The Palynology and Geology of the Lower Cretaceous (Aptian-Albian

Proceedings of the Geologists’ Association 128 (2017) 599–612

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Proceedings of the Geologists’ Association

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The palynology and geology of the Lower Cretaceous (Aptian–Albian) of

Munday’s Hill Quarry, Bedfordshire, UK

a, b

Darrin Stead *, Jill Eyers

Wellstrat Services Limited, 1 Castle Grange, Caergwrle, Wrexham LL12 9HL, United Kingdom

Chiltern Archaeology, 13 Pusey Way, Lane End, High Wycombe, Bucks HP14 3LG, United Kingdom

A R T I C L E I N F O A B S T R A C T

Article history:

– ’

Received 16 September 2016 Early Cretaceous sediments of Aptian Albian age outcrop at Munday s Hill Quarry, Bedfordshire, England.

Received in revised form 25 May 2017 Previous papers describing the section have resulted in different terminologies being applied. The Lower

Accepted 31 May 2017 Cretaceous in Bedfordshire is represented by sediments belonging to the Lower Greensand Group and the

Available online 27 June 2017

Gault Clay Formation. Within the Lower Greensand Group in the study area the Woburn Sands Formation,

are of Aptian–Albian age. Selected samples have been analysed for palynology. The analysis reveals

Keywords:

diverse palynomorph assemblages, including well-preserved dinoﬂagellate cysts and sporomorphs.

Palynology

Comparison of the assemblages with published records indicates that the lower samples are of Late

Lower Cretaceous

Aptian age. Forms recorded include common Kiokansium unituberculatum,Cerbia tabulata, Aptea

Albian

polymorpha and Cyclonephelium inconspicuum. An Early Albian age is indicated for the uppermost sample.

Aptian

Dinoﬂagellate cysts

1. Introduction they are invariably re-worked and phosphatised, and therefore not

indigenous, and do not date this horizon.

Munday’s Hill Quarry is located to the north of the town of During a ﬁeld visit in 2012 four samples from the quarry were

Leighton Buzzard, in Heath & Reach, Bedfordshire, England at SP collected and analysed for palynomorphs (Fig. 2).

942 284. The entrance lies off Eastern Way and it is currently under

Aggregate Industries ownership (Fig. 1). 2. Geological background

The Leighton Buzzard area of Bedfordshire is well-known for its

sand deposits which have both been exploited as a valuable local 2.1. Lower Greensand Group

resource and also well researched from the 19th century onwards

(Shepard-Thorn et al., 1994). The sands lie within the Lower The Lower Cretaceous in Bedfordshire is represented only by

Cretaceous sequence upon an eroded Jurassic surface. The Lower sediments of the Lower Greensand Group and Gault Clay

Cretaceous of Bedfordshire is represented by the Aptian to Albian Formation. This sequence is represented by three distinct units:

stages only—any earlier Lower Cretaceous stages, if they were Aptian arenaceous formations (deposited in a tidally-inﬂuenced

deposited, have been subject to erosion (Eyers,1992). Earlier Lower marine environment known as the Lower Greensand Group and a

Cretaceous units may be found to the north and to the south of this tidal ﬂat environment called the Silty Beds); a number of deposits

region and indicate that the area of Bedfordshire remained a occurring at the junction between the lower sands and upper clays;

relatively uplifted region during this time (Eyers, 1991, 1995). and Albian age sediments representing a deepening of the sea,

Fossils belonging to these earlier stages may be found within the which include the Shenley Limestone and the clays of the Gault

lowest pebble beds of the Lower Greensand (Woburn Sands), but Formation.

The literature covering the Lower Greensand Group is full of

misnomers from the earliest accounts in the early 1800s to the

present-day, the principle name ‘Lower Greensand’ being the ﬁrst

misnomer on account of these sands not being green in exposures.

