Results of conodont-based δ¹⁸O_phos studies from two core sections in Estonia (Mehikoorma-421 and Valga-10) indicate that the pre-Hirnantian Late Ordovician was characterized by a general cooling trend: a rapid climate cooling in the early Sandbian and a less intense cooling in the late Sandbian through Katian. During this time interval, sea-surface temperatures probably decreased by up to 9^o C. This fits with earlier ideas of a colder Late Ordovician climate before the Hirnantian. On the background of general cooling trend in the pre-Hirnantian Late Ordovician, tendencies in the temperature changes were quite variable. Several episodes of SST decrease and increase of different magnitudes and durations are evident from the δ¹⁸O_phos curves in the studied sections. In the interval sampled in detail, 7 cooling events are recognized and tentatively called (in stratigraphical order): Early Kukruse, Haljala, Keila, Early Nabala, Vormsi, Early Pirgu and Middle Pirgu CE-s. Duration of these events and amplitudes of changes in seawater temperatures increased from Sandbian to late Katian. All cooling events may have triggered the waxing of polar and subpolar Gondwana icecaps and are reflected in the sedimentary succession by major sea-level lowstands recognized also outside the study region. Results of our research do not support a simple, straightforward correlation between temperature trends inferred from δ¹⁸O_phos measurements and changes in the δ¹³C record. Comparison of δ¹⁸O_phos and δ¹³C curves reveal that these two variables behave quite independently: in some intervals their trends fit quite well, in others they might show completely the opposite. For this comparison we provide also a new, detailed δ¹³C curve from the Valga-10 core section.

结果牙形石为基础的δ ¹⁸ ö _PHOS研究由两个芯部区段在爱沙尼亚（Mehikoorma-421和瓦尔加-10）指示预赫南特晚奥陶特征为一般冷却趋势：在Sandbian早期快速气候冷却和桑迪安（Sandbian）后期通过凯迪安（Katian）的降温幅度较小。在这段时间间隔，海面温度可能下降多达9 ^Ø与赫南特前一个寒冷的晚奥陶世气候的早期思想C.这符合。在先南后奥陶纪的总体降温趋势的背景下，温度变化趋势变化很大。SST降低和不同的幅度和持续时间的增加的几集是明显的从δ ¹⁸ ö研究部分的_phos曲线。在详细采样的时间间隔中，识别出7个降温事件，并按地层顺序试行性地称呼它们：早期库克吕兹，哈尔哈拉，凯伊拉，早期纳巴拉，沃姆西，早期皮尔古和中皮尔古CE-s。这些事件的持续时间和海水温度变化的幅度从桑甸到卡蒂安晚期都增加了。所有的降温事件都可能触发了冈瓦纳极地和亚极冰盖的注蜡，并由研究区域以外公认的主要海平面低位反映在沉积演替中。我们的研究结果不支持简单的，从δ推断温度趋势之间存在直接的相关性^18个Ø _PHOS测量和变化的δ ¹³ C ^纪录。δ比较^18个Ø _PHOS和δ ^13条C曲线的显示，这两个变量的行为完全独立：在一些间隔的趋势十分吻合良好，在其他人，他们可能会完全展现相反。对于此比较，我们还提供一种新的，详细的δ ¹³从瓦尔加-10核心C节曲线。