Rhodolith-bearing limestones as transgressive marker beds: fossil and modern examples from North...

Rhodolith-bearing limestones as transgressive marker beds:fossil and modern examples from North Island, New Zealand

RONALD NALIN*1, CAMPBELL S. NELSON� , DANIELA BASSO� andFRANCESCO MASSARI**Dipartimento di Geoscienze, Universita di Padova, Via Giotto 1, 35137 Padova, Italy (E-mail:[email protected])�Department of Earth and Ocean Sciences, University of Waikato, Private Bag 3105, Hamilton, NewZealand�Dipartimento di Scienze Geologiche e Geotecnologie, Universita di Milano Bicocca, Piazza della Scienza4, 20126, Milano, Italy

ABSTRACT

Rhodoliths are nodular structures composed mainly of the superimposed thalli

of calcareous red algae. Because their development is controlled by an array of

ecological parameters, rhodoliths are a valuable source of

palaeoenvironmental information. However, despite their common use in

palaeoecological reconstructions, the stratigraphic significance of rhodolith

accumulations seldom has been addressed in detail. In a study of Cenozoic

rhodolith-bearing deposits from the North Island of New Zealand, rhodolithic

units, usually of limited lateral extent, typically occur above major

unconformities at the base of deepening upwards successions. Two types of

transgressive rhodolith-bearing deposits may be distinguished on the basis of

texture and rhodolith internal structure: (i) type A deposits are clast-supported

rhodolithic rudstones containing abundant pebbles and cobbles reworked from

the substrate, and are characterized by rhodoliths with a compact concentric to

columnar internal structure and a high nucleus to algal cover ratio; (ii) type B

deposits are rhodolithic floatstones with a matrix usually consisting of

bryozoan fragments, benthic foraminifera and echinoid fragments or

terrigenous silty fine sand. The rhodoliths of type B units usually have a

loose internal framework with irregular to branched crusts. The two

contrasting rhodolith-bearing units are interpreted as characteristic facies of

transgressive systems tract deposits, analogous to shell concentrations formed

under conditions of low net sedimentation. Type A deposits are correlated

with relatively high-energy settings and/or narrow submerged

palaeotopographic lows, whereas type B deposits are interpreted as forming

in lower-energy settings. The association between transgression and

development of rhodolithic facies is confirmed by observations of a modern

rhodolith production site at Whangaparaoa Peninsula in North Island, where

algal nodules grow above a ravinement surface cut during the Holocene sea-

level rise, and also by a review of published fossil examples, many of which

show stratigraphic and compositional attributes analogous to those of the New

Zealand occurrences. The review indicates that transgressive rhodolith

accumulations develop more commonly in, but are not restricted to, non-

tropical settings. It is suggested that a combination of factors, such as low net

sedimentary input, nature of the substrate, sea-level rise and inherited

1Present address: Geoscience Research Institute, 11060 Campus St, Loma Linda, CA 92350, USA.

Sedimentology (2007) doi: 10.1111/j.1365-3091.2007.00898.x

� 2007 The Authors. Journal compilation � 2007 International Association of Sedimentologists 1

physiography contribute to determine the relationship between rhodolith-

bearing deposits and transgressive settings.

Keywords Calcareous red algae, heterozoan carbonates, New Zealand, rho-doliths, shellbeds, transgressive systems tract.

INTRODUCTION

Rhodoliths are nodular structures composedmainly of the superimposed thalli of calcareousred algae. Other organisms, such as bryozoans,annelids and encrusting foraminifera may con-tribute to the growth of the nodules and skeletalfragments, as well as detrital material, are oftenincluded within them.

Rhodoliths are a valuable source of palaeoen-vironmental information because of their sensi-tivity to ecological dynamics. In fact, changes inthe taxonomical composition and internal struc-ture of rhodoliths are related closely to theconditions characterizing the depositional setting(Bosence, 1976,1983; Basso, 1998; Nebelsick &Bassi, 2000). An understanding of the signifi-cance of specific features in rhodoliths has beengained and greatly enhanced by studying modernoccurrences and their distribution (Bosellini &Ginsburg, 1971; Reid & Macintyre, 1988; Prager &Ginsburg, 1989; Tsuji, 1993; Basso & Tomaselli,1994; Lund et al., 2000). This actualisticapproach is the rationale for many palaeoecolog-ical interpretations of ancient rhodolith-bearingdeposits. Fossil examples, however, may in turncontribute to a more thorough comprehension ofthe ecology of algal nodules, providing a timeperspective unattainable from modern observa-tions. In particular, the application of a strati-graphic approach may outline potentialcorrelations between the development of rhodo-lithic limestones and specific segments of arelative sea-level change curve. Indeed, exami-nation of the rock record reveals that rhodolith-bearing facies often are found as the firstlithological unit above major unconformities.Such a consistent pattern suggests that variationof ecological parameters, caused by marine trans-gressions, may repeatedly create favourable con-ditions for the development of rhodolithic andred-algal-rich deposits.

After examining some Cenozoic examples ofrhodolithic limestones and a modern site of algalnodule production from the North Island of NewZealand (Fig. 1), this paper attempts to addressthe issue of what controls may account for therecurrent association between transgressive set-

tings and rhodolithic deposits. The emphasis ofthe present work is placed on fieldwork observa-tions, supplemented by thin section analysis ofmore than 200 samples.

ANCIENT RHODOLITH OCCURRENCES

This section describes Cenozoic occurrences ofrhodolith-bearing limestones from the Te KuitiGroup and Mahoenui Group in central westernNorth Island, and from the Takiritini formation atTinui in southeastern North Island (Fig. 1). Asummary of the general stratigraphic and litho-logical attributes of the limestones at these studysites is presented in Table 1.

Te Kuiti Group (Late Eocene–earliest Miocene,Bartonian-Aquitanian)

A succession of Upper Eocene to lowest Mio-cene mixed siliciclastic-carbonate rocks, up to350 m thick, is preserved in the South Auck-land region of central-western North Island,New Zealand. This succession is assigned to theTe Kuiti Group (Kear & Schofield, 1959; Nelson,1978) and rests unconformably on Mesozoicbasement rocks (Fig. 2). The formations in theTe Kuiti Group include basal non-marine coalmeasures and mudstones overlain by regionallywidespread marine deposits of calcareous mud-stones, calcareous sandstones and skeletal lime-stones, all variably glauconitic. The sedimentsaccumulated during an overall north to southsubmergence event over a shallow marine(<150 m depth), temperate latitude (cool-water)platform or seaway diversified by low topo-graphic relief in the Mesozoic basement rocks(Nelson et al., 1988; Anastas et al., 2006). Sev-eral of the formations in the Te Kuiti Groupmay be divided into cyclically arrangedsequences, usually displaying an upwards suc-cession of limestone, mudstone and sandstone.Rhodolith-bearing facies are not widespread inthe group, but are localized at particular strati-graphic horizons within the basal portions oflimestone units onlapping the Mesozoic base-ment rocks (Fig. 2).

2 R. Nalin et al.

� 2007 The Authors. Journal compilation � 2007 International Association of Sedimentologists, Sedimentology

https://www.researchgate.net/publication/223627203_Burial-dominated_cementation_in_non-tropical_carbonates_of_the_Oligocene_Te_Kuiti_Group_New_Zealand?el=1_x_8&enrichId=rgreq-2f56e7be-f364-422c-9bfb-4da8d231fa44&enrichSource=Y292ZXJQYWdlOzIyOTY4NDk4MTtBUzo5NzQ0MDg2Njc2Njg0OUAxNDAwMjQzMTIxNDI2

Rhodoliths of the Elgood Limestone(Early Oligocene, Rupelian)The Elgood limestone (Member) is the lowermostlimestone unit in the Te Kuiti Group, and isdeveloped best where it lies directly with majorerosional unconformity upon the Mesozoic base-ment rocks. Relief of the basal surface of the orderof several metres indicates the existence of anuneven palaeolandscape at the time of transgres-sion, and the limestone appears to have beenoften deposited in topographic depressions, lat-erally confined by prominent highs. The lime-stone has an average thickness of 6 to 10 m and,despite its limited and impersistent aerial distri-bution, is well-represented in the Te Kuiti Groupoutcrop area. Petrographically, the Elgood lime-stone consists of rhodolithic rudstone and grain-stone to packstone dominated by benthic

foraminifera and calcareous red algae, with addi-tional contributions from bryozoan, and occa-sionally echinoid, bivalve and brachiopodfragments. Some specific examples of Elgoodlimestone rhodolith occurrences are as follows.

1. Te Anga – A rhodolith-rich unit resting onbasement rocks is well-exposed along a hill flanknear Te Anga (Fig. 3, Table 1). The unit forms aflattened lens about 200 m across that graduallythins from 7 m in its central portion to practicallyzero at its margins. The markedly lensoidal shaperesults from the original confined deposition in ashallow depression of the basement substrate. An80 cm thick conglomerate, consisting of basementclasts locally with cobbles and boulders up to70 cm in size, overlies the basal unconformityand grades upsection into a strongly cemented

Fig. 1. Location of rhodolith-bearing units studied in this work, and some other New Zealand occurrences noted inthe literature (see Table 3). Map on right-hand side is an enlargement of the rectangular area on the New Zealandmap, and illustrates more closely the location of studied sections within the Te Kuiti and Mahoenui Groups.

Transgressive rhodolithic deposits 3


Table

1.

Str

ati

gra

ph

ican

dli

tholo

gic

al

att

ribu

tes

of

stu

die

drh

od

oli

th-b

eari

ng

un

its.

Locali

ty

Gri

dre

fere

nce

from

NZ

Top

oM

ap

Seri

es

260

1:5

0000

Str

ati

gra

ph

icu

nit

Age

Th

ickn

ess

of

basa

lrh

od

oli

th-

beari

ng

un

it

Tota

lth

ickn

ess

of

sequ

en

ce

Geom

etr

yof

basa

lrh

od

oli

th-

beari

ng

un

itP

etr

ogra

ph

icatt

ribu

tes

of

basa

lrh

od

oli

thic

un

it

Typ

eof

rhod

oli

thic

un

it

Te

An

ga

R16/6

89241

Elg

ood

Lim

est

on

eE

arl

yO

ligocen

e5

m67

mL

en

soid

al,

infi

llin

gd

ep

ress

ion

200

macro

ss

Rh

od

oli

thic

floats

ton

e,

matr

ixof

mic

riti

cm

ud

wit

hsc

att

ere

dp

lan

kto

nic

fora

min

fera

an

dfi

ne

bio

cla

stic

debri

sor,

alt

ern

ati

vely

,m

atr

ixof

poorl

yso

rted

packst

on

econ

sist

ing

of

red

alg

al,

ech

inoid

,an

dbry

ozoan

fragm

en

ts,

an

dli

thic

cla

sts

an

dben

thic

fora

min

ifera

.G

lau

con

ycon

ten

tu

pto

5%

.

B

Waik

are

tuR

13/6

92041

Elg

ood

Lim

est

on

eE

arl

yO

ligocen

e�

1m

Not

measu

red

Tabu

lar

Rh

od

oli

thic

rud

ston

eto

floats

ton

e,

matr

ixis

ap

ackst

on

eof

larg

er

ben

thic

fora

min

ifera

(Am

ph

iste

gin

a,

Op

erc

uli

na,

Hete

rost

egin

aan

dra

reN

um

mu

lite

s),

bry

ozoan

s,ech

inod

erm

an

dre

dalg

al

fragm

en

ts,

an

dabu

nd

an

tbase

men

tcla

sts;

matr

ixis

mod

era

tely

sort

ed

wit

hro

un

ded

gra

ins.

Gla

ucon

ycon

ten

tu

pto

5%

.

Inte

rmed

iate

Aote

aH

arb

ou

rR

15/7

68584

Elg

ood

Lim

est

on

eE

arl

yO

ligocen

e0Æ5

m56

mL

en

ticu

lar,

infi

llin

gre

lief

of

the

basa

lsu

rface,

10

macro

ss

Cla

st-s

up

port

ed

rhod

oli

th-b

eari

ng

con

glo

mera

te.

