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How did rising sea level affect preservation of the Precambrian-Cambrian transition?

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Cambrian paleogeography — Cambrian Period Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the late Cambrian Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

The preservation of the Precambrian-Cambrian transition was significantly influenced by global fluctuations in sea level. During the latest Precambrian, relatively low sea levels resulted in spatially restricted oceans and expanded landmasses. As a result, the sedimentary and fossil records of this transition are generally most complete only toward the outer margins of continental shelves.1

Throughout much of the Cambrian, rising sea levels caused widespread marine transgression, flooding vast areas of the continents. Because of the low sea levels at the start of this period, the boundary surface often represents a time gap that increases in landward directions. This led to a widespread absence or serious incompleteness of the transitional record in many areas, particularly those central to classical geological studies. This incompleteness, coupled with a historical lack of knowledge regarding Precambrian communities, contributed to the long-held, inaccurate perception that the appearance of Cambrian fossils was an abrupt or sudden event.21