Whiting–related sediment export along the Middle Miocene carbonate ramp of Great Bahama Bank.

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Microconchids of the species Microconchus valvatus (Münster in Goldfuss, 1831) from the Upper Muschelkalk (Middle Triassic) of Germany

In the present paper, the commonly mentioned but poorly recognised microconchid species Microconchus valvatus (Münster in Goldfuss, 1831) is redescribed on the basis of material from the Upper Muschelkalk of Germany. ESEM studies of the microconchid tubes with clear morphological and microstructural characters were compared to the existing known Triassic species. Microconchus valvatus is characterised by fine growth lines and transverse riblets. ESEM analysis shows that tubes which appear smooth under the binocular microscope are in fact abraded. Thus, taphonomy must be taken into account and scanning microscopy must be used during studies of microconchid tubes. Quantitative ecology shows that particular microconchid populations developed various size ranges punctuated by some gaps, have non-normal distributions as expected in time-averaged assemblages, and suggests that differences among populations may reflect distinct hydrologic settings. This study provides a multidimensional investigation of microconchids and offers compelling evidence that microconchids were an important faunal group during the post-recovery Middle Triassic interval