Matr

ixis

poorl

yso

rted

are

nit

e,

bio

cla

stcon

ten

tu

pto

30%

(red

alg

al

fragm

en

tsan

dben

thic

fora

min

ifera

).G

lau

con

ycon

ten

tu

pto

15%

.

A

Mair

oa

R16/8

25108

Aw

aro

aL

imest

on

eE

arl

yO

ligocen

e1Æ5

m3Æ7

5m

Len

soid

al,

infi

llin

gd

ep

ress

ion

200

macro

ss

Rh

od

oli

th-b

eari

ng

cla

st-s

up

port

ed

con

glo

mera

te.

Matr

ixis

poorl

yso

rted

are

nit

e,

wit

hcon

ten

tof

bio

cla

stic

gra

ins

(Am

ph

iste

gin

a,

small

rota

lifo

rmfo

ram

inif

era

,re

dalg

al,

bry

ozoan

,biv

alv

ean

dech

inoid

fragm

en

ts)

up

to20

to40%

.G

lau

con

ycon

ten

tu

pto

5%

.

A

4 R. Nalin et al.


Table

1.

(Con

tin

ued

)

Hon

ikiw

iS

16/9

68374

Waim

ai

Lim

est

on

eE

arl

yO

ligocen

e3Æ8

m22

mF

an

-lik

e,

pro

bably

infi

llin

gd

ep

ress

ion

Cla

st-s

up

port

ed

rhod

oli

th-b

eari

ng

con

glo

mera

te,

inte

rlayere

dw

ith

mod

era

tely

sort

ed

calc

are

nit

ew

ith

bio

cla

sts

con

sist

ing

of

larg

er

ben

thic

fora

min

ifera

(Am

ph

iste

gin

a,

Op

erc

uli

na,

Hete

rost

egin

aan

dra

reA

lveoli

nid

ae),

small

rota

lifo

rmfo

ram

inif

era

,re

dalg

al,

biv

alv

e,

bry

ozoan

an

dech

inoid

fragm

en

ts.

No

gla

ucon

y.

A

Pio

pio

R17/8

45005

Oto

roh

an

ga

Lim

est

on

eE

arl

iest

Mio

cen

e0Æ8

mN

ot

measu

red

Tabu

lar

Matr

ix-s

up

port

ed

rhod

oli

th-b

eari

ng

bre

ccia

.M

atr

ixis

aw

ackest

on

ew

ith

poorl

yso

rted

an

dw

ell

-rou

nd

ed

bry

ozoan

,biv

alv

ean

dech

inoid

fragm

en

tsd

isp

ers

ed

inm

icri

tic

matr

ix.

No

gla

ucon

y.

Inte

rmed

iate

Aw

akau

Road

R18/5

90793

Aw

akin

oL

imest

on

eE

arl

yM

iocen

e7

mN

ot

measu

red

Tabu

lar

Rh

od

oli

thic

floats

ton

e.

Matr

ixis

mod

era

tely

sort

ed

packst

on

e,

con

sist

ing

of

ben

thic

fora

min

ifera

(Am

ph

iste

gin

a,

Lep

idocycli

nae,

porc

ela

neou

san

dagglu

tin

ate

dfo

rms)

,bry

ozoan

s,re

dalg

al,

ech

inoid

,an

dm

oll

usc

fragm

en

ts,

silt

-siz

ed

sili

cic

last

icgra

ins,

an

dp

lan

kto

nic

fora

min

ifera

.N

ogla

ucon

y.

B

Taip

o,

Tin

ui

U26/7

62391

Takir

itin

iF

orm

ati

on

Late

Earl

yM

iocen

e3

mA

tle

ast

33

mT

abu

lar

Well

rou

nd

ed

an

dm

od

era

tely

sort

ed

packst

on

e,

con

sist

ing

of

red

alg

al

fragm

en

tsan

dben

thic

fora

min

ifera

wit

hsu

bord

inate

biv

alv

e,

bry

ozoan

an

dech

inoid

fragm

en

ts.

Gla

ucon

yra

reto

abse

nt.

A

Wh

an

gap

ara

oa

Pen

insu

laR

10/7

31104

–R

ecen

tU

pto

0Æ3

m–

Infi

llin

gn

arr

ow

ch

an

nels

(0Æ5

to2

mw

ide)

an

dd

ep

ress

ion

su

pto

10

macro

ss

Rh

od

oli

th-b

eari

ng

poorl

yso

rted

san

dy

top

ebbly

sed

imen

t,ri

ch

inbio

cla

stic

debri

s(m

ain

lybiv

alv

es,

bry

ozoan

san

dech

inoid

fragm

en

ts).

A



rhodolithic floatstone to rudstone, also compris-ing scattered basement clasts up to 6 cm in sizeand rare bivalve shells, with a matrix of calcare-ous silty sandstone. A 50 cm thick bed of silt-stone containing sparse large (ca 5Æ5 cm)rhodoliths occurs approximately at the middle ofthe unit. The portion of the limestone above thesiltstone bed is characterized by millimetre tocentimetre-scale sub-horizontal flagginess,whereas the portion above has a massiveappearance (Fig. 3). This basal rhodolithic unit isoverlain abruptly, but conformably, by siltstonesof the Dunphail Siltstone Member.

2. Waikaretu – A basal rhodolithic unit isexposed along Waikaretu Valley Road (Fig. 3,Table 1). The contact with the underlying base-ment rocks is not seen, but the latter are visible inplace about a metre below the road surface. Therhodolithic unit consists of a 70 cm thick tabularbed with good lateral continuity, composed ofpebble-size to cobble-size rhodoliths immersed ina sandy to silty matrix. Lithologically the unit is arhodolithic rudstone to floatstone. Rare Ostreashells and scattered well-rounded pebbles ofbasement rocks, up to 3 cm in size, are alsopresent and are, at times, encrusted by bryozoans.Crude horizontal bedding results from the pref-

erential arrangement of elongated clasts and rho-doliths. The basal rhodolithic layer isgradationally overlain by 7 m of horizontallybedded, benthic foraminiferal-bryozoan-red algalgrainstones and packstones that pass abruptlyinto the siltstone of the Dunphail SiltstoneMember.

3. Aotea Harbour – A rhodolithic unit of lim-ited lateral extent, overlying basement rocks,occurs at Aotea Harbour (Fig. 3, Table 1). Thisunit infills a lenticular depression about 60 cmdeep and 10 m across resulting from the irregularrelief of the erosional unconformity upon theunderlying basement rocks (Fig. 4). The rhodo-liths in the unit are part of a very poorly sortedbasal conglomerate, mainly consisting of well-rounded, highly elongated to subspherical base-ment clasts ranging from a few millimetres to 8 to10 cm in size. Intensive bioerosion is character-istic on the external surface of the larger pebbles.The conglomerate has a clast-supported textureand its matrix is also poorly sorted, consistingmainly of fine sand and silt particles. No sedi-mentary structures are evident, apart from crudehorizontal bedding. The coarse rhodolithic con-glomerate is overlain by ca 2Æ5 m of poorly sortedgravelly sandstone without traces of stratification,

Fig. 2. Schematic chronostratigraphic classification of the Te Kuiti Group (as modified from White & Waterhouse,1993), showing major depositional sequences and formation names, generalized lateral facies changes and thelocations of rhodolith-bearing units wherever marine sequences onlap directly upon Mesozoic basement rocks.Examples from each of the stratigraphic intervals labelled as rhodolith occurrences are described in the text. Notethat a single major basement high is shown for cartographic convenience only and that, in reality, basementpalaeorelief was quite varied throughout the Te Kuiti Group depocentre and, depending on elevation, was coveredlocally by different formations of the group (Nelson, 1978; Anastas et al., 2006). Rhodolithic limestone also occursat the base of the overlying Mahoenui Group where it rests unconformably on the basement or the Te Kuiti Grouprocks.

6 R. Nalin et al.


Fig

.3.

Deta

iled

stra

tigra

ph

iclo

gs

of

secti

on

sm

easu

red

from

Te

Ku

iti

an

dM

ah

oen

ui

Gro

up

san

dd

iscu

ssed

inth

ete

xt;

f,fi

ne;m

,m

ed

ium

;c,

coars

e;

gr,

gra

vel;

pb,

pebble

;cb,

cobble

.



mainly consisting of basement-derived clasts andsubordinate bioclasts. The gravelly sandstone isgradationally overlain by siltstones of the Dunp-hail Siltstone Member.

Rhodoliths of the Awaroa Limestone(Early Oligocene, Rupelian)The Awaroa limestone (Member) is a locallydeveloped shallow marine facies at the base ofthe calcareous mudstone dominated sequence 3of the Whaingaroa formation (Fig. 2) (White &Waterhouse, 1993). The example described hereoccurs at Mairoa, where a basal cobbly unit, richin rhodoliths and algal-encrusted pebbles, restson Mesozoic basement (Fig. 3, Table 1) and islaterally traceable for about 200 m. The unit isfound in a mild depression between two base-ment highs and its thickness decreases laterallyfrom about 1Æ5 m in the centre to zero at theextremities. This unit consists of a pebble tocobble clast-supported conglomerate, with rareboulders up to 30 cm in size, and is rich inrhodoliths and algal-encrusted clasts. The peb-bles and cobbles are derived from the basementand generally are moderately rounded. Themajority of elongated clasts are disposed in asub-horizontal position. Despite the massiveappearance of the unit, at least three normallygraded beds may be distinguished within it. Theconglomerate unit grades upwards into a pebblycalcareous sandstone, enriched in rounded base-ment pebbles up to 3 cm in size. Two additionalconglomerate layers, several centimetres thickwith cobbles up to 6 cm in size, are interbedded

within the calcareous sandstone but a clearoverall fining upwards trend occurs upsection,where the calcareous sandstone grades into anextensively bioturbated fine glauconitic sand-stone.

Rhodoliths of the Waimai Limestone(Early Oligocene, Rupelian)A 6 m thick unit of rhodolith-bearing conglomer-ate and calcareous sandstone, a correlative of theWaimai limestone (Member) at the base of theAotea formation (Fig. 2; White & Waterhouse,1993), is exposed for some 80 m near Honikiwi(Fig. 3, Table 1). Here the unit rests on Meso-zoic basement and is overlain, via an abruptlygradational contact, by a thick succession ofsandy mudstone. Poor exposure of the basalcontact with Mesozoic rocks hampers clear recon-struction of the geometry of the sedimentarybody. Nevertheless, the dip of the rhodolith-bearing beds decreases progressively upsection,away from a nearby basement high. This arrange-ment suggests that the deposits represent afan-like body infilling a shallow topographicdepression. The first bed of the basal unit is aclast-supported pebble to cobble conglomerate,about 2 m thick, with basement clasts up to 15 cmin size, variably rounded and moderately sorted.The majority of the clasts are coated by algallaminae, with an average ratio of algal cover tonucleus around 0Æ5. The conglomerate has amassive appearance, but the longer axis of elon-gated pebbles and cobbles is generally orientedparallel to the stratification. A tabular bed 90 cm

Fig. 4. Elgood limestone correlativeat Aotea Harbour section (Table 1).Irregular contact (marked by whiteline) between Mesozoic basementand overlying rhodolithic unitwhich grades upwards into poorlysorted gravelly sandstone (hammerfor scale is 33 cm long).

8 R. Nalin et al.


thick of pebbly calcareous sandstone overlies theconglomerate unit with a sharp planar contact.The majority of larger pebbles in the calcareoussandstone consist of basement clasts, but somescattered rhodoliths also are present. This unitshows well-defined horizontal bedding (Fig. 5).Several tabular normally graded conglomeratelayers, from 5 to 60 cm thick, are interbeddedwithin the calcareous sandstone. These layersmay contain basement pebbles up to 12 cm insize. The clasts are mainly rounded and, ifelongated, are characteristically disposed withtheir longer axes parallel to the plane of stratifi-cation. Despite these conglomerate intercalations,the calcareous sandstone unit shows an overalldecrease in grain size upsection, finally gradinginto the overlying sandy mudstone.

