Coastal areas on carbonate islands commonly contain two types of caves: sea caves developed by wave erosion processes, and flank margin caves developed by dissolution at the edge of the fresh-water lens. Differentiating sea caves and flank margin caves in coastal settings is important, but can it be done reliably and quantitatively? Current methods use the degree of intricate wall-rock dissolution and the presence or absence of dense calcite speleothems to separate the two cave types. This study reports how analysis of cave maps creates three separate tools to differentiate coastal caves: area to perimeter ratio, entrance width to maximum width ratio, and rectangle short axis to long axis ratio. The study also presents some of the first sea cave data from eogenetic carbonate islands, specifically eolian calcarenites. The morphological and geometrical comparisons between Bahamian flank margin cave and sea cave maps using the three tools allows the two cave types to be statistically differentiated. The Bahamian sea cave data were also compared to sea cave data from California and Maine to demonstrate that Bahamian sea caves have a unique quantitative signature based on the youth and homogeneity of the host eolian calcarenite rock. The Bahamian sea cave data also indicate that sea cave formation may not be solely determined by differential rock weaknesses, as reported in the literature, but may also be a result of wave dynamics such as constructive interference.
Z namenom, da odkrijemo prisotnost jam nastali� v priobalnem pasu mešanja slane in sladke vode (jame tipa "Flank margin"), smo raziskovali diagenetsko zrele apnence Severnega (pristanišče Raglan in Kaw�ia, drage Napier in waipu) in Južnega otoka (Po�ara, reka Paturau, Piunakaiki, Kakanui in Kaikoura) Nove Zelandije. Na obalni� področji� so jame v karbonati� la�ko rezultat različni� psevdokraški� (npr. erozija valovanja) in kraški� procesov, ki niso povezani z mešanjem slane in sladke vode (npr. epikraške oblike in jame nastale z meteorno kraško drenažo). Jame tipa "Flank margin" smo uspešno ločili od ostali� tipov jam z opazovanjem naslednji� značilnosti: morfologija freatični� skalni� oblik v različni� merili�, odsotnost skalni� oblik in sedimentov, ki so rezultat �itrega turbulentnega toka, nepovezanost sosednji� jam z zvezno vodno potjo. Zaradi aktivne tektonike je nivo morske gladine na Novi Zelandiji zelo spremenljiv, obdobja stabilnega vodnega nivoja so kratka, zato so jame tipa "Flank margin" na Novi Zelandiji manjše v primerjavi s tistimi v tektonsko stabilnejši� okolji�, kot so Ba�ami, kjer nivo morske gladine uravnava zgolj glacioevstazija. Poudarjen vertikalni razvoj jam tipa "Flank margin" kaže na počasno in enakomerno tektonsko dvigovanje, razširitve in kanali v diskretni� �orizonti�, ki sekajo strukturo, pa kažejo na občasna (nezvezna) tektonska dogajanja. Jame tipa "Flank margin" nosijo neodvisen zapis o trajanju in �itrosti dvigovanja območij na Novi Zelandiji in tako nudijo možnost umeritve ostali� metod vrednotenja tektonski� dogodkov. Ključne besede: jame tipa "Flank margin", Nova Zelandija, telogenetski karbonati, priobalne jame.
Izvleček UDK 911.2:551.44(497.5 ) Bojan Otoničar, Nenad Buzjak, John Mylroie & Joan Mylroie: Jama tipa »Flank margin«, nastala v pobočni breči v območju mešanja sladke in slane vode: primer z otoka Cresa na HrvaškemJama Plava Grota na Hrvaškem otoku Cresu se je izoblikovala ob obali v pobočni breči. Relativno majhni jamski vhodi, geometrija jamskih rovov z dvoranami, ki jih povezujejo relativno nizki in ozki prehodi, ostanki raztopljenih stebrov prikamnine in nizki oboki predstavljajo oblike značilne za jame "Flank margin" tipa, hkrati pa jih te oblike ločijo od epigenetskih na eni, in morskih jam na drugi strani. Plava Grota se nahaja, kakor tudi sosednje manjše jame, izključno v breči, ki je verjetno pleistocenske starosti. Gradijo jo klasti, katerih izvor so bližnje diagenetsko zrele oziroma telegenetske karbonatne kamnine kredne starosti. Klaste na rahlo povezujejo vadozni kalcitni cementi. Breča predstavlja tridimenzionalno porozno in permeabilno telo, ki se obnaša v hidravličnem smislu podobno kot mlade eugenetske karbonatne kamnine Bahamov in Puerto Rica ali kot nekatere tektonsko močno pretrte karbonatne kamnine Nove Zelandije. Plava Grota je prva jama "Flank margin" tipa opisana v obalnih karbonatnih kamninah Jadranskega morja. Glede na položaj jame in sedanjega nivoja morske gladine, izvire sladke vode v jami in njeni okolici, generalno tektonsko pogrezanje območja in kvartarno eustatično nihanje morske gladine domnevamo, da se je jama prvotno oblikovala v obdobju visoke morske gladine pred okoli 130.000 do 114.000 leti (MIS 5e). AbstractUDC 911.2:551.44(497.5) Bojan Otoničar, Nenad Buzjak, John Mylroie & Joan Mylroie: Flank margin cave development in carbonate talus breccia facies: An example from Cres Island, CroatiaPlava Grota, Cres Island, Croatia, is a flank margin cave developed in a coastal setting in talus breccia facies. The internal cave geometry of small entrances, intersecting adjacent chambers, remnant dissolutional bedrock pillars, and low arches matches diagnostic features used to separate flank margin caves from epigenic stream caves on one hand, and sea caves on the other. Plava Grota is found, along with adjacent smaller caves, solely in a breccia facies that is most probably of Pleistocene age. This breccia is comprised of clasts derived from diagenetically mature, or telogenetic, Cretaceous carbonate rocks. The clasts are loosely cemented by vadose calcite cements. The breccia facies provide a three-dimensional porosity and permeability structure that behaves hydraulically in a manner similar to the high primary porosity and permeability of young eogenetic carbonate rocks in settings such as the Bahamas or Puerto Rico, and the many flow paths found in highly-tectonized telogenetic carbonate rocks in New Zealand. Plava Grota is the first described flank margin cave from the coastal carbonate rocks of the Adriatic Sea. According to present sea-level position in relation to the cave, fresh-water springs in and adjacent to the cave, general tectonic subsidence of the area and Quaternary ...
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