Comparing a fossil sea urchin found at Solnhofen with modern sea urchins found on a strand line along the coast of a recent inter-tidal mudflat

This post is one in a series of posts which compares the depositional environment of the late Jurassic lithographic limestones at Solnhofen in Germany based on extracts from Solnhofen: A Study in Mesozoic Palaeontology with observations made at a modern inter-tidal mudflat at Ha Pak Nai, Deep Bay, New Territories, Hong Kong and proposes an inter-tidal mudflat origin for the examples cited.

This post compares comments on, and a photograph of a fossil sea urchin (Tetragramma sp) found at Solnhofen with photographs of stranded sea urchins (Salamacis dussumieri) found along the coast at the inter-tidal mudflats at Ha Pak Nai, Deep Bay, Hong Kong.

Extracts from: Solnhofen: A Study in Mesozoic Palaeontology

“Echinoids have a globular test covered by spines….  Shortly after death the spines fall away and become separated from the animal. However, in the plattenkalk, echinoids are found with their spines still attached” (Barthel et al - Pages 155 – 156).

Photographs of sea urchins found stranded at Ha Pak Nai in June 2012

References

Barthel, K.W., Swinburne, N.H.M., and Conway Morris, S. (1994). Solnhofen: A Study in Mesozoic Palaeontology. Cambridge University Press, Cambridge.

Comparing a fossil jellyfish found at Solnhofen with jellyfish found stranded along the coast of a recent inter-tidal mudflat

This post is one in a series of posts which compares the depositional environment of the late Jurassic lithographic limestones at Solnhofen in Germany based on extracts from Solnhofen: A Study in Mesozoic Palaeontology with observations made at a modern inter-tidal mudflat at Ha Pak Nai, Deep Bay, New Territories, Hong Kong and proposes an inter-tidal mudflat origin for the examples cited.

This post compares comments on, and a photograph of a fossil jellyfish (Rhizostomites admirandus) found at Solnhofen with photographs of stranded jellyfish found along the coast at the inter-tidal mudflats at Ha Pak Nai, Deep Bay, Hong Kong.

It should be noted, there are individual jellyfish strandings at Ha Pak Nai year round, while mass strandings occur around October.

Extracts from: Solnhofen: A Study in Mesozoic Palaeontology

“These animals stopped functioning in hypersaline solutions because water is drawn osmotically from the tissues. The shriveled appearance of many Solnhofen jellyfish (especially those from Gungolding-Pfalzpaint area) is quite consistent with this idea of hypersalinity” (Barthel et al - Page 59).

“The weaker swimmers, or really floaters, lived in the quieter surface waters. Of these the jellyfish, and free-swimming hydrozoans and planktonic crinoids, were most numerous and most susceptible to being swept into the lagoon” (Barthel et al - Page 84).

“Amongst the early post-mortem features to develop was the osmotic wrinkling of normally turgid animals when bathed in these hypersaline solutions, as exemplified by some jellyfish” (Barthel et al - Page 90).

Photographs of jellyfish found stranded at Ha Pak Nai

(Scale where shown: 30 centimetre/12 inch ruler)

October 2009 - Mass strandings

  

Photographs of individual jellyfish in the mass strandings of October 2009. 

October 2009 - Jellyfish showing beginnings of dessication and burial.

June 2009 - Jellyfish showing effects of mild dessication (the haloes may be due to ant predation).

October 2009 - Jellyfish showing effects of advanced dessication.

References

Barthel, K.W., Swinburne, N.H.M., and Conway Morris, S. (1994). Solnhofen: A Study in Mesozoic Palaeontology. Cambridge University Press, Cambridge.

Comparing the “mass mortality” events at Solnhofen with seasonal mass mortality events along the coast of a recent inter-tidal mudflat

This post is one in a series of posts which compares the depositional environment of the late Jurassic lithographic limestones at Solnhofen in Germany based on extracts from Solnhofen: A Study in Mesozoic Palaeontology with observations made at a modern inter-tidal mudflat at Ha Pak Nai, Deep Bay, New Territories, Hong Kong and proposes an inter-tidal mudflat origin for the examples cited.

This post compares comments on mass mortality events at Solnhofen with photographs of the seasonal mass mortality events along the coast at the inter-tidal mudflats at Ha Pak Nai, Deep Bay, Hong Kong.

Extracts from: Solnhofen: A Study in Mesozoic Palaeontology

“The peculiar composition of the waters not only deterred normal marine organisms from living in this environment, but for any organism unfortunate to be washed over the reef and steeped in this solution, death followed very shortly afterwards. Hence the examples of mass mortality and sudden death seen in some of the fossils” (Barthel et al - Page 58)

“In the central and western regions of the plattenkalk area, there are cases where tens or even hundreds of animals of the same species are found strewn over a single bedding plane. Evidently currents carried away local, perhaps seasonal, shoals through gaps in the reef… … In addition, there are numerous well-preserved jellyfish from the Gungolding-Pfalzpaint area” (Barthel et al - Page 90).

Photographs of seasonal mass mortality events at Ha Pak Nai

April/May

Seaweed attached to small rock anchors.

May 2009

April 2010

May 2011

April/May

Sea hare (Bursatella leachi) mass strandings

June

Sea urchins (Salamacis dussumieri)

October

Jellyfish mass strandings

References

Barthel, K.W., Swinburne, N.H.M., and Conway Morris, S. (1994). Solnhofen: A Study in Mesozoic Palaeontology. Cambridge University Press, Cambridge.

Comparing the “reef mounds” at Solnhofen with modern seagrass bed mounds

This post is one in a series of posts which compares the depositional environment of the late Jurassic lithographic limestones at Solnhofen in Germany based on extracts from Solnhofen: A Study in Mesozoic Palaeontology with observations made at a modern inter-tidal mudflat at Ha Pak Nai, Deep Bay, New Territories, Hong Kong and proposes an inter-tidal mudflat origin for the examples cited.

This post compares comments made on the presence of “reef-mounds” with photographs of seagrass bed mounds (Halophila beccari) exposed at low tide on the inter-tidal mudflat at Ha Pak Nai, Deep Bay, Hong Kong.

Extract from: Solnhofen: A Study in Mesozoic Palaeontology

“Mounds, made from sponges and cyanobacteria (now dead) and their trapped sediment, protruded from the lagoon floor, leaving depressions where the plattenkalk sediments accumulated. The irregular topography formed by the dead sponge – algal and coral – encrusted mounds would have helped to limit the strength of water currents” (Barthel et al - Page 73).

Photographs of seagrass mounds exposed at low tide at Ha Pak Nai

April 2011

April 2011

April 2011

April 2011 

May 2012

June 2010

June 2010

June 2012

June 2012

August 2011

November 2011

November 2011

November 2011

References

Barthel, K.W., Swinburne, N.H.M., and Conway Morris, S. 1994. Solnhofen: A Study in Mesozoic Palaeontology. Cambridge University Press, Cambridge.

Solnhofen and the inter-tidal mudflat at Ha Pak Nai, Hong Kong – Environmental factors

This post is one in a series of posts which compares the depositional environment of the late Jurassic lithographic limestones at Solnhofen in Germany based on extracts from Solnhofen: A Study in Mesozoic Palaeontology with observations made at a modern inter-tidal mudflat at Ha Pak Nai, Deep Bay, New Territories, Hong Kong and proposes an inter-tidal mudflat origin for the examples cited.

This post gives an overview of some of the factors influencing life on the inter-tidal mudflat at Ha Pak Nai, Deep Bay, West New Territories, Hong Kong.

Geology

Ha Pak Nai lies at the south end of Deep Bay in the North West New Territories in Hong Kong. The underlying rocks in this area are fine to medium grained Jurassic granite, giving way to superficial geological deposits along the coast including silts, sands and gravels, which form pockets of low lying coastal plain along the edge of Deep Bay.

The land backing Ha Pak Nai comprises significant areas of eroded natural hillside, where chemical weathering has not only resulted in large scars on the hillsides, but also serves to constantly feed the coast with new sediment in the form of quartz grains, minerals and clay materials, washed down by the streams which run off these granite hills (Langford et al 1989).

The coastal habitats around the stream mouth regularly change in nature due to a variety of influences.

Seasonal variations

The coastal area of Ha Pak Nai is fluvial dominated delta in summer, dominated by beach and deltaic channel facies. In winter, tides and waves rework and sort the sediment, with seasonal lagoons, sand bars, sandy flats and mudflats developing. Beach deposits have formed in coastal embayments (Lee 1999).

Monthly variations

Each month Ha Pak Nai is subject to Spring Tides (semi-diurnal tide of large range occurring when the moon is new or full) and Neap Tides (tides of small range when the moon is at its first or last quarter). The tides in Hong Kong range from extreme lows of below 0.00 metres to highs of 3.1 metres, although in Ha Pak Nai they usually range between 0.1 to 2.7 metres.

At certain times of the year, the tide cycles result in abnormally low high tides, which leave large areas of the mudflat exposed for a number of days. This phenomenon may be a factor in some of the fossil preservation at Solnhofen.

Daily variations

Ha Pak Nai is subject to semi-diurnal tides – a tidal pattern in which there are two high tides and two low tides each day. Mudflat animal behavior is synchronized with these tidal cycles. As the tide starts to come in, animals retreat to their burrows or bury themselves. After the tide recedes, and the mudflat is exposed, they emerge to forage.

Photographs of Ha Pak Nai 

Aerial view of Ha Pak Nai showing eroded granite hills feeding the coastal area (Image: Google Earth)

Aerial photograph of steam mouth at Ha Pak Nai at low tide, showing position of seagrass beds in relation to stream mouth. (Image: Aerial Photograph. Ha Pak Nai. 2 December 2008. Survey and Mapping Office, Lands Department, HKSAR Government)

Stream mouth at Ha Pak Nai at low tide.

Sandy Beach (A) at Ha Pak Nai. 

Sand bars at stream mouth at Ha Pak Nai at low tide.

Seagreass Beds A showing pools forming at low tide between the mounds.

Seagrass Beds B showing pools forming at low tide between the mounds.

References

Langford, R.L., Lai, K.W., Arthurton, R.S. & Shaw, R. (1989). Geology of the Western New Territories. Geotechnical Control Office, Hong Kong. (Hong Kong Geological Survey Memoir No 3).

LEE, M.F. (1999). Sedimentary facies of fluvial-marine transition environments in Hong Kong: Ting Kok and Pak Nai deltas. MPhil Thesis. University of Hong Kong.

Solnhofen – Palaeoenvironment

This post is one in a series of posts which compares the depositional environment of the late Jurassic lithographic limestones at Solnhofen in Germany based on extracts from Solnhofen: A Study in Mesozoic Palaeontology with observations made at a modern inter-tidal mudflat at Ha Pak Nai, Deep Bay, New Territories, Hong Kong and proposes an inter-tidal mudflat origin for the examples cited.

This post covers details of the palaeoenvironment as documented in Solnhofen: A Study in Mesozoic Palaeontology. Comparisons with the inter-tidal mudflat at Ha Pak Nai, Deep Bay, New Territories, Hong Kong will be made in the following posts.

Extracts from: Solnhofen: A Study in Mesozoic Palaeontology

Early depositional model

“Early depositional models envisaged the Southern Franconian Alb as a vast mudflat where sediment was brought onshore by storms to consolidate and dry out under the sun” (Barthel et al - Page 56).

Comment: This model was rejected and the deposits at Solnhofen are currently interpreted to have formed in a “restricted basin” - see below.

The restricted basin model

“It is now generally agreed that the plattenkalk basins lay permanently submerged under a stable body of water” (Barthel et al - Page 56).

“The Solnhofen area may then be thought of, in a broad sense, as a lagoon bordered to the north by low-lying land and to the south by a chain of coral reefs which protected it from the Tethys Ocean. The base of the lagoon was covered by dome-shaped mounds, built by sponges and cyanobacteria (blue-green algae) in the Kimmeridgian stage of the Late Jurassic. The mounds shielded intervening hollows from the effects of currents and, in the quiet basinal waters, the plattenkalk sediment was deposited” (Barthel et al - Page 57).

Stagnation of the bottom waters

“The peculiar composition of the waters not only deterred normal marine organisms from living in this environment, but for any organism unfortunate to be washed over the reef and steeped in this solution, death followed very shortly afterwards. Hence the examples of mass mortality and sudden death seen in some of the fossils” (Barthel et al Page 58) 

References

Barthel, K.W., Swinburne, N.H.M., and Conway Morris, S. (1994). Solnhofen: A Study in Mesozoic Palaeontology. Cambridge University Press, Cambridge.