Rhodoliths of the Otorohanga Limestone(earliest Miocene, Aquitanian)The Otorohanga limestone is the uppermostformation of the Te Kuiti Group (Fig. 2). Typi-cally, the Otorohanga limestone directly overlies

other Te Kuiti Group formations and may attain athickness of several tens of metres. In some areas,however, structural basement highs, that hadremained subaerially exposed during depositionof earlier Te Kuiti Group formations, weresubmerged for the first time during Otorohangalimestone deposition. As a result, the Otorohangalimestone can onlap and thin onto basementhighs, especially in the vicinity of Piopio, whererhodoliths occur in basal breccias up to about 1 mthick (Figs 3 and 6; Table 1). The breccias consistof basement-derived clasts, with boulders up to50 cm in size, floating in a skeletal packstone richin bioclasts and scattered rhodoliths. The base-ment clasts are very angular to sub-rounded, maybe intensely bioeroded, and are commonlyencrusted by moderately developed algal coat-ings. The bioclasts are dominated by bryozoanfragments, but bivalve shells and well-roundedalgal fragments are also well-represented. Thebreccia is overlain gradationally by a 1 m thickbryozoan grainstone, almost entirely consisting ofwell-rounded fragments of bryozoan colonies,

Fig. 5. Waimai limestone correla-tive at Honikiwi section (Table 1).This rhodolith-bearing unit repre-sents a fan-like infill of a shallowtopographic depression in the base-ment. Backpack circled for scale is56 cm long.

Fig. 6. Near Piopio (Table 1), theOtorohanga limestone rests directlywith angular unconformity onMesozoic basement rocks. Personcircled for scale is 185 cm tall.



with an average size of 4 mm. The bioclasts arewell sorted and evidently are arranged in a planarhorizontal stratification. The bryozoan grainstonegrades into a thin unit of fine glauconitic sand-stone. The succession is capped conformably byupper-slope mudstone of the Mahoenui Group(see next section) for a thickness of several tens ofmetres.

Mahoenui Group (Early Miocene, Aquitanian-Burdigalian)

In the central-western portion of North Island, asuccession of Lower Miocene massive mudstoneand flysch deposits up to 1100 m thick representsthe next stratigraphic unit above the Te KuitiGroup. The unit has been named the MahoenuiGroup (Nelson & Hume, 1977) and records a rapiddeepening of the basin after the deposition of theuppermost Te Kuiti Group formation (Otorohangalimestone). The rapid onset of dramatic subsi-dence was the response to a prominent phase ofcrustal shortening linked to the evolution of theAustralia-Pacific plate boundary through the NewZealand subcontinent during Early Miocenetimes (Kamp et al., 2004).

Although a distinctive change of facies com-monly marks the initiation of this deepeningphase, the contact between the Te Kuiti Groupand the Mahoenui Group most often is conform-able, especially towards the south of the outcroparea (Nelson, 1978). However, in the proximityof the basin edges, the base of the MahoenuiGroup may rest unconformably on the basementand Te Kuiti Group rocks. Here, the highlyirregular and channellized nature of the contactimplies a phase of significant subaerial exposurebefore the deposition of the Mahoenui Group(Nelson et al., 1994). In these marginal settings,a rhodolithic limestone, named Awakino lime-stone, is found occasionally above the basalunconformity. The Awakino limestone is wellexposed at Awakau Road, where it overlies themarl of the Dunphail Siltstone Member (Te KuitiGroup) with an unconformity resulting from theerosion of all the upper formations of the TeKuiti Group (Fig. 3, Table 1). The unconformityis roughly planar, with a relief of several deci-metres. The limestone has a thickness of about7Æ5 m and its first 2Æ5 m consist of a basal matrix-supported breccia, with angular boulders up to80 cm in size. The clasts are basement-derivedand are characterized by poor sorting and anabsence of preferential arrangement. This basalunit shows a tabular geometry for the whole

extension of the outcrop of about 100 m. Atabular geometry is displayed also by the upperunit of the limestone, where rhodoliths occurfloating in a limestone matrix rich in largerbenthic foraminifera (mainly Amphistegina,Table 1). No sedimentary structures are evident,apart from crude horizontal bedding. A 50 cmthick layer of matrix-supported conglomerate,with basement clasts up to 40 cm in size, isinterbedded in the upper part of the rhodolithiclimestone. Upsection, the Awakino limestonebecomes markedly enriched in fine terrigenousmaterial and this compositional variation marksthe conformable transition into the overlyingthick mudstone.

Takiritini Formation (late Early Miocene,Burdigalian)

The Takiritini Formation is a succession oflimestone and silty sandstone deposited in rel-atively shallow water, and is now exposed in theTinui district in south-eastern North Island(Fig. 1). The Takiritini Formation is of EarlyMiocene age and may attain a thickness of600 m. This formation unconformably overliesupper slope mudstone and turbiditic gradedbeds of the Whakataki Formation, and theunconformity is well-exposed at Taipo. Here,the basal unit of the Takiritini Formation is analgal-rich limestone about 3 m thick, with tabu-lar geometry and good lateral continuity (Fig. 7,Table 1). The contact with the underlyingWhakataki Formation is broadly planar, withminor relief of several tens of decimetres. Thelimestone is texturally a grainstone to packstone,consisting mainly of larger benthic foraminifera,well-rounded algal fragments and subordinatebivalve fragments. The skeletal grains averageabout 2 mm in size and are well sorted. Smallrhodoliths up to 3 cm in size are scatteredwithin the bioclastic matrix, although theyappear to be more concentrated in the lowerportion of the unit. No sedimentary structuresare evident and the limestone has a massive tovaguely horizontally bedded appearance. Asudden increase in fine micritic matrix in theuppermost 10 cm of the basal limestone marksan abruptly gradational transition into the over-lying monotonous succession of silty sandstone.The sandstone is several tens of metres thick,and preserves horizontal bedding with beds 50to 70 cm thick. The sandstone also is character-ized by intense bioturbation and the presence ofsparse centimetre-thick shell concentrations.

10 R. Nalin et al.


https://www.researchgate.net/publication/240512296_Sedimentology_and_petrography_of_mass-emplaced_limestone_Orahiri_Limestone_on_a_late_Oligocene_shelf_western_North_Island_and_tectonic_implications_for_eastern_margin_development_of_Taranaki_Basin?el=1_x_8&enrichId=rgreq-2f56e7be-f364-422c-9bfb-4da8d231fa44&enrichSource=Y292ZXJQYWdlOzIyOTY4NDk4MTtBUzo5NzQ0MDg2Njc2Njg0OUAxNDAwMjQzMTIxNDI2

https://www.researchgate.net/publication/254286006_Relative_intensity_of_tectonic_events_revealed_by_the_Tertiary_sedimentary_record_in_the_North_Wanganui_Basin_and_adjacent_areas_New_Zealand?el=1_x_8&enrichId=rgreq-2f56e7be-f364-422c-9bfb-4da8d231fa44&enrichSource=Y292ZXJQYWdlOzIyOTY4NDk4MTtBUzo5NzQ0MDg2Njc2Njg0OUAxNDAwMjQzMTIxNDI2

MODERN RHODOLITHS ATWHANGAPARAOA PENINSULA

A modern rhodolith production site, at Whanga-paraoa Peninsula in North Island (Fig. 1), wasstudied to complement information obtainedfrom the ancient rhodolith occurrences. TheWhangaparaoa Peninsula is located on the east

coast of North Island, north of Auckland, at36�36¢S (Fig. 1). The peninsula is characterizedby a cliffed coast, connected to a modern marineabrasion platform cut into flysch deposits of theEarly Miocene Waitemata Group (Ballance,1974). In the Hauraki Gulf, where the Whanga-paraoa Peninsula protrudes, water salinityranges between 34Æ5& and 35Æ7& (Black et al.,

Fig. 7. Tinui section (Table 1). Analgal-rich limestone about 3 m thickrests with an angular unconformityon graded beds of the WhakatakiFormation, and grades upwardsquite abruptly (dashed line) intosilty sandstones. Hammer circled forscale is 33 cm long.

Fig. 8. Whangaparaoa Peninsula site (Table 1). View of abrasion platform cut across mass flow deposits of the EarlyMiocene Waitemata Group. The backing coastal cliffs expose the dominant flysch deposits of the group, whereas theproduction sites of the modern rhodoliths (arrowed channels and pools) occur within the more competent interbedsof volcaniclastic bouldery (basaltic) grit deposits which impart a much more irregular and locally upstanding relief tothe outer portion of the intertidal platform at this location. Ellipse encircles backpack 50 cm long for scale.



2000), sea-surface temperature (SST) shows a 20-year mean value of 17Æ1 ± 3Æ3 �C with the highesttemperatures in February and the lowest inAugust (Bell & Goring, 1998). The mean tidalrange is 2Æ18 m. The Whangaparaoa Peninsula isthe only known site in North Island wheremodern rhodoliths are growing in subtidal tointertidal settings.

The production site is localized in the transi-tional area between open sea and emerged abra-sion platform at low tide, for a linear distanceparallel to the coastline of about 300 m (Fig. 8,Table 1). Here, the shore platform is dissected byseveral narrow (0Æ5 to 2 m wide) channels, inter-connecting small pools, up to 10 m in diameter,carved in the rocky substrate. At low tide thechannels are still covered by 30 to 50 cm of waterand moderate drainage between pools is observedeven at slack tide. This very limited productionarea coincides with the occurrence of a competentand thick volcaniclastic (basaltic) debris flow(Parnell Grit) unit within the bedded flysch ofthe Waitemata Group (Allen, 2004). Living rho-doliths develop in the pools and channels carvedin the substrate, half buried in a poorly sortedsandy to pebbly sediment rich in bioclastic debrisand abraded mollusc shells. The rhodoliths areabundant and commonly closely spaced, with anaverage percentage of bottom coverage of 40%.Dead rhodoliths and large pebbles also occur nearthe production site on the exposed abrasionplatform at low tide, concentrated in troughs andon the landward continuation of the narrowchannels (Fig. 9). These accumulations clearlyindicate the existence of recurrent hydrodynamic

conditions sufficient to transport and move eventhe larger rhodoliths. Interestingly, the red-col-oured living thalli are at times located on theburied side of the rhodolith, and this could beinterpreted as evidence of displacement coupledwith the effect of pigment degradation caused bythe direct sunlight and periodical emersion. Incip-ient encrustation by red algae and bryozoans alsois observed often on the surface of larger pebbles.

GENERAL CHARACTERISTICS OF THERHODOLITH-BEARING UNITS

A remarkable pattern of consistency emerges fromthe study of the described rhodolithic units,despite their variable distribution in space andtime.

1. The rhodolithic units are always found directlyabove a major unconformity; this is also true for themodern rhodoliths of the Whangaparaoa Peninsula,which accumulate above a ravinement surface cutduring the Holocene transgression. Interestingly,the substrate below the unconformity always con-sists of hard basement rocks that typically, if erodedand reworked during transgressions, generate peb-bly tocobbly basal lags.Where the substrateconsistsof softer lithologies, the rhodoliths still encrustbasement pebbles derived from nearby sources(e.g. Awakino Limestone) or are less developed andscattered in a bioclastic matrix (TakiritiniFormation).

2. The rhodolithic units are usually overlain byfacies indicative of middle shelf to upper slope

Fig. 9. Dead rhodoliths and sub-strate pebbles hydrodynamicallyconcentrated in small depressionsof the substrate on an exposed mar-ine abrasion platform at low tide atWhangaparaoa Peninsula. Hammerfor scale is 35 cm long.

12 R. Nalin et al.


https://www.researchgate.net/publication/254287028_The_Parnell_Grit_beds_revisited_Are_they_all_the_products_of_sector_collapse_of_western_subaerial_volcanoes_of_the_Northland_Volcanic_Arc?el=1_x_8&enrichId=rgreq-2f56e7be-f364-422c-9bfb-4da8d231fa44&enrichSource=Y292ZXJQYWdlOzIyOTY4NDk4MTtBUzo5NzQ0MDg2Njc2Njg0OUAxNDAwMjQzMTIxNDI2

settings, generally mudstone enriched in terrige-nous material.

