白垩纪 Cretaceous Period

构造运动

During the Cretaceous the late-Paleozoic-to-early-Mesozoic supercontinent of Pangaea completed its tectonic breakup into present day continents, although their positions were substantially different at the time.

在白垩纪从晚古生代到早中生代的泛大陆已经完成了它的构造运动分裂成现如今的大陆板块，尽管它们的位置在那时与现在差异很大。

As the Atlantic Ocean widened, the convergent-margin orogenies that had begun during the Jurassic continued in the North American Cordillera, as the Nevadan orogeny was followed by the Sevier and Laramide orogenies.

随着大西洋的加宽，在侏罗纪就已经开始的山脉边缘造山运动在北美科迪拉山系继续进行，就像内华达造山运动紧跟着塞维尔与燕山造山运动。

Though Gondwana was still intact in the beginning of the Cretaceous, it broke up as South America, Antarctica and Australia rifted away from Africa (though India and Madagascar remained attached to each other); thus, the South Atlantic and Indian Oceans were newly formed.

尽管在白垩纪初期冈瓦纳大陆还是完整的，但随着南美洲、南极洲和澳大利亚洲从非洲分裂出去（尽管印度和马达加斯加仍旧彼此相连）而分裂；于是，新形成了南太平洋和印度洋。

Such active rifting lifted great undersea mountain chains along the welts, raising eustatic sea levels worldwide. To the north of Africa the Tethys Sea continued to narrow.

类似的大型的海底山脉沿着断裂带的断裂，造成了全球范围的海平面上升。在非洲北部，特提斯海洋继续缩小。

Broad shallow seas advanced across central North America (the Western Interior Seaway) and Europe, then receded late in the period, leaving thick marine deposits sandwiched between coal beds.

宽阔的浅海区域先行穿过北美（西部聂鲁海道）和欧洲，后期又退却，留下巨厚的海相沉积夹煤层。

At the peak of the Cretaceous transgression, one-third of Earth’s present land area was submerged.

在白垩纪海侵的最高峰，约有三分之一的当时的陆地被淹没了。

气候特征

The Berriasian age showed a cooling trend that had been seen in the last epoch of the Jurassic. There is evidence that snowfalls were common in the higher latitudes and the tropics became wetter than during the Triassic and Jurassic.

冰川仅为高纬度地区的高山冰川，但季节性的降雪在离极点很远的地区也广泛存在。

Glaciation was however restricted to alpine glaciers on high-latitude mountains, though seasonal snow may have existed farther from the poles. Rafting by ice of stones into marine environments occurred during much of the Cretaceous but evidence of deposition directly from glaciers is limited to the Early Cretaceous of the Eromanga Basin in southern Australia.

随冰川漂浮在海洋上的冰碛物贯穿白垩纪始终，但直接证据只有澳大利亚南部 Eromanga 盆地的早白垩纪冰川沉积物。

After the end of the Berriasian, however, temperatures increased again, and these conditions were almost constant until the end of the period.

后来，气温再次上升，这种趋势持续到白垩纪结束。频繁的火山活动产生了巨量二氧化碳，从而导致了气温升高。

This trend was due to intense volcanic activity which produced large quantities of carbon dioxide. The production of large quantities of magma, variously attributed to mantle plumes or to extensional tectonics, further pushed sea levels up, so that large areas of the continental crust were covered with shallow seas. The Tethys Sea connecting the tropical oceans east to west also helped in warming the global climate.

地幔羽或张性构造产生了更多的岩浆，推动海平面上升，致使大面积陆地被浅海淹没。特提斯洋连接了从东到西的热带海洋，也起到了使全球变暖的作用。

A very gentle temperature gradient from the equator to the poles meant weaker global winds, contributing to less upwelling and more stagnant oceans than today.Sediment cores show that tropical sea surface temperatures may have briefly been as warm as 42 °C (107 °F), 17 °C ( 31 °F) warmer than at present. Meanwhile, deep ocean temperatures were as much as 15 to 20 °C (27 to 36 °F) higher than today’s.

赤道与两极之间的较小温差使得全球风力微弱，导致当时的海洋与现在相比，上升流少、停滞流多。沉积证据表明当时热带海洋表面温度约42摄氏度，比现在高17摄氏度。深海温度也比现在高15至20摄氏度。

 

生物特征

 

被子植物开始出现于白垩纪早期，中期大量增加，到晚期在陆生植物中居统治地位，山毛榉、榕树、木兰、枫、栎、杨、樟、胡桃、悬铃木等都已出现，接近新生代植物群的面貌。

脊椎动物中爬行类从极盛走向衰落，主要代表有暴龙（霸王龙）、古魔翼龙、青岛龙等。侏罗纪以前的硬鳞鱼被真骨鱼所代替。

海洋无脊椎动物中浮游有孔虫异军突起，底栖大型有孔虫中也出现了许多标准化石。菊石和箭石演化迅速而明显，分布广泛，是传统的划分阶和带的标准化石。群生底栖的固着蛤类(Rudistids)可形成礁体,为典型的暖水动物群。海胆在特提斯海中颇为繁盛，有少数标准种属。珊瑚和腕足动物在白垩纪居于次要地位。鸟类是脊椎动物向空中发展取得最大成功的类群。白垩纪早期鸟类开始分化，并且飞行能力及树栖能力比始祖鸟大大提高。代表为“孔子鸟”。

白垩纪末，地球上的生物经历了又一次重大的灭绝事件：在地表居统治地位的爬行动物大量消失，恐龙完全灭绝；一半以上的植物和其他陆生动物也同时消失。

一种说法为有可能是陨石撞击地球导致的生物大灭绝。