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Morphology and palaeoecology of new, non-marine microconchid tubeworm from Lower Carboniferous (Upper Mississippian) of West Virginia, USA

Zatoń M., Peck R. L.

Annales Societatis Geologorum Poloniae

2013

Vol. 83, No. 1

37--50

A new species of a non-marine microconchid (Tentaculita) tubeworm, Microconchus hintonensis, from the Lower Carboniferous (Upper Mississippian, Chesterian) of West Virginia, USA, is described. Non-marine microconchids occur abundantly in the deposits of the Bluefield, lower Hinton, Princeton and Bluestone Formations of the Mauch Chunk Group, where they are either associated with land plant remains and bivalve shells, or are preserved loose in the host sediment. The specimens attached to plant remains and bivalve shells, are poorly preserved, but those occurring loose in the deposits are well-preserved in three dimensions. The interpretation pre sented here, is that the loose specimens of Microconchus hintonensis sp. nov. also originally encrusted plants (land plants, algae) and bivalve shells, but became detached after substrate degradation and dissolution. The association of land plant remains, charophyte gyrogonites, bivalves, ostracodes, conchostracans, and fish teeth and scales, and the concomitant lack of strictly marine fossils indicate that the microconchid-bearing deposits of the lower Hinton, Princeton and Bluestone Formations were deposited in fresh-water environments. Microconchus hintonensis sp. nov. is regarded as a highly fecund, opportunistic species that in large numbers colonized every available substrate in its habitat. Its abundance in the deposits investigated indicates that the species was welladapted to the environments it occupied, even during episodes of higher sedimentation rates and/or competition with other soft-bodied encrusters. During such episodes, microconchids were able to grow vertically by uncoiling and elevating their tubes, in order to escape potential burial and/or overgrowth by other encrusters.

Konkrecje hiatusowe z iłów rudonśnych Wyżyny Krakowsko-Częstochowskiej

Zatoń M., Marynowski L., Bzowska G.

Przegląd Geologiczny

2006

Vol. 54, nr 2

131-138

Hiatus concretions are arly-diagenetic sedimentary bodies, which in their history of formation, underwent exhumation during sedimentation break and/or erosion of sea-floor. Then they were colonized by various encrusters and borers, before they were buried again. Within Middle Jurassic (Bajocian through Bathonian) clays, hiatus concretions occur in four localities in the Cracow-Częstochowa Upland (south and central Poland): Ogrodzieniec, Bugaj, Mokrsko and Krzyworzeka. Preliminary data about their mineralogy, organic geochemistry and palaeoecology is given. Mineralogical analyses showed, that except dominant high Mg-calcite (up to 87.10% of total carbonates), concretions possess minor amounts of such compounds as quartz, clay minerals (kaolinite and illite), pyrite, siderite or Mg-kutnahorite. However, high differences are observed between total organic carbon contents of concretions (TOC=0.46%) and surrounded clays (TOC = 2.16%), but their molecular composition is similar. Most of identified biomarkers are of terrestrial origin. In clay lithology, the hiatus concretions are the only sedimentary bodies that clearly mark the sedimentation pauses (hiatuses). In the investigated area, they form more or less continuous horizons. The concretions are calcitic, possessing various encrusting fauna such as bryozoans, oysters and oyster-like bivalves, serpulids, solitary corals and foraminifers. They often post-date the borings, belonging to such ichnogenera as Gastrochaenolites, Trypanites and Entobia. Some of the nodules show distinct transition from firmground (characterized by the presence of Glossifungites ichnocoenosis) to hardground (presence of Trypanites ichnocoenosis), pointing to the fact, that they formed at, or very close to, the sediment-water interface. Some concretions, like those from Bugaj and Mokrsko, are characterized by their high diversity of hard bottom communities. Those concretions are also irregular in shape; others, like those from Ogrodzieniec and Krzyworzeka, possess lower diversity. The concretions from Krzyworzeka are especially dominated by the borers, while the encrusters are sparse and not diverse. Those nodules that are wide and flat tend to be more bored on one surface only, while those that are more roundish, are bored on both sides more evenly. The degree of diversity is probably correlated with physical disturbance, causing the rolling and overturning of the exhumed concretions in the littoral zone. On the other hand, the overall diversity could be lowered due to destructive abrasion either of the shallowest borings, echinoid/gastropod scratch marks and shells of nestling bivalves, as well as more delicate epilithozoans.