3. A common feature of the rhodolithic units istheir limited lateral extent, with linear lateraltraceability in outcrop, always less than 1 km.Limited aerial distribution characterizes also themodern rhodoliths of the Whangaparaoa Penin-sula, where the production site is much localized.In most of the studied examples the thickness ofthe rhodolithic limestone is usually modestcompared with the overall thickness of the suc-cession. Some of the rhodolithic units (e.g.Te Anga and Mairoa) clearly have been depositedin shallow erosional depressions within the sub-strate, but others display a rather tabular geome-try and no indication of having been depositedbetween prominent highs.

4. Regardless of age and locality, the studiedrhodoliths are intensely bioeroded. Diffuse boringtraces of different sizes indicate the activity ofboth microborers and macroborers such as endo-lithic cyanobacteria, clionid sponges and boringbivalves. At times, single bioerosion holes cuttingthrough both the algal cover and the nucleus areobserved. When present, bioclastic rhodolithnuclei generally are heavily bored.

5. Glaucony is common in most of the exam-ined sections (with the exception of Honikiwi,Piopio and Awakau Road), both as infill of intra-skeletal porosity (i.e. chambers of foraminiferaltests) and as pellets. The total percentage ofglaucony in the collected samples is never higherthan 15%.

6. Apart from the rhodoliths, bryozoans andlarger benthic foraminifera are the dominantbioclastic constituents of all the examined lime-stones, with additional contributions from echi-noderms, bivalve molluscs, smaller benthic andplanktonic foraminifera, barnacles and brachio-pods. Such a skeletal composition implies thatthe studied deposits are Heterozoan carbonates(sensu James, 1997).

DISTINCTION OF TYPES A AND BRHODOLITHIC UNITS

The rhodolithic units, notwithstanding the manyshared characteristics, still can be divided intotwo distinct types, A and B, on the basis ofdifferences in rhodolith internal structure andcomposition (Table 2) and in texture of therhodolith-bearing lithology.

Type A is generally a clast-supported conglom-erate, with rhodoliths and lithic clasts equally

represented. Rhodoliths of this first type usuallyencrust a clastic nucleus and algal materialaccounts for about 20 to 60% of the rhodoliths.The internal arrangement of the algal laminaepredominantly results in a concentric to colum-nar very dense framework (Fig. 10).

Type B is a rhodolithic floatstone, with rela-tively large rhodoliths up to 10 cm in sizeimmersed in a bioclastic matrix. These rhodolithsgenerally have a columnar to branched structure,and lack a clastic nucleus; they are characterizedby a rather loose framework, rich in internal finematrix trapped between the algal thalli andinfilling bioerosional cavities. Bryozoans, serpu-lids and encrusting foraminifera may be signifi-cant contributors to the growth of this secondtype of rhodolith (Fig. 11).

The algal flora is represented by taxa of subfam-ilies Melobesioideae Bizzozero, 1885 (Mesophyl-lum, Lithothamnion), Mastophoroideae Setchell,1943 (Lithoporella, Spongites), and Lithophylloi-deae Setchell, 1943 (?Lithophyllum), family Sporo-lithaceae Verheij, 1993 (Sporolithon), and thepeyssonneliacean alga Peyssonnelia. Althoughsome genera (like Mesophyllum) are almost ubiq-uitous and others (such as Lithoporella and Peys-sonnelia) do not show a preferential distributionin the two unit types, melobesioids consistentlydominate in rhodoliths of type B units but may beabsent in those of type A, whereas Spongites isonly found in rhodoliths of type A units.

The two described types of rhodolithic unitsshould be considered more as end members of aspectrum of possibilities rather than as mutuallyexclusive categories, because they may at timescontain rhodoliths of both types A and B or haveintermediate features.

DISCUSSION

In this section transgressive rhodolithic units arediscussed as analogous to shell concentrationsand a literature review is presented to documenttheir wide geographic and recurrent stratigraphicdistribution. Factors controlling the genesis ofthese units and occurrence in tropical versus non-tropical carbonate deposits are also addressed.

Rhodolithic deposits as analogues of shellconcentrations

Shell concentrations are defined generally asdensely packed accumulations of ‘biomineralizedremains ‡2 mm in size from any invertebrate



Table

2.

Gen

era

latt

ribu

tes

of

rhod

oli

ths

sam

ple

dfr

om

stu

die

du

nit

s.

Locali

ty

Rh

od

oli

thavera

ge

size*

Rh

od

oli

thavera

ge

shap

eN

ucle

us

Alg

al

cover

ton

ucle

us

rati

oIn

tern

al

stru

ctu

reM

atr

ixcon

ten

tB

ioero

sion

Asy

mm

etr

yA

lgal

gen

era

�

Te

An

ga

5Æ5

cm

(n¼

25)

Ell

ipso

idal

toir

regu

lar

Bio

cla

st(�

50%

)or

no

nu

cle

us

‡0Æ7

5M

ed

ium

den

sity

boxw

ork

,in

tern

al

layers

irre

gu

lar

con

cen

tric

tofr

uti

cose

,exte

rnal

layers

lam

inar

tocolu

mn

ar

Hig

hto

med

ium

,in

terl

am

inar

an

din

fill

ing

of

bio

ero

sion

Med

ium

den

sity

,m

ed

ium

an

dla

rge-s

cale

Mod

era

tely

pre

sen

tM

eso

ph

yll

um

,Lit

hoth

am

nio

n,

?Lit

hop

hyll

um

,P

eyss

on

neli

a,

Lit

hop

ore

lla

Waik

are

tu4Æ3

cm

(n¼

11)

Ell

ipso

idal

tosp

heri

cal

Abse

nt,

rare

lybio

cla

st�

1C

om

pact,

con

cen

tric

,p

ass

ing

toexte

rnal

colu

mn

ar

pro

tubera

nces

Low

toabse

nt,

infi

llin

gof

bio

ero

sion

an

dth

inin

terl

am

inar

layers

Low

tom

ed

ium

den

sity

,m

ed

ium

an

dla

rge-s

cale

Rare

,at

tim

es

con

fin

ed

toin

tern

al

layers

Meso

ph

yll

um

,S

poro

lith

on

,?L

ith

op

hyll

um

,P

eyss

on

neli

a,

Lit

hop

ore

lla

Aote

aH

arb

ou

r4Æ6

cm

(n¼

10)

Ell

ipso

idal

tod

iscoid

al,

oft

en

con

troll

ed

by

nu

cle

us

shap

e

Base

men

tcla

st(�

50%

)or

no

nu

cle

us

Vari

able

from

0Æ1

to1,

avera

ge

0Æ4

Com

pact,

con

cen

tric

,th

inir

regu

lar

lam

inae,

som

eti

mes

pro

tubera

nt

tow

ard

sth

eexte

rnal

layer

Low

toabse

nt

Med

ium

toh

igh

den

sity

,all

sizes

Rare

Lit

hoth

am

nio

n,

Meso

ph

yll

um

Mair

oa

4Æ7

cm

(n¼

14)

Ell

ipso

idal

tod

iscoid

al,

gen

era

lly

nu

cle

us-

con

troll

ed

Base

men

tcla

st(>

50%

)or

bio

cla

st

Vari

able

from

0Æ1

to0Æ9

,avera

ge

0Æ6

Com

pact,

con

cen

tric

tocolu

mn

ar

gro

wth

wit

hso

me

rare

pro

tubera

nces

Non

eto

low

,bio

ero

sion

infi

llin

g

Hig

hto

med

ium

den

sity

,m

ed

ium

an

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cale

Rare

an

dw

eak

Meso

ph

yll

um

,S

poro

lith

on

,P

eyss

on

neli

a,

?Lit

hop

hyll

um

,Lit

hoth

am

nio

n

Hon

ikiw

i6Æ0

cm

(n¼

13)

Ell

ipso

idal

tosl

igh

tly

irre

gu

lar

Pre

dom

inan

tly

base

men

tcla

sts

�0Æ5

to0Æ6

Med

ium

den

sity

,con

cen

tric

tocolu

mn

ar

lam

inae

giv

ing

way

top

rotu

bera

nces

Mod

era

te,

inte

rlam

inar

an

dbio

ero

sion

infi

llin

g

Med

ium

den

sity

,sm

all

,m

ed

ium

an

dla

rge-s

cale

Abse

nt

Meso

ph

yll

um

,S

pon

git

es,

Lit

hop

ore

lla,

Peyss

on

neli

a

14 R. Nalin et al.


Table

2.

(Con

tin

ued

)

Pio

pio

2Æ9

cm

(n¼

12)

Ell

ipso

idal,

nu

cle

us-

con

troll

ed

Base

men

tcla

st(�

60%

)or

bio

cla

st

Betw

een

0Æ1

an

d0Æ5

,avera

ge

0Æ2

Den

secon

cen

tric

lam

inae

Non

eto

low

,in

fill

ing

bio

ero

sion

Hig

hd

en

sity

,sm

all

tom

ed

ium

-sc

ale

Abse

nt

Meso

ph

yll

um

,?S

pon

git

es

Aw

akau

Road

5Æ7

cm

(n¼

14)

Ell

ipso

idal,

som

eir

regu

lar

Abse

nt,

rare

lybio

cla

st�

1M

ed

ium

den

sity

fram

ew

ork

,fr

uti

cose

toir

regu

lar

con

cen

tric

gro

wth

Med

ium

,in

terb

ran

ch

es

an

din

terl

am

inar

an

dbio

ero

sion

infi

ll

Med

ium

den

sity

,m

ed

ium

an

dla

rge-s

cale

Abse

nt

Meso

ph

yll

um

,Lit

hoth

am

nio

n,

?Lit

hop

hyll

um

Taip

o,

Tin

ui

2Æ5

cm

Ell

ipso

idal

Abse

nt

or

alg

al

bra

nch

1D

en

se,

irre

gu

larl

ycon

cen

tric

lam

inae

Non

eto

low

Med

ium

den

sity

,m

ed

ium

-sc

ale

Abse

nt

Not

dete

rmin

ed

Wh

an

gap

ara

oa

Pen

insu

la5Æ0

cm

(n¼

101)

Ell

ipso

idal

tod

iscoid

al,

oft

en

nu

cle

us-

con

troll

ed

Base

men

tcla

st(�

70%

),alg

al

bra

nch

or

bio

cla

st

�0Æ6

to0Æ7

Very

den

se,

thic

kcolu

mn

ar

pro

tubera

nces

Non

eM

ed

ium

den

sity

,sm

all

an

dm

ed

ium

-scale

Abse

nt

Sp

oro

lith

on

du

rum

(Fosl

ie)

Tow

nse

nd

&W

oelk

erl

ing

*A

vera

ge

size

refe

rsto

lon

ger

axes

of

rhod

oli

ths

an

dis

calc

ula

ted

from

measu

rem

en

tsof

alg

al

nod

ule

sth

at

cou

ldbe

extr

acte

dfr

om

sou

rce

rock

(n¼

nu

mber

of

alg

al

nod

ule

sm

easu

red

).D

esp

ite

the

small

nu

mber

of

sam

ple

sfo

rse

vera

llo

cali

ties,

the

avera

ge

size

was

ch

ecked

for

con

sist

en

cy

wit

hvis

ual

est

imati

on

of

rhod

oli

thsi

ze

inou

tcro

p.

Th

evalu

efo

rT

inu

ise

cti

on

isbase

don

lyon

vis

ual

est

imati

on

,as

extr

em

eli

thifi

cati

on

of

sam

ple

sd

idn

ot

all

ow

coll

ecti

on

of

en

tire

nod

ule

s.�I

nd

ecre

asi

ng

ord

er

of

abu

nd

an

ce.



