Triassic Sediments of the Inner Moray Firth, Scotland: Early Rift Deposits

Journal of the Geological Society, London, Vol. 145, 1988, pp. 235-248, 12 figs, 1 table. Printed in Northern Ireland

Triassic sediments of the Inner Moray Firth, Scotland: early rift deposits

L. FROSTICK,l I. REID,’ J. JARVIS’ & H. EARDLEY’ Royal Holloway & Bedford New College, University of London, Egham, Surrey 7W20 OEX, UK ’Birkbeck College, University of London, Malet St, London WClE 7HX, UK

Abstract: Patterns of Triassic sedimentation in the Inner Moray Firth are examined in the light of a new model of continental rift sedimentation that has been developed in the Tertiary to Recent rifts of East Africa. The major tectonic control during the Trias was the Great Glen fault to the northwest, which can be shown to have been moving in dip-slip fashion at this time. The structure of the Firth appears to have resembled the simple half-graben that makes up the great East African rift system. Depositsboth thicken and get finer towards thefault. Sediments found in off-shore wells are dominated by laminated fine sandand silty-clay with sporadicevaporites. Similar sequences are characteristic of, or associated with, ephemeral lakes in modern semi-arid continental rift settings. No alluvial fans have been detected close to the faulted margin. Again, this is consistent with general patterns of sedimentation against boundaryfaults in the Kenyan rift. The coarsest sedimentary sequences in the Moray Firth are on the unfaulted margin to the south around Burghead. They consist of fluviatile, lakeshore and aeoliandeposits. The fluvial sediments show evidence of tectonically induced cycles of sedimentation which are interpreted in terms of waves of detritus working down the drainage system. Beds dominated by pebbly horizontal laminae and reminiscent of steep, straight and shallow ephemeralstreams alternate with troughedsands of deeper, moresinuous, but equally ephemeral rivers. These are the coarsest sediments of the unfaulted margin of the basin. However the lack of thick conglomerate sheets, which are a feature of East African sequences at equivalent positions within the rift basin, suggests only small-scale fault activity and a relatively subdued topography during Triassic times. This is supported by evidence of extensive calichification during the Rhaetic which produced a top-Trias marker horizon found throughout the Inner Moray Firth.

Triassic sequencesin thenorthern North Sea are thinning, doming and rifting had begun which heralded the increasingly important as targets for oil and gas exploration. fragmentation of Pangea, andled to a new structural Within the Central Graben, gas has been proved in sands framework forthe North Sea area (Hallam 1971; Zeigler interpreted as Lower Triassic (Fisher 1984). In the Viking 1981; Wood & Barton 1983; Glennie 1984; Barr 1985). The Graben on the Norwegian side of the Median Line, one of pattern of deposition that hadbeen established in the the principal reservoirs is the Statfjord Formation which is Permian of two broad post-orogenic troughs was to give way thought to range in age from Rhaetic to Sinemurian (Kirk to a series of narrow rift basins that developed as a direct 1980; Roe & Steel 1985). result of proto-Atlantic extension. It was in these that the Despite the economic potential of Triassic sediments, the thickest sequences of Triassic sediments accumulated data available fortheir interpretation andfor the (Zeigler 1975, 1981; Glennie 1984). construction of predictive palaeogeographical models are few. Of all the ‘released’ wells in the UK sector, only Structural setting of the Moray Firth 350 penetrate Triassic sequences. Unfortunately, on-shore information is equally sparse, with outcrops limited to an The Moray Firth forms one arm of the North Sea trilete rift area less than 30 km2 onthe northwesternand southern system (Whiteman et al. 1975, after Burke & Dewey 1973). shores of the Moray Firth (Fig. 1). It can be divided intoan inner and an outer basin, the In view of the limited availability of off-shore data, transition being marked by an abrupt change in fault trend especially core information, the on-shore sequences gain an from SW-NE to WNW-ESE in the region of the Halibut importance in environmental reconstruction that far exceeds Horst. Patterns of faulting are very complex (Fig. 1). Major their geographical extent.In the Inner Moray Firth, they faults include the Great Glen, Helmsdale and Wick faults to provide a basis for interpreting the evolution of the basin. the northwest, and the Banff fault to the south.But much of As such, they carry implications for Triassic developments the movement on these as well as on a host of minor faults in the northern North Sea as a whole. occurred in Jurassic times. The question arises as to which By combining field observations with information from of the faults, if any, controlled basin development during shallow on- and off-shore cores, seismic sections, and the the Triassic. There is no doubt that faults were active during wire-line records of commercially drilled wells, it has been the period. Brennand (1975) suggests that there were throws possible to infer the structuraland palaeoenvironmental in excess of3500 m in his general review of structure and development of the Triassic Inner Moray Firth. sedimentation in theNorth Seaprovince, but he is not specific about which faults were active. Glennie (1984), in his review of Permian North Sea basin development, refers General geological setting to Zeigler’s (1982) diagrams which suggest early movements The Triassic deposits of the North Sea were laid down on the Great Glen and Wick faults,although there is no during a significant period of crustal evolution. A cycle of supporting discussion. Zeigler in his earlier work 235

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4OW 2OW 59'

SB'N

PERYIAN

\\ I TT*-LI

Fig. 1. Geological map of the Moray Firth. Inset shows details of Triassic stratigraphy. (W) Off-shore wells used in this study; B, Burghead; E, Elgin; G, Golspie; L, Lossiemouth.

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NW SE

PRE-OXFORDIAN

ENDTRIASSIC Fig. 2. NW-SE sections across theMoray Firth. Top, present-day; Middle, with the effects of all post-Callovian faults removed; Bottom, with all post-Triassic fault movements removed. Heavy line is top-Trias marker horizon. K

(1975, 1981) shows movement onthe Great Glen fault the generalized west-east axis of the Firth, and there is an alone,and suggests that it continued to act as adextral indication that it increased eastwards towards the inferred strike-slip system fromPermian times onwards. McQuillin triple junction. The wedge-shaped basin that this differential et al. (1982), using detailed seismic evidence, concluded that movement produced is characteristic of aulacogens world- the basin developedin four distinct phases. Firstly, it wide (Burke & Dewey 1973). became a broad half-graben with dip-slip movement on the Atthe end of the Trias,during Rhaetic times, the GreatGlen faultduring Permo-Triassic times. Secondly, Helmsdale fault took over the role of boundary fault and dextral strike-slip movementsin the Jurassicand early eventually controlledJurassic basin development Cretaceous led to the greaterseparation of the Wick and (McQuillin et al. 1982). The sedimentaryconsequences of Banff faults.Epeirogenic subsidence of the region then this enlargement of the basin are discussed below. However, followed, to be overtakenby the final stage of Tertiary uplift the Rhaeticheralds the transition from exclusively and erosion. continental to dominantlymarine conditions (Brennand Are-evaluation of seismic information as part of the 1975) and is merely an interesting epilogue of the present present study confirms that the Great Glen fault was indeed study. the majorstructural element of theInner Moray Firth during the Trias. However, what remains contentious is the sense of regional movement-was it tensional or trans- Continental rift sedimentation tensional?Some lines of evidencefavour tensional In order to assess the significance of sedimentary patterns in movement. For instance, by removing the effects of later theInner Moray FirthBasin, a brief review of present faulting in cross-sections derived from seismic data, it is models of continental rift sedimentation is essential. Up to possible to see dip-slip displacement onthe Great Glen the beginning of the present decade, rifts were generally fault during the Trias (Fig. 2). In addition, a close considered to be full-graben, bounded on both margins by examination of a network of seismic sections over the Firth planarnormal faults (Illies 1981). An analysis of more reveals little evidence of any pre-Jurassic development of recent seismic data from the East African Rift (Rosendahl small-scale extension and compression thatare both & Livingstone 1983; Rosendahl et al. 1986) as well as from characteristic of strike-slipfaulting according to Reading elsewhere (Gibbs 1984) has prompted a move away from the (1980) and Gibbs (1983). classical structural model and replaced it with the Indeed,there appears to have beena comparatively asymmetrical half-graben as the commoneststructural simple structure, with at least one small antithetic fault on setting.Rosendahl et al. (1986) highlight both the listric the southern margin of the basin trending sub-parallel with nature of the boundary faults and the fact that they alternate theGreat Glen fault, possibly forming the topographical in polarity, shifting from one side of the rift to the other. barrier against which the aeolian dunes of theHopeman The rift valley consists, in effect, of aseries of linked Sandstone were banked. It is likely that the Great Glen fault half-graben,each

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A <:

2* i

COBBLE/CRAVEL m SAND 0 Fig. 3. Model of early sedimentation in SILT continental half-graben developed from work in the E. African Rift (after Frostick & Reid ctAy B EVAPORITE 1987a).

therefore notextensive. The diverteddrainage may get Sandstone,the Burghead Beds, and the Lossiemouth, caught in saddle basins between tilted fault blocks and may Spynie and Findrassie Sandstone (Fig. 1). They are run sub-parallel with, but outside of the rift for hundreds of interpreted as representing predominantly aeolian, fluviatile kilometres before finding access, often at the transfer fault and lake-margin (aeolian and lacustrine)environments, zone between adjacent half-graben. respectively. The unfaulted margin is the major source of sediment for Off-shore, data are sparse. However, it can be seen that eachsegment of the rift valley during this earlyphase of the succession is generally finer, comprising silt and fine rifting, and is characterized by sometimes thick alluvial sand. Because of this, it is assigned to theSmithbank sequences.Movements on the boundaryfault increase the Formation (Deegan & Scull 1977). Both the Cormorant and gradients of drainage crossing the roll-over and cause a wave the Smithbank Formations are lithostratigraphical units, and of coarse(pebbly) sediment to move intothe basin; long must often be time equivalents, though synchroneity would intervening periods of tectonic quiescence are characterized be difficult to establish because of the poor biostratigraphy. by reworking and particle comminution and are marked by In fact, no palynomorphs arereported for Moray Firth prograding channel sands, sandy deltas and other shoreline Triassic sediments; dating relies dubiously upon the Cutties deposits. Hillock reptiles of Upper Permian age (Benton & Walker The basin depocentre is frequently occupied by an 1985) andupon the reptilefootprints of theHopeman ephemeral or perennial lake, while axial drainage, at least in Sandstone datedas top Permian/base Trias by Walker the earlyphase of rift development, is restricted by the (1973) and Clemrnensen (1987). segmented nature of the half-graben. The lake often abuts theboundary fault, as in the case of LakesTurkana, Bogoria, Tanganyika and Malawi in E. Africa,though shallow lakes may fill hollows between syn- andantithetic Hopeman Sanhtone faults on the rollover, e.g. Lakes Baringo and Magadi. Lake The Hopeman Sandstone is a >70 m thick sequence of dune deposits are dominated by laminated fine sand, silt and clay. beddedaeolian sands (Peacock 1966; Peacock et al. 1968; Access forcoarser clasts is provided only in exceptional Fig. 4) The palaeotopographyhas been most recently circumstances, e.g. through gravity flows triggered by the interpreted as a family of complex star dunes (Clemmensen debouchment of flash-flood waters into the lake or through 1987) that was probablyheaped against topographica theencroachment of streams during climatically or barrier (? a fault scarp) by a net SSW sand transport vector tectonically induced lake regression. in a manner similar to those of modern deserts (Breed & It must be stressed that Fig. 3 depicts an idealized model Grow 1979). of early rift sedimentation. The actual pattern encountered One particularly interesting feature of the Hopeman in rifts will depend inevitably upon thenature of the Sandstone is the pervasive large-scale contortion of the dune topography anddrainage created by the developing bedding(Peacock 1966; Glennie & Buller 1983; Fig. 4A). structure. One important factor is surface gradient. Broad This has been explained as liquefaction structures associated structures with approximately the same relief as narrow ones with heavy rainfall (Peacock 1966), and as air escape might be expected to attract finer sediments because of their structures associated with rapid marine inundation (Glennie lower overall gradients. Nevertheless, the general nature of & Buller 1983). Slumping on the flanks of these large dunes the model should be equally applicable. after heavy rainfall seems the most likely explanation. Corroborative evidence comes from the well-developed, if minor, river channels that cut into the base of the dunes as Triassic sediments of the Inner Moray Firth Basin they meander between them (Fig. 4B), if only because they The Triassic outcrops of the MorayFirth Fall generally suggest substantial runoff despite an expectation that the within the Cormorant Formation as defined by Deegan & dune sand must have been highly porous. The mechanism of Scull (1977). On the southern shore they comprise a series rapid marine inundation, though ingenious, seems less of sandstones and pebbly sandstones that have traditionally likely. This is because thereappears to have been no been given separate formation status (Warrington et al. wholesale wave erosion of what would have been poorly 1980; Benton & Walker 1985), viz. theHopeman indurated sand; there are no superimposed marine deposits;

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Fig. 4. (A) Hopeman Sandstone on the coast approximately 4 km east of Hopeman Village showing intact dune bedding (D) and disrupted bedding due to subaerial slumping (S). (B) Hopeman Sandstone c. 100 m west of the outcrop in Fig. 4A showing contemporary fluvial channelling (C) in dune sands (D).

and the contortions occur at different stratigraphical levels, which would require repeated small-scale inundationand not a single catastrophic event.

Burghead Beds Fig. 5. (A) Pebbly sand and sand with sporadic pebbles of the The Burghead Beds have a proven thickness of 73 m, and Burghead Beds at Burghead Harbour showing horizontal bedding are fluviatile deposits contrasting markedly in structure and and overpassing pebble stringers. (B) Section cut in the bed of a petrology with the underlying Hopeman Sandstone.They modern ephemeral streamin northern Kenya showing horizontal are poorly sorted arkosic pebbly sands (Fig. 5A). The a axis bedding and overpassing pebble stringers. of the pebblesranges in size upto 10cm; the sand is dominantly medium to coarse grained. The balance between pebbles and sand vanes from sand-packed conglomerate to Frostick et al. 1983; Reid & Frostick 1987; Fig. 5B). Locally pebblestringers or clusters over-passing a sand bed. there are small-scale (<30 cm thick) planar cross-sets, but Horizons that include abundant silty-clay intraclasts occur at there is no evidence of major asymmetrical channel scour. different levels throughout the succession, while single beds This further suggests the large channel width/depth ratios, of laminated overbank silt <30cm thick occur locally. The the planar beds andthe high sediment loads thatare so dominant primary structure is plane-parallellamination, characteristic of ephemeral streams. which makes up c. 60% of the exposed succession (Figs 5A, However, the plane-bed facies give way to trough 6 & 7). The dominance of plane bedding, together with the cross-bedded sand facies at intervals in the succession (Figs abundance of clay intraclasts (mud curls ripped from pools 6 & 7). This suggests a change in channelcharacter; the where suspendedsediment had settled out),and the cross-bedded facies imply morea incised channeland presence of over-passing pebbles are all typical of modern deeper flood flows with better developed secondary ephemeralstream deposits (Frostick & Reid 1977, 1979; currents. The alternation of plane-bed and trough-bed facies

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sand with sporadic pebbles

pebbly 1 sand

0 5m

Fig. 6. Sketch section of the Burghead Beds at Burghead Harbour. 1, horizontal plane-bedded and small-scale tabular cross-bedded pebbly sand; 2, overbank fines; 3, wide shallow channels cut into overbank fines; 4 & 5, parallel laminated sand with sporadic pebbles;6 & 7, cross-cutting channel depositswith trough cross-beds.

is almost certainly associated with changes in the flux rate of modern silcretes. In fact, Ca levels are high even in the most sediment in the channels draining the unfaulted margin. The siliceous example of the deposit,i.e. thataround mechanism behind this will be discussed below. Lossiemouth. An interesting feature of the Burghead Beds is evidence Infact, detaileda examination reveals relics of of early cementation. Quartz overgrowths are corroded and concretionary layering that would be expected in calcretes. smothered by calcitecements which are disruptive and On the northwestern shore, calcite pseudomorphs of sometimes nodular in character. A likely sequence of events dolomite rhombs, together with the partial replacement of started with the release of silica as the feldspars weathered, calcite with microcrystalline silica, suggests a complex and its incorporation in the quartz overgrowths; these were history of dolomitization,de-dolomitization and silicifica- then etched in the alkaline environment of a soil that was tion.From this, several environmental inferences are undergoing calichification, which itself produced the possible. Firstly, the formation and extensive preservation calcrete-like carbonate cements. of a palaeosol requires a considerable period of time and benefits from tectonicquiescence. This suggests thatthe end-Trias was a period of comparative structural stability in Lossiemouth, Spynie and Findrassie Sandstone the Inner Moray Firth; indeed, the geographical extent of TheLossiemouth, Spynie and FindrassieSandstone is an such a thin deposit suggests a landscape of subdued relief in interleaved sequence of aeolian dune-beddedand water- which erosionand sediment transfer were discouraged. lain, parallel-bedded, medium to fine sand. It is dated on the Secondly, the fact that calcretes form exclusively in basis of scanty reptile fossils as lower Norian (Peacock et al. semi-arid environments gives an indication of the nature of 1968). The water-lain sediments show extensive invertebrate the contemporaryclimate. Thirdly, dolomitization implies bioturbation suggesting a lake-shore environment. the influx of brackish water, and may therefore be the earliest evidence of the close of the exclusively continental period of the basin. Stotfield Cherty Rock The Cherty Rock is a >20 m thick marker bed that occurs Deposits of the northwestern shore throughout the Inner MorayFirth and has generally been Only the topmost Trias is present on the northwestern shore acknowledged as top-Trias. It crops out at Lossiemouth on of the Firth. The base of the sequence is represented by a thesouthern shore of the Firthwhere it consists of few metres of sand and mar1 immediately beneaththe microcrystalline silica that includes scatteredsand grains. Cherty Rock. Overlying this is theDunrobin Pier However, the deposit is calcareousboth on the northwes- Conglomerate, dated tentatively by Batten et al. (1986) as tern shore of the Firth where it crops out near Golspie, and late RhaetiantoHettangian. This is cross-bedded,a in offshore wells (Linsley et al. 1980). It has been variously fluviatile pebbly sand which containssome palynomorphs interpreted as a silcrete and as an altered calcrete (Williams and carbonaceous material. It is continental in character and 1974). has some bearing on general basin development. Because of The geochemical nature of the ChertyRock is more this, it has been included in this analysis despite its Jurassic consistent with an altered calcrete (Table 1). Titanium is not affinities. However, the overlying Dunrobin Castle Member concentrated as might beexpected for silcretes (Summer- shows an increasing frequency of marineinundation with field 1983), while calcium, magnesium and phosphorus are time, indicating the final close of continental conditions in notdepleted (bypedogenic leaching). This is especially the Moray Firth. obviouswhen comparison is made with the underlying Lossiemouth Sandstone and Burghead Beds (Table 1) which would havebeen equally subject to any overprintingas a Offshore deposits result of later diagenetic alterations should this be thought Sequences penetrated by off-shore wells are very different to have been partly responsible for the poor resemblance to fromthose encountered in on-shoreoutcrops. The

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BURCHEAD CLIFFS

GRAIN SIZE 6 SEDIMENTARY STRUCT.

BURCHEAD HARBOUR

4 STEPS

CLARKLY HILL 3 QUARRY

BURGHEAD\\ l

0 0 i

Key

: trough cross-bedded sand

. horizontaVsub-horizontal bedded

I sandwith sporadic pebbles ...... ~ horizontal & small scale tabular cross-bedded pebbly sand

Fig. 7. Measured sections at four sites around Burghead showingcharacteristic sequences and lateral relationships.

sediments are predominantly fine-grained and can be unit is the lateralequivalent of theBurghead beds. Thin divided into two lithostratigraphicalunits, a lower limestone and evaporite beds in the lower part of the upper predominantly sandy unit and an upper unit comprising unit suggest the presence of an ephemeral lake and sporadic interbedded fine sand, silt and clay. The coarser grain size of periods of greater aridity. This unit is tentatively interpreted the lower unit suggests greater transporting power during as a basinwards equivalent of the Lossiemouth, Spynie and the early stages of basin development. It is possible that this Findrassie Sandstone.

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Table 1. Bulk chemical analyses (major oxides, wt%) of Triassic sediments from the Inner Moray Firth. Locations are shown on Fig. 1.

Sample LocationSample AI,O, TiO, Fe,O, MnO MgO CaO Na,O K,O P,O,

Stotfield0.06 0.40 0.02Lossiemouth 0.60 0.05 7.44 0.04 0.08 0.03 Cherty Rock Stotfield Golspie0.58 Burn 0.06 0.11 0.02 0.55 52.22 0.250.04 0.00 Cherty Rock Stotfield Dunrobin(near 0.80 0.09 0.80 0.360.04 16.23 0.20 0.77 0.03 ChertyGolspie) Rock LossiernouthLossiernouth 3.82 0.11 1.17 0.01 0.08 0.24 0.60 1.97 0.02 Sp. & Find. Sandstone Burghead 3.08 0.22 0.35 0.06 0.19 26.91 0.1926.91 0.19 Burghead 0.06 0.35 0.22 3.08Burghead 2.03 0.04 Beds Bokkeveld South Africa 0.30 1.57 1.041.57 0.30 AfricaBokkeveld South 0.00 0.00 0.06 - 0.01 0.01 SiIcrete'

From Surnrnerfield (1983).

Evolution of Inner Moray Firth Basin and in the isopach map of Fig. 9. Up to 500m of sediment There are many similarities between the general model of are recorded close to the fault (McQuillin et al. 1982). In rift sedimentationthat hasbeen outlined and the Triassic contrast, the sequence on the southern margin is less than deposits of the Inner Moray Firth. 150m thick', despite the fact that the deposits range in age from Scythian to Norian. The universal presence of the Cherty Rock indicates little post-Trias erosion over most of Gross geometry of the sediments the basin, and the general northward thickening suggests a The thickening of the Triassic wedge towards theGreat sinking depocentre close to the Great Glen fault that was Glen fault is very evident both in the cross-section of Fig. 8 attracting sediment from the south. There is, however, some

NW SE HELYSDALE GREAT GLEM FAULT FAULT UNRELEASEU UNRELEASEU 11/30-6 GAMMA SONIC

/ / I / \ I / f / \ / \ f / \ / / l / / / / /' 0 S 1Okm

100

CHERTY ROCK I m PEBBLY SANDSTONES SANDSTONES INTtRBEDDED SANDSTONES h SHALL5 500

Fig. 8. Relationship between onshore outcrops of Triassic sedirnents at Elgin and Golspie and sequences proved in offshore wells.

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conditions in an enclosed basin where the balance of rainfall andevaporation changes markedly from year to year, as well as over longer time spans (Reid & Frostick 1985, 1986). The overall fining tendency in the off-shore Triassic sequence might betaken as ameasure of the declining magnitude of successive tectonic shocks to the system. This would be in sympathy with the impression that rifting was more intense in the North Sea province only during early and very late phases of the Trias. However, the growth of a lake in theInner Moray Firth would have actedas a sedimentarygovernor, checking the movement of coarse detritusand trapping it preferentially at its margins. As a result, the fining tendency atthe basin centre cannotbe taken as an infallible guide to any fluctuations in erosion that might have beentaking place onthe rift flanks in response to changes in tectonic activity.

The unfaulted margin Accepting thatthe Triassic Inner Moray Firth was a Fig. 9. Isopachs of Triassic deposits (feet) in the Inner Moray Firth. half-graben, the sediments of the southern shore would have accumulated on the unfaulted margin. For this locality in the indication that the throw on the boundary fault was unequal basin, the sedimentarymodel predicts a complex alluvial along its length-the sedimentary wedge is thicker towards sequence, with an increase in lacustrine influence towards the NE (Fig. 9). the depocentre. There would havebeen extensive alluvial plains fringed with reworked shoreline sediments, all of very low relief (Frostick & Reid 1979). These would have acted The faulted margin as a source for aeolian sediments (cf. Carruthers 1987). Thereappear to be no coarsedeposits that might be The Moray Firth deposits fit extremely well within this interpreted as alluvial fans close to the faulted margin. Any framework. The Burghead Beds represent alluvial en- such deposits that might occur must lie inshore (i.e. north) croachment; the LossiemouthSandstone is bioturbatedas of the wells drilled in the basin and must be either very would be expected of shoreline deposits (Frostick & Reid small or highly localized. The absence of extensive fans or 1986); while the Hopeman Sandstone and to some degree fan-deltas fed by streams issuing from the boundary fault is the Lossiemouth Sandstone indicate localized ancient dune consistent with observations in the Recent rift basins of the fields. However,one sedimenttype missing from the East African system where back-tilting of fault blocks southern outcrops that might have been expectedas a minimizes the drainage area of local streams and hence the consequence of sporadicboundary fault activity and the delivery of detritus (Frostick & Reid 1987~). steepening of the hanging wall streams that would have The thin sequence of comparatively coarsesediments ensued is very coarse sediment, such as the Pleistocene nearGolspie onthe northwesternshore occupies anarea Koobi Fora Plateau Gravel of theTurkana trough in that was outside of the basin for most of the Triassic period. northern Kenya (Frostick & Reid 1980). Either the The deposits are Rhaetic or younger in age and may well remaining outcrop is too small and sediments of this type representstrike drainage that had beendiverted into the have been eroded, or the development of the Inner Moray saddle basin between the Great Glen and Helmsdale faults. half-graben was too gentle to induce the violent sedimentary The palaeocurrents of theDunrobin Grit supportthis, response thatsheet conglomerates represent. While this suggesting a NE flow (Batten er af. 1986), parallel with the particular facies is absent, the general pattern of changing faults. However, the absence of older sediments helps to fix texture across the basin asa whole is consistent with the the first movements of the Helmsdale fault, which, together sedimentarymodel. Figure 10 gives isopleths of the with the Wick fault, may have been activated by a renewal proportion of the Triassic sediment that is of sand grade and of dextral slip on the Great Glen fault during Rhaetic times. coarser. The value ateach off-shore data pointhas been weighted according to formation thickness. There is a well-defined northward-fining trend. Outcrops on the The depocentre southern shore of the Firth are almost 100% sand-pebble, The model of continental rift sedimentation given in Fig. 3 while the sandfraction close intothe Great Glen fault is emphasizes the importance of lacustrine fine sedimentsat much less than 50%. thedepocentre. The sediments of theInner Moray Firth off-shore wells are reasonably consistent with this model in that they are dominated by clay, silt andsand (Fig. 8). Cyclical sedimentation ofroll-over zone alluvium However, the basal fine sandstone givesway to a thicker The alternation of gravel- and sand-dominated deposits is a sequence of interbedded sand and shale suggesting that the feature of hanging wall or roll-over zone sedimentation in lake was less important in theearly phase of rifting than continental rifts (Frostick & Reid 1987a, 19876). It during the later (?longer) phase. The interleaving of sand represents a riverine response to changes in both base level andshale in the younger sequencepoints to a shifting and the gradient of the catchment. Although there are no shoreline-something that would beexpected of semi-arid consistently coarse gravel spreadsinterdigitated with finer

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sediments in the Moray Firth, there is evidence of a cyclical change in sedimentary style in the Burghead Beds (Figs 6 & 7). Sets of pebbly sand (with a typical thickness of 1-2m) aresuperceded by sand with sporadicpebbles (typical thickness of6-7 m).Both are dominated by horizontal planelamination; pebbles oftenform laminae, locally of limited continuity but nevertheless indicative of overpassing and segregation fromthe subjacent sandlaminae in a manner suggested by Moss (1963), Frostick & Reid (1977) and Allen (1983); there is cut-and-fill but the cuts are generally shallow (<20 cm) and horizontal (Fig. 6). In the sand with sporadic pebbles, the pebbles often form isolated clustersbut arean insignificant fraction of the deposit. These beds aresuperceded by troughcross-bedded sand (Fig. 7). The pebblysand and sand with sporadicpebble facies were undoubtedly laid down by wide, single-thread, straight but shallow ephemeralstreams, since theycorrespond almost exactly to the descriptions of the channel deposits of such streams in modern semi-aridsettings (McKee et al. 1967; Frostick & Reid 1977). The vertical change to Fig. 10. Isopleths of the percentage of Triassic sediment whichis trough-bedded sand suggests a shift in river character sand grade and coarser in wellsof the Inner Moray Firth. towards deeper,more incised channel form.There is a possibility that periodic climatic changeled togreater rainfall and runoff, though the increase in vegetation cover same tectonic shock would trigger an episode of accelerated that is concomitent with an increase in rainfall is a limiting slope erosion.The sedimentaryproducts of this erosion factor onboth runoff and sediment yield (Langbein & would move down eachdrainage system as a barely Schumm 1959). Onthe other hand, it is tempting to detectable wave with substantial wavelength. An expected speculate that this change is directa response tothe time-scale for the passage of one of these waves is not yet alterations in river gradient that would follow successive defined by modern process studies, but might be in the movements onthe northwesternboundary fault. By order of 102-103 years. The manifestation of the wave at any invoking Leopold & Wolman’s (1957) relationship between point in thedrainage system would bea change in river bankfull discharge, channel slope and channel character, it character; bearing in mind Shahjahan’s (1970) observations, might be suggested that the straight shallow channels which streams would become less wide but more sinuous in haddeveloped in response to highergradient would be response to the increased flux of sand. As a result of this, replaced eventually by more incised channels as basin slope flood-water depth would increase, so creatinga hydraulic decreased with time. It should be pointed out, however, that environment in which secondary currents were ableto thissegregation of channeltype by channelslope has not exploit the sandy bed. This would produce, in turn,the been demonstrated conclusively, andthat Leopold & trough bedding that characterizes this facies of the cycle. Wolman’s field data are in conflict with those of Ackers & The difference in sediment composition between the two Charlton (1970) for controlled laboratory flume studies. alternating facies types can be explained as part of the same However, besides the question of changing channel scheme of events. The pebbles that had moved through the character, there is a need to explain the alternation of the system when stream gradientswere high asa result of horizontally bedded pebbly sandand sand with sporadic boundary fault movements and which became incorporated pebbles with the troughcross-bedded sand. Shahjahan’s in the horizontally bedded facies would be replaced by a (1970) work provides a possible explanation that ties in with pebble-freesand-dominated bedload both asgradients the expectedreaction of a fluvial sediment system to declined with time and as the erosion-fed sand wave moved spasmodictectonic activity. He points tothe complex down-system. interaction of factors determining channelcharacter. In particular,he highlights the role of sediment supply and concludes that an increase in sediment load alone tends to cause both a decrease in channel width and a concomitant Palaeocurrents increase in flow depth. On the other hand, McClure (1978) The direction of sedimenttransport can oftenprovide has invoked an increase in runoff in explaining increased important indications of basin character and evolution. channel incision inSaudi Arabian wadis duringwetter However, the limited outcrop of Trias in the Moray Firth phases of the Pleistocene. reduces the chance of obtaininga representative pattern, Despite the multiplicity of possible causes, the repeated and increases the probability of sampling local rather than cycles of facies in the Burghead Beds can be accounted for regional patterns. by suggesting thatthe shallow planar cut-and-fill of the Nevertheless,palaeocurrents were established for the pebbly sandand sand with sporadic pebbles doesindeed exposed Burghead Beds using four flow direction indicators indicate a response of the streams to a tectonically induced (Fig. 11). High angle foresetswere measured as the most higher gradient; in these circumstances, straight, shallow conclusive evidence, but the predominance of horizontal streams would be expectedas the norm according tothe primary structures reduces the number of examples relationship of Leopold & Wolman (1957). However, the available. In order to compensatefor this, the streamline

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ORIENTAT-\PEBBLE N

TROUGH N FORESETS N ORIENTATIONS \

Fig. 11. Rosediagrams of four differentpalaeocurrent indicators in the - Beds.

axes of pebble clusters were established following general consistent with other studies (Williams 1974; Trommestad principles worked out by Brayshaw (1985). Examples of 1982). different kinds of pebble cluster (one stoss and one wake Theapparent conflict between an expectednortherly accumulation around alarger obstacle clast) exposed on current direction andthe pattern that emergesfrom the bedding planes of the Burghead foreshore are given in Fig. Burghead Beds may reflect the limited outcrop of fluviatile 12. The a axis orientations of elongate isolated pebbles were sediments, and shouldbe seen in the context of drainage also measured on the assumption that overpassing pebbles patterns in modern rift valleys where small antithetic faults at rest but exposed to the flow would be realigned with the in the roll-over can divert drainage in its general fall towards flow. Besides all these, the azimuths of trough axes in the the depocentre(Baker 1986). It is possible, for example, trough-beddedsandy facies weremeasured on bedding that earlymovement onthe faults tothe north of the planes conveniently exposed on the wave-cut platform. present coast deflected Triassic drainage in the area around Despite the general picture of a northward increase in Burghead. Besides this, the topography of theHopeman basin sediment thickness (Fig. 9) and a north-northwestward Sandstone dune field, with its estimated original relief of fining of sediment (Fig. lO), all four sets of palaeocurrent >l00 m (Clemmensen 1987), onto which the rivers of the data for theoutcrops of Burghead Beds given in Fig. 11 Burghead Beds would have flowed, would have had its own indicate flow towards the east or east-northeast.This is highly localized influence on drainage direction.

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according to adjustments in the rainfall-runoff-evaporation relationship and to movements on the boundary fault. A cyclical pattern of fluviatile facies onthe unfaulted margin is explained interms of successive disequilibria which are caused by boundary fault activity, and which are followed eachtime by adjustments in channelcharacter during interveningperiods of relaxation. Fault movement causes the development of steep straight but shallow streams dominated by horizontal primary structures that are made of pebbly sands or sands with sporadic pebbles; the adjusting drainage finally produces more incised, narrower channels which are overloaded with sedimentthat is laid as trough-beddedsands. However, the limited exposure of streamsediments onthe unfaulted margin provides palaeocurrent data that conflict with the generaldrainage direction expectedfrom considerationa of the gross basin-wide pattern of sedimentation. A possible explanation for the shift in transport direction from N to ENE in the depositsaround Burghead is given in local diversion by antithetic faults and by a pre-existing dune topography. Of great interest is the lack of very coarse sediments in the basin. In particular, no large fans were found emanating from the Great Glen fault scarp. However, observations of facies distributions in the active rift setting of East Africa would suggest that this is to be expected, if only because the doming normally associated with early phases of rifting restricts the catchment size of obsequentstreams onthe fault scarp. On the other hand, very coarse sediments are also absentfrom the hanging wall-the coarsest arethe pebbly sands of the Burghead Beds. Without any evidence of erosional removal, this suggests that tectonically induced gradients in theInner Moray Firth half-graben were not greatand may account forthe absence of extensive conglomerates onboth margins of the bzsin. In fact, the Fig. 12. Pebble clusters in the Burghead Beds at Burghead. (A) A basin is comparatively wide (c. 50 km). This, together with a typical wake accumulation and (B) a typical stoss accumulation. relatively small Triassic throw onthe Great Glenfault would indeed produce comparatively gentle gradients on the roll-over zone streams. Besides this, the pervasive nature of the Stotfield Cherty Rock palaeosol suggests that there were Conclusions long periods of tectonic quiescence that would have reduced TheInner Moray Firth was a continentia1 rift of the frequency of the disequilibria needed to produce the comparatively simple half-graben structureduring Triassic gravel spreads. times. The major controlling fault was to the northwest (the The Moray Firthsediments have beeninterpreted by Great Glen fault) and appears to have developed largely in analogy with a sedimentary model that has been developed a dip-slip manner during this period. Late in the Trias, the in a modern rift system. The environments of the ancient basin sensu Iato was extended on the northwestern margin andmodern equivalents differ only in the intensity of by motion on the Helmsdale fault. This development may surface processes as dictated by local gravitational gradients. have been related to minor transtensional movement on the Great Glen fault. The Triassic Northern North Sea Project is funded by grants from Triassic sediments have limited on-shore exposure, and Shell UK Exploration & Production, Norsk Hydro, Birkbeck released off-shore dataare sparse.Nevertheless, there is College, and the University of London Central Research Fund. We sufficient information to provide a picture of structural and are indebted toboth KenGlennie and Ron Steel for their sedimentary evolution in the context of recent observations encouragement and discussions. We acknowledge the British made in the E. African rift system. A section orthogonal to Geological Survey MarineGeology Unit for allowing access to the basin strike shows a wedge-shape deposit thickening shallow cores, and thank John Chesher and Graham Tulloch for towards the Great Glen fault. Theunfaulted margin allowed their assistance in this matter. Our thanks also go to Derek Blundell rivers into the basin and was probably the major source of and David Rhind for making facilities available without which the sediment.Deposits in this part of the basin range from project could not function. fluviatile pebbly sands to the bioturbated fine sands of an ancient lake shore. In general, there is a consisient fining of References sediment northwards towards the depocentre where silt and ACKERS,P. & CHARLTON,F. G. 1970. Thegeometry of small meandering clay with occasional evaporitesform the majority of the streams. Proceedings of the Institution of Civil Engineers, Paper 73285, sequence and indicate a lake, the size of which fluctuated 289-317.

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ALLEN, J.R. L. 1983. Gravel overpassing on humpback bars supplied with HALLAM,A. 1971. Mesozoic geology and the opening of the North Atlantic. mixed sediment: examples from the Lower Old Red Sandstone, southern Journal of Geology, 19, 129-57. Britain. Sedimentology, 30, 285-94. ILLIES, J. H. 1981. Mechanism of grabenformation. Tectonophysics, 73, BACON,M. & CHESHER,J. A. 1974. Evidence against post-Hercynian 249-66. transcurrentmovement on the Great Glen Fault. Scottish Journal of KIRK, R. H. 1980. Stratfjord field-A North Sea giant. In: HALBOUTY,M. T. Geology, 11, 79-82. (ed.) Giant oil and gm fields of the decade 1968-1978. Memoir of the BAKER B. H.1986. Tectonics and volcanism of the southern Kenya rift valley American Association of Petroleum Geologists, 30, 95-116. and its influence on rift sedimentation. In: FROSTICK, L.E., RENAUT,R., LANGBEIN, W. B.& SCHUMM,S. A. 1958. Yield of sediment in relationto REID,1. & TIERCELIN,J. J. (eds) Sedimentation in the AfricanRifts. meanannual precipitation. Transactiom of the AmericanGeophysical Special Publication of the Geological Society, London, 25, 45-57. Union, 39, 1076-84. BARR,D. 1985. 3-D Palinspastic restoration of normalfaults in theInner LEOPOLD,L. B. & WOLMAN, M.G. 1957. Riverchannel patternsbraided, Moray Firth: implications for extensional basin development. Earth and meanderingand straight. United States GeologicalSurvey Professional Planetary Science Letters, 75, 191-203. Paper, B2B, 39-85. BATEN, D.J..TREWIN, N. H. & TUDHOPE,A.W. 1986. The LINSLEY,P. N., POTTER,H. C., MCNAB, G. & RACHER,D. 1980. The Triassic-Jurassic junction at Golspie, Inner Moray Firth Basin. Scottish Beatrice field, Inner Moray Firth, U.K. North Sea. In: HALBOUTY,M. T. Journal of Geology, 22, 85-98. (ed.) Giant oil and gas fields ofthe decade 1968-1978. Memoir of the BENTON, M. J. & WALKER,A. D. 1985. Palaeoecology,taphonomy and American Association of Petroleum Geologists, 30, 117-29. dating of Permo-Triassic reptilesfrom Elgin, North-east Scotland. MCCLURE,H. A. 1978. Ar Rub’ AI Khali. In: AL-SAYARI,S. S. & ZOTL,J. Palaeontology, B,207-34. G. (eds) QuaternaryPeriod in Saudi Arabia, Vol. I. SpringerVerlag, BRAYSHAW,A. C. 1985. Bed microtopography and entrainment thresholds in Vienna, 252-63. gravel-bed rivers. Geological Society America Bulletin, %, 218-23. MCKEE, E. D., CROSBY,E. J. & BERRYHILL,H. L. 1967. Flooddeposits, BREED,C. S. & GROW,T. 1979. Morphologyand distribution of dunes in Bijou Creek, Colorado, June 1965. Journal of Sedimentary Petrology, 37, sand seas observed by remote sensing. In: MCKEE,E. D. (ed.) A study 829-51. of global sand seas. United States Geological Survey Professional Paper, MCQUILLIN,R., DONATO,J. & TULSTRUP,J. 1982. Development of basins in 1052, 253-302. the Inner Moray Firth and the NorthSea by crustal extension and dextral BRENNAND,P. T. 1975. The Triassic of the North Sea. In: WOODLAND, W.A. displacement of theGreat Glen Fault. Earth and Planetary Science (ed.) Petroleum and the Continental Shelfof North-westEurope. The Letters, 60, 127-39. Institute of Petroleum, London, 295-312. Moss, A. J. 1963. The physical nature of common sandy and pebbly deposits. BURKE,K. & DEWEY,J. F. 1973. Plume-generatedtriple junctions, key Part 11. American Journal of Science, 261, 297-343. indicators in applying plate tectonics to old rocks. Journal of Geology, PEACOCK,J. D. 1966. Contopedbeds in the Permo-Triassic aeolian 81, 406-34. sandstones of Morayshire. Bulletin of the Geological Survey of Great CARRUTHERS,A. 1987 Aeolian sedimentation from the Galtymore Formation Britain, 24, 157-62. (Devonian),Ireland. In: FROSTICK,L. E. & REID,1. (eds) Desert -, BERRIDGE, N. G., HARRIS, A. L.& MAY, F. 1968. The geology of the Sediments:Ancient and Modern. Special Publication of the Geological Elgin district. Memoir of the Geological Survey, Edinburgh. Society, London. 35, 250-67. READING,H. G., 1980. Characteristicsand recognition of strike-slipfault CLEMMENSEN,L. B. 1987. Complexstar dunes and associated aeolian systems. Special publication theof International Associationof bedforms,Hopeman Sandstone (Permo-Triassic), Moray Firth Basin, Sedimentologists, 4, 7-26. Scotland. In: FROSTICK, L. E. & REID. I. (eds) Desert Sediments: Ancient REID, I.& FROSTICK, L. E. 1985. Beach orientation, bar morphology and the and Modern. Special Publication of the Geological Society, London, 35, concentration of metalliferousplacer deposits: a case study,Lake 213-31. Turkana, N. Kenya. Journal of the GeologicalSociety, London, 142, DEEGAN,C.E. & SCULL.B. J. 1977. A standard lithostratigraphic 837-48. nomenclature for the central and northern North Sea. I.G.S.Report - & - 1986. Slopeprocesses, sediment derivation and landform 77/25, Norwegian Petroleum Directorate Bulletin 1. evolution in a rift valley basin, N Kenya. In: FROSTICK, L.E., RENAUT, FISHER,M. J. 1984. Triassic. In: GLENNIE.K. W. (ed.). Introduction to the R., REID, 1. & TIERcELIN, J. J. (eds) Sedimentation inthe African rifts. petroleumgeology of the North Sea. Blackwell Scientific Publications, Special publication of the Geological Society, London, 25, 99-111. Oxford. 85-101. -& -1987. Flow dynamics and suspended sediment properties in arid FROSTICK,L.E. & REID.I. 1977. The origin of horizontallaminae in zone flash floods. Hydrological Processes, l, 239-53. ephemeral stream channel-fill. Sedirnentology. 24, 1-9. ROE, S. L. & STEEL, R. J. 1985. Sedimentation,sea level changeand - & - 1979. Drainage-netcontrol of sedimentaryparameters in tectonicsatthe Triassic-Jurassic boundary(Statfjord Formation), sand-bedephemeral streams. In: PITTY, A.F. (ed.) Geographical TampenSpur, Northern North Sea. Journal of Petroleum Geology, 8, approaches to fluvial processes. Geoabstracts, Norwich, 173-201. 163-86. - & - 1980. Sorting mechanisms in coarse-grained alluvial sediments: ROSENDAHL,B. R. & LIVINGSTONE,D. A. 1983. Riftlakes of East Africa: freshevidence from a basalt plateaugravel, Kenya. Journal of the new seismic dataand implications forfuture research. Episodes, 83, Geological Society. London, 137, 431-41. 14-9. -& -1986. Evolution and sedimentary character of lake deltas fed by -, REYNOLDS,D. J., LORBER,P. M,, BURGESS,C. F., MCGILL,J., Sco-rr, ephemeral rivers in theLake Turkana Basin. In: FROSTICK,L. E., D., LAMBIASE,J. J. & DERKSEN,S. J. 1986. Structuralexpressions of RENAUT.R.. REID. 1. & TIERCELIN,J.J. (eds) Sedimentation inthe rifting: lessons fromLake Tanganika, Africa. In: FROSTICK,L. E., African Rifts. Special publication of the Geological Society, London, 25, RENAW,R., REID, I. & TIERCELIN,J. J.(eds) Sedimentation in 113-25. African Rifts. Special Publication of the Geological Society, London, 25, -& -1987~. Tectonic control of desert sediments in rift basins ancient 29-43. and modern. In: FROSTICK.L. E. & REID.1. (eds) Desert Sediments: SHAHJAHAN, M.1970. Factors controlling the geometry of fluvial meanders. Ancient and Modern. Special publication of the Geological Society, International Association of Scientific Hydrologists Bulletin, 15, 13-24. London. 35, 53-68. SUMMERFIELD,M. A. 1983. Geochemistry of weathering profile silcretes, -& - 19876. A new look at rifts. Geology Today, 3, 122-6. SouthernCape Province, South Africa. In: WILSON.R. C. L. (ed.) _-, & LAYMAN, J.T. 1983. Changing size distribution of suspended Residual deposits. Special Publication of the Geological Society, London, sediment in arid-zone flash floods. Special Publication of the Internationa[ 11, 167-78. Association of Sedimentologists, 6, 97-106. TROMMESTAD,K.E. 1982. Feltsrudium i den sydlige delen av det GIBES,A. D., 1983. Structural interpretation with emphasis on extensronal Permo-TriassiskeMoray Firth-Bassenget. Eksempler fluvial-,pa tectonics. JAPEC course notes, No. 18. Module 2. 131 pp. eolisk-og calichesedimenter. MSc thesis, University of Bergen. GIBES,A. D. 1984. Structural evolution of extensional basin margins. Journal WALKER, A. D. 1973. The age of theCutties Hillock Sandstone of the Geological Society, London. 141, 609-20. (Permo-Trias) of the Elgin area. Scottish Journal of Geology, 9, 177-83. GLENNIE.K. W. 1984. The structural framework and pre-Permian history of WARRINGTON, G., AUDLEY-CHARLES,M. G., ELLIOTT,R. E., EVANS, W. B., theNorth Sea area. In: GLENNIE.K. W.(ed.) Introduction to the IVIMEY-COOK, H. C.,KENT, P. E., ROBINSON,P. L., SHOTTON,F. W. & Petroleum Geology of the North Sen. Blackwell Scientific Publications, TAYLOR,F. M. 1980. A correlation of Triassic rocks in the British Isles. Oxford, 17-39. Special Report of the Geological Society of London 13, 78 pp. - & BULLER,A. T. 1983. ThePermian Weissliegend of North-west WHITEMAN,A., NAYLOR,D., PEGRUM, R. & REES, G. 1975. NorthSea Europe.The partial deformation of aeoliandune sands caused by the troughs and plate tectonics. Tectonophysics, 26, 39-54. Zechstein transgression. Sedimentary Geology, 35, 43-81. WILLIAMS,D. 1974. The sedimentology and petrology of the New Red

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/145/2/235/4889406/gsjgs.145.2.0235.pdf by guest on 23 September 2021 248 L. FROSTICK ET AL.

Sandtone of the Elgin Basin, North-east Scotland.PhD thesis, University London, 131-50. of Hull. -1981. Evolution of sedimentary basins in North-west Europe. In: ILUNG, WOOD,R. & BARTON, P. 1983. Crustal thinning and subsidence in the North L. V. & HOBSON,G. D. (eds) Petroleum Geology of the Continental Shelf Sea. Nature, Joz, 561. of North-west Europe. The Institute of Petroleum, London, 3-39. ZEIGLER,P. A. 1975. North Sea basin history in the tectonic framework of - 1982. GeologicalAtlas of Western and Central Europe. Elsevier, North-westernEurope. In: WOODLAND,A. W. (ed.) Petroleumand the Amsterdam. Continental Shelf of North-westEurope. The Institute of Petroleum, London, 131-50.

Received 6 March 1987; revised typescript accepted 24 June 1987.

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