Sentences about mode of occurrence of fossil mollusk
貝化石の産出状況を英文で書くにあたり,有用であると考えられる例文集です.
日本の優れた研究者による論文から,38の文例を引用し整理してあります.
1. 産状
1-1. 地層中の密度
散在
- They are generally inarticulated and scattered in the fossil bed.
- Molluscan specimens occur sporadically.
- These fossils are usually sporadically disseminated in the sediments, rarely abraded or broken.
- Shell remains occur sporadically in the silty sandstone and siltstone facies of the Yutorinuma and near the top of the Utsuno formations.
- At Locality 1, molluscan fossils are scattered in a very fine-grained sandstone, and three species have been discriminated.
密集
- Shells are trapped and accumulated in boulder gravel.
- Molluscan remains occur showing dense aggregation and form a fossil bed.
- Anadara often forms loose shell-beds of 15 to 20 cm thick, in which shells including many confined individuals are randomly oriented.
- These mollusks are usually found closely accumulated in the coarse-grained sandstone layer.
- On the other hand rather well preserved shell remains of the sandstone facies in the Ginzan and Utsuno formations constitute shell beds of a few meters thick.
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1-2. 地層中の姿勢
層理面に平行
- Bivalve shells are oriented nearly parallel to the bedding plane with convex side turned upwards.
- Macoma is found conjoined, lying on the bedding plane.
- These shells, both conjoined and separated, lie on the bedding plane, usually with the convex side upward.
- Bivalves clearly predominated over gastropods in abundance despite the specific richness of the latter, and always occur as separate valves arranged convex side up parallel to the stratification of the gravel-bearing medium- and coarse-grained sand.
- Among them, bivalves of Macoma occur as articulated shells and are oriented with the commissure line lying parallel to the bedding plane.
層理面と斜交
- Orientations of shells are oblique or nearly perpendicular to the bedding plane with convex side turned downwards.
- Some rather well preserved pectinid specimens exhibit a downward-convex mode of occurrence, but some shells are arranged perpendicularly to the bedding plane.
ランダム
- Anadara often forms loose shell-beds of 15 to 20 cm thick, in which shells including many confined individuals are randomly oriented.
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1-3. 二枚貝の入り方
片殻/両殻
- They are generally inarticulated and scattered in the fossil bed.
- Crassostrea occurs with articulated or disarticulated valve.
- Disarticulated shells of Venatomya of which surface sculpture is nearly perfect were obtained.
- Macoma is found conjoined, lying on the bedding plane.
- These shells, both conjoined and separated, lie on the bedding plane, usually with the convex side upward.
- Bivalves clearly predominated over gastropods in abundance despite the specific richness of the latter, and always occur as separate valves arranged convex side up parallel to the stratification of the gravel-bearing medium- and coarse-grained sand.
- Most bivalves occur as articulated specimens, which suggest that the fauna is autochthonous.
- With the exception of pectinids, nearly all of the bivalve specimens are entombed with their paired valves still articulated.
- Almost all the bivalve molluscs such as Anadara, Diplodonta and Cycladicama occur as conjoined valves.
- Among them, bivalves of Macoma occur as articulated shells and are oriented with the commissure line lying parallel to the bedding plane.
- All bivalve specimens obtained from this locality occur as disarticulated valves, most of which are very poorly preserved because of shell dissolution and water-wear.
凸面が上/下
- Bivalve shells are oriented nearly parallel to the bedding plane with convex side turned upwards.
- Orientations of shells are oblique or nearly perpendicular to the bedding plane with convex side turned downwards.
- These shells, both conjoined and separated, lie on the bedding plane, usually with the convex side upward.
- Bivalves clearly predominated over gastropods in abundance despite the specific richness of the latter, and always occur as separate valves arranged convex side up parallel to the stratification of the gravel-bearing medium- and coarse-grained sand.
- Some rather well preserved pectinid specimens exhibit a downward-convex mode of occurrence, but some shells are arranged perpendicularly to the bedding plane.
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2. 化石の保存
2-1. 破壊の程度
- Tateiwaia suffers little injury and wear.
- These fossils are usually sporadically disseminated in the sediments, rarely abraded or broken.
- Turritella is rarely broken.
- Although bivalves are sometimes abraded or broken, minute ornamentation is still discernible on every shell.
- Gastropods and scuphopods are also found as water-worn and fractured specimens, but their fine sculpture or even the protoconch are observed in detail in some cases.
- Almost all specimens are complete or nearly so, but all except those from Locality 7 lack original shell material.
- The pectinids occur generally as fragmented shells
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2-2. 溶失の程度
- Almost all specimens are complete or nearly so, but all except those from Locality 7 lack original shell material.
- The specimens from the lower horizon are almost represented as molds or casts, but some specimens from the upper horizon are rather well preserved, especially the pectinid shells are all very well preserved.
- These mollusks occur as molds or casts but their morphological characteristics are rather well preserved.
- Some of these molluscan fossils particularly those species belonging to the genera Nemocardium, Lucinoma, Macoma, Cycladicama and Peronidia are preserved only as inner and outer molds, whereas pectinids and brachiopods are very well preserved still retaining their original shells.
- All molluscs of the present report occurred as inner and outer molds or casts but the delicate surface sculpture is rather well preserved.
- All bivalve specimens obtained from this locality occur as disarticulated valves, most of which are very poorly preserved because of shell dissolution and water-wear.
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2-3. 表面装飾
- Disarticulated shells of Venatomya of which surface sculpture is nearly perfect were obtained.
- Although bivalves are sometimes abraded or broken, minute ornamentation is still discernible on every shell.
- Gastropods and scuphopods are also found as water-worn and fractured specimens, but their fine sculpture or even the protoconch are observed in detail in some cases.
- These mollusks occur as molds or casts but their morphological characteristics are rather well preserved.
- All molluscs of the present report occurred as inner and outer molds or casts but the delicate surface sculpture is rather well preserved.
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3. 考察
3-1. 現地生
- These mode of occurrence indicate autochthonous or semiautochthonous in origin.
- ___, ___ and so on are in a good state of preservation that represents in situ origin.
- Most bivalves occur as articulated specimens, which suggest that the fauna is autochthonous.
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3-2. 異地性/運搬距離
- Such a mode of occurrence indicates little movement after death.
- This indicates that these shells were not transported far after death from their original habitats.
- These facts indicate that these molluscs were transported from shallower depths.
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