GOLDEN SPIKE DEFINITION SERIES

At the time, these rocks were referred to as the 'transition' rocks. Using the new and powerful technique of correlating strata with fossils, Sedgwick and Murchison both began to study the stratigraphy of some of the most ancient sedimentary rocks known in Britain. Secord (1986) has written an analysis of this tempestuous episode in Victorian science. These British geologists began their studies of ancient fossil-bearing rocks in friendly collaboration, but their relationship deteriorated into a bitter feud over a terminological dispute. Its initial definition involved two great early stratigraphers, Adam Sedgwick and Roderick Murchison. The Cambrian System was a product of the pioneering geological research of the 1830s. The golden spike is very useful, nevertheless, as the objective criterion against which a stratigraphic boundary can be correlated the world over. The definition of a stratotype point is merely a formal, legalistic variant of the technique that resulted in the breakthrough in correlation made by European geologists in the 1830s (discussed in the first chapter). When a stratotype point and section is finally agreed upon, geologists will be able to 'drive the golden spike,' and thus formally define the Pre-cambrian-Cambrian boundary. Criteria for what is 'best' include the ability to locate in other stratigraphic sections a point which is the same age as the point located in the formally defined standard section or stratotype section. A great deal of effort has been expended in recent years trying to locate the 'best' point in rock to define the base of the Cambrian. Neither the instant of time nor the point in the layered sedimentary sequence has yet been formally defined. There is one problem regarding the recognition of the beginning of the Cambrian Period and its time-rock equivalent, the base of the Cambrian System. Both Western and Soviet rock terms are shown. Comparison of time, rock, and time-rock units.

GOLDEN SPIKE DEFINITION SERIES

In this time-stratigraphic hierarchy, the 'Early Cambrian Epoch' corresponds to the 'Lower Cambrian Series.' In other words, 'Cambrian Period' and 'Early Cambrian Epoch' are used in the same sense as 'the year 1963,' whereas the 'Cambrian System' and 'Lower Cambrian Series' are used in the same sense as 'all the red wine bottled in 1963.' The relationships between period, system, epoch and series are shown in figure 5.1.įIGURE 5.1. Series correspond exactly to the Early, Middle, and Late epochs introduced above. The Cambrian System is a 'time-rock unit.' In contrast to the Cambrian Period which is purely a time unit, a time-rock unit refers to all the rocks that formed within a certain period of time, fust as time units like 'Cambrian Period' can be subdivided into epochs, the time unit 'Cambrian System' can be subdivided into series. The 'Lower' and 'Upper' used for series refer, naturally, to the physical positions of the strata from different parts of the Cambrian System.

The Cambrian System is divided into the Lower Cambrian, the Middle Cambrian, and the Upper Cambrian Series. One would need a legion of bulldozers to do this, because many surviving Cambrian rocks are buried quite deeply below the present-day surface of the earth. With the help of a magic bulldozer, one could theoretically excavate all the patches of Cambrian rock worldwide and pile them into an enormous heap that would constitute the entire Cambrian System. The term Cambrian System is used to refer to the sum total of rocks deposited during the Cambrian Period. These are all the rocks (both sedimentary and igneous) that were formed during the Cambrian Period. The second usage of 'Cambrian' is as a designation of a particular body of rocks. It is not possible to know the beginning of the Cambrian Period with anything approaching stopwatch precision. Radiometric dating of rocks can provide estimates of these times, but there are tens of millions of years of uncertainty with all radiometric dates of Cambrian age. Periods and epochs are subdivisions of geologic time, and could have been measured with a stopwatch had anyone been there to time them. This time interval is called the Cambrian Period, and it is subdivided into the Early Cambrian, the Middle Cambrian, and the Late Cambrian Epochs. Their importance is that they mark the beginning and ending of the sum total of Cambrian time. No one was there with a stopwatch to mark these events, so these moments must remain theoretical instants of the geological past. The first, and most commonly used, designates an interval of geologic time spanning from the second in which the first Cambrian sand grain was deposited until the instant that the first sediments of the Ordovician were laid down.

In geological parlance, the word 'Cambrian' can have two meanings.

Golden spike definition