Contradictory coeval vertical facies changes in upper Miocene heterozoan carbonate–terrigenous deposits (Sierra de Gádor, Almería, SE Spain)
Author:
Sola Fernando1, Braga Juan C.2, Sælen Gunnar3
Affiliation:
1. Departamento de Biología y Geología, Universidad de Almería, 04120 Almería, Spain 2. Departamento de Estratigrafía y Paleontología, Universidad de Granada, Campus Fuentenueva, 18002 Granada, Spain 3. Department of Earth Science, University of Bergen, Allégaten 41, N-5007 Bergen, Norway
Abstract
ABSTRACT
While spatial facies patterns can be observed in modern systems, only vertical facies successions can usually be examined in ancient deposits. Lateral facies relationships (depositional models) and relative sea-level changes throughout time are traditionally deduced from correlation of vertical facies successions along transects perpendicular to inferred paleo-shorelines. Establishing vertical facies successions and their corresponding time-equivalent proximal to distal facies patterns are, therefore, paramount in reconstructing ancient carbonate depositional systems and their response to sea-level change. In the present study of well-exposed panoramics of late Tortonian (8.1 Ma) mixed heterozoan carbonate and terrigenous deposits in La Chanata area in Sierra de Gádor, Almería, SE Spain, we show that frequent changes in facies width make it difficult to predict how variation in sea level impacts the facies distribution. The following facies are recognized: shoreline conglomerates directly overlie an erosion surface on the basement; terrigenous coralline-algal packstones extend basinwards from the conglomerates and are interpreted as shallow-water deposits stabilized by seagrass. There exist three types of facies consisting of relatively well-preserved, parautochthonous bioclasts, which occur generally seawards of the packstones: a) branching-coralline rudstones that formed from rhodolith (maërl) beds, both shorewards and basinwards from seagrass meadows where b) foliose-coralline rudstones to floatstones accumulated, and c) lenses of Heterostegina rudstones to floatstones changing laterally to any of the coralline algal facies. The factory facies of a–c show a patchy distribution with no definite arrangement in shoreline-parallel belts. The evolution of the depositional system is as follows: after filling paleovalleys in the erosion surface, deposition took place on a homoclinal ramp. The hybrid heterozoan carbonate–terrigenous deposits show a general retrogradation altered by one episode of proximal facies progradation. The width of facies across the ramp changes markedly in different episodes of relative sea-level rise: in several episodes of transgression, terrigenous coralline-algal packstones spread across the ramp locally overlying more distal facies, such as branching-coralline rudstones, thus generating regressive vertical patterns during relative sea-level rise. In other transgressive episodes packstones disappear, and the a–b factory facies pass laterally into conglomerate. The stratigraphic changes in facies width might be due to changes in general energy caused by climate variations or, alternatively, to the amount of relative sea-level rise. Large sea-level rise would result in relatively deep and calm conditions, thus favoring little fragmentation of large bioclasts during accumulation of the factory facies. Conversely, little change in accommodation would have resulted in higher-energy environments with concomitant increased physical erosion of the coralline-algae factories, thus resulting in mostly sand-size bioclasts in the packstones. In this environmental context, vertical change from distal to proximal facies can result from relative sea-level rise with increased mobilization and lateral expansion of proximal facies across the ramp. This outcome challenges the adequacy of using vertical lithofacies successions to reconstruct relative sea-level change in carbonate depositional systems.
Publisher
Society for Sedimentary Geology
Reference88 articles.
1. Aguirre,
J.,
Braga,
J.C.,
and
Bassi,D.,
2017,
Rhodoliths and rhodolith beds in the rock record,
inRiosmena-Rodríguez,R.,Nelson,W.,Aguirre,J.,eds.,Rhodolith/Mäerl Beds: A Global Perspective:
Springer,
Coastal Research Library 15,
p.105–
138. 2. Amado-Filho,
G.M.,
Moura,
R.L.,
Bastos,
A.C.,
Salgado,
L.T.,
Sumida,
P.Y.G.,
Guth,
A.Z.,
Francini-Filho,
R.B.,
Pereira-Filho,
G.H.,
Abrantes,
D.P.,
Brasileiro,
P.S.,
Bahia,
R.G.,
Leal,
R.N.,
Kaufman,
L.,
Kleypas,
J.,
Farina,
M.,
and
Thompson,F.L.,
2012,
Rhodolith beds are major CaCO3 bio-factories in the tropical South West Atlantic: PLoS One, v. 7, e35171. 3. Baena,
J.,
and
Voermans,F.,
1983,
Mapa geológico de España, Memoria y Hoja geológica, no. 1044 (Alhama de Almería), scale1:
50,000. 4. Basso,
D.,
Babbini,
L.,
Ramos-Esplá,
A.A.,
and
Salomidi,M.,
2017,
Mediterranean rhodolith beds,
inRiosmena-Rodríguez,R.,Nelson,W., and
Aguirre,J.,eds.,Rhodolith/Maërl Beds: A Global Perspective:
Springer,
Coastal Research Library 15,
p.281–
298. 5. Beavington-Penney,
S.J.,
Wright,
V.P.,
and
Woelkerling,W.J.,
2004,
Recognising macrophyte-vegetated environments in the rock record: a new criterion using “hooked” forms of crustose coralline red algae:
Sedimentary Geology,
v.166,
p.1–
9.
Cited by
2 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献
|
|