Abstract

This paper investigates the much-debated Jurassic/Cretaceous (J/K) boundary as well as the Early Cretaceous climate using palynomorphs of the Chichali Formation, Upper Indus Basin, North Pakistan. Based on the palynostratigraphy, two dinoflagellates and one spore/pollen assemblage are recorded, suggesting a Kimmeridgian to Valanginian age for the sediments of the Chichali Formation. The palynostratigraphic results further suggest that the Tithonian to Berriasian strata are truncated along the J/K boundary. The warm and humid conditions are supported by the consistent dominance of ferns corresponding to the Schizaeaceae and the intermittent appearance of herbs from Gleicheniaceae. Such climatic conditions are further supported by the consistent presence of evergreen trees with a broad leave of Cyatheaceae and Matoniaceae. The warm and humid conditions are also supported by conifers of the Araucariaceae in association with Cycadaceae. Such conditions during the Valanginian are further supported by the switch from the Bajocian–Oxfordian shallow carbonates of the Samana Suk Formation to the Kimmeridgian–Valanginain clastics of the Chichali Formation. Hence, the expansion of warm and humid tropical flora to the middle latitude (∼40°S) during the Valanginain hints strongly for global warming instead of previously suggested global cooling.

1. KEY POINTS:

2. Palynostratigraphic investigation shows Kimmeridgian to Valanginian age for the Chichali Formation, Upper Indus Basin, Pakistan.

3. The J/K boundary is marked by an unconformity along which the Tithonian to Berriasian time record is missing.

4. The reconstruction of paleovegatation indicates warm humid climate during the Valanginian instead of previously reported global cooling.

摘要

本文利用巴基斯坦北部上印度河流域 Chichali 组的孢粉形态研究备受争议的侏罗纪/白垩纪 (J/K) 边界以及早白垩世气候。根据孢粉地层学，记录了两种甲藻和一种孢子/花粉组合，表明 Chichali 组沉积物的年代为 Kimmeridgian 至 Valanginian。孢粉地层结果进一步表明 Tithonian 到 Berriaasian 地层沿 J/K 边界被截断。温暖和潮湿的条件得到了与 Schizaeaceae 相对应的蕨类植物的一贯优势和 Gleicheniaceae 草药的间歇性出现的支持。这种气候条件得到了持续存在的常绿乔木和广泛的 Cyatheaceae 和 Matoniaceae 的支持。南洋杉科与苏铁科的针叶树也支持温暖和潮湿的条件。从 Samana Suk 组的 Bajocian-Oxfordian 浅层碳酸盐岩到 Chichali 组的 Kimmeridgian-Valanginain 碎屑岩的转变进一步支持了 Valanginian 期的这种条件。因此，暖湿热带植物群在 Valanginain 期间向中纬度（~40°S）的扩张强烈暗示着全球变暖，而不是之前提出的全球变冷。

1. 关键点：

2. 孢粉地层调查显示巴基斯坦上印度河流域 Chichali 组的 Kimmeridgian 至 Valanginian 时代。

3. J/K 边界以不整合面为标志，沿该不整合面缺少 Tithonian 到 Berriasian 时间记录。

4. 古植被的重建表明瓦兰吉期气候温暖潮湿，而不是之前报道的全球变冷。