(A) (B)

(C) (D)

(E) (F)

Fig. 10. General characteristics of type A rhodolithic units. (A) Clast-supported texture and abundance of lithic clasts(Mairoa section). Hammer for scale is 33 cm long. (B) to (E) Views of sectioned rhodoliths. Note low algal material tonucleus ratio and high-density, predominantly concentric, algal framework. Matrix-infilled bioerosion, occurring bothon algal framework and bioclastic nucleus, is well evident in (C) and (D). Sample (B) is modern rhodolith, Whan-gaparaoa Peninsula; rhodolith sample (C) from Waikaretu section; rhodolith samples (D) and (E) from Mairoa section.(F) Thin section photograph showing high density of type A algal framework in rhodolith from Mairoa section.

16 R. Nalin et al.


animal’ (Kidwell, 1991a). Coralline algae arefloral rather than faunal components of the ben-thic community; nevertheless they secrete miner-alized tissue which is subjected to the same rangeof taphonomical and diagenetic processes affect-ing other skeletal particles of the carbonatefactory biota. This paper, therefore, considersthat stratigraphic concepts developed in thestudy of shell concentrations may be applied torhodolithic deposits accumulated in transgressivesettings, and have the potential to better highlighttheir significance.

Shell concentrations may be considered con-densed deposits when they develop as a result oflow autochthonous production and low sedimen-tary dilution. Kidwell (1989,1991b) recognizedthat shell concentrations can occur anywherestratal surfaces converge in a stratigraphic se-quence and can be located at specific positions in

a depositional cycle in association with discon-tinuity surfaces (Fig. 12). Kidwell therefore dis-tinguished various types of shellbeds according totheir stratigraphic position. In particular, onlapand backlap shellbeds were defined as beingformed in the context of marine transgression.Onlap shellbeds commonly rest on a transgressivesurface of erosion, grade upwards into deeperdeposits and contain abundant material reworkedfrom the substrate surface. These shellbeds oftenpreserve taphonomical and sedimentologicalindications of an active hydrodynamic regime,and are therefore interpreted as forming in sub-tidal wave and/or current dominated settings,where low terrigenous input and bypassing offine sediment result in low net accumulationrates (Kidwell, 1991b; Naish & Kamp, 1997;Abbott, 1998). Backlap shellbeds form duringtransgression at the basinward termination of a

(A) (B)

(C) (D) (E)

Fig. 11. General characteristics of type B rhodolithic units. (A, B) Matrix-supported texture evident in outcrop (TeAnga section) and in a polished slab (Awakau Road section). Head of hammer for scale is 15 cm long in (A). (C) to (E)Views of sectioned rhodoliths. Note loose algal framework, abundance of fine matrix and branched thalli, andabsence of nucleus. Samples (C) and (D) from Te Anga section; sample (E) from Awakau Road section.



https://www.researchgate.net/publication/253858457_Stratigraphic_Condensation_of_Marine_Transgressive_Records_Origin_of_Major_Shell_Deposits_in_the_Miocene_of_Maryland?el=1_x_8&enrichId=rgreq-2f56e7be-f364-422c-9bfb-4da8d231fa44&enrichSource=Y292ZXJQYWdlOzIyOTY4NDk4MTtBUzo5NzQ0MDg2Njc2Njg0OUAxNDAwMjQzMTIxNDI2

backstepping sediment body; they are usuallydispersed in a fine matrix and are often amal-gamated with onlap shellbeds, resulting in com-pound (mixed onlap–backlap) shellbeds (Naish &Kamp, 1997; Kondo et al., 1998).

This study proposes that the type A and Brhodolithic units are condensed deposits analo-gous respectively to onlap and backlap shellconcentrations. The compact structure of type Arhodolith frameworks, the clast-supported texturewith scarce fine matrix, and the abundance oflithic clasts reworked from the substrate suggestthat type A rhodolithic units are formed in higherhydrodynamic energy settings in contrast to typeB units. Moreover, type A units preferentiallydeveloped in areas where coarse unconsolidateddeposits covered the sea floor, as indicated by thedominance of rhodoliths with a high nucleus/algal cover ratio (Table 2).

Differences in rhodolith internal structure sim-ilar to those observed between type A and B unitshave been documented from several modernsettings (Minnery, 1990; Bosence, 1991; Basso,1998; Marrack, 1999; Lund et al., 2000) and havebeen related to depth, sedimentation rate andhydrodynamic regime. Shallower or higherenergy rhodoliths usually display a high nucleusto algal cover ratio, and a compact structureconsisting of thick laminae. Deeper or lowerenergy rhodoliths comprise large constructionalvoids, may lack an identifiable nucleus and arecomposed of thin irregular crusts often with leafygrowth form. These morphological attributes havealso been applied in palaeoenvironmental inter-pretations of ancient deposits (Braga & Martın,1988; Bassi, 1998,2005; Bassi et al., 2006; Barat-tolo et al., 2007). On the basis of these consider-ations, the difference in internal arrangementobserved between rhodoliths of type A and Bunits may be interpreted as a function of depth. Inthis case, the floral composition of the rhodolithsstudied in this work (Table 3) would be consis-tent with current depth distribution models of

coralline algae (Perrin et al., 1995; Bassi,1998,2005; Braga & Aguirre, 2001; Brandanoet al., 2005; Kroeger et al., 2006). These modelsindicate that melobesioids increase in dominancein deeper settings, whereas mastophoroids, suchas Spongites, are more abundant in shallowersettings. However, it is also possible that type Aand B units developed locally at a similar depth,and the structure of their rhodoliths simplyreflects different degrees of movement inducedby turbulence and/or bioturbation (Reid & Mac-intyre, 1988; Prager & Ginsburg, 1989; Basso,1998).

The ubiquitous presence of bioerosion, the pro-cess of encrustation implied by the rhodolithgrowth mode, and the frequent association withauthigenic minerals like glaucony, strongly supportconditions of low net sedimentation at the time ofdeposition of type A and B rhodolithic units. It isnot, however, necessary to invoke total sedimentstarvation for the development of transgressivecondensed deposits, as bypassing of fines may givea similar result (Kidwell, 1989). Such a situation isrecorded at the Tinui locality in North Island, wherethe basal shoreface deposit is a siliciclastic-freerhodolithic unit, but terrigenous grains dominate inthe overlying thick succession of silty sandstonedeposited in mid to outer shelf settings.

Comparison with other published examples

A marked association between transgressive set-tings and the development of rhodolith-bearingunits emerges from the stratigraphic attributes ofthe studied examples. Namely, all the describedrhodolithic units are found above a major uncon-formity, often in deposits containing pebblesreworked from the substrate, at the base of adeepening upwards succession (Fig. 13). Theassociation is reinforced by the fact that theexamined occurrences from the North Island ofNew Zealand are taken from a variety of contextsin space and time.

Fig. 12. Diagram showing differenttypes of shellbeds developed withina stratigraphic sequence and theirnomenclature (after Kidwell, 1991b;Naish & Kamp, 1997). HST, high-stand systems tract; TST, transgres-sive systems tract; mfs, maximumflooding surface.

18 R. Nalin et al.


https://www.researchgate.net/publication/222894033_The_relationship_between_shellbed_type_and_sequence_architecture_examples_from_Japan_and_New_Zealand?el=1_x_8&enrichId=rgreq-2f56e7be-f364-422c-9bfb-4da8d231fa44&enrichSource=Y292ZXJQYWdlOzIyOTY4NDk4MTtBUzo5NzQ0MDg2Njc2Njg0OUAxNDAwMjQzMTIxNDI2

https://www.researchgate.net/publication/253858457_Stratigraphic_Condensation_of_Marine_Transgressive_Records_Origin_of_Major_Shell_Deposits_in_the_Miocene_of_Maryland?el=1_x_8&enrichId=rgreq-2f56e7be-f364-422c-9bfb-4da8d231fa44&enrichSource=Y292ZXJQYWdlOzIyOTY4NDk4MTtBUzo5NzQ0MDg2Njc2Njg0OUAxNDAwMjQzMTIxNDI2

A review of similar rhodolithic units describedin the literature confirms that rhodoliths devel-oping during transgressions have a wide geo-graphical distribution and are recurrent ingeological time (Table 3). These units often areconfined to the transgressive portion of deposi-tional sequences because sea-level rise may causethe carbonate factory to drown or shift landward(Vecsei & Sanders, 1999). In other cases, such asMiocene reef complexes from the Mediterraneanregion, the predominance of rhodalgal facies(Carannante et al., 1988) in the transgressivesystems tract has been interpreted in terms ofclimatic and oceanographic factors (Esteban,1996).

It is important to acknowledge that the strati-graphic distribution of rhodolith-bearing lime-stones is not always restricted to thetransgressive systems tract. Substantial accumu-lations of rhodolithic units may develop in otherportions, or over the entire length, of deposi-tional cycles (Bosence & Pedley, 1982; Bassi,1998,2005; Pomar et al., 2004), especially whena balance between production rates and creationof accommodation space is achieved (Pomar L.,2001). However, transgressive rhodolithic units,such as those described in this paper, are readilyidentified and distinguished when placed intheir stratigraphic context and appear to repre-sent a consistent response to the onset of marinetransgression.

Controls on genesis and distribution

Despite their stratigraphic recurrence, transgres-sive rhodolith-bearing deposits tend to be ofrelatively limited lateral extent and algal nodulesare not consistently present in many other shal-low-water transgressive units (Wilson, 1988;Carey et al., 1995; Naish & Kamp, 1997; Caronet al., 2004). Given that primary ecologicalrequirements (such as light and salinity) arefavourable for growth of coralline red algae, acomplex combination of factors must be achievedfor a rhodolith concentration to develop duringtransgressions. Some suggested major controls arementioned briefly in the following.

Low net sedimentary inputAs noted earlier, sedimentary dilution, as a resultof low sediment supply or sediment bypass, isnecessary for the formation of condensed depos-its. During transgressions, the landward migra-tion of coastal depocentres may result insediment starvation on the shelf, therefore,

favouring the development of biogenic concen-trations. Moreover, limited discharge of terrige-nous material implies lower levels of nutrientavailability and water turbidity, which are knownto play an important role in the formation ofrhodalgal deposits (Glaser & Betzler, 2002; Halfaret al., 2004).

SubstrateThe role of substrate becomes evident whenconsidering type A rhodolithic units, wheremost of the rhodoliths start their growth encrust-ing pebbles or coarse biogenic fragments. Theavailability of a mobile substrate consisting ofpebble-size to cobble-size hard clasts seems,therefore, to be a major factor controlling theinitial stages of development of type A rhodo-lithic units. This observation could explain whyrhodolith-bearing units of the Te Kuiti Groupnearly always overlie on-basement unconformi-ties and are seldom seen developed abovetransgressive surfaces eroding on soft substrates.It could also account for the location of themodern Whangaparaoa rhodolith production sitein association with one of the Parnell Grit beds,because the erosion of this coarse volcaniclasticsubstrate produces far more competent basalticcobbles and pebbles than the adjacent rather softand friable flysch deposits.

Sea-level riseChange of water depth during transgressions mayinduce conditions of stress for many organisms.Different species of coralline red algae are adaptedto living in a wide range of light conditions, fromeuphotic (Bosellini & Ginsburg, 1971) to oligoph-otic (Basso, 1998). Rhodoliths may be produced byany of these species and, because of their encrust-ing habit, those growing in deeper water maycolonize rhodoliths which were initially formed atshallower depths. The persistence, during trans-gression, of suitable conditions for the develop-ment of coralline red algae explains why it ispossible to find, in the same unit, rhodolithscomposed of different species and rhodolithsshowing an ecological succession from the nu-cleus to the external layers (Braga & Martın, 1988;Bassi, 1998). In the long-term, however, continu-ous sea-level rise may determine changes inenvironmental parameters (such as light availabil-ity, temperature and hydrodynamic regime) likelyto result in the termination or landward displace-ment of the carbonate factory. Rhodolith-richdeposits will therefore be overlain by deeper-water facies, unless production rates of carbonate



https://www.researchgate.net/publication/248232777_Carannante_G_Esteban_M_Milllman_J_D_Simone_L_-_Carbonate_lithofacies_as_paleolatitude_indicators_Problems_and_limitations_Sedimentary_Geology?el=1_x_8&enrichId=rgreq-2f56e7be-f364-422c-9bfb-4da8d231fa44&enrichSource=Y292ZXJQYWdlOzIyOTY4NDk4MTtBUzo5NzQ0MDg2Njc2Njg0OUAxNDAwMjQzMTIxNDI2

https://www.researchgate.net/publication/248232994_Vecsei_A_Sanders_D_G_K_-_Facies_analysis_and_sequence_stratigraphy_of_a_Miocene_warmtemperate_carbonate_ramp_Montagna_della_Maiella_Italy_Sedimentary_Geology?el=1_x_8&enrichId=rgreq-2f56e7be-f364-422c-9bfb-4da8d231fa44&enrichSource=Y292ZXJQYWdlOzIyOTY4NDk4MTtBUzo5NzQ0MDg2Njc2Njg0OUAxNDAwMjQzMTIxNDI2

https://www.researchgate.net/publication/249182052_Form_and_Internal_Structure_of_Recent_Algal_Nodules_Rhodolites_from_Bermuda_A_Reply?el=1_x_8&enrichId=rgreq-2f56e7be-f364-422c-9bfb-4da8d231fa44&enrichSource=Y292ZXJQYWdlOzIyOTY4NDk4MTtBUzo5NzQ0MDg2Njc2Njg0OUAxNDAwMjQzMTIxNDI2

https://www.researchgate.net/publication/236656956_Basso_D_-_Deep_rhodolith_distribution_in_the_Pontian_Islands_Italy_A_model_for_the_paleoecology_of_a_temperate_sea_Palaeogeography_Palaeoclimatology_Palaeoecology?el=1_x_8&enrichId=rgreq-2f56e7be-f364-422c-9bfb-4da8d231fa44&enrichSource=Y292ZXJQYWdlOzIyOTY4NDk4MTtBUzo5NzQ0MDg2Njc2Njg0OUAxNDAwMjQzMTIxNDI2

Table

3.

Som

ep

ubli

shed

exam

ple

sof

tran

sgre

ssiv

erh

od

oli

th-b

eari

ng

un

its.

Locali

tyA

ge

Refe

ren

ces

Un

itd

esc

rip

tion

Rh

od

oli

thic

un

itty

pe

as

use

din

this

stu

dy

Waia

uR

iver,

Sou

thIs

lan

d,

New

Zeala

nd

Oli

gocen

eB

urg

ess

&A

nd

ers

on

(1983)

Con

den

sed

sequ

en

ce

rest

ing

on

base

men

t,con

sist

ing

of

ph

osp

hati

zed

an

dgla

ucon

itiz

ed

rhod

oli

ths

an

dall

och

em

s.T

hic

kn

ess

of

un

itis

on

ly1

m.

A?

Sch

ool

Cre

ek,

Sou

thIs

lan

d,

New

Zeala

nd

Oli

gocen

eB

urg

ess

&A

nd

ers

on

(1983)

Rh

od

oli

thic

un

it,

len

soid

insh

ap

e,

overl

yin

ggra

nit

icbase

men

t.E

rod

ed

cla

sts

from

the

subst

rate

are

abu

nd

an

t.T

he

un

ith

as

am

axim

um

thic

kn

ess

of

30

man

dgra

des

vert

icall

yin

tom

ud

ston

e.

A?

West

Coast

,S

ou

thIs

lan

d,

New

Zeala

nd

Oli

gocen

eB

urg

ess

&A

nd

ers

on

(1983)

Late

rall

ycon

tin

uou

su

nit

,re

stin

gon

base

men

t.R

hod

oli

ths

ass

ocia

ted

wit

hA

mp

his

tegin

a,

bry

ozoan

s,bra

ch

iop

od

san

dech

inoid

s.?

Wait

em

ata

Basi

n,

Nort

hIs

lan

d,

New

Zeala

nd

Earl

yM

iocen

eR

ickett

set

al.

(1989)

Pebbly

coqu

ina

basa

lfa

cie

s,d

esc

ribed

as

rhod

oli

th-r

ich

dep

osi

tw

ith

alg

al

cru

sts

coati

ng

bed

rock-d

eri

ved

cla

sts;

occu

pie

ssh

all

ow

dep

ress

ion

s40

to50

macro

ss,

an

dlo

call

yd

irectl

yoverl

ies

basa

lu

ncon

form

ity.

Overa

ll,

the

success

ion

record

san

abru

pt

tran

siti

on

from

coast

al

an

dsh

all

ow

shelf

sed

imen

tsto

bath

yal

sed

imen

ts

A

Gorn

jiG

rad

,S

loven

iaE

arl

yO

ligocen

eN

ebels

ick

&B

ass

i(2

000)

Gorn

jiG

rad

bed

s,u

nit

5to

30

mth

ick

form

ing

part

of

atr

an

sgre

ssiv

esu

ccess

ion

overl

yin

gboth

con

tin

en

tal

terr

igen

ou

sd

ep

osi

tsan

dE

ocen

em

ari

ne

carb

on

ate

s,as

well

as

tran

sgre

ssin

gd

irectl

yover

Tri

ass

icli

mest

on

es.

Th

eu

nit

gra

des

into

mari

ne

marl

s.C

ora

llin

ealg

ae

are

dom

inan

t,bu

tcora

ls,

biv

alv

es,

larg

eben

thic

,sm

all

ben

thic

an

den

cru

stin

gfo

ram

inif

era

are

als

ore

pre

sen

ted

.G

ast

rop

od

s,bry

ozoan

s,bra

ch

iop

od

s,ech

inod

erm

s,se

rpu

lid

san

dgre

en

alg

ae

are

subord

inate

.

B?

Carp

ath

ian

Fore

deep

,P

ola

nd

Mid

dle

Mio

cen

e(e

arl

yB

ad

en

ian

)S

tud

en

cki

(1999)

Rh

od

oli

thp

avem

en

tan

dbra

nch

ing

alg

ae

facie

s.U

ncon

form

ably

overl

ies

pre

-Mio

cen

esu

bst

rate

,u

pto

8m

thic

k,

con

tain

sals

om

oll

usc

s,bry

ozoan

s,la

rge

fora

min

ifera

,barn

acle

s,p

oly

ch

aete

san

dbra

ch

iop

od

s.

?

Gra

nad

aB

asi

n,

Sp

ain

Late

Mio

cen

e(e

arl

yT

ort

on

ian

)B

raga

&A

gu

irre

(2001)

Bio

cla

stic

bre

ccia

,u

pto

1Æ5

mth

ick,

un

con

form

ably

overl

yin

gT

riass

icro

cks.

Rh

od

oli

ths

oft

en

have

acla

stic

nu

cle

us,

deri

ved

from

ero

sion

of

the

subst

rate

.B

ivalv

es,

bry

ozoan

s,cora

llin

ealg

al

fragm

en

tsan

dsu

bst

rate

cla

sts

are

als

oabu

nd

an

t.

A

Azagad

or

Mem

ber,

Sorb

as

Basi

n,

Sp

ain

Late

Mio

cen

e(l

ate

Tort

on

ian

-earl

yM

ess

inia

n)

Bra

ga

&A

gu

irre

(2001)

10

mth

ick

un

itof

cru

dely

lam

inate

dli

mest

on

eri

ch

inop

en

-bra

nch

ing

rhod

oli

ths,

un

con

form

ably

overl

yin

gu

pp

er

Tort

on

ian

dep

osi

ts.

Bry

ozoan

s,biv

alv

es,

serp

uli

d-w

orm

tubes,

barn

acle

s,bra

ch

iop

od

san

dech

inoid

fragm

en

tsare

als

op

rese

nt.

Th

eu

nit

gra

des

up

ward

sin

tooff

shore

basi

nal

marl

s.

B

20 R. Nalin et al.


Table

3.

(Con

tin

ued

)

Alm

an

zora

Basi

n,

Sp

ain

Late

Mio

cen

e(L

ate

Tort

on

ian

)B

raga

&M

art

ın(1

988)

Tw

od

iffe

ren

tty

pes

of

rhod

oli

thaccu

mu

lati

on

form

ed

on

coast

al

pla

tform

san

dta

lus

slop

es

above

an

ero

sion

al

un

con

form

ity.

Th

efi

rst,

inte

rpre

ted

as

ash

all

ow

er

facie

s,is

dom

inate

dby

rhod

oli

ths

wit

ha

hig

hn

ucle

us

toalg

al

cover

rati

oan

doli

gosp

ecifi

ccon

cen

tric

tocolu

mn

ar

cru

sts.

Th

ese

con

d,

inte

rpre

ted

as

form

ing

at

dep

ths

of

30

to40

m,

isch

ara

cte

rized

by

rhod

oli

ths

wit

hbra

nch

ing

an

dth

in,

leafy

gro

wth

s,oft

en

wit

hou

ta

cla

stic

nu

cle

us.

A+

B

Calc

ari

aB

riozoi

eL

itota

mn

i,C

en

tral-

Sou

thern

Ap

en

nin

es,

Italy

Mio

cen

e(A

qu

itan

ian

-T

ort

on

ian

)

Cara

nn

an

te&

Sim

on

e(1

996);

Civ

itell

i&

Bra

nd

an

o(2

005)

Rh

od

oli

thfl

oats

ton

ean

dru

dst

on

ein

matr

ixof

bio

cla

stic

gra

inst

on

ean

dp

ackst

on

e,

wit

hth

ickn

ess

vary

ing

from

afe

wcen

tim

etr

es

to60

m.

Larg

er

ben

thic

fora

min

ifera

,bry

ozoan

s,m

oll

usc

s,ech

inoid

fragm

en

ts,

barn

acle

san

dse

rpu

lid

sare

com

mon

.T

he

un

itli

es

wit

hsh

arp

con

tact

on

Cre

taceou

s-P

ala

eocen

esu

bst

ratu

man

dgra

des

up

ward

sin

toh

em

ipela

gic

marl

yli

mest

on

eth

rou

gh

ap

hosp

hati

cin

terv

al

up

to1Æ5

mth

ick.

B?

Maie

lla

Pla

tform

,C

en

tral

Ap

en

nin

es,

Italy

Mid

dle

–L

ate

Mio

cen

e(L

an

gh

ian

-T

ort

on

ian

)

Vecse

i&

San

ders

(1999)

Low

er

facie

su

nit

of

Sequ

en

ce

6Æ3

of

Vecse

ian

dS

an

ders

(1999).

Rh

od

oli

thfl

oats

ton

ew

ith

dis

pers

ed

larg

er

fora

min

ifera

,sm

all

er

ben

thic

fora

min

ifera

,bry

ozoan

s,biv

alv

es,

gast

rop

od

s,verm

eti

dtu

bes

an

dech

inoid

fragm

en

ts.

Un

itgra

des

up

secti

on

into

marl

yli

mest

on

eth

rou

gh

acon

den

sed

hori

zon

.

B?

Cu

tro

Mari

ne

Terr

ace,

Cala

bri

a,

Sou

thern

Italy

Late

Ple

isto

cen

eN

ali

net

al.

(2006)

30

cm

thic

kp

avem

en

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sediment are sufficiently high to keep pace withthe amplitude and speed of sea-level rise.

Inherited physiographyCattaneo & Steel (2003) showed how inheritedphysiography has an important role in controllingthe architecture and development of transgressivedeposits. This role appears in several of thedescribed examples from New Zealand, wherethe rhodolithic units are located within basementdepressions (e.g. Te Anga, Mairoa and Honikiwisections). In particular, topographic highs sub-merged during transgression act as a source ofcoarse clastics which, in turn, modify the natureof the substrate. Moreover, geomorphic constric-tion of submarine currents produces an increasein their velocity that results in local modificationof the hydrodynamic regime. Anastas et al. (2006)have extensively documented this scenario fordeposits of the Te Kuiti Group. Active hydrody-

namic conditions could influence the locus ofrhodolith accumulation because water motion isknown to play a role in the development ofshallow-water rhodoliths (Marrack, 1999).

