影响侏罗纪双壳动物群分异度的主要因素

古大西洋地区侏罗纪双壳动物群分异度的变化主要受沉积相的多样性和相类型、温度梯度、盐度以及海平面变化的影响．在这些环境因素的控制下，双壳类分异度的分布特点主要表现在：①位于中纬度地区的法国北部和英国南部地区分异度值最高，由此向南向北逐渐降低；②低纬度地区的分异度高于高纬度地区；③尽管经历了２次下降期，在Ｋｉｍｍｅｒｉｄｇｉａｎ期前双壳类分异度总的变化趋势是逐渐增高的，并在Ｋｉｍｍｅｒｉｄｇｉａｎ期达到最大．此后，开始第３次下降期

Primary Factors Influencing the Diversity of Jurassic Bivalves

The variations in Jurassic bivalve diversity of the Proto Atlantic are primarily influenced by sedimentary facies diversification and facies type, latitudinal temperature gradients, salinity, and sea level changes. The bivalve diversity patterns, controlled by these environmental factors, are characterized by the following. The highest diversity invariably occurs in the central regions, i.e. in southern England or northern France. From there bivalve diversity decreases northwards and southwards. Bivalve diversity is higher at the lower latitudes than at the higher latitudes. In spite of two declining phases, bivalve diversity exhibits a general trend of increasing until the Kimmeridgian, when a peak occurs. Thereafter is a sharp drop in diversity