Despite their discontinuous occurrence and poor preservation, knowledge about Triassic carbonates from North America has increased considerably during recent years. Their characterization represents a unique way to better assess evolution and recovery of the biosphere after the major Permo-Triassic biological crisis in the Panthalassa Ocean. The Eastern Klamath terrane, located in Northern California, is a key terrane due to its geographic position. It is placed halfway between the terranes of the Canadian Cordillera and the Northern Mexico counterparts, both extensively studied and characterized in recent decades, leaving a gap in knowledge along the Pacific coast of the United States. A few kilometers north-east of Redding, Shasta County, California, Upper Triassic carbonates (i.e., the Hosselkus limestone) crop out as a narrow north–south belt about 20 km long, near the artificial reservoir of Lake Shasta. All the accessible localities in this region have been extensively sampled for microfacies and micropaleontological analysis, leading to new insights about the depositional condition and age of the Hosselkus limestone. A depositional model has been proposed for the first time, corresponding to a steep slope system subjected to platform progradation and collapse, recording shallow water facies and associated fauna in the form of calcareous breccia. Numerous conodont specimens have dated the whole succession as Upper Carnian. Identification of shallow water organisms, associated to a reliable stratigraphic interval, allowed comparison of the Hosselkus limestone with other Upper Triassic carbonates from the Panthalassan domain. Despite the faunal affinities, especially with buildups developed at middle-paleolatitudes, the Hosselkus limestone is among the oldest of the terrane-based carbonates in Eastern Panthalassa. Thanks to peculiar geodynamical and bathymetrical conditions, allowing carbonate deposition slightly earlier than in other terranes, the Hosselkus limestone probably acted like a pioneer reef and may have had a great influence in the further expansion of carbonate buildups in the eastern part of the Panthalassa Ocean.

尽管它们的出现不连续且保存不佳，但近年来对北美三叠纪碳酸盐岩的了解却大大增加。他们的表征代表了一种独特的方式，可以更好地评估泛海三叠纪重大生物危机后生物圈的演化和恢复。位于加利福尼亚州北部的东克拉马斯地体因其地理位置而成为关键地体。它位于加拿大科迪勒拉山脉和北墨西哥山脉之间的中间，近几十年来，两者都被广泛研究和表征，在美国太平洋沿岸留下了知识空白。加利福尼亚州沙斯塔县雷丁东北几公里处，上三叠统碳酸盐岩（即 Hosselkus 石灰岩）是一条约 20 公里长的狭窄南北带，靠近沙斯塔湖的人工水库。该地区所有可到达的地点都已被广泛采样用于微相和微古生物分析，从而对 Hosselkus 石灰岩的沉积条件和年龄有了新的认识。首次提出沉积模型，对应经历台地进积和塌陷的陡坡系统，以钙质角砾岩的形式记录浅水相和相关动物群。许多牙形石标本已将整个序列确定为上卡尼阶。识别与可靠地层间隔相关的浅水生物，允许将 Hosselkus 石灰岩与来自 Panthalassan 域的其他上三叠统碳酸盐岩进行比较。尽管具有动物群亲缘关系，尤其是在中古纬度地区形成的堆积物，Hosselkus 石灰岩是东泛塔拉萨最古老的地层碳酸盐岩之一。由于特殊的地球动力学和测深条件，允许碳酸盐沉积比其他地体稍早，Hosselkus 石灰岩可能起到了先锋礁的作用，可能对 Panthalassa 洋东部碳酸盐岩堆积的进一步扩张产生了很大影响。