Watch Hill Park Field Guide

Location satellite imageSatellite image of the Watch Hill Park locality. Click on image to enlarge.

Summary

The length of the coastal exposure at the Watch Hill Park locality is approximately 250 m  (0.15 miles). It is recommended that not less than 1 1/2  hours be allowed to walk the route while following this guide.

The exposed limestones at this locality are dominated by  beach deposits and small dunes of the Belmont Formation. There are, older, Town Hill Formation dunes at the eastern end as well as small patches (outliers) of Rocky Bay (Devonshire) marine conglomerate scattered along the length of this shoreline. Watch Hill Park marks the eastern end of an almost continuous exposure of  Belmont and Rocky Bay foreshore and shoreface deposits which starts, in the west, at Grape Bay. What differentiates this locality from others along Bermuda’s south shore is the unusually high elevation – up to 8 m (25ft) – of depositional, erosional and biological sea-level indicators thought to be associated with  the Belmont and Rocky Bay sea level highstands.at 120,000 and 200,000 years before present, respectively.

The shoreline at this locality, unlike most others, is consistently orientated parallel to the strike of the strata and therefore does not expose cross-sections of prograding sub-tidal and beach deposits from which their evolution through time can be interpreted. The sites of interest, 1 to 13,  comprise isolated features or deposits, which could be termed outliers. They are not parts of successions and in many cases do not have an obvious stratigraphic relationship to nearby deposits.  This is why they are identified as “sites”, below,  rather than “sections”, as at other localities.

Site 1

A reddish stain on the surface of the Lower Town Hill formation dune limestones is all that remains of a well developed – terra rossa – fossil soil which has been stripped away. Circular soil-filled solution pipes typical of this type of surface are evident. The absence of any soil remnants, other than the staining, can be attributed to wave erosion associated with two sea level transgressions (above present sea level) which occurred subsequent to development of the soil. These occurred at 120,000 and 200,000 years before present.  All other depositional, erosional and biological features at this Watch Hill Park locality are younger than this surface.

Site 1

Site 2

Slip-face strata of an Upper Town Hill formation dune dip down towards the east and flatten at their base where they merge into a thin layer of bottom-sets which  rest on, and conform to,  an older surface of eroded Lower Town Hill dunes  (Photo is taken facing northwest).

Site 2

Site 3

At this site, slip face strata, of an Upper Town Hill formation dune, have been eroded by wave action during a mid- to late-Pleistocene high sea level event (higher than today). Prior to the retreat of sea level, boulders in a matrix of marine sand were deposited against the eroded surface, in a wave-cut angle. This event could have occurred either at the last interglacial period (120,000 years bp) or the penultimate one (200,000 years bp).  . The presence of  Belmont beach deposits at the same elevation nearby and the absence of characteristics typical of Rocky Bay (Devonshire) marine conglomerates (see Site 10) favour a 200,000 year bp Belmont origin. (Photo taken facing northeast. Yellow 1 m rule provides scale)

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Site 4

Lithophagous bivalves, which bore into rocks, and encrusting vermetid worms (not shown) are preserved on a well cemented portion of an Upper Town Hill dune at Site4, just above Site 3 (same dune). The elevation of these life-position intact (articulated) marine  fossils is indicative of a past sea level which exceeded 6.5 m (21 ft) above present sea level.   (Note that the small colony of bivalves shown below (approx 2 cm or 1 inch in length) are no longer obvious at this site and may have been partially removed) 4

Site 5

Belmont beach deposits, on the left (east), rest against an Upper Town Hill dune, on the right (west), separated by a vertical erosional contact. This marks the eastern end of an almost continuous coastal outcrop of Belmont formation deposits (primarily foreshore) which begins, in the west at Grape Bay. This is also the locality where Belmont beach deposits are at their highest elevation,- incorporating features indicative of a sea level which reached over 6.5 m (21 ft)  (ME2, VO3, RO4)

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Site 6

Shelly marine deposit, thought to be part of the Belmont formation, at approximately 7 m (23 ft) above present sea level. 

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Site 7

Shelly layer, consisting of several Lucina bivalves, situated at 7.2 m (24 ft) above present sea level. The orientation of the valves – concave-down – is diagnostic of a wave-affected shallow water environment such as the shoreface or foreshore, possibly a beach.

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Site 8

A hardened horizontal surface, or platform, with some embedded marine molluscs and patchy superposed remains of a weak soil with land snails is the key feature at this site.  The surface, at 7.7 m (25 ft) above present sea level, coincides with the base of a dune with leeward strata dipping landward  at 15 to 20 degrees. This beach-foredune succession is typical of that found in coastal exposures of the Rocky Bay and Belmont formations where it represents an upper beach environment, which formed 1.5 to 2.5 m (5 to 7 ft) above contemporaneous sea level. The  altitude of these deposits at this site, thought to be of the Belmont formation, is consistent with other evidence at Watch Hill Park of a 6+ m high palaeo-sea-level event tentatively attributed to the penultimate interglacial period.  (Yellow 1m rules rests on the platform at at the base of the dune).

