, zoologists, paleontologists, and mineralogists to determine what facies characteristics exist in a present-day sedimentary record. The results show that geologically recognizable subfacies can be established by primary physical and biogenic sedimentary structures. Beach zone: The rather low energy of the Sapelo Island shoreline and the low dip of the beach surface, combined with a tidal range of 2.1 m, result in characteristic morphology, grain-size distribution, and types of sedimentary structures. Most beach features are controlled by wave activity, and obvious bioturbation is not abundant in the beach zone. The backshore and upper foreshore contain few species and few individuals. The lower foreshore has few species but numerous individuals. Nearshore zone: At 100 m offshore (water depth, 1.5 m) there is a marked increase in the fine fraction; at the same place, biogenic sedimentary structures increase. Dominant sedimentary structures are ripple-laminated sand. Species of infaunal organisms are more abundant than in the beach but few individuals are present. At a distance of 2,500 m offshore (water depth, 2.7 m) biogenic sedimentary structures become the dominant characteristic of the fine silty sand. The unreworked part of the substrate is characterized by parallel to subparallel laminated sand. These beds, referred to as laminated-to-burrowed are separated by erosional bedding planes. Farther seaward at a distance of 5,500 m (water depth, 6 m) the substrate is almost completely reworked due to increased biogenic activity. This is the most densely populated zone in the beach-to-offshore sequence. Offshore zone: At a distance of 10 km seaward (water depth, 10.5 m) the substrate consists of clean, medium- to coarse-grained sands. Megaripples are the dominant physical sedimentary structure in the offshore area and few species and few individuals are found, but biogenic reworking by heart urchins is abundant. End_of_Article - Last_Page 629------------

Depressions in shallow marine sediment made by benthic fish

ABSTRACT Certain benthic marine fish, including rays, skates, and flatfish, temporarily bury themselves in sediment and thereby create shallow depressions. These have been observed near shore in the Pacific Ocean off southern California, the Gulf of California, and Long Island Sound. If preserved, such biogenic sedimentary structures could aid in interpreting former depositional environments.

Fossil and recent 'tadpole nests'; a discussion

Tadpole are a true biogenic sedimentary structure known only from the Recent. All known occurrences of supposed fossil forms have been disputed and are considered to be interference ripple marks of inorganic rather than of organic origin. Silurian, Carboniferous, and Triassic tadpole nest-like structures could not have been produced by tadpoles because frogs did not appear until the Jurassic Period. A new occurrence of Recent tadpole from New York indicates that tadpoles produce nests with their tails while feeding from bottom sediments and that their delicate nature severely limits their chances of preservation in the fossil record. The term tadpole holes (Dionne, 1969) is unnecessary because the term it was meant to replace, tadpole nests, is correct by definition. Although Benjaminichnus Boekschoten, 1964, was proposed for Recent tadpole and was also intended for any fossil forms that may some day be found, it is an objective synonym of Batrachiodes Hitchcock, 1858 ( non Lacepede, 1800), an inorganic sedimentary structure (interference ripple marks). We recommend strongly that Recent biogenic sedimentary structures, and other potential trace fossils with known producers, not be given formal taxonomic names. Instead, the taxonomic (or colloquial) name of the organisms responsible for a structure should be used for reference. The possibility of such a structure being found as a trace fossil is insufficient justification for giving it a taxonomic name.

Recognizing Estuarine and Tidal Creek Sandbars by Biogenic Sedimentary Structures: ABSTRACT

Estuarine and tidal creek sandbars bear many similarities to fluvial channel sandbars in their physical sedimentary structures, but are considerably different with respect to biogenic sedimentary structure. Consideration of these biogenic structures with current-produced physical sedimentary structures and with facies geometry produces unique, readily recognizable, paleoenvironmental indicators. The abundant burrowing fauna collectively found in estuarine and tidal-creek bars represents species which are individually characteristic or very common in other intertidal environments, such as beach (burrowing shrimp, Callianassa major), tidal flat (burrowing shrimp, Callianassa atlantica, and polychaete worms Onuphis and Diapatria), marsh (fiddler crab, Uca), estuarine channels (burrowing shrimp, Upogebia), and sand flats (acorn worm, Balanaglossis). Other biogenic structures found in tidal creek bars include tracks, trails, and markings produced by more typical subtidal organisms such as the sand-collar snail, Polinicies; hermit crab, Clibanarius; blue crab, Callinectus; mantis shrimp, Squilla; and feeding depressions made by rays. Two subenvironments are found on most of the tidal creek sandbars studied and each contains a characteristic suite of biogenic and physical sedimentary structures. The channel side of the bar consists predominantly of sand and preserves a record of megaripples and small current ripples. Associated with these structures are burrows of Onuphis, Callianassa major, Callianassa atlantica, and Uca. Energy is less and muddy sand accumulates on the side of the bar away from the channel current. Ripple laminae generally are not developed here and bioturbated sediments comprise the principal structures. A great density of burrows is found in this subenvironment, and Upogebia, Diapatria, and the razor clam, Tagelus, are typical burrowing forms. End_of_Article - Last_Page 731------------

Profile of Biogenic Sedimentary Structures in Holocene Barrier Island--Salt Marsh Complex, Georgia: ABSTRACT

Biogenic sedimentary structures, many of which are characteristic of particular depositional environments, are abundant among Holocene barrier island-salt marsh habitats of coastal Georgia. The major environments represented are (1) beaches, including the shoreface, lower and upper foreshore, backshore, dunes, and washover fans; (2) salt marshes, consisting of the low marsh, high marsh, and salt pans; and (3) estuaries and tidal streams, including channel deposits, point bars, stream banks, and natural levees. Biogenic sedimentary structures in these environments consist of bioturbate textures and tracks, trails, burrows, and dwelling tubes, and are produced chiefly by polychaetes, gastropods, pelecypods, decapods, amphipods, and insects. Such structures, either singly or as assemblages of lebensspuren, are ordinarily sufficient to delimit major habitats. Further, most of these structures are capable of preservation, and many of them have been documented in the Pleistocene of Georgia and Florida. End_of_Article - Last_Page 2036------------