桂林中、晚泥盆世环境旋回和生物事件

MIDDLE AND LATE DEVONIAN ENVIRONMENTAL CYCLES AND BIOEVENTS IN GUILIN,GUANGXI

关键词:  中、晚泥盆世  环境旋回  生物事件

Key words:  Middle and Late Devonian  environmental cycle  bioevent

摘要:

桂林地区中、晚泥盆世的沉积包含了两个主要的环境旋回,从艾菲尔到维特期为一个旋回,从费拉斯到法门早期为另一个旋回。生物事件主要发生在第一个旋回的海侵高峰时期,而生物事件的直接结果则在第二个旋回充分显示出。在吉维特期和费拉斯期曾一度兴旺的许多生物类群(其中以可造礁生物居多)在法门期开始时结束了生命活动。这种环境的变化与全球海平面升降相一致,绝灭事件在当时地处热带的地区显示更为明显。

Abstract:

The Middle and Late Devonian stratigraphic sequences in Guilin,Guangxi record two major en-vironmental cycles in a vast of epicontinental seas.The first cycle began with a transgressive phase in the Effelian that reached its maximum in the early and middle Givetian,and was followed by a regressive phase during the late Givetian.The transgressive phase of the second cycle reached its peak in the Frasnian,and was followed by a regressive phase during the early Famennian.In gener-al,the greatest water depth and most open marine conditions were attained during the first cycle,and seas were shallowest and most restricted toward the end of the second cycle.
The bioevents took place mainly during the transgressive maximum of the first cycle,while their direct results were displayed fully during the second cycle.Many taxa,which were prosperous during the Givetian and Frasnian,ended their living action at the very onset of the Famennian.The changes in environments are correlated with the rise and fall of the global sea level.The mass extinc-tion took place even more clearly in the tropical zone during the Devonian.