ISSN:1042-0940    

DOI:10.1080/10420949809386435

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Analysis of 201 crayfish burrows (Camborygma eumekenomos)from three fluvial beds of the Chinle Formation (Upper Triassic, Utah, U.S.A.) provides results consistent with knowledge of Holocene crayfish ecology. Thus, many aspects of their population ecology may have remained unchanged since the early Mesozoic. A significant increase in crayfish size away from the fluvial channel reflects size (age) segregation along an environmental gradient. The high lateral (within‐bed) variation in burrow density may have been caused by spatial heterogeneity in water table and soil moisture levels. In each of the three analyzed beds, the burrows record a single ecologic generation of a monospecific crayfish population. The three beds differ in terms of the mean burrow diameter (this may reflect differences either in the average size/age of the resident crayfish or in the lateral extent of sampling). However, the overall shape of the burrow‐size distribution is similar for all three beds (unimodal and close‐to‐normal). This reflects similar paleohydrologic and paleoecologic conditions through time, as substantiated by independent ichnologic and sedimentologic evidence.

ISSN:1042-0940    

DOI:10.1080/10420949809386436

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Phytnatodermais a complex, branching biogenic structure that is seldom mentioned in the ichnologic literature, although it may have been misidentified recently as“Zonarites”and large pellet‐filled“Chondrites”.The ichnogenus is usually interpreted as the product of subsurface deposit‐feeding animals. Well‐preserved examples from Pliocene slope mudstone in Ecuador are assignable toP. granulatum(Schlotheim, 1822). These structures are typically 30–40 cm in overall diameter; consist of outward‐branching, horizontal to subhorizontal, overlapping tunnels grouped in bundles; and have tunnel fills consisting of pelleted volcanic ash. The EcuadorianPhymatodermaoccur with a moderately rich ichnoassemblage that includesAlcyonidiopsisichnosp.,Chondrites intricatus, several kinds ofPhycodes‐likestructures,Phycosiphon incertum, Planolitesichnosp.,Rorschachichnus amoeba, Scoliciaichnosp.,Taenidium barretti, andZoophycosichnosp. Benthic foraminiferids and geologic context point to deposition on the upper trench slope, ca. 3–4 Ma.

ISSN:1042-0940    

DOI:10.1080/10420949809386437

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Although amber has never been cited as a medium for trace fossils, the present study shows that fossilized resin does contain ichnofossils. Examples of impressions, secretions, protective coverings, domiciles, excretory products and feeding behavior occur in amber. These ichnofossils can be used to determine not only the presence of invertebrates and vertebrates at particular periods in the past, but also aspects of their behavior. Such fossils play a role in understanding past terrestrial ecosystems.

ISSN:1042-0940    

DOI:10.1080/10420949809386438

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A siliciclastic tidal‐inlet sequence within the Tombigbee Sand Member of the Upper Cretaceous Eutaw Formation, central Alabama, is composed of two subfacies distinguished primarily on the basis of form, scale, and orientation of cross‐stratification. These subfacies record spatial and temporal variations in net‐sedimentation rate, frequency of reworking, and relative importance of slack‐water stages, most of which were governed by variations in tidal‐current asymmetries and associated hydrodynamic regimes. The dominant ichnocoenosis in both subfacies is characterized by, in general order of decreasing abundance: (1)Macaronichnus, produced by vagile, deep deposit‐feeding polychaetes; (2)Conichnus, produced as temporary dwellings or during equilibrium/ escape movements of anemone‐like animals; (3) a branched form ofSkolithos, attributed to deposit‐feeding worms; and (4)Dactyloidites, a subsurface feeding structure made by worms or worm‐like organisms. Relative abundances of these ichnotaxa, and degree of bioturbation in general, vary within and between subfacies, in a manner consistent with variations in reworking and net‐sedimentation rates.Ophiomorphadefines a subordinate ichnocoenosis that developed only during relatively rare, extended slack‐water periods associated with subfacies 2.

ISSN:1042-0940    

DOI:10.1080/10420949809386439

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Teredolites‐infested log‐grounds are abundant in the late Turonian‐Coniacian Garudamangalam Sandstone Formation in the Cauvery Basin, Southeast India. The morphological characteristics of the borings deviate from those of the idealTeredolites clavatusLeymerie andTeredolites longissimusKelly and Bromley, reflecting the response of the boring animals to substrate overcrowding and competition for space. Ichnological and sedimentological evidence indicate deposition of log‐bearing intervals in a delta‐plain or estuarine setting. Application of sequence stratigraphic principles indicates that log‐ground accumulation in the Cauvery Basin was closely linked to episodes of sea‐level rise (transgressive events).

ISSN:1042-0940    

DOI:10.1080/10420949809386440

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Turritellid gastropods are diverse and abundant in Mesozoic to Cenozoic marine assemblages. Despite their ubiquity and biostratigraphic utility, little is known about their ecology, paleoecology, or taphon‐omy. Living positions of fossil turritellids, for example, are not well known. Additionally, encrusting and boring organisms (epi‐and endobionts) present on fossilTurritellashells are interpreted to occur exclusively on empty shells. Living snails, hermit crabinhabited shells, and empty shells ofTurritella gonostomawere examined from Cholla Bay, northern Gulf of California, for the presence of endobionts to determine if bioerosion (via endobionts) is limited to empty shells. LivingT. gonostoma, which are semi‐infaunal to infaunal, had three types of endobionts in low frequencies associated with the shell: microborers (green algae/blue‐green bacteria), spionid polychaetes (ichnogenusCaulostrepsis), and clionid sponges (ichnogenusEntobia).Biont distribution on the shells indicate life positions. Hermited shells ofT. gonostomahad similar endobionts in higher frequencies, with the addition of the spionid trace fossil(Helicotaphrichnus)and coralline algae (which appears to decalcify the shell). Empty shells had extensive clionid borings. Empty shells were also more likely to have drill holes (ichnogenusOichnus)from predatory gastropods. Thus, endobiont infestation is not restricted to empty shells, nor may it be a reliable guide for “time‐since‐death” for fossil turritellids. FossilTurritellafrom this region had primarily clionid borings; the patchy occurrence and distribution of these bionts indicate diverse burial histories for turritellid shells.

ISSN:1042-0940    

DOI:10.1080/10420949809386441

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Numerous circular, 30 to 270 μm‐diameter bore holes in several species of gastropod and bivalve shells from Julian Lake, southern Ontario, Canada are similar in appearance to theichnotaxa Oichnus simplex, Oichnus paraboloides, andTremichnusisp. These ichnotaxa are well described from marine systems but are rarely reported from freshwater environments.

ISSN:1042-0940    

DOI:10.1080/10420949809386442

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:1042-0940    

DOI:10.1080/10420949809386434

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor