Round Hill, Aldeburgh, Suffolk

[TM 4442 5732]

Highlights

This pit is of great interest in providing a contrast with other exposures of the Aldeburgh Member in the Aldeburgh area. It provides a rare opportunity in the northern part of the Coralline Crag outcrop to see preserved aragonitic skeletal material.

Introduction

The small pit at Round Hill was probably excavated in the 1970s and was first visited by the author in 1977. The section exposes a small section in the Aldeburgh Member of the Coralline Crag.

Description

This small pit lies about 1 km to the north-west of the exposure at Aldeburgh Hall and is roughly at the same elevation. However, the two pits differ considerably in the features they exhibit. The pit at Round Hill shows a section of Coralline Crag of just over 2 m. Some indistinct bedding can be seen which appears to dip gently to the south. The most conspicuous feature of the leached Coralline Crag sediments here is the very extensive bioturbation. The lower part of the face in particular shows almost complete reworking by burrowers. Although nearly all the sediments here have been leached of aragonitic material, at one point at the lowest part of the pit and close to the level of the water table poorly preserved aragonitic shells can be found. In common with other exposures of the Aldeburgh Member there is only a small component of terrigenous sediment (approximately 10%), and occasional silt drapes may indicate episodic events.

A particular feature of this small pit is the undulose and piped uppermost surface which is sharply overlain by reddish-brown silty sand (Figure 10.25). This sand probably represents the insoluble residue left after solution of the carbonate grains in the Coralline Crag.

The fauna of the pit at Round Hill is rather sparse. Some small specimens of Meandropora aurantium have been found but they are by no means as common as at Aldeburgh Hall. Calcitic shells of Aequipecten are fairly common but most notable of the bivalves are abundant specimens of Mytilus which appear to be rather rare elsewhere in the Coralline Crag.

Interpretation and evaluation

The pit at Round Hill provides information on the lateral facies variations within the Aldeburgh Member of the Coralline Crag. This section shows extensive reworking of the sediment by burrowers in a shallow marine environment, together with evidence of carbonate solution of the Coralline Crag.

Conclusions

The site at Round Hill is significant as it exhibits a rare section in the Aldeburgh Member of the Coralline Crag and together with sites at Crag Pit Nursery and Aldeburgh Hall forms a network to illustrate lateral facies variations.

References