Controls on the Sedimentological Heterogeneity of Visean Carbonate Platforms in England and Wales

碳酸盐岩（石灰岩）可以记录史前海洋的沉积环境。海洋在空间和时间上的位置控制着生活在其中的生物的类型，它们是如何分布的，以及它们是如何形成一个地形起伏的沉积体的，这就是所谓的碳酸盐台地。这是因为石灰石是由海洋生物的碳酸钙骨架构成的，而海洋生物对光线、营养、温度和盐度高度敏感（“碳酸盐工厂”）。在下石炭纪（3.625亿年前），板块通过大陆漂移重新组合，形成了泛古陆。这导致英国位于赤道以南14度左右，相当于今天的巴西或马达加斯加。英国北部位于海底，有可能沉积石灰岩。碳酸盐台地在大约1110万年的时间里分两个阶段沉积：阿斯比亚（最古老）和布里甘特（最年轻）。阿斯比亚的岩石（地层）是在一个温室气候期间形成的，温室气候被定义为两极没有冰的世界。这意味着海平面不会波动太大，因为海水不会周期性地冻结成冰盖。一个巨大的冰团（冈瓦纳冰盖）在阿斯比亚时期开始在南极发展，而一个冰室气候已经由布里冈特人建立。因此，海平面波动相当大的布里甘蒂，在频率和幅度方面，和季节（如周期性的湿/旱季）被放大。这意味着碳酸盐岩工厂存在于更大的压力条件下，并受到陆地（陆地）系统（如河流和三角洲）的影响。除了气候的显著变化外，碳酸盐岩台地还受到活跃的构造运动的影响。在阿斯比安期，岩石被拉开，形成一系列断层边界块（半地堑），大小为1000平方公里，具有地形高点。生物体生长的最佳条件是在最高的地形上，那里的光照和温度都是最佳的。到布里冈阶末期，地层已经被拉开到足以发生热沉降的程度，因此冷却的地幔（地壳下面）收缩成为岩石圈（地壳和上地幔）的一部分，岩石圈比周围的物质更致密，因此在碳酸盐台地周围下沉，海平面上升。

Carbonate rocks (limestones) can record the depositional environments of prehistoric seas. Theposition of the sea in space and time controls the types of organisms which live within it, how they aredistributed, and how they build into a body of sediment with topographic relief, known as a carbonateplatform. This is because limestones are built from the calcium-carbonate skeletons of marine organismswhich are highly sensitive to light, nutrition, temperature, and salinity (the "carbonate factory"). Duringthe Lower Carboniferous Period (362.5 million years ago), tectonic plates reassembled by continental driftto build supercontinent Pangaea. This led the UK to be positioned at around 14 degrees south of the equator,comparable to the present-day position of Brazil or Madagascar. The north of the UK was positionedunder the sea, giving the potential for limestones to be deposited.The carbonate platforms were deposited in two stages over approximately 11.1 million years: theAsbian (oldest) and the Brigantian (youngest). Asbian rocks (strata) were laid down during a greenhouseclimate, defined as a world with no ice at the poles. This meant that sea-level did not fluctuate muchbecause sea water was not periodically frozen into ice caps. A large ice mass (the Gondwanan ice sheet)began to develop at the south pole during Asbian, and an Icehouse climate had established by theBrigantian. As a result, sea-level fluctuated considerably by the Brigantian, in terms of frequency andamplitude, and seasons (e.g. periodic wet/dry seasons) were amplified. This meant that the carbonatefactory existed under more stressed conditions and was influenced by systems on land (terrestrial), suchas rivers and deltas.As well as a significant change in climate, the carbonate platforms were also subjected to activetectonic movement. During the Asbian, the rocks were being pulled apart, to form a series of faultboundedblocks (half-grabens) which are 1000s of km2 in size, which have topographic highs. The bestconditions for organisms to thrive was upon the highest topography, where light and temperature wereoptimal. By the end-Brigantian, the strata had been pulled apart enough for thermal subsidence to occur,whereby the cooling mantle (beneath the crust) contracted to become part of the lithosphere (crust andupper mantle) which is denser than the surrounding material and consequently subsided and sea-levelincreased around the carbonate platform.