COCCOLITH-AGGLUTINATING FORAMINIFERA FROM THE EARLY CRETACEOUS AND HOW THEY CONSTRUCTED THEIR TESTS
COCCOLITH-AGGLUTINATING FORAMINIFERA FROM THE EARLY CRETACEOUS AND HOW THEY CONSTRUCTED THEIR TESTS
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白垩纪早期的颗石藻凝集有孔虫及其如何构建测试
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
T. L. Rasmussen
中科院分区：
文献类型：
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作者：
E. Thomsen;T. L. Rasmussen
扫描电子显微镜下的有孔虫最低Barremian（下白垩纪）存款在英格兰东部的斯皮顿，揭示了约4%的凝集测试几乎完全是由种Watznaueria barnesae的cocoliths。大多数的有孔虫的凝聚球蚴是类似于Trochammina depressa的锥螺旋形式，但也观察到平旋，单室，单轴，双轴和三列形式。测试很小，很少超过125 μm的长度。由于测试尺寸小、建筑材料和压缩不寻常，具体识别很困难。在最简单的状态下，轮藻的壁由单层球壳组成。有孔虫在选择和处理球蚴方面效率很高，球蚴总是以其远端表面朝外的方式放置。球石的轮廓从椭圆形变为六边形，可能是通过溶解过程，显然是为了使球石更紧密地结合在一起，并减少它们之间的空隙。在更大的测试中，第二层水泥覆盖在球石层上。今天的水泥由二氧化硅组成，但它最初可能是有机的。二氧化硅含有少量混合沉积和骨骼成因的颗粒。富水泥层中的大多数颗粒是颗石，但与内部颗石层相反，内部颗石层完全由W。barnesae，外层含有大量的形式显然是随机挑选的物种之间的海底。第二个溶解过程影响了10-20%的测试，通过攻击所有的球石晶体，而不仅仅是它们的边缘，如在初级层。溶解有时导致几乎全部的球孢子破坏。在大多数试验中，溶解发生在死后。然而，在少数情况下，溶解发生在原生生物仍然活着的时候。在许多系列种中，球孢子像球孢子一样互锁，产生类似的球形结构。在一个三系种，测试显示了一个明显的个体发育转变，从早期的一部分主要由球石建造，到后来的一部分由沉积颗粒和硅水泥建造。
Scanning electron microscopy of foraminifera from the lowermost Barremian (Lower Cretaceous) deposits at Speeton, eastern England, reveals that about 4% of the agglutinated tests are constructed almost exclusively of coccoliths of the species Watznaueria barnesae . The majority of the foraminifera that agglutinate coccoliths are trochospiral forms resembling Trochammina depressa , but planispiral, unilocular, uniserial, biserial and triserial forms have also been observed. The tests are small, rarely exceeding 125 μm in length. Specific identification is difficult due to the small size of the tests, the unusual building material and compression. In the simplest state, the walls of the trochamminids consist of a single layer of coccoliths. The foraminifera were highly efficient in selecting and handling the coccoliths, which were always placed with their distal surfaces facing outward. The outline of the coccoliths was modified from oval to hexagonal, probably by a dissolution process, apparently in order to fit the coccoliths closer together and to diminish the amount of empty spaces between them. On larger tests, a secondary layer of cement coated the layer of coccoliths. Today the cement consists of silica, but it was probably originally organic. The silica contains a few grains of mixed sedimentary and skeletal origin. Most of the grains in the cement-rich layer are coccoliths, but in contrast to the inner coccolith layer, which was constructed exclusively of W. barnesae , the outer layer contains a large number of forms apparently picked at random among the species available on the sea bottom. A second dissolution process affected 10–20% of the tests by attacking all the crystals of the coccoliths, not just their edges as in the primary layer. The dissolution resulted sometimes in the almost total destruction of the coccoliths. In most tests, the dissolution occurred post mortem. However, in a few cases the dissolution took place while the protists were still alive. In many of the serial species, the coccoliths interlock as in coccospheres, producing similar globular structures. In a triserial species, the tests show a distinct ontogenetic shift from an early part constructed mainly of coccoliths to a later part constructed of sedimentary grains and silica cement.