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Site 9

Fenestrae, or fenestral pores, are spherical oversized pores created in a sedimentary deposit. There  are a number of occurrences at Watch Hill Park, particularly  towards the western end of the locality, such as at  Site 9. The pores form in association with entry of water into a sediment in which air gets tapped. This occurs in the swash zone of a beach which is why fenestrae are also known as “beach bubbles”. There are other circumstances in which they can form, for example where there is an influx of water into a sediment associated with heavy rainfall. However, at Watch Hill Park their origin as beach bubbles is considered  the most credible explanation because of the other evidence of a high sea level event, at this locality, which  would account for their elevation at 6+m above present sea level. Furthermore the planar strata in which they are found generally dip gently seaward as would be expected had the deposit accumulated on a beach-face. 

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Site 10

A few small patches, or outliers, of marine conglomerate exist at the Watch Hill locality. They have similar characteristics to those found elsewhere along the south shore where they are interpreted as the marine member of the Rocky Bay formation (Devonshire marine)  superposed on Belmont deposits. As here, at Site 10, they sometimes incorporate brown soil and even land snails in the matrix. There is no reason to believe that the succession is  at Watch Hill Park is any different from that elsewhere and it is, therefore, probable that bulk of the stratified deposits here, on which the isolated patches of conglomerate rest, belong to the Belmont Formation. 

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Site 11

A notch is infilled by a conglomerate at Site 11 situated 6 m (20 ft) above present mean sea level. These are interpreted  as a Rocky Bay (also known as Devonshire marine) erosional and depositional features respectively.  

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Site 12

A slot-shaped cave at Site 12 is situated at 8.2 m (27 ft) above present mean sea level. It extends approximately 10 m (30 ft) or so back into the hillside, and was either formed by erosion or by phreatic limestone dissolution (by ground water). In either case sea level, must have been in the range of 7 to 8 m above present sea level at the time of its creation. The limestone in which the cave formed is considered to belong to the Belmont formation – probably a beach. The cave could be a late Belmont feature or, more likely,  it formed during aa high sea level contemporaneous with the Rocky Bay formation i.e. MIS stage 5e. (yellow rule  in photo is 25 cm (10 in) long)

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Site 13

Near the car park, a shelly conglomerate is situated at approximately 5 m (16 ft) above present mean sea level.  It occupies a soil-filled solution pocket on a Town Hill formation dune. Unlike other conglomerates further to the west (e.g. at Site 10), this one on a Town Hill  substrate,  may be a Belmont formation, or even Town Hill formation, marine deposit. Fortunately it included a fragment of Oculina coral (shown below the key) which will potentially yield an age. 

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Site 14

A terra rossa palaeosol with solution pockets is exposed at Site 14, where the hillside has been excavated to accommodate a  private driveway on the north side of South Shore Road. No such intact palaeosol exists along the shoreline on the south side of the road, due to marine erosion when sea level exceeded that of today on at least two  occasions in the Mid to Late Pleistocene. Epoch. It has been mapped as the boundary between the Belmont and the Upper Town Hill formation. This is, however,  not certain and given the presence of a contact between Upper and Lower Town Hill dunes on the shoreline nearby, the palaeosol could conceivably represent an inter-Town Hill division. (1m yellow rule is included for scale)

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Interpretation

The Watch Hill Park locality comprises a steep rocky coast rising more than 10 m (30 ft) above present sea level.  Lower and Upper Town Hill dunes are exposed at the eastern end. These are replaced, towards the west,  by younger beach and dune deposits. The relatively ancient Town Hill shore would have been partially flooded during at least two  Pleistocene interglacial high sea level events. Thus, the occurrences of elevated marine deposits wave-eroded notches are not unexpected. Belmont Formation beach deposits, extending eastward from Site 5, are attributed to the penultimate interglacial period  (200,000 years bp); while the relatively scarce, patchy overlying Rocky Bay Formation conglomerates (Site 10) are attributed to the last interglacial period (120,000 years bp) . The interpreted sea level elevation in both cases exceeds 6 m (16 ft) above present sea level (ME2,RO4,VO3)  which is higher than the interpreted sea levels of the same ages at most other locations in Bermuda . This is not a contradiction. It simply means that conditions varied from one  stretch of coastline to another. At a given position of sea level, the type of imprint (if any) would have varied from place to place. .As today, there would have been segments of shoreline where beaches were forming, and others where there was contemporaneous erosion of cliffs  As sea level rose above present sea level and then fell,  the processes which formed imprints (e.g. beaches and notches) would have been be turned on and off at different times along the length of Bermuda’s shoreline. Potentially any sea-level position between present sea level and peak sea level for a given Interglacial period might, therefore, be recorded.  Arguably, only the highest among near-contemporaneous imprints is significant, because it provides the best estimate for the maximum, or peak, sea level at Bermuda at a given Interglacial period. In this case, the record of palaeo-sea-levels at Watch Hill Park is potentially as important as any on Bermuda.