On the Kinds of Fossil Enclosure

Abstract

Previously the writers (1949) described on the mode of dense occurrence of fossils in the Pleistocene Narita formation in Chiba Prefecture and stated: "In the fossil bed in broad sense, a fossil-rich part which is named as 'fossil enclosure' by the writers, is situated within the non fossiliferous deposits in irregular form. Such a mode of occurrence of fossils may originate from the contemporaneous deposition of fossils and inorganic detritus, lamina by lamina." In this paper, the writers compared the said fossil enclosure with the mode of occurrence of the fossils hitherto recorded. The genesis of the fossil enclosure resembles that of the biostrome of Cummings and Shrock (1928, 1932), and is distinguished from the bioherm of the same authors, although all of these grade abruptly into the non-fossiliferous parts of the strata. The category of the fossiliferous mass within the rocks which are called as fossil enclosure in broad sense is subdivided into two according to the condition of the laminae, namely biostrome and bioherm. The fossiliferous part of the biostrome is contemporaneous with the non-fossiliferous rocks in laminal unit, but that of the bioherm is not. The former is the tepee rock (core) of Gilbert and Gulliver (1895) and the so-called lens, of which the tepee agree with the fossil enclosure in narrow sense. The latter includes ball stone (crag ball) of Bulter (1939) and the so-called fossil reef. The heap, bank, channel deposits and the stromatolith of Kalkowsky (1908) remain unknown or as to their systematic position, owing to that they are not accompanied with detail description. The fossil mass due to differential melting of a fossil layer belongs to "Stylolite".