* Corresponding author. The glauconite content (sometimes seen green at depth) oxides to

E-mail addresses: [email protected] (D. Stead),

a variety of brown and red colours and testiﬁes to the nearshore [email protected] (J. Eyers).

http://dx.doi.org/10.1016/j.pgeola.2017.05.011

600 D. Stead, J. Eyers / Proceedings of the Geologists’ Association 128 (2017) 599–612

Fig. 1. Location of Munday’s Hill Quarry, east of Heath & Reach, Bedfordshire. The sampling location is marked *.

marine origin for these sands. A second aspect to this misnomer is elsewhere in England (Eyers, 1992, 1995). The whole of the

‘sand,’ since the deposit is not always sand, but also comprises beds Bedfordshire sequence is now recognised as the Lower Greensand

of silts, clays and ironstones. Nevertheless, the term has remained Group (Woburn Sands Formation), but with stratotypes designated

in geological use since it originated with William Smith between for the Group in the Weald Basin under the Atherﬁeld Clay

about 1800 and 1812 (Jukes-Brown, 1900) despite the fact that Formation, Hythe Formation, Sandgate Formation and Folkestone

Smith’s original use of the name was applied to the ‘green sand’ he Formation.

mapped between the Gault and the Chalk (and now called the Unfortunately, after Cameron’s naming (1892) and Rawson’s

Upper Greensand Formation). Upper Greensand is stratigraphically reﬁning of the designation (1992) confusion was further intro-

distinct to the Lower Greensand—they are separated by the Gault duced by the use of alternative terms for parts of the Woburn Sands

and by a timespan of some 100 million years. which are rather localised and based on colour (as the list above).

Proposals for changing the names of these units came The terms Red Sands, Silver Sands and Brown Sands were used

subsequently from Fitton, Webster, Mantell and Martin, with colloquially by quarry workers, but gradually crept into geological

names such as Firestone, Merstham Beds, Shanklin Sands and usage. These terms now abound in the literature and include many

Malm Stone being applied in the literature. The matter was ﬁnally alternatives for the same beds. The terms are listed in Table 1 along

brought to an end by Fitton’s 1836 memoir entitled On the strata with a summary of all alternative names. This table will allow other

between the Chalk and the Oxford Oolite (Fitton, 1836). In this he papers to be read successfully and the sands researched and

ﬁnally proposed the adoption of the names Upper and Lower described within them identiﬁed with more ease, and hence

Greensand stating that although it could be criticised, the results correlated and compared more efﬁciently.

nomenclature is now probably too well established to be changed The samples obtained for this study were obtained from the

without inconvenience. Thus, with the adoption of the terms in upper part of the Lower Woburn Sands (Brown Sands), since this is

1839 by the Geological Survey the discussion came to a close. the only unit to contain clay drapes—the Upper Woburn Sands

(Silver Sands) have no clay; and one from the junction with the

2.2. The Woburn Sands Formation base of the Gault. Clay is again present at the basal Gault. While the

Gault continues to be a conﬁrmed and recorded marine

The name ‘Woburn Sands’ was ﬁrst proposed by Cameron transgression, it was of interest to establish the depositional

(1892) for the outcrop of Lower Greensand covering Bedfordshire environment of this basal clay layer.

to the Midlands. This name later became much more restricted to

that area of Bedfordshire which is the main outcrop, and Rawson 2.3. Lower Woburn Sands (Brown Sands)

(1992) ﬁnally formalised the name as the Woburn Sands

Formation. In Bedfordshire the Woburn Sands is composed of The base of this unit is seen elsewhere in the county. It is erosive

4 divisions, which in stratigraphical order are: and highly irregular, but it is not visible in Munday’s Hill Quarry or

other pits in the area where the full depth of the Brown Sands is

The Silty Beds* (youngest) believed to be 60–70 m (Fig. 2). The base lies unconformably over

‘Red Sands’ eroded Jurassic strata—the gently folded Oxford Clay, West Walton,

‘Silver Sands’ Ampthill Clay and Kimmeridge Clay formations. Thus considerable

‘Brown Sands’ (oldest) thicknesses of uppermost Jurassic and Lower Cretaceous

sediments are missing in this area (Shepard-Thorn et al., 1994;

(*Note that this is not now a formal subdivision recognised by Eyers, 1992).

the BGS, although it is sufﬁciently different in lithology, The Brown Sands at Munday’s Hill consist of thinly-bedded,

sedimentology and environmental interpretation (a tidal ﬂat) cross-stratiﬁed sands and bioturbated sands displaying a wide

from the remainder of the Woburn Sands to be recognised and range of sedimentary structures and trace fossils. Small and large-

recorded separately. It is also clear from some of the literature that scale burrows are found in these sediments including Taenidium,

confusion exists over the stratigraphical relationship). Siphonites, Planolites and Teichichnus. No body fossils occur in the

As studies of the sands continued it became clear that the sands sands except for wood. Wood is reasonably abundant, mostly

in the Bedfordshire region were very different to those found limonite-cemented and ranging in size from small fragments of a Download English Version: https://daneshyari.com/en/article/5786401

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