Diverse Trace Fossil Assemblage Research Articles

Sedimentary fades, depositional environments, and faunal associations of the lower Llandovery (Silurian) Beechill Cove Formation, Arisaig, Nova Scotia

Six facies are recognised in the Beechill Cove Formation. These are: (1) conglomerate facies deposited as a transgressive beach lag; (2) red shale facies deposited in shoreface environments; (3) mottled mudstone facies; extensively bioturbated sediments indicative of shallow subtidal areas influenced by low sedimentation rates; (4) regular layered facies; shelf turbidites generated by storm activity and superimposed on quiescent subtidal environments; (5) lenticular facies, including a thinner bedded more persistent and a thicker bedded lenticular subfacies, induced by storm activity and deposited in shallow subtidal environments; and (6) laminated shale facies produced by sediment fallout from suspension in a low-energy environment where the oxygen, minimum layer intersected the sediment–water interface. Three faunal associations occur, which have distinct distributional patterns. The Lingula clintoni association, which is characterized by L. clintoni in life position and a moderately diverse but abundant trace-fossil assemblage, is restricted to the mottled mudstone facies. The Leptostrophia beechillensis association, a transported residue, is dominated by brachiopods and restricted to the regular layered facies. The low-diversity Dalmanella primitiva association is transported and restricted to the lenticular facies. No faunas are known from the conglomerate or laminated shale facies, and only rare trace fossils occur in the red shale facies.

Trace Fossil Assemblages of Upper Cretaceous Sand Units, Delaware and New Jersey: ABSTRACT

End_Page 694------------------------------Siliciclastic formations of Upper Cretaceous age on the Delaware-New Jersey coastal plain contain diverse trace fossil assemblages. When used with physical sedimentary structures and textural data, the assemblages can differentiate intertidal and shallow subtidal depositional environments. Most close modern analogs can be recognized for the Cretaceous trace makers. The Englishtown Formation (Campanian) crops out along the C & D Canal in Delaware. The basal part of the unit is characterized by mottling due to dense concentrations of gently meandering, essentially horizontal Planolites burrows outlined by rims of dark organic-rich material. Other zones are mottled primarily by small-diameter branched shafts of Chondrites. Clumps of quartz sand-lined tubes of Terebellina are dispersed throughout. These tubes have gently curved shafts which form tunnels with distinctive feeding-probe structures at their distal ends. At the top of the unit, the assemblage is dominated by stacked Ophiomorpha nodosa systems with basal mazes. Also present are several types of Chondrites, which commonly surround and/or infest the walls of Ophiomorpha shafts, and deli ate Skolithos shafts. In New Jersey, the Wenonah Formation, Mt. Laurel Formation, and Shrewsbury Member of the Red Bank Formation (all Maestrichtian) each contain a distinctive trace fossil assemblage. The Wenonah Formation is characterized by Cylindrichnus, large concentrically laminated, subvertical, and tapering clay tubes. The Mt. Laurel Formation exhibits two facies, one characterized by small-diameter Ophiomorpha shafts and associated Chondrites forms and the other containing an Ophiomorpha, Chondrites, Skolithos, and Cylindrichnus assemblage. Large-diameter Ophiomorpha nodosa systems and associated Chondrites characterize sands of the Shrewsbury Member of the Red Bank Formation. The trace fossil assemblages and primary sedimentary characteristics suggest the following depositional environments: Englishtown Formation, shallow subtidal shoals transitional to lower foreshore; Wenonah Formation, subtidal, inner shelf; Mt. Laurel Formation, shoreface and transition zones to shallow shoal complex; and Shrewsbury Member of Red Bank Formation, offshore bar complex. End_of_Article - Last_Page 695------------

Petrology and Depositional Environments of Boyle Dolomite (Middle Devonian) in East-Central Kentucky: ABSTRACT

The Middle Devonian Boyle Dolomite is a sequence of dolomite, dolomitic limestone, limestone, chert, and shale which has been deposited on a regional unconformity that truncates successively older units toward the axis of the Cincinnati arch. The Boyle varies in thickness (0 to 11 m) and crops out in a 40-km-wide, northeast-trending, arcuate belt on the eastern margin of the Blue Grass region. The Boyle Dolomite is divided into the following four lithofacies: Kiddville, Winston (Boyle limestone), Casey, and Duffin. The basal Kiddville is a quartzose dolomicstone with abundant fish remains and represents the slow accumulation of a lag deposit in a platform environment. The Winston (Boyle limestone) is a crinoidal grainstone-packstone and indicates a full marine transgression with high-energy winnowing action on the shelf. The Casey is a cherty dolomicstone with a sparse fauna and represents continued transgression of carbonate mud environments. The Duffin is an interbedded dolomicstone and shale with an abundant and diverse trace-fossil assemblage and marks the transition between carbonate and clastic deposition in Middle to Late Devonian time. An upward decrease in fossil abundance, diversity, and detrital clastics corresponds to an increase in the percentage of dolomite. Iron substitution in the dolomite crystal lattice increases upward and suggests an influence of reducing diagenetic environments. Trace-fossil analysis reveals a shelf to slope assemblage in the Boyle. The Boyle Dolomite represents the marine transgression in the western margin of the basin during Middle Devonian time. The transition between open-marine carbonate and anoxic black shale is a shelf to slope carbonate mud with a predominant infaunal assemblage. End_of_Article - Last_Page 1589------------