Tropical versus non-tropical transgressiverhodolith accumulations

All the rhodolith-bearing units studied in thiswork, and most of those mentioned in the liter-ature review (Table 3), may be broadly defined ascomprising Heterozoan-dominated skeletal asso-ciations (sensu James, 1997), and have beeninterpreted as temperate or cool-water carbonates(Nelson et al., 1988). Because rhodoliths areknown to form also in a variety of tropical settings(Bosence, 1983; Adey, 1986), transgressive rho-dolith accumulations would be expected todevelop also at low latitudes. However, tropicalexamples seem to be under-represented with

Substrate

Substrate

Initial stage of transgression

B

A

Advanced stage of transgressionSea level

Rise in sea level

Sea level

Type A rhodolithic unit Type B rhodolithic unit Offshore fines Unconformity

Fig. 13. Model of the development of types A and B transgressive rhodolithic units. No scale implied. (A) In theinitial stage of transgression, type A units form in shallow high-energy settings and are often localized in topographicdepressions of the substrate. Type B units develop in calmer, possibily deeper, waters and present a matrix-sup-ported texture with rhodoliths showing a loose internal structure. (B) In the advanced stage of transgression, basinalfine-grained units are deposited directly above the rhodolithic accumulations. The resulting succession rests above amajor unconformity and is characterized by a deepening upwards trend.

22 R. Nalin et al.


https://www.researchgate.net/publication/247819114_The_cool_water_carbonate_depositional_realm?el=1_x_8&enrichId=rgreq-2f56e7be-f364-422c-9bfb-4da8d231fa44&enrichSource=Y292ZXJQYWdlOzIyOTY4NDk4MTtBUzo5NzQ0MDg2Njc2Njg0OUAxNDAwMjQzMTIxNDI2

https://www.researchgate.net/publication/270260962_The_Relationship_between_Water_Motion_and_Living_Rhodolith_Beds_in_the_Southwestern_Gulf_of_California_Mexico?el=1_x_8&enrichId=rgreq-2f56e7be-f364-422c-9bfb-4da8d231fa44&enrichSource=Y292ZXJQYWdlOzIyOTY4NDk4MTtBUzo5NzQ0MDg2Njc2Njg0OUAxNDAwMjQzMTIxNDI2

https://www.researchgate.net/publication/223627203_Burial-dominated_cementation_in_non-tropical_carbonates_of_the_Oligocene_Te_Kuiti_Group_New_Zealand?el=1_x_8&enrichId=rgreq-2f56e7be-f364-422c-9bfb-4da8d231fa44&enrichSource=Y292ZXJQYWdlOzIyOTY4NDk4MTtBUzo5NzQ0MDg2Njc2Njg0OUAxNDAwMjQzMTIxNDI2

respect to non-tropical occurrences. This phe-nomenon might be explained considering that, inthe euphotic zone of tropical seas, red algaeusually compete with organisms of the chlorozo-an association (Lees & Buller, 1972) and become amajor component of the carbonate biota only atgreater depth (Bourrouilh-Le Jan & Hottinger,1988; Reid & Macintyre, 1988; Prager & Ginsburg,1989; Minnery, 1990; Iryu et al., 1995). Thechlorozoan factory is often able to keep pace withsea-level rise, and a transgressive bed of corallinealgal deposits may be preserved over facies of theshallow coral reef only if the platform drowns(Webster et al., 2004a,b). When environmentalconditions are hostile to the establishment of reefcorals and calcareous green algae, rhodalgal faciesmay entirely dominate the shallow waters oftropical seas (Carannante et al., 1988; Pomaret al., 2004; Wilson & Vecsei, 2005) and may, inthis specific case, give rise to genuine rhodolithaccumulations during transgression (Bourrouilh-Le Jan & Hottinger, 1988).

CONCLUSIONS

1. The study of Cenozoic rhodolith-bearingdeposits from the North Island of New Zealandhas shown how rhodolithic units, usually oflimited lateral extent, are often found above majorunconformities at the base of deepening upwardssuccessions. These units are interpreted as acharacteristic facies of transgressive systems tractdeposits.

2. The association between transgressive set-tings and development of rhodolithic facies isconfirmed by a modern coastal platform examplefrom the Whangaparaoa Peninsula on North Islandand an array of fossil occurrences described in theliterature. These examples show stratigraphic andcompositional attributes analogous to those at theCenozoic North Island sites.

3. Two types of transgressive rhodolith-bearingdeposits have been distinguished on the basis oftexture and rhodolith internal structure. Type Adeposits are clast-supported rhodolithic rud-stones containing abundant pebbles and cobblesreworked from the substrate and characterized byrhodoliths with dense concentric to columnarinternal structure and a high nucleus/algal coverratio. These deposits are interpreted as forming inrelatively high-energy settings and/or in narrowsubmerged palaeotopographic lows. Type Bdeposits are rhodolithic floatstones with a matrixusually consisting of bryozoan fragments, larger

benthic foraminifera and echinoid fragments orterrigenous silty sand. The algal nodules of type Bunits usually have a loose internal frameworkwith irregular to branched thalli and a high pro-portion of internal matrix; they are interpreted asforming in lower-energy settings.

4. Despite being floral rather than faunal com-ponents of the carbonate-producing biota, coral-line red algae are subject to the same range ofprocesses controlling the deposition of otheranimal-derived skeletal particles. Rhodolithaccumulations may therefore be consideredanalogous to shell concentrations.

5. Applying the stratigraphic concepts devel-oped for the interpretation of shell concentra-tions, type A and B rhodolithic units areinterpreted as onlap, backlap or compound(mixed onlap–backlap) shellbeds within thetransgressive systems tract.

6. A complex combination of factors regulatesthe association in space and time between trans-gressions and rhodolith-bearing deposits. Low netsedimentary input, attributes of the substrate, riseof sea-level and inherited physiography areproposed as important controls favouring theoccurrence of this association.

7. Although transgressive rhodolith accumula-tions are found commonly in non-tropicalsuccessions, they may develop in tropical settingswhere environmental conditions are hostile to theestablishment of reef corals and calcareous greenalgae in the euphotic zone or when sea-level riseis sufficiently high to cause drowning of thecarbonate platform.

ACKNOWLEDGEMENTS

Anand Tripathi and Peter Kamp are gratefullyacknowledged for fruitful discussions in thefield. Adam Vonk, Kyle Bland and AnandTripathi kindly offered technical assistance. Isa-bella Premoli Silva helped in foraminifera iden-tification. The authors thank Anand Tripathi andAlex Johansen for provision of some strati-graphic information, and Terry Hume for sup-plying oceanographic data for the Whangaparaoalocality. The manuscript benefited greatly fromconstructive reviews by Dan Bosence, an anon-ymous referee and editor Peter Haughton. Ron-ald Nalin was funded by a scholarship of theFondazione Ing. Aldo Gini and was assisted withfield expenses through a New Zealand Founda-tion for Research Science and Technology con-tract (UOWX0301) with the University of



https://www.researchgate.net/publication/223022492_Modern_temperate-water_and_warm-water_shelf_carbonate_contrasted?el=1_x_8&enrichId=rgreq-2f56e7be-f364-422c-9bfb-4da8d231fa44&enrichSource=Y292ZXJQYWdlOzIyOTY4NDk4MTtBUzo5NzQ0MDg2Njc2Njg0OUAxNDAwMjQzMTIxNDI2

Waikato. He also thanks Margaret Nelson andstaff of the Department of Earth and OceanSciences at the University of Waikato for theirlogistical support and friendship while visitingNew Zealand.

REFERENCES

Abbott, S.T. (1998) Transgressive systems tracts and onlap

shellbeds from mid-Pleistocene sequences, Wanganui

Basin, New Zealand. J. Sed. Res., 68/2, 253–268.

Adey, W.H. (1986) Coralline algae as indicators of sea-level. In:

Sea-Level Research: A Manual for the Collection and Eval-uation of Data (Ed. O. van de Plasche), pp. 229–280. Geo

Books, Norwich.

Allen, S.R. (2004) The Parnell Grit beds revisited: are they all

products of sector collapse western subaerial volcanoes of

the Northland Volcanic Arc? NZ J. Geol. Geophys., 47, 509–

524.

Anastas, A.S., Dalrymple, R.W., James, N.P. and Nelson, C.S.(2006) Lithofacies and dynamics of a cool-water carbonate

seaway: mid-Tertiary, Te Kuiti Group, New Zealand. In:

Cool-Water Carbonates: Depositional Systems and Palaeo-

environmental Controls (Eds H.M. Pedley and G. Carann-

ante), Geol. Soc. London Spec. Publ., 255, 245–268.

Ballance, P.F. (1974) An inter-arc flysch basin in northern

New Zealand: Waitemata Group (upper Oligicene to lower

Miocene). J. Geol., 82, 439–471.

Barattolo, F., Bassi, D. and Romano, R. (2007) Upper Eocene

larger foraminiferal-coralline algal facies from the Klokova

Mountain (southern continental Greece). Facies, doi:

10.1007/s1034-007-0108-2.

Bassi, D. (1998) Coralline algal facies and their palaeoenvi-

ronments in the Late Eocene of Northern Italy (Calcare di

Nago, Trento). Facies, 39, 179–202.

Bassi, D. (2005) Larger foraminiferal and coralline algal facies

in an Upper Eocene storm-influenced, shallow-water car-

bonate platform (Colli Berici, north-eastern Italy). Palaeo-

geogr., Palaeoclimatol., Palaeoecol., 226, 17–35.

Bassi, D., Carannante, G., Murru, M., Simone, L. and Tos-cano, F. (2006) Rhodalgal/bryomol assemblages in temper-

ate-type carbonate, channelized depositional systems: the

Early Miocene of the Sarcidano area (Sardiania, Italy). In:

Cool-Water Carbonates: Depositional Systems and Palaeo-

environmental Controls (Eds H.M. Pedley and G. Carann-

ante), Geol. Soc. London Spec. Publ., 255, 35–52.

Basso, D. (1998) Deep rhodolith distribution in the Pontian

Islands, Italy: a model for the palaeoecology of a temperate sea.

Palaeogeogr., Palaeoclimatol., Palaeoecol., 137, 173–187.

Basso, D. and Tomaselli, V. (1994) Palaeoecological potenti-

ality of rhodoliths: a Mediterranean case history. Boll. Soc.

Palaeont. Ital., Spec. Vol., 2, 17–27.

Basso, D., Morbioli, C. and Corselli, C. (2006) Rhodolith facies

evolution and burial as a response to Holocene transgres-

sion at the Pontian Islands shelf break. In: Cool-Water Car-

bonates: Depositional Systems and Palaeoenvironmental

Controls (Eds H.M. Pedley and G. Carannante), Geol. Soc.

London Spec. Publ., 255, 23–34.

Bell, R.G. and Goring, D.G. (1998) Seasonal variability of sea-

level and sea-surface temperature on the north-east coast of

New Zealand. Estuar. Coast. Shelf Sci., 46, 307–318.

Black, K.P., Bell, R.G., Oldman, J.W., Carter, G.S. and Hume,T.M. (2000) Features of 3-dimensional and baroclinic

circulation in the Hauraki Gulf, New Zealand. NZ J. Mar.

Freshwat. Res., 34, 1–28.

Bosellini, A. and Ginsburg, R.N. (1971) Form and internal

structure of recent algal nodules (rhodolithes) from Ber-

muda. J. Geol., 79, 669–682.

Bosence, D.W.J. (1976) Ecological studies on two unattached

coralline algae from Western Ireland. Palaeontology, 19/2,365–395.

Bosence, D.W.J. (1983) The occurrence and ecology of recent

rhodoliths – a review. In: Coated Grains (Ed. T.M. Peryt),

pp. 225–242. Springer-Verlag, Berlin Heidelberg.

Bosence, D.W.J. (1991) Coralline algae mineralization, taxon-

omy and palaeoecology. In: Calcareous Alage and Stro-

matolites (Ed. R. Riding), pp. 98–113. Springer-Verlag,

Berlin Heidelberg.

Bosence, D.W.J. and Pedley, H.M. (1982) Sedimentology and

palaeoecology of a Miocene coralline algal biostrome from

the Maltese Islands. Palaeogeogr. Palaeoclim. Palaeoecol.,

38, 9–43.

Bourrouilh-Le Jan, F.G. and Hottinger, L.C. (1988) Occurrence

of rhodolites in the tropical Pacific – a consequence of Mid-

Miocene palaeo-oceanographic change. Sed. Geol., 60, 355–

367.

Braga, J.C. and Aguirre, J. (2001) Coralline algal assemblages

in upper Neogene reef and temperate carbonates in South-

ern Spain. Palaeogeogr., Palaeoclimatol., Palaeoecol., 175,27–41.

Braga, J.C. and Martın, J.M. (1988) Neogene coralline-algal

growth-forms and their palaeoenvironments in the

Almanzora river valley (Almeria, S.E. Spain). Palaeogeogr.,Palaeoclimatol., Palaeoecol., 67, 285–303.

Brandano, M., Vannucci, G., Pomar, L. and Obrador, A.(2005) Rhodolith assemblages from the lower Tortonian

carbonate ramp of Menorca (Spain): Environmental and

palaeoclimatic implications. Palaeogeogr., Palaeoclimatol.,

Palaeoecol., 226, 307–323.

Burgess, C.J. and Anderson, J.M. (1983) Rhodoids in temper-

ate carbonates from the Cenozoic of New Zealand. In:

Coated Grains (Ed. T.M. Peryt), pp. 243–258. Springer-

Verlag, Berlin Heidelberg.

Carannante, G. and Simone, L. (1996) Rhodolith facies in the

Central-Southern Apennines Mountains, Italy. In: Models

for Carbonate Stratigraphy from Miocene Reef Complexes of

Mediterranean Regions (Eds E.K. Franseen, M. Esteban,

W.C. Ward and J.-M. Rouchy), SEPM Concepts Sedimentol.Palaeontol., 5, 261–275.

Carannante, G., Esteban, M., Milliman, J.D. and Simone, L.(1988) Carbonate lithofacies as palaeolatitude indicators:

problems and limitations. Sed. Geol., 60, 333–346.

Carey, J.S., Moslow, T.F. and Vaughn Barrie, J. (1995) Origin

and distribution of Holocene temperate carbonates, Hecate

Strait, Western Canada continental shelf. J. Sed. Res., 65/1,184–194.

Caron, V., Nelson, C.S. and Kamp, P.J.J. (2004) Transgressive

surfaces of erosion as sequence boundary markers in cool-

water shelf carbonates. Sed. Geol., 164, 179–189.

Cattaneo, A. and Steel, R.J. (2003) Transgressive deposits: a

review of their variability. Earth-Sci. Rev., 62, 187–228.

Civitelli, G. and Brandano, M. (2005) Atlante delle litofacies e

modello deposizionale dei calcari a briozoi e Litotamni

nella Piattaforma carbonatica laziale-abruzzese. Boll. Soc.

Geol. It., 124, 611–643.

Esteban, M. (1996) An overview of Miocene reefs from Medi-

terranean areas: general trends and facies models. In: Mod-

els for Carbonate Stratigraphy from Miocene Reef

24 R. Nalin et al.


Complexes of Mediterranean Regions (Eds E.K. Franseen,

M. Esteban, W.C. Ward and J.-M. Rouchy), SEPM Concepts

Sedimentol. Palaeontol., 5, 3–53.

Glaser, I. and Betzler, C. (2002) Facies partitioning and

sequence stratigraphy of cool-water, mixed carbonate-silic-

iclastic sediments (Upper Miocene Guadalquivir Domain,

southern Spain). Int. J. Earth Sci., 91, 1041–1053.

Halfar, J., Godinez-Orta, L., Mutti, M., Valdez-Holguın, J.E.and Borges, J.M. (2004) Nutrient and temperature controls

on modern carbonate production: an example from the Gulf

of California, Mexico. Geology, 32/3, 213–216.

Iryu, Y., Nakamori, T., Matsuda, S. and Abe, O. (1995) Dis-

tribution of marine organisms and its geological significance

in the modern reef complex of the Ryukyu Islands. Sed.

Geol., 99, 243–258.

James, N.P. (1997) The cool-water carbonate depositional

realm. In: Cool-Water Carbonates (Eds N.P. James and A.D.

Clarke), SEPM Spec. Publ., 56, 1–20.

Kamp, P.J.J., Vonk, A.J., Bland, K.J., Hansen, R.J., Hendy,A.J.W., McIntyre, A.P., Ngatai, M., Cartwright, S.J., Hayton,S. and Nelson, C.S. (2004) Neogene stratigraphic architec-

ture and tectonic evolution of Wanganui, King Country, and

eastern Taranaki Basins, New Zealand. NZ J. Geol. Geo-

phys., 47, 625–644.

Kear, D. and Schofield, J.C. (1959) Te Kuiti Group. NZ J. Geol.

Geophys., 2, 685–717.

Kidwell, S.M. (1989) Stratigraphic condensation of marine

transgressive records: origin of major shell deposits in the

Miocene of Maryland. J. Geol., 97, 1–24.

Kidwell, S.M. (1991a) The stratigraphy of shell concentrations.

In: Taphonomy: Releasing the Data Locked in the Fossil

Record (Eds P.A. Allison and D.E.G. Briggs), pp. 211–290.

Plenum, New York.

Kidwell, S.M. (1991b) Condensed deposits in siliciclastic

sequences: expected and observed features. In: Cycles and

Events in Stratigraphy (Eds G. Einsele, W. Ricken and A.

Seilacher), pp. 682–695. Springer-Verlag, Berlin.

Kondo, Y., Abbott, S.T., Kitamura, A., Kamp, P.J.J., Naish,T.R., Kamataki, T. and Saul, G. (1998) The relationship

between shellbed type and sequence architecture: examples

from Japan and New Zealand. Sed. Geol., 122, 109–127.

Kroeger, K.F., Reuter, M. and Brachert, T.C. (2006) Palaeo-

environmental reconstruction based on non-geniculate cor-

alline red algal assemblages in Miocene limestone of central

Crete. Facies, 52, 381–409.

Lees, A. and Buller, A.T. (1972) Modern temperate-water and

warm-water shelf carbonate sediments contrasted. Mar.

Geol., 13, M67–M73.

Lund, M., Davies, P.J. and Braga, J.C. (2000) Coralline algal

nodules off Fraser Island, Eastern Australia. Facies, 42,25–34.

Marrack, E.C. (1999) The relationship between water motion

and living rhodolith beds in the southwestern Gulf of Cal-

ifornia, Mexico. Palaios, 14, 159–171.

Minnery, G.A. (1990) Crustose coralline algae from the Flower

Garden Banks, northwestern Gulf of Mexico: controls on

distribution and growth morphology. J. Sed. Petrol., 60/6,992–1007.

Naish, T. and Kamp, P.J.J. (1997) Sequence stratigraphy of

sixth order (41k.y.) Pliocene-Pleistocene cyclothems,

Wanganui basin, New Zealand: a case for the regressive

systems tract. GSA Bull., 109/8, 978–999.

Nalin, R., Basso, D. and Massari, F. (2006) Pleistocene coral-

line algal build-ups (coralligene de plateau) and associated

bioclastic deposits in the sedimentary cover of Cutro marine

terrace (Calabria, southern Italy). In: Cool-Water Carbonates:

Depositional Systems and Palaeoenvironmental Controls

(Eds H.M. Pedley and G. Carannante), Geol. Soc. London

Spec. Publ., 255, 11–22.

Nebelsick, J.H. and Bassi, D. (2000) Diversity, growth forms

and taphonomy: key factors controlling the fabric of coral-

line algae dominated shelf carbonates. In: Carbonate Plat-

form Systems: Components and Interactions (Eds E.

Insalaco, P.W. Skelton and T.J. Palmer), Geol. Soc. London

Spec. Publ., 178, 89–107.

Nelson, C.S. (1978) Stratigraphy and palaeontology of the

Oligocene Te Kuiti Group, Waitomo County, South Auck-

land, New Zealand. NZ J. Geol. Geophys., 21/5, 553–594.

Nelson, C.S. and Hume, T.M. (1977) The relative intensity of

tectonic events revealed by the Tertiary sedimentary record

in the North Wanganui Basin and adjacent areas, New

Zealand. NZ J. Geol. Geophys., 20, 369–392.

Nelson, C.S., Harris, G.J. and Young, H.R. (1988) Burial-

dominated cementation in non-tropical carbonates of the

Oligocene Te Kuiti Group, New Zealand. Sed. Geol., 60,233–250.

Nelson, C.S., Kamp, P.J.J. and Young, H.R. (1994) Sedimen-

tology and petrography of mass-emplaced limestone

(Orahiri Limestone) on a late Oligocene shelf, western North

Island, and tectonic implications for eastern margin devel-

opment of Taranaki Basin. NZ J. Geol. Geophys., 37, 269–

285.

Perrin, C., Bosence, D.W.J. and Rosen, B. (1995) Quantitative

approaches to palaeozonation and palaeobathymetry of

corals and coralline algae in Cenozoic reefs. In: MarinePalaeoenvironmental Analysis from Fossils (Eds D.W.J.

Bosence and P.A. Allison), Geol. Soc. London Spec. Publ.,

83, 181–229.

Pomar, L. (2001) Types of carbonate platforms: a genetic

approach. Basin Res., 13, 313–334.

Pomar, L., Brandano, M. and Westphal, H. (2004) Environ-

mental factors influencing skeletal grain sediment associa-

tions: a critical review of Miocene examples from the

Western Mediterranean. Sedimentology, 51, 627–651.

Prager, E.J. and Ginsburg, R.N. (1989) Carbonate nodule

growth on Florida’s outer shelf and its implications for

fossil interpretations. Palaios, 4, 310–317.

Reid, R.P. and Macintyre, I.G. (1988) Foraminiferal-algal

nodules from the Eastern Caribbean: growth history and

implications on the value of nodules as palaeoenviron-

mental indicators. Palaios, 3, 424–435.

Ricketts, B.D., Ballance, P.F., Hayward, B.W. and Mayer, W.(1989) Basal Waitemata lithofacies: rapid subsidence in an

early Miocene interarc basin, New Zealand. Sedimentology,

36, 559–580.

Studencki, W. (1999) Red-algal limestones in the Middle

Miocene of the Carpathian Foredeep in Poland: facies var-

iability and palaeoclimatic implications. Geol. Quart., 43/4,395–404.

Tsuji, Y. (1993) Tide influenced high energy environments and

rhodolith-associated carbonate deposition on the outer shelf

and slope off the Miyako Islands, southern Ryukyu Island

Arc, Japan. Mar. Geol., 113, 255–271.

Vecsei, A. and Sanders, D.G.K. (1999) Facies analysis and

sequence stratigraphy of a Miocene warm-temperate car-

bonate ramp, Montagna della Maiella, Italy. Sed. Geol., 123,103–127.

Webster, J.M., Fallace, L., Silver, E., Potts, D., Braga, J.C.,Renema, W., Riker-Coleman, K. and Gallup, C. (2004a)

Coralgal composition of drowned carbonate platforms in the



Huon Gulf, Papua New Guinea; implications for lowstand

reef development and drowning. Mar. Geol., 204, 59–89.

Webster, J.M., Clague, D.A., Riker-Coleman, K., Gallup, C.,Braga, J.C., Potts, D., Moore, J.G., Winterer, E.L. and Paull,C.K. (2004b) Drowning of the –150 m reef off Hawai: a

casualty of global meltwater pulse 1A? Geology, 32/3, 249–

252.

White, P.J. and Waterhouse, B.C. (1993) Lithostratigraphy of

the Te Kuiti Group: a revision. NZ J. Geol. Geophys., 36,255–266.

Wilson, J.B. (1988) A model for temporal changes in the faunal

composition of shell gravels during a transgression on

the continental shelf around the British Isles. Sed. Geol., 60,95–105.

Wilson, M.E.J. and Vecsei, A. (2005) The apparent paradox of

abundant foramol facies in low latitudes: their environ-

mental significance and effect on platform development.

Earth-Sci. Rev., 69, 133–168.

Manuscript received 30 June 2006; revision accepted 